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Anatomy of a Real Time Building Energy modelINTRODUCTIONWhen the “Oil Embargo” of 1973 occurred, I was a member of a small group of computer simulation engineers at Texas Instruments Inc. (T.I.) designing and evaluating military systems via computer simulations. The modeled systems included the Shrike missile, laser guided systems, and anti-tank missiles. The oil embargo occurred the fourth quarter of 1973 and in 1974 (T.I.) gave me the task of modeling the energy consumption of (T.I.) buildings and processes for the purpose of defining what could be done to reduce energy consumption. I used building energy computer programs available at the time that were based on simulating the yearly energy use of a building based on utility bills. I became convinced that a 24-hour real-time model was needed3. On retiring I decided to see if I could develop a model based on basic thermodynamic equations1,2 and perhaps develop a real time model7,8,9. This effort has resulted in the System Energy Equilibrium (SEE) Model summarized by this paper.Best regards to all,Kirby Nelson P.E.Life Member ASHRAEIntroductionThe objective of this paper is to present a building energy model and procedure for judging the energy performance of a building and plant on any day of the year. The System Energy Equilibrium (SEE) Model incorporates the basic equations, data, and analysis procedures used by engineers to design a building and plant. These equations are solved simultaneously by computer. The (SEE) Model requires, just as a real system operates, that the energy into the system equals the energy out of the system. This is a major check on the accuracy of the model; a model that does not balance energy in equals energy out has problems that must be resolved.
The procedure for evaluating the energy use of a building system is to first establish a (SEE) Model of the as designed building and plant (system). If on a given day the actual energy consumption of the system is greater than the as designed (SEE) Model then the real system may not be operating efficiently. A comparison of actual to modeled performance may show that the as designed model needs to be updated. For example, if the lights (watts/ft2) are different than modeled and cannot be changed, then the real value, as constructed, should be input to the model. The goal of this (SEE) Model is to duplicate each hour of a 24-hour performance of a real system within about 3% on any day of weather and operational conditions. To accomplish this the (SEE) Model must obey the laws of thermodynamics and model the nonlinear characteristics of the real system components and all details of the system that contribute to the performance of the real system.Real time models for control System models are used in the real time control of systems as evidenced by the real time modeling and control NASA employs on space missions. Modeling the flight of a space vehicle after it has returned to earth is too late. Similarly, modeling the energy consumption of a building over the past year is too late and impossible to perform with reasonable accuracy3. A real-time 24-hour building and plant energy model that can be used on site on a given day to evaluate the performance of the system is needed and that is the purpose of the (SEE) Model presented here. This paper demonstrates the (SEE) model characteristics and procedure for evaluating a real system on a given day, in this case a Kansas City six building office campus designed to ASHRAE Standard 90.1-20105.Chapter 1 Defines the ASHRAE Standard 90.1-2010 building to be modeled, model characteristics,
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estimates of annual (EUI), and energy balance analysis of the Table 1 System. Chapter 2 Defines the plant model.Chapter 3 Defines a Table 1.5 system and installs fan powered terminals and return fans.Chapter 4 Installs other Table 2 conditions defined as constructed system.To be addedChapter 5 defines the performance of the assumed Table 4 real system with several control problems. Chapter 6 presents real weather performance & Benchmark data.Chapters 7 thru 16 will define and illustrate each of the control problems of the assumed real system.
References 1. Introduction to Thermodynamics and
Heat Transfer. 1956 Prentice-Hall, Inc. by David A. Mooney.
2. Thermal Environmental Engineering third edition. 1998 Prentice-Hall Inc. by Thomas H. Kuehn, chapter 3.
3. ASHRAE Journal May 2016. “Modeled Performance Isn’t Actual Performance”
4. Nelson, Kirby. “System Energy Equilibrium (SEE) Building Energy Model Development & Verification”. http://kirbynelsonpe.com/
5. Liu, B. May 2011. “Achieving the 30% Goal: (copy and paste) https://www.energycodes.gov/sites/default/files/documents/BECP_Energy_Cost_Savings_STD2010_May2011_v00.pdf
6. Real weather data www.wunderground.com/
7. Nelson, K. “7 Upgrades to, Reduce Building Electrical Demand” ASHRAE Journal, December, 2006,
8. Nelson, K. “Simulation Modeling of a Central Chiller Plant” CH-12-002. ASHRAE 2012 Chicago Winter Transactions.
9. Nelson, K. “Simulation Modeling of Central Chilled Water System” CH-12-
003. ASHRAE 2012 Chicago Winter Transactions.
10. Kavanaugh, S. “Fan Demand and Energy” ASHRAE Journal, 2000.
11. Faris, Gus “Fan-Powered VAV Terminal Units” ASHRAE Journal November 2017
12. Kettler, John “Return Fans or Relief Fans” ASHRAE Journal April 2004.
13. Taylor, S. 2011. “Optimizing design & control of chiller plants.” ASHRAE Journal (12).
14. Nelson, Kirby “The System Energy Equilibrium Model for Chiller Plants, Part 1” Engineered Systems, July 2020.
15. Marley Tower SPX Cooling Technologies UPDATE Version
16. Steven Taylor. ASHRAE Journal June 2007. “VAV System Static Pressure Setpoint Reset”
SCHEMATIC STRUCTURE
Schematic A defines the basic structure of the air side system and plant schematics.
Schematic A: System schematic structure.
Understanding the system with only charts is a difficult task so a system performance schematic was developed so that the system can be viewed and studied at any
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hour. Schematic A illustrates the basic system components that make up the system schematic, the building, duct system, coil, exhaust & fresh air, VAV fans, water distribution, chiller evaporator-compressor-condenser, and the tower. Schematic A illustrates the location of the components of a building served by a (CCWS). The building is in the upper right of Schematic A with the duct system that serves the interior and perimeter of the building shown below. The fan system including exhaust and fresh air is shown in the lower right of the schematic with the coil on top of the VAV fan outlet. The right half of Schematic A represents the air side of the system or site and the left side is the plant. Water enters and leaves the coils therefore transferring the air side or site load to the plant evaporators. The chiller motor pumps refrigerant from the evaporator transferring the load to the condenser and the cooling tower picks up the load from the condenser and exhausts the load to the atmosphere. The lower left of the Schematic A gives system data for the hour. The most relevant values of the model are placed in the schematic to give a much better understanding of the system at a steady state condition hour. Schematic 1 below illustrates the system values at 4PM steady state condition.
NOMENCLATURE Each of the more than 200 variables will be defined.
Building structure;BLD ft2 = air-conditioned space# Floors = number of building floorsRoof ft2 = roof square feetN/S wall ft2 =north/south wall square feetE/W wall ft2 =east/west wall square feetWall % glass = percent of each wall that is glassGlass U = glass heat transfer coefficientWall U = wall heat transfer coefficientGlass SHGC = glass solar heat gain coefficientWall emit = wall solar indexBuilding interior space;Rooftrans-ton =transmission through roof (ton)Roofsky-lite-ton =sky lite load (ton)Peopleton sen&lat = sensible & latent cooling load due to people (ton)Plugton&kW = cooling load & kW due to plug loadsLightton&kW = cooling load & kW due to lightsTotal Bldint-ton = total building interior load (ton)(int-cfm) to-per-return = CFM of interior supply air that returns to perimeter of buildingTstat-int = interior stat set temperature (F)Bldint-air-ton = supply air ton to offset interior load
BLD kW = total building kW demandFAN kW = total fan kWHEAT kW = total kW due to heatSITE kW = total site kW=Bld+ Fan+HeatBuilding perimeter space;%clear sky = percent clear skyTdry bulb = outside dry bulb temperature (F)Twet bulb = outside wet bulb temperature (F)Ex/Infillat-ton = latent air infiltration or exfiltration (ton)Ex/InfilCFM = air infiltration or exfiltration CFMExfilsen-ton =sensible air exfiltration or infiltration (ton)Walln trans ton = north wall transmission (ton)Walls trans ton = south wall transmission (ton)WallE trans ton = east wall transmission (ton)Wallw trans ton = west wall transmission (ton)Walltot-trans-ton = total wall transmission (ton)GlassN-trans-ton = north wall glass transmission (ton)GlassS-trans-ton = south wall glass transmission (ton)GlassE-trans-ton = east wall glass transmission (ton)GlassW trans-ton = west wall glass transmission (ton)Glasstot-trans-ton = total transmission thru glass (ton) GlassN-solar-ton = north glass solar load (ton)GlassS-solar-ton = south glass solar load (ton)GlassE-solar-ton = east glass solar load (ton)GlassW-solar-ton = west glass solar load (ton)Glasstot-solar-ton = total glass solar load (ton)(int cfm)per-ton = effect of interior CFM to wall (ton)Total Bldper-sen-ton total perimeter sensible load (ton)Tstat-per = perimeter stat set temperature (F)Bldper-air-ton = supply air ton to offset perimeter load Air handler duct system-Interior duct Tair supply int = temp air supply to building interior (F)(fan)int ter ton&kW = interior ton & kW due to terminal fans (D)int-air-ton = cooling (ton) to building interior ductTair coils = supply air temperature off coils to duct (F)(D)int-CFM = supply air CFM to building interior ductPerimeter ductTair supply per =temp (F) air supply to building perimeter (fan)per ter ton&kW = perimeter ton & kW of terminal fansTheat-air = temp supply air before terminal fan heat (F)(D)heat-ton&kW = heat to perimeter supply air ton & kWTreheat air = temp perimeter supply air after reheat (F) (D)reheat ton&kW = reheat of perimeter supply air ton & kW(D)per-air-ton = cooling (ton) to perimeter duct Tair coils = supply air temperature off coils to duct (F)(D)per-CFM = supply air CFM to perimeter ductCoil(Coil)sen-ton = sensible load on all coils (ton)(Coil)cap-ton = LMTD * UA = capacity (ton) one coilLMTD = Coil log mean temperature difference (F)
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(Coil)L+s-ton = latent + sensible load on all coils (ton) transferred to PlantUA = coil heat transfer coefficient * coil area. UA varies as a function water velocity (coil)gpm thru the coil, as the (coil)gpm decreases the coil capacity decreases.(one Coil)ton = load (ton) on one coilVAV Fan systemFresh airstatFA = fresh air freeze stat set temperature (F)TFA to VAV = temperature of fresh air to VAV fan(FA)sen-ton = fresh air sensible load (ton)(FA)CFM = CFM fresh air to VAV fan inlet(FA)Lat-ton = fresh air latent load (ton)(FA)kW = heat kW to statFA set temperatureAir return TBLD-AR = return air temp (F) before return fans(Air)ret-CFM = CFM air return from building(FAN)ret-kW = return fans total kW(FAN)ret-ton = cooling load (ton) due to (FAN)ret-kW
(Air)ret-ton = return air (ton) before return fansTAR to VAV = TBLD-AR + delta T due to return fans kWVAVret-sen ton = return sensible (ton) to VAV fans inletVAVret-lat ton = return latent (ton) to VAV fans inletVAVret-CFM = return CFM to VAV fans inletExhaust air ExLat-ton = latent load (ton) exhaustedExCFM = CFM of exhaust airTEx = temperature of exhaust air Exsen-ton = sensible load (ton) exhaustedVAV Fans Tret+FA = return and fresh air mix temperature (F)(dh) = VAV air static pressure (in)Efan-VSD = VAV fans efficiencyVAVinlet-sen-ton = sensible load (ton) inlet to VAV fansVAVinlet-lat-ton = latent load (ton) inlet to VAV fansTair-VAV = temp air to coils after VAV fan heat(FAN)VAV-CFM = CFM air thru coils(FAN)ton-VAV = load (ton) due to VAV fan kW(FAN)kW-VAV = total VAV fan kW demandAIR SIDE SYSTEM PLUS BUILDINGFAN kW = total air handlers kWSITE kW = total site or air side kWPlantton = (COIL)L+s ton load (ton) to plantCENTRAL PLANT# Buildings = number of buildings served by plantPlant ton = total load (ton) to plant Primary/secondary pumping nomenclaturegpmevap = total gpm flow thru one evaporators(H)pri-total = total primary pump head (ft) = (H)pri-pipe + (H)pri-
fittings + (H)pri-bp + (H)evap
(H)pri-pipe = primary pump head due to piping (ft)
(H)pri-fittings = primary head due to pump & fitting (ft)(Ef)c-pump = efficiency of chiller pumpPc-heat-ton = chiller pump heat to atmosphere (ton)Pc-kW = one chiller pump kW demand (kW)Pchiller-# = number chiller pumps operating(lwt)evap = temperature water leaving evaporator (F)Tbp = temperature of water in bypass (F)gpmbp = gpm water flow in bypass(H)pri-bp = head if chiller pump flow in bypass (ft)(ewt)evap = temp water entering evaporator (F)Psec-heat-ton = secondary pump heat to atmosphere (ton)Psec-kW = kW demand of secondary pumpsEfdes-sec-p = design efficiency of secondary pumpingEfsec-pump = efficiency of secondary pumping(H)sec = secondary pump head (ft) = (H)sec-pipe + (H)sec-bp + (H)coil + (H)valve
(H)sec-pipe = secondary pump head due to pipe (ft)(H)sec-bp = head in bypass if gpmsec > gpmevap
GPMsec = water gpm flow in secondary loop(ewt)coil = water temperature entering coil (F)Pipesize-in = secondary pipe size (inches)(lwt)coil = temperature of water leaving coil (F)Evaporator(evap)ton = load (ton) on one evaporatorTER = evaporator refrigerant temp (F)TER-app = evaporator refrigerant approach (F)EVAPton = total evaporator loads (ton)(H)evap = pump head thru evaporator (ft)(evap)ft/sec = velocity water flow thru evaporator(evap)des-ft/sec = evaporator design flow velocityCompressor:(chiller)kW = each chiller kW demand(chiller)lift = (TCR – TER) = chiller lift (F)(chiller)% = percent chiller motor is loaded(chiller)# = number chillers operating(CHILLER)kW = total plant chiller kW(chiller)kW/ton = chiller kW per evaporator tonPlant kW = total kW demand of plant(Plant)kW/site ton = Plant kW per site tonCondenser nomenclature:(cond)ton = load (ton) on one condenserTCR = temperature of condenser refrigerant (F)TCR-app = refrigerant approach temperature (F)(COND)ton = total load (ton) on all condensers(H)cond = tower pump head thru condenser (ft)(cond)ft/sec = tower water flow thru condenserTower piping nomenclaturePipesize-in = tower pipe size (inches)gpmT = each tower water flow (gpm)GPMT = total tower water flow (gpm)(H)T-total = total tower pump head (ft)
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PT-heat = pump heat to atmosphere (ton)PT-kW = each tower pump kW demandEfT-pump = tower pump efficiencyPtower # = number of tower pumps(H)T-pipe = total tower pump head (ft)(ewt)T = tower entering water temperature (F)(H)T-static = tower height static head (ft)Trange = tower range (F)= (ewt)T – (lwt)T
(lwt)T = tower leaving water temperature (F)Tapproach = (lwt)T – (Twet-bulb)Tower nomenclature
tfan-kW = kW demand of one tower fanTfan-kW = tower fan kW of fans ontfan-% = percent tower fan speedtton-ex = ton exhaust by one tower
T# = number of towers onTton-ex = ton exhaust by all towers onTrg+app = tower range + approach (F)One hour performance indicesBLDkW = kW demand of building lights & plug loadsFankW = air side fans kW, VAV, return terminalsDuctheat = perimeter heat to air supplyFAheat = heat added to fresh airHeattotal = total heat added to airPlantkW = total plant kWSystkW = total system kWCCWSkW = air side system + plant kWChillerkW/evap ton = chiller kW/evaporator ton performancePlantkW/site ton = plant kW per site or air side tonCCWSkW/site ton = CCWS kW per load to plantWeatherEin-ton = weather energy into the systemSitekW-Ein-ton = load (ton) due to site kWPlantkW-Ein-ton = load (ton) due to plant kWTotalEin-ton = total energy in to system (tonPumptot-heat-ton = total pump heat out (ton)AHU Exlat ton = air exhausted latent tonAHU Exsen ton = air exhausted sensible tonTower Tton Ex = energy exhausted by tower (ton)Total Eout ton = total energy out of system (ton)24 hour performance indicesBLD24hr-kW = building 24 hour kW usageFan24hr-kW = fan system 24 hour kW usageDuct24hr-heat kW or therm = duct heatFA24hr heat kW or therm = fresh air heatHeat24hr total kW or therm = total heat into systemPlant24hr kW = plant 24 hour kW usageSyst24hr kW & therm = total system 24 hour energy usagePeoplesen+lat ton =total load (ton) due to peopleEnfil24hr cfm energy = change in internal energyWeather24hr-Ein-ton = 24 hour weather energy into systemSITE24hr-kW-Ein-ton = 24 hour energy into site
Plant24hr-kW-Ein-ton = 24 hour kW energy into plantTotal24hr-Ein-ton = total 24 hour energy into systemPump24hr Heat out-ton = pump heat to atmosphere (ton)AHU Ex24hr Lat ton = exhausted latent load from buildingAHU Ex24hr-sen-ton = exhausted sensible load from bl
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CHAPTER 1 Description of Building to be Modeled, Model Characteristics, Estimates of Annual (EUI), and Energy Balance Analysis
The Building and Weather Conditions of this Study
Figure 1: Building Description-Kansas City Missouri Large Office Building Designed to Std. 90.1-20105
Figure 1 presents the modeled building of this study, a 565,000 square foot large office building based on the data provided by Liu5. The office campus is assumed to consist of six Figure 1 buildings. The plant load for one building is 864.6-ton, Figure 3, therefore the design load on the plant is (6 * 864.6 = 5,187.6 ton). The plant is modeled as six chiller/towers each with a design capacity of 1,000 ton; therefore, the design plant capacity is 6,000 ton. Figure 2 top chart gives the assumed design day weather conditions with a peak dry bulb of 101F and wet bulb of 78F occurring at 4PM. Figure 2 also gives assumed winter weather that will also be (SEE) modeled to illustrate the (SEE) Model capability to go from summer design conditions to winter conditions. The secondary horizontal axis of Figure 2 gives the percent clear sky as 100% for
both summer and winter conditions. Real weather6 conditions addressed by articles 2 & 3 input percent clear sky based on cloud conditions.
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Figure 2: Top Chart-Design & Winter Weather-Bottom Chart-Light kW, Plug kW, & # people
Figure 2 bottom chart gives the light and plug kW demand per time of day and also the number of people in the building as interpreted from Liu5. The lights and plug loads track well to the number of people in the building illustrating a good shut down system is defined by Liu5. Figures 1 & 2 give the basic data required to define the as designed (SEE) Model building.
Model Characteristics
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Building 13 StoryEach Building=565,000 Ft-Sq
Building height=169 Ft13 story building
Roof = 43,462 Ft-SqAll walls 37.5% glass
Roof U=.048 Wall U=.090Glass U=.55 Glass SHGC=.40
FootprintSouth=240 Ft North=240 Ft
Each wall=40,560 Ft-SqEast=181.09 Ft West=181.09 Ft
Each Wall=30,604 Ft-Sq
The following summarizes the basic characteristics of this (SEE) Model;
1. The simultaneous solution of basic HVAC equations.
2. The model is of any 24-hour day. 3. The building is modeled as five zones,
four walls and the building interior. 4. The building is modeled with all loads of
Figure 2 in the interior of the building plus the roof load. The perimeter load is defined by the weather conditions of Figure 2 plus infiltration or exfiltration.
5. The author expects some load values, efficiencies, and analyses will be questioned. That’s good; the objective is to present an approach to real time building energy modeling and not present the (SEE) Model given here as the final model. Modifications to the model based on better data is a part of this (SEE) Model concept.
6. The (SEE) Model requires that the energy into the building and plant equals the energy out1,2 just as occurs with a real building and plant.
7. The (SEE) Model provides the ability to benchmark a building’s energy performance, on any day, against any ASHRAE Standard design, in this case ASHRAE Standard 90.1-2010 as interpreted from Liu5.
Table 1 gives building design and control characteristics of the system to be established here as the benchmark best designed and controlled Standard 90.1-2010 building5 and plant13.
Building Location and Design1. Location=Kansas City Missouri. 2. Ambient temperatures Figure 2 3. Percent clear sky 100%. 4. Building design per Liu5 5. Percent wall glass 37% 6. Peak lights kW .81 watts/ft2
7. Peak plugs kW .66 watts/ft2
8. Return air is to building perimeter.9. Duct design static 5.5 inches water.10. Fan powered terminals not installed11. Return air fans not installed
Building Control 12. Lights on/off control- 6% on after hours.13. Plugs on/off control-44% on after hours14. Building pressure control, yes 15. Supply air = 55F16. Supply water 44F-44.6F17. Stats controlled, Yes 18. Perimeter heat air temp, 105F.19. VAV fan duct pressure control, yes 20. Fresh air CFM control, yes21. Fresh air heat stat set point, 42F
Plant Design & Control22. Chiller/Tower selection13.
Table 1: System
Chiller/Tower Defined
Tower for (SEE) model Low cost towerDesign Wet bulb 78.0FDesign Load 1173 tonTower water flow 2000 gpmApproach temperature 8.0 FCalculated range 14.13FRange + approach 22.13FOne cell with 50HP fans
40 kW
Selected Tower9 NC8409UAN1Cold water 86FReturn water to tower 100.13FCapacity 104.4%ASHRAE 90.1 56.4 gpm/HPStatic lift 12.0 ft.
Table A: Selected Tower
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Design Tons 1000.0Chiller kW 583.0Chiller kW/ton .583Evap water flow rate (gpm) 1500.0Evap enter water temp (F) 60.0Evap leave water temp (F) 44.0Evap refrigerant temp (F) 41.4Evap refrig. approach (F) 2.6Evap press. drop (ft. water) 34.5Evap water vel. (ft. /sec.) 8.38Cond heat rejection (ton) 1172.5Cond water flow rate (gpm) 2010Cond enter water temp (F) 86.0Cond leave water temp (F) 100.13Cond refrigerant temp (F) 101.73Cond refrig. approach (F) 1.6Cond press. drop (ft. water) 43Cond water vel. (ft. /sec) 9.71
Table B: Chiller selection data for Kansas City
Table A gives design data for the selected tower and Table B for the selected chiller.Energy Balance System energy balance analyses is a fundamental requirement and therefore a tool of a (SEE) Model. Figure 3 top chart gives the energy balance of the building design defining the plant load as 864.6 ton for one of the six buildings served by the central chilled water plant. This design energy balance of Figure 3 would have been determined during the design of the building and plant. The basic equations and manufactures data required to determine the design energy balance are the basic equations of this (SEE) Model4. Figure 3 also gives the (SEE) Model energy balance of the building at the 4PM winter temperature of 42F dry bulb and wet bulb. The building shell load and fresh air load are negative values and 27.6 ton of perimeter heat is required to maintain space comfort. Comparing the charts of Figures 3 illustrates that the lights and plug loads are the same for design day and the winter day.
130.2 105.665.55 67.4 45.0
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lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
Figure 3: Table 1 System- Top chart energy balance at 4PM design conditions of Figure 2-Bottom chart energy balance at 4PM winter conditions of Figure 2. Total building kW slightly decreased at winter weather conditions. Summing the lights, plugs, and fans of the top chart gives 301.35 ton. The bottom chart includes perimeter heat and sums to 290.9 ton. Perimeter heat of 27.6 ton is required for winter operation and the fans kW decreased due to less load. One building gives a plant load, at 101F outside temperature, of 864.6 ton, reducing to 230.3 ton at winter conditions of 42F outside temperature. As stated above the top chart would have been determined during the design of the building and plant. The bottom chart could also have been determined by desk top calculations, however the (SEE) Model accomplished the task by inputting the winter weather temperatures and adjusting the number of chiller/towers on to provide 44F supply water. The system schematic at 4PM is given by Schematic 1.
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Each BLD ft2 = 565,000 %clear sky = 100.0% InfilLat-ton = 0.00Condenser >pumpT-kW = 29.5 # floors = 13 Tdry-bulb = 101.0 Ex-/Infil+-CFM = 0 <<
(cond)ton= 1030.6 Pipesize-in = 6.0 (H)T-pipe= 9.6 Tower Roof ft2 = 43,462 Twet-bulb= 78.0 Infilsen-ton = 0.0TCR= 98.7 > GPMT= 12060 > (ewt)T= 97.2 tfan-kW= 40.0 N/S wall ft2 = 40,560 WallNtrans ton= 5.15
TCR-app= 1.51 (H)T-total= 64.6 (H)T-static = 12.0 Tfan-kW= 240.0 E/W wall ft2 = 30,604 WallStrans ton= 5.73(COND)ton= 6184 PT-heat ton = -8.55 < gpmT = 2010 tfan-%= 100% Wall % glass= 37.5% WallEtrans ton= 3.88
(H)cond= 43.0 <PumpT-kW= 176.8 < (lwt)T = 84.9 tton-ex= -1042 Glass U = 0.55 WallWtranston= 3.88 WallTot trans ton = 18.6(cond)ft/sec= 9.7 EfTpump= 0.83 Tapproach = 6.9 T#= 6 Wall U = 0.09 GlassN trans ton = 18.13
Ptower # = 6 Trange= 12.3 T-Ton-ex= -6252 Glass SHGC = 0.40 GlassS trans ton = 18.13Trg+app = 19.2 Wall emitt = 0.55 GlassE-trans ton = 13.68
Compressor RoofTrans ton = 43.1 GlassW-trans ton = 13.68 GlassTot-trans-ton= 63.6(chiller)kW= 507.2 Kansas City Office Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0(chiller)lift= 56.8 Total Bld ft2= 3,390,000 Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 6.1(chiller)%= 87% Time of Day= 4PM plugton&kW = 106 371.2 GlassE-solar ton = 4.6(chiller)#= 6 Weather %clear sky = 100% Lightton&kW= 130 457.7 GlassW-solar ton = 62.0 GlassTot-solar-ton = 82.6
(CHILLER)kW= 3043 conditions Tdry bulb = 101.0 Total Bldint-ton = 346.3 BLD kW= 828.9 (int cfm)per-ton = 0.00 >(chiller)kW/ton= 0.577 Twet bulb = 78.0 (int-cfm)to-per-ret= 192399 FAN kW= 230.6 Tot Bldper-sen-ton = 164.9 v
Plant kW = 3860 Tstat-int= 75.0 HEAT kW = 0.0 Tstat-per = 75.0 returnPlantkW/ton = 0.744 (Bld)int-air-ton= -346.3 ^ SITE kW = 1059.4 ^ (Bld)per-air-ton= -164.9 air
Tair supply int= 55.00 Bld Shell (ton)= 208.0 Tair supply per= 55.00 ^ Fresh Air (ton)= 335.7 ^
> Evaporator Ton kW Ton kW V(evap)ton= 879.4 (fan)int-ter ton&kW= 0.0 0.0 (fan)per-ter ton&kW= 0.0 0.0
TER= 41.9 Theat-air= 55.0 TER-app= 2.32 (D)heat ton&kW = 0.0 0.0
^ EVAPton= 5276 Treheat air = 55.0(H)evap= 34.5 (D)reheat ton&kW = 0.0 0.0
(evap)ft/sec= 8.38 0.0(evap)des-ft/sec= 8.38 (D)int-air-ton= -346.3 Interior Peri
^ V Tair coils = 55.00 duct Tair coils= 55.00 ductgpmevap= 1500 <pumpc-kW = 13.79 Psec-heat-ton = -20.2 GPMSEC = 7914.7 (D)int-CFM= 192,399 ^ (D)per-CFM= 91,607 ^Pchiller-# = 6 (lwt)evap = 44.24 > Psec-kW= 316.9 > (ewt)coil= 44.24 >>>(Coil)sen-ton= 688 ^ ^
(H)pri-total= 39.5 Efdes-sec-p = 0.80 Coil UA = 2.91 ^ (H)pri-pipe= 1.1 Tbp= 44.24 Efsec-pump = 0.78 # Buildings = 6.0 One Building (TON) COIL LMTD = 15.58
(H)pri-fitings= 3.9 gpmbp= -1085 (H)sec= 165 PLANTton = 5187 CoilCap-ton = 45.3(Ef)c-pump= 0.81 (H)pri-bp= 0.02 (H)sec-pipe= 102 Coilload-ton = 33.3 VPc-heat-ton= -4.47 (H)sec-bp= 0.00 Pipesize-in = 10.0 (COIL)L+s-ton= 864.6 ^ ^ ^
^ < Pumpc-kW= 82.7 (ewt)evap = 58.31 < (GPM)sec= 7915 < (lwt)coil= 60.24 <<<< Tair VAV= 81.90 TBLD-AR = 75.00(FAN)VAV-CFM= 284,005 (Air)ret-CFM = 284,005 Return
chillerkW/evapton= 0.577 4PM All Electric Fuel Heat 4PM (FAN)ton-VAV= 65.6 (FAN)ret-kW= 0.0 Fan(plant)kW/site ton= 0.744 kW Ton (FAN)kW-VAV= 230.6 (FAN)ret-ton= 0.0 V
CCWSkW/bld+FA ton= 1.094 BLD.kW= 4973.1 ^ (Air)ret-ton = 511.2Peoplesen+lat ton = 674 (Fan)kW = 1383.3 26 F.A.Inlet ^ Tar-to-VAV = 75.00
WeatherEin-ton = 3262 Ductheat= 0.0 0.00 statFA= 42 26 VAV FANS VAVret-sen ton = 425.9(Site)kW-Ein-ton = 1808 (FA)heat= 0.0 0 TFA to VAV = 101.0 > Tret+FA = 79.34 VAVret Lat-ton = 37.45PlantkW-Ein-ton = 1098 Heat total = 0.0 0.00 >(FA)sen-ton = > 196.2 (dh) = 4.404 < VAVret-CFM = 236,619 <Enfil cfm energy = 0 PlantkW= 3859.7 Plant > (FA)CFM= 47,386 > Efan-VSD= 0.638 V
Total Ein-ton = 6842 SystkW = 10216.2 10216.2 (SEE) Schematic > (FA)Lat-ton= 139.5 VAV inlet-sen-ton = 622.1Pumptot-heat-ton = -33 Ton Blue (FA)kW= 0.0 VAVinlet-lat-ton= 176.9 ExLat-ton = -7.5
Exfillat+sen-ton = 0 BLD.kW= 4973.1 kW Red ExCFM = -47,386Exhtsen+lat-ton= -557 CCWSkW = 5243.1 Water temp pink SEE Schematic air side TEx = 75.00
Tower Tton-Ex = -6252 SystkW = 10216.2 Water gpm orange Air temp green kW red Time= 4PM Exsen-ton = -85.3 V Total Eout-ton = -6842 6 Buildings Kansas City air temp green Air CFM purple Ton blue v
Schematic 1: Table 1 System at 4PM Design Conditions
9
System kW Demand
1,142 1,142
3,439
4,973 4,973
2,763
1,9051,600
510 426 400674
1757
2930
3390
3860
2216
1067846
150 129513
1,0131,212
1,383
593269 203
1 1 1 1 3 5 5 5 6 4 2 2 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(kW
)
TIME OF DAYTable 1 System kW demand with elect heat-Design Day
(Blds)kW (plant)kW (AHU)Fan kW
Total heat kW # Chiller/Towers on
1,142 1,1421,295
3,439
4,973 4,973
2,763
1,9051,600
4,153
4,811
4,1134,390
1,744
583
2,647
3,965
185
539 580294
204324 309
616 588
266
316 324
1 1 1 1 1 1 1 2 2 1 1 1 0
500
1000
1500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(AHU
)&Fa
n kW
(Bld
s) &
Hea
t kW
TIME OF DAYTable 1 System kW demand with elect heat-Winter Day
(Blds)kW Total heat kW (AHU)Fan kW
(plant)kW # Chiller/Towers
Figure 4: Table 1 System kW Demand
Figure 4 gives the six-building campus and plant kW demand of the Table 1 system at design and winter conditions of Figure 2. Figure 4 illustrates the capability of the (SEE) Model to give essentially any desired data due to the detail equations of the model. Figure 4 illustrates the significant change in system kW as given by the secondary horizontal axis. The plant and air system kW drop with winter
conditions but heat energy approaches the kW demand of the lights and plug loads. Design conditions require six chiller/towers on at 4PM reducing to one chiller/tower after hours. Winter conditions requires two chiller/towers at 2PM and 4PM with one required for all other hours. The kW demand of the plant and air system is determined by detail simulations. For example, adding fan powered terminals11 and return fans12 is addressed by Nelson4 to illustrate the detail of the air system model. The following computations are to demonstrate that charts of the (SEE) Model are consistent with all other charts. Figure 3 is the energy balance for one building and the load due to kW demand at design is; (130.2 + 105.6 + 65.55 = 301.3 ton) (301.3-ton x 12,000 btu/ton)/3413 btu/kW) = 1059.36 kW x six buildings = 6,356 kWThis is the kW demand of the system minus the plant kW. The secondary horizontal axis of the top chart of Figure 4 gives 10,216 kW as the total system demand at 4PM. Subtracting the 3,860-plant kW gives 6,356 kW as determined above from the 4PM energy balance of Figure 3.
(EUI) Estimates (kbtu/ft2-yr)
78 7672
68
7578
8286
88
8683
80
68 67 66
68
70 71 72 73 74 72 70 68
42 40 3835
4044
48 5053
50 48 46
40 38 3835
40 4246 48 50 48 46 44
34 3228 26
24 30
38 40 42 40 38 36
6260
5860
6466
6870
7270
6866
5250
4648
50
5658
6062
6058
56
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
20
30
40
50
60
70
80
90
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
% Clear Sky
Tem
pera
ture
(F)
TIME of DAYSummer, Spring, Fall, & Winter Weather
Summer Dry Bulb (F) Summer Wet Bulb (F) Fall dry bulb (F)Fall wet bulb (F) Winter dry bulb (F) Winter wet bulb (F)Spring Dry Bulb (F) Spring Wet Bulb (F)
Figure 4A: Assumed weather for (kbtu/ft2) estimates
10
The following are (SEE) Model estimates of annual (EUI) values that put into perspective the effect of changes in design and control of a building and plant as given by Tables 1 & 2. The (EUI) estimates are based on average seasonal weather conditions of Kansas City Missouri, shown by Figure 4A. For Table 1 conditions Figure 5 top chart gives the (SEE) Model (EUI) estimated of about 38 (kbtu/ft2-yr), a value that is close to the DOE value of about 43 (kbtu/ft2-yr) for new constructed large office buildings. Kansas City reports values in the order of 73 (kbtu/ft2-yr) for existing office buildings. Table 1 gives 22 design and control decisions that were made for the building as defined by the figures and discussion thus far. Changing any one of the 22 items would change the building energy consumption and therefore the (EUI) value, perhaps explaining the Kansas City real building values being greater than the DOE values.Figure 5 bottom chart breaks the (SEE) Model (EUI) estimate into four values for each of the four seasons. The largest value is the building load due to lights and plug loads and is the same for all seasons. The fan value is relatively constant and the plant load is high at summer conditions and significantly less for the other three seasons. The heat load is high during the winter and fall seasons. Figure 5 illustrates that the building lights and plug loads are dominate for all seasons.
8.45
10.05
11.79
7.85
0
5
10
15
20
25
30
35
40
kbtu
/sq
ft-y
ear
Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Summer (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Spring (kbtu/sqft-yr)
5.18
35.
183
5.18
35.
183
0.76
40.
599
0.59
40.
674
2.48
10.
827
0.72
0 1.20
30.
018
3.43
65.
292
0.79
2
0
1
2
3
4
5
6
kbtu
/sq
ft-y
ear
Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Bld-Summer Bld-Fall Bld-Winter Bld SpringFan-Summer Fan Fall Fan-Winter Fan-SpringPlant-summer Plant-Fall Plant-winter Plant-SpringHeat-summer Heat-Fall Heat-winter Heat-Spring
Figure 5: Table 1 System (EUI) estimate & System Components (EUI) per season
(SEE) Building ModelThe following gives detail of the Building (SEE) Model.Perimeter & Interior LoadsFigure 6 top chart gives the building perimeter loads due to design day weather conditions of Figure 2, with the exception, as stated above in model characteristics, the roof load is modeled as an interior load. The bottom chart gives the perimeter loads due to winter conditions. The only change made in the (SEE) Model going from the top chart to the bottom chart was inputting the winter
11
weather conditions of Figure 2. The (SEE) Model equations made all changes of Figure 6 bottom chart consistent with the requirement that energy into the building equals energy out of the building.Figure 6 top chart, secondary horizontal axis, gives the perimeter sensible load. At 4PM the 165-ton load is made up of 82.6 ton solar, 63.6-ton glass transmission, and 19-ton wall transmission for a total of 165-ton sensible load as shown on the chart. Add to this the roof load of 43.1 ton of Figure 7 top chart gives the 208-ton shell load of Figure 3 top chart where shell load is a measure of a buildings structural design as related to energy. Figure 6 bottom chart is consistent with the winter energy balance of Figure 3 bottom chart. All return air is modeled as returning to the perimeter of the building, therefore during winter operation a one-degree F difference in stat set points can transfer heat energy from the interior of the building to the perimeter if the perimeter stat is set one degree less than the interior stat. At 4PM stat control results in a 15.6-ton energy transfer from the interior of the building to the perimeter of the building as shown by Figure 6 bottom chart. The bottom chart of Figure 3 shows the shell load is minus 24.6 ton at 4PM winter conditions. Figure 6 bottom chart, secondary horizontal axis, gives a perimeter sensible load of minus 17.14 ton at 4PM made up of 64.2 ton solar, minus 19-ton wall
11 7 6 59
15 16 17 19 17 16 14
37
2722
17
32
4651 54
63.656
4944
0.0
69.878.7
66.5
40.1
68.4
82.6
62.5
2.0 0.0
0.0
0.0
-10
0
10
20
30
40
50
60
70
80
90
100
-10
0
10
20
30
40
50
60
70
80
90
100
Perimeter total sensible ton
(TO
N)
(TO
N)
TIME OF DAYBuilding Perimeter Loads-Peak Summer Day
Wall Trans-Ton Glass Trans-Ton Glass solar Ton
infiltration Sen-Ton infiltration Lat. Ton
-26 -28 -31 -32 -33 -29 -22 -20 -19 -20 -22 -25
-98 -103-113 -117 -122
-108-88 -86 -78.3 -83 -88 -93
0.0
26.4
55.2
102.0 93.3 106.4
64.2
21.72.0
0.00.0
14.8 15.63.8
-140-120-100-80-60-40-20020406080100120
-140-120-100
-80-60-40-20
020406080
100120
Perimeter total sensible ton
(TO
N)
(TO
N)
TIME OF DAYBuilding Perimeter Loads-Typical Winter Day
Wall Trans-Ton Glass Trans-Ton Glass solar Ton
infiltration Sen-Ton infiltration Lat. Ton Stat control-ton
Figure 6: Building Perimeter Loads
transmission and minus 78.3-ton glass transmission for a total of minus 33.1-ton building wall load; offset by the 15.6-ton stat control energy transfer for a total perimeter load of minus 17 ton as shown by Figure 12 bottom chart secondary horizontal axis. The shell load of Figure 3 bottom chart is made up of the minus 33.1-ton wall load plus the roof load of 8.1 ton of Figure 7 bottom chart for a shell load of (-33.1 + 8.1 = -25 ton) as shown by the winter energy balance of Figure 3 bottom chart. Figure 7 gives the interior loads that do not change with winter conditions except for the roof load. The roof load is negative for most of the winter hours
12
as shown by the bottom chart and becomes positive 8.1 ton due to roof solar load.
67 67
45.0 45.0
4.7
8.4
43.1
8.27
130 130
2947
106 106
47
0
20
40
60
80
100
120
140
0
20
40
60
80
100
120
140
Interior total sensible ton
(TO
N)
TIME OF DAYBuilding interior loads (ton)-Peak Summer Weather
People-Sen Ton People Lat Ton Roof Trans-TonLights Ton Plug-Ton
67 67
7
-8.2 -7.8
8.1
-6.8
7
130 130
2947
106 106
47
0.0
45.0 45.0
4.7
-40
-20
0
20
40
60
80
100
120
140
-40
-20
0
20
40
60
80
100
120
140
Interior total sensible ton
(TO
N)
TIME OF DAYBuilding interior loads (ton)-Typical Winter Weather
People-Sen Ton Roof Trans-Ton Lights TonPlug-Ton People Lat Ton
Figure 7: Building Interior Loads
VAV Fan Performance at Design Conditions Figure 8 gives the VAV fan performance at design day and winter day conditions of Figure 2. Time of day is not shown but is the same as given by all above figures. Both charts of Figure 8 illustrate that the interior CFM of air supply is significantly greater than the perimeter. Winter perimeter CFM is very low at mid-day conditions illustrating a reason, other than energy transfer, that interior air
is modeled as returning to the perimeter of the building to assist in fresh air ventilation.At 4PM design day the interior sensible load is;Air (ton) = CFM * 1.08 * (75F – 55F)/12,000Where 75F is the interior stat set point and 55F is the temperature of the supply air to the interior.Air (ton) = 192,399 CFM * 1.08 * (20F)/12,000 = 346 ton as shown by Figure 7 top chart.At 4PM design day the perimeter sensible load is;Air (ton) = 91,607 * 1.08 * (20)/12,000 = 165 ton as shown by Figure 6 top chart.
30,955
99,712
173,070
182,590189,568
192,399
105,825
68,181
50,627
15,567
70,942
91,607
32,245
55 55 55
45
50
55
60
0
50,000
100,000
150,000
200,000
FAN VAV-CFM
AIR
TEM
P. (F
)
(CFM
)
FAN kW-VAV
VAV Fan performance-Peak Summer Weather
(Duct)interior-CFM (Duct)perimeter-CFM(Temp)air-supply-interior (Temp)air-supply-perimeter
25,546
93,531
164,082165,579
170,028172,938
86,189
51,26742,315
50,508
6,992 192 6,143 40,91055 55
105.0 105.0
45
55
65
75
85
95
105
0
50,000
100,000
150,000
200,000
FAN VAV-CFM
AIR
TEM
P. (F
)
(CFM
)
FAN kW-VAV
VAV Fan performance-Typical Winter Day
(Duct)interior-CFM (Duct)perimeter-CFM(Temp)air-supply-interior (Temp)air-supply-perimeter
Figure 8: VAV Fan PerformanceVAV Fan Performance at Winter ConditionsAt winter conditions the supply air temperature to the perimeter at 4PM is 105F as shown by the bottom chart of Figure 8 and the perimeter stat is
13
set at 74F as discussed above, therefore perimeter sensible load at winter conditions is;Air (ton) = 6,143 CFM * 1.08 * (74 – 105)/12,000= - 17 ton as shown by Figure 6 bottom chart.Interior Air (ton) = 172,938*1.08*(75-55)/12,000= 311 ton as shown by Figure 7 bottom chart. The bottom chart of Figure 8 shows that 105F heating air is required on the building perimeter except for 2PM when perimeter heat is not required and 55F air is supplied to the perimeter. Figure 9 gives more detail.
799
111 97
647
105 105 105 105
55 55
74.0 74.0 74.0 75.0 74.0 74.0
50556065707580859095100105110
0
100
200
300
400
500
600
700
800
900
1,000
Perimeter air supply (CFM)
Air T
empe
ratu
re (F
)
Perim
eter
Hea
t (kW
)
Time of DayVAV Fan Performance-Winter Weather Perimeter air
Total perimeter air heat (kW) Perimeter air supply temp (F)Perimeter Heating air temp (F) Supply air off coil (F)Perimeter stat (F)
Figure 9: VAV Performance-Perimeter
Figure 6 bottom chart shows the perimeter sensible load at 10PM is minus 114.14 ton. To meet this load the air supply temperature to the perimeter is 105F. The 55F supply air off the coil must be heated to 105F. From Figure 9 at 10PM;Air heat ton = 40,910 CFM * 1.08 * (105F - 55F) = 184.1-ton heat.184.1-ton heat * 3.517 kW/ton = 647 kW required to heat the 55F coil supply air to 105F to meet the heating requirement of the perimeter, as shown by Figure 9 at 10PM.VAV Fan CFM & Air TemperaturesFigure 10 illustrates the air CFM and temperatures for design day. At 4PM the building return air to the inlet of the VAV fans is 236,619 CFM as shown
by the bottom chart and 75F return air as shown by top chart. Mixed with 47,386 CFM of fresh air at 101F resulting in an air mixed temperature of 79.34F and 284,005 CFM of air to the inlet of the VAV fans as shown by Figure 10. The VAV fans require 231 kW, Figure 12, to move the 284,005 CFM of air and in the process heats the air from 79.34F to 81.90F as shown by Figure 10 bottom chart. The heating of the air as it passes through the VAV fans is an example of a required characteristic of the (SEE) Model.
84.0
94.0
101.0
93.0
75.11
78.69 79.34
76.5475.00 75.00
76.57
80.88 81.90
77.82
70
75
80
85
90
95
100
105
70
75
80
85
90
95
100
105
Plant load ton-Sensible-one Bld
Air T
empe
ratu
re (F
)
Air T
empe
ratu
re (F
)
Time of DayVAV Fan Performance-Peak summer weather
(FA) Temp (F) Air mixed (return + FA) (F)
Return air to VAV inlet (F) (Temp)air-VAV to coil
45,957
196,626
236,619
75,802
565 47,386 47,386 7,070
46,522
244,012284,005
82,871
75.11
78.69 79.34
76.54
76.57
80.8881.90
77.82
55 55
50
55
60
65
70
75
80
85
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Plant load ton-Sensible + Latent-one Bld
AIR
TEM
PERA
TURE
(F)
(CFM
)
Time of DayVAV Fan Performance-Peak summer weather
(VAV)minus exhaust inlet CFM (FA)-CFM(FAN)VAV-CFM Return + FA temp(F)(Temp)air-VAV to coil Supply air off coil (F)
Figure 10: VAV Fan Performance-Design DayAs the air is heated it adds load and in turn the VAV fans must increase CFM to meet the increased load which increases VAV kW and so on until steady state is achieved. The set of (SEE) Model equations
14
are analogues to a set of feedback control equations that seek a new steady state for a change in conditions.The Table 1 building is modeled as zero air infiltration into the building; therefore, the exhaust CFM, not shown by Figure 10, is equal to the fresh air CFM into the building. Infiltration and/or exfiltration significantly changes the air system which will be addressed by a later chapter.
42.0 42.0 42.0 42.0
73.76
65.14 65.53
71.28
74.00 74.0075.04
66.79 67.24
72.57
55 55
40
45
50
55
60
65
70
75
80
40
45
50
55
60
65
70
75
80
Plant load ton-Sensible-one Bld
Air T
empe
ratu
re (F
)
Air T
empe
ratu
re (F
)
Time of DayVAV Fan Performance-Winter Weather
(FA) Temp (F) Air mixed (return + FA) (F)Air return to VAV inlet(F) (Temp)air-VAV to coilSupply air off coil (F)
75,490
123,688
131,694
76,155
565
47,386 47,386
7,070
76,055
171,075179,080
83,225
75.04
66.79 67.24
72.57
73.76
65.14 65.53
71.28
55 55
40
45
50
55
60
65
70
75
80
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Plant load ton-Sensible + Latent-one Bld
AIR
TEM
PERA
TURE
(F)
(CFM
)
Time of DayVAV Fan Performance-Typical Winter Weather
(VAV)minus exhaust inlet-CFM (FA)-CFM(FAN)VAV-CFM (Temp)air-VAV to coilReturn + FA temp(F) Supply air off coil (F)
Figure 11: VAV Fan Performance-Winter Day
The secondary horizontal axis of Figure 10 gives the load the VAV fans transferred to the coils and the coils present to the plant. At 4PM the sensible load is 688 ton and the sensible plus latent plant load is
865 ton. Figure 13 below gives the latent loads transferred by the VAV fans to the plant.Figure 11 gives the same data as Figure 10 but for winter weather conditions. Figure 11 illustrates the air CFM and temperatures for winter weather of Figure 2. At 4PM the building return air to the inlet of the VAV fans is 131,694 CFM at 74F; mixed with 47,386 CFM of fresh air at 42.0F resulting in an air mixed temperature of 65.53F and 179,080 CFM of air to the inlet of the VAV fans. The VAV fans require 97 kW, Figure 12 bottom chart, to move the 179,080 CFM and heats the air to 67.24F as shown by Figure 11. As stated above the building is modeled as zero air infiltration into the building; therefore, the exhaust CFM is equal to the fresh air CFM into the building as shown by Figure 11. The secondary horizontal axis of Figure 11 gives the load the VAV fans transfer to the coils and the coils present to the plant. At 4PM the sensible load is 197 ton and the sensible plus latent is 230 ton. Note the outside temperature of Figure 2 is 42F or less. The fresh air temperature to the VAV fan inlet is controlled to 42F with heat added. Figure 14 below defines the kW required. Figure 13 below gives the latent loads transferred by the VAV fans to the plant.
15
VAV FANS Performance
46,522
244,012284,005
82,871
21
169
231
34
116 97 90 164 366 568 573 631 688 434 225 170
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
240,000
280,000
320,000
109 91 84 155 342 520 526 574 622 406 212 161
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
VAV Fan performance-Design Summer Weather
(FAN)VAV-CFM (VAV Fan kW)
76,055
171,075 179,080
83,225
31
90 97
34
127 130 137 131 127 182 172 191 197 96 125 132
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
119 121 128 122 111 156 148 166 170 83 115 122
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
VAV Fan performance-Typical Winter Weather
(FAN)VAV-CFM (VAV Fan kW)
Figure 12: VAV Fan Performance
Figure 12 gives the VAV fan kW, (CFM), and inlet sensible load (ton) and sensible load exiting the VAV fans where load is added by the VAV fan kW. The VAV fan model is based on Kavanaugh10 and is the most complex set of model equations, as illustrated by above Figures, with the exception of the chiller/tower model to be addressed by Chapter 2.
2.3 0.0 0.0 0.07.4
36.2 36.2 37.0 37.5
11.24.2 4.3
1.6 0.7 0.6 0.9
65.0
94.3104.2
118.5139.5
77.0
24.29.3
-20
0
20
40
60
80
100
120
140
160
-20
0
20
40
60
80
100
120
140
160
Plant latent load (ton)
(TO
N)
(TO
N)
Time of DayVAV Fan performance- Design latent load (ton) to Plant
VAV inlet return air-Lat-Ton (FA)Lat-Ton
2.30.0 0.0 0.0
6.7
32.5 32.2 32.4 33.1
9.4
4.1 4.3
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
-20
0
20
40
-20
0
20
40
Plant latent load (ton)
(TO
N)
(TO
N)
Time of DayVAV Fan performance- Winter latent load (ton) to Plant
VAV inlet return air-Lat-Ton (FA)Lat-Ton
Figure 13: VAV Fan transfer of latent load to Plant
Figure 13 gives the latent load transferred by the VAV fans to the plant. Latent load is a result of people in the building and fresh air input to the inlet of the VAV fans. Air infiltration will add latent load but is modeled as zero for the Table 1 system.
16
Building and Air handler kW Demand
190 190 190 216
573
829 829 829 829
460
318267
25 22 21 3586
169 167202 231
9945 34
0
100
200
300
400
500
600
700
800
900
1000
0
100
200
300
400
500
600
700
800
900
1000
TOTAL SITE OR AIR SIDE kW
Air S
yste
m (k
W)
Build
ing
Ligh
ts &
Plu
g (k
W)
Time of Day
One Bld-Site or air side (kW)
One Bld (kW) VAV Fans (kW) Duct reheat (kW)
Duct heat (kW) Fresh Air (kW)
190
573
829 829 829 829
460
267
31
90 97
34
304
4237
246
496
69 60
401
2.5
180
0.0 13.4-50
0
50
100
150
200
250
300
350
400
450
500
-100
0
100
200
300
400
500
600
700
800
900
1000
TOTAL SITE OR AIR SIDE kW
Air S
yste
m (k
W)
Build
ing
Ligh
ts &
Plu
g (k
W)
Time of DayOne Bld-Site or air side (kW)-Typical Winter Weather
One Bld (kW) VAV Fans (kW) Duct reheat (kW)
Duct heat (kW) Fresh Air (kW)
Figure 14: One Building & Fan System (kW)
Figure 14 gives the kW demand total for a building and air handler system or site, not including the plant kW. Comparing the total site kW on the secondary horizontal axis’s illustrates that kW demand during winter operation is significantly greater for all hours except noon, 2PM, & 4pm. Figure 9 above gives the total perimeter air heat kW required and Figure 14 bottom chart breaks it down into duct reheat kW to bring the 55F coil supply air up to 75F, and duct heat kW required to
bring the air from 75F to 105F to meet the perimeter heat load requirement. For example, at 10PM the bottom chart of Figure 14 shows 401 kW for duct heat and 246 kW for duct reheat for a total of 647 kW as shown by Figure 9 at 10PM. Fresh air kW to maintain 42F fresh air into the building is shown by Figure 14 bottom chart as 13.4 kW at 10PM and VAV fan kW at 34 kW for a total site kW of 962 as shown by the secondary horizontal axis of bottom chart Figure 14.
System kW Performance-Six BuildingsDesign Day & Winter Day Performance
1,142 1,1421,295
3,439
4,973 4,973
2,763
1,9051,600
510 426 400674
1757
293030263390
3860
2216
1067846
129513
1,0131,2121,383
593269 203
1 1 1 1 3 5 5 5 6 4 2 2 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(kW
)
TIME OF DAYSystem kW demand with elect heat-Design Day-Table 1
(Blds)kW (plant)kW (AHU)Fan kWTotal heat kW # Chiller/Towers on
Figure 15: System Performance-Design Day
To this point Chapter 1 has addressed one building with characteristics as defined by Table 1. Introducing the plant requires defining the performance of the six-building campus. All six buildings are modeled with the same characteristics as defined above for one building. Each building could be defined with different characteristics, however that requires more computing power than the author presently has available.Figure 15 gives the design day performance and Figures 16 & 17 give winter day performance with
17
weather defined by Figure 2. Figure 16 is the electric heat system and Figure 17 is the system with fuel heat.
1,142 1,1421,295
3,439
4,973 4,973
2,763
1,9051,600
185 539580
204324 309
616 588266 316 324
4,153
4,811
4,1134,390
1,744
583
2,647
3,965
1 1 1 1 1 1 1 2 2 1 1 1 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(kW
)
TIME OF DAYSystem kW demand with elect heat-Winter Day-Table 1
(Blds)kW (AHU)Fan kW(plant)kW Total heat kW
Figure 16: System Performance-Winter DayElectric Heat
1,142 1,142
3,439
4,973 4,973
2,763
1,9051,600
185539 580
294 219 204324 312 309 278
616588 266 316 324
1181
1368
11701248
496
166
753
10331127
1 1 1 1 1 1 1 2 2 1 1 1 0100200300400500600700800900100011001200130014001500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
Heat
n (to
n)
(kW
)
TIME OF DAYSystem kW demand with fuel heat-Winter Day-Table 1
(Blds)kW (AHU)Fan kW(plant)kW Total heat (ton)
Figure 17: System Performance-Winter DayFuel Heat
Comparing the system kW values of Figures 15 & 16 given by the secondary horizontal axis illustrates that winter operation requires significantly more kW during unoccupied hours and close to the
design values during occupied hours. The number of chiller/towers on varies from one to six for design day weather and only one to two for winter operation. Comparing Figures 15 & 16 illustrates that the kW demand during unoccupied hours is close to the same for design day and winter operation of the fuel heat system.
Chapter 1 Summary Chapter 1 had two purpose; one to give values and understanding of the Table 1 system operation at design day and winter day weather, and also demonstrate the detail that must exist in a (SEE) Model if it is to model the real time performance of a system. The author has found that system schematics often provide understanding of the system that is difficult with multiply charts. The next Chapter 2 will address plant performance.
18
Chapter 2-System Energy Equilibrium (SEE) Plant Model The following will describe the Plant (SEE) Model performance operating against the load of six buildings as defined by Table 1.
722 588 545
992
2630
4193 4282
4721 5187
3131
15191103
510 426 400674
1757
2930 30263390
3860
2216
1067846
1 1 1 1 3 5 5 5 6 4 2 2
05001000150020002500300035004000450050005500
0500
1000150020002500300035004000450050005500
Number (#) Chiller/Towers on
(TO
N o
r kW
)
Time of DayPlant load (ton) & Plant kW for six buildings-Design Summer Day
All Blds Plant load (Ton) Plant kW
776 778 823 784 801
12851228
1341 1382
635
775 816
324 312 309 278 273
616 628548 588
266316 324
1 1 1 1 1 1 1 2 2 1 1 1
0
500
1000
1500
0
500
1000
1500
Number (#) Chiller/Towers on
(TO
N o
r kW
)
Time of DayPlant load (ton) & Plant kW for six buildings-Winter Day
All Blds Plant load (Ton) Plant kW
Figure 1: Plant load (ton) & kW demand
Figure 1 gives the plant load (ton) and plant kW demand for design day and winter weather conditions defined by Figure 2 of Chapter 1. The horizontal axis shows the number of chiller/towers on illustrating the plant operates with only one chiller/tower most of the time during the winter
with two chiller/towers required at 2PM & 4PM. During design day operation only one chiller/tower is required during off hours peaking to six chiller/towers at 4PM design hour conditions.
1,093 891 8271,502
3,987
6,3796,5167,190
7,915
4,753
2,3021,674
1,500 1,500
4,500
7,5009,000
3,000
-407 -609 -6732
-513-1,121-984
-310-1,085-1,247
-698-1,326
1 1 1 1 3 5 5 5 6 4 2 2
-2,000-1,00001,0002,0003,0004,0005,0006,0007,0008,0009,00010,000
-2,000-1,000
01,0002,0003,0004,0005,0006,0007,0008,0009,000
10,000
# Chillers on
(gpm
)
Plant load (ton)P/S pumping (gpm)
Secondary pump (gpm) Evaporators (gpm) Bypass (gpm)
44.20
44.0
4
44.7
1
44.6
2
60.2
2
44.5
3
44.4
6
44.4
5
44.1
8
44.2
4
44.1
9
44.5
3
44.2
0
60.0
4
60.7
1
60.6
2
60.2
2
60.5
3
60.4
6
60.4
5
60.1
8
60.2
4
60.1
9
60.5
3
60.2
0
55.7
0
54.2
2
53.4
5
60.2
2
58.7
1
58.0
6
58.3
5
59.5
2
58.3
1
56.8
7
56.8
0
53.1
3
40
45
50
55
60
65
40
45
50
55
60
65
Total -Evaporator TON
Wat
er Te
mp.
(F)
Wat
er Te
mp.
(F)
Time of DayP/S pumping-water temperatures (F)
Evaporator leaving water (F) Bypass water(Tbp)(F)Coil leaving water (lwt)coil(F) Evap. Entering water(ewt)evap (F)
Figure 2: Primary/Secondary pumping-design day
Figure 2 shows the plant load to be picked up by the primary/secondary pumping and delivered to the chiller evaporators. The P/S pumping adds heat to the water therefore the evaporator load as shown by the secondary horizontal axis of Figures 2 & 3 is a little greater than the plant load shown by the primary horizontal axis. The (SEE) plant model assumes that pumping energy is transferred to the water as a function of the pumping efficiency. For example, if the pump is 80% efficient then 80% of
19
the energy to the pump heats the water and 20% goes to the atmosphere.
1,17
5
1,17
8
1,24
6
1,18
7
1,21
4
1,94
3
1,85
7
2,03
2
2,09
4
963
1,17
3
1,23
5
1,500 1,500 1,5001,
500
3,000
1,500
-325 -322 -254 -313 -286
443 357
-968 -906-537
-327 -265
1 1 1 1 1 1 1 2 2 1 1 1
-2,000
-1,000
0
1,000
2,000
3,000
4,000
-2,000
-1,000
0
1,000
2,000
3,000
4,000
# Chillers on
(gpm
)
Plant load (ton)P/S pumping (gpm)
Secondary pump (gpm) Evaporators (gpm) Bypass (gpm)
39.4
0
40.5
9
44.3
1
44.3
1
44.6
9
44.3
1
44.4
8
60.1
2
60.3
9
44.2
8
44.3
2
44.5
3
44.3
8
44.1
0
60.3
1
60.3
1
60.6
9
60.3
1
60.4
8
60.1
2
60.3
9
60.2
8
60.3
2
60.5
3
60.3
8
60.1
0
56.8
4
56.8
9
57.9
8
56.9
8
57.4
3 60.1
2
60.3
9
55.1
2
55.4
9
54.8
0 56.9
0
57.2
7
35
40
45
50
55
60
65
35
40
45
50
55
60
65
Total -Evaporator TON
Wat
er Te
mp.
(F)
Wat
er Te
mp.
(F)
Time of DayP/S pumping-water temperatures (F)
Evaporator leaving water (F) Bypass water(Tbp)(F)Coil leaving water (lwt)coil(F) Evap. Entering water(ewt)evap (F)
Figure 3: Primary/Secondary pumping-winter
Figure 2, for design day conditions, shows the flow (gpm) is in the wrong direction at 6AM as also shown by the bottom chart. The top chart shows only 2 (gpm) wrong way flow in the bypass therefore essentially no effect on the temperature of water to the coils. Figure 3 shows the same condition for 10AM and noon for winter operation. The top chart shows 443 (gpm) & 357 (gpm) bypass flow requiring the temperature supply off the evaporator to be dropped to 39.4F and 40.59F, shown by the bottom chart, to supply 44F supply water to the coils. A second chiller/tower could be
turned on to eliminate the wrong flow in the bypass but that might increase the plant kW. However, that is not necessarily true and is an issue for plant control. Controlling the plant to minimize plant kW is an issue the (SEE) plant model can address and will address in later chapters.
131 120 149357
627
635 679
816
467240
510 400674
1757
29303026
33903860
2216
1067846
280
2303
3043
606
1 1 1 1 3 5 5 5 6 4 2 2
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
# Chiller/Towers on
kWTime of Day
Plant, Chillers, Pumps & Towers (kW)
Total pump & tower fan-kW Plant-kW Chiller-kW
108 111 109 110155 155
239 239
126 138
324 309278 273
616 628
548 588
266316 324
216 204 198169 163
461 472
309350
140181 187
1 1 1 1 1 1 1 2 2 1 1 1
0
100
200
300
400
500
600
700
0
100
200
300
400
500
600
700
# Chiller/Towers on
kW
Time of DayPlant, Chillers, & Pumps (kW)
Total pump + tower fan-kW Plant-kW Chiller-kW
Figure 4: Plant kW-Design day top chart,Winter day bottom chartChiller kW plus pumps and tower fan kW equals plant kW as shown by Figure 4. Plant kW is significantly less during winter operation especially during occupied hours. Afterhours operation with one chiller/tower required brings the plant kW values design day and winter day closer together.
20
42.0
3
42.9
4
42.9
3
41.6
0
42.2
0
42.2
0
42.1
5
41.6
8
41.9
3
42.0
6
42.4
4
42.4
9
44.0
4
44.7
1
44.6
2
44.2
0
44.5
3
44.4
6
44.4
5
44.1
8
44.2
4
44.1
9
44.5
3
44.2
0
1 1 1 13
5 5 56
42 2
0
5
10
15
20
25
30
35
40
45
50
Evaporator Refrigerent approach (F)Te
mpe
ratu
re (F
)
Time of DayEvaporator performance
Evap refrig (Ter) Evap leaving water (F) # Chiller/Towers on
42.1
9
42.2
0
42.4
8
42.1
8
42.3
2
35.9
6 37.3
2 42.3
7
42.3
7
42.6
8
42.2
7
41.9
0
44.3
1
44.3
1
44.6
9
44.3
1
44.4
8
39.4
0 40.5
9
44.2
8
44.3
2
44.5
3
44.3
8
44.1
0
1 1 1 1 1 1 12 2
1 1 1
0
5
10
15
20
25
30
30
35
40
45
50
Evaporator Refrigerent approach (F)
Tem
pera
ture
(F)
Time of DayEvaporator performance
Evap refrig (Ter) Evap leaving water (F) # Chiller/Towers on
Figure 5: Evaporator performance-top chart design day-bottom chart winter day.Plant models that duplicate plant performance must model refrigerant temperatures because chiller lift drives chiller kW. The charts of Figure 5 illustrate the importance of evaporator refrigerant approach that is a design characteristic of an evaporator, in general the lower the value the greater the cost of the evaporator and therefore the cost of the chiller. Note how the refrigerant and chilled water supply temperatures must drop when the bypass flow is in the wrong direction, Figures 25 & 26, because colder water must be produced to provide 44F supply water to the coils.
88.584.7 82.9
93.7 92.7 93.5 94.697.3
97.2
93.0
91.7
85.6
78.476.5 75.3
79.9 80.4 81.7 82.6 84.0 84.982.0 81.0
77.8
2,010 2,010
6,030
10,050 10,050
12,060
8,040
4,020 4,020
71.0 70.0 69.0 70.0 72.0 74.0 75.0 76.0 78.0 75.0 74.0 72.0
0
5,000
10,000
15,000
20,000
25,000
50
55
60
65
70
75
80
85
90
95
100
105
Wet bulb (F)
(gpm
)
Tow
er w
ater
tem
pera
ture
s (F)
Time of dayTower Performance
(ewt)tower (F) (lwt)tower (F) Total Tower water (gpm)
10.07
8.217.62
13.8212.2511.8012.08
13.3712.31
11.0310.65
7.78
7.386.46 6.27
9.91
8.437.66 7.56 7.96
6.90 7.00
7.035.82
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
1 1 1 1
3
5 5 56 4
2 2
0
5
10
15
0
5
10
15
Each tower exhausted (ton)
Tow
er ra
nge
& a
ppro
ach
(F)
Tow
er ra
nge
& a
ppro
ach
(F)
Total Towers Exhaust (ton)Tower Performance
Tower range (F) Tower approach (F)Tower % fan speed # chiller/towers on
Figure 6: Tower Performance15-Design Day
The selected tower is given by Chapter 1 Table A and tower performance for design day operation is given by Figure 6. The figure illustrates the wide range of operation as the wet bulb and load on the tower changes. The tower leaving water temperature varies from 84.9F at design hour 4PM down to 75.3F at 4AM. At 4PM peak summer design conditions six chiller/towers are on and the range plus approach is (12.31 + 6.9 = 19.21F) consistent with the design procedures of Taylor13. Five chiller/towers are on at 2PM and the range plus approach increased to (13.37 + 7.96 = 21.33F). at 4AM the range plus approach drop to about 14F.
21
66.965.5 64.2
61.1 60.3
72.8
76.6
61.463.7
60.462.7 62.3
56.855.3
53.551.0 50.0
55.7
60.2
52.754.7
52.2 52.7 51.7
2,010 2,010 2,010 2,010 2,010 2,010 2,010
4,020 4,020
2,010 2,010 2,010
34.0 32.0 28.0 26.0 24.0 30.0 38.0 40.0 42.0 40.0 38.0 36.0
0
5,000
10,000
15,000
20,000
25,000
30
35
40
45
50
55
60
65
70
75
80
Wet bulb (F)
(gpm
)
Tow
er w
ater
tem
pera
ture
s (F)
Time of dayTower Performance
(ewt)tower (F) (lwt)tower (F) Total Tower water (gpm)
10.1
7
10.1
6
10.6
8
10.1
1
10.3
0
17.1
1
16.4
7
8.69 9.01
8.22 10
.04
10.5
5
22.7
7
23.3
4 25.5
1
25.0
3
26.0
0
25.6
5
22.1
6
12.7
2
12.6
7
12.1
9 14.6
8
15.7
4
67% 67% 67% 67% 67% 100% 100% 100% 100% 100% 100% 100%
1 1 1 1 1 1 12 2
1 1 1
0
5
10
15
20
25
30
0
5
10
15
20
25
30
Each tower exhausted (ton)To
wer
rang
e &
app
roac
h (F
)
Tow
er ra
nge
& a
ppro
ach
(F)
Total Towers Exhaust (ton)Tower Performance
Tower range (F) Tower approach (F)Tower % fan speed # chiller/towers on
Figure 7: Tower Performance15-Winter day
The selected tower is given by Table A of Chapter 1 and tower performance for winter operation is given by Figure 7. A comparison of Figures 6 & 7 illustrates the wide difference in operation for summer design verses winter operation. The tower leaving water temperature is much colder, as low as 50F. Tower range and approach is also very different from summer operation. Note how tower approach drops at 2PM when two chiller/towers are turned on.The (SEE) Model must accurately model tower performance, as demonstrated by Nelson14, if the goal of duplicating plant performance is to be achieved.
89.8
6
85.9
8
84.1
9
95.3
2
94.1
8
94.9
5
96.1
4 98.9
0
98.7
1
94.4
7
93.1
1
86.9
0
88.4
6
84.6
6
82.8
9
93.7
3
92.6
7
93.4
6
94.6
4 97.3
3
97.2
0
93.0
3
91.6
8
85.6
0
1 1 1 1
3
5 5 56
4
2 2
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 0
10
70
75
80
85
90
95
100
105
Cond. Refrigerent approach (F)
Tem
pera
ture
(F)
Time of dayCondenser performance
Cond refrig (Tcr) Condenser leaving water (F)# Chiller/Towers on Tower % fan speed
68.3
5
66.9
0
65.6
2
62.5
5
61.7
1
74.5
4
78.3
7
62.7
5
65.0
4
61.7
2
64.1
2
63.7
1
66.9
4
65.4
9
64.1
9
61.1
4
60.2
9
72.7
6
76.6
3
61.4
1
63.6
8
60.4
1
62.7
2
62.2
8
1 1 1 1 1 1 1
2 2
1 1 1
67% 67% 67% 67% 67%100% 100% 100% 100% 100% 100% 100%
0
1
2
3
4
5
6
20253035404550556065707580859095
Cond. Refrigerent approach (F)
Tem
pera
ture
(F)
Time of dayCondenser performance
Cond refrig (Tcr) Condenser leaving water (F)# Chiller/Towers on Tower % fan speed
Figure 8: Design/Winter condenser performance
The tower in large part determines the performance of the condenser; except condenser refrigerant approach temperature which is a chiller design selected characteristic. Figure 8 illustrates the condenser conditions for both design and winter conditions. Figure 9 essentially summarizes the plant performance at design day conditions. The top chart gives chiller lift and the bottom chart gives chiller and plant kW/ton values. Figure 10 summarizes the plant performance at winter conditions illustrating a significant improvement in both chiller and plant kW per ton values.
22
47.8
3
43.0
4
41.2
6 53.7
2
51.9
8
52.7
5
53.9
8 57.2
2
56.7
9
52.4
1
50.6
7
44.4
0
1 1 1 1
3
5 5 56
4
2 2
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 0
5
10
15
30
35
40
45
50
55
60
65
70
Load (ton) on each evaporatorCh
iller
Lift
(F)
Time of DayChiller performance
Chiller Lift (F) # chiller/towers on Tower % fan speed
65%
52%48%
90%
80% 79% 82%
93%87%
75%71%
52%
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
379 303 280525
1399 2303 23902711
3043
1749
828606
1 1 1 1 3 5 5 5 6 4 2 2
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0%10%20%30%40%50%60%70%80%90%
100%110%120%
NUMBER (#) CHILLERS/TOWERS ON
kW
Chill
er &
Tow
er fa
n %
pow
er
Plant TonChiller/Tower performance
(Chiller)% power Tower fan % Total Chiller-kW
0.52 0.51 0.51 0.52 0.53 0.54 0.55 0.57 0.580.55 0.54 0.54
0.71 0.72 0.73
0.68 0.670.70 0.71 0.72
0.740.71 0.70
0.77
379 303 280 525 466 461 478 542 507 437 414 303
0.4
0.5
0.6
0.7
0.8
0.9
0.4
0.5
0.6
0.7
0.8
0.9
Each Chiller (kW)
(kW
/ton
)
Time of dayPlant performance
Chiller (kW/evap ton) Plant (kW/site ton))
Figure 9: Plant Performance-Design conditions
26.1
6
24.7
0
23.1
4
20.3
7
19.3
9
38.5
8
41.0
5
20.3
8
22.6
7
19.0
4
21.8
5
21.8
1
1 1 1 1 1 1 1
2 2
1 1 1
67% 67% 67% 67% 67%100% 100% 100% 100% 100% 100% 100%
0
5
10
0
5
10
15
20
25
30
35
40
45
50
Load (ton) on each evaporator
Chill
er Li
ft (F
)
Time of DayChiller performance
Chiller Lift (F) # chiller/towers on Tower % fan speed
37% 35% 34%29% 28%
79% 81%
27%30%
24%31% 32%
67% 67% 67% 67% 67%
100% 100% 100% 100% 100% 100% 100%
216 204 198 169 163461 472 309 350
140 181 187
1 1 1 1 1 1 1 2 2 1 1 1
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0%10%20%30%40%
50%60%70%80%
90%100%110%120%
NUMBER (#) CHILLERS/TOWERS ON
kW
Chill
er &
Tow
er fa
n %
pow
er
Plant TonChiller/Tower performance
(Chiller)% power Tower fan % Total Chiller-kW
0.28 0.260.24
0.21 0.20
0.360.38
0.230.25
0.22 0.23 0.23
0.42 0.400.38
0.35 0.34
0.480.51
0.41 0.43 0.42 0.41 0.40
216 204 198 169 163 461 472 154 175 140 181 187
0.0
0.2
0.4
0.6
0.0
0.2
0.4
0.6
Each Chiller (kW)
(kW
/ton
)
Time of dayPlant performance
Chiller (kW/evap ton) Plant (kW/site ton))
Figure 10: Plant Performance-Winter conditions
Summary-Table 1 System Plant The purpose of this Chapter 2 is to give an understanding of the complexity and detail necessary in a (SEE) Model that is to duplicate real plant performance. Verification of the plant (SEE) Model can be reviewed at references 4 & 14.
23
Chapter 3-Install fan powered terminals and return fans Into Table 1 System defined as Table 1.5 SystemTo further demonstrate the (SEE) Model detail and capabilities the following scenario will be assumed. The building and HVAC system was originally designed to Table 1 conditions of article 1.
Building Location and Design1. Location=Kansas City Missouri. 2. Ambient temperatures Figure 2 3. Percent clear sky 100%. 4. Building design per Liu5 5. Percent wall glass 37% 6. Peak lights kW .81 watts/ft2
7. Peak plugs kW .66 watts/ft2
8. Return air is to building perimeter.9. Duct design static 5.5 inches water.10. Fan powered terminals installed11. Return air fans installed
Building Control 12. Lights on/off control- 6% on after hours.13. Plugs on/off control-44% on after hours14. Building pressure control, yes 15. Supply air = 55F16. Supply water 44F-44.6F17. Stats controlled, Yes 18. Perimeter heat air temp, 105F.19. VAV fan duct pressure control, yes 20. Fresh air CFM control, yes21. Fresh air heat stat set point, 42F
Plant Design & Control22. Chiller/Tower selection13.
Table 1.5: System
During construction an engineering change installed fan powered terminals11 and return fans12 into the design. Therefore, the as designed (SEE) Model must be upgraded to include fan powered terminals and return fans.
System (watt/sq ft)
90.086.0 84.0 82.0
88.094.0 96.0 97.0
101.0 98.0 95.0 93.0
71.0 70.0 69.0 70.0 72.0 74.0 75.0 76.0 78.0 75.0 74.0 72.0
0.38 0.38 0.37 0.44
1.17
1.77 1.76 1.82 1.88
0.99
0.64 0.53
0.53 0.50 0.490.64
1.68
2.63 2.65
2.823.01
1.64
0.960.78
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% Clear Sky
(watt
/sqft
)
Tem
pera
ture
(F)
TIME of DAYTable 1 System-Peak Summer design weather & Building & System
(watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)Building (watt/sqft) System (watt/sqft)
90.086.0 84.0 82.0
88.094.0 96.0 97.0
101.0 98.0 95.0 93.0
71.0 70.0 69.0 70.0 72.0 74.0 75.0 76.0 78.0 75.0 74.0 72.0
0.43 0.42 0.41 0.51
1.31
2.01 2.01 2.11 2.19
1.150.73 0.60
0.58 0.55 0.540.73
1.86
2.92 2.95
3.173.39
1.84
1.060.85
-0.5
0.5
1.5
2.5
3.5
4.5
5.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% Clear SkyTe
mpe
ratu
re (F
)
TIME of DAYTable 1.5 System-Summer design weather-Building & System
(watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)Building (watt/sqft) System (watt/sqft)
Figure 1: Building & Plant = System (watt/sq ft)
Figure 1 illustrates that the addition of fan powered terminals and return fans resulted in an increase of about 13% in (watt/sq ft) at 4PM design hour conditions.
24
34.032.0
28.026.0
24.0
30.0
38.040.0
42.040.0
38.036.0
34.032.0
28.026.0 24.0
30.0
38.040.0
42.040.0
38.036.0
1.61 1.68 1.81 1.65
2.412.14
1.75 1.68 1.81 1.68 1.70 1.70
1.71 1.77 1.90 1.73
2.49 2.321.93 1.84 1.98
1.76 1.79 1.80
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
% Clear Sky
(watt
/sqft
)
Tem
pera
ture
(F)
TIME of DAYTable 1 System-Winter weather-Building & System (watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)Buildings (watt/sqft) System (watt/sqft)
34.032.0
28.026.0
24.0
30.0
38.040.0
42.040.0
38.036.0
34.032.0
28.026.0 24.0
30.0
38.040.0
42.040.0
38.036.0
1.64 1.71 1.84 1.67
2.492.28
1.89 1.83 1.961.75 1.74 1.74
1.74 1.80 1.93 1.76
2.58 2.50
2.04 2.01 2.151.84 1.84 1.84
0.0
1.0
2.0
3.0
4.0
5.0
6.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
% Clear Sky
Tem
pera
ture
(F)
TIME of DAYTable 1.5 System-winter weather-Building & System (watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)Buildings (watt/sqft) System (watt/sqft)
Figure 2: Building & Plant = System (watt/sq ft)
Figure 2 illustrates about a 9% increase at 4PM winter weather conditions.
Estimates of (EUI) Values
8.45
10.07
11.79
8.08
0
5
10
15
20
25
30
35
40
45
kbtu
/sq
ft-y
ear
Table 1 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Summer (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Spring (kbtu/sqft-yr)
5.18
35.
183
5.18
35.
183
0.76
40.
599
0.59
40.
709
2.48
10.
830
0.72
21.
415
0.01
83.
459
5.29
20.
770
0
1
2
3
4
5
6kb
tu/s
q ft
-yea
r
Table 1 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Bld-Summer Bld-Fall Bld-Winter Bld SpringFan-Summer Fan Fall Fan-Winter Fan-SpringPlant-summer Plant-Fall Plant-winter Plant-SpringHeat-summer Heat-Fall Heat-winter Heat-Spring
Figure 3: Table 1 System (EUI) Estimate
Comparing Figures 3 & 4 illustrates the (EUI) estimate increased from 38.5 to 41.0 (kbtu/sq ft-year) with the installation of the fan powered terminals and return fans. Note that the lights and plug values are the same for both Figure 3 & 4. The fan (EUI) values almost doubled with the installation of the terminals and return fans but the heat input to the building slightly decreased.
25
9.25
10.65
12.30
8.77
0
5
10
15
20
25
30
35
40
45
kbtu
/sq
ft-y
ear
Table 1.5 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year) Terminal & return fans installed
Summer (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Spring (kbtu/sqft-yr)
5.18
35.
183
5.18
35.
183
1.44
91.
188
1.18
21.
360
2.60
20.
903
0.76
61.
475
0.01
73.
378
5.16
90.
749
0
1
2
3
4
5
6
kbtu
/sq
ft-y
ear
Table 1.5 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)Terminal fans & return fans installed
Bld-Summer Bld-Fall Bld-Winter Bld SpringFan-Summer Fan Fall Fan-Winter Fan-SpringPlant-summer Plant-Fall Plant-winter Plant-SpringHeat-summer Heat-Fall Heat-winter Heat-Spring
Figure 4: Table 1.5 System (EUI) Estimate
The reason is that the terminals add heat to the supply air and therefore less air heat and reheat is required to maintain space temperatures. The return fans add heat to the return air so the air inlet to the VAV fans is slightly increased. However, as shown by the following the air system is a bit more complicated due to the increased load caused by the terminals and return fans and therefore the increased VAV kW.
Energy Balance & Schematic-Table 1 System at Design Conditions-One Building
130.2 105.665.55 67.4 45.0
208.0 196.2139.5
-85.3-7.5
-864.6
-1000
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
Ton
Table 1 System-One Building Load on Plant (ton)-4PM Peak Design Hour Weather-Ein = Eout
lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
Figure 5: Energy Balance at Table 1 System Design Conditions
The Figure 5 energy balance and Schematic 1 are at the same conditions and therefore present the same numbers in different format. The introduction gives a discussion of the schematic structure and nomenclature providing understanding of the values shown on Schematic 1.Air enters the coils at 81.90F and exist at 55F resulting in a load to the plant of 864.6 ton. 91,607 CFM of 55F air to the building perimeter is required to meet the load of 164.9 ton. The building interior requires 192,399 CFM of 55F air to meet the 346.3-ton load. Of the 284,005 CFM of 75F return air, 47,386 CFM is exhausted and 236,619 CFM enters the VAV fan inlet mixed with 47,386 CFM of 101F fresh air resulting in 284,005 CFM of 79.34F air to the inlet of the VAV fan system. As the air passes thru the VAV fans it is heated by the 230.6 kW fan power to an exit air temperature of 81.90F to the coils. All perimeters just discussed and many others, as shown by Schematic 1, are iterating to an energy balance condition, i.e., the (SEE) Model is a set of equations solved simultaneous. A change in any one of the input parameters, for example outside air temperature, will result in all equations
26
seeking a new equilibrium or energy balance just as occurs in a real system.
Each BLD ft2 = 565,000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 101.0 Ex-/Infil+-CFM = 0 <<Roof ft2 = 43,462 Twet-bulb= 78.0 Infilsen-ton = 0.0
N/S wall ft2 = 40,560 WallNtrans ton= 5.15E/W wall ft2 = 30,604 WallStrans ton= 5.73
Wall % glass= 37.5% WallEtrans ton= 3.88Glass U = 0.55 WallWtranston= 3.88 WallTot trans ton = 18.6
Wall U = 0.09 GlassN trans ton = 18.13Glass SHGC = 0.40 GlassS trans ton = 18.13
Wall emitt = 0.55 GlassE-trans ton = 13.68RoofTrans ton = 43.1 GlassW-trans ton = 13.68 GlassTot-trans-ton= 63.6
Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 6.1
plugton&kW = 106 371.2 GlassE-solar ton = 4.6Lightton&kW= 130 457.7 GlassW-solar ton = 62.0 GlassTot-solar-ton = 82.6
Total Bldint-ton = 346.3 BLD kW= 828.9 (int cfm)per-ton = 0.00 >(int-cfm)to-per-ret= 192399 FAN kW= 230.6 Tot Bldper-sen-ton = 164.9 v
Tstat-int= 75.0 HEAT kW = 0.0 Tstat-per = 75.0 return(Bld)int-air-ton= -346.3 ^ SITE kW = 1059.4 ^ (Bld)per-air-ton= -164.9 air
Tair supply int= 55.00 Bld Shell (ton)= 208.0 Tair supply per= 55.00 ^ Fresh Air (ton)= 335.7 ^
Ton kW Ton kW V(fan)int-ter ton&kW= 0.0 0.0 (fan)per-ter ton&kW= 0.0 0.0
Theat-air= 55.0 (D)heat ton&kW = 0.0 0.0
Treheat air = 55.0(D)reheat ton&kW = 0.0 0.0
0.0(D)int-air-ton= -346.3 Interior Peri
Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 192,399 ^ (D)per-CFM= 91,607 ^
>>>(Coil)sen-ton= 688 ^ ^Coil UA = 2.91
One Building (TON) COIL LMTD = 15.58CoilCap-ton = 45.3Coilload-ton = 33.3 V
(COIL)L+s-ton= 864.6 ^ ^ ^<<<< Tair VAV= 81.90 TBLD-AR = 75.00
(FAN)VAV-CFM= 284,005 (Air)ret-CFM = 284,005 Return4PM (FAN)ton-VAV= 65.6 (FAN)ret-kW= 0.0 Fan
(FAN)kW-VAV= 230.6 (FAN)ret-ton= 0.0 V^ (Air)ret-ton = 511.2
26 F.A.Inlet ^ Tar-to-VAV = 75.00 statFA= 42 26 VAV FANS VAVret-sen ton = 425.9
TFA to VAV = 101.0 > Tret+FA = 79.34 VAVret Lat-ton = 37.45>(FA)sen-ton = > 196.2 (dh) = 4.404 < VAVret-CFM = 236,619 <
> (FA)CFM= 47,386 > Efan-VSD= 0.638 V> (FA)Lat-ton= 139.5 VAV inlet-sen-ton = 622.1
(FA)kW= 0.0 VAVinlet-lat-ton= 176.9 ExLat-ton = -7.5ExCFM = -47,386
SEE Schematic air side TEx = 75.00Air temp green kW red Time= 4PM Exsen-ton = -85.3 V Air CFM purple Ton blue v
Schematic 1: Table 1 System at design conditions
Energy Balance & Schematic-Table 1.5 System at Design Conditions-One Building
130.2 105.6115.4167.4 45.0
208.0 196.2139.5
-87.5-7.1
-912.7
-1000
-900
-800
-700
-600
-500
-400
-300
-200
-100
0
100
200
300
Ton
Table 1.5 System-One Building Load on Plant (ton)-4PM Peak Design Hour Weather-Ein = Eout
lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
Figure 6: Energy Balance at design conditions with fan powered terminals and return fan installed Table 1.5 SystemComparing Schematics 1 & 2 shows that the air entering the perimeter and interior space is 56.04F not 55F due to the heat of the powered terminals. Therefore, the CFM of air must increase and increased air CFM increases the VAV fan kW from 230.6 to 259.1 kW. The 75F return air passes thru the return air system and is heated by the fans to 75.51F. This all results in an air temperature to the coils of 82.27F verses 81.90F of Schematic 1 and load to the plant of 912.7-ton verses 864.6-ton of Schematic 1. The net result, at design conditions for one building, of installing the fan powered terminals and return fans is an increase site kW from 1059.4 kW to 1234.8 kW and a plant load increase from 864.6 ton to 912.7 ton. Next will look at winter conditions.
27
Each BLD ft2 = 565,000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 101.0 Ex-/Infil+-CFM = 0 <<Roof ft2 = 43,462 Twet-bulb= 78.0 Infilsen-ton = 0.0
N/S wall ft2 = 40,560 WallNtrans ton= 5.15E/W wall ft2 = 30,604 WallStrans ton= 5.73
Wall % glass= 37.5% WallEtrans ton= 3.88Glass U = 0.55 WallWtranston= 3.88 WallTot trans ton = 18.6
Wall U = 0.09 GlassN trans ton = 18.13Glass SHGC = 0.40 GlassS trans ton = 18.13
Wall emitt = 0.55 GlassE-trans ton = 13.68RoofTrans ton = 43.1 GlassW-trans ton = 13.68 GlassTot-trans-ton= 63.6
Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 6.1
plugton&kW = 106 371.2 GlassE-solar ton = 4.6Lightton&kW= 130 457.7 GlassW-solar ton = 62.0 GlassTot-solar-ton = 82.6
Total Bldint-ton = 346.3 BLD kW= 828.9 (int cfm)per-ton = 0.00 >(int-cfm)to-per-ret= 202979 FAN kW= 405.9 Tot Bldper-sen-ton = 164.9 v
Tstat-int= 75.0 HEAT kW = 0.0 Tstat-per = 75.0 return(Bld)int-air-ton= -346.3 ^ SITE kW = 1234.8 ^ (Bld)per-air-ton= -164.9 air
Tair supply int= 56.04 Bld Shell (ton)= 208.0 Tair supply per= 56.04 ^ Fresh Air (ton)= 335.7 ^
Ton kW Ton kW V(fan)int-ter ton&kW= 19.0 67.0 (fan)per-ter ton&kW= 9.1 31.9
Theat-air= 55.0 (D)heat ton&kW = 0.0 0.0
Treheat air = 55.0(D)reheat ton&kW = 0.0 0.0
31.9(D)int-air-ton= -365.4 Interior Peri
Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 202,979 ^ (D)per-CFM= 96,644 ^
>>>(Coil)sen-ton= 735 ^ ^Coil UA = 3.01
One Building (TON) COIL LMTD = 15.63CoilCap-ton = 47.0Coilload-ton = 35.1 V
(COIL)L+s-ton= 912.7 ^ ^ ^<<<< Tair VAV= 82.27 TBLD-AR = 75.00
(FAN)VAV-CFM= 299,624 (Air)ret-CFM = 299,624 Return4PM (FAN)ton-VAV= 73.7 (FAN)ret-kW= 47.9 Fan
(FAN)kW-VAV= 259.1 (FAN)ret-ton= 13.6 V^ (Air)ret-ton = 553.0
26 F.A.Inlet ^ Tar-to-VAV = 75.51 statFA= 42 26 VAV FANS VAVret-sen ton = 465.5
TFA to VAV = 101.0 > Tret+FA = 79.54 VAVret Lat-ton = 37.84>(FA)sen-ton = > 196.2 (dh) = 4.738 < VAVret-CFM = 252,238 <
> (FA)CFM= 47,386 > Efan-VSD= 0.644 V> (FA)Lat-ton= 139.5 VAV inlet-sen-ton = 661.7
(FA)kW= 0.0 VAVinlet-lat-ton= 177.3 ExLat-ton = -7.1ExCFM = -47,386
SEE Schematic air side TEx = 75.51Air temp green kW red Time= 4PM Exsen-ton = -87.5 V Air CFM purple Ton blue v
Schematic 2: Table 1.5 System at design condition
Energy Balance & Schematic-Table 1 System at Winter Conditions-One Building
130.2105.6
27.5 27.6
67.445.0
-24.6-55.4
0.0
-81.0
-11.9
-230.3
-300
-200
-100
0
100
200
Ton
Table 1 System-One Building Load on Plant (ton)-4PM Winter Weather-Ein = Eout
lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
Figure 7: Energy Balance at Table 1 System Winter Conditions
Heat is required on the perimeter of the building with 6,143 CFM of 105F air to meet a load of -17.1 ton. the perimeter stat is set at 74F and because return air is at the perimeter 15.56 ton of heating is provided to the perimeter by the internal return air. The interior of the building requires 172,938 CFM of 55F air to meet a load of 311.3 ton. the 74F return air to the VAV fans is mixed with 47,386 CFM of fresh air for an air temperature of 67.24F to the inlet of the VAV fans. The VAV fan heat the air to 67.24F delivered to the coils for a plant load of 230.3 ton, a significant reduction from design conditions of Schematic 1. Compared to Schematic 1 the site kW of 1059.4 kW at design slighting decreased to 1022.8 kW as given by Schematic 3. The VAV fan kW decreased to less than half at winter conditions but the perimeter air heat required 97.2 kW. Next we look at winter conditions with terminals and return fans installed.
28
BLD ft2 = 565000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 42.0 Ex-/Infil+-CFM = 0 <<Roof ft2 = 43,462 Twet-bulb= 42.0 Infilsen-ton = 0.0
N/S wall ft2 = 40,560 WallNtrans ton= -5.94E/W wall ft2 = 30,604 WallStrans ton= -3.69
Wall % glass= 37.5% WallEtrans ton= -4.48Glass U = 0.55 WallWtranston= -4.48 WallTot trans ton = -18.6
Wall U = 0.09 GlassN trans ton = -22.31Glass SHGC = 0.40 GlassS trans ton = -22.31
Wall emitt = 0.55 GlassE-trans ton = -16.83RoofTrans ton = 8.1 GlassW-trans ton = -16.83 GlassTot-trans-ton= -78.3
Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 25.9
plugton&kW = 106 371 GlassE-solar ton = 0.8Lightton&kW= 130 458 GlassW-solar ton = 27.5 GlassTot-solar-ton = 64.2
Total Bldint-ton = 311.3 BLD kW= 828.9 (int cfm)per-ton = 15.56 >(int-cfm)to-per-re t= 172938 FAN kW= 96.7 Tot Bldper-sen-ton = -17.1 v
Tstat-int= 75.0 HEAT kW = 97.2 Tstat-per = 74.0 return(Bld)int-air-ton= -311.3 ^ SITE kW = 1022.8 ^ (Bld)per-air-ton= 17.1 air
Tair supply int= 55.00 Bld Shell (ton)= -24.6 Tair supply per= 105.00 ^ Fresh Air (ton)= -55.4 ^
Ton kW Ton kW V(fan)int-te r ton&kW= 0.0 0.0 (fan)per-ter ton&kW= 0.0 0.0
Theat-air= 105.0 (D)heat ton&kW = 17.1 60.3
Treheat air = 74.0(D)reheat ton&kW = 10.5 36.9
97.2(D)int-air-ton= -311.3 Interior Peri
Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 172,938 ^ (D)per-CFM= 6,143 ^
>>>(Coil)sen-ton= 197.3 ^ ^Coil UA = 1.31
One Building (TON) COIL LMTD = 8.67CoilCap-ton = 11.4Coilload-ton = 8.9 V
(COIL)L+s-ton= 230.3 ^ ^ ^<<<< Tair VAV= 67.24 TBLD-AR = 74.00
(FAN)VAV-CFM= 179,080 (Air)re t-CFM = 179,080 Return(FAN)ton-VAV= 27.5 (FAN)ret-kW= 0.0 Fan(FAN)kW-VAV= 96.7 (FAN)ret-ton= 0.0 V
^ (Air)re t-ton = 306.226 F.A.Inlet ^ Tar-to-VAV = 74.00
statFA= 42 26 VAV FANS VAVret-sen ton = 225.2 TFA to VAV = 42.0 > Tret+FA = 65.53 VAVre t Lat-ton = 33.06
>(FA)sen-ton = > -55.4 (dh) = 2.662 < VAVret-CFM = 131,694 <> (FA)CFM= 47,386 > Efan-VSD= 0.579 V
> (FA)Lat-ton= 0.0 VAV inlet-sen-ton = 169.8(FA)kW= 0.0 VAVinle t-lat-ton= 33.1 ExLat-ton = -11.9
ExCFM = -47,386SEE Schematic air side 4PM TEx = 74.00Air temp green kW red Exsen-ton = -81.0 V Air CFM purple Ton blue v
Schematic 3: Table 1 System at winter weather
Energy Balance & Schematic-Table 1.5 System at Winter Conditions-One Building
130.2105.6
53.125.7
67.445.0
-24.6-55.4
0.0
-82.4
-11.3
-253.2
-300
-200
-100
0
100
200
300
Ton
Table 1.5 System-One Building Load on Plant (ton)-4PM Winter Weather-Ein = Eout
lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
Figure 8: Energy Balance at winter conditions with fan powered terminals and return fans installed Table 1.5 System
Comparing Schematics 2 & 4 illustrates that the powered terminals add heat to the perimeter air and therefore in part decrease the air heat kW required from 97.2 kW of Schematic 3 to (55.3 + 35.1 = 90.4 kW) of Schematic 4. The net result is that the plant load and site kW increased with the installation of the fan powered terminals and return fans.
29
BLD ft2 = 565000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 42.0 Ex-/Infil+-CFM = 0 <<Roof ft2 = 43,462 Twet-bulb= 42.0 Infilsen-ton = 0.0
N/S wall ft2 = 40,560 WallNtrans ton= -5.94E/W wall ft2 = 30,604 WallStrans ton= -3.69
Wall % glass= 37.5% WallEtrans ton= -4.48Glass U = 0.55 WallWtranston= -4.48 WallTot trans ton = -18.6
Wall U = 0.09 GlassN trans ton = -22.31Glass SHGC = 0.40 GlassS trans ton = -22.31
Wall emitt = 0.55 GlassE-trans ton = -16.83RoofTrans ton = 8.1 GlassW-trans ton = -16.83 GlassTot-trans-ton= -78.3
Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 25.9
plugton&kW = 106 371 GlassE-solar ton = 0.8Lightton&kW= 130 458 GlassW-solar ton = 27.5 GlassTot-solar-ton = 64.2
Total Bldint-ton = 311.3 BLD kW= 828.9 (int cfm)per-ton = 16.42 >(int-cfm)to-per-re t= 182448 FAN kW= 186.8 Tot Bldper-sen-ton = -16.3 v
Tstat-int= 75.0 HEAT kW = 90.4 Tstat-per = 74.0 return(Bld)int-air-ton= -311.3 ^ SITE kW = 1106.1 ^ (Bld)per-air-ton= 16.3 air
Tair supply int= 56.04 Bld Shell (ton)= -24.6 Tair supply per= 105.00 ^ Fresh Air (ton)= -55.4 ^
Ton kW Ton kW V(fan)int-te r ton&kW= 17.1 60.2 (fan)per-ter ton&kW= 0.5 1.9
Theat-air= 104.0 (D)heat ton&kW = 15.7 55.3
Treheat air = 75.0(D)reheat ton&kW = 10.0 35.1
92.4(D)int-air-ton= -328.4 Interior Peri
Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 182,448 ^ (D)per-CFM= 5,836 ^
>>>(Coil)sen-ton= 219.5 ^ ^Coil UA = 1.39
One Building (TON) COIL LMTD = 8.62CoilCap-ton = 11.9Coilload-ton = 9.7 V
(COIL)L+s-ton= 253.2 ^ ^ ^<<<< Tair VAV= 67.96 TBLD-AR = 74.00
(FAN)VAV-CFM= 188,284 (Air)re t-CFM = 188,284 Return(FAN)ton-VAV= 29.9 (FAN)ret-kW= 19.5 Fan(FAN)kW-VAV= 105.2 (FAN)ret-ton= 5.5 V
^ (Air)re t-ton = 327.526 F.A.Inlet ^ Tar-to-VAV = 74.33
statFA= 42 26 VAV FANS VAVret-sen ton = 245.1 TFA to VAV = 42.0 > Tret+FA = 66.19 VAVre t Lat-ton = 33.64
>(FA)sen-ton = > -55.4 (dh) = 2.784 < VAVret-CFM = 140,898 <> (FA)CFM= 47,386 > Efan-VSD= 0.586 V
> (FA)Lat-ton= 0.0 VAV inlet-sen-ton = 189.6(FA)kW= 0.0 VAVinle t-lat-ton= 33.6 ExLat-ton = -11.3
ExCFM = -47,386SEE Schematic air side TEx = 74.33Air temp green kW red Exsen-ton = -82.4 V Air CFM purple Ton blue v
Schematic 4: Table 1.5 System at winter weather
VAV Fan System Performance-One Building
46,522
244,012284,005
82,871
21
169
231
34
116 97 90 164 366 568 573 631 688 434 225 170
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
240,000
280,000
320,000
109 91 84 155 342 520 526 574 622 406 212 161
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)Table 1 System-VAV Fan performance-Design Summer
Weather
(FAN)VAV-CFM (VAV Fan kW)
76,055
171,075 179,080
83,225
31
90 97
34
127 130 137 131 127 182 172 191 197 96 125 132
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
119 121 128 122 111 156 148 166 170 83 115 122
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
Table 1 System-VAV Fan performance-Winter Weather
(FAN)VAV-CFM (VAV Fan kW)
Figure 9: Table 1 VAV Fan System performance
Figure 9 & 10 give the VAV fan system air CFM and kW demand illustrating the increase with the installation of the fan powered terminals and return fans.
30
49,081
257,431299,624
87,429
22
188
259
36
124 104 96 176 388 606 611 674 735 459 238 181
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
240,000
280,000
320,000
117 97 90 165 362 552 558 610 662 428 225 171
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
Table 1.5 System-VAV Fan performance-Peak Summer DayTerminal fans & return fans installed
(FAN)VAV-CFM (VAV Fan kW)
77,415
179,807 188,284
85,477
31
97 105
35
131 134 141 135 139 202 193 214 220 107 132 137
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
123 125 132 127 121 175 167 186 190 92 121 127
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
Table 1.5 System-VAV Fan performance-Winter DayTerminal fans & return fans installed
(FAN)VAV-CFM (VAV Fan kW)
Figure 10: Table 1.5 VAV Fan System Performance
Figures 9 & 10 also show the increase in sensible load (ton) as the air moves thru the VAV fans. clearly the installation of the terminals and return fans increased the required air CFM and increased the VAV fan kW demand. Figure 10 does not include the kW demand of the terminals and return fans, shown by the next figures.
VAV Fan System Performance plus Fan Powered Terminals & Return Fans One Building
26 23 2237
93
188 185
226259
108
4836
25.6 21.8 20.336.7
75.0
119.7118.7134.7
146.8
83.2
45.535.5
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
Total AH (kW)-not including heat (kW)
(kW
)
(kW
)Time of DayTable 1.5 System-One Bld-Site or air side (kW)-Design Day
Weather-Terminal fans & return fans installed
VAV Fans (kW) Ter + Ret fans (kW)
29.5 29.6 31.3 29.9
60.4
97.493.3
97.2 105.2
51.6
37.7 35.0
29.6 29.7 31.3 30.0
54.6
77.4 75.1 77.281.6
48.2
37.1 34.7
0
10
20
30
40
50
60
70
80
90
100
110
0
10
20
30
40
50
60
70
80
90
100
110
Total AH (kW)-not including heat (kW)
(kW
)
(kW
)
Time of DayTable 1.5 System-One Bld-Site or air side (kW)-Winter Weather-Terminal fans & return fans installed
VAV Fans (kW) Ter + Ret fans (kW)
Figure 11: Table 1.5 VAV Fan System Performance plus Terminal and Return Fans
Figure 11 & 12 illustrate the increase in kW demand of the air side system with the installation of the fan powered terminals and return fans.
31
26 23 2237
93
188 185226
259
108
483635
48
6.6
60.3 67.0
17.6
24.7 31.9 11.20
20
40
60
80
100
120
140
160
180
200
220
240
260
020406080
100120140160180200220240260280
Total AH (kW)-not including heat (kW)
(kW
)
(kW
)
Time of DayTable 1.5 System-One Bld-Site or air side (kW)-Design day Weather-Terminal fans & return fans installed
VAV Fans (kW) Return fans kWInterior terminal fans (kW) Perimeter terminal fans (kW)
29 30 31 30
60
9793
97 105
52
38 35
5.8
18 19
6.5
8.9
57.160.2
14.716.7
2.2 1.913.5
0
10
20
30
40
50
60
70
80
90
100
110
0
10
20
30
40
50
60
70
80
90
100
110
Total AH (kW)-not including heat (kW)
(kW
)
(kW
)
Time of DayTable 1.5 System-One Bld-Site or air side (kW)-Typical Winter Weather-Terminal fans & return fans installed
VAV Fans (kW) Return fans kWInterior terminal fans (kW) Perimeter terminal fans (kW)
Figure 12: Table 1.5 VAV Fan System Performance plus Terminal and Return Fans
The return fan kW demand is modeled as proportional to the return CFM and the terminals kW demand is proportional to the CFM of supply air to the respective interior and perimeter of the building.
Air Supply Temperatures & CFM
At design conditions the fan powered terminals slightly increase the supply air temperature to the perimeter and interior of the building and the return fans slightly increase the air return temperature to the VAV fans. Figure 13 illustrates the effect of adding fan powered terminals and return fans to the air handler system. The temperature and CFM of air to the coils sets the plant load. At 4PM comparing the top and bottom charts shows the VAV air handler CFM increased from 284,005 to 299,624 and the temperature to the coils increased from 81.90F to 82.27F. The air supply CFM and air supply temperature increased because the load increased due to the electrical demand of the terminals and return fans. The plant load increased from 865 ton to 913 ton therefore adding 48-ton load to the plant as a result of adding the powered terminals and return fans.
32
45,957
196,626
236,619
75,802
565 47,386 47,386 7,070
46,522
244,012284,005
82,871
75.11
78.69 79.34
76.54
76.57
80.8881.90
77.82
55 55
50
55
60
65
70
75
80
85
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Plant load ton-Sensible + Latent-one Bld
AIR
TEM
PERA
TURE
(F)
(AIR
CFM
)
Time of DayTable 1 System-VAV Fan Performance-Peak summer weather
(VAV)minus exhaust inlet CFM (FA)-CFM(FAN)VAV-CFM Return + FA temp(F)(Temp)air-VAV to coil Supply air off coil (F)
48,516
210,045
252,238
80,359
565 47,386 47,386 7,070
49,081
257,431299,624
87,429
75.36
78.85 79.54
76.68
76.79
81.1582.27
77.97
55 55
50
55
60
65
70
75
80
85
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Plant load ton-Sensible + Latent-one Bld
AIR
TEM
PERA
TURE
(F)
(CFM
)
Time of DayTable 1.5 System-VAV Fan Performance-Peak summer weatherFan powered terminals & return fans installed
(VAV)minus exhaust inlet CFM (FA)-CFM(FAN)VAV-CFM Return + FA temp(F)(Temp)air-VAV to coil Supply air off coil (F)
Figure 13: Design Weather-Top Chart Table 1 System-Bottom Chart Table 1.5 System.
Figures 3 & 4 above state that the terminal and return fans increased the estimated (EUI) value of the Table 1 system from about 38.5 (kbtu/ft2-yr) to 41 (kbtu/ft2-yr) for Table 1.5, an increase of about 6.5%.
75,490
123,688
131,694
76,155
565
47,386 47,386
7,070
76,055
171,075179,080
83,225
75.04
66.79 67.24
72.57
73.76
65.14 65.53
71.28
55 55
40
45
50
55
60
65
70
75
80
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Plant load ton-Sensible + Latent-one Bld
AIR
TEM
PERA
TURE
(F)
Air (
CFM
)
Time of DayTable 1 System VAV Fan Performance-Typical Winter Weather
(VAV)minus exhaust inlet-CFM (FA)-CFM(FAN)VAV-CFM (Temp)air-VAV to coilReturn + FA temp(F) Supply air off coil (F)
76,850
132,421
140,898
78,407
565
47,386 47,386
7,070
77,415
179,807188,284
85,477
75.28
67.51 67.96
72.87
74.00
65.80 66.19
71.57
55 55
40
45
50
55
60
65
70
75
80
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Plant load ton-Sensible + Latent-one Bld
AIR
TEM
PERA
TURE
(F)
(CFM
)
Time of DayTable 1.5 System-VAV Fan Performance-Winter WeatherFan powered terminals & return fans installed
(VAV)minus exhaust inlet-CFM (FA)-CFM(FAN)VAV-CFM (Temp)air-VAV to coilReturn + FA temp(F) Supply air off coil (F)
Figure 14: Winter Weather- Top Chart Table 1 System-Bottom Chart Table 1.5 System.
Figure 14 illustrates the effect the powered terminals and return air fans have on the system during winter operation. Comparing the top chart, Table 1 system, to the bottom chart Table 1.5 System at 4PM the air temperature to the coils increased (67.96F – 67.24F = .72F). The secondary horizontal axis illustrates the increase in sensible plant load at 4PM from 230-ton top chart, to 253-ton, bottom chart, due to the powered terminals and return fans. The reason the effect at winter
33
operation is less than at design conditions is that the VAV fan CFM is less and the terminals11 and return fans12 CFM and therefore kW demand is proportional to VAV CFM to the interior and to the perimeter. The 26 VAV air handlers in each building, two per floor, have a design value of 13,200 CFM, the powered terminals design value per air handler is 4.36 kW and the VAV fans design are 10.67 kW.
49,081
257,431299,624
87,429
22
188
259
36
124 104 96 176 388 606 611 674 735 459 238 181
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
240,000
280,000
320,000
117 97 90 165 362 552 558 610 662 428 225 171
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
Table 1.5 System-VAV Fan performance-Peak Summer DayTerminal fans & return fans installed
(FAN)VAV-CFM (VAV Fan kW)
77,415
179,807 188,284
85,477
31
97 105
35
131 134 141 135 139 202 193 214 220 107 132 137
0
40
80
120
160
200
240
280
320
0
40,000
80,000
120,000
160,000
200,000
123 125 132 127 121 175 167 186 190 92 121 127
VAV outlet sensible (ton)
kW(CFM
)
VAV inlet sensible (ton)
Table 1.5 System-VAV Fan performance-Winter DayTerminal fans & return fans installed
(FAN)VAV-CFM (VAV Fan kW)
Figure 15: VAV fan kW-One BuildingThe fan system operates at less than design, for example at peak summer conditions, top chart, each VAV air hander is operating at 11,524 CFM with a demand of 9.96 kW and the powered terminals associated with each air handler draws
3.80 kW as demonstrated by the top charts of Figures 11 & 12. Figure 15 top chart gives the design day VAV fans CFM and kW demand and the bottom chart gives the winter values. Operation during the winter requires significantly less CFM and therefore less VAV fan kW demand. The horizontal axis illustrates an important characteristic of a real system. As the air passes thru the VAV fan system the air is heated. The top chart primary horizontal axis at 4PM shows 662 ton entering the VAV fan system and the secondary horizontal axis shows 735 ton exiting due to VAV fan motor heat added to the air. As the load increases due to the VAV fan heat the VAV fan CFM increases therefore increasing the load until a steady state condition develops. The (SEE) Model equations iterate to a steady state condition just as a real system. This feature of the (SEE) Model is a necessary calculation; analogous to a feedback control system. Table 1 & 1.5 System Performance at Design Day Conditions of Figure 1,Six Buildings plus Plant
Figure 16 gives the kW demand of the six office buildings served by the plant plus the plant kW demand. The total at 4PM, for the Table 1 System top chart, is 10,216 kW. The bottom chart shows the total system kW demand increased to 11,481 kW for the Table 1.5 System, a 12% increase due to the installation of the fan powered terminals and return fans. The building lights and plug kW is the largest, for both systems, at 4,973 kW with plant kW of 3,860 for the Table 1 System and 4,072 plant kW for the Table 1.5 System. The total AHU fan kW significantly increased with the installation of the fan powered terminals and return fans to almost double at 4PM design conditions. The AHU kW increased due to the kW of the terminals and return fans and also due to the increased load on the fan system.
34
1,142 1,142
3,439
4,973 4,973
2,763
1,9051,600
510 426 400674
1757
2930
3390
3860
2216
1067846
150 129513
1,0131,212
1,383
593269 203
1 1 1 13 5 5 5 6 4
2 2 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(kW
)
TIME OF DAYTable 1 System kW demand with elect heat-Design Day
(Blds)kW (plant)kW (AHU)Fan kW
Total heat kW # Chiller/Towers on
1,142 1,1421,295
3,439
4,973 4,973
2,763
1,9051,600
531 446 419731
1850
3097 31933594
4072
2318
1114869
255
1,009
1,8452,164
2,435
1,148
561 429
1 1 1 13 5 5 5 6 4 2
2 0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(kW
)
TIME OF DAYTable 1.5 System kW demand with elect heatTerminal and Return Fans Installed
(Blds)kW (plant)kW (AHU)Fan kW '# Chiller/Towers on
Figure 16: System Performance-Six Buildings plus plant-Design Day-Table 1 System top chart-Table 1.5 System bottom chart
Comparing the charts of Figure 16 illustrates the number of chiller/towers on to meet the load is the same for both system with six required at 4PM and only one from midnight to 6AM.
Table 1 & 1.5 System Performance at Winter Conditions of Figure 2-Six Buildings plus Plant-kW Building Heat & Fuel Heat
1,142 1,1421,295
3,439
4,973 4,973
2,763
1,9051,600
4,153
4,811
4,1134,390
1,744
583
2,647
3,965
185
539 580294
204324 309
616 588
266
316 324
1 1 1 1 1 1 1 2 2 1 1 1 0
500
1000
1500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
System kW
(AHU
)&Fa
n kW
(Bld
s) &
Hea
t kW
TIME OF DAYTable 1 System kW demand with elect heat-Winter Day
(Blds)kW Total heat kW(AHU)Fan kW (plant)kW# Chiller/Towers
1,142 1,142
3,439
4,973 4,973
2,763
1,600
337 328738
636 338376
6901,048 1,121
418
4,063
4,707
4,023
4,309
1,703
543
2,580
3,877
1 1 1 1 1 1 2 2 2 1 1 1 0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
5,500
System kW
(kW
)
TIME OF DAYTable 1.5 System kW demand with elect heatTerminal & Return Fans Installed
(Blds)kW (plant)kW (AHU)Fan kWTotal heat kW # Chiller/Towers on
Figure 17: System Performance-Six Buildings plus Plant-Winter Day-Electric Heat
Figure 17 illustrates the total system kW performance for Table 1 System, top chart, and Table 1.5 System, bottom chart. The secondary horizontal axis of each chart gives the total system kW, the sum of values given in the charts. For
35
example, at 4PM the Table 1 System total 6,725 kW;(Blds) light & plug kW = 4,973 kWPlant kW = 588 kW(AHU) Fan kW = 580 kWTotal heat kW = 583 kW Total = 6,725 kW The Table 1.5 System with fan powered terminals and return fans installed has a greater system kW demand for all hours. However, the kW of building heat is less for the Table 1 System, top chart, versus the Table 1.5 system, bottom chart. The above charts and discussion have demonstrated the details, the simple reason is that the fan powered terminals and return fans kW add heat to the air and therefore the perimeter air reheat requirement is less. Schematics 3 & 4 show details. Figure 17 looks very different if the building utilizes fuel for perimeter and fresh air heat as shown by Figure 18.
1,142
3,439
4,973 4,973
2,763
1,9051,600
1368 1248
496166 753
1127
185
539 580
294
219 204309
616 588
266 316
324
1 1 1 1 1 1 1 2 2 1 1 1 0
500
1000
1500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
System kW
(AHU
) & P
lant
kW
(Bld
s) k
W &
Hea
t (to
n)
TIME OF DAYSystem kW demand with fuel heat-Winter Day-Table 1
(Blds)kW Total heat (ton) (AHU)Fan kW
(plant)kW # Chiller/Towers
1,142
3,439
4,973 4,973
2,763
1,9051,600
1338 1225
484154
1102328
738636
338376
1,0481,121
418
1 1 1 1 1 1 2 22
1 1 10
500
1,000
1,500
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
System kW
(AHU
) & P
lant
kW
(Bls)
kW
& H
eat (
ton)
TIME OF DAYTable 1.5 System kW demand with fuel heatTerminal & Return Fans Installed
(Blds)kW Total heat (ton) (plant)kW
(AHU)Fan kW # Chiller/Towers on
Figure 18: System Performance-Six Buildings plus plant-Winter Day-Fuel Heat
Figure 18 gives the system kW and fuel heat performance illustrating the significant drop in kW demand as given by the secondary horizontal axis. Note the vertical axis have different scales so that the (AHU) system and plant kW can be clearer. Also note that the fuel heat is given in ton. As with Figure 17 the secondary horizontal axis illustrates the Table 1.5 System kW demand is greater for all hours. Comparing the charts once again illustrates that the fuel heat (ton) is less for the Table 1.5 System for the reasons discussed above.
36
SummaryThis Chapter 3 has shown the difference in supply air and system kW performance due to the installation of fan powered terminals and return fan. The next Chapter 4 will install the other conditions of the Table 2 system;
1. Peak lights kW .81 to 1.01 watts/ft2
2. Peak plugs kW .66 to .822 watts/ft2
3. Duct design 5.5 to 7.0 in. water4. Fan powered terminals installed5. Return air fans installed.
Chapter 4-Table 2 System For many projects it is a given that the construction of a system will not be exactly as designed. The first challenge for the (SEE) Model, after the system is constructed, is to develop a (SEE) Model of the system that can be used to define how the system should operate at any conditions of weather. Table 1, Chapter 1 is the as designed system and Table 2 below illustrates the assumed as constructed system. Table 2 assumes design changes were made to install fan powered terminals11 and return fans12 defined by Chapter 3. It is also assumed that the peak light (watts/ft2) was determined to be 1.01 versus the .81 design value. The peak plug value was determined to be .822 (watts/ft2) versus the .66 design value of Table 1.
Building Location and Design1. Location=Kansas City Mo. 2. Ambient temperatures-Figure 23. Percent clear sky 100%. 4. Building design per Liu5 changed.5. Percent wall glass 37%6. Peak lights kW .81 to 1.01 watts/ft2
7. Peak plugs kW .66 to .822 watts/ft2
8. Return air to perimeter-no change.9. Duct design 5.5 to 7.0 in. water10. Fan powered terminals installed11. Return air fans installed
Building Control 12. Lights on/off control 6% on after hours.13. Plugs on/off control 44% on after hours.14. Building pressure control, no infiltration. 15. Supply air = 55F16. Supply water = 44F to 44.5F17. Stats control-yes. 18. Perimeter heat air temp-105F.19. VAV fan static control-yes. 20. Fresh air CFM control-yes.21. Fresh air heat stat set 42F.
Plant Design & Control22. Chiller/Tower selection13.
Table 2: System
37
The static pressure of the air duct systems was determined to be about 7.0 versus the 5.5 design value. Table 2 illustrates these design changes that will be defined as the Table 2 as constructed system.Table 2 conditions increased the estimated annual (EUI) from 38 (btu/ft2-yr) of Chapter 1 to 48 (btu/ft2-yr) of Figure 1 top chart, a 26% increase. Comparing Chapter 1 Figure 5 top chart to Figure 1 the summer (kbtu/ft2-yr) value increased from 8.45 to 11.12, a 32% increase.
11.42
12.57
14.07
10.84
0
5
10
15
20
25
30
35
40
45
50
55
kbtu
/sq
ft-y
ear
Table 2 System (EUI) Estimate-(kbtu/sq ft-year)-Lights 1.01 (watts/ft2) Plug .822 (watts/sq ft)-Fans (dh) =7.0 in water
Summer (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Spring (kbtu/sqft-yr)
6.48
16.
481
6.48
16.
481
1.97
91.
610
1.58
11.
877
2.95
11.
180
0.96
4 1.76
50.
013
3.30
2 5.04
50.
719
0
1
2
3
4
5
6
7
kbtu
/sq
ft-y
ear
Table 2 System (EUI) Estimate-(kbtu/sq ft-year)-Terminal & return fans installed 1.01 light & .822 plug (watts/sqft)-Fans (dh=5.5 in water
Bld-Summer Bld-Fall Bld-Winter Bld SpringFan-Summer Fan Fall Fan-Winter Fan-SpringPlant-summer Plant-Fall Plant-winter Plant-SpringHeat-summer Heat-Fall Heat-winter Heat-Spring
Figure 1: (EUI) values-Table 2 System
The bottom charts of Chapter 1 Figures 5 & Figure 1 above give the (EUI) values of the system components. The building values increased from 5.183 to 6.481 due to the increased peak lights kW and plug kW. The plant (kbtu/ft2-yr) increased from 2.481 to 2.951 during summer conditions. The biggest percent increase is fan power that more than doubled for all seasons due to the increase in duct static pressure from 5.5 to 7.0 inches water and also due to increased load. The energy required for perimeter heat and fresh air heat decreased with Table 2 conditions. The increased electrical load of the building and fan system kWplus, the installation of the fan powered terminals and return fans decreased the required building heat. The charts and discussion of Chapter 3 regarding the installation of fan powered terminals and return fans provides an understanding of this rather complex system characteristic.
System (watt/sqft)
90.086.0 84.0 82.0
88.094.0 96.0 97.0
101.0 98.0 95.0 93.0
71.0 70.0 69.0 70.0 72.0 74.0 75.0 76.0 78.0 75.0 74.0 72.0
0.70 0.66 0.640.88
2.283.68 3.71
3.984.28
2.19
1.261.02
0.53 0.51 0.51 0.63
1.66
2.63 2.62 2.78 2.90
1.450.90 0.74
-0.5
0.5
1.5
2.5
3.5
4.5
5.5
6.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% Clear Sky
Tem
pera
ture
(F)
TIME of DAYTable 2 System-Peak Summer design weather-System & Site
(watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)System (watt/sqft) Site (watt/sqft)
Figure 2: All Electric Table 2 System (watt/sqft)
Figure 2 gives the total system (watt/sqft) for an all-electric system at design day weather. The difference in the system value and the site value of Figure 2 is the (watt/sqft) of the plant.
38
34.032.0
28.026.0
24.0
30.0
38.040.0
42.040.0
38.036.0
34.032.0
28.026.0 24.0
30.0
38.040.0
42.040.0
38.036.0
1.84 1.90 2.03 1.87
2.95 2.942.59 2.58 2.70
2.10 2.01 1.98
1.72 1.79 1.92 1.77
2.78 2.752.37 2.33 2.44
1.98 1.89 1.86
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
% Clear Sky
(watt
/sqft
)
Tem
pera
ture
(F)
TIME of DAYTable 2 System-winter weather-System & Site (watts/sqft)
All Electric Heat
Design Dry Bulb (F) Design Wet Bulb (F)
System (watt/sqft) Site with Elect Heat (watts/sqft)
34.032.0
28.026.0
24.0
30.0
38.040.0
42.040.0
38.036.0
34.032.0
28.026.0 24.0
30.0
38.040.0
42.040.0
38.036.0
0.55
2.28 2.31
0.74
1.36
0.15 0.13
1.10
0.000.32
0.020.0
1.0
2.0
3.0
4.0
5.0
6.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
% Clear Sky
Tem
pera
ture
(F)
TIME of DAYTable 2 System-winter weather-System, Site, & Heat (watts/sqft)
System with fuel heat given in (watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)Buildings (watt/sqft) Perimeter heat (watt/sqft)Fresh air heat (watt/sqft)
Figure 3: Table 2 System (watt/sq ft)-Top chart electric heat-Bottom chart Fuel heat expressed as (watt/sq ft) Figure 3 illustrates the energy use of the Table 2 System if heat is provided by electric or fuel where fuel is given in (watt/sqft) but would be in (btu/sqft) of gas or some other measure of fuel. The resulting site (watt/sqft) of the bottom chart is a much smaller value than given by the top chart.
Energy Balance & Schematic-Table 2 System at Design Conditions-One Building
Figure 4 gives the energy balance for the Table 2 system and Schematic 1 gives the system details at the same hour. The structure of Figure 4 is that all loads to the left of the plant load equal the plant load and the values to the right sum to the energy out at the tower. Figure 4 is in (btu/ft2) values verses (ton) of Chapter 1 Figure 3. For example, Figure 1-3 gives a design hour plant load of 864.6 ton and Figure 4 chart gives;21.83 btu/ft2 x 565,000 ft2/ (12,000 btu/ton) = 1,027.8 ton for the conditions of Table 2 verses 864.6 ton for the Table 1 system. Schematic 1 shows the same plant load for one building. At design conditions the Table 2 system plant now requires seven chiller/towers to provide 44F supply water as shown by Figure ?.
3.46 2.80 3.65 2.394.42
-2.01
7.13
-21.83
4.71
-0.14
-26.39-30
-25
-20
-15
-10
-5
0
5
10
(btu
/hr-
ft2)
System (btu/ft2)-4PM Design Hour Weather-Table 2 System-Ein = Eout
lights (btu/ft2) Plug (btu/ft2) Fans (btu/ft2)
Fuel or elect. heat (btu/ft2) People load btu/sqft Bld shell btu/sqft
Exhaust btu/sqft Fresh air (btu/ft2) Plant load (btu/ft2)
Plant kW btu/ft2 Pump heat out btu/ft2 Tower btu/ft2 out
Figure 4: Table 2 System- Energy balance at 4PM design conditions of Chapter 1-One building
39
Each BLD ft2 = 565,000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 101.0 Ex-/Infil+-CFM = 0 <<Roof ft2 = 43,462 Twet-bulb= 78.0 Infilsen-ton = 0.0
N/S wall ft2 = 40,560 WallNtrans ton= 5.15E/W wall ft2 = 30,604 WallStrans ton= 5.73
Wall % glass= 37.5% WallEtrans ton= 3.88Glass U = 0.55 WallWtranston= 3.88 WallTot trans ton = 18.6
Wall U = 0.09 GlassN trans ton = 18.13Glass SHGC = 0.40 GlassS trans ton = 18.13
Wall emitt = 0.55 GlassE-trans ton = 13.68RoofTrans ton = 43.1 GlassW-trans ton = 13.68 GlassTot-trans-ton= 63.6
Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 6.1
plugton&kW = 132 464.3 GlassE-solar ton = 4.6Lightton&kW= 163 572.1 GlassW-solar ton = 62.0 GlassTot-solar-ton = 82.6
Total Bldint-ton = 405.3 BLD kW= 1036.3 (int cfm)per-ton = 0.00 >(int-cfm)to-per-ret= 237564 FAN kW= 603.9 Tot Bldper-sen-ton = 164.9 v
Tstat-int= 75.0 HEAT kW = 0.0 Tstat-per = 75.0 return(Bld)int-air-ton= -405.3 ^ SITE kW = 1640.2 ^ (Bld)per-air-ton= -164.9 air
Tair supply int= 56.04 Bld Shell (ton)= 208.0 Tair supply per= 56.04 ^ Fresh Air (ton)= 335.7 ^
Ton kW Ton kW V(fan)int-ter ton&kW= 22.3 78.4 (fan)per-ter ton&kW= 9.1 31.9
Theat-air= 55.0 (D)heat ton&kW = 0.0 0.0
Treheat air = 55.0(D)reheat ton&kW = 0.0 0.0
31.9(D)int-air-ton= -427.6 Interior Peri
Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 237,564 ^ (D)per-CFM= 96,644 ^
>>>(Coil)sen-ton= 850 ^ ^Coil UA = 3.23
One Building (TON) COIL LMTD = 16.09CoilCap-ton = 52.0Coilload-ton = 39.5 V
(COIL)L+s-ton= 1027.8 ^ ^ ^<<<< Tair VAV= 83.25 TBLD-AR = 75.00
(FAN)VAV-CFM= 334,209 (Air)ret-CFM = 334,209 Return4PM (FAN)ton-VAV= 118.4 (FAN)ret-kW= 77.1 Fan
(FAN)kW-VAV= 416.5 (FAN)ret-ton= 21.9 V^ (Air)ret-ton = 623.5
26 F.A.Inlet ^ Tar-to-VAV = 75.73 statFA= 42 26 VAV FANS VAVret-sen ton = 535.1
TFA to VAV = 101.0 > Tret+FA = 79.31 VAVret Lat-ton = 38.58>(FA)sen-ton = > 196.2 (dh) = 6.965 < VAVret-CFM = 286,822 <
> (FA)CFM= 47,386 > Efan-VSD= 0.657 V> (FA)Lat-ton= 139.5 VAV inlet-sen-ton = 731.3
(FA)kW= 0.0 VAVinlet-lat-ton= 178.1 ExLat-ton = -6.4ExCFM = -47,386
SEE Schematic air side TEx = 75.73Air temp green kW red Time= 4PM Exsen-ton = -88.4 V Air CFM purple Ton blue v
Schematic 1: Table 2 System at design conditionsOne building
Energy Balance & Schematic-Table 2 System at Design Conditions-One Building
3.462.80
1.62
0.44
2.39
-0.52
-1.96-1.18
-7.04
0.89
-0.06
-7.87-9-8-7-6-5-4-3-2-1012345
(btu
/hr-
ft2)
System (btu/ft2)-4PM Winter Weather-Table 2 System-Ein = Eout
lights (btu/ft2) Plug (btu/ft2) Fans (btu/ft2)Fuel or elect. heat (btu/ft2) People load btu/sqft Bld shell btu/sqftExhaust btu/sqft Fresh air (btu/ft2) Plant load (btu/ft2)Plant kW btu/ft2 Pump heat out btu/ft2 Tower btu/ft2 out
Figure 5-Energy balance at 4PM winter conditions of Chapter 1 Figure 2.
Figure 5 shows the plant load and tower energy out are about one third the design conditions shown by Figure 4. The lights, plug, and people load are the same for both design and winter conditions. The fan load due to fan kW is less during winter conditions due to less load. The building shell and fresh air load are negative for the winter conditions in large part reducing the plant load and energy out at the tower.All loads on Figure 5 are the same as on Schematic 2.
40
BLD ft2 = 565000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 42.0 Ex-/Infil+-CFM = 0 <<Roof ft2 = 43,462 Twet-bulb= 42.0 Infilsen-ton = 0.0
N/S wall ft2 = 40,560 WallNtrans ton= -5.99E/W wall ft2 = 30,604 WallStrans ton= -3.72
Wall % glass= 37.0% WallEtrans ton= -4.52Glass U = 0.55 WallWtranston= -4.52 WallTot trans ton = -18.7
Wall U = 0.09 GlassN trans ton = -22.01Glass SHGC = 0.40 GlassS trans ton = -22.01
Wall emitt = 0.55 GlassE-trans ton = -16.61RoofTrans ton = 8.1 GlassW-trans ton = -16.61 GlassTot-trans-ton= -77.2
Roofsky lite ton = 0.0 GlassN-solar-ton = 10.0Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 25.5
plugton&kW = 132 464.3 GlassE-solar ton = 0.8Lightton&kW= 163 572.1 GlassW-solar ton = 27.2 GlassTot-solar-ton = 63.4
Total Bldint-ton = 370.3 BLD kW= 1036.3 (int cfm)per-ton = 19.53 >(int-cfm)to-per-ret= 217033 FAN kW= 267.7 Tot Bldper-sen-ton = -13.0 v
Tstat-int= 75.0 HEAT kW = 72.2 Tstat-per = 74.0 return(Bld)int-air-ton= -370.3 ^ SITE kW = 1376.2 ^ (Bld)per-air-ton= 13.0 air
Tair supply int= 56.04 Bld Shell (ton)= -24.4 Tair supply per= 105.00 ^ Fresh Air (ton)= -55.4 ^
Ton kW Ton kW V(fan)int-ter ton&kW= 20.4 71.6 (fan)per-ter ton&kW= 0.4 1.5
Theat-air= 104.0 (D)heat ton&kW = 12.6 44.2
Treheat air = 74.0(D)reheat ton&kW = 8.0 28.0
73.7(D)int-air-ton= -390.7 Interior Peri
Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 217,033 ^ (D)per-CFM= 4,659 ^
>>>(Coil)sen-ton= 296.1 ^ ^Coil UA = 1.63
One Building (TON) COIL LMTD = 10.05CoilCap-ton = 16.4Coilload-ton = 12.7 V
(COIL)L+s-ton= 331.4 ^ ^ ^<<<< Tair VAV= 69.84 TBLD-AR = 74.00
(FAN)VAV-CFM= 221,691 (Air)ret-CFM = 221,691 Return(FAN)ton-VAV= 46.7 (FAN)ret-kW= 30.4 Fan(FAN)kW-VAV= 164.2 (FAN)re t-ton= 8.6 V
^ (Air)ret-ton = 387.726 F.A.Inlet ^ Tar-to-VAV = 74.43
statFA= 42 26 VAV FANS VAVret-sen ton = 304.9 TFA to VAV = 42.0 > Tret+FA = 67.50 VAVret Lat-ton = 35.35
>(FA)sen-ton = > -55.4 (dh) = 3.825 < VAVret-CFM = 174,305 <> (FA)CFM= 47,386 > Efan-VSD= 0.607 V
> (FA)Lat-ton= 0.0 VAV inlet-sen-ton = 249.4(FA)kW= 0.0 VAVinlet-lat-ton= 35.3 ExLat-ton = -9.6
ExCFM = -47,386SEE Schematic air side TEx = 74.43Air temp green kW red Exsen-ton = -82.9 V Air CFM purple Ton blue v
Schematic 2: Table 2 System at winter conditions-One building
Table 2 System Performance-Six Buildings plus Plant Figure 6 compared to Figure 4 of Chapter 1 gives some detail how the Table 2 system requires more energy than the Table 1 system. At 4PM design conditions the system kW has increased from 10,216 kW to 14,517 kW, a 42% increase. The (blds) kW or lights plus plug kW increased from 4,973 to 6,218 due to the light & plug peak (watts/ft2) increases. The peak plant kW increased from 3,860 to 4,675 and the air system kW increased from 1,383 to 3,623 kW, about 2.6 times the Table 1 system. At 4PM winter weather the system kW has increased from 6,725 kW to 9,137 kW, a 36% increase. The (blds) kW or lights plus plug kW increased from 4,973 to 6,218 due to the peak (watts/ft2) increases, same as at design conditions. The plant kW increased from 588 to 879 and the air system kW increased from 580 to 1,606 kW, about 2.8 times the Table 1 system. Building heat at 4PM slightly dropped with the Table 2 system, from 583 kW to 433 kW. The drop in heat kW with the Table 2 system is across the 24 hours. For example, at 10PM the Table 1 system heat is 3,965 kW and the Table 2 system heat is 3,809 kW, a 3.9% drop. Less heat is required because of the increased kW demand in the building due to lights, plugs, fans, and the installation of the fan powered terminals and return fans. Figure 7 gives the system kW demand with fuel heat.
41
1,429 1,4291,619
4,300
6,218 6,218
3,454
2,3822,001
589 466846
2096
354036754094
4675
2500
1211938
355 286
517
1,341
2,7023,196
3,623
1,472
681 512
1 1 1 23 5 6 6 7 4 2
2 0500100015002000250030003500400045005000550060006500
0500
100015002000250030003500400045005000550060006500
TOTAL SYSTEM kW(k
W)
TIME OF DAYTable 2 System kW-elect heat-Design day
(Blds)kW (plant)kW (AHU)Fan kWTotal heat kW # Chiller/Towers ON
1,429 1,429
4,300
6,218 6,218
3,454
2,3822,001
395381 643
879407
405430
9141,504
1,606
763496
4,002
4,641
3,9644,216
1,604
433
2,497
3,809
1 1 1 1 1 2 2 2 2 1 1 1 0500100015002000250030003500400045005000550060006500
0500
100015002000250030003500400045005000550060006500
TOTAL SYSTEM kW
(kW
)
TIME OF DAYTable 2 System kW-elect heat-winter day
(Blds)kW (plant)kW (AHU)Fan kWTotal heat kW # Chiller/Towers ON
Figure 6: Table 2 System kW Demand
430914 1,504
1,606
763 544 496
381643
735 844 879
416 405
1,429 1,4291,619
4,300
6,218 6,218
3,454
2,3822,001
11381201
1320
11271199
456
102 51123
710
9891083
0100200300400500600700800900100011001200130014001500
0500
100015002000250030003500400045005000550060006500
TOTAL SYSTEM kW with fuel heat
Heat
n (t
on)
(kW
)
TIME OF DAYTable 2 System kW-fuel heat-winter day
(AHU)Fan kW (plant)kW (Blds)kW Total heat (ton)
Figure 7: Table 2 System kW with fuel heat
The secondary horizontal axis of Figures 6 & 7 illustrates the significant drop in total kW with the fuel heat system. The building perimeter heat and fresh air heat is provided by fuel and given by Figure 7 in terms of (12,000 btu/hr = ton). Note that all other kW values of Figures 6 & 7 are the same with the exception of heat.
42
SUMMARY Chapter 4-Table 2 System
The following charts give the 24-hour performance of the Table 2 system at design weather and weather during the four seasons.
90.086.0 84.0 82.0
88.094.0 96.0 97.0
101.0 98.0 95.0 93.0
71 70 69 70 72 74 75 76 78 75 74 72
49.43
0.66 0.62 0.610.83
2.21
3.63 3.653.96
4.27
2.11
1.200.96
0.00.51.01.52.02.53.03.54.04.55.05.56.06.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% Clear Sky
(watt
s/ft
2)
Tem
pera
ture
(F)
TIME of DAYSummer Design day weather & System (watts/sqft)-Electric Heat
Dry Bulb (F) Wet Bulb (F)24 Hour System (watts/ft2) System (watt/sqft)
49.43
0.00
0.66 0.62 0.610.83
2.21
3.63 3.653.96
4.27
2.11
1.200.96
0.000.00 0.00 0.00
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
0.00.51.01.52.02.53.03.54.04.55.05.56.06.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
% Clear Sky
(watt
s/ft
2) &
(btu
/ft2)
24 H
our (
watt
s/ft
2) &
(btu
/ft2)
TIME of DAYSummer Design day weather & System (watts/sqft)Fuel Heat (btu/ft2)
24 Hour System (watts/ft2) 24 Hour Fuel (btu/ft2)
System (watt/sqft) Fuel Heat (btu/ft2)
Figure 8: Table 2 System at Design day weatherFigures 8 thru 12 give the hourly performance of the system and the 24-hour sum.
78.0 76.072.0
68.075.0 78.0
82.086.0 88.0 86.0 83.0 80.0
6671 74
68
43.44
0.58 0.57 0.59 0.72
2.02
3.16 3.203.48
3.66
1.85
1.070.83
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
% Clear Sky
(watt
s/ft
2)
Tem
pera
ture
(F)
TIME of DAYSummer day weather & System (watts/sqft)-Electric Heat
Dry Bulb (F) Wet Bulb (F)24 Hour System (watts/ft2) System (watt/sqft)
43.382
0.19
0.58 0.57 0.56 0.72
2.02
3.16 3.203.48
3.66
1.85
1.070.83
0.100.00 0.00 0.00
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
% Clear Sky
(watt
s/ft
2) &
(btu
/ft2)
24 H
our (
watt
s/ft
2) &
(btu
/ft2)
TIME of DAYSummer day weather & System (watts/sqft)-Fuel Heat (btu/ft2)Table 2 System Performance
24 Hour System (watts/ft2) 24 Hour Fuel (btu/ft2)
System (watt/sqft) Fuel Heat (btu/ft2)
Figure 9: Table 2 System at Summer day weather
Each Figure 8 thru 12 gives the 24-hour performance of the Table 2 System both for an electric heat system and a fuel heat system. Generally, the watt/sq ft and btu/sq ft data will be available due to the installation of utility meters. Therefore, the Figures 8 thru 12 provide an method to judge the performance of a real system when the weather conditions and season is close to the values given.
43
42.040.0
38.035.0
40.044.0
48.050.0
53.050.0
48.046.0
4038 38
35
4042
4648
5048
4644
48.01
1.54 1.61 1.67 1.84 1.86
2.55 2.54 2.65 2.65
1.851.63 1.61
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
% Clear Sky
(watt
s/ft
2)
Tem
pera
ture
(F)
TIME of DAYFall day weather & System (watts/sqft)-Electric Heat
Dry Bulb (F) Wet Bulb (F)24 Hour System (watts/ft2) System (watt/sqft)
34.87
44.84
0.59 0.59 0.59 0.67
1.54
2.55 2.54 2.65 2.65
1.330.93 0.80
3.69
0.00 0.00
2.78
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
% Clear Sky(w
atts/
ft2)
& (b
tu/ft
2)
24 H
our (
watt
s/ft
2) &
(btu
/ft2)
TIME of DAYFall day weather & System (watts/sqft)-Fuel Heat (btu/ft2)Table 2 System performance
24 Hour System (watts/ft2) 24 Hour Fuel (btu/ft2)
System (watt/sqft) Fuel Heat (btu/ft2)
Figure 10: Table 2 System at Fall day weather
34.032.0
28.026.0
24.0
30.0
38.040.0
42.040.0
38.036.0
53.92
1.82 1.88 2.01 1.85
2.89 2.872.51 2.51 2.63
2.05 1.98 1.95
0.00.51.01.52.02.53.03.54.04.55.05.56.06.57.07.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
% Clear Sky
(watt
s/ft
2)
Tem
pera
ture
(F)
TIME of DAYWinter day weather & System (watts/sqft)-Electric Heat
Dry Bulb (F) Wet Bulb (F)24 Hour System (watts/ft2) System (watt/sqft)
33.89
68.35
0.62 0.61 0.62 0.66
1.63
2.39 2.41 2.46 2.49
1.300.94 0.81
4.752
1.633
0.453
3.900
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
0.00.51.01.52.02.53.03.54.04.55.05.56.06.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
% Clear Sky
(watt
s/ft
2) &
(btu
/ft2)
24 H
our (
watt
s/ft
2) &
(btu
/ft2)
TIME of DAYWinter day weather & System (watts/sqft)-Fuel Heat (btu/ft2)Table 2 System performance
24 Hour System (watts/ft2) 24 Hour Fuel (btu/ft2)
System (watt/sqft) Fuel Heat (btu/ft2)
Figure 11: Table 2 System at Winter day weather
The 24-hour sum of the all-electric system gives a perspective of how energy consumption of the Table 2 System changes with weather and season.
Design Day 24-hour sum = 49.43 (watt/sq ft)Summer day 24-hour sum = 43.44 (watt/sq ft)Fall day 24-hour sum = 48.01 (watt/sq ft)Winter day 24-hour sum = 53.92 (watt/sq ft)Spring day 24-hour sum = 41.17 (watt/sq ft)
44
62 60 58 6064 66 68 70 72 70 68 66
52 5046 48 50
56 58 60 62 60 58 56
41.17
0.90 0.96 1.020.61
1.74
2.88 2.813.02 3.14
1.55
1.01 0.95
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
% Clear Sky
(watt
s/ft
2)
Tem
pera
ture
(F)
TIME of DAYSpring day weather & System (watts/sqft)-Electric Heat
Dry Bulb (F) Wet Bulb (F)24 Hour System (watts/ft2) System (watt/sqft)
38.29
9.83
0.57
0.56 0.56 0.61
1.74
2.88 2.813.02 3.14
1.55
0.940.77
1.575
0.000 0.000 0.60
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0
10.0
20.0
30.0
40.0
50.0
60.0
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
% Clear Sky(w
atts/
ft2)
& (b
tu/ft
2)
24 H
our (
watt
s/ft
2) &
(btu
/ft2)
TIME of DAYSpring day weather & System (watts/sqft)-Fuel Heat (btu/ft2)Table 2 System performance
24 Hour System (watts/ft2) 24 Hour Fuel (btu/ft2)
System (watt/sqft) Fuel Heat (btu/ft2)
Figure 12: Table 2 System at Spring day weather
The required building heat, during winter weather, drives the 24-hour sum to a value grater than the design day sum. Also note that the winter heat required is about 37% of the total energy for this winter day as defined by the top chart of Figure 11.
The next Chapter 5 will illustrate how bad control of the Table 2 System can drive the energy consumption of the system to more than two times the values given here.
45