independet study report 2012 2 28_zgl.pdf

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Building Control Systems Modeling A Case Study using Syracuse COE Headquarter

Independent Study Final Report

By

Korbaga F. Woldekidan

Wenyi Jin

Zhigao Li

Advisor:

Jianshun (Jensen)Zhang

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1. Introduction………………………………………………………………………………………………………….…………………4

2. SYRACUSE COE Builiding……………………………….……………………………………………………….………..………5

2.1 Background………………………………………………………………………………………………….……….……………5

2.1.1 Objective …………………………………………………………………………………………………..…………6

2.1.2 Scope ………………………………………………………………………..……………………………………………6

2.2 Building Features ……………………………………………………………………………………………………………..7

2.2.1 Overall Building Features …………………………………………………………………………….………..7

2.2.2 Building Envelope ………………………………………………………………………………………….………..11

2.2.3 Zones and Occupancy …………………………………………………………………………………...………14

2.2.4 Internal Heat Sources …………………………………………………………….…………….…...………….15

2.2.5 Set Point Temperatures …………………………………………………………………….………………………18

2.3 HVAC System ……………………………………………………………………………………….………………..…………19

2.3.1 HVAC System Overview ……………………………………………………………….………….…….…………19

2.3.2 Air System ……………………………………………………………………………………….……….……….…20

2.3.3 Water System ……………………………………………………………………………………….……….….………27

3. Modeling and Simulation with BCVTB and Energy+ ……………………………………………..….…….……36

3.1 Introduction ……………………………………………………………………………………………………………………36

3.2 BCVTB Platform ……………………………………………………………………………………………………………36

3.2.1 Structure and Functionality ………………………………………………………………………….…………36

3.2.2 Interface with Energy+ ………………………………………………………………………………….…………37

3.2.3 Interface with Dymola …………………………………………………………………………………….………38

3.3 Energy+ Model for COE Enclosure ………………………………………………………….……….…………40

3.3.1 Create an EnergyPlus idf file for COE enclosure ………………………………………………………40

3.3.2 Add the exchanged schedule and variable with BCVTB ………………………………………40

3.4 Modelica Model for HVAC system …………………………………….………………….……. ……………41

3.5 Whole Building Model using BCVTB to couple Enclosure and HVAC system ………… ……42

3.5.1 Create a configuration file for Energy+ IDF file ………………………………………… ….………42

3.5.1 Create a BCVTB model to integrate Energy+ and Dymola ………………………………………43

4. Modeling and Simulation Using Modelica ………………..…………………………………….………….…………44

4.1 Introduction ………………………………………………………………………………………….……..…………………44

4.1.1 Features of Modelica ……………………………………………………………………………….……………44

4.1.2 Objective and Scope ……………………………………………………………………………….……………44

4.2 Case Study: Heat Transfer Lab ……………………………………………………………………………….……45

4.2.1 Description of the facility ………………………………………………………………………….…………45

4.2.2 Model assumptions and representation. …………………………………………………………..…46

4.2.3 Communication logic between Energy plus and Dymola ………………………………………48

5. Results and Discussion ……………………………………………………………………………………………………49

5.1 Simulatoin ……………………………………………………………………………………………………………………49

5.2 Results ……………………………………………………………………………………………………………………………49

6. Conclusion ……………………………………………………………………………………………………………………………52

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1. INTRODUCTION

In the modern world, Buildings consume quite enormous amount of energy and different

researches are emerging with the objective of making buildings more efficient from energy

consumption point of view. In practical application it is often difficult to see the effect of

different energy saving strategies until those strategies are implemented in the actual

Building. Usually investors don’t want to take risk before knowing whether the strategy could

really save the claimed energy saving or not. To alleviate this problem different simulation

tools are coming that can be used for checking the performance of new energy saving

strategies before being implemented in the actual building. Some of the existing energy

simulation tools include Energy Plus, google scetchup, Design Builder, Ecotec etc

Even if Energy plus has quite a variety of models that can be used for representing a building

with its HVAC system it is not friendly to use for the fact that it uses a high level language

(text based) for defining the configuration of the building geometry and HVAC systems. One

way of reducing the difficulty of Energy plus is through the use of other software with

graphical user interface like Design builder and Scatchup for geometry definition and some

simple HVAC system definition which can be later transported as an idf file to energy plus for

detail definition of the system

Currently Energy plus is the most widely used and matured simulation software in the

building simulation research society. Despite the richness of Energy plus in terms of available

mechanical component models, it lacks a way to define modern control system and

Lawrence Berkley National laboratory is coming up with an idea of interfacing Energy plus

with other simulation software or programming languages like Matlab through the use of

BCVTB (Building controls virtual test bed) so that modern control systems can be designed

outside Energy plus and can dictate the components in the energy plus.

In this paper we make use of a new simulation tool known as Modelica , an object oriented

programming language to define our HVAC system together with its control system so that It

can be interfaced with Energy plus for whole building energy simulation through the use of

BCVTB. Modelica is used for its ease of graphical representation and possibility to develop

our own component model or models from existing library.

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2. SYRACUSE COE BUILDING

2.1 Background The LEED Platinum Certified Syracuse CoE Headquarters building is a test bed for

environmental and energy technologies and building innovations. The facility includes an

array of high-end technologies which is foreseen as an excellent source to carry out

research and development.

The various features are - Total Indoor Environmental Quality [TIEQ] Lab, Green Roof,

Geothermal System, Lighting and Control Systems, Natural Ventilation, Personal

Ventilation Systems, Advanced Building Heat Recovery/Reuse Systems, Air Quality

Monitoring of Outside Air and Integrated Controls for Improving/Protecting Indoor Air,

Building Materials Testing, Rain Water Capture and Reuse. As we can see, most of these

features are concerned with improving the energy performance.

And more importantly the Syracuse CoE Headquarters building has lab and office space

available. Companies and organizations are going to be investing in the building areas for

offering services, development and research by making use of the thoroughly unique

facilities and/or functions in the building.

Figure2.1.1: Syracuse CoE Headquarters building

This iconic, high-performance, LEED-Platinum designed "living laboratory" is the

realization of a dream shared by leaders in government, industry, and academia to create

a world-renowned location for collaborations that address global challenges in clean and

renewable energy, indoor environmental quality, and water resources.

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Syracuse Center of Excellence Headquarters Quick Facts:

Cost: $41 million (funded from state and private sources)

Size: 55,000 square feet

Location: 727 E. Washington Street, Syracuse, NY, 13210. The three-acre site on the

corner of Almond and Washington streets is a designated “brownfield,” the former site

of the LC Smith typewriter factory and Midtown Plaza.

Number of Stories: 5

LEED Rating: Platinum

Uses: Offices for SyracuseCoE staff; classrooms; public spaces; indoor environmental

quality (IEQ), biomass fuel, and other research laboratories for use by SyracuseCoE

academic and industry partners.

Main Laboratory: Willis H. Carrier Total Indoor Environmental Quality Lab—the only

research facility of its kind in the world, a space to conduct controlled experiments on

the human response to indoor environments (temperature, air quality, odor, light, etc).

Funded by NY State Offi ce of Science, Technology, and Academic Research (NYSTAR)

and Carrier Corp.

Urban Ecosystem Observatory: The 150-foot Urban Ecosystem Observatory takes

measurements of outdoor air quality to help research into urban air pollution and the

impact of buildings on urban ecosystems.

2.1.1 Objective

The objectives of Chapter 2 are,

1. Introducing the SyracuseCoE Headquarter.

2. Giving information to another two partners for Building control system modeling.

2.1.2 Scope

The Mechanical Control Systems of the SyracuseCoE Building include Heat Pump system,

Control Heating Water System, Chilled Water System, Radiant System, Air System, and TIEQ

Air System. In this study, we will only cover the Mechanical Control Systems. Other systems

like Sound Control System and Lighting System will not be included in this study.

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2.2 Building Features

2.2.1 Overall Building Features

The COE building has five floors each floor having different zones with different activities and

floor area. Below is an overview of some of the features of the SyracuseCoE Headquarter

that make it so "green" .

1. Restrooms - Restrooms feature waterless urinals, dual flush low-flow toilets and faucets,

and sustainable paper and cleaning products.

2. Furniture - Furniture by Haworth and Herman Miller is made from recycled materials

and FSC wood and wood products. Furniture is also 100% recyclable by the

manufacturers upon return.

3. Insulation - Solid façades include superior insulation to reduce heating and cooling loads.

Interior insulation uses Demilec, a 100% soy-based spray foam. Exterior insulation

boards were created from sustainable natural fiber materials.

4. Vapor Intrusion System - Ventilation below the foundation prevents underground vapors

from entering the building, eliminating a potential source of contaminants in indoor air.

5. Storm Water Retention Tank - The southwest corner of the property features a storm

water retention tank to control run-off entering the sewer system.

6. Urban Ecosystem Observatory - The 150-foot Urban Ecosystem Observatory tower is

being used for a long-term, one-of-a-kind study that will assess Syracuse’s urban air

quality, air flow, and how outside air affects air quality inside a building.

7. Demand-Controlled Ventilation - The amount of fresh air delivered to a room varies

depending on the number of people who are present, saving energy when rooms are

partially occupied.

8. Building Shape and Form - The building is relatively narrow with extensive windows,

providing a high level of occupant comfort with ample natural light and opportunities for

views and natural ventilation.

9. Windows - The south façade features highly insulated glass with integrated electronically

controlled blinds that provide solar heat and glare control, capable of operation at

15-degree increments. The ceramic white dots on the windows passively reduce glare

and solar heat gain.

10. Radiant Ceilings - Most of the heating and cooling in rooms is provided via ceiling panels

that are embedded with copper piping that efficiently carries warm or cool water.

11. Underfloor Ventilation and Raised Flooring - Ventilation is provided close to occupants

for improved thermal comfort using a raised floor system, allowing for even air

distribution with lower fan speeds. The Tate raised floor system, situated 12 inches

above the concrete deck, also provides convenient wire routing.

12. Brownfield Remediation - Environmental contamination associated with previous

industrial site uses was remediated, restoring the site for sustained use by future

generations.

13. Sustainable Construction Practices - The construction team, led by LeChase, diverted 98%

of construction waste from going to a landfill.

14. Roof - The building roof is designed to reflect most of the sunlight, minimizing solar heat

gain and reducing the cooling load. The roof is also designed to allow future installation

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of photovoltaics, building-scale wind turbines, and roof top HVAC units.

Features of the Lobby:

1. Regenerative Elevator - The Otis elevator generates electricity on the way down, which

can then be used for going back up, used elsewhere in the building, or fed back into the

grid.

2. Reception Desk - The desk, built by Syracuse firm CabFab, features an e2e Materials

product that uses renewable fibers processed with a soy protein-based resin system.

3. Underfl oor Heating - Hot water is circulated through tubes embedded in the lobby floor

to provide efficient heating with a high level of comfort.

Features of the Lab Wing:

1. Façade Testbed - The south façade of the laboratory wing includes an opening of the

building envelope that can be used to test future building envelope and window systems.

The current research apparatus was installed into the curtain wall unit by licensees

HeliOptix and Island External Fabricators.

2. Solar Power Prototype - This is the first building-integrated concentrating photovoltaic

system, developed by researchers at Rensselaer Polytechnic Institute with collaborators

at Harvard University, and tracks the motion of the sun and uses lenses to concentrate

sunlight 500 times, generating both electricity and heat. This system was developed with

funding from NYSERDA, NYSTAR, and the US Department of Energy. It is being tested in

collaboration with SyracuseCoE.

3. Biofuels R&D Lab - An advanced biofuels laboratory is planned in the east end of the

laboratory wing to develop new methods of extracting and synthesizing fuels and

chemicals using woody biomass as feed material.

4. Water Tank - Rain and meltwater are collected from the roof, stored in an 8,000-gallon

Figure2.2.1-1: Syracuse CoE Headquarters building

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tank, and used to flush toilets, reducing both the consumption of drinkable water and

the amount of water that is discharged to the sewer.

5. Laboratory Exhaust - Air from laboratories is exhausted at low speed via a tall stack,

which saves energy compared to conventional high-speed designs.

6. Energy Recovery Ventilator - All buildings need to breathe fresh air. In winter and

summer replacing indoor air consumes energy to heat or cool incoming air. This

advanced energy recovery ventilator exchanges heat and moisture between outgoing

and incoming air streams, significantly reducing the amount of energy required to

condition incoming air.

Features of the 2nd Floor:

1. Carpet - Carpet tiles by InterfaceFLOR are made from recycled materials and installed

with minimal adhesive. Zero waste was created by our order: extra carpet tiles were sent

back to the manufacturer to be used for another order.

2. Boiler - The boiler, made by The Fulton Companies, touts 93% efficiency and uses the

latent heat of vaporization to create more heat.

3. Heat Pumps - Carrier heat pumps optimally manage the heating and cooling needs of

the building.

4. Geothermal Pipes - Heat exchanged with the ground—via water circulated through more

than five miles of tubing installed in 49 300-foot-deep wells—is used for both heating

and cooling, saving about 35% of energy compared to traditional systems. With a

constant temperature of 53 degrees, the groundwater helps heat the building in the

winter and cools it in the summer.

Features of the 3rd Floor:

1. Green Roof - Plantings on the

laboratory roof, made up of six

different varieties of sedum,

provide rainwater retention and a

visible connection to nature, while

also reducing the heat island effect.

2. Kitchenette - Cabinets were

created by RB Woodcraft out of a

unique e2e Materials product that

uses renewable fibers processed

with a soy protein-based resin

system.

3. SyracuseCoE Offices - The third

floor houses SyracuseCoE staff, who

works to catalyze collaborations

among academic, industry, and

government partners to create environmental and energy innovations for a sustainable

Figure 2.2.1-2: The layers of the green roof at

SyracuseCoE

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future. The open office configuration allows for maximum daylighting, air circulation, and

enhanced views. This suite will be used for testing of new heating, ventilation, and air

conditioning systems.

4. EFC Offices - This space houses the Environmental Finance Center at Syracuse University

(EFC) staff, who work to enhance the administrative and financial capacities of state and

local government officials and the nonprofit and private sectors as they endeavor to

improve environmental infrastructure and quality of life.

5. Natural Ventilation Indicator Lights - Manual windows are provided to allow for natural

ventilation throughout the building. Red and green lights alert occupants when it is best

to open windows based on measurements of outdoor temperature, humidity, air quality,

and wind speeds. While the windows are open, sensors notify the building management

system to reduce the amount of mechanical ventilation to save energy.

Features of the 4th Floor:

1. Building Management System - The building automation system installed by Siemens

ensures that heating, ventilation, air conditioning (HVAC), and other building systems

perform in harmony. The system provides information needed to maximize energy

efficiencies and optimize indoor air quality, such as advising occupants when outside

conditions are favorable for natural ventilation, controlling the amount of artificial

lighting, and managing the blind controls to reduce glare and heat gain.

2. Interstitial Mechanical Equipment Room - This area provides flexible space to install and

test new heating, ventilation, and air conditioning systems.

3. Air Treatment Modules (ATMs) - These Carrier ATM units are European technologies

being introduced in the US for the first time. They allow individuals to control their

environment to meet personal preferences at desktops located at the Carrier TIEQ Lab.

Energy use measurements for these units allow for optimal control of comfort while

balancing energy consumption.

Features of the 5th Floor:

1. Willis H. Carrier Total Indoor

Environmental Quality (TIEQ)

Laboratory - A unique facility,

funded by NYSTAR, Carrier, and

Empire State Development, in

which researchers will study how

multiple factors—including

temperature, humidity, air quality,

lighting, and sound—combine to

affect human health and

performance in built

environments.

2. P. Ole Fanger Room - This room is

dedicated to the memory of Prof. Figure 2.2.1-2: Room on the 5th floor with

electronically controlled blinds

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P. Ole Fanger of Denmark for his contributions to the field of thermal comfort and

ventilation, and for his service as University Professor at Syracuse University during

2006-07.

2.2.2 Building Envelope

The COE building has five floors each floor having different zones with different activities and

floor area. Data with regards to building geometry, materials, zones, occupancy, openings,

lighting, internal heat source has been collected from

Architectural and mechanical design drawings of the case study building

From the final reports of class HVAC in 2009.

Textbook and references for the thermal properties of materials.

Site visit to see geometry, outlook, materials and orientation of the building

Own estimates and approximations on issues where data is not available or difficult

to get (internal heat and pollutant source)

The building envelop is made out of different materials at different wall sections. The figure

below shows the different wall types used to make the outer envelops of the case building.

Figure 2.2.2-1: Different wall types on case building

Wall type 2, 3 and 4 are curtain walls with different type of glazing materials. Whereas wall

type 1, 6 and 7 are external walls with different cross sections.

The following figures show the different cross sections of the wall materials, partitions, floor,

roof, doors and windows used in the model and their thermal properties.

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U= 0.139 Btu/hr- ft2-F



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2.2.3 Zones and Occupancy

Floor Zone Area (Sq. Ft) Max. Occupancy No. People /sq.ft

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Assembly lobby 1432 95 0.0663

Storage/Mech. 2727 9 0.0033

Labs/educational 2886 58 0.0201


Labs 2518 50 0.0199

Labs/educational 4178 83 0.0199

Circulation 4563 46 0.0101

II

Assembly 449 30 0.0668

Classrooms 982 49 0.0499

Kitchen 125 1 0.0080

Storage/Mech. 2956 10 0.0034


Business area 1472 15 0.0102

III


Assembly 940 63 0.0670

Kitchen 123 1 0.0081

Assembly 335 22 0.0657


Assembly 589 39 0.0662

Storage 250 1 0.0040

IV

Educational shops/ voc. Rooms 3298 66 0.0200





VI

Storage 215 1 0.0047





Mechanical 241 1 0.0041


Table 2.2.3 Different Zones and Their Area in the Case Building

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2.2.4 Internal Heat Sources

The internal heat sources like occupancy, lighting, computers and office equipment and

other sources have to be inputted in the building model to get reliable building performance

results. These sources vary with time as they are very much dependent on the occupancy

pattern of the different zones of building. The tables below show the occupancy schedule

and internal heat source schedule for the case building.

Floor 1

Hr. Foot traffic Percent Comp/light Percent

Occupancy #

people

Lighting

Btu/hr Equipments Btu/hr

Maximum Value 113 50154.32 10160

1 5 5 5 2507.72 508

2 5 5 5 2507.72 508

3 5 5 5 2507.72 508

4 5 5 5 2507.72 508

5 8 5 15 2507.72 508

6 15 5 17 2507.72 508

7 30 10 34 5015.43 1016

8 70 50 79 25077.16 5080

9 75 80 85 40123.45 8128

10 80 85 90 42631.17 8636

11 82 95 93 47646.60 9652

12 85 95 96 47646.60 9652

13 80 85 90 42631.17 8636

14 90 87 102 43634.26 8839

15 98 90 111 45138.88 9144

16 90 98 102 49151.23 9957

17 80 95 90 47646.60 9652

18 70 50 79 25077.16 5080

19 50 30 20 15046.29 3048

20 40 20 15 10030.86 2032

21 25 10 12 5015.43 1016

22 5 5 10 2507.72 508

23 5 5 5 2507.72 508

24 5 5 5 2507.72 508

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Floor 2 Floor 3

Occupancy

Lighting

Btu/hr

Equipments

Btu/hr Occupancy

Lighting

Btu/hr

Equipments

Btu/hr

Max 120 87955.53 15240 158 80548.22 23368

1 6 4397.78 762 5 4027.41 1168.4

2 6 4397.78 762 5 4027.41 1168.4

3 6 4397.78 762 5 4027.41 1168.4

4 6 4397.78 762 20 4027.41 1168.4

5 9 4397.78 762 15 4027.41 1168.4

6 17 4397.78 762 24 4027.41 1168.4

7 34 8795.55 1524 47 8054.82 2336.8

8 79 43977.77 7620 111 40274.11 11684

9 85 70364.43 12192 119 64438.57 18694.4

10 90 74762.20 12954 126 68465.98 19862.8

11 93 83557.76 14478 130 76520.81 22199.6

12 96 83557.76 14478 134 76520.81 22199.6

13 90 74762.20 12954 126 68465.98 19862.8

14 102 76521.31 13258.8 142 70076.95 20330.16

15 111 79159.98 13716 155 72493.40 21031.2

16 102 86196.42 14935.2 142 78937.25 22900.64

17 90 83557.76 14478 126 76520.81 22199.6

18 79 43977.77 7620 111 40274.11 11684

19 57 26386.66 4572 79 24164.47 7010.4

20 45 17591.11 3048 20 16109.64 4673.6

21 28 8795.55 1524 10 8054.82 2336.8

22 6 4397.78 762 5 4027.41 1168.4

23 6 4397.78 762 5 4027.41 1168.4

24 6 4397.78 762 5 4027.41 1168.4

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Hr.

Floor 4

Floor 5

Occupancy

Lighting

Btu/hr

Equipments

Btu/hr Occupancy

Lighting

Btu/hr

Equipments

Btu/hr

Max 97 100739.1 33528 61 94554.96 44704

1 5 5036.95 1676.4 3 4727.75 2235.2

2 5 5036.95 1676.4 3 4727.75 2235.2

3 5 5036.95 1676.4 3 4727.75 2235.2

4 5 5036.95 1676.4 3 4727.75 2235.2

5 8 5036.95 1676.4 5 4727.75 2235.2

6 15 5036.95 1676.4 9 4727.75 2235.2

7 29 10073.91 3352.8 18 9455.50 4470.4

8 68 50369.54 16764 43 47277.48 22352

9 73 80591.26 26822.4 46 75643.97 35763.2

10 78 85628.22 28498.8 49 80371.71 37998.4

11 80 95702.12 31851.6 50 89827.21 42468.8

12 82 95702.12 31851.6 52 89827.21 42468.8

13 78 85628.22 28498.8 49 80371.71 37998.4

14 87 87643.00 29169.36 55 82262.81 38892.48

15 95 90665.17 30175.2 60 85099.46 40233.6

16 87 98724.30 32857.44 55 92663.86 43809.92

17 78 95702.12 31851.6 49 89827.21 42468.8

18 68 50369.54 16764 43 47277.48 22352

19 49 30221.72 10058.4 31 28366.49 13411.2

20 39 20147.82 6705.6 24 18910.99 8940.8

21 24 10073.91 3352.8 15 9455.50 4470.4

22 5 5036.95 1676.4 3 4727.75 2235.2

23 5 5036.95 1676.4 3 4727.75 2235.2

24 5 5036.95 1676.4 3 4727.75 2235.2

Table 2.2.4 Floors Internal Heat Source and Occupancy Schedule

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2.2.5 Set Point Temperatures

Floor Zone Heating Set point

Temperatures

Cooling set point

Temperatures

Heating (F) Heating set

back (F)

Cooling (F) Cooling set

back (F)

I

Assembly lobby 75 60 65 77

Storage/Mech. 73 58 66 78

Labs/educational 77 62 62 75


Labs 77 62 62 75

Labs/educational 77 62 62 75

Circulation 70 55 68 80

II

Assembly 75 60 65 77

Classrooms 73 58 66 79

Kitchen 65 55 70 84



Business area 75 60 65 77

III



Kitchen 65 55 70 84




Storage 73 58 66 78

IV

Educational shops/ voc. Rooms 73 58 66 79





VI

Storage 73 58 66 78





Mechanical 73 58 66 78


Table 2.2.5 Zones Set Point Temperatures

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2.3 HVAC System

2.3.1 HVAC System Overview

HVAC System of the Syracuse CoE Building makes use of Hydronic radiant cooling and

heating (HRC&H) systems. Using of HRC &H systems allow the separation of the tasks

of ventilation and thermal space conditioning.

While the primary air distribution is used to fulfill the ventilation requirements for a

high level of indoor air quality, the secondary water distribution system provides

thermal conditioning to the building. Most of the heating and cooling in rooms is

provided via ceiling panels that are embedded with copper piping that efficiently

carries warm or cool water.

HRC&H Systems significantly reduce the amount of air transported through buildings,

as the ventilation is provided by outside air systems without the re-circulating air

fraction.

Due to the physical properties of water, HRC&H Systems remove a given amount of

thermal energy and use less than 5% of the otherwise necessary fan energy. The

separation of tasks not only improves comfort conditions, but increases indoor air

quality and improves the control and zoning of the system as well.

Major Subsystems of the HVAC System:

Air(ventilation) system

Water System -- Heating system

Water System -- Cooling system

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2.3.2 Air System

The air system is used for supplying fresh air requirement for the space based on ASHRAE

standards and to take hot air from the rooms. The air system has a very small role in

offsetting the cooling or heating load and is set to be supplied at a constant temperature of

72°F.

Figure 2.3.2-1: AHU-1 (Air Handling Unit-1)

There are two air handling units in the faculty,

1. AHU1- supports the air requirement of the whole building except the cubicles in the

TIEQ.

2. AHU2 -especially assigned to supply air to the TIEQ cubicles.

The drawing below is the Air System Riser Diagram for the whole building, New air is took

from the OA Intake Louver at north wall of MER., then the AHU-1 would treat the new air

then supply the fresh air directly to the whole building. The air supply mode for the building

is Under Floor Air Supply. Return air would be taken from the rooms, and the enthalpy wheel

in the AHU-1 would make heat exchange between the fresh air and the return air. But there

is no mix between return air and fresh air. Because the air system has a very small role in

offsetting the cooling or heating load, the air system just take the work of supplying fresh air

to the building.

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Figure 2.3.2-2: Air System Riser Diagram (AHU-1)

(Refer to the SyracuseCoE drawing M-301 for detail)

The drawing below is the TIEQ Air System Flow Diagram. The AHU-2 is just serving for the

TIEQ lab. The supply air mode is also Under Floor Air Supply. Except the fresh air send from

the AHU-2, each cubicle in the TIEQ lab equipped with its own ATM (Air Treatment Modules)

that enable each individual to control and adjust his own comfort condition.

Figure 2.3.2-3: TIEQ Air System Flow Diagram (AHU-2)


AHU-1

AHU-2

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ATM ( Air Treatment Modules)

1. The TIEQ lab is equipped with ATMs that enable each individual to control and adjust

his own comfort condition.

Figure 2.3.2-4: ATM (Air Treatment Modules)

AHU2 supply air to ATMs for further treatment according to individual preferences. In the ATM,

the return air will mix with the fresh air from the AHU-2. Then the mixed air would be sent to the

cubicle. People can adjust the temperature and humidity according to his own comfort condition.

One ATM only serves one cubicle.

Figure 2.3.2-5: Air Treatment Modulus (ATM) Air Flow Diagram


ATM

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Below is the AHU-2 Control System for TIEQ lab. You can see many dampers. Their job is

controlling the fresh air amount from the AHU and the air from ATMs which are controlled by

individuals for their specific comfort need. If the CO2 level in the cubicle over the set point,

the damper which controls the fresh air from AHU will open more to let more fresh air go

into the cubicle.

Figure 2.3.2-6: AHU-2 Control System for TIEQ lab


Currently the set up of dampers closing and opening is based on

Time of the day

Day mode and night mode

Level of CO2

Depending on the level of CO2 ,which is a an indication of the number of

occupants ,the damper will automatically adjust to bring the level of CO2 to the

acceptable range.

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Major components supporting Air System,

1. Supply and return fans

Supply and return fans are used to supply and

return fresh air to and from the facility.

Both fans have variable frequency drive to control

the mass flow rate.

2. Enthalpy wheel

used for heat and moisture

exchange.

3. Desiccant wheel

used when more dehumidification

is needed.

4. Pre heater

used to preheat the incoming air

during winter.

Uses hot water from the ground water loop as a heat source.

5. Cooling coil

Uses chilled water supply as a cooling media.

6. Heating coil

Uses hot water supply as a heating media.

7. Air outlets

Different diffusers and registers are used for supply, return and exhaust systems.

The registers are equipped with dampers to controls the flow of air in to the

room.

24

Below is the design data for the major components supporting Air System, refer to the

drawing M-004.

AIR HANDLING UNIT SCHEDULE

ITEM HOT WATER COIL

MAX

FACE

VEL

(FPM)

TOTAL

CAP

(MBH)

FLOW

RATE

(GPM)

WATER

PD

(FT)

ENT

DB

TEMP

(°F)

LVG

DB

TEMP

(°F)

ENT

WATER

TEMP

(°F)

LVG

WATER

TEMP

(°F)

AHU-1 475 266 53.2 6 52.3 72 130 120

AHU-2 475 84.9 17 6 32.7 72 130 120


ITEM COOLING COIL

MAX

FACE

VEL

(FPM)

TOTAL

CAP

(MBH)

SENS

CAP

(MBH)

FLOW

RATE

(GPM)

WATER

PD

(FT)

LVG

DB

TEMP

(°F)

LVG

AIR

WB

(°F)

ENT

DB

TEMP

(°F)

ENT

AIR

WB

(°F)

ENT

WATER

TEMP

(°F)

LVG

WATER

TEMP

(°F)

AHU-1 475 510.4 257.9 113.4 3.46 56.2 55.7 75.3 68.7 50 60

AHU-2 475 100 57.3 20 12 54.2 63.6 81.1 69.6 45 55


ITEM PRE-HEAT COIL

MAX

FACE

VEL

(FPM)

TOTAL

CAP

(MBH)

FLOW

RATE

(GPM)

WATER

PD

(FT)

ENT

DB

TEMP

(°F)

LVG

DB

TEMP

(°F)

ENT

WATER

TEMP

(°F)

LVG

WATER

TEMP

(°F)

AHU-1 500 254 103.0 5 -15 0 45 40

AHU-2


ITEM ENTHALPY WHEEL

WINTER SUMMER

ENT

AIR

DB

(°F)

ENT

AIR

DB

(°F)

LVG

AIR

DB

(°F)

LVG

AIR

DB

(°F)

ENT

AIR

DB

(°F)

ENT

AIR

DB

(°F)

LVG

AIR

DB

(°F)

LVG

AIR

DB

(°F)

AHU-1 0 -0.2 38.6 32.6 85.0 75.0 75.3 68.7

25

AHU-2 -15 -15 32.6 31.3 85.0 75.0 81.2 69.6


ITEM DESICCANT WHEEL

WINTER SUMMER

ENT

AIR

DB

(°F)

ENT

AIR

DB

(°F)

LVG

AIR

DB

(°F)

LVG

AIR

DB

(°F)

ENT

AIR

DB

(°F)

ENT

AIR

DB

(°F)

LVG

AIR

DB

(°F)

LVG

AIR

DB

(°F)

AHU-1 38.6 32.6 52.3 42.5 56.2 55.7 62.9 56

AHU-2 NOT APPLICABLE


ITEM SUPPLY FAN RETURN FAN

FLOW

RATE

(CFM)

EXTL

SP

(IN

WG)

MOTOR DATA MOTOR DATA

MAX

HP

VOLT PH HZ MAX

HP

VOLT PH HZ

AHU-1 14,840 1.5 25 460 3 60 12,844 1.5 20 460 3 60

AHU-2 2,315 1 3 460 3 60 2,315 1 1.5 460 3 60

26

2.3.3 Water System

Below is the Mechanical Plant Single Line Diagram. The hot water is supplied by the 7 heat

pumps and 2 boilers installed in the facility. The first stage of heating is provided by the

geothermal heat pumps and the second stage of heating is provided by boiler 1 and boiler 2.

Currently four heat pumps are dedicated for heating only but all of the heat pumps have a

reversing valve to change the mode of operation (heating and cooling mode).

Figure 2.3.3: Mechanical Plant Single Line Diagram

Heat pumps Heat Exchanger (HX-5)

Ground Loop Pumping Zone

Cooling Tower Pumping Zone

Boiler Heating Pumping Zone

27


In Heating mode any cooling demand will use water directly from the geothermal loop or

cooling tower.

2.1.1.1 Heating System

The hot water system is used to offset the heating load during cold season through the

radiant panels. It is also used as a heat source for the coils in the AHUs, Fan coil units, finned

radiation units (FTR) and unit heaters and ATMs.

Figure 2.3.3.1-1: Mechanical Heating Single Line Diagram


Below is the Radiant Ceiling/Floor water Single Line Diagram. Radiant Ceiling/Floor Panels

can offset the cooling or heating load. The control valves can regulate between the hot water

tubes and chilled water tubes. The Radiant Ceiling/Floor Panels take the main role in offset

the cooling and heating. But the air system is set just to supply fresh air at a constant

temperature of 72°F.

28

Figure 2.3.3.1-2: Radiant Ceiling/Floor water Single Line Diagram


The control logic for the heating system is based on,

1. Time of the day

During nights only the boilers are set to operate

2. Load on the building

Depending on the load 1 2 3 or 4 heat pumps work at a time

Besides there are control valves that regulate the flow of hot water to each room depending

on the heating load.

Components of the hot water system,

1. Boiler

for heating water to the required temperature

2. Heat pump

for heating water to the required temperature

3. Liquid to liquid heat exchanger

4. Air separators

used for separating air from going to the pumps

5. Chemical pot feeder

used for treating the water to prevent corrosion in the system

6. Hot water pump

29

Used to circulate hot water in the system

7. Radiant panels

8. Finned tube radiation(FTR)

9. Fan coil unit(FCU)

10. Unit heater(UH)

11. ATM

Used to condition the air based on the occupant preference

12. Duplex basket strainer

used for filtering the water before it goes to the pump

Below are tables of Mechanical Schedule of the Components of the hot water system.

HOT WATER BOILER SCHEDULE

ITEM CAPACITY FUEL

TYPE

FLOW

RATE

GPM

WATER

TEMPERATURE

(°F)

ELECTRICAL DATA

INPUT

(MBH)

OUTPUT

(MBH)

ENT LVG AMPS VOLT PHASE HZ

B-1 500 440 NATURAL

GAS

22 120 160 4 115 1 60

B-2 500 270 NATURAL

GAS

13.5 120 160 4 115 1 60

HEAT EXCHANGER PACKAGE

ITEM SOURCE LOAD

FLOW

RATE

(GPM)

WATER TEMP MAX

PRESS

DROP

(PSIG)

FLOW

RATE

(GPM)

WATER TEMP MAX

PRESS

DROP

(PSIG)

ENT

(°F)

LVG

(°F)

ENT

(°F)

LVG

(°F)

HX-1 46.0 50 60 0.5 115.0 66 62 2.6

HX-2 5.1 50 60 0.1 10.2 60 55 0.3

HX-3 6.8 160 120 0.5 3.4 40 120 0.1

30

HX-4 2.5 160 120 0.4 1.3 40 120 0.1

HX-5 217.0 40 45 2.3 217.0 60 50 0.6

31

Table 2.3.3.1: Mechanical Schedule of the Components of the hot water system


32

2.1.1.2 Cooling System

The cooling system is responsible for offsetting the cooling load of the building. Cooling is

achieved through the use of chilled water.

Major components using chilled water,

2 Radiant panels

3 Cooling coils of AHU1 and AHU2 and ATMs

4 Separate fan cooling units(FCU) in each level of the building

33

Figure 2.3.3.2: Mechanical Cooling Single Line Diagram


Chilled water generation:

Chilled water is generated in the facility through the geothermal heat pumps and also

through heat exchange with cold water from the ground loop.

towers are used for heat rejection from the heat pump.( condenser side heat rejection).

Currently there are three heat pumps which are dedicated to generate cold water needed to

exchange heat

Ground loop or cooling with the chilled water system.

Components supporting Chilled water system,

1. Water to water heat exchangers

2. Chilled water pumps

3. Cold water pumps

4. Ground water pumps

5. Cooling tower

6. Automatically regulated valves

7. Air separators

8. Chemical pot feeder

HEAT EXCHANGER PACKAGE

ITEM SOURCE LOAD

FLOW

RATE

(GPM)

WATER TEMP MAX

PRESS

DROP

(PSIG)

FLOW

RATE

(GPM)

WATER TEMP MAX

PRESS

DROP

(PSIG)

ENT

(°F)

LVG

(°F)

ENT

(°F)

LVG

(°F)

HX-1 46.0 50 60 0.5 115.0 66 62 2.6

HX-2 5.1 50 60 0.1 10.2 60 55 0.3

HX-3 6.8 160 120 0.5 3.4 40 120 0.1

HX-4 2.5 160 120 0.4 1.3 40 120 0.1

HX-5 217.0 40 45 2.3 217.0 60 50 0.6

COOLING TOWER SCHEDULE

ITEM TYPE GPM CAPACITY

(TONS)

ANTIFREEZE COIL

PRESSUR

E DROP

(FT)

WATER

TEMP

WEB

BULB

TEMP

(DEG

F)

AIR

FLOW

(CFM)

34

CT-1 CLOSED

CIRCUIT

300 125 DYNALENE

HC-20

8.9 95 85 75 59,550

35

3. Modeling and Simulation with BCVTB and Energy+

3.1 Introduction We need to analyse the energy and control system of COE building. As we all know, Energy+

is good at energy simulation and Dymola is good at control simulation, so we use those two

tools to analyse the simulation. The energy and control simulation are coupled, however,

Energy+ and Dymola cannot directly connect with each other, so we plan to use Building

Controls Virtual Test Bed (BCVTB) to connect Energy+ and Dymola.

3.2 BCVTB Platform

3.2.1 Structure and Functionality

BCVTB is a software environment that allows expert users to couple different simulation

programs for co-simulation. For example, the BCVTB allows the simulation of a building and

HVAC system in EnergyPlus and the control logic in Modelica or in MATLAB/Simulink, while

exchanging data between the software as they simulate. A system model for such a coupled

simulation is shown in Figure 3.2.1.1.

Figure 3.2.1.1: System model that links EnergyPlus with Simulink

The BCVTB is based on the Ptolemy II software environment that has been developed by the

University of California at Berkeley. The BCVTB is aimed at expert users of simulation that hit

limitations of existing simulation programs.

Programs that are currently linked to the BCVTB are

• EnergyPlus

• Dymola, which is a Modelica modeling and simulation environment,Building Controls

Virtual Test Bed

• Radiance

36

• MATLAB

• Simulink

• the BACnet stack

3.2.2 Interface with Energy+

Figure 3.2.2.1 shows the architecture of the connection between EnergyPlus and Ptolemy II.

Ptolemy II connects to the external interface in EnergyPlus. In the external interface, the

input/output signals that are exchanged between Ptolemy II and EnergyPlus are mapped to

EnergyPlus objects. The subject of this section is to show how to configure this mapping and

how to use these objects.

Figure 3.2.2.1: Architecture of the BCVTB with the EnergyPlus client (black) and other clients (grey)

The external interface can map to three EnergyPlus input objects called “ExternalInterface:

Schedule”, “ExternalInterface: Actuator” and “ExternalInterface: Variable”. The

“ExternalInterface: Schedule” can be used to overwrite schedules. The other two objects can

be used in place of Energy ManagementmSystem (EMS) actuators and EMS variables. The

objects have similar functionality as the objects “Schedule:Compact”,

“EnergyManagementSystem:Actuator” and

“EnergyManagementSystem:GlobalVariable” ,except that their numerical value is obtained

from the external interface at the beginning of each EnergyPlus zone time step, and will

remain constant during this zone time step.

This element will contain child elements that define the variable mapping. In between the

element tags, a user needs to specify how the exchanged data is mapped to EnergyPlus

objects. Hence, the order of these elements matter, and it need to be the same as the order

of the elements in the input and output signal vector of Ptolemy II actor that calls EnergyPlus.

The exchanged variables are declared in elements that are called “variable” and have an

attribute “source.” As described above, the external interface can send data to

ExternalInterface:Schedule, ExternalInterface:Actuator, and ExternalInterface:Variable. For

these objects, the source attribute needs to be set to Ptolemy, because they are sent by

37

Ptolemy II. The xml elements for these objects are defined as follows:

1) For ExternalInterface:Schedule, use

<variable source="Ptolemy">

<EnergyPlus schedule="NAME"/>

</variable>

where NAME needs to be the EnergyPlus schedule name.

2) For ExternalInterface:Actuator, use


<EnergyPlus actuator="NAME" />

</variable>

where NAME needs to be the EnergyPlus actuator name.

3) For ExternalInterface:Variable, use


<EnergyPlus variable="NAME"/>

</variable>

where NAME needs to be the EnergyPlus Energy Runtime Language (Erl) variable name.

The external interface can also read data from any Output:Variable and

EnergyManagementSystem:OutputVariable. For these objects, set the "source" attribute to

"EnergyPlus," because they are computed by EnergyPlus.

In order to connect Energy+ and Dymola, we also need to syntax of an xml file that

configures the data mapping between EnergyPlus and the externalinterface.The data

mapping between EnergyPlus and the external interface is defined in an xml file called

variables.cfg. This file needs to be in the same directory as the EnergyPlus idf file. The file has

the following header:

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE BCVTB-variables SYSTEM "variables.dtd">

Following the header is an element of the form

<BCVTB-variables>

</BCVTB-variables>

3.2.3 Interface with Dymola To create a new Modelica model, proceed as follows: First, open Dymola and the Buildings library,

which may be downloaded from http://simulationresearch.lbl.gov/modelica . From the Buildings

library, add the block Buildings.Utilities.IO.BCVTB.BCVTB to your model. Next, connect the bcvtb block

to your other Modelica models to create a system model that takes signals from the bcvtb block and

writes signals to the bcvtb block. This may yield a system model as shown in Figure 3.2.3.1

38

Figure 3.2.3.1: Graphical view of the dymola model exchanging data with BCVTB.

To configure the bcvtb interface, double-click on the bcvtb block that is shown in the left of the

figure. This will open the input form shown in Figure 3.2.3.2.

Figure 3.2.3.2: Configuration of the bcvtb block in the Modelica Buildings library

In the above setting example, a vector with two double values are obtained from the BCVTB and

written to the BCVTB every 60 seconds of simulation time. Additional information about this

block can be obtained by pressing the Info button.

39

3.3 Energy+ Model for COE Enclosure

3.3.1 Create an EnergyPlus idf file for COE enclosure

We build a code simulation model in DesignBuilder. The figure is shown in Figure 3.3.1

Figure 3.3.1 The enclosure of COE building inDesign Builder.

And then we export the building into IDF file. Finnally, we can have the Energy+ Model for COE

Enclosure.

Figure 3.3.2 IDF file of COE Building from Design Builder

4.3.2 Add the exchanged schedule and variable with BCVTB

To enter schedules to which the external interface writes , we should add the following code in

the IDF file, which is created in 4.3.1 part.

ExternalInterface, PtolemyServer

TSetCoo,

40

Temperature,

24;

ExternalInterface:Schedule,

TSetHea,

Temperature,

20;

The function of each line is in the below table.

ExternalInterface,

keywords in IDF, Object to activate the external

interface

PtolemyServer; Name of external interface

ExternalInterface:Schedule, keywords in IDF

TSetCoo, Name

Temperature, ScheduleType

24; Initial Value, used during warm-up

!Heating schedule. This schedule is set directly by the external interface. During warm-up

and system-sizing, it is fixed at 20 degC.


TSetHea, Name



! Heating schedule. This schedule is set directly by the external interface.During warm-up

and system-sizing, it is fixed at 20 degC.


TSetHea, Name



3.4 Modelica Model for HVAC system We can build a modelica model in Dymola (we will introduce the method in the next chart).

41

3.5 Whole Building Model using BCVTB to couple Enclosure and HVAC system

3.5.1 Create a configuration file for Energy+ IDF file

Note that we have not yet specified the order of the elements in the signal vector that is

exchanged between EnergyPlus and Ptolemy II. This information is specified in the file

variables.cfg. The file variables.cfg needs to be in the same directory as the EnergyPlus idf file. For

the objects used in the section above, the file looks like

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE BCVTB-variables SYSTEM "variables.dtd">

<BCVTB-variables>



<variable source="Ptolemy">Building Controls Virtual Test Bed

<EnergyPlus schedule="TSetHea"/>

</variable>


<EnergyPlus schedule="TSetCoo"/>

</variable>



<variable source="EnergyPlus">

<EnergyPlus name="ENVIRONMENT" type="OUTDOOR DRY BULB"/>

</variable>


<EnergyPlus name="ZSF1" type="ZONE/SYS AIR TEMPERATURE"/>

</variable>




<EnergyPlus name="TSetHea" type="Schedule Value"/>

42

</variable>


<EnergyPlus name="TSetCoo" type="Schedule Value"/>

</variable>

</BCVTB-variables>

This file specifies that the actor that calls EnergyPlus has an input vector with two elements that

are computed by Ptolemy II and sent to EnergyPlus, and that it has an output vector with four

elements that are computed by EnergyPlus and sent to Ptolemy II. The order of the elements in

each vector is determined by the order in the above XML file.

Hence, the input vector that contains the signals sent to EnergyPlus has elements “TsetHea” and

“TsetCoo”. The output vector that contains values computed by EnergyPlus has elements

“Environment” (Outdoor drybulb temperature), “ZSF1” (ZONE/SYS AIR TEMPERATURE), “TSetHea

“(Schedule Value), and “TsetCoo” (Schedule Value).

3.5.1 Create a BCVTB model to integrate Energy+ and Dymola

Create a model in BCVTB as figure 3.5.1.1

Figure 3.5.1.1 BCVTB model that links a model of a Energy+ with the Dymola modeling

43

4. MODELING AND SIMULATION USNG MODELICA

4.1 Introduction

4.1.1 Features of Modelica

Modelica primarily is a modeling language, sometimes called hardware description

language, that allows to specify mathematical models of complex physical systems, e.g.

for the purpose of computer simulation of dynamic systems where behavior evolves as a

function of time. Modelica is also an object-oriented equation based programming

language, oriented towards computational applications with high complexity requiring

high performance.

The four most important features of Modelica are:

Modelica is based on equations instead of assignment statements. This permits

acausal modeling that gives better reuse of classes since equations do not specify a

certain data flow direction. Thus a Modelica class can adapt to more than one data

flow context. Modelica has multi-domain modeling capability, meaning that model components

corresponding to physical objects from several different domains such as e.g.

electrical, mechanical, thermodynamic, hydraulic, and biological and control

applications can be described and connected.

Modelica is an object-oriented language with a general class concept that unifies

classes, generics —known as templates in C++, and general subtyping into a single

language construct. This facilitates reuse of components and evolution of models.

Modelica has a strong software component model, with constructs for creating

and connecting components. Thus the language is ideally suited as an architectural

description language for complex physical systems, and to some extent for software

systems.

4.1.2 Objective and Scope

As mentioned in the introduction of this paper Energy Plus, which is one of the most

developed and matured energy simulation tool available, lacks the following basic features

from simulation point of view

1- Energy plus is a text based simulation tool which is very difficult and takes lots of

time for system definition.

2- The control strategy developed in Energy plus is very simplified type and there is no

way of checking the effect of implementing modern control strategy in a building

system.

3- The users of Energy plus are restricted to use only the models available and no way

to incorporate a new model

To circumvent those problems we are planning to use Modelica for the fact that

2- It is an object oriented language which is easy for system definition

44

3- Most of the Common HVAC systems are already developed and are ready to use

which in this case is just dragging and dropping unlike that of Energy plus which

needs lots of node generation and definition

4- New components and systems which are not available can be developed by the user.

Thus the objective of this paper is to study the thermal behavior of a building through

simulation by making use of the good feature of both simulation tools, Energy Plus and

Modelica, by bridging them through the use of BCVTB

4.2 Case Study : Heat Transfer Lab

4.2.1 Description of the facility

The heat transfer lab of Mechanical and Aerospace lab is used as a case study for the HVAC

system simulation. The facility contains all the basic components needed for full air conditioning.

The following are list of components comprising the whole system

Figure 4.2.1.1 Heat transfer Lab

a-Water cooled heat pump- this heat pump is responsible for cooling down the moist air and for

pumping air to the whole system. And it has a continues supply of cold water as a cooling media

for the condenser.

b-Electric heater

a duct mounted electric heater with a capacity of 5kw is for heating the moist air to the required

temperature level. Its operation is controlled by a PID controller which is acting as a switch to

turn on and off depending on the system requirement.

c-Electric humidifier

The last air conditioning component in the system before supplying the moist air to the room in

the facility is the electric humidifier. It has a duct mounted steam outlet which is used for

injecting steam to the moist air. A PID controller is used to control the function of the humidifier

depending on the relative humidity set point of the room.

45

d- insulated duct

A duct is used as a means of transporting the treated moist air to the room. The surface of the

duct is insulated to minimize interaction of heat with the surrounding which otherwise would

increase the load on the air conditioning system.

e- test room

The Test Room has supply diffusers, one in the roof and one in the floor. During the

experiment it is optional to use either of the two supply diffusers or both at the same

time depending on the objective of the experiment. A manual damper is installed for

switching the flow to the roof or floor.

Three sides of the test room are covered with ¼” polycarbonate sheet and the fourth

side is equipped with a wall divided into three test panels. Two of the panels are made

of plywood while the third one is made of gypsum board, fiber glass insulation and

plywood.

Inside the room there is a manikin which is designed to mimic an occupant which can generate

heat. Beside there are two fluorescent lumps which contribute to the total cooling load.

4.2.2 Model assumptions and representation.

We have used Modelica for modeling the components and see the energy consumption of the

system. For the modeling we used the available models in the library of Modelica and Buildings

library developed by the Lawrence Berkley national laboratory. Below are the different

assumptions used for modeling the different components of the system.

a- Water cooled heat pump.

The water cooled pump used in the facility gives a constant cooling and there is no control device

for switching on and off. Thus at steady state it is acting as a simple heat exchanger with a

constant cooling duty. We have found experimentally that the unit gives a temperature of 8oC for

an inlet temperature of 23 oC at a flow rate of 480cfm. Besides the fan in the heat pump is a

constant speed fan and it always give a flow rate of 460 to 480cfm irrespective of the load. So to

make the simulation model simple we represent the water cooled pump by a combination of a

fan and a heat exchanger which is acting as a cooling coil.

b- Electric heater

The electric heater is providing a heating effect for the moist air passing over and besides the

main switch there is a PID controller which switch on and off the heater depending on the set

point. The PId controller has two input, the set point temperature and the temperature of the

room and it acts based on the difference in value between the two. At nominal condition the

heater has a power output of 5kw. We have picked a component from the buildings library that

mimics the actual operation of the heater which is a heater with a nominal power output similar

to the capacity of the actual heater with an input signal coming from the PID controller which

regulates the power outage from the power supply depending on the system requirement.

46

c- Electric humidifier

The humidifier section of the system is responsible for maintaining the required relative humidity

of the system. The actual humidifier is similar to a boiler with the steam generated ejected to the

moist air system. Since the objective is just to see how the air property would be affected

through introduction of a humidifier, we represent the humidifier as a simple heat exchanger

with mass interaction. Because of the simplicity of the model we didn’t consider the effect of

steam temperature on the temperature of the moist air and we only consider the effect of the

humidifier on the moisture content of the air.

d- Insulated duct

The duct in the actual system has an effect both on the pressure and temperature of the system.

In our simplified model we assume the duct to be adiabatic so that there would be no energy

interaction with the surrounding air. We account the pressure loss of 200pa to account for its

resistance so that it would be incorporated in the power requirement of the fan.

e- Test room

The test room is made of walls with ¼” polycarbonate glass in the three sides and with ply wood

on the remaining side. The model available in the building for a room model is very much

simplified and it doesn’t take the effect of moist air for the room and it is designed for a case of

ideal air to show the effect of different loads in the room temperature. Since our model is for a

medium of moist air instead of ideal air we were not able to use it due to its incompatibility. So to

represent the actual thermodynamics of the room we make use of energy plus for modeling the

room and use BCVTB to interface it with the other components modeled in modelica.

Figure 4.2.2.1 Definition of the Model using Dymola.

47

4.2.3 Communication logic between Energy plus and Dymola

An energy plus model for the room is developed with no AC system. Thus the room

temperature in the room will keep on increasing with the influence of loads incoming to the

room. In practice the air conditioning system is responsible for taking off the heat added to

the room by supplying an air with a lower temperature in such a way that the desired room

temperature and relative humidity will be maintained. The load in the room can be

categorized to sensible load and latent load and in other terms the air conditioning system

should send equal and opposite amount of those loads so that the room condition will be

maintained. In the simulation model those to forms of heat loads (sensible and Latent) are

supplied by the HVAC system developed in the Dymola platform. And to calculate the values

of sensible and latent load Dymola need outdoor condition and desired indoor conditions as

an input.

Since the facility is inside a conditioned room the outdoor conditions are assumed to be 23oC

and 30% relative humidity. These two values are obtained through experimental

measurement. The desired indoor conditions are obtained through simulation of the room

with energyPlus making use of the existing loads in the system. These values will be sent to

dymola through BCVTB as a communication bridge.

On the other hand Energy plus make use of the computed values of the sensible and latent

loads for the next time step computation of indoor air conditions and it gets those values

through BCVTB.

Thus for “to and from” kind of communication BCVTB requires a variable configuration file

called .cfg that describes which values are to be read from Energy plus and which values

from Dymola. The cfg. File used for the communication is shown in figure 3.2.2.2

Figure 4.2.2.2 Variables defined for communication between Dymola and EnergyPlus.

48

5. Results and Discussion

5.1 Simulatoin Having built the energy+ IDF file, Dymola model and BCVTB connector, we can do the whole

simulation right now, as shown in Figure 5.1.

Figure 5.1: whole simulation configuration of the Energy+ Simulator actor and Dymola.

5.2 Results As can be seen from figure 5.2the model tries to maintain the set temperature of 20oC by

varying the supply temperature based on the load available in the test room. As can be seen

there is a big variation in the supply temperature because of the fact that there is load

variation throughout the day. The result shows a higher supply air temperature during night

where there is no sunlight and lower supply temperature when there is sunlight. Even if we

are simulating an indoor condition we were not able to neglect the effect of environmental

condition for computation of indoor air condition since Energy plus uses weather data for

the computation. One thing that can be done is to edit the TMY3 weather data neglecting

the solar radiation and making the outdoor condition to be the same as 23 oC. But this takes

a lot of time to edit and we didn’t consider this option.

Figure 5.2 Indoor temperature and supply temperature profile for two day simulation.

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Figure 5.3Indoor relative humidity.

Besides the temperature the relative humidity of the room is maintained to the set point of

40%. The PID controllers were responsible for maintaining 20oC and 40% relative humidity

by sending the right signals to the heater and the humidifier respectively. The time variation

of the signals from the two pid controllers is indicated in figure 4.2.3

Figure 5.4 Signals from PID controllers for heater and humidifier

As can be seen from the figure above, the humidifier has been working around 40% of its

capacity for most of the time and the heater uses a maximum of around 37% of its nominal

capacity of 5KW. And from this we can conclude that the humidifier and heater are oversized

for the system.

As discussed in the previous section the HAVC system in the dymola provide a moist air to

the room with specific temperature and relative humidity at each time step in such a way

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that the resulting sensible heat and latent heat from the supply moist air will offset the

available sensible and latent load in the room so that a constant room temperature and

relative humidity will be maintained. The time variation of the latent heat and sensible heat

computed by dymola as an input to Energy Plus is shown in figure 3.2.4.

Figure 5.5 Sensible heat and latent heat computed by Dymola

As can be seen we have to send more sensible heat to the system during day time compared

to night time to offset the load due to solar radiation and hot outdoor condition.

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6. Conclusion

During the course of this research we have seen the different features of energy plus and

modelica. We were able to integrate energy plus with modelica making use of Modelica as a

bridge for communication. The integration of the two simulation tools provide us a way to

use better features of both tools for a better understanding of interaction of HVAC system

and building.

During the modeling we found the debugging part of modelica to be far more complex than

we thought it would be. With the time limitation we had we were forced to use the available

component models in the library. Besides some of the components we wanted for the

simulation like water cooled heat pumps are not available and we were forced to use

simplified models available. Actually one can also develop a model using modelica and we

found it to be not that straight forward especially for a moist air since it is a mixture of water

and air.

Other than the above mentioned drawbacks, we found modeling using modelica to be very

much straightforward and very easy to see the system structure. Since it is graphic based

simulation environment it takes very less time to define a model compared to energy plus

which needs text based node definition for connection each component in the system.

Another interesting feature about modelica is that it has different algorithms for control

system which makes it very suitable for designing and simulation of control system. As

mentioned in the introduction section Energy plus lucks modern control strategy and use of

energy plus together with Dymola can improve the performance of Energy plus.

It is found that BCVTB is very friendly to use and the procedures to follow are very easy to

catch. One can use BCVTB as a tool for communicating Energyplus and Dymola as well as a

tool to display some of the required outputs both from Modelica and EnergyPlus.

independet study report 2012 2 28_zgl.pdf

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