wine cold stabilization energy analysis

Pacific Gas and Electric Company

Emerging Technologies Program

Application Assessment Report No. 0715

Wine Cold Stabilization Energy Analysis

Issued: October 2007 Revised: December 2007 Project Manager: Steve Fok, P.E. Pacific Gas and Electric Company Prepared by: Ricardo A. Sfeir, P.E. Sandra Chow, P.E. Electrical Engineer Mechanical Engineer BASE Energy, Inc. BASE Energy, Inc.

Pacific Gas & Electric Company Emerging Technologies Program

ACKNOWLEDGEMENTS Contributions from numerous individuals and organization have been taken to develop this report. We would like to thank Steve Fok at PG&E for initiating and following-up the project. We would like to thank the personnel from the host winery (Winery A) for allowing us to perform this study in their facility, providing technical support on their equipment, helping to setup the measurement instrumentation and helping collect data throughout the study. Lorna Rushforth of Resource Solutions Group (RSG) provided the results for electrodialysis (ED) energy savings for comparison to the test results. A special thanks to everyone for their interest and commitment to see this project through.

Legal Notice This report was prepared by Pacific Gas and Electric Company for exclusive use by its employees and agents. Neither Pacific Gas and Electric nor any of its employees and agents: 1) makes any written or oral warranty, expressed or implied, including, but not limited to those

concerning merchantability or fitness for a particular purpose; 2) assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of

any information, apparatus, product, process, method, or policy contained herein; or 3) represents that its use would not infringe any privately owned rights, including, but not

limited to, patents, trademarks, or copyrights.

Cold Stabilization Energy Analysis B A S E

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Table of Contents 1. EXECUTIVE SUMMARY .................................................................................................. 1

1.1. Objective of Study .......................................................................................................... 1 1.2. Major Conclusions .......................................................................................................... 1

2. PROJECT BACKGROUND................................................................................................ 2 2.1. Wine Stabilization........................................................................................................... 2 2.2. Technologies for Cold Stabilization Enhancement......................................................... 2 2.3. Metric for Cold Stabilization .......................................................................................... 4

3. FIELD EVALUATION OF ENERGY CONSUMPTION OF COLD STABILIZATION ............................................................................................................... 5

3.1. Overall Measurement Plan.............................................................................................. 5 3.2. Description of the Site .................................................................................................... 7 3.3. Instrumentation and Measurement Systems ................................................................... 9

4. RESULTS ............................................................................................................................ 10 4.1. Cold Stabilization Measurements and Analysis ........................................................... 10 4.2. Cold Stabilization Comparison..................................................................................... 11 4.3. Comparison with ED Analysis Tool ............................................................................. 13

5. CONCLUSIONS ................................................................................................................. 14 6. BIBLIOGRAPHY............................................................................................................... 14 7. APPENDIX.......................................................................................................................... 15

7.1. Thermodynamic Model for Cold Stabilization............................................................. 15 7.2. Equations Used for Thermodynamic Model Analysis.................................................. 16 7.3. Sample Calculations from Thermodynamic Model Analysis....................................... 20 7.4. Glycol Cooling Model Analysis ................................................................................... 22 7.5. Graphs of Data Recorded During Cold Stabilization Test............................................ 25


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1. EXECUTIVE SUMMARY

1.1. Objective of Study Analysis of the electrical energy consumption of the cold stabilization of Chardonnay wine at a winery (Winery A) in Northern California.

1.2. Major Conclusions The energy used for cold stabilization varies significantly for different wine varieties and stability tests at different wineries. Table 1-1 summarizes the performance of cold stabilization at Winery A, the host for this study.

TABLE 1-1 WINE COLD STABILIZATION Energy Consumption (Thermodynamic Model) 392 kWh

Energy Consumption (Glycol Cooling Model) 538 kWh

Stabilization Period 122 hours Volume of Stabilized Wine 24,000 gallons

Table 1-2 summarizes the type of wine that was tested in this study as well as some background information regarding the tanks that the wine was cold stabilized in.

TABLE 1-2 INFORMATION REGARDING WINE AND TANKS IN STUDY Parameter Tank 267 Tank 270

Wine Variety Tested 2006 Chardonnay 2006 Chardonnay Initial Volume of Wine 12,000 gallons 12,000 gallons

Type of Tank Insulated, jacketed stainless steel tank

Insulated, jacketed stainless steel tank

Tank Capacity 12,000 gallons 12,000 gallons Tank Location Outdoor under canopy Outdoor under canopy


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2. PROJECT BACKGROUND

2.1. Wine Stabilization Wine stabilization as part of the winemaking process reduces the concentration of potassium bitartrate (cream of tartar) in wine. Traditionally, wineries lower the potassium bitartrate solubility in wine by chilling the wine to approximately 27 ºF. Wines are typically maintained at this temperature for a period of 1.5 to 3 weeks, depending on how easy it is to crystallize the potassium bitartrate, i.e. how “stable” the wine is. Several factors can influence the crystallization rate of potassium bitartrate, among them1:

• Nucleation: the number of nuclei on which crystals can form and grow. • Diffusion: the rate at which the dissolved potassium bitartrate comes into contact with the

crystal formations. • The rate at which crystals grow. • Grape variety.

Once the desired potassium bitartrate concentration is achieved, the wine is filtered and pumped to holding tanks, ready to be bottled. It should be noted that a significant body of literature on the principles and technology for wine stabilization exists. Some distinct references are cited in Section 6 o f the report.

2.2. Technologies for Cold Stabilization Enhancement There are different kinds of cold stabilization enhancement that may expedite the process1. One variation of this process is the Contact Process, where the chilled wine is seeded with potassium bitartrate and mixed into the wine. Mixing in the potassium bitartrate seeds hastens the crystallization rate in the wine. The crystals left behind after wine filtration can be ground and reused to seed the next batch. Another variation of cold stabilization is the Filtration Process, where wine is filtered through a potassium bitartrate bed. As wine flows through the bed, the potassium bitartrate in the wine crystallizes in the filter bed. Wine may be passed through the crystal bed several times, until wine is stabilized. A third variation of cold stabilization is the Crystal Flow Process. This process involves chilling the wine to temperatures between 14 ºF and 21 ºF (freezing point of wine). Freezing the wine will generate potassium bitartrate and ice crystals. These crystals act as nuclei for further crystal growth. This process requires using scraped-surface heat exchangers.

1 Refrigeration for Winemakers, Ray White, Ben Adamson, Bryce Rankine, Winetitles, Winemaking Series, 1998


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The enhancement used in this study is the Contact Process. The tested wine was seeded with potassium bitartrate, which accelerates the crystallization rate allowing for a shorter cold stabilization period. The wine is circulated and mixed once after the wine is seeded.


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2.3. Metric for Cold Stabilization There are various methods used to determine wine stability with respect to potassium bitartrate crystallization and they vary depending on the winemaker2. Some of these methods include:

• Chill proofing followed by a Concentration Product (CP) Test • Chill proofing followed by visual inspection (Cold Color Test) • Filtering at 25 ºF for 24 hours followed by visual inspection • Wine freeze/slush test • Conductivity test

The stability test used in this study is the Cold Color Test and is described below. Cold Color Test: The chill proofing test is performed by taking a wine sample from the stabilization tank. The sample wine is placed in a refrigerator at 32°F for a period of 7 days. After the 7 days a visual inspection is performed to check for potassium bitartrate in the sample wine. If no potassium bitartrate is visibly seen in the sample wine the wine is considered stable and the cold stabilization process is completed.

2 A Review of Potassium Bitartrate Stabilization of Wines, Bruce Zoecklein, Department of Horticulture, Virginia Polytechnic Institute and State University, 1998


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3. FIELD EVALUATION OF ENERGY CONSUMPTION OF COLD STABILIZATION

3.1. Overall Measurement Plan This study focuses on the electrical energy consumption of traditional wine stabilization (cold stabilization). A total of approximately 24,000 gallons of wine was cold stabilized during this study. Wine temperatures, tank surface temperature, ambient temperature and flow rates were monitored and logged for the duration of the study (from August through September 2007). A detailed description of measurement points for each system is described in the Instrumentation and Measurement Systems in Section 3.3. The facility has two main chiller systems. The chiller system used to supply glycol to cool the two 12,000 gallon wine tanks is located on the Back Pad. In addition to supplying glycol to cool the two wine tanks in this study, this chiller system also provides cooling for the building and glycol for the fermentation process. The Back Pad chiller system is comprised of two 125-hp water-cooled, open-drive reciprocating compressors, a 205-ton evaporative condenser, a 7.5-hp chiller pump and a 20-hp glycol supply pump. Since the chiller system was serving other areas in the facility and not just the two stabilization tanks in this study, the electrical energy consumption of the chiller system was not data-logged in this study. Glycol is chilled through the reciprocating compressors and pumped to the stabilization tanks. The two 12,000 gallon Polarclad-insulated stabilization tanks are located outside of the Fermentation Room under a large canopy. A simplified schematic of the cold stabilization system is shown in Figure 3-1 on the following page. The specifications for the refrigeration system used for cold stabilization are shown in Table 3-1.

TABLE 3-1 COLD STABILIZATION EQUIPMENT Equipment Manufacturer Model Motor(s) (hp)

Carlyle 5H120-A219 125 Refrigeration Compressors Carlyle 5H120-A194 125

Evaporative Condenser Baltimore Aircoil VC1-205 15 (fan) 1.5 (spray pump)

Glycol Supply Pump ITT Bell & Gossett 3AC-5.750BF 20 Condenser Water Pump ITT Bell & Gossett 4AC-6.875BF 7.5


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liquid

Receiver

vapor

ExpansionTank

Glycol SupplyPumps

ReciprocatingCompressors

HeatExchangers

EvaporativeCondenser

To WineTanks

Glycol fromPlant

Figure 3-1 Simplified Schematic of the Cold Stabilization System


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3.2. Description of the Site The study was hosted by a winery (Winery A) located in Northern, California. As stated earlier, the insulated wine tanks used for cold stabilization were located outdoors under a canopy partially shading the tanks from the sunlight. Figure 3-2 below shows a picture of the tanks (Tanks 267 and 270) used in this study.

Figure 3-2 Polarclad-Insulated Cold Stabilization Tanks (Left) Tank 267; (Right) Tank 270 The chiller system and evaporative condenser were located on a pad outside the Fermentation Room. Figure 3-3 shows the various components of the refrigeration system used for supplying glycol to the cold stabilization tanks.


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Figure 3-3 Refrigeration System used for Cold Stabilization (Upper Left) Chiller System; (Upper Right) Evaporative Condenser;

(Lower Left) Chiller Pump; (Lower Right) Glycol Supply Pump


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3.3. Instrumentation and Measurement Systems The following equipment was used to log the parameters needed for the present analysis:

• Temperature: o PACE XR440 Pocket Logger with thermistor sensor o HOBO H08-032-08 Pro RH/TEMP

• Flow Meter: o Controlotron 1010WDP1 with clamp-on ultrasonic sensor

In addition, Winery A personnel helped record the wine temperature in the cold stabilization tanks throughout the duration of the study both manually and using their tank monitoring and control system (TankNet). Table 3-2 identifies the measurement points for the Cold Stabilization system.

TABLE 3-2 COLD STABILIZATION MEASUREMENT POINTS Measured Parameter Logging Method Logging Interval Outdoor Air Temperature Data Logger 15 min. Stabilization Tank Surface Temperature (T267) Data Logger 15 min. Stabilization Tank Surface Temperature (T270) Data Logger 15 min. Stabilization Tank Well Temperature (T267) Data Logger 15 min. Stabilization Tank Well Temperature (T270) Data Logger 15 min. Wine Temperature (T267) Winery A - Manual Log 2/day Wine Temperature (T270) Winery A - Manual Log 2/day Glycol Supply Flow Rate Spot Measurement Once Glycol Supply Temperature Data Logger 15 min. Glycol Return Temperature Data Logger 15 min. Glycol Return Temperature Data Logger 15 min.

T267 = Stabilization Tank 267 and T270 = Stabilization Tank 270.


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4. RESULTS

4.1. Cold Stabilization Measurements and Analysis Cold Stabilization Timeline Figure 4-1 helps illustrate the cold stabilization progression throughout the study.

0

10

20

30

40

50

60

8/2 8/4 8/6 8/8 8/10 8/12 8/14 8/16 8/18 8/20 8/22 8/24 8/26 8/28

Tem

pera

ture

(F)

Set Point Tank 267 Tank 270

Wine is considered stable at 8/8/07 11:00

Figure 4-1 Wine Temperatures for Tanks 267 and 270

Figure 4-1 shows the temperature measurements provided by plant personnel inside the two stabilization tanks used in the study. The timeline for cold stabilization can be described as follows:

• Wine is temperature stabilized in tanks at approximately 55°F. • The wine is seeded and mixed once prior to the start of cold stabilization. • Glycol is circulated through the jacketed stabilization tanks and cold stabilization begins on

August 3, 2007 at approximately 9:40 a.m., where the stabilization tanks’ setpoint temperature is lowered from 55°F to 28°F.

• Based on the Cold Color Test results, the wine is considered stable as of August 8, 2007 at approximately 11:00 a.m. This is considered the end of the cold stabilization period, although wine was kept chilled until August 28, 2007 when it was pumped out of the stabilization tanks.


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Since the wine is considered stable by August 8, 2007, the total cold stabilization period is considered to be approximately 5 days, or a total of 122 hours. During this period, as seen in Figure 4-1 above, the wine temperature drops from approximately 55°F to 31°F.

4.2. Cold Stabilization Comparison A study was performed for another winery (Winery B) in Northern California assessing the electrical energy and demand savings that could result from using an Electrodialysis System in place of cold stabilization of wine. The results from that study is presented in Table 4-1 below to compare the electrical energy consumption for cold stabilization of wine in the two wineries.

TABLE 4-1 COLD STABILIZATION COMPARISON IN TWO WINERIES

Winery B Winery A (Host) Wine and Stabilization Tank Parameters

Wine Variety Tested 2006 Pino Grigio 2006 Chardonnay Volume of Wine Cold Stabilized 18,063 gallons 24,000 gallons

Type of Tank Uninsulated, jacketed stainless steel tank

Polarclad insulated, jacketed stainless steel tank

Tank Capacity 9,250 gallons (each) 12,000 gallons (each) Tank Location Indoors Outdoors (under a canopy)

Refrigeration System and Temperatures Average Ambient Temperature 51.75°F 70°F*

Initial Temperature of Wine 47.5°F 55°F Cold Stabilized Wine Temperature 28.5°F 31.4°F Cold Stabilization Time 1,108 hours 122 hours Refrigeration System COP 2.84 4.25 Glycol Supply Temperature 19.1°F 29°F Glycol Return Temperature 23.1°F 32°F Glycol Flow 115 gal/min 26 gal/min Enhancement(s) Used None Seeding Wine Stability Test Conductivity Test Cold Color Test

Thermodynamic Model Analysis Total Energy to Compensate for Heat Gain During Cold Stabilization 9,135 kWh 392 kWh

Glycol Cooling Model Analysis Energy Required by Refrigeration to Provide Cooling to Wine Tanks 22,391 kWh 538 kWh

Measured Energy Consumption Energy Consumption of Refrigeration System (Measured) 26,891 kWh Refrigeration system shared

with other applications. * This is based on weather data for the area. An ambient data logger was installed in the facility, but it failed to log measurements.

This data logger was replaced after the cold stabilization period had ended. Thus, we compared the measured temperature data with the weather data for the same period to estimate the ambient temperature of the stabilization tank area.


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From Table 4-1, it can be seen that the energy consumption of the cold stabilization process in the 2 wineries differed significantly based on the thermodynamic and glycol cooling model analyses. Some factors attributing to this significant difference in energy consumption include but are not limited to the following:

• Wine Variety – The wine studied in Winery A is easier to stabilize than the wine at Winery B

• Enhancement – The wine at Winery A was seeded, which according to plant personnel reduces the cold stabilization time by approximately one-third.

• Stability Test – The stability test method for the 2 wineries were very different. Winery A uses a visual inspection (Cold Color Test) to check for potassium bitartrate presence in the wine. Winery B analyzes the wine conductivity to determine whether the wine is stable. It should also be noted that with the Winery B stability test, the wine never did reach the conductivity goal that the facility was hoping for, which would account for the longer holding period during cold stabilization.

• Tank Insulation – The stabilization tanks at Winery A were well insulated with 3-inches of Polarclad insulation. The tanks at Winery B were not insulated, causing a layer of ice to build-up on the surface of the tanks during the cold stabilization process, resulting in additional energy used by the facility’s refrigeration system.

• Refrigeration System Efficiency – The refrigeration system at Winery A was approximately 33% more efficient than the refrigeration system at Winery B. This results in a significant increase in energy consumption.

• Refrigeration System Failure – The refrigeration system at Winery B failed twice during the cold stabilization period. The refrigeration system was shut down during these 2 breakdowns causing the wine temperature to fluctuate, disrupting the stabilization of the wine in the tanks.

• Glycol Leak – There was a glycol leak in the glycol lines at Winery B. It was unclear how much glycol leaked from the lines, but this would increase the load on the facility’s refrigeration system to make up for the glycol lost due to the leak.

• Wine Temperature – The wine at Winery B was cooled and held at a lower temperature (28.5°F) compared to at Winery A (31.4°F). This cooler wine temperature results in increased energy consumed by the refrigeration system.

• Glycol Temperature – The glycol supply temperature was significantly lower at Winery B (19°F) compared to at Winery A (29°F), which means the refrigeration system would have to work harder to produce the low temperature required at Winery B.

• Glycol Flow Measurement – The flow meter malfunctioned during logging of the flow at Winery A. Thus, only a spot flow measurement was taken, which may not accurately reflect the actual glycol flow through the two stabilized tanks. At Winery B, we were unable to measure the flow of the glycol supply due to the fact that the lines were uninsulated and covered with a thick layer of ice. Thus, we had to measure the glycol flow at the bypass pipe and using the nominal flow of the glycol supply pump to estimate the glycol supply flow.


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4.3. Comparison with ED Analysis Tool An Excel analysis tool for comparison of energy consumption of electrodialysis (ED) wine stabilization which has been developed by Kenwood Energy and Resource Solutions Group was applied to the tests performed at Winery A and Winery B. Table 4-2 compares the test results and ED analysis tool results on cold stabilization. It should be noted that the ED analysis tool does not take the type of wine and the stabilization enhancing mechanisms into consideration. The energy consumption of the ED tool is based on the machinery distributed by Winesecrets of Napa, CA. It appears that the ED Tool and the Thermodynamic Model both present reasonably consistent “baseline” estimate of cold stabilization.

Table 4-2 Comparison of Results from Measurement, Thermodynamic Model and ED Analysis Too

Winery Glycol Cooling Model Thermodynamic Model ED Analysis Tool Winery B 22,391 kWh 9,135 kWh 9,173 kWh WInery A 538 kWh 392 kWh 401 kWh Notes:

1. The difference between the results of Glycol Cooling Model and Thermodynamic Model are most probably due to uncertainty in measurements especially the flow rate of glycol. Since the glycol supply pump was shared between several applications, it is suspected that the flow of glycol in the tanks varied, but the variance could not be captured because of malfunctioning of the flow meter.

2. Based on information from Resource Solutions Group (RSG), the input to the ED Analysis Tool needed to be adjusted to agree with the present thermodynamic model. The results could not be independently confirmed.

3. In evaluating the results of ED analysis tool, it was noticed that for the case of Winery B, the ED Analysis tool estimated the ED machine energy consumption to be 114.5 kWh while the actual measurement of energy consumption was 165 kWh for wine stabilization.


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5. CONCLUSIONS Energy Consumption of Cold Stabilization Process Based on the study performed for both wineries, it can be seen that the electrical energy consumption for the cold stabilization process varies significantly. These results vary depending on the type of wine, enhancements, chilling system, cold stabilization method, tank insulation and many other factors mentioned in the previous section. Electrodialysis wine stabilization can significantly reduce the energy consumption as compared to cold stabilization, depending on the stabilization method and technique. Comparison of results from the Thermodynamic Model and the ED Tool illustrates reasonably consistent “baseline” estimate for cold stabilization. Minor adjustment to incorporate compensation for heat gain from ground and spreadsheet input parameter listing would provide further consistency. Other Associated Issues A full energy balance of the system would require a more detailed analysis of the wine chemistry for the crystallization process to accurately reflect the total energy used for the cold stabilization process. The authors did extensive search of any discussion associated with the importance of crystallization energy in energy consumption for wine stabilization to no avail. The exception is one personal contact that cited the crystallization process to be endothermic, which is counter intuitive.

6. BIBLIOGRAPHY Ribereau-Gayon, P., Glories, Y., Maujean, A. and Dubourdieu, “Handbook of Enology, Vol. 2, The Chemistry of Wine Stabilization and Treatment, 2nd Edition, John Wiley & Sons, 2005. Boulton, R. B., Singleton, V. L., Bisson, L.F. and Kunkee, R. E., Principles and Practices of Winemaking, Chapman and Hall, 1995. Margalit, Y., Concepts in Wine Chemistry, The Wine Appreciation Guild Ltd., 1997. Zoeckliein, B., “A Review of Potassium Bitartrate Stabilization of Wines”, Department of Horticulture, Virginia Polytechnic Institute and State University, 1998.


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7. APPENDIX

7.1. Thermodynamic Model for Cold Stabilization The thermodynamic analysis for cold stabilization includes the following:

Estimate of electrical energy required for initially cooling the wine to the desired (steady state) temperature.

Estimate of electrical energy required by the refrigeration system to compensate for the heat gain to the wine tank (from the sides, top and bottom of tank) from warmer ambient conditions.

Estimate the cooling load provided by the glycol based on measured data. Section 7.3 shows the equations that were used in our thermodynamic analysis of the system and Section 7.4 shows a sample of the spreadsheet analysis for the two tanks. A summary of the thermodynamic analysis yields the results presented in Table 7-1 below.

TABLE 7-1 RESULTS OF THERMODYNAMIC ANALYSES Tank 267 Tank 270 Both Tanks

(kWh) (kWh) (kWh) Initial Cooling of Wine to Desired Temperature

Energy Required to Cool Wine to Desired Temperature 168 170 339 Energy Required to Compensate for Heat Gain to Tank Sides and Top of Tank 18 18 36

Energy Required to Compensate for Heat Gain from Bottom of Tank 9 9 18

Total Energy Required to Compensate for Heat Gain During Cold Stabilization 392 kWh

From Table 7-1, it can be seen that the total energy required by the refrigeration system during the cold stabilization process is estimated to be 392 kWh based on our thermodynamic model. A separate analysis of the cooling load provided by the glycol was performed for comparison with the two above methods. Based on measured data for the following parameters:

Glycol supply temperature Glycol tank temperature Glycol supply flowrate

the electrical energy required by the refrigeration system to provide the necessary glycol cooling was calculated to be 538 kWh. A comparison of the 2 sets of analysis shows that the glycol cooling analysis compares fairly close with the thermodynamic model, with a difference approximately 27%. This can be attributed, but not limited, to the following issues:

Energy required for crystallization Glycol flow measurement


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7.2. Equations Used for Thermodynamic Model Analysis This section presents the equations that were used in our thermodynamic model to estimate the energy required by the facility’s refrigeration system to compensate for the various sources of heat losses. Volume of Tank

HTank

DTank

x

The volume of wine in a tank can be calculated as follows: V = (ΠDTank

2/4) × (HTank – x) Where, DTank = diameter of tank, feet HTank = height of tank, feet x = distance from top of tank to the level of wine, feet Notes:

1. According the plant personnel, they try to keep the wine tanks full all the time because they do not want any oxidation. Therefore, ‘x’ is taken to be 0 throughout the cold stabilization process.

2. It should be noted that 50% of the tank is jacketed and insulated for glycol circulation and the rest of the tank is not jacketed but insulated. Calculations have been modified to reflect the fact that the cold temperature inside the tank is the refrigerant temperature.


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Equations for Analysis of Energy Used for Cold Stabilization a - Amount of Energy to Cool Wine to Desired Temperature The amount of electrical energy required to cool a given volume of wine, ERCooling, can be estimated as follows: ERCooling = V × ρ × CP × (Tinitial – Tfinal) / (COP × C4) Where, V = volume of wine being cooled, gallons ρ = density of wine, lbm/gallon CP = specific heat of wine, Btu/lbm-°F Tinitial = initial temperature of wine, °F Tfinal = final (or desired) temperature of wine, °F C4 = conversion factor, 3,412.2 Btu/kW-hr COP = coefficient of performance of refrigeration system b & c – Energy to Compensate for Tank Heat Gain (i) Convective Heat Transfer Coefficient (ASHRAE Fundamentals Eq. 24-6) The convective heat transfer coefficient, hcv, is calculated as hcv = C × (1/d)0.2 × (1/Tavg)0.181 × (Tamb - Ts)0.266 × [1 + 1.277(vwind)]0.5

where, C = constant depending on shape and heat flow condition,

(1.235 for longer vertical cylinders; 0.89 for horizontal plates, cooler than air facing upward)

d = for flat surfaces and large cylinders, d = 24 inches Tavg = average temperature (Tavg = (Tamb + Ts) / 2), °F Tamb = average ambient air temperature during cold stabilization (from measured data), °F Ts = average tank surface temperature during cold stabilization, °F vwind = average air speed, mph (ii) Radiative Heat Transfer Coefficient (ASHRAE Fundamentals Eq. 24-7) The radiation heat transfer coefficient, hrad, is calculated as: hrad = [ε × σ × (Tamb

4 – Ts4)] / (Tamb – Ts)

where, ε = surface emittance


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σ = Stefan-Boltzmann constant, 0.1713 × 10-8 Btu/hr-ft2-R4 The total heat transfer coefficient, h, is the sum of the convective and radiative heat transfer coefficients: h = hcv + hrad (iii) Heat Gain from Tank Surfaces Tank Sides The heat gain (energy) rate, HGside,ss, from the sides of the tank surface during the cold stabilization can be estimated as follows:

sideins

ins

sidek

k

sidesidess

wineambside

Akx

Akx

Ah

TTHG

Δ+

Δ+

−=

tan

tan

,

1

Where, Tamb = average ambient air temperature during cold stabilization, °F Twine = average wine temperature during cold stabilization, °F hside = the sum of the convective heat and radiation heat transfer coefficients for tank sides3, Btu/hr-ft2-°F Aside = area of sides of tank, ft2

∆xtank = thickness of tank wall, feet ktank = thermal conductivity of tank wall material, Btu/hr-ft-°F ∆xins = thickness of tank insulation, feet kins = thermal conductivity of tank insulation, Btu/hr-ft-°F Top of Tank The heat gain (energy) rate, HGtop, from the top of the tank during the cold stabilization can be estimated as follows:

sidek

k

toptopss

wineambtop

Akx

Ah

TTHG

tan

tan

,

1 Δ+

−=

Where, hi = the sum of the convective heat and radiation heat transfer coefficients for top of tank, 3 Calculated from equations (6) and (7) on pages 24.16 and 24.17, Chapter 24 of ASHRAE 1997 Fundamentals


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Atop = area of top of tank, ft2

(iv) Energy to Compensate for Heat Gain from Tank Sides and Top of Tank The amount of electrical energy (kWh) required to compensate for the heat gain from the sides and top of the tank during cold stabilization, ERside, can be estimated as follows: ERside = (HGside + HGtop)× Hcs / (COP × C4) Where, HGside = heat gain rate to the tank from tank sides during cold stabilization period, Btu/hr Hcs = hours that tank of wine is cold stabilized, hr COP = coefficient of performance of refrigeration system (estimated based on

manufacturer’s data) C4 = conversion constant, 3,412.2 Btu/kW-hr f – Energy to Compensate for Heat Gain from Ground The amount of electrical energy (kWh) required to compensate for the heat gain from the bottom of the tank due to the ground during the initial cooling period, ERground,i, can be estimated using the following relation extracted from Holman (1990) 4 as follows: ERground = 2 × kg × Atop × (Tg – Twine) × [Hcs / (π × α)]0.5 / (COP × C4) Where, kair = thermal conductivity of ground, Btu/hr-ft-°F Atop = area of top of tank, ft2

Tg = average ground temperature, °F Twine = average wine temperature during cold stabilization period, °F Hcs = hours that tank of wine is cold stabilized, hr α = thermal diffusivity of ground, ft2/s

4 Calculated from equation 4-12 on page 145 of Holman, J.P. Heat Transfer, 7th Edition. McGraw-Hill, Inc. 1990.


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7.3. Sample Calculations from Thermodynamic Model Analysis This section presents snapshots taken from the Excel spreadsheet model in which the measured data were entered into to calculate the energy requirements for the two stabilization tanks in this study. Snapshot of Excel Spreadsheet for Tank Thermodynamic Model


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Snapshot of Excel Spreadsheet Showing Summary of Energy Requirements (for both tanks)


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7.4. Glycol Cooling Model Analysis This section presents the equations and calculations that were used in our glycol cooling model to estimate the energy required by the facility’s refrigeration system based on our measured data. Measured Data Glycol Supply Line Outside Diameter = 1.92 inches Glycol Supply Line Thickness = 0.086 inches Tank 267 Glycol Velocity = 3.71 ft/s Average Glycol Supply Temperature = 31.60°F Average Glycol Return Temperature = 28.87°F Tank 270 Glycol Velocity = 3.28 ft/s Average Glycol Supply Temperature = 32.1°F Average Glycol Return Temperature = 29.55°F Refrigeration System Coefficient of Performance (COP) = 4.25 (Based on information from refrigeration system manufacturer for current saturated suction temperature and estimated saturated discharge temperature) Glycol Flow The volumetric flow of glycol to the wine tanks can be estimated as follows: Q = v × (πDi

2 / 4) × C1 × C2 Where, v = velocity of glycol supplied to wine tanks, ft/s Di = inner diameter of glycol supply pipeline, ft C1 = conversion constant, 7.48 gallons / ft3

C2 = conversion constant, 60 sec/min The inner diameter of the glycol supply line is: Di = [(1.92 inch) – 2(0.086 inch)] / (12 inch/ft) Di = 0.146 ft The volumetric glycol flow of glycol to Tank 267 is: Q267 = (3.71 ft/s)[π(0.146 ft)2 / 4](7.48)(60)


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Q267 = 27.77 gal/min Similarly, the volumetric glycol flow of glycol to Tank 267 is: Q270 = (3.28 ft/s)[π(0.146 ft)2 / 4](7.48)(60) Q270 = 24.54 gal/min Cooling Load by Glycol The cooling load provided by the glycol to the tanks, CL, can be estimated as follows: CL = Q × ρ × cp × (Tret – Tsup) × C3 Where, ρ = density of glycol, 8.66 lbm/gal cp = specific heat of glycol, 0.89 Btu/(lbm-°F) Tret = average glycol return temperature, °F Tsup = average glycol supply temperature, °F C3 = conversion constant, 60 min/hr The cooling load provided by the glycol to Tank 267 is estimated to be: CL267 = (27.77)(8.66)(0.89)[(31.6) – (28.87)]( 60) CL267 = 35,059 Btu/hr Similarly, the cooling load provided by the glycol to Tank 270 is: CL270 = (24.54)(8.66)(0.89)[(32.16) – (29.55)]( 60) CL270 = 28,938 Btu/hr Energy Required by Refrigeration System The energy required by the facility’s refrigeration system to provide the necessary cooling to the two stabilization tanks, ER, is estimated as follows: ER = (CL267 + CL270) × Hcs / [COP × C4] Where, Hcs = hours that the tank of wine is cold stabilized, 122 hrs COP = coefficient of performance of facility’s refrigeration system, 4.25 C4 = conversion constant, 3412.2 Btu/kWh


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Thus, the energy required by the facility’s refrigeration system to provide the necessary cooling to Tanks 267 and 270 is: ER = [(35,059) + (28,938)](122)/[(4.25)(3412.2)] ER = 538 kWh


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7.5. Graphs of Data Recorded During Cold Stabilization Test This section presents some graphs of the various measurements that were recorded throughout the cold stabilization test.

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Tank 267 Tank 270 Ambient

Figure 7.5-1 Tank Surface Temperatures and Ambient Temperature

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Tank 270 Return Tank 267 Return Tank 267 Supply Tank 270 Supply

Figure 7.5-2 Glycol Supply and Return Temperatures


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wine cold stabilization energy analysis

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