Anatomy of a Real Time System Energy Equilibrium (SEE) Building Energy model Part 1-Background, Model Description and Characteristics, Description of Building Modeled, Energy Balance Analysis Salt Lake City Utah Building & Plant Abstract This series of chapters will present a system energy equilibrium (SEE) model that simulates the real time performance of a building and plant on any given day. A (SEE) model of an “as designed building and plant” would be a tool for commissioning or evaluating the real time performance of a facility, on any day, against what the performance should be if constructed and controlled as designed. (SEE) models of ASHRAE Standard designs, for a given City, could be put on the internet so that building owners could evaluate their building’s energy performance on days of different weather and operation. Energy balance analysis is a powerful energy analysis tool and a fundamental requirement of a (SEE) model. Background When the “Oil Embargo” of 1973 occurred, I was a member of a small group of computer simulation engineers at Texas Instruments Inc. (T.I.) designing and evaluating military systems via hybrid (analog/digital) computer simulations. The modeled systems included the Shrike missile, laser guided systems, and anti-tank missiles. The oil embargo occurred the fourth quarter of 1973 and early 1974 (T.I.) gave me the task of modeling the energy consumption of (T.I.) buildings and processes for the purpose of defining what could be done to reduce energy consumption. I used building energy computer programs available at the time to simulate the annual energy use of a building and plant and the hybrid computer to simulate processes and attempted to simulate a building and plant on any given day. In 1982 I left T.I. and the enormous power of the hybrid computer. That experience convinced me that a real time model of one 24-hour day was needed 3 so that a new building or plant could be commissioned on any day and the performance of old buildings and plants could be evaluated on any day. On retiring I decided to see if I could develop such a model. This effort has resulted in the System Energy Equilibrium (SEE) Model summarized by this series of chapters. The (SEE) Model 1
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Anatomy of a Real Time System Energy Equilibrium (SEE) Building Energy modelPart 1-Background, Model Description and Characteristics, Description of Building Modeled, Energy Balance AnalysisSalt Lake City Utah Building & Plant AbstractThis series of chapters will present a system energy equilibrium (SEE) model that simulates the real time performance of a building and plant on any given day. A (SEE) model of an “as designed building and plant” would be a tool for commissioning or evaluating the real time performance of a facility, on any day, against what the performance should be if constructed and controlled as designed. (SEE) models of ASHRAE Standard designs, for a given City, could be put on the internet so that building owners could evaluate their building’s energy performance on days of different weather and operation. Energy balance analysis is a powerful energy analysis tool and a fundamental requirement of a (SEE) model.Background When the “Oil Embargo” of 1973 occurred, I was a member of a small group of computer simulation engineers at Texas Instruments Inc. (T.I.) designing and evaluating military systems via hybrid (analog/digital) computer simulations. The modeled systems included the Shrike missile, laser guided systems, and anti-tank missiles. The oil embargo occurred the fourth quarter of 1973 and early 1974 (T.I.) gave me the task of modeling the energy consumption of (T.I.) buildings and processes for the purpose of defining what could be done to reduce energy consumption. I used building energy computer programs available at the time to simulate the annual energy use of a building and plant and the hybrid computer to simulate processes and attempted to simulate a building and plant on any given day. In 1982 I left T.I. and the enormous power of the hybrid
computer. That experience convinced me that a real time model of one 24-hour day was needed3 so that a new building or plant could be commissioned on any day and the performance of old buildings and plants could be evaluated on any day. On retiring I decided to see if I could develop such a model. This effort has resulted in the System Energy Equilibrium (SEE) Model summarized by this series of chapters.The (SEE) Model The objective of the (SEE) model is to provide the ability to visit a building or plant on any day, with the (SEE) model on a lap top computer, and evaluate the building and plant performance, against expected performance, on that day’s conditions of weather and operation. This (SEE) model has been developed over a period of several years and the authors modeling experience goes back to 1968. The following lists an estimated 501 equations and calculations, per hour, performed by this (SEE) model.
1. Building Model 282. Solar Model 943. Tower Model 624. Pumping Model 535. Chiller Model 736. Coil Model 237. Fans-Supply Air Model 448. Infiltration Model 219. Fresh Air Model 2710. Perimeter Heat Model 4311. Performance Calculations 33
Total 501Essentially nothing is constant in the model, no look up tables or constants, every value is a function of other values in the model. At design weather conditions the 501 equations would be at steady state for design dry bulb, wet bulb, and solar conditions. A change in any one of these three conditions of weather causes the set of equations to reach a new energy equilibrium or load to the plant. Input to the plant consists of adjusting the number of chiller/towers on and the power to the chiller motor to achieve 44F supply
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water. The accuracy of the (SEE) model is a function of how well the performance of the system components is understood and how well that understanding can be described by equations. Calculating a new steady state condition every 2 hours over 24 hours gives (12 x 501 = 6,012) calculations per modeled day and each variable’s equation must be reasonable correct over changing conditions of weather and load.The following summarizes the basic characteristics of the (SEE) Model.
1. The model is of the total building and plant as illustrated by Figure 1.
2. The model is the simultaneous solution of basic HVAC equations.
3. The model is of any 24-hour day. 4. The building is modeled as five zones,
four walls and the building interior. 5. The building is modeled with all loads of
Figure 2 in the interior of the building plus the roof load. The perimeter load is defined by the weather conditions of Figure 2 plus infiltration if it exists.
6. The author expects some values will be questioned. That is good; the objective is to present an approach to real time building energy modeling and not present the (SEE) Model given here as the final model. Modifications to the model based on better data/equations is a part of this (SEE) Model concept.
7. The (SEE) Model requires that the energy into the building and plant equals the energy out1,2 just as occurs with a real building and plant.
8. The (SEE) Model provides the ability to benchmark a building’s energy performance, on any day, against any ASHRAE Standard design, in this case ASHRAE Standard 90.1-2010 as interpreted from Liu5. This concept offers the opportunity for a city to provide benchmark data each day so that building owners can on any day benchmark their building against an ASHRAE Standard design.
IntroductionThe System Energy Equilibrium (SEE) Model incorporates the basic equations, data, and analysis procedures used by engineers to design a building and plant, solved simultaneously by computer. The (SEE) Model requires, just as a real system operates, that the energy into the system equals the energy out of the system. This is a major check on the accuracy of the model; any model that does not balance energy in equals energy out has potential problems that should be resolved.The procedure for evaluating the energy use of a building system is to first establish a (SEE) Model of the “as designed” building and plant. If on a given day the actual energy consumption of the system is greater than the as designed (SEE) Model, with real weather input, then the real system may not be operating as designed. A comparison of actual to modeled performance, on a given day of weather and operational conditions, may also show that the as designed model needs to be updated. For example, if the lights (watts/ft2) are different than designed and cannot be changed in the real building, then the real value, as constructed, should be input to the (SEE) model. The goal of the (SEE) Model is to duplicate each hour of the 24-hour performance of a real system within about 6% and do so on any day of weather and operational conditions. To accomplish this the (SEE) Model must obey the laws of thermodynamics and model the nonlinear characteristics of the real system components and all details of the system that contribute to the performance of the real system. These chapters demonstrate the (SEE) model characteristics and procedure for evaluating a real system on a given day, in this case a Salt Lake City Utah six building office campus designed to ASHRAE Standard 90.1-20105.Chapter 1 defines the building to be modeled and presents the concept of energy balance analysis.Chapter 2 presents the building (SEE) model.Chapter 3 presents the plant (SEE) model.
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Chapter 4 demonstrates the (SEE) model energy balance analysis on real weather days. Additional Chapters may be added.
Chapter 1The Building and Weather Conditions
Figure 1: Building Description-Salt Lake City Large Office Building Designed to Std. 90.1-20105
Figure 1 presents the modeled building of this study, a 565,000 square foot large office building based on the data provided by Liu5. The office campus is assumed to consist of six Figure 1 buildings. The design plant load for one building is 728.6-ton, Figure 3 top chart, therefore the design load on the plant is (6 * 728.6 = 4,371.6 ton). The plant is modeled as five chiller/towers each with a design capacity of 1,000 ton; therefore, the plant design capacity is 5,000 ton with a sixth chiller/tower for backup. Schematics and nomenclature are given below.Figure 2 top chart gives the assumed design day weather conditions with a peak dry bulb of 102F and wet bulb of 66F occurring at 4PM. Figure 2 also gives assumed winter weather that will also be (SEE) modeled to illustrate the (SEE) Model capability to go from summer design conditions to winter conditions. The secondary horizontal axis of Figure 2 gives the percent clear sky as 100% for peak design summer conditions. Real weather6
conditions addressed by article 4 input percent clear sky based on cloud conditions. Article 2 addresses the solar model in some detail.
TIME OF DAYOne Building Interior- People & Lights & Plug kW
People-# Lights kW Plug-kW
Figure 2: Top Chart-Design & Winter Weather-Bottom Chart5-Light kW, Plug kW, & # people
Figure 2 bottom chart gives the lights and plug kW demand per time of day and the number of people in the building as interpreted from Liu5. The lights and plug loads track well to the number of people in the building illustrating a good shut down system is defined by Liu5& input to the (SEE) Model.
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Building 13 StoryEach Building=565,000 Ft-Sq
Building height=169 Ft13 story building
Roof = 43,462 Ft-SqAll walls 37.5% glass
Roof U=.048 Wall U=.090Glass U=.55 Glass SHGC=.40
FootprintSouth=240 Ft North=240 Ft
Each wall=40,560 Ft-SqEast=181.09 Ft West=181.09 Ft
Each Wall=30,604 Ft-Sq
Figures 1 & 2 and Table 1 give the basic data required to define the building as designed.Table 1 gives building design and control characteristics of the system to be established here as the benchmark best designed and controlled Standard 90.1-2010 building5 and plant13. Building Location and Design
1. Location= Salt Lake city Utah. 2. Building 565,000 ft2
3. No external solar shading.4. Ambient temperatures Figure 2 5. Percent clear sky 100%. 6. Building design per Liu5 7. Percent wall glass 37% 8. Peak lights kW .81 watts/ft2
9. Peak plugs kW .66 watts/ft2
10. Return air is to building perimeter.11. Duct design static 5.5 inches water.12. Fan powered terminals not installed.13. Return air fans not installed.
Building Control 14. Lights on/off control- 6% on after hours.15. Plugs on/off control-44% on after hours16. Building pressure control, yes 17. Supply air = 55F18. Supply water 44F-44.6F19. Stats controlled, yes 20. Perimeter heat air temp, 105F.21. VAV fan duct pressure control, yes 22. Fresh air CFM control, yes23. Fresh air heat stat set point, 42F
Energy Balance System energy balance is a fundamental (SEE) model requirement and therefore a tool of a (SEE) Model. Figure 3 top chart gives the energy balance of the building design defining the plant load as 728.6 ton for one of the six buildings served by the central chilled water plant. The design energy balance of Figure 3 would have been determined during the design of the building and plant and is the basis for the 501 equations of the model. The
basic equations and manufactures data required to determine the design energy balance are the basic equations of this (SEE) Model. Figure 3 also gives the (SEE) Model energy balance of the building at 4PM winter temperatures of 38F dry bulb and 36F wet bulb; input to the 501 equations resulting in the winter energy balance. The building shell load and fresh air load are negative values, and 119.0 ton of perimeter heat is required to maintain space comfort at winter weather.
130.2 105.6 65.38 67.4 45.0
207.4 200.4
0.0
-85.3-7.5
-728.6
-1000-900-800-700-600-500-400-300-200-100
0100200300
Ton
Table 1 System-One Building Load on Plant (ton)-4PM Peak Design Hour Weather-Ein = Eout
lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
130.2105.6
31.6
119.0
67.445.0
-89.8-55.4
0.0
-81.0
-11.0
-261.5-300
-200
-100
0
100
200
Ton
Table 1 System-One Building Load on Plant (ton)-4PM Winter Weather-Ein = Eout
lights (ton) Plug (ton) Fans total (ton)Fuel or elect. heat (ton) People load-sen (ton) People lat load (tonBld shell (ton) Fresh air sen (ton) Fresh air lat (ton)Exhaust sen (ton) Exhaust lat (ton) Plant load (ton)
Figure 3: Table 1 System- Top chart energy balance at 4PM design weather of Figure 2-Bottom chart energy balance at 4PM winter weather conditions of Figure 2. Comparing the charts of Figures 3 illustrates that the lights and plug loads are the same for design day and the winter day. Total building kW slightly increased at winter weather conditions. Summing the lights, plugs, and fans of the top chart gives 301.18 ton. The bottom chart includes heat and sums to 386.4 ton. Building perimeter heat of
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119.0 ton is required for winter operation and the fans kW decreased due to less load. One building gives a plant load, at 102F outside temperature, of 728.6 ton, reducing to 261.5 ton at winter conditions of 38F outside temperature. As stated above the top chart of Figure 3 would have been determined during the design of the building and plant. The bottom chart could also have been determined by desk top calculations, however the (SEE) Model accomplished the task by inputting the winter weather temperatures and adjusting the number of chiller/towers on and chiller power to provide 44F supply water.
Figure 4: Table 1 System- Top chart 24 Hour Energy Balance at Design Weather-Bottom chart 24 Hour Energy Balance at Winter Weather Figure 4 gives the energy balance data in (btu/ft2) so that data for any building can be judged against this (SEE) model Standard 90.1-2010 building5. From the top chart at 4PM; 15.47 btu/ft2 x 565,000
ft2/12,000 btu/ton = 728.6 ton as given by the top chart of Figure 3.Building Plus Plant Watts/ft2
TIME of DAYSalt Lake City Table 1 System-Peak Summer weather
System & Heat (watts/sqft)
Design Dry Bulb (F) Design Wet Bulb (F)24 Hour System (watts/ft2) 24 Hour Heat (watts/ft2)Heat (watt/sqft) System (watt/sqft)
28.026.0
24.026.0
28.030.0
33.036.0
38.036.0
34.030.0
28.0 26.024.0
26.024.0
26.030.0
34.0 36.0 35.0 33.0
28.0
55.98
1.92 1.97 2.04 2.032.65
2.97 2.81 2.62 2.722.24 2.00 2.03
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0
5
10
15
20
25
30
35
40
45
50
55
60
% Clear Sky
(watt
/sqft
)
Tem
pera
ture
(F)
TIME of DAYSalt Lake City Table 1 System-Winter weather
System (watts/sqft)-All Electric
Design Dry Bulb (F) Design Wet Bulb (F)24 Hour System (watts/ft2) System (watt/sqft)
26.07
29.91
1.42
1.551.42
0.980.85
1.39
0.50 0.49 0.49
0.55
1.23
1.83 1.84 1.84 1.87
1.01
0.74
0.65
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0.0
5.0
10.0
15.0
20.0
25.0
30.0
% Clear Sky(w
att/s
qft)
24 H
our (
watt
s/sq
ft)
TIME of DAYSalt Lake City Table 1 System-Winter weather
System & Heat (watts/sqft)
24 Hour System (watts/ft2) 24 Hour Heat (watts/ft2)
Heat (watt/sqft) System (watt/sqft)
Figure 5: Building plus Plant (watts/ft2)
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Figure 5 gives total system, building plus plant, watts/ft2 for 24-hours of design and winter weather of Figure 2. Total kW demand meters are usually provided by utility companies, so the figures give data to judge a building and plant operating at or close to the weather conditions of Figure 2. The top chart is for design weather conditions and gives the total 24-hour sum as 33.32 watts/ft2. The middle and bottom charts are for winter weather. The middle chart is for a system that uses electric heat and does not have separate heat energy metering. The total 24-hour sum is 55.98 watts/ft2, an increase over design day weather. The bottom chart is for a system that uses fuel heat and the total 24-hour electric use is 26.07 watts/ft2 and the fuel consumption is 29.91 watts/ft2. Note the two values total the middle chart value. The fuel meter would be in terms of btu/ft2 but watts/ft2 is given so relative values can be seen.Figure 5 bottom chart illustrates that the heat energy required by the ASHRAE Standard 90.1-2010 building and plant during winter operation is more than the summed value for lights, plugs, fans, and the plant. Chapter 2 will address this characteristic in some detail.The middle and bottom charts of Figure 5 illustrate the energy use visibility offered by separate metering on the heat required by the building. Chapter 4 suggests six energy meters required for a system energy balance.
1. Plant load (ton)2. Tower exhaust (ton)3. Plant (watts/ft2) 4. Site (watts/ft2)5. Heat (watts/ft2)6. System (watts/ft2)
System (EUI) Estimates (kbtu/ft2-yr) for the Table 1 SystemFigure 6 is the (SEE) Model estimate of annual (EUI) value. The (SEE) model (EUI) estimates are based on average seasonal weather conditions of Salt Lake City. Programs that model 365 days, for example Energy-Plus, are better for determining annual (EUI) values, however these estimates based on average weather are close to published data.
7.88
9.37
14.33
9.46
0
5
10
15
20
25
30
35
40
45
kbtu
/sq
ft-y
ear
Table 1 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Summer (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Spring (kbtu/sqft-yr)
5.18
35.
183
5.18
35.
183
0.72
90.
558
0.68
50.
571
1.85
61.
009
0.80
50.
938
0.11
62.
618
7.65
72.
766
0
1
2
3
4
5
6
7
8
kbtu
/sq
ft-y
ear
Table 1 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Bld-Summer Bld-Fall Bld-Winter Bld SpringFan-Summer Fan Fall Fan-Winter Fan-SpringPlant-summer Plant-Fall Plant-winter Plant-SpringHeat-summer Heat-Fall Heat-winter Heat-Spring
Figure 6: Table 1 System (EUI) estimate & System Components (EUI) per seasonFor Table 1 conditions Figure 6 top chart gives the (SEE) Model (EUI) estimated of about 42 (kbtu/ft2-yr), a value that is within 11% of the DOE value of about 43 (kbtu/ft2-yr) for new constructed large office buildings. Table 1 gives 24 design and control decisions that were made for the building as defined by the
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figures and discussion thus far. Changing any one of the 24 items would change the building energy consumption and therefore the (EUI) value, perhaps explaining real building values being greater than the DOE value.Figure 6 bottom chart breaks the (SEE) Model (EUI) estimate into four values for each of the four seasons. The largest value is the building load due to lights and plug loads and is the same for all seasons. The fan value is relatively constant, and the plant load is high at summer conditions and significantly less for the other three seasons. The heat load is high during the winter season and almost zero at summer conditions. Figure 6 illustrates that the building lights and plug loads are dominate for all seasons and building heat is the largest energy consumer during the winter. Poor control can drive these values to more than double the design values given by Figure 6, to be discussed below.
SchematicsSchematics of the Table 1 system will be presented to illustrate the value of schematics. The author developed the schematics as a necessary tool to understand the changes occurring in a system as conditions changed. Going from one chart to the other to try and understand the system was impractical, therefore the development of the schematics. Nomenclature is given below.The Table A gives 24-hour data and Schematic 1 is at design hour conditions & Schematic 2 at 4PM winter conditions.
Table A: Design Day & Winter 24-hour kW & 24-hour Energy Balance.
Table A illustrates why the winter kW demand is significantly greater than design data kW. Perimeter heat drives the total value up even though the plant and fan kW are down. Note the Building kW due to lights and plug loads as given by Figure 2 bottom chart above is the same for design day and winter conditions.The (SEE) Model requires Energy into the system equals Energy out of the system and Table A illustrates the Energy Balance for both design & winter conditions. The kW demand during winter is greater during the winter but the energy in and out is less as illustrated. The thermodynamics of the system can not be ignored and is a major check on the accuracy of any building energy model, Energy in must equal Energy out. Now to the schematics.
Total Ein-ton = 5758 SystkW = 9269.7 9269.7 (SEE) Schematic > (FA)Lat-ton= 0.0 VAV inlet-sen-ton = 625.7Pumptot-heat-ton = -29 Ton Blue (FA)kW= 0.0 VAVinlet-lat-ton= 37.4 ExLat-ton = -7.5
Exfillat+sen-ton = 0 BLD.kW= 4973.1 kW Red ExCFM = -47,386Exhtsen+lat-ton= -557 CCWSkW = 4296.6 Water temp pink SEE Schematic air side TEx = 75.00
Tower Tton-Ex = -5172 SystkW = 9269.7 Water gpm orange Air temp green kW red Time= 4PM Exsen-ton = -85.3 V Total Eout-ton = -5758 6 Buildings Salt Lake City air temp green Air CFM purple Ton blue v
(H)cond= 31.2 <PumpT-kW= 71.7 < (lwt)T = 59.94 tton-ex= -875 Glass U = 0.55 WallWtranston= -5.12 WallTot trans ton = -22.9(cond)ft/sec= 10.3 EfTpump= 0.83 Tapproach = 23.9 T#= 2 Wall U = 0.09 GlassN trans ton = -25.10
Ptower # = 2 Trange= 7.0 T-Ton-ex= -1751 Glass SHGC = 0.40 GlassS trans ton = -25.10Trg+app = 30.9 Wall emitt = 0.55 GlassE-trans ton = -18.94
Compressor RoofTrans ton = -0.9 GlassW-trans ton = -18.94 GlassTot-trans-ton= -88.1(chiller)kW= 243.8 Salt Lake City Office Roofsky lite ton = 0.0 GlassN-solar-ton = 0.4(chiller)lift= 29.3 Total Bld ft2= 3,390,000 Peopleton-sen&lat= 67.4 45.0 GlassS-solar-ton = 10.3(chiller)%= 48% Time of Day 4PM plugton&kW = 106 371 GlassE-solar ton = 0.3(chiller)#= 2 Weather %clear sky = 40% Lightton&kW= 130 458 GlassW-solar ton = 11.0 GlassTot-solar-ton = 22.1
(CHILLER)kW= 488 conditions Tdry bulb = 38.0 Total Bldint-ton = 302.3 BLD kW= 828.9 (int cfm)per-ton = 15.11 >(chiller)kW/ton= 0.308 Twet bulb = 36.0 (int-cfm)to-per-ret= 167933 FAN kW= 111.1 Tot Bldper-sen-ton = -73.8 v
Pump-heat-ton = -17 Ton Blue (FA)kW= 60.0 VAVinlet-lat-ton= 34.0 ExLat-ton = -11.0Exfillat+sen-ton = 0 BLD.kW= 4973.1 kW Red ExCFM = -47,386Exhsen+lat-ton= -552 CCWSkW = 4235.0 Water temp pink SEE Schematic air side 4PM TEx = 74.00
Tower Tton-Ex = -1751 SystkW = 9208.1 Water gpm orange Air temp green kW red Exsen-ton = -81.0 V Total Eout-ton = -2319 6.00 Buildings Salt Lake City air temp green Air CFM purple Ton blue v
Schematic 2: System at 4PM winter conditions.
Nomenclature is given below. At first glance the data on the schematics can seem overwhelming. With study the schematics will become a necessary tool for understanding the system equations and performance.Next fan powered terminals & return fans will be installed in the system and defined as the Table 2 system. Stay tuned.Best Regards to allKirby
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References 1. Introduction to Thermodynamics and
Heat Transfer. 1956 Prentice-Hall, Inc. by David A. Mooney.
2. Thermal Environmental Engineering third edition. 1998 Prentice-Hall Inc. by Thomas H. Kuehn, chapter 3.
3. ASHRAE Journal May 2016. “Modeled Performance Isn’t Actual Performance”
4. Nelson, Kirby. “System Energy Equilibrium (SEE) Building Energy Model Development & Verification”. http://kirbynelsonpe.com/
5. Liu, B. May 2011. “Achieving the 30% Goal: (copy and paste) https://www.energycodes.gov/sites/default/files/documents/BECP_Energy_Cost_Savings_STD2010_May2011_v00.pdf
6. Real weather data www.wunderground.com/
7. Nelson, K. “7 Upgrades to, Reduce Building Electrical Demand” ASHRAE Journal, December, 2006,
8. Nelson, K. “Simulation Modeling of a Central Chiller Plant” CH-12-002. ASHRAE 2012 Chicago Winter Transactions.
9. Nelson, K. “Simulation Modeling of Central Chilled Water System” CH-12-003. ASHRAE 2012 Chicago Winter Transactions.
10. Kavanaugh, S. “Fan Demand and Energy” ASHRAE Journal, 2000.
12. Kettler, John “Return Fans or Relief Fans” ASHRAE Journal April 2004.
13. Taylor, S. 2011. “Optimizing design & control of chiller plants.” ASHRAE Journal (12).
14. Nelson, Kirby “The System Energy Equilibrium Model for Chiller Plants, Part 1” Engineered Systems, July 2020.
15. Marley Tower SPX Cooling Technologies UPDATE Version
16. Steven Taylor. ASHRAE Journal June 2007. “VAV System Static Pressure Setpoint Reset”
NOMENCLATURE Each of the more than 200 variables are defined.
Building structure.BLD ft2 = air-conditioned space# Floors = number of building floorsRoof ft2 = roof square feetN/S wall ft2 =north/south wall square feetE/W wall ft2 =east/west wall square feetWall % glass = percent of each wall that is glassGlass U = glass heat transfer coefficientWall U = wall heat transfer coefficientGlass SHGC = glass solar heat gain coefficientWall emit = wall solar indexBuilding interior space;Rooftrans-ton =transmission through roof (ton)Roofsky-lite-ton =sky lite load (ton)Peopleton sen&lat = sensible & latent cooling load due to people (ton)Plugton&kW = cooling load & kW due to plug loadsLightton&kW = cooling load & kW due to lightsTotal Bldint-ton = total building interior load (ton)(int-cfm) to-per-return = CFM of interior supply air that returns to perimeter of buildingTstat-int = interior stat set temperature (F)Bldint-air-ton = supply air ton to offset interior loadBLD kW = total building kW demandFAN kW = total fan kWHEAT kW = total kW due to heatSITE kW = total site kW=Bld+ Fan+HeatBuilding perimeter space;%clear sky = percent clear skyTdry bulb = outside dry bulb temperature (F)Twet bulb = outside wet bulb temperature (F)Ex/Infillat-ton = latent air infiltration or exfiltration (ton)Ex/InfilCFM = air infiltration or exfiltration CFMExfilsen-ton =sensible air exfiltration or infiltration (ton)Walln trans ton = north wall transmission (ton)Walls trans ton = south wall transmission (ton)WallE trans ton = east wall transmission (ton)Wallw trans ton = west wall transmission (ton)Walltot-trans-ton = total wall transmission (ton)GlassN-trans-ton = north wall glass transmission (ton)GlassS-trans-ton = south wall glass transmission (ton)
GlassE-trans-ton = east wall glass transmission (ton)GlassW trans-ton = west wall glass transmission (ton)Glasstot-trans-ton = total transmission thru glass (ton) GlassN-solar-ton = north glass solar load (ton)GlassS-solar-ton = south glass solar load (ton)GlassE-solar-ton = east glass solar load (ton)GlassW-solar-ton = west glass solar load (ton)Glasstot-solar-ton = total glass solar load (ton)(int cfm)per-ton = effect of interior CFM to wall (ton)Total Bldper-sen-ton total perimeter sensible load (ton)Tstat-per = perimeter stat set temperature (F)Bldper-air-ton = supply air ton to offset perimeter load Air handler duct system-Interior duct Tair supply int = temp air supply to building interior (F)(fan)int ter ton&kW = interior ton & kW due to terminal fans (D)int-air-ton = cooling (ton) to building interior ductTair coils = supply air temperature off coils to duct (F)(D)int-CFM = supply air CFM to building interior ductPerimeter ductTair supply per =temp (F) air supply to building perimeter (fan)per ter ton&kW = perimeter ton & kW of terminal fansTheat-air = temp supply air before terminal fan heat (F)(D)heat-ton&kW = heat to perimeter supply air ton & kWTreheat air = temp perimeter supply air after reheat (F) (D)reheat ton&kW = reheat of perimeter supply air ton & kW(D)per-air-ton = cooling (ton) to perimeter duct Tair coils = supply air temperature off coils to duct (F)(D)per-CFM = supply air CFM to perimeter ductCoil(Coil)sen-ton = sensible load on all coils (ton)(Coil)cap-ton = LMTD * UA = capacity (ton) one coilLMTD = Coil log mean temperature difference (F)(Coil)L+s-ton = latent + sensible load on all coils (ton) transferred to PlantUA = coil heat transfer coefficient * coil area. UA varies as a function water velocity (coil)gpm thru the coil, as the (coil)gpm decreases the coil capacity decreases.(one Coil)ton = load (ton) on one coilVAV Fan systemFresh airstatFA = fresh air freeze stat set temperature (F)TFA to VAV = temperature of fresh air to VAV fan(FA)sen-ton = fresh air sensible load (ton)(FA)CFM = CFM fresh air to VAV fan inlet(FA)Lat-ton = fresh air latent load (ton)(FA)kW = heat kW to statFA set temperatureAir return TBLD-AR = return air temp (F) before return fans(Air)ret-CFM = CFM air return from building(FAN)ret-kW = return fans total kW(FAN)ret-ton = cooling load (ton) due to (FAN)ret-kW
(Air)ret-ton = return air (ton) before return fansTAR to VAV = TBLD-AR + delta T due to return fans kWVAVret-sen ton = return sensible (ton) to VAV fans inletVAVret-lat ton = return latent (ton) to VAV fans inletVAVret-CFM = return CFM to VAV fans inletExhaust air ExLat-ton = latent load (ton) exhaustedExCFM = CFM of exhaust airTEx = temperature of exhaust air Exsen-ton = sensible load (ton) exhaustedVAV Fans Tret+FA = return and fresh air mix temperature (F)(dh) = VAV air static pressure (in)Efan-VSD = VAV fans efficiencyVAVinlet-sen-ton = sensible load (ton) inlet to VAV fansVAVinlet-lat-ton = latent load (ton) inlet to VAV fansTair-VAV = temp air to coils after VAV fan heat(FAN)VAV-CFM = CFM air thru coils(FAN)ton-VAV = load (ton) due to VAV fan kW(FAN)kW-VAV = total VAV fan kW demandAIR SIDE SYSTEM PLUS BUILDINGFAN kW = total air handlers kWSITE kW = total site or air side kWPlantton = (COIL)L+s ton load (ton) to plantCENTRAL PLANT# Buildings = number of buildings served by plantPlant ton = total load (ton) to plant Primary/secondary pumping nomenclaturegpmevap = total gpm flow thru one evaporators(H)pri-total = total primary pump head (ft) = (H)pri-pipe + (H)pri-
fittings + (H)pri-bp + (H)evap
(H)pri-pipe = primary pump head due to piping (ft)(H)pri-fittings = primary head due to pump & fitting (ft)(Ef)c-pump = efficiency of chiller pumpPc-heat-ton = chiller pump heat to atmosphere (ton)Pc-kW = one chiller pump kW demand (kW)Pchiller-# = number chiller pumps operating(lwt)evap = temperature water leaving evaporator (F)Tbp = temperature of water in bypass (F)gpmbp = gpm water flow in bypass(H)pri-bp = head if chiller pump flow in bypass (ft)(ewt)evap = temp water entering evaporator (F)Psec-heat-ton = secondary pump heat to atmosphere (ton)Psec-kW = kW demand of secondary pumpsEfdes-sec-p = design efficiency of secondary pumpingEfsec-pump = efficiency of secondary pumping(H)sec = secondary pump head (ft) = (H)sec-pipe + (H)sec-bp + (H)coil + (H)valve
(H)sec-pipe = secondary pump head due to pipe (ft)(H)sec-bp = head in bypass if gpmsec > gpmevap
GPMsec = water gpm flow in secondary loop
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(ewt)coil = water temperature entering coil (F)Pipesize-in = secondary pipe size (inches)(lwt)coil = temperature of water leaving coil (F)Evaporator(evap)ton = load (ton) on one evaporatorTER = evaporator refrigerant temp (F)TER-app = evaporator refrigerant approach (F)EVAPton = total evaporator loads (ton)(H)evap = pump head thru evaporator (ft)(evap)ft/sec = velocity water flow thru evaporator(evap)des-ft/sec = evaporator design flow velocityCompressor:(chiller)kW = each chiller kW demand(chiller)lift = (TCR – TER) = chiller lift (F)(chiller)% = percent chiller motor is loaded(chiller)# = number chillers operating(CHILLER)kW = total plant chiller kW(chiller)kW/ton = chiller kW per evaporator tonPlant kW = total kW demand of plant(Plant)kW/site ton = Plant kW per site tonCondenser nomenclature:(cond)ton = load (ton) on one condenserTCR = temperature of condenser refrigerant (F)TCR-app = refrigerant approach temperature (F)(COND)ton = total load (ton) on all condensers(H)cond = tower pump head thru condenser (ft)(cond)ft/sec = tower water flow thru condenserTower piping nomenclaturePipesize-in = tower pipe size (inches)gpmT = each tower water flow (gpm)GPMT = total tower water flow (gpm)(H)T-total = total tower pump head (ft)PT-heat = pump heat to atmosphere (ton)PT-kW = each tower pump kW demandEfT-pump = tower pump efficiencyPtower # = number of tower pumps(H)T-pipe = total tower pump head (ft)(ewt)T = tower entering water temperature (F)(H)T-static = tower height static head (ft)Trange = tower range (F)= (ewt)T – (lwt)T
(lwt)T = tower leaving water temperature (F)Tapproach = (lwt)T – (Twet-bulb)Tower nomenclature
tfan-kW = kW demand of one tower fanTfan-kW = tower fan kW of fans ontfan-% = percent tower fan speedtton-ex = ton exhaust by one tower
T# = number of towers onTton-ex = ton exhaust by all towers onTrg+app = tower range + approach (F)One hour performance indices
BLDkW = kW demand of building lights & plug loadsFankW = air side fans kW, VAV, return terminalsDuctheat = perimeter heat to air supplyFAheat = heat added to fresh airHeattotal = total heat added to airPlantkW = total plant kWSystkW = total system kWCCWSkW = air side system + plant kWChillerkW/evap ton = chiller kW/evaporator ton performancePlantkW/site ton = plant kW per site or air side tonCCWSkW/site ton = CCWS kW per load to plantWeatherEin-ton = weather energy into the systemSitekW-Ein-ton = load (ton) due to site kWPlantkW-Ein-ton = load (ton) due to plant kWTotalEin-ton = total energy in to system (tonPumptot-heat-ton = total pump heat out (ton)AHU Exlat ton = air exhausted latent tonAHU Exsen ton = air exhausted sensible tonTower Tton Ex = energy exhausted by tower (ton)Total Eout ton = total energy out of system (ton)24 hour performance indicesBLD24hr-kW = building 24 hour kW usageFan24hr-kW = fan system 24 hour kW usageDuct24hr-heat kW or therm = duct heatFA24hr heat kW or therm = fresh air heatHeat24hr total kW or therm = total heat into systemPlant24hr kW = plant 24 hour kW usageSyst24hr kW & therm = total system 24 hour energy usagePeoplesen+lat ton =total load (ton) due to peopleEnfil24hr cfm energy = change in internal energyWeather24hr-Ein-ton = 24 hour weather energy into systemSITE24hr-kW-Ein-ton = 24 hour energy into sitePlant24hr-kW-Ein-ton = 24 hour kW energy into plantTotal24hr-Ein-ton = total 24 hour energy into systemPump24hr Heat out-ton = pump heat to atmosphere (ton)AHU Ex24hr Lat ton = exhausted latent load from buildingAHU Ex24hr-sen-ton = exhausted sensible load from bld.
