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Kansas City MO. Benchmark at Real Weather Conditions. Analysis with (SEE) Energy ModelIntroduction/Building DescriptionA system energy equilibrium (SEE) model is a tool for commissioning and evaluating the performance of a building and plant on any day. The purpose of this paper is to provide performance data on specify days so that building owners can judge the energy performance of their buildings against an ASHRAE Standard design, in this case a 90.1-20105 building and plant design.Reader should review Anatomy of a Real Time Building Energy Model on this site.
Figure 1: Building Description-Kansas City Missouri Large Office Building Designed to Std. 90.1-20105
Figure 1 presents the modeled building of this study, a 565,000 square foot large office building based on the data provided by Liu5. The office campus is assumed to consist of six Figure 1 buildings. Figure 2 top chart gives the assumed design day weather conditions. The secondary horizontal axis of gives the design day percent clear sky.
9086 84 82
88
94 96 97101
9895 93
71 70 69 70 72 74 75 76 7875 74 72
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
40
50
60
70
80
90
100
110
40.0
50.0
60.0
70.0
80.0
90.0
100.0
110.0
% Clear Sky
Tem
pera
ture
(F)
TIME of DAYDesign Day Weather
Design Dry Bulb (F) Design Wet Bulb (F)
568
2697
852
28425.4
457.7 457.7
101.7165
371 371
165
0
50
100
150
200
250
300
350
400
450
500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Lights + Plug (kW)
kW# pe
ople
TIME OF DAYOne Building Interior- People & Lights & Plug kWPeak Summer Weather
People-# Lights kW Plug-kW
Figure 2: Top Chart-Design Day 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. Figures 1 & 2 plus Table 2 give sufficient data to (SEE) model the ASHRAE Standard 90.1-20105 building and plant.
Kirby Nelson P.E. 1
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
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
Building Location and Design1. Location=Kansas City Mo.2. Building 565,000 ft2.3. No external solar shading. 4. Design weather-Figure 2 5. Building design from Liu5.6. Percent wall glass 37%7. Peak lights kW .81 watts/ft2
8. Peak plugs kW .66 watts/ft2
9. Return air to perimeter-no change.10. One VAV AHU/floor 26,400 CFM11. Duct design 7.0 in. water12. Fan powered terminals installed.13. Return air fans installed.
Building Control 14. Lights on/off control 6% on after hours.15. Plugs on/off control 44% on after hours.16. Building pressure control, no infiltration. 17. Supply air = 55F18. Supply water = 44F to 44.5F19. Stats control-yes. 20. Perimeter heat air temp-105F.21. VAV fan static control-yes. 22. Fresh air CFM control-yes.23. Fresh air heat stat set 42F.
Plant Design & Control24. Chiller/Tower selection13.
Table 2: System
Table 2 gives the building and plant design defined here as an efficient design and the as constructed system.
42.030
28.658
13.37
0.00
0.536
3.015
3.526
0.860
0.412
2.0882.295
0.604
0.124
0.928
1.231
0.256
0.000.00 0.00
0.00
100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100% 100%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
10
20
30
40
50
% Clear Sky
(watt
/sqft
)
24 H
our W
atts/
sq ft
TIME of DAYTable 2 System-Design Day Weather(SEE) Model Data (watts/sqft)
24 Hour System (watts/ft2) Site 24 Hour (watts/ft2)24 Hour Plant (watts/ft2) 24 Hour Heat (watts/ft2)System (watt/sqft) Site (watts/ft2)Plant (watts/ft2) Heat (watt/sqft)
Figure 3: Watts/ft2 Design Day Weather Table 2 SystemFigure 3 gives the watts/ft2 performance of the Figures 1, 2 and Table 2 building and plant, defined here as the ASHRAE Standard 90.1-20105 design, also defined here as the “Table 2 system”. The total 24-hour consumption operating at the design weather conditions of Figure 2 is 42.030 watts/ft2 made up of the site at 28.658 watts/ft2, the plant at 13.37 watts/ft2, and heat is zero. These values can be used to judge office buildings when operating close to design weather of this city. Specific days of weather will be addressed below showing performance of the Table 2 system and the Table 3 system defined below as the Table 2 system with poor control.
Energy Balance of Table 2 System
Kirby Nelson P.E. 2
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
130.2105.6132.9567.4 45.0
204.1196.2139.5
-87.9-7.2
-925.8
-1100-1000
-900-800-700-600-500-400-300-200-100
0100200300
Ton
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)
2.76 2.24 2.82 2.394.34
-2.02
7.13
-19.663
4.20
-0.13
-23.74-25
-20
-15
-10
-5
0
5
10
(btu
/hr-
ft2)
Table 2 System (btu/ft2)-4PM Design Day WeatherSystem Ein = Eout
lights (btu/ft2) Plug (btu/ft2) Fans (btu/ft2)Fuel or elect. heat (btu/ft2) People load btu/sqft E cfm chg btu/ft2Bld shell btu/sqft Exhaust btu/sqft Fresh air (btu/ft2)Plant load (btu/ft2) Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out
Figure 4: Table 2 System Energy Balance at Design conditions of Figure 2 top chart 4PM
Figure 4 top chart would have been determined during the design of this building and plant. The bottom chart gives the 24-hour energy balance data in (btu/ft2) so that data for any building can be judged against this (SEE) model Standard 90.1-2010 building5 as defined by Table 2. From the bottom chart at 4PM; 19.663 btu/ft2 x 565,000 ft2/12,000 btu/ton = 925.8 ton as given by the top chart of Figure 4. Figure 5 gives the 24-hour energy balance of the plant load and the energy out at the tower.
1.2 1.2 1.2 1.3 3.5 5.0 5.0 5.0 5.0 2.8 1.9 1.6-2.71 -2.22 -2.06 -3.77
-9.88-15.90-16.36-17.91-19.66
-11.93-5.65 -4.15
2.76 2.24 2.08 3.79
11.35
17.94 18.40 19.93 21.68
13.48
6.15 4.43
-2.76 -2.24 -2.08 -3.79
-11.35
-17.94-18.40-19.93 -21.68
-13.48
-6.15 -4.43
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
(BTU
/sq
ft)
Time of DayTable 2 System-Design Day WeatherPlant Load Energy Balance-Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft Weather load btu/sqft Exhaust btu/sqft
Plant load (btu/ft2) Plant Load Ein (btu/ft2) Plant Load Eout (btu/ft2)
1.2 1.2 1.2 1.3 3.5 5.0 5.0 5.0 5.0 2.8 1.9 1.60.3 0.3 0.3 0.51.1
2.1 2.1 2.5 2.81.3 0.6 0.41.2 0.8 0.7 2.0
6.3
8.4 8.9 10.0 11.5
8.63.4 2.1
-3.2 -2.6 -2.4 -4.5
-11.7-19.0 -19.6 -21.5 -23.7
-14.3-6.7 -5.0
-3.29 -2.69 -2.50-4.53
-13.23
-21.10-21.69-23.64-25.88
-15.89
-7.27-5.30
3.29 2.69 2.504.53
13.23
21.10 21.69 23.6425.88
15.89
7.27 5.30
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
(btu
/hr)
Time of DayTable 2 System Energy Balance-Ein = Eout at TowerDesign day Weather
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft Exhaust btu/sqft Weather load btu/sqftPlant kW btu/ft2 Pump heat out btu/ft2 Tower btu/ft2 outEnergy out (btu/ft2) Energy in (btu/ft2)
Figure 5: Table 2 System 24 Hour Energy Balance Top chart plant energy balance, Bottom chart system energy balance.
Chiller/Tower Design DataTables 1 gives (SEE) model input design data for the chiller and tower and Table 1A defines the chiller/tower lift. The chiller/tower has 1,000-ton capacity at design conditions of 101F dry bulb and 78F wet bulb. The chiller evaporator is selected with a 2.6F refrigerant approach and the condenser is 1.6F refrigerant approach. The tower is selected15 at 1,173-ton load and 78F wet bulb with an approach to wet bulb of 8F and flow of 2,000 gpm with a calculated range of 14.13F. The tower is a one cell unit with a 50hp fan.
Kirby Nelson P.E. 3
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
Condenser design leaving water temperature is 100.13F and tower leaving water is 86F.
Chiller Design Load (Ton) 1000.0Chiller kW 583.0Chiller kW/ton .583Evap water flow rate (gpm) 1500.0Evap entering water temp (F) 60.0Evap leaving water temp (F) 44.0Evap refrigerant temp (F) 41.4Evap refrigerant approach (F) 2.6Evap pressure drop (ft. water) 34.5Evap water velocity (ft. /sec.) 8.38Cond heat rejection (ton) 1173Cond water flow rate (gpm) 2000Cond entering water temp (F) 86Cond leaving water temp (F) 100.13Cond refrigerant temp (F) 101.73Cond refrigerant approach (F) 1.6Cond pressure drop (ft. water) 43Cond water velocity (ft. /sec) 9.71Tower for (SEE) model Tower15
Design Wet bulb 78.0FDesign Load 1173 tonTower water flow 2000 gpmApproach temperature 8.0 FCalculated range 14.13FRange + approach 22.13FOne cells with 50HP fan 40 kWSelected Tower15 NC8409UAN1Cold water 86FReturn water to tower 100.13FCapacity 104.4%Static lift 12 ft.
Table 1: Chiller/Tower Design Data
Chiller/Tower Lift
Chiller lift20 equals condenser refrigerant temperature minus evaporator refrigerant temperature as defined by Table 1A for this chiller/tower selection. Table 1A illustrates the design values that define the refrigerant temperatures and therefore chiller lift. All values are taken from Tables 1. The condenser refrigerant temperature is the sum of wet bulb + tower approach = entering condenser water + tower range = leaving condenser water + condenser refrigerant approach = 101.73F refrigerant
temperature. The evaporator refrigerant temperature is determined by the design values of Table 1. Evaporator entering water minus evaporator delta T equals leaving chiller water temperature minus evaporator refrigerant approach temperature equals evaporator refrigerant temperature. The evaporator refrigerant temperature can also be determined by simply subtracting the evaporator refrigerant approach temperature from the evaporator supply water temperature, (44F – 2.6F = 41.4F). Therefore, chiller lift = 101.73F – 41.4F = 60.33F. Chilled water supply temperature has a significant effect on chiller lift and therefore chiller kW demand.
Design Chiller Lift (F)Condenser refrigerant 101.73FCondenser refrigerant approach 1.6FLeaving condenser water 100.13FTower range 14.13FEntering condenser water 86FTower approach 8.0FWet bulb temperature 78.0FChiller lift = 101.73F – 41.4F = 60.33FEvaporator entering water 60FEvaporator delta temperature 16FLeaving chilled water temperature 44FEvaporator refrigerant approach 2.6FEvaporator refrigerant temperature 41.4F
Table 1A: Design Chiller/Tower Lift
Table 1 & 1A are chiller/tower design selection values for a Kansas City Missouri plant. Operating at the design conditions of this city is illustrated by the plant schematic. Detail plant design/selection is a (SEE) plant model capability that will be presented at, “System Energy Equilibrium (SEE) Building Energy Model Development & Verification”. http://kirbynelsonpe.com/
Kirby Nelson P.E. 4
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
Condenser >pumpT-kW = 29.5(cond)ton= 1106.2 Pipesize-in = 6.0 (H)T-pipe= 9.6 Tower
TCR= 100.4 > GPMT= 12060 > (ewt)T= 98.8 tfan-kW= 40.0TCR-app= 1.56 (H)T-total= 64.6 (H)T-static = 12.0 Tfan-kW= 240.0
(COND)ton= 6637 PT-heat ton = -8.55 < gpmT = 2010 tfan-%= 100%(H)cond= 43.0 <PumpT-kW= 176.8 < (lwt)T = 85.6 tton-ex= -1118
(cond)ft/sec= 9.7 EfTpump= 0.83 Tapproach = 7.6 T#= 6Ptower # = 6 Trange= 13.2 T-Ton-ex= -6706
Trg+app = 20.8Compressor
(chiller)kW= 548.0 Kansas City Office(chiller)lift= 58.5 Total Bld ft2= 3,390,000(chiller)%= 94% Time of Day= 4PM(chiller)#= 6 Weather %clear sky = 100%
(CHILLER)kW= 3288 conditions Tdry bulb = 101.0(chiller)kW/ton= 0.581 Twet bulb = 78.0
Plant kW = 4174PlantkW/ton = 0.751
> Evaporator(evap)ton= 943.4
TER= 41.9TER-app= 2.46
^ EVAPton= 5660(H)evap= 34.5
(evap)ft/sec= 8.38(evap)des-ft/sec= 8.38
^ Vgpmevap= 1500 <pumpc-kW = 13.79 Psec-heat-ton = -23.1 GPMSEC = 8490.6Pchiller-# = 6 (lwt)evap = 44.34 > Psec-kW= 386.0 > (ewt)coil= 44.34
(H)pri-total= 39.5 Efdes-sec-p = 0.80 ^ (H)pri-pipe= 1.1 Tbp= 44.34 Efsec-pump = 0.79 # Buildings = 6.0
(H)pri-fitings= 3.9 gpmbp= -509 (H)sec= 191 PLANTton = 5555(Ef)c-pump= 0.81 (H)pri-bp= 0.00 (H)sec-pipe= 117Pc-heat-ton= -4.47 (H)sec-bp= 0.00 Pipesize-in = 10.0
^ < Pumpc-kW= 82.7 (ewt)evap = 59.43 < (GPM)sec= 8491 < (lwt)coil= 60.34
chillerkW/evapton= 0.581 4PM All Electric Fuel Heat(plant)kW/site ton= 0.751 kW Ton
CCWSkW/bld+FA ton= 1.467 BLD.kW= 4973.1Peoplesen+lat ton = 674 (Fan)kW = 2805.6
WeatherEin-ton = 3239 Ductheat= 0.0 0.00 statFA=(Site)kW-Ein-ton = 2212 (FA)heat= 0.0 0 TFA to VAV = PlantkW-Ein-ton = 1187 Heat total = 0.0 0.00Enfil cfm energy = 0 PlantkW= 4173.7 Plant
Total Ein-ton = 7312 SystkW = 11952.4 11952.4 (SEE) SchematicPumptot-heat-ton = -36 Ton Blue
Exfillat+sen-ton = 0 BLD.kW= 4973.1 kW RedExhtsen+lat-ton= -570 CCWSkW = 6979.3 Water temp pink
Tower Tton-Ex = -6706 SystkW = 11952.4 Water gpm orangeTotal Eout-ton = -7312 6 Buildings Kansas City air temp green
Table 2 System Schematic at Design Weather ConditionsThe schematic is plant at peak summer design weather. Table 1A gives a chiller/tower design lift as 60.33F and the schematic shows 58.5F lift at the design weather conditions. The chiller kW/ton = .581 and the plant kW/ton = .751. The six building of the model put a load of 5,555 ton on the plant.The lower left of the schematic gives energy balance data and total kW demand of the system. Nomenclature is provided below.
(EUI) Estimates (kbtu/ft2-yr) for the
Table 2 System
9.26
10.84
15.20
9.61
0
5
10
15
20
25
30
35
40
45
50
55
60
kbtu
/sq
ft-y
ear
Table 2 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Spring (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Summer (kbtu/sqft-yr)
5.18
3
5.18
3
5.18
3
5.18
3
1.28
91.
207 1.74
5
1.45
7
1.27
5
0.96
5
2.66
7
1.13
2
1.51
7
3.48
2
0.01
7
7.42
9
0
1
2
3
4
5
6
7
8
9
10
kbtu
/sq
ft-y
ear
Table 2 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Table 2 Bld-Spring Table 2 Bld-Fall Table 2 Bld-Summer Table 2 Bld Winter
Table 2 Fan-Spring Table 2 Fan-Fall Table 2 Fan-Summer Table 2 Fan-Winter
Table 2 Plant-Spring Table 2 Plant-Fall Table 2 Plant-Summer Table 2 Plant-Winter
Table 2 Heat-Spring Table 2 Heat-Fall Table 2 Heat-Summer Table 2 Heat-Winter
Figure 6: Table 2 System (EUI) estimate & System Components (EUI) per seasonFigure 6 is an estimate of annual (EUI) for the Table 2 system and Figure 7 is for the Table 3 system. The bottom charts of Figures 6 & 7 give the (EUI) values of the system components at the four seasons. The Table 3 system is the Table 2 system with poor control. Poor control of the Table 2 system more than doubled the (EUI) value to 100 verses 45 for the Table 2 system.
Table 3 System-Poor Control
Kirby Nelson P.E. 5
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
Each of the building controls listed are changed with Table 3 except the 55F supply air temperature and the plant control. The (SEE) model can evaluate each of these poor control issues, and others, as standalone or as additive effect on the performance of the system. System aging can also have a significant effect on the performance of a system but will not be addressed here.
Building Location and Design1. Location=Kansas City Mo.2. Building 565,000 ft2.3. No external solar shading. 4. Average ambient temperatures5. Percent clear sky s defined below. 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 to perimeter-no change.11. One VAV AHU/floor 26,400 CFM12. Duct design 5.5 to 7.0 in. water13. Fan powered terminals installed14. Return air fans installed
Building Control 15. Lights on/off control from 6% on after
hours to 67% on.16. Plugs on/off control 44% on after hours
to 67% on.17. Building pressure control; infiltration
of .2 cfm/ft2 walls max-varies as AHU cfm.
18. Supply air = 55F19. Supply water = 44F to 44.5F20. Stats control-NO. 21. Perimeter heat air temp-90F.22. VAV fan static control-NO. 23. Fresh air CFM control-NO.24. Fresh air heat stat set from 42F to 60F.
Plant Design & Control25. Chiller/Tower selection13.
Table 3: System-Poor Control
The (EUI) estimates of Figure 6 & 7 are at average weather for the four seasons with 80% clear sky for summer, 60% clear sky for spring and fall, and 20% clear sky for winter weather.Figures 6 & 7 provide annual (EUI) values so the annual performance of a real building and plant can be judged. Below will provide performance on specific days for Energy Balance Analysis. See Anatomy of a Real Time Building Energy Model for analysis procedures.
18.08
25.89
42.62
13.54
0
10
20
30
40
50
60
70
80
90
100
110
kbtu
/sq
ft-y
ear
Table 3 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Spring (kbtu/sqft-yr) Fall (kbtu/sqft-yr)
Winter (kbtu/sqft-yr) Summer (kbtu/sqft-yr)
7.02
8
7.02
8
7.02
8
7.02
8
2.92
8
3.58
32.
607 5.
805
2.06
8
2.42
5
3.52
6
3.91
8 6.05
412
.850
0.37
6
25.8
67
0
5
10
15
20
25
30
kbtu
/sq
ft-y
ear
Table 3 System-Energy Use Intensitity (EUI) Estimate-(kbtu/sq ft-year)
Table 3 Bld-Spring Table 3 Bld-Fall Table 3 Bld-Summer Table 3 Bld Winter
Table 3 Fan-Spring Table 3 Fan-Fall Table 3 Fan-Summer Table 3 Fan-Winter
Table 3 Plant-Spring Table 3 Plant-Fall Table 3 Plant-Summer Table 3 Plant-Winter
Table 3 Heat-Spring Table 3 Heat-Fall Table 3 Heat-Summer Table 3 Heat-Winter
Figure 7: Table 3 System (EUI) estimate & System Components (EUI) per season
Kirby Nelson P.E. 6
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
An office building or campus for this city should have an annual (EUI) close to Figure 6. If the annual (EUI) is greater than Figure 6 then a (SEE) model analysis of the building might be in order. This site4 will provide an approach to energy balance analysis with (SEE) model.
This completes the introduction that give the performance of the Table 2 & 3 systems at design day conditions. The remaining sections of this paper will give performance of the Table 2 & 3 systems at real weather. Nomenclature is given at the end.
Suggest reader visit; Anatomy of a Real Time Building Energy Model on this site that gives (SEE) model analysis procedures.
Stay tuned for more real weather days to be Benchmarked.Best Regards to AllKirby Nelson P.E.Life Member ASHRAE
References
1. Introduction to Thermodynamics and Heat Transfer. 1956 Prentice-Hall, Inc. by David A. Mooney.
2. Thermal Environmental Engineering third edition. 1998 Prentice-Hall Inc. by Thomas H. Kuehn, chapter 3.
3. ASHRAE Journal May 2016. “Modeled Performance Isn’t Actual Performance”
4. Nelson, Kirby. “System Energy Equilibrium (SEE) Building Energy Model Development & Verification”. http://kirbynelsonpe.com/
5. Liu, B. May 2011. “Achieving the 30% Goal: (copy and paste) https://www.energycodes.gov/sites/default/files/documents/BECP_Energy_Cost_Savings_STD2010_May2011_v00.pdf
6. Real weather data www.wunderground.com/
7. Nelson, K. “7 Upgrades to, Reduce Building Electrical Demand” ASHRAE Journal, December, 2006,
8. Nelson, K. “Simulation Modeling of a Central Chiller Plant” CH-12-002. ASHRAE 2012 Chicago Winter Transactions.
9. Nelson, K. “Simulation Modeling of Central Chilled Water System” CH-12-003. ASHRAE 2012 Chicago Winter Transactions.
10. Kavanaugh, S. “Fan Demand and Energy” ASHRAE Journal, 2000.
11. Faris, Gus “Fan-Powered VAV Terminal Units” ASHRAE Journal November 2017
12. Kettler, John “Return Fans or Relief Fans” ASHRAE Journal April 2004.
13. Taylor, S. 2011. “Optimizing design & control of chiller plants.” ASHRAE Journal (12).
14. Nelson, Kirby “The System Energy Equilibrium Model for Chiller Plants, Part 1” Engineered Systems, July 2020.
15. Marley Tower SPX Cooling Technologies UPDATE Version 5.4.2
16. Steven Taylor. ASHRAE Journal June 2007. “VAV System Static Pressure Setpoint Reset”
17. Carrier System Design Manual18. Miles Ryan. ASHRAE Journal February 2021.
“Understanding Cascade Control and Its Applications For HVAC”
19. Schwedler, Mick. July 1998 “Take It to The Limit…Or Just Halfway?” ASHRAE Journal.
20. 2020 ASHRAE HANDBOOK, HVAC Systems and Equipment, page 43.10 Figure 11 Temperature Relations in a Typical Centrifugal Liquid Chiller.
Kirby Nelson P.E. 7
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
Real Weather Performance of Table 2 & Table 3 SystemsThe following will give (SEE) model results at real weather conditions so that building owners can judge their buildings against ASHRAE Standard 90.1-2010 design. Values close to Table 2 values suggests a building that is operating close to ideal performance. Values close to Table 3 values suggests a building that is out of energy control.
Spring April 21, 2021
35 3336 34
3741
44 4346
49
4340
31 3033 32
35 36 37 37 38 3835 33
100% 50% 30% 100% 50% 50% 50% 30% 50% 50% 70% 100%
0
10
20
30
40
50
60
70
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
% Clear Sky
Tem
pera
ture
(F)
TIME of DAYKC April 21, 2021
Design Dry Bulb (F) Design Wet Bulb (F)
Figure A: Real Weather
Figure A illustrates rather cold weather for a spring day.
Figure B bottom chart illustrates that the lights and plug loads are not being turned down at night as designed.
568
2697
852
28425
458 458
102165
371 371
165
0
50
100
150
200
250
300
350
400
450
500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Lights + Plug (kW)
kW# pe
ople
TIME OF DAYTable 2 Building Interior- People & Lights & Plug kWKC April 21, 2021 Weather
People-# Lights kW Plug-kW
568
2697
852
284
305
458 458
305
247
371 371
247
0
50
100
150
200
250
300
350
400
450
500
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Lights + Plug (kW)
kW# pe
ople
TIME OF DAYTable 3 Building Interior- People & Lights & Plug kWKC April 21, 2021 Weather
People-# Lights kW Plug-kW
Figure B: Interior Loads-Table 2&3 Systems
Kirby Nelson P.E. 8
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
47.067
25.454
3.36
18.25
1.673
2.5612.387
1.691
0.439
1.844 1.855
0.596
0.093 0.203
0.2380.105
1.14
0.510.29
0.99
100% 50% 30% 100% 50% 50% 50% 30% 50% 50% 70% 100%
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
10
20
30
40
50
% Clear Sky
(watt
/sqft
)
24 H
our W
atts/
sq ft
TIME of DAYTable 2 System-April 21, 2021 Weather(SEE) Model Data (watts/sqft)
24 Hour System (watts/ft2) Site 24 Hour (watts/ft2)24 Hour Plant (watts/ft2) 24 Hour Heat (watts/ft2)System (watt/sqft) Site (watts/ft2)Plant (watts/ft2) Heat (watt/sqft)
127.33
44.356
10.54
72.43
5.6445.963 5.202 5.147
1.6272.363 2.271 1.599
0.4190.559
0.518 0.380
3.60 3.04
2.413.17
100% 50% 30% 100% 50% 50% 50% 30% 50% 50% 70% 100%
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
0
20
40
60
80
100
120
140
% Clear Sky
(watt
/sqft
)
24 H
our W
atts/
sq ft
TIME of DAYTable 3 System-April 21, 2021 Weather(SEE) Model Data (watts/sqft)
24 Hour System (watts/ft2) Site 24 Hour (watts/ft2)24 Hour Plant (watts/ft2) 24 Hour Heat (watts/ft2)System (watt/sqft) Site (watts/ft2)Plant (watts/ft2) Heat (watt/sqft)
Figure C: 24 Hour Performance-Table 2&3 Systems
Figure C top chart gives a 24-hour total watts/ft 2 for the Table 2 system that is much less than the Table 3 system.
This Figure C is probable the best data to judge a real system. If the real system falls close to the Table 2 system, then the real system is probably operating efficiently on
this date. However, the system should be checked at other weather conditions and different seasons.
1.2 1.2 1.2 1.33.5 5.0 5.0 5.0 5.0
2.8 1.9 1.6
-2.82 -2.81 -2.69-2.25
-2.81-5.70 -6.13 -6.16
-6.23
-2.71 -3.05 -2.94
5.62 5.72 5.384.04
6.88
10.34 10.40 10.719.72
5.39 5.66 5.64
-5.62 -5.72 -5.38-4.04
-6.88
-10.34-10.40-10.71
-9.72
-5.39 -5.66 -5.64
-15
-10
-5
0
5
10
15
(BTU
/sq
ft)
Time of DayTable 2 System-April 21, 2021 WeatherPlant Load Energy Balance-Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft Weather load btu/sqft Exhaust btu/sqft
Plant load (btu/ft2) Plant Load Ein (btu/ft2) Plant Load Eout (btu/ft2)
3.3 3.3 3.3 3.3 3.5 5.0 5.0 5.0 5.0 3.3 3.3 3.3
-11.17-11.50-10.79-8.91 -9.51
-14.05-14.09-14.69-13.14-8.08
-9.98 -10.25
17.72 18.31 17.1214.01 14.74
20.14 19.85 20.7918.08
11.7015.11 15.97
-17.72-18.31-17.12-14.01-14.74
-20.14-19.85-20.79
-18.08-11.70
-15.11-15.97
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
(BTU
/sq
ft)
Time of DayTable 3 System-April 21, 2021 WeatherPlant Load Energy Balance-Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft E cfm chg btu/ft2 Weather load btu/sqftExhaust btu/sqft Infil btu/sqft Plant load (btu/ft2)Plant Load Ein (btu/ft2) Plant Load Eout (btu/ft2)
Figure D: 24 Hour Energy Balance
Figure D gives the 24-hour energy balance for the two-systems illustrating the Table 3 system values is more than twice the Table 2 system.
Kirby Nelson P.E. 9
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
33.48 35.6317.76
61.27
22.86
-43.03-23.46-11.94
-92.59
11.47
-1.16
-102.87
-300
-250
-200
-150
-100
-50
0
50
100
24 H
our (
btu/
ft2)
24 hour sum-Table 2 System (btu/ft2)April 21, 2021 Weather-System Ein = Eout
lights (btu/ft2) Plug (btu/ft2) Fans (btu/ft2)Fuel or elect. heat (btu/ft2) People load btu/sqft Bld shell (btu/sqft)Exhaust btu/sqft Fresh air (btu/ft2) Plant load (btu/ft2)Plant kW (btu/ft2) Pump heat out btu/ft2 Tower btu/ft2 out
51.60 42.11 57.68
212.11
22.86 20.72
-81.62-62.16
9.01
-272.32
35.99
-1.80
-306.46-350
-300
-250
-200
-150
-100
-50
0
50
100
150
200
250
24 H
our (
btu/
ft2)
24 hour sum-Table 3 System (btu/ft2)April 21, 2021 Weather-System Ein = Eout
lights (btu/ft2) Plug (btu/ft2) Fans (btu/ft2)Fuel or elect. heat (btu/ft2) People load btu/sqft E cfm chg btu/ft2Bld shell (btu/sqft) Exhaust btu/sqft Fresh air (btu/ft2)Plant load (btu/ft2) Plant kW (btu/ft2) Pump heat out btu/ft2
Figure E: 24 Hour Summed Energy Balance
Figure E gives the 24-hour summed energy balance. These values offer the reader the opportunity to judge the 24-hour performance of a real system on this day and Figure D gives each hour energy balance.
Suggest reader visit. Anatomy of a Real Time Building Energy Model on this site gives (SEE) model analysis procedures.Stay tuned for more real weather days to be (SEE) modeled.Best Regards to AllKirby Nelson P.E.Life Member ASHRAE
NOMENCLATURE Each of the more than 200 variables are defined.
Building structure;BLD ft2 = air-conditioned space
Kirby Nelson P.E. 10
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
# 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 temperature.Air 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) exhausted
Kirby Nelson P.E. 11
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
VAV Fans Tret+FA = return and fresh air mix temperature (F)(dh) = VAV air static pressure (in)Efan-VSD = VAV fans efficiencyVAVinlet-sen-ton = sensible load (ton) inlet to VAV fansVAVinlet-lat-ton = latent load (ton) inlet to VAV fansTair-VAV = temp air to coils after VAV fan heat(FAN)VAV-CFM = CFM air thru coils(FAN)ton-VAV = load (ton) due to VAV fan kW(FAN)kW-VAV = total VAV fan kW demandAIR SIDE SYSTEM PLUS BUILDINGFAN kW = total air handlers kWSITE kW = total site or air side kWPlantton = (COIL)L+s ton load (ton) to plantCENTRAL PLANT# Buildings = number of buildings served by plantPlant ton = total load (ton) to plant Primary/secondary pumping nomenclaturegpmevap = total gpm flow thru one evaporators(H)pri-total = total primary pump head (ft) = (H)pri-pipe + (H)pri-
fittings + (H)pri-bp + (H)evap
(H)pri-pipe = primary pump head due to piping (ft)(H)pri-fittings = primary head due to pump & fitting (ft)(Ef)c-pump = efficiency of chiller pumpPc-heat-ton = chiller pump heat to atmosphere (ton)Pc-kW = one chiller pump kW demand (kW)Pchiller-# = number chiller pumps operating(lwt)evap = temperature water leaving evaporator (F)Tbp = temperature of water in bypass (F)gpmbp = gpm water flow in bypass(H)pri-bp = head if chiller pump flow in bypass (ft)(ewt)evap = temp water entering evaporator (F)Psec-heat-ton = secondary pump heat to atmosphere (ton)Psec-kW = kW demand of secondary pumpsEfdes-sec-p = design efficiency of secondary pumpingEfsec-pump = efficiency of secondary pumping(H)sec = secondary pump head (ft) = (H)sec-pipe + (H)sec-bp + (H)coil + (H)valve
(H)sec-pipe = secondary pump head due to pipe (ft)(H)sec-bp = head in bypass if gpmsec > gpmevap
GPMsec = water gpm flow in secondary loop(ewt)coil = water temperature entering coil (F)Pipesize-in = secondary pipe size (inches)(lwt)coil = temperature of water leaving coil (F)Evaporator(evap)ton = load (ton) on one evaporatorTER = evaporator refrigerant temp (F)TER-app = evaporator refrigerant approach (F)EVAPton = total evaporator loads (ton)(H)evap = pump head thru evaporator (ft)
(evap)ft/sec = velocity water flow thru evaporator(evap)des-ft/sec = evaporator design flow velocityCompressor:(chiller)kW = each chiller kW demand(chiller)lift = (TCR – TER) = chiller lift (F)(chiller)% = percent chiller motor is loaded(chiller)# = number chillers operating(CHILLER)kW = total plant chiller kW(chiller)kW/ton = chiller kW per evaporator tonPlant kW = total kW demand of plant(Plant)kW/site ton = Plant kW per site tonCondenser nomenclature:(cond)ton = load (ton) on one condenserTCR = temperature of condenser refrigerant (F)TCR-app = refrigerant approach temperature (F)(COND)ton = total load (ton) on all condensers(H)cond = tower pump head thru condenser (ft)(cond)ft/sec = tower water flow thru condenserTower piping nomenclaturePipesize-in = tower pipe size (inches)gpmT = each tower water flow (gpm)GPMT = total tower water flow (gpm)(H)T-total = total tower pump head (ft)PT-heat = pump heat to atmosphere (ton)PT-kW = each tower pump kW demandEfT-pump = tower pump efficiencyPtower # = number of tower pumps(H)T-pipe = total tower pump head (ft)(ewt)T = tower entering water temperature (F)(H)T-static = tower height static head (ft)Trange = tower range (F)= (ewt)T – (lwt)T
(lwt)T = tower leaving water temperature (F)Tapproach = (lwt)T – (Twet-bulb)Tower nomenclature
tfan-kW = kW demand of one tower fanTfan-kW = tower fan kW of fans ontfan-% = percent tower fan speedtton-ex = ton exhaust by one tower
T# = number of towers onTton-ex = ton exhaust by all towers onTrg+app = tower range + approach (F)One hour performance indicesBLDkW = kW demand of building lights & plug loadsFankW = air side fans kW, VAV, return terminalsDuctheat = perimeter heat to air supplyFAheat = heat added to fresh airHeattotal = total heat added to airPlantkW = total plant kWSystkW = total system kWCCWSkW = air side system + plant kW
Kirby Nelson P.E. 12
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA
ChillerkW/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 bl
Kirby Nelson P.E. 13
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL BENCHMARK DATA