SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL by Kirby Nelson P.E. · Web viewDesign Performance Page 2....
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E. Austin Texas Design, Benchmark, and/or analyze Office Building Performance At 24 Hours of Real Weather Contents 1. Design Performance Page 2 2. March 13, 2019 performance Page 9 1
Transcript of SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL by Kirby Nelson P.E. · Web viewDesign Performance Page 2....
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
Austin TexasDesign, Benchmark, and/or analyze
Office Building Performance At 24 Hours of Real Weather
Contents
1. Design Performance Page 22. March 13, 2019 performance Page 9
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
Benchmark, Judge, and/or analyze Office Building Performance over 24 hour period--Austin Texas The purpose of this paper is to give an understanding of how to benchmark, judge, and/or analyze the energy performance of office buildings for a given City. The plan is to give notice ahead of a given date for a given City so that building owners of that City can set up to measure their buildings energy consumption, over 24 hours, and compare it against the data given by this (SEE) Model. The reader should review (System Energy Equilibrium (SEE) Model Development, Verification & Real Weather Analysis of Office Buildings & Plants14). IntroductionAs stated in the Introduction14 a (SEE) plant model provides;
1. Plant design tool.2. Answers “Is the plant operating as designed”?3. Define why plant performance is substandard.4. Define plant control strategies.5. Define causes of plant degradation.6. Define upgrading or expansion of the plant.7. Model issues raised by technical publications.
The paper has shown that the plant model duplicates manufacturing data of Schwedler1, Trane19 and Marley2 and then applied those same principles of modeling to the model of a large office building defined by Pacific Northwest National laboratory, Liu8. The building (SEE) Model will, in this paper, illustrate the ability to evaluate the following building performance issues.
1. Design conditions & performance.2. Real weather performance3. Plant kW per plant load (ton).1. Chiller kW per evaporator load (ton).2. Energy balance analysis
This paper will present data per square foot so that readers can compare their buildings to the (SEE) Model analysis.First we must define the system as designed and performance at design conditions before we can evaluate the systems performance at real weather conditions.
THE STANDARD DESIGNED SYSTEM DEFINED
Figure 1: Building description
The building of this study is defined by the Pacific Northwest National Laboratory (PNNL) study of ASHRAE Standard 90.1-2010, (Liu 2011)8, a large 13 story office building, Figure 1. The (Liu 2011) study is based on an office building of 498, 600 square feet. The square feet here is increased for this (SEE) Model analysis so that the evaporator load is about 1000 ton for the Standard Design as is the case of Chapter 1 Model Verification14. A link to the (PNNL) study is given under references8. The building schedules and other details of the building, as defined by the (PNNL) study, are in this model design but the plant of this study is designed to a series of articles in the ASHRAE Journal, (Taylor 2011)7 and to GreenGuide6.The (SEE) Model can include any number of the buildings and design the central plant to meet the load. The plant model of this analysis assumes six buildings as defined by Figure 1 are served by the central plant. Min kW Design System DefinedThe building lights and plug loads are the same for the Standard Design & Min kW design. The Standard building kW Design includes infiltration as defined by the (PNNL) study of ASHRAE Standard 90.1-2010, and also includes return air fans and fan powered terminals as part of the air handler system. The min kW design building pressurizes the building resulting in exfiltration
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Building 13 Story603,000 Ft-Sq
Building height=169 FtRoof = 46,385 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=193.3 Ft West=193.3 Ft
Each Wall=32,663 Ft-Sq
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.providing for the elimination of return air fans and also modifies the fan system to eliminate the fan powered terminals from the air supply system. The heating system of the min kW design also has changes that minimize perimeter heat that will be demonstrated. The result of these air side system modifications provides a significant reduction in total system kW as will be shown. Most of the data provided by this chapter is in watts per square foot and btu per square foot so that the reader can judge existing building systems against the ASHRAE Standard 90.1-2010 design given here.
0.88 0.84 0.80 0.93
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Figure 2: Design weather Day & system performance
Figure 2 gives the assumed summer design day conditions and the system energy use per square foot of building. The min kW design has a significantly less energy use to be further defined below.
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(plant)W/sq-ft Electric heat (W/sq-ft)
Figure 3: 24 hour performance-Design day Figures 2 & 3 gives the 24 hour performance of the two systems. The building watts per square foot is due to the lights and plug loads and is the same for both designs. The difference in fan system performance is due to the pressurization of the min kW design building and the resultant removal of the return fans and fan powered terminals. This results in less load to the plant and therefore the plant watts per square foot is less with the min kW design. Figure 4 illustrates that the site
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.watt/sq ft plus the plant watt/sq ft equals the system watt/sq ft.
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Site watts/sg-ft (plant)watt/sq-ft System watts/sq-ft
Figure 4: 24 hour performance-Design day
Figure 3 shows the perimeter and fresh air heat as zero for these design conditions, however this value will become significant during winter real weather conditions. The system watt/sq ft is shown on the secondary horizontal axis of Figure 3 which is the sum of the building, plant, and fan system values plus the electric heat illustrating a significant reduction with the min kW design.
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Figure 5: Summed 24 hour watt/sq ft-Design day
Figure 5 sums the values given by Figures 3 & 4. The building watt/sq ft is the same for both designs as defined by Liu8. The big difference is in the reduction of air handler system kW demand for the min kW design (see Chapter 1714) followed by the reduction in plant electrical demand due to less load but also due to the low lift chiller design of the min kW plant. The above provides the reader the ability to compare an as designed system to the ASHRAE Standard 90.1-2010 Large Office as modeled by Pacific Northwest National Laboratory8. Next we will provide system performance & indices data of the two systems at design day conditions.
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.Chiller/Tower Performance Figure 6 & 7 give (SEE) Model data that can be compared to real chiller data to arrive at conclusions regarding the design performance of the real chiller.
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Evap refrig (Ter) Cond refrig (Tcr)# Chiller/Towers on Evap leaving water (F)Condenser leaving water (F)
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Evap refrig (Ter) Cond refrig (Tcr)# Chiller/Towers on Evap leaving water (F)Condenser leaving water (F)
Figure 6: Chiller performance-Design dayThe condenser refrigerant temperature of the Standard Design, top chart of Figure 6, is generally greater than the min kW design, bottom chart, and therefore chiller lift is greater for the Standard Design. Chiller lift is the condenser refrigerant temperature (Tcr) minus the evaporator refrigerant temperature (Ter).
Tower Performance Figure 7 provides (SEE) Model data of the tower performance giving tower water temperatures, tower approach to wet bulb, and % tower fan speed.
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ater
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Wet Bulb Temp. (F)Std Design-design weather-Tower performance-high lift chiller
(ewt)tower (F) (lwt)tower (F) Tower approach (F) Tower % fan speed
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ater
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(ewt)tower (F) (lwt)tower (F) Tower approach (F) Tower % fan speed
Figure 7: Tower performance-Design dayThe Standard Design generally has a higher tower entering water temperature (ewt) as discussed in Chapter 914, resulting in increased chiller lift and therefore increased chiller kW. Tower water temperature approach to wet bulb temperature is given by both charts and illustrates at design conditions, where the min kW tower speed is 100%, the approach is about half that of the Standard Design, top chart. Operating the min kW tower at 67% speed minimizes plant kW as discussed in Chapter 914.
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E. Plant & Chiller Performance Indices at design day conditions
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on
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High lift chiller plant (kW/plant ton)& Std kW BldLow lift chiller plant (kW/plant ton) & min kW Bld
Figure 8: Chiller & Plant kW/ton
Figure 8 compares the two designs plant & chiller performance at design day conditions of Figure 2 illustrating the improved performance of the low lift chiller design plant operating at 67% tower fan speed verses the high lift chiller plant as called for by GreenGuide6 & Taylor7.
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.Plant Load Energy Balance-Design Day
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Weather load btu/sqft Plant load (btu/ft2)
Figure 9: Plant load energy balance-design conditions.
Figure 9 gives the plant load energy balance for both designs at design weather conditions. The top chart, Standard Design, shows a plant and the other seven loads add up to this plant load value i.e. energy in, the seven loads, equals energy out, the plant load. Similarly for the bottom chart min kW design. The weather energy into the top chart is more than the bottom chart because of infiltration for the Standard Design and exfiltration for the min kW Design. The values of Figure 9 can be measured or estimated to give an understanding of the building energy effectiveness at real weather conditions. The weather load is a measure of the building design with regard to weather. Therefore measuring or estimating the other components of Figure 9 provides an estimate of the buildings effectiveness against weather.
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Figure 10: 24 Hour Plant load Energy Balance-Design day
Figure 10 illustrates the hourly plant energy balance for both systems. The Standard design, top chart, has one component of energy out, air handler exhaust. The min kW design, bottom chart, has air handler exhaust plus exfiltration as energy out components. The plant load is greater for the Standard design for all hours.
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.System energy in = Energy out
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2)
Min kW Design-Design Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect heat (btu/ft2)People load btu/sqft Exfil btu/sqft Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out
Figure 11: System Ein = Eout-design weather conditions
Figure 11 illustrates the (SEE) Model requirement of system Energy in = Energy out. Ten energy components make up the energy balance as shown by Figure 11. Energy into the system primarily consists of the building plus fan system electrical demand, or site btu/ft2, plus the weather energy into the system. The cooling tower removes most of the energy from the system followed by air handler exhaust. Pump heat not going into the thermodynamic system is a relatively small value.
1.2 1.2 1.2 1.3 3.5 5.0 5.0 5.0 5.0 2.8 1.9 1.61.0 0.9 0.9 1.01.6 2.3 2.4 2.8 3.1
1.7 1.3 1.11.9 1.5 1.3 2.1
7.08.5 9.0 10.5 11.2
9.15.0 2.9
-4.9 -4.2 -3.9 -5.2
-12.9-19.2 -19.9 -22.2 -23.4
-15.0-9.4 -6.5
-5.3 -4.6 -4.3 -5.6
-14.9
-21.7 -22.5-24.8 -26.0
-17.0
-10.3-7.2
5.3 4.6 4.3 5.6
14.9
21.7 22.524.8 26.0
17.0
10.37.2
-30-25-20-15-10
-505
1015202530
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Standard Design-Design Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out Energy out (btu/ft2) Energy in (btu/ft2)
1.2 1.2 1.2 1.3 3.5 5.0 5.0 5.0 5.0 2.8 1.9 1.60.1 0.1 0.1 0.20.5
0.9 0.9 1.2 1.30.5 0.3 0.21.8 1.4 1.2 2.1
6.2
7.7 8.2 9.6 10.2
8.14.1 2.1
-3.4 -2.8 -2.6 -3.8
-10.7-16.3 -16.9 -18.9 -20.0
-12.5-7.2 -4.5
-3.8 -3.2 -2.9 -4.2
-12.2
-18.5 -19.1-21.1 -22.1
-14.1
-7.7-4.9
3.8 3.2 2.9 4.2
12.2
18.5 19.121.1 22.1
14.1
7.74.9
-25
-20
-15
-10
-5
0
5
10
15
20
25
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Min kW Design-Design Weather-System Ein = Eout
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 Exfil btu/sqft Pump heat out btu/ft2Tower btu/ft2 out Energy out (btu/ft2) Energy in (btu/ft2)
Figure 12: 24 hour Energy Balance-Design Day
Figure 12 gives the system hourly energy balance illustrating the hourly advantage of the min kW design over the Standard design. If the reader has design data for a real system, the values at peak conditions provide a way to judge the real design. Next we will consider real weather operation.
8
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
Austin Texas Real Weather Performance- March 13, 2019This real weather analysis will be for the Standard design and min kW design as given above plus a third system that is defined as the Standard system design with bad control. Go to the Orlando Florida real weather analysis as part of this blog to review the bad control issues one at a time. This study will give the net result of the bad controls input to the (SEE) Model.
90.086.0 84.0
80.088.0
94.098.0 100.0102.0
98.0 95.0 93.0
73.0 72.0 71.0 71.0 72.0 73.0 74.0 75.0 75.0 75.0 74.0 74.0
69.0 70.0 71.073.0
56.0 57.0
63.0
73.0
82.0 82.0
76.0
71.0
67.0 68.0 68.0 67.0
54.0 53.0
59.062.0
64.0 63.0 62.0 62.0
50
60
70
80
90
100
110
0
10
20
30
40
50
60
70
80
90
100
110
(% clear sky-real)
Real
Tem
pera
ture
(F)
Desi
gn D
ay Te
mpe
ratu
res
(F)
%clear sky-Design dayDesign Day & real weather temperatures
Dry Bulb-Design Day (F) Wet Bulb-Design Day (F)
Dry Bulb-Winter day (F) Wet Bulb-Winter day (F)
Figure 13: Design & Real weather
Figure 13 gives the assumed design day weather and the real winter weather of March 8, 201920, a day that requires building perimeter heat and therefore represents a major change in the system performance, energy consumption, and energy balance of the systems.
Figure 14 gives the 24 hour energy use per square foot for the all-electric system and Figure 15 for the system with fuel heat. The difference in electric use of Figure 14 to the top chart of Figure 15 is the fuel heat of the bottom chart of Figure 15. The fuel heat of the bottom chart is the energy going into the thermodynamic system and therefore does not comprehend boiler efficiency. Therefore the net fuel consumed will be 10% to 20% more than bottom chart of Figure 15.
29.810
39.124
56.776
0
10
20
30
40
50
60
70
80
90
100
24 h
our (
watt
hr/
sq ft
)
24 Hour System watt hours/sq ft with electric heat
Min kW Bld & plant-Real weather Std Bld & Plant-Real weather
Std kW design-real weather-poor control
Figure 14: Real weather 24 hour watt-hour per square foot for min kW design, Standard design, & Standard design with bad light, stat, infiltration, heating air temperature control, plus VAV static pressure min set at 5.5 inches of water-see Orlando study.
27.978
35.961
49.644
0
10
20
30
40
50
60
70
24 h
our (
watt
hr/
sq ft
)
24 hour System watt hours/sq ft with fuel heat
Min kW Bld & plant-Real weather Std Bld & Plant-Real weather
Std kW design-poor control
6.254 10.797
24.340
0102030405060708090
100110120130140
24 h
our (
btu/
sq ft
)
Duct fuel heat btu/sq ft
min kW Bld & plant-Real weather Std Bld & Plant-Real weather
Std kW design-poor control
9
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.Figure 15: Real weather watt-hour per square foot-top chart electric use, bottom chart fuel heat use Figures 14 & 15 give 24 hour data that the reader can use to judge-benchmark a real building in Atlanta on a day when the weather is similar to Figure 13. A study of the other papers of this blog is recommended, especially the paper that verifies the (SEE) model, System Energy Equilibrium (SEE) Model Development, Verification & Real Weather Analysis of Office Buildings & Plants14.
0.57 0.54 0.51 0.49
1.60
2.121.93
2.29 2.34
1.14
0.73 0.64
0.92 0.860.71 0.77
2.282.91
2.27
2.70 2.78
1.47
1.020.86
2.19 2.10 2.021.85
3.263.06
2.55
2.93 3.03
1.841.57
1.99
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
% clear sky
Watt
s/sq
ft
Watt
s/sq
ft
TIME of DAYSystem watts/sq ft at real weather conditions-Electric Heat
Min kW System (watt/sqft) Std Design System (watt/sqft))Std System-bad control (watt/sqft)
0.11 0.09 0.060.00
0.24
0.00 0.00 0.00 0.00 0.00 0.05
0.480.41
0.34
0.21
1.26
0.00 0.00 0.00 0.00 0.00
0.35
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
% clear sky
Watt
s/sq
ft
Watt
s/sq
ft
TIME of DAYDuct watts/sq ft at real weather conditions-Electric Heat
Min kW System (watt/sqft) Std Design System (watt/sqft))Std System-bad control (watt/sqft)
Figure 16: Real weather 24 hour watt-hour per square foot for min kW design, Standard design, & Standard design with bad control-Top chart is total electric use & bottom chart is heat electric use.
0.45 0.45 0.45 0.49
1.23
1.88 1.93
2.29 2.34
1.14
0.730.60
0.74 0.74 0.71 0.77
1.59
2.32 2.27
2.70 2.78
1.47
1.020.86
1.71 1.69 1.68 1.64
2.00
2.54 2.55
2.93 3.03
1.841.57 1.64
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Watt
s/sq
ft
Watt
s/sq
ft
TIME of DAYSystem watts/sq ft at real weather conditions-Fuel heat
Min kW System (watt/sqft) Std Design System (watt/sqft))
Std System bad control (watt/sqft)
0.39 0.30 0.210.00
1.25
0.00 0.000.16
1.631.40
1.17
0.72
4.30
1.77
0.00 0.00 0.00 0.00 0.00
1.19
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
(btu
/sqft
)
(btu
/sqft
)
TIME of DAYSystem btu/sq ft at real weather conditions-Fuel heat
Min kW System-Duct (btu/sqft) Std System-bad control-Duct (btu/sqft)
Std Design System-Duct (btu/sqft))
Figure 17: : Real weather 24 hour watt-hour per square foot for min kW design, Standard design, & Standard design with bad control-Top chart is electric use & bottom chart is btu of fuel use.
Figures 16 & 17 give the hourly values for the three systems at real weather conditions.
10
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
20.249
2.7874.942
1.832
29.810
0
10
20
30
40
24 h
our w
att-h
r/sq
ft
24 hour total -Minimum kW System-Electric heat-Real weather
(Bld)W/sg-ft (AHU)Fan W/sq-ft
(plant)W/sq-ft Total elect heat (W/sq-ft)
(System)W/sq-ft
20.249
9.098 6.6133.164
39.124
0
10
20
30
40
50
60
70
80
24 h
our w
att-h
r/sq
ft
24 hour total -Standard design System-Electric heat-Real weather
(Bld)W/sg-ft (AHU)Fan W/sq-ft
(plant)W/sq-ft Total elect heat (W/sq-ft)
(System)W/sq-ft
25.559
14.7189.367 7.132
56.776
0102030405060708090
100
24 h
our w
att-h
r/sq
ft
24 hour total -Standard design System-Electric heatBad control-Real weather
(Bld)W/sg-ft (AHU)Fan W/sq-ft
(plant)W/sq-ft Total elect heat (W/sq-ft)
(System)W/sq-ft
Figure 18: 24 hour summed values-Electric heat
Figures 18 & 19 offer an opportunity to judge/benchmark an all-electric system, Figure 18, or a fuel heat system, Figure 19, over 24 hours at the real weather defined by Figure 13.
20.249
2.7876.254 4.942
27.978
0
10
20
30
40
50
60
70
80
24 h
our (
watt
hr/
sq ft
)-or b
tu/s
q ft
24 Hour total-Min kWSystem-watt hours/sq ft with fuel heat (btu/sqft)-
Building watt-hr/sqft Air handler system watt-hr/sqftFuel heat-btu/sqft Plant watt-hr/sqftSystem watt-hr/sqft
20.249
9.098 10.7976.613
35.961
0
10
20
30
40
50
60
70
80
90
100
24 h
our (
watt
hr/
sq ft
)-and
btu
/sq
ft
24 Hour-Standard Bld & Plant-Fuel Heat-Real Weather
Building watt-hr/sqft Air handler system watt-hr/sqftFuel heat-btu/sqft Plant watt-hr/sqftSystem watt-hr/sqft
25.55914.718
24.340
9.367
49.644
0102030405060708090
100110120130140
24 h
our (
watt
hr/
sq ft
)-and
btu
/sq
ft
24 Hour-Standard Bld & Plant-Fuel Heat-Real Weather-Bad control
Building watt-hr/sqft Air handler system watt-hr/sqftFuel heat-btu/sqft Plant watt-hr/sqftSystem watt-hr/sqft
Figure 19: 24 hour summed values-Fuel heat
11
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
69.11
9.51 6.2522.86
-6.44-18.66
26.26
-108.90
-150
-100
-50
0
50
100
24 H
our (
btu/
hr-ft
2)
Min kW Design-Real Weather-Plant load-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect heat (btu/ft2)
People load btu/sqft Exfil btu/sqft Exhaust btu/sqft
Weather load btu/sqft Plant load (btu/ft2)
69.11
31.0510.80
22.866.32
-32.45
25.96
-133.66
-150
-100
-50
0
50
100
150
24 H
our (
btu/
hr-ft
2)
Standard Design-Real Weather-Plant load-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqft
Weather load btu/sqft Plant load (btu/ft2)
87.23
50.2324.34 22.86 12.87
-40.66
30.33
-187.20
-250
-200
-150
-100
-50
0
50
100
150
24 H
our (
btu/
hr-ft
2)
Standard Design-Bad control-Real Weather-Plant load-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqft
Weather load btu/sqft Plant load (btu/ft2)
Figure 20: 24 Hour Plant load Energy Balance
Figures 20 & 21 provide Energy in = Energy out data where energy out is the plant load. Each of these loads can be measured or estimated and therefore give a judgement of the performance of a real system as it compares to ASHRAE Standard 90.1-20108.
1.2 1.2 1.2 1.33.5
5.0 5.0 5.0 5.02.8 1.9 1.6
0.13 0.00 0.00 0.00
0.50
2.392.39 2.39 2.39
0.750.25 0.25
-0.03 -0.03 -0.03 -0.03 -1.14 -1.69 -1.68 -1.62 -1.63 -1.22 -0.22 -0.03
0.13 0.26 0.32 0.40
-1.00 -0.74
0.83
4.24 5.00
2.91
0.75 0.031.6 1.5 1.5 1.5
3.1
6.16.9
10.911.6
5.3
2.61.9
-4-3-2-10123456789
1011121314
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Min kW Design-Real Weather-Plant load-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft Exhaust btu/sqft Weather load btu/sqft
Exfil btu/sqft Plant load (btu/ft2)
1.2 1.2 1.2 1.33.5
5.0 5.0 5.0 5.02.8 1.9 1.6
0.9 0.9 0.9 0.9
1.7 1.5 2.2 2.2
1.21.0 0.9
2.392.39 2.39
-0.39 -0.36 -0.38 -0.35-1.76 -2.38 -2.46 -2.39 -2.39 -1.91 -0.83 -0.62
0.1 0.2 0.3 0.3
-1.3 -1.0
0.8
4.4 5.2
3.1
0.90.1
2.73 2.55 2.15 2.42
4.75
8.00 7.55
11.8612.73
6.14
3.432.53
-5-4-3-2-10123456789
10111213
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Standard Design-Real Weather-Plant load-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqft
Weather load btu/sqft Plant load (btu/ft2)
2.8 2.8 2.8 2.8 3.55.0 5.0 5.0 5.0
3.1 2.8 2.8
1.8 1.8 1.7 1.72.2
2.4 2.3 2.8 2.9
1.9 1.7 1.8
2.39 2.39 2.39
-0.77 -0.74 -0.74 -0.73-2.18 -2.60 -2.73 -2.62 -2.61 -2.41 -1.23 -0.98
0.5 0.6 0.7 0.7
-1.7 -1.2
0.9
4.6 5.6
3.2
1.00.2
6.66 6.43 6.25 5.797.21
8.32 8.42
12.7213.71
7.15
5.075.88
-6-5-4-3-2-10123456789
1011121314
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Standard Design-Bad control-Real Weather-Plant load-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)
People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqft
Weather load btu/sqft Plant load (btu/ft2)
Figure 21: Hourly Plant Load Energy Balance
12
SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
69.11
9.51 6.2522.86
-6.44-18.66
26.2616.87
-1.01
-124.76
-150
-100
-50
0
50
100
24 H
our (
btu/
hr-ft
2)
Min kW Design-Real Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect heat (btu/ft2)People load btu/sqft Exfil btu/sqft Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out
69.11
31.0510.80 22.86
6.32
-32.45
25.96 22.57
-1.27
-154.97
-200
-150
-100
-50
0
50
100
150
24 H
our (
btu/
hr-ft
2)
Standard Design-Real Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out
87.2350.23
24.34 22.86 12.87
-40.66
30.33 31.97
-1.40
-217.78
-300
-250
-200
-150
-100
-50
0
50
100
150
24 H
our (
btu/
hr-ft
2)
Standard Design-Bad control-Real Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out
Figure 22: Total System 24 Hour Energy Balance
Figures 22 & 23 provide total system Energy in = Energy out data. Each of these loads can be measured or estimated and therefore give a judgement/benchmark of the performance of a real system at real weather conditions of Figure 13 as it compares to ASHRAE Standard 90.1-20108.
1.2 1.2 1.2 1.3 3.5 5.0 5.0 5.0 5.0 2.8 1.9 1.60.1 0.1 0.1 0.10.3
0.6 0.6 1.1 1.10.3 0.2 0.10.1 0.3 0.3 0.4
-1.0 -0.7
0.84.2 5.0
2.90.8 0.0
-1.9 -1.8 -1.8 -1.8-3.5
-6.9 -7.8-12.5 -13.4
-6.0-3.0 -2.1
-2.2 -2.1 -2.1 -2.1
-6.0
-9.6 -9.8
-14.4 -15.4
-7.6
-3.5 -2.5
2.2 2.1 2.1 2.1
6.0
9.6 9.8
14.4 15.4
7.6
3.5 2.5
-18-17-16-15-14-13-12-11-10-9-8-7-6-5-4-3-2-10123456789
101112131415161718
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Min kW Design-Real Weather-System Ein = Eout
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 Exfil btu/sqft Pump heat out btu/ft2Tower btu/ft2 out Energy out (btu/ft2) Energy in (btu/ft2)
1.2 1.2 1.2 1.3 3.5 5.0 5.0 5.0 5.0 2.8 1.9 1.60.9 0.9 0.9 0.91.3
1.7 1.5 2.2 2.21.2 1.0 0.90.6 0.4 0.0 0.0
2.32.0 0.0 0.0 0.0
0.0 0.0 0.0
-3.2
-3.0
-2.5
-2.8
-5.4
-9.1 -8
.7
-13.
8
-14.
9
-7.1 -4
.0 -2.9
-3.6 -3.4 -2.9 -3.2
-8.6
-12.6 -11.2
-16.2 -17.3
-9.1
-4.9 -3.6
3.6 3.4 2.9 3.2
8.6
12.6 11.2
16.2 17.3
9.1
4.9 3.6
-20
-15
-10
-5
0
5
10
15
20
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Standard Design-Real Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out Energy out (btu/ft2) Energy in (btu/ft2)
2.8 2.8 2.8 2.8 3.5 5.0 5.0 5.0 5.0 3.1 2.8 2.81.8 1.8 1.7 1.7 2.2
2.4 2.3 2.8 2.91.9 1.7 1.8
1.6 1.4 1.2 0.74.3 1.8 0.0 0.0 0.0
0.0 0.0 1.2
-7.8
-7.5
-7.3
-6.8
-8.3
-9.5 -9.7
-14.
8
-16.
1 -8.4 -5
.9
-6.8
-8.6 -8.3 -8.1 -7.6
-12.2 -13.3 -12.5
-17.5 -18.8
-10.8
-7.2 -7.9
8.6 8.3 8.1 7.6
12.2 13.3 12.5
17.5 18.8
10.8
7.2 7.9
-20
-15
-10
-5
0
5
10
15
20
MN 2AM 4AM 6AM 8AM 10AM NOON 2PM 4PM 6PM 8PM 10PM
(btu
/hr)
Time of Day
Standard Design-Bad control-Real Weather-System Ein = Eout
light & plug btu/ft2 Fans (btu/ft2) Fuel or elect. heat (btu/ft2)People load btu/sqft E cfm chg btu/ft2 Exhaust btu/sqftWeather load btu/sqft Plant kW btu/ft2 Pump heat out btu/ft2Tower btu/ft2 out Energy out (btu/ft2) Energy in (btu/ft2)
Figure 23: Total System Hourly Energy Balance
Review of, System Energy Equilibrium (SEE) Model Development, Verification & Real Weather Analysis of Office Buildings & Plants14 is recommended by the author.Other days will be modeled so stay tuned in to http://kirbynelsonpe.com .
Best Regard,Kirby Nelson PELife Member ASHRAE
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.
Final WordIn the July 201410 ASHRAE Journal under letters; Pete Menconi P.E. makes the point; “I used my first building simulation in 1973, and have used a variety of methods and on-site comparisons. In general, I’ve found typical +/- 50% variance between simulation and actual energy.”Peter Rumsey P.E. responds; “In my experience I have found the same thing.” “My experience after having modeled and measured dozens of buildings is that models do not accurately capture system performance.”
The author of this paper was modeling buildings of Texas Instruments Inc. in 1974 using DOE and ECUBE. These two programs could rack up the total electrical use for a year if you input the schedule, and could also do a fair job at simulating the loads due to weather. However the models could not accurately simulate the air side system or the plant performance. Sure the models had inputs for the air side and plant but system models they were not.In the late 1970’s some of us made the argument for ASHRAE models based on the equations of thermodynamics, but the decision was made to stick with the DOE approach and that is where we are today. DOE is the basis of eQUEST and Energy Pro as stated by Rumsey. The reason these DOE based models have not, cannot, and will not in the future model building energy is given on page 70 of the July 2014 ASHRAE Journal. The article (Improving Infiltration in Energy Modeling) makes the obvious but not stated point; 40 years after the oil embargo that an air side model is still not in the ASHRAE and Pacific Northwest National Laboratory (PNNL) accepted energy models. The article also clearly illustrates why; empirical equations with several coefficients that have no relation to the laws of thermodynamics can never accurately model a real system. A real system operates according to the laws of thermodynamics and therefore so must our models.
The hypothesis of energy conservation (first law) was established by J.P. Joule in the 1840’s. For the past 170 years the first law has provided easy to understand relations that define the performance of thermodynamic systems. Is it not time for all to admit we have been on the wrong modeling path for more than 40 years?Kirby Nelson11 P.E.ASHRAE life memberReferences:
1. Schwedler, Mick. July 1998 “Take It to The Limit…Or Just Halfway?” ASHRAE Journal.
2. SPX Cooling Technologies (Marley). UPDATE Version 5.4.2
3. Introduction to Thermodynamics and Heat Transfer. 1956 Prentice-Hall, Inc. by David A. Mooney, page 325.
4. Thermal Environmental Engineering third edition. 1998 Prentice-Hall Inc. by Thomas H. Kuehn, chapter 3.
5. 2012 ASHRAE HANDBOOK, HVAC Systems and Equipment, page 43.10 Figure 11 Temperature Relations in a Typical Centrifugal Liquid Chiller.
6. ASHRAE. 2010. ASHRAE GreenGuide: The Design, Construction, and Operation of Sustainable Buildings, 3rd ed. Atlanta: ASHRAE.
7. Taylor, S. 2011. “Optimizing design & control of chiller plants.” ASHRAE Journal (12).
8. Liu, B. May 2011. “Achieving the 30% Goal: Energy and Cost Savings Analysis of ASHRAE Standard 90.1-
2010” Pacific Northwest National Laboratory. http://www.energycodes.gov/achieving-30-goal-energy-and-cost-savings-analysis-ashrae-standard-90.1-2010 9. Schwedler, M. 2017. “Using Low-Load
Chillers to Improve System Efficiency.” ASHRAE Journal.
10. July 2014 ASHRAE Journal, page 70. The article (Improving Infiltration in Energy Modeling) makes the obvious but not stated point; 40 years after the oil embargo and an air side model is still not in the ASHRAE models.
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.11. ASHRAE Journal September 2014.
Letters, “Energy Modeling”, by Kirby Nelson
12. ASHRAE Journal May 2016. “Modeled Performance Isn’t Actual Performance”
13. Nelson, K. “Simulation Modeling of a Central Chiller Plant” CH-12-002. ASHRAE 2012 Chicago Winter Transactions.
14. Nelson, K. System Energy Equilibrium (SEE) Building Energy Model Verification. http://kirbynelsonpe.com/
15. Tredinnick, Steve. 2015. “District Energy Enters The 21st Century”. ASHRAE Journal.
16. Morrison, Frank. 2014. “Saving energy with cooling towers.” ASHRAE Journal
17. Kavanaugh, Steve. June 2000 “Fan Demand and Energy” ASHRAE Journal
18. Nelson, Kirby. July 2010 “Central-Chiller-Plant Modeling” HPAC Engineering
19. Trane chiller selection data received by Kirby Nelson from Springfield Missouri Trane office 1/30/01.
20. Real weather data www.wunderground.com/
NOMENCLATURE Each of the more than 200 variables will be defined.Building structure;BLD ft2 = air conditioned space# Floors = number of building floorsRoof ft2 = roof square feetN/S wall ft2 =north/south wall square feetE/W wall ft2 =east/west wall square feetWall % glass = percent of each wall that is glassGlass U = glass heat transfer coefficientWall U = wall heat transfer coefficientGlass SHGC = glass solar heat gain coefficientWall emit = wall solar indexBuilding interior space;Rooftrans-ton =transmission through roof (ton)Roofsky-lite-ton =sky lite load (ton)Peopleton sen&lat = sensible & latent cooling load due to people (ton)Plugton&kW = cooling load & kW due to plug loadsLightton&kW = cooling load & kW due to lightsTotal Bldint-ton = total building interior load (ton)(int-cfm) to-per-return = CFM of interior supply air that returns to perimeter of building
Tstat-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)
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.(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(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 nomenclature
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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.Pipesize-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 kW
CCWSkW = 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 bl
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18BENCHMARKING BUILDING ENERGY
SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL by Kirby Nelson P.E.
