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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.

ORLANDO FLORIDA Design, Benchmark, Judge,

and/or analyze Office Building Performance

At Real Weather Condition, Contents

1. Design Performance Page 22. February 26, 2019 performance Page 9

1


Benchmark, Judge, and/or analyze Office Building Performance, Orlando Florida 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. This data is for Orlando Florida. 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, with 582,000 square feet of air conditioned space. 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 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

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Building 13 Story582,000 Ft-Sq

Building height=169 FtRoof = 44,769 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=186.54 Ft West=186.54 Ft

Each Wall=31,525 Ft-Sq

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.as part of the air handler system. The min kW design building pressurizes the building resulting in exfiltration 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.

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System (watt/sqft) Dry Bulb (F) Wet Bulb (F)

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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(Bld)W/sg-ft (AHU)Fan W/sq-ft(plant)W/sq-ft Elect heat (W/sq-ft)

0.337

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Time of dayMin kW low lift chiller Plant & Building-Design weather-fuel heat

(Bld)W/sg-ft (AHU)Fan W/sq-ft (plant)W/sq-ft Gas heat (btu/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

3

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.with the min kW design. Figure 4 illustrates that the site watt/sq ft plus the plant watt/sq ft equals the system watt/sq ft.

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0.37

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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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Building Air handler system Electric heat Plant System

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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. Approach (F)Standard Design-design weather-Plant performance-High lift chiller

Evap refrig (Ter) Cond refrig (Tcr)# Chiller/Towers on Evap leaving water (F)Condenser leaving water (F)

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Evap. Refrig. Approach (F)Min kW Design-design weather-Plant performance-low lift chiller

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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(ewt)tower (F) (lwt)tower (F) Tower approach (F) Tower % fan speed

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Wet Bulb Temp. (F)Min kW Design-design weather-Tower performance-low lift chiller

(ewt)tower (F) (lwt)tower (F) Tower approach (F) Tower % fan speed

Figure 7: Tower performance-Design day

The 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.

5

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E. Plant & Chiller Performance Indices at design day conditions

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min kW design plant (ton)

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on

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Chiller kW/evap ton-Design day weather

High lift chiller plant (kW/plant ton)& Std kW BldLow lift chiller plant (kW/plant ton) & min kW Bld

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Plant kW/plant ton-Design day weather

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 8 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.

Plant Energy Balance-Design Day

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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

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light & plug btu/ft2 Fans (btu/ft2) Fuel or elect heat (btu/ft2)

People load btu/sqft Exfil btu/sqft Exhaust btu/sqft


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 load of 239.09 btu/sqft. 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.

6


1.2 1.2 1.2 1.33.5 5.0 5.0 5.0 5.0

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Exfil btu/sqft Plant load (btu/ft2)

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.

7

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.System energy in = Energy out

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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.

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7.2 8.1 10.2 12.2

9.65.2 2.9

-4.7 -4.1 -3.8 -5.3-11.7

-17.2 -18.4 -21.5 -24.4-15.6

-9.6 -6.5-5.2 -4.5 -4.2 -5.7

-13.6

-19.8 -21.0-24.1

-27.0

-17.7

-10.5-7.2

5.2 4.5 4.2 5.7

13.6

19.8 21.024.1

27.0

17.7

10.57.2

-30-25-20-15-10

-505

1015202530


(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 0.20.4

0.8 0.8 1.0 1.20.5 0.3 0.21.6 1.4 1.2 2.1

5.4

6.4 7.3 9.2 11.1

8.54.1 2.0

-3.2 -2.8 -2.5 -3.8-9.6

-14.6 -15.7 -18.3 -20.9

-12.9-7.2 -4.4

-3.6 -3.1 -2.9 -4.2

-11.2

-16.8 -17.9-20.5

-23.1

-14.6

-7.7-4.8

3.6 3.1 2.9 4.2

11.2

16.8 17.920.5

23.1

14.6

7.74.8

-25

-20

-15

-10

-5

0

5

10

15

20

25


(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 Long Beach at real weather of December 10, 2018.

8


Orlando Real Weather Performance- February 26, 2019

This 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. The bad control issues will be installed into the model one at a time so that the effect of each can be illustrated. Each bad control issue will be added to the previous installed bad control issues building to a bad controlled system. The first bad control will be manual control of lights.

88.0 86.0 84.0 82.0 80.086.0

90.094.0 96.8 94.0 92.0 90.0

65.4 64.0 62.6 61.1 63.0 66.0 67.0 69.0 71.0 69.6 68.2 66.8

55.0 55.0 55.0 55.0 56.0 57.0 56.0 56.059.0 57.0 57.0

53.0

54.0 54.0 54.0 54.0 54.0 54.0 54.0 54.0 54.0 53.0 53.0 52.0

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

(% clear sky-winter)

Win

ter t

empe

ratu

res (

F)

Desi

gn D

ay Te

mpe

ratu

res

(F)

%clear sky-Design dayDesign Day & real winter temperatures (F)-Dec. 10, 2018

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 of Feb. 26, 2019

Figure 13 gives the assumed design day weather and the real winter weather of February 26, 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. The first bad control will be;

1. LIGHTS-The lights are manually controlled i.e. depending on people to turn lights off. This procedure sometimes works well for a few months but usually degenerates. This analysis will assume that 67% of lights are on after hour’s verses 6% for the standard design8 with good control.

32.683

43.882 43.882

0

10

20

30

40

50

60

70

80

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

32.683

43.88250.910

0

10

20

30

40

50

60

70

80

24 h

our (

watt

hr/

sq ft

)




Figure 14: 24 Hour watt hours per building square foot-min kW design-Standard design-& Standard design with bad control of (1. LIGHTS), bottom chart. Top chart illustrates the same values for the Std design.

Figure 14 gives the 24 hour watts hours per building square foot illustrating the min kW design is about 25% less than the Standard Design building & plant & the Standard design with bad light control of (1. LIGHTS), bottom chart is about 16% greater than the Standard design.

9


Figure 15 gives the 24 hour sum of the main four components of energy consumption, building, air handler system, electric heat, and plant. The sum of the four components is also given. The building use per building square foot is due to lights and plug loads and is the same for the min kW design & Standard design but increases with bad manual control of lights as shown by the bottom chart. The min kW design air handler energy use, plant energy use, and electrical heat energy use are all significantly less than the Standard design and the bad light controls further increases these three components over the Standard design. The electrical energy for heat is less for the min kW design primarily because the heat supply air is 110F verses 94F for the Standard design. Heat energy is the same for the Standard design and the Standard design with bad light control.

20.249

2.9625.572 3.900

32.683

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

9.462 7.572 6.598

43.882

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

10.013 6.598 8.740

50.910

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-ftTotal elect heat (W/sq-ft) (plant)W/sq-ft(System)W/sq-ft

Figure 15: 24 hour energy use summed-all electric system at real weather conditions-top chart min kW design-middle chart Standard design-bottom chart Bad light control of Standard design.

10


0.337

1.467

0.37

0.347

0.000

0.79

0.79

0.85

0.84

1.26

2.28

2.28

2.35

2.04

1.13

0.91

0.81

0.0

0.5

1.0

1.5

0.0

0.5

1.0

1.5

System (W/sqft)

Watt

s/sq-

ft

Time of dayMinimum kW Plant & Building-Electric heat-Real weather

(Bld)W/sg-ft (AHU)Fan W/sq-ft(plant)W/sq-ft Total elect heat (W/sq-ft)

0.337

1.467

0.50

0.14

0.46

0.55

0.55 0.

65

0.55

0.19

0.00

0.00

0.00

0.00

0.17

0.32

0.32

1.30

1.30

1.41

1.36

1.76

2.69

2.70

2.75

2.42

1.56

1.39

1.28

0.0

0.5

1.0

1.5

0.0

0.5

1.0

1.5

System (W/sqft)

Watt

s/sq-

ft

Time of dayStandard Bld & Plant-Electric Heat-Real Weather


0.832

1.467

0.33

0.33

0.33

0.33

0.34

0.61

0.61 0.

66

0.50

0.33

0.32

0.32

0.22 0.

29

0.29

0.22

0.21

0.62

0.62

0.63

0.46

0.27

0.26

0.26

0.55

0.55 0.

65

0.55

0.19

0.00

0.00

0.00

0.00

0.17

0.32

0.32

1.93

2.01

2.11

1.94

1.76

2.69

2.70

2.75

2.42

1.68

1.73

1.73

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.5

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.5

System (W/sqft)

Watt

s/sq-

ft

Time of dayStd Bld & Plant-Elect Heat-Real Weather-bad design/control


Figure 16: 24 hour energy use watts/sq ft-Bottom chart bad (1.LIGHT) controlFigures 16 & 17 provide the hourly detail of energy use illustrating the effect of bad (1. LIGHTS) control.

0.72

0.73 0.

78

0.77

1.12

1.76

1.76 1.80

1.67

0.95

0.79

0.71

0.07

0.06

0.07

0.07 0.

14

0.52

0.52 0.55

0.37

0.19

0.12

0.11

0.79

0.79 0.

85

0.84

1.26

2.28

2.28 2.

35

2.04

1.13

0.91

0.81

0.0

0.5

1.0

1.5

2.0

2.5

0.0

0.5

1.0

1.5

2.0

2.5

Watt

s/sq-

ft

Time of dayMinimum kW Plant & Building-Electric heat-Real weather

Site watts/sg-ft (plant)W/sq-ft System watts/sq-ft

1.16

1.17 1.

27

1.22

1.54

2.08

2.08 2.13

1.96

1.31

1.17

1.07

0.14

0.13

0.14

0.14 0.21

0.62

0.62

0.63

0.46

0.25

0.22

0.21

1.30

1.30 1.

41

1.36

1.76

2.69

2.70 2.75

2.42

1.56

1.39

1.28

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

Time of dayStd design Plant & Building-Electric heat-Real weather


1.71

1.71 1.81

1.71

1.54

2.08

2.08 2.13

1.96

1.41 1.47

1.47

0.22 0.29

0.29

0.22

0.21

0.62

0.62

0.63

0.46

0.27

0.26

0.26

1.93 2.01 2.11

1.94

1.76

2.69

2.70 2.75

2.42

1.68 1.73

1.73

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

Watt

s/sq-ft

Time of dayStd design Plant & Building-Electric heat-bad control-Real weather


Figure 17: 24 hour energy use watts/sq ft-Bottom chart bad (1. LIGHT) control The middle & bottom charts of Figure 17 illustrate no change with bad lights control during building occupied hours but significant change after hours.

11


2. THERMOSTATES not controlled can have a significant effect on the energy consumption of a building. Thermostat set points and return air paths must be considered in minimizing building energy consumption. In general this analysis models all return air to the perimeter of the building. Therefore if the internal and perimeter thermostats are set different then energy can be transferred from the interior of the building to the perimeter. Bad thermostat control will be modeled as, during heating, 76F perimeter stat set and 75F interior stat set point and during perimeter cooling 74F perimeter stat set point. A perimeter stat set at 75F would be neutral and less than 75F would be good control because of transferring interior energy to the perimeter during heating.

32.683

43.882

54.750

0

10

20

30

40

50

60

70

80

24 h

our (

watt

hr/

sq ft

)




Figure 18: 24 Hour watt hours per building square foot-min kW design-Standard design-& Standard design with bad control of (1. LIGHTS) & (2. THERMOSTATS)Setting the perimeter stats at 76F during perimeter heating and the internal stats at 75F and all return air goes to the perimeter results in a significant increase in system energy use as shown by Figure 18 & 19. This arrangement results in all supply air being heated to 76F. During cooling bad stat control is the perimeter stat set lower than the internal stat, in this model 74F. Figure 19 shows that the building watt/sq ft consisting of light & plug loads did not change with the bad control of thermostats. The air handler and plant increased but

the big increase was in heat required to maintain the perimeter at 76F thermostat set point with the condition that all internal supply air returns to the perimeter.

25.559

10.013 6.598 8.740

50.910

0102030405060708090

100

24 h

our w

att-h

r/sq

ft



25.559

10.590 9.594 9.007

54.750

0102030405060708090

100

24 h

our w

att-h

r/sq

ft


(Bld)W/sg-ft (AHU)Fan W/sq-ft

Total elect heat (W/sq-ft) (plant)W/sq-ft

(System)W/sq-ft

Figure 19: 24 hour energy use summed-all electric system at real weather conditions-top chart bad LIGHTS control, bottom chart plus bad THERMOSTAT control. The heat enegy into the system, bottom chart, is 9.594 watts-hr/sq ft. This can be converted to btu by;9.594 watt-hr/sq ft x 3.412 btu/watt-hr= 32.73 btu/sq ft. This is the heat energy going into the system whether electric or from fuel burning. The efficiency of a boiler system will determine how much fuel is consumed at

12

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.the boiler. For example assume 80% efficiency. Therefore the boiler will consume over 24 hours; 32.73 btu/sq ft/.80 = 40.91 btu/sq ft.

0.832

1.467

0.33

0.33

0.33

0.33 0.34

0.61

0.61 0.

66

0.50

0.33

0.32

0.32

0.22 0.

29

0.29

0.22

0.21

0.62

0.62

0.63

0.46

0.27

0.26

0.26

0.55

0.55 0.

65

0.55

0.19

0.00

0.00

0.00

0.00

0.17

0.32

0.32

1.93

2.01

2.11

1.94

1.76

2.69

2.70

2.75

2.42

1.68

1.73

1.73

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.5

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.5

System (W/sqft)

Watt

s/sq

-ft



0.832

1.467

0.34

0.34

0.35

0.34 0.35

0.66

0.66 0.

72

0.53

0.34

0.33

0.33

0.25

0.24

0.25

0.25

0.23

0.64

0.64

0.65

0.48

0.30

0.29

0.28

0.74

0.74 0.

84

0.74

0.39

0.00

0.00

0.00

0.00

0.36

0.49

0.50

2.16

2.16

2.27

2.16

1.98

2.77

2.77

2.83

2.47

1.91

1.95

1.94

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.5

0.00.10.20.30.40.50.60.70.80.91.01.11.21.31.41.5

System (W/sqft)

Watt

s/sq

-ft



Figure 20: Top chart Bad (1. LIGHT) control, bottom chart plus bad (THERMOSTAT) control.

The bottom chart of Figure 20 with bad light control plus bad stat control compared to the top chart with bad light control illustrates the heat energy due to the bad stat control significantly increases.

1.71

1.71 1.81

1.71

1.54

2.08

2.08 2.13

1.96

1.41 1.47

1.47

0.22 0.29

0.29

0.22

0.21

0.62

0.62

0.63

0.46

0.27

0.26

0.26

1.93 2.01 2.11

1.94

1.76

2.69

2.70 2.75

2.42

1.68 1.73

1.73

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

Watt

s/sq

-ft



1.91

1.91 2.02

1.91

1.75

2.13

2.13 2.18

2.00

1.61 1.66

1.66

0.25

0.24

0.25

0.25

0.23

0.64

0.64

0.65

0.48

0.30

0.29

0.28

2.16

2.16 2.

27

2.16

1.98

2.77

2.77 2.83

2.47

1.91 1.95

1.94

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

Watt

s/sq

-ft



Figure 21: Top chart Bad (1. LIGHT) control, bottom chart plus bad (THERMOSTAT) control.

Figures 20 & 21 illustrate that bad stat control, as defined here with all return air to the building perimeter, increases the plant and site energy for all hours.

13


0.79 0.79 0.85 0.84

1.26

2.28 2.28 2.35

2.04

1.130.91 0.81

1.30 1.30 1.41 1.36

1.76

2.69 2.70 2.75

2.42

1.561.39 1.28

2.16 2.16 2.27 2.161.98

2.77 2.77 2.83

2.47

1.91 1.95 1.94

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

% 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)

Figure 22: Real weather of Feb., 26, 2019, watts per square foot of min kW design, Standard design, & Standard design with bad (1.LIGHT) control & bad (2. THERMOSTATE) control.

Figure 22 shows the hourly watts/sq ft for the systems as thus far discussed showing the Standard design watts/sq ft has been significantly increased during uccupied hours and increased about (2.35w/ft2 – 2.83w/ft2 = .48 w/ft2) at noon conditions with bad (1. LIGHT) & (2. THERMOSTAT) control. The big reason for the increase is no light control and the increase in perimeter heat.

3. INFILTRATION doubled from 7,266 CFM to 14,532 CFM.

Figure 23 shows the effect of adding the bad control (3. INFILTRATION) by doubling from 7,266 CFM to 14,532 CFM. The Standard design has 7,266 CFM of infiltration as the author interoperates Liu8. Comparing Figures 22 & 23 illustrates an hourly increase in system watts per building square foot with the addition of more outside air infiltration into the building. The increase is primarily due to increased perimeter heat required due to the cold air infiltration and also an increase in fan CFM and therefore fan kW, Figure 24 illustrates..

0.79 0.79 0.85 0.84

1.26

2.28 2.28 2.35

2.04

1.130.91 0.81

1.30 1.30 1.41 1.36

1.76

2.69 2.70 2.75

2.42

1.561.39 1.28

2.31 2.302.44

2.312.11

2.77 2.78 2.84

2.48

1.99 2.06 2.06

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

% clear sky

Watt

s/sq

ft

Watt

s/sq

ft



Figure 23: Real weather of Feb., 26, 2019, watts per square foot of min kW design, Standard design, & Standard design with bad (1.LIGHT) control, bad (2. THERMOSTATE) control & doubled outside air(3. INFILTRATION).

14


25.559

10.590 9.594 9.007

54.750

0102030405060708090

100

24 h

our w

att-h

r/sq

ft




(System)W/sq-ft

25.559

10.697 11.341 9.305

56.902

0102030405060708090

100

24 h

our w

att-h

r/sq

ft




(System)W/sq-ft

Figure 24: 24 hour energy use summed-all electric system at real weather conditions-top chart bad LIGHTS & Stat control, bottom chart plus bad infiltration control.

Figure 24 illustrates that increased infiltration increased the system 24 hour energy use about 2.1 watt-hr per square foot. Most of the increase was due to heat energy for the building perimeter.

32.683

43.882

56.902

0

10

20

30

40

50

60

70

80

24 h

our (

watt

hr/

sq ft

)




Figure 25: : Real weather 24 hour watt-hour per square foot for min kW design, Standard design, & Standard design with bad (1.LIGHT) control, bad (2. THERMOSTATE) control & doubled outside air (3. INFILTRATION) into the building. Figure 25 illustrates that the three bad control issues thus discussed have significantly increased the 24 hour energy use of the Standard design.

15


HEATING AIR TEMPERATURE. Decreasing the heat air temperature from 94F to 90F.

41,486 39,256

183,055192,301

187,942

56,429

30,844 35,627

66,528 72,56420,624 20,040

59.8

60.0

60.0

59.5

56.8 58.0

58.5

94.0

94.0

94.0

94.0

94.0

58.0

94.0

94.0

94.0

40

50

60

70

80

90

100

0

50,000

100,000

150,000

200,000

250,000

FAN VAV-CFM

AIR

TEM

P. (F

)

(CFM

)

Time of DayStd kW Design-Real weather-Interior & Perimeter air supply

(Duct)interior-CFM (Duct)perimeter-CFM

(Temp)air-supply-interior (Temp)air-supply-perimeter

9

53 6038

9

225.5

126.9

125 125 125 125 125

152

58

30

177199

126

31

0

50

100

150

200

250

300

0

50

100

150

200

250

300

ONE BUILDING TOTAL SITE OR AIR SIDE kW

(kW

)

(kW

)

ONE BUILDING TOTAL BUILDING kW

Std. kW Design-Real weather-Air side (kW)

Return fan kW Duct reheat (kW) Terminal fans (kW)

Duct heat (kW) VAV Fans (kW) Fresh Air (kW)

Figure 26: Air supply to interior & perimeter of building-Standard design at real weather-One building

To demonstrate why decreasing the heating supply air temperature increases system kW we will give values for one building but not in per square foot terms. Figures 26 & 27 illustrate the complexity of the air supply to the interior and perimeter of the building10,11. Figure 26 gives the Standard design and Figure 27 gives the standard design with the three bad control issues

thus far discussed, lights, stats, and increased infiltration.

87,007 84,777

110,082

183,055192,301

187,942

105,57689,535

45,797 51,529

28,529

81,12688,731

33,063 32,515

57.3 56.8

56.9

57.2

57.2

94 94 94 94 94

57 57 57

61

94 94 94

40

50

60

70

80

90

100

0

20,000

40,000

60,000

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100,000

120,000

140,000

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200,000

FAN VAV-CFM

AIR

TEM

P. (F

)

(CFM

)Time of DayStd kW Design- Real weather-Bad control -

Interior & Perimeter air supply



19

5942

16

342.5

216.1

125 125

125

125

231

12364

198

140

55

0

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TOTAL SITE OR AIR SIDE kW

(kW

)

(kW

)

TOTAL BUILDING kW

Std. kW Design-Real weather-Bad control-Air side (kW)



Figure 27: Air supply to interior & perimeter of building-Standard design-Bad control, lights, stats, infiltration, at real weather conditions-One building

The top charts of the figures illustrates that leaving more lights on at night increased the interior supply air CFM after hours and therefore the VAV fan kW. Duct heat and reheat significantly increased with increased infiltration and bad stat control. The primary horizontal axis show the increase in building kW that consists of

16

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.light & plug loads and the secondary horizontal axis of the two figures illustrates the significant increase in the building plus air system kW. Next we will look at increases due to dropping the heating supply air to 90F.

87,007 84,777

110,082

183,055192,301

187,942

105,57689,535

45,797 51,529

28,529

81,12688,731

33,063 32,515

57.3 56.8

56.9

57.2

57.2

94 94 94 94 94

57 57 57

61

94 94 94

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50

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90

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0

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40,000

60,000

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FAN VAV-CFM

AIR

TEM

P. (F

)

(CFM

)

Time of DayStd kW Design- Real weather-Bad control -Interior & Perimeter air supply



19

5942

16

342.5

216.1

125 125

125

125

231

12364

198

140

55

0

50

100

150

200

250

300

350

0

50

100

150

200

250

300

350


(kW

)

(kW

)

TOTAL BUILDING kW




Figure 27: Air supply to interior & perimeter of building-Standard design-Bad control, lights, stats, infiltration, at real weather conditions-One building

Comparing Figures 27 & 28 shows that the perimeter air CFM had to increase to meet the perimeter heat load

and therefore the increased CFM increased duct reheat but did not increase duct heat.

87,007 84,777

110,082

183,055192,301

187,942

105,57689,535

58,88166,252

36,680

81,12688,731

33,06341,805

57.3 56.8

56.9

57.2

57.2

90 90 90 90 90

57 57 57

61

90 90 90

40

50

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80

90

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0

20,000

40,000

60,000

80,000

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120,000

140,000

160,000

180,000

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FAN VAV-CFM

AIR

TEM

P. (F

)

(CFM

)Time of DayStd kW Design- Real weather-Bad control -

Interior & Perimeter air supply



22

5942

18

440.4

277.9

125 125

125

125

231

12374

198

140

60

0

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450

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(kW

)

(kW

)

TOTAL BUILDING kW




Figure 28: Air supply to interior & perimeter of building-Standard design-Bad control, lights, stats, infiltration, 90F supply air, at real weather conditions-One building

Following are two building schematics at 4AM that give better understanding.

17


BLD ft2 = 582000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 59.0 Ex-/Infil+-CFM = 14532 <<Roof ft2 = 44,769 Twet-bulb= 57.0 Infilsen-ton = -22.2

N/S wall ft2 = 40,560 WallNtrans ton= -3.23E/W wall ft2 = 31,525 WallStrans ton= -3.23

Wall % glass= 37.5% WallEtrans ton= -2.51Glass U = 0.55 WallWtranston= -2.51 WallTot trans ton = -11.5

Wall U = 0.09 GlassN trans ton = -11.85Glass SHGC = 0.40 GlassS trans ton = -11.85

Wall emitt = 0.55 GlassE-trans ton = -9.21RoofTrans ton = -2.9 GlassW-trans ton = -9.21 GlassTot-trans-ton= -42.1

Roofsky lite ton = 0.0 GlassN-solar-ton = 0.0Peoplesen&lat ton = 0.0 0.0 GlassS-solar-ton = 0.0

plugton&kW = 48 169.9 GlassE-solar ton = 0.0Lightton&kW= 89 314.3 GlassW-solar ton = 0.0 GlassTot-solar-ton = 0.0

Total Bldint-ton = 134.9 BLD kW= 484.2 (int cfm)per-ton = -7.63 >(int-cfm)to-per-ret= 84777 FAN kW= 220.9 Tot Bldper-sen-ton = -83.5 v

Tstat-int= 75.0 HEAT kW = 671.6 Tstat-per = 76.0 return(Bld)int.air-ton= -134.9 ^ SITE kW = 1376.7 ^ (Bld)per-air-ton= 83.5 airTair supply int= 57.33 Standard design 4AM Tair supply per= 90.00

^ Bad Control ^Ton kW Ton kW V

(fan)int-ter ton&kW= 17.7 62.4 (fan)per-ter ton&kW= 17.7 62.4Theat-air= 87.0

(D)heat ton&kW = 65.7 231.2Treheat air = 75.0

(D)reheat ton&kW = 125.2 440.4734.0

(D)int-air-ton= -152.6 Interior (D)per-air-ton= -119.3 PeriTair coils = 55.00 duct Tair coils= 55.00 duct

(D)int-CFM= 84,777 ^ (D)per-CFM= 66,252 ^>>>(Coil)sen-ton= 311 ^ ^

COILOne Building (TON)

V(COIL)L+s-ton= 311 ^ ^ ^

<<<< Tair VAV= 77.90 TBLD-AR = 76.00(FAN)VAV-CFM= 151,029 (Air)ret-CFM = 165,561 Return(FAN)ton-VAV= 21.0 (FAN)ret-kW= 22.2 Fan(FAN)kW-VAV= 73.9 (FAN)ret-ton= 6.3 V

^ (Air)ret-ton = 319.226 F.A.Inlet ^ Tar-to-VAV = 76.42

statFA= 42 26 VAV FANS VAVret-sen ton = 290.1 TFA to VAV = 59.0 > Tret+FA = 76.36 VAVret Lat-ton = 0.00

>(FA)sen-ton = > 0.2 (dh) = 2.316 < VAVret-CFM = 150,447 <> (FA)CFM= 582 > Efan-VSD= 0.556 V

> (FA)Lat-ton= 0.0 VAVinlet-sen-ton= 290.3(FA)kW= 0.0 VAVinlet-lat-ton= 0.0 ExLat-ton = 0.0

ExCFM = -15,114(SEE) Schematic air side TEx = 76.42Air temp green kW red Exsen-ton = -29.1 V Air CFM purple Ton blue V

Schematic 1: Perimeter supply air = 90F

Schematic 1 is consistent with Figure 28 at 4AM. Schematic 2 has increased the perimeter supply air to 110F, same as in the min kW Design, to more clearly illustrate the effect of heating supply air temperature, however the bad control Standard system will proceed to the next bad control concept with 90F supply air.

BLD ft2 = 582000 %clear sky = 100.0% InfilLat-ton = 0.00# floors = 13 Tdry-bulb = 59.0 Ex-/Infil+-CFM = 14532 <<Roof ft2 = 44,769 Twet-bulb= 57.0 Infilsen-ton = -22.2

N/S wall ft2 = 40,560 WallNtrans ton= -3.23E/W wall ft2 = 31,525 WallStrans ton= -3.23

Wall % glass= 37.5% WallEtrans ton= -2.51Glass U = 0.55 WallWtranston= -2.51 WallTot trans ton = -11.5

Wall U = 0.09 GlassN trans ton = -11.85Glass SHGC = 0.40 GlassS trans ton = -11.85

Wall emitt = 0.55 GlassE-trans ton = -9.21RoofTrans ton = -2.9 GlassW-trans ton = -9.21 GlassTot-trans-ton= -42.1

Roofsky lite ton = 0.0 GlassN-solar-ton = 0.0Peoplesen&lat ton = 0.0 0.0 GlassS-solar-ton = 0.0

plugton&kW = 48 169.9 GlassE-solar ton = 0.0Lightton&kW= 89 314.3 GlassW-solar ton = 0.0 GlassTot-solar-ton = 0.0

Total Bldint-ton = 134.9 BLD kW= 484.2 (int cfm)per-ton = -7.63 >(int-cfm)to-per-ret= 84777 FAN kW= 188.1 Tot Bldper-sen-ton = -83.5 v

Tstat-int= 75.0 HEAT kW = 412.5 Tstat-per = 76.0 return(Bld)int.air-ton= -134.9 ^ SITE kW = 1084.8 ^ (Bld)per-air-ton= 83.5 airTair supply int= 57.33 Standard design 4AM Tair supply per= 110.00

^ Bad Control ^Ton kW Ton kW V

(fan)int-ter ton&kW= 17.7 62.4 (fan)per-ter ton&kW= 17.7 62.4Theat-air= 102.8

(D)heat ton&kW = 65.7 231.2Treheat air = 75.0

(D)reheat ton&kW = 51.6 181.3474.9

(D)int-air-ton= -152.6 Interior (D)per-air-ton= -49.1 PeriTair coils = 55.00 duct Tair coils= 55.00 duct

(D)int-CFM= 84,777 ^ (D)per-CFM= 27,280 ^>>>(Coil)sen-ton= 228 ^ ^

COILOne Building (TON)

V(COIL)L+s-ton= 228 ^ ^ ^

<<<< Tair VAV= 77.65 TBLD-AR = 76.00(FAN)VAV-CFM= 112,057 (Air)ret-CFM = 126,590 Return(FAN)ton-VAV= 13.8 (FAN)ret-kW= 14.6 Fan(FAN)kW-VAV= 48.7 (FAN)ret-ton= 4.2 V

^ (Air)ret-ton = 243.426 F.A.Inlet ^ Tar-to-VAV = 76.36

statFA= 42 26 VAV FANS VAVret-sen ton = 214.3 TFA to VAV = 59.0 > Tret+FA = 76.27 VAVret Lat-ton = 0.00

>(FA)sen-ton = > 0.2 (dh) = 1.900 < VAVret-CFM = 111,475 <> (FA)CFM= 582 > Efan-VSD= 0.514 V

> (FA)Lat-ton= 0.0 VAVinlet-sen-ton= 214.6(FA)kW= 0.0 VAVinlet-lat-ton= 0.0 ExLat-ton = 0.0

ExCFM = -15,114(SEE) Schematic air side TEx = 76.36Air temp green kW red Exsen-ton = -29.1 V Air CFM purple Ton blue V

Schematic 2: Perimeter supply air = 110F

With 110F supply air the CFM has decreased to less than half therefore decreasing the reheat kW from 440.4 to 181.3 kW which reduces the plant load from 311 ton to 228 ton. Many other changes occur in the system, but will leave that to the reader to study.

18


0.79 0.79 0.85 0.84

1.26

2.28 2.28 2.35

2.04

1.130.91 0.81

1.30 1.30 1.41 1.36

1.76

2.69 2.70 2.75

2.42

1.561.39 1.28

2.31 2.302.44

2.312.11

2.77 2.78 2.84

2.48

1.99 2.06 2.06

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0.79 0.79 0.85 0.84

1.26

2.28 2.28 2.35

2.04

1.130.91 0.81

1.30 1.30 1.41 1.36

1.76

2.69 2.70 2.75

2.42

1.561.39 1.28

2.50 2.502.66

2.512.23

2.77 2.78 2.84

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2.10 2.20 2.20

100%100%100%100% 30% 100%100%100% 40% 10% 10% 10%

0.0

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Figure 29: Orlando real weather of Feb., 26, 2019, watts per square foot of min kW design, Standard design, & Standard design with bad (1.LIGHT) control, bad (2. THERMOSTATE) control & doubled outside air(3. INFILTRATION), Top Chart.Bottom Chart add bad control 90F supply heating air.

0.35 0.350.41

0.35

0.00

0.00 0.00 0.000.07

0.19 0.19

0.55 0.550.65

0.55

0.19

0.00

0.17

0.32 0.32

1.01 1.02 1.151.02

0.59

0.00 0.00 0.00

0.50

0.69 0.69

100%100%100%100% 30% 100%100%100% 40% 10% 10% 10%

0.0

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0.4

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s/sq

ft

Watt

s/sq

ft

TIME of DAYDuct watts/sq ft at real weather conditions-Electric Heat


Figure 30: Perimeter heat

Figure 29 bottom chart gives the increase in energy per square foot by decreasing the heating air temperature from 94F to 90F and Figure 30 illustrates the big difference in perimeter heat for the three systems at real weather conditions.

19


25.559

10.697 11.341 9.305

56.902

0102030405060708090

100

24 h

our w

att-h

r/sq

ft




(System)W/sq-ft

25.559

10.960 13.349 9.671

59.540

0102030405060708090

100

24 h

our w

att-h

r/sq

ft



Figure 31: 24 hour energy use summed-all electric system at real weather conditions-top chart bad LIGHTS, Stat, & infiltration control. Bottom chart plus 90F supply heating air control.

Figure 31 illustrates that reducing the heating air temperature from 94F to 90F increased the system 24 hour energy use about 2.6 watt-hr. per square foot. Most of the increase was due to heat energy for the building perimeter plus a little increase in plant energy.

32.683

43.882

56.902

0

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our (

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sq ft

)




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43.882

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our (

watt

hr/

sq ft

)




Figure 32: : Real weather 24 hour watt-hour per square foot for min kW design, Standard design, & Standard design with bad light, stat, & infiltration control-Top Chart. Bottom Chart add change of 94F supply heating air to 90F supply heating air to poor control system. VAV STATIC PRESSURE SETPOINTAll above models have included VAV reset of static pressure to minimize fan kW. This bad control issue will set the VAV static pressure at a minimum of 5.5 inches of water resulting in higher VAV fan CFM and therefore significant increase in air handler energy use.

20


32.683

43.882

65.361

0

10

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30

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80

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our (

watt

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sq ft

)




Figure 33: 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.

Comparing the bottom chart of Figure 32 to Figure 33 shows about a 5.8 watt-hr. per building square foot increase in system energy use with the increase in VAV static pressure.

Figure 34 gives the same data as Figure 33 except Figure 34 is for a fuel burning system. Therefore the electric use is less as show by comparing Figure 33 and the top chart of Figure 34. The bottom chart of Figure 34 gives the btu of fuel consumed.

Figures 33 & 34 give 24 hour data that the reader can use to judge-benchmark a real building in Orlando on a day when the weather is similar to Figure 13. A study of the other papers of this blog is recommended, System Energy Equilibrium (SEE) Model Development, Verification & Real Weather Analysis of Office Buildings & Plants14.

0.44 0.44 0.44 0.49

1.23

2.28 2.28 2.35

2.04

1.06

0.73 0.62

0.75 0.75 0.76 0.81

1.57

2.69 2.70 2.75

2.42

1.39

1.08 0.97

1.75 1.74 1.78 1.751.90

2.97 2.97 3.012.73

1.86 1.78 1.78

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Watt

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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)

1.18 1.211.41

1.20

0.13

0.24

0.63 0.66

3.46 3.48 3.94 3.48

2.02

0.00 0.00 0.00 0.00

1.72

2.34 2.35

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/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 34: : 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. Top chart is electric use & bottom chart is btu of fuel use.

Other days will be modeled so stay tuned in.

Best Regard,Kirby Nelson PELife Member ASHRAE

21


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 member

References:

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

22

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.embargo and an air side model is still not in the ASHRAE models.

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 lights

Total 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)

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http://www.wunderground.com/

SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.(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 plant

Plant 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

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SYSTEM ENERGY EQUILIBRIUM (SEE) BUILDING ENERGY MODEL by KIRBY NELSON P.E.(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 kW

SystkW = 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

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26BENCHMARKING BUILDING ENERGY

SYSTEM ENERGY EQUILIBRIUM (SEE) MODEL by Kirby Nelson P.E.

system energy equilibrium (see) model by kirby nelson … · web views for a given city. the plan...

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