EXHAUST AIR ENERGY RECOVERY ANALYSIS by SYSTEM ENERGY EQUILIBRIUM (SEE) MODELThe objective of a System Energy Equilibrium (SEE) building energy model is to duplicate the hourly performance of a real building energy system at all operating conditions of weather and load; giving flows, temperatures, cooling loads, kW demand of equipment, and total site kW as weather and operational conditions change. The (SEE) model, as presented here, consists of a set of simultaneous equations that obey the laws of thermodynamics, models the hour by hour loads of the building and the response of the central chilled water system (CCWS) to the building loads and air side system, and includes the nonlinear performance characteristics of the plant equipment and air side equipment. A (SEE) model iterates to steady state energy equilibrium after a perturbation to the system just as a real system responds; a defining characteristic of a (SEE) model. The primary objective of this paper is to investigate the energy savings potential of an exhaust air energy recovery system applied to a large office building located in weather zone 4. (SEE) MODEL CHARACTERISTICS Understanding the performance of a complex system, in this case a building and (CCWS) that serves the building, requires a model that includes detail model equations of all components of the system. These equations of each system component are solved simultaneous, by computer, giving the effect of each component on the

operation of the total system and the effect of the system on the performance of the component. Real building energy systems operate according to the laws of thermodynamics and the performance characteristics of the equipment installed; therefore the model must incorporate equations that duplicate the laws of thermodynamics and input the characteristics of the system components consistent with the manufactures verified data. To accomplish this objective the model must incorporate every design and control feature of the real system; resulting in a model, as presented here, consisting of more than 150 performances and design variables, each variable defined by an equation and/or is a design constant that changes if the design is changed. The set of equations is solved simultaneously by computer and will duplicate the performance of a real system if sufficient detail has been incorporated into the model and the detail is consistent with the actual equipment and controls of the real system. The model is always at System Energy Equilibrium (SEE).The challenge developing a (SEE) model might be summarized as; a real system is very complex where minor changes in weather, design, and control, can have a major effect on the performance of the system; therefore the system (SEE) model must be equally complex incorporating all characteristics of the real system within a set of simultaneous equations solved by a computer.

THE BUILDING & ASSUMED WEATHERFigure 1 illustrates the building and Figure 2 the assumed weather for this analysis of exhaust air energy recovery.

Figure 1 Building

The building of this study is defined by the

Pacific Northwest National Laboratory (PNNL)

study of ASHRAE Standard 90.1-2010, a large 13

story office building, Figure 1, with 498,600

square feet of air conditioned space. The

(PNNL) study is given by 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-901-2010. 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).

Figure 2 Assumed peak summer design weather

BUILDING SCHEMATIC

Figure 3 defines the components of the building schematic and nomenclature is given at the end of this paper.

Figure 3 Building schematic defined

BLD ft2 = 498600 %clear sky = 100.0% InfilLat-ton = 30.84# floors = 13 Tdry-bulb = 99.8 Ex-/Infil+-CFM = 6811 <<Roof ft2 = 38,354 Twet-bulb= 77.2 Infilsen-ton = 15.2

N/S wall ft2 = 40,560 WallNtrans ton= 4.92E/W wall ft2 = 27,008 WallStrans ton= 5.30

Wall % glass= 37.5% WallEtrans ton= 4.09Glass U = 0.55 WallWtranston= 3.28 WallTot trans ton = 17.6

Wall U = 0.09 GlassN trans ton = 17.29Glass SHGC = 0.40 GlassS trans ton = 17.29

Wall emitt = 0.55 GlassE-trans ton = 11.51RoofTrans ton = 33.3 GlassW-trans ton = 11.51 GlassTot-trans-ton= 57.6Roofsky lite ton = 0.0 GlassN-solar-ton = 7.1

Peopleton-sen&lat = 59.5 39.7 GlassS-solar-ton = 20.8plugton&kW = 93 327.6 GlassE-solar ton = 4.7Lightton&kW= 115 403.9 GlassW-solar ton = 33.1 GlassTot-solar-ton = 65.7

Total Bldint-ton = 300.8 BLD kW= 731.4 (int cfm)per-ton = 0.00 >(int-cfm)to-per-ret= 176985 FAN kW= 479.1 Tot Bldper-sen-ton = 156.1 v

Tstat-int= 75.0 SITE kW = 1210.5 Tstat-per = 75.0 return(Bld)int-air-ton= -300.8 ^ Design 4PM ^ (Bld)per-air-ton= -156.1 air

Tair supply int= 56.11 ASHRAE Design Tair supply per= 57.04 ^ ABS Bld Ton = 456.91 ^

Ton kW Ton kW V(fan)int-ter ton&kW= 17.7 62.4 (fan)per-ter ton&kW= 17.7 62.4

Theat-air= 55.0 (D)heat ton&kW = 0.0 0.0

Treheat air = 55.0(D)reheat ton&kW = 0.0 0.0

62.4(D)int-air-ton= -318.6 Interior (D)per-air-ton= -173.8 Peri

Tair coils = 55.00 duct Tair coils= 55.00 duct(D)int-CFM= 176,985 ^ (D)per-CFM= 96,565 ^

>>>(Coil)sen-ton= 682 ^ (coil)gpm= 39.9 ^(coil)cap-ton= 35.7 UAdesign= 2.66

(coil)H2O-ft/sec= 1.10 COIL UA= 2.52(coil)des-ft/sec= 1.20 (one coil)ton= 32.88

LMTD= 14.17 (H)coil= 1.8 V(COIL)L+s-ton= 855 ^ ^ ^ (H)coil-des= 2.1

<<<< Tair VAV= 82.72 TBLD-AR = 75.00(FAN)VAV-CFM= 273,551 (Air)ret-CFM = 280,361 Return(FAN)ton-VAV= 77.5 (FAN)ret-kW= 81.8 Fan(FAN)kW-VAV= 272.5 (FAN)ret-ton= 23.2 V

^ (Air)ret-ton = 527.926 F.A.Inlet ^ Tar-to-VAV = 75.92

statFA= 42 26 VAV FANS VAVret-sen ton = 436.3 TFA to VAV = 99.8 > Tret+FA = 79.57 VAVret Lat-ton = 58.28

>(FA)sen-ton = > 168.6 (dh) = 5.568 < VAVret-CFM = 231,733 <> (FA)CFM= 41,817 > Efan-VSD= 0.657 V

> (FA)Lat-ton= 114.1 VAV inlet-sen-ton = 604.9(FA)kW= 0.0 VAVinlet-lat-ton= 172.4 ExLat-ton = -12.2

ExCFM = -48,628

SEE SCHEMATIC air side TEx = 75.92Air temp green kW red Exsen-ton = -91.6 V Air CFM purple Ton blue v

Figure 4 Air side system-no exhaust energy recovery at peak design weather

Figure 4 illustrates the air side system without exhaust energy recovery and Figure 5 gives the effect of recovery. Note that all system values are the same for the building, duct system, and VAV kW fan performance. With recovery, Figure 5, the exhaust air temperature increases from 75.92F to 92.27F and the fresh air into the VAV fans

Figure 5 Air side system with exhaust energy recovery at peak design weather

decreases from 99.8F, the outside dry bulb temperature, to 80.8F; resulting in a drop of load to the plant of (855 - 783 = 72 ton). Exhaust air energy recovery only reduces the load on the plant.

Figures 6 & 7 are of the VAV fan systems of Figures 4 & 5.

Figure 6 VAV fan system of Figure 5-exhaust air recovery on

Figure 7 VAV fan system of Figure 4-no exhaust air recovery

Comparing Figures 6 & 7 illustrates the effect of exhaust air energy recovery at peak summer design conditions. Transferring energy from the exhaust air to the fresh air decreases the air into the VAV fans from 79.57F to 76.67F; resulting in a return air load to the VAV fans of 533.4 ton sensible load verses 604.9 ton without recovery. Note that the VAV kW and CFM are not changed by the exhaust air recovery systems.

The load presented to the plant is reduced from 855 ton to 783 ton; let’s look at the response of the plants.

BLD ft2 = 498600 %clear sky = 100.0% Ex/InfilLat-ton = 30.84Condenser # floors = 13 Tdry-bulb = 99.8 Ex-/Infil+ CFM = 6811 <<

(cond)ton= 464 Pipesize-in = 6" (H)T-pipe= 13.5 Tower Roof ft2 = 38,354 Twet-bulb= 77.2 Ex/Infilsen-ton = 15.2TCR= 98.9 > gpmT= 1800 > (ewt)T= 97 tfan-kW= 12.4 N/S wall ft2 = 40,560 WallNtrans ton= 4.92

TCR-app= 1.53 (H)T-total= 68.7 (H)T-static = 12.2 Tfan-kW= 24.8 E/W wall ft2 = 27,008 WallStrans ton= 5.30(COND)ton= 928 PT-heat ton = -1.36 Trange= 12.4 tfan-%= 100% Wall % glass= 37.5% WallEtrans ton= 4.09

(H)cond= 43.0 < pT-kW= 28.1 < (lwt)T = 85.0 tton-ex= -467 Glass U = 0.55 WallWtranston= 3.28 WallTot trans ton = 17.6(cond)ft/sec= 9.7 EfTpump= 0.83 Tapproach = 7.8 T#= 2 Wall U = 0.09 GlassN trans ton = 17.29

Ptower # = 2 T-Ton-ex= -935 Glass SHGC = 0.40 GlassS trans ton = 17.29Trg+app = 20.2 Wall emitt = 0.55 GlassE-trans ton = 11.51

Compressor ASHRAE Design RoofTrans ton = 33.3 GlassW-trans ton = 11.51 GlassTot-trans-ton= 57.6(chiller)kW= 226.5 St Louis 90.1-2010 #people Roofsky lite ton = 0.0 GlassN-solar-ton = 7.1(chiller)lift= 56.9 Large Office 2380 Peopleton sen&lat = 59.5 39.7 GlassS-solar-ton = 20.8(chiller)%= 89% Peak day Design 4PM plugton&kW = 93 327.6 GlassE-solar ton = 4.7(chiller)#= 2 Weather %clear sky = 1.00 Lightton&kW= 115 403.9 GlassW-solar ton = 33.1 GlassTot-solar-ton = 65.7

(CHILLER)kW= 453.0 conditions Tdry bulb = 99.8 Total Bldint-ton = 300.8 BLD kW= 731.4 (int cfm)per-ton = 0.00 >(chiller)kW/ton= 0.572 Twet bulb = 77.2 (int-cfm)to-per-ret= 176985 FAN kW= 479.1 Tot Bldper-sen-ton = 156.1 vPlant kW = 546.9 Tstat-int= 75.0 SITE kW = 1210.5 Tstat-per = 75.0 return

(Bld)int-air-ton= -300.8 ^ Design 4PM ^ (Bld)per-air-ton= -156.1 airTair supply int= 56.11 ASHRAE Design Tair supply per= 57.04

^ ABS Bld Ton = 456.91 ^ > Evaporator Ton kW Ton kW V

(evap)ton= 396.1 (fan)int-ter ton&kW= 17.7 62.4 (fan)per-ter ton&kW= 17.7 62.4TER= 42.0 Theat-air= 55.0

TER-app= 2.39 (D)heat ton&kW = 0.0 0.0 ^ EVAPton= 792 Treheat air = 55.0

(H)evap= 34.5 (D)reheat ton&kW = 0.0 0.0(evap)ft/sec= 8.38 62.4

(evap)des-ft/sec= 8.38 (D)int-air-ton= -318.6 Interior (D)per-air-ton= -173.8 Peri ^ V Tair coils = 55.00 duct Tair coils= 55.00 duct

gpmevap= 1200 Psec-heat-ton = -2.1 (D)int-CFM= 176,985 ^ (D)per-CFM= 96,565 ^(lwt)evap = 44.43 > Psec-kW= 28.6 > (ewt)coil= 44.4 >>>(Coil)sen-ton= 611 ^ (coil)gpm= 36.6 ^

(H)pri-total= 44.1 v Efdes-sec-p = 0.80 (coil)cap-ton= 30.7 UAdesign= 2.66 ^ (H)pri-pipe= 2.5 Tbp= 44.43 Efsec-pump = 0.75 (coil)H2O-ft/sec= 1.00 COIL UA= 2.39

(H)pri-fitings= 7.0 gpmbp= -249 (H)sec= 119 PLANTton = 783 (coil)des-ft/sec= 1.20 (one coil)ton= 30.12(Ef)c-pump= 0.81 (H)pri-bp= 0.11 (H)sec-pipe= 58 LMTD= 12.83 (H)coil= 1.5 VPc-heat-ton= -0.66 v (H)sec-bp= 0.00 Pipesize-in = 8.0 (COIL)L+s-ton= 783 ^ ^ ^ (H)coil-des= 2.1

^ < pc-kW= 12.3 (ewt)evap = 60.27 < (gpm)sec= 951 < (lwt)coil= 64.4 <<<< Tair VAV= 79.81 TBLD-AR = 75.00Pchiller-# = 2 (FAN)VAV-CFM= 273,551 (Air)ret-CFM = 280,361 Return

chillerkW/evapton= 0.572 4PM All Electric Fuel Heat (FAN)ton-VAV= 77.5 (FAN)ret-kW= 81.8 Fan(plant)kW/site ton= 0.698 Design kW THERM Tdry bulb = 99.8 (FAN)kW-VAV= 272.5 (FAN)ret-ton= 23.2 VCCWSkW/bld ton= 2.25 BLD.kW= 731.4 Exhaust air recovery ON ^ (Air)ret-ton = 527.9

Peoplesen+lat ton = 99.2 (Fan)kW = 479.1 26 F.A.Inlet ^ Tar-to-VAV = 75.92WeatherEin-ton = 431.4 Ductheat= 0.0 0.00 statFA= 42 26 VAV FANS VAVret-sen ton = 436.3(Site)kW-Ein-ton = 344.3 (FA)heat= 0.0 0 TFA to VAV = 80.8 > Tret+FA = 76.67 VAVret Lat-ton = 58.28PlantkW-Ein-ton = 155.5 Heat total = 0.0 0.00 >(FA)sen-ton = > 97.1 (dh) = 5.568 < VAVret-CFM = 231,733 <

Total Ein-ton = 1030 PlantkW= 546.9 Plant > (FA)CFM= 41,817 > Efan-VSD= 0.657 VPumptot-heat-ton = -4.1 SystkW = 1757.4 0.0 SEE SCHEMATIC > (FA)Lat-ton= 114.1 VAV inlet-sen-ton = 533.4

AHU ExLat-ton = -12.2 Ton Blue (FA)kW= 0.0 VAVinlet-lat-ton= 172.4 ExLat-ton = -12.2AHU Exsen-ton = -91.6 BLD.kW= 731.4 kW Red ExCFM = -48,628Tower Tton-Ex = -935 CCWSkW = 1025.9 Water temp pink SEE SCHEMATIC air side TEx = 75.92

Einternal energy chg = 12.3 SystkW = 1757.4 Water gpm orange Air temp green kW red Exsen-ton = -91.6 V Total Eout-ton = -1030 St Louis air temp green Air CFM purple Ton blue Exair recovery ON Tex-recoc = 92.27 v

Figure 8 Total system with exhaust air energy recovery.

Comparing 8 & 9 illustrates the plant kW reduces from 597.4 kW to 546.9 kW and the total system kW reduces from 1807.9 kW to 1757.4 kW at peak summer design conditions. Each chiller kW reduces from 249.4 kW to 226.5 kW. A 9% smaller chiller with exhaust air energy recovery; the only

significant effect of exhaust air energy recovery as we will show with an analysis of 24 hour energy consumption.

Figure 9 Total system without exhaust air energy recovery

Figure 10: 24 hour performance with recovery

Figure 10 illustrates the 24 hour performance of the system with exhaust air energy recovery. The bottom chart illustrates the maximum possible energy transfer to the fresh air as a function of air CFM and delta temperature. For the conditions of this design and the fact that it is a one shift office building; the exhaust air has more max possible energy than the fresh air. The bottom chart also gives the energy transferred to the fresh air.

The top chart of Figure 10 shows the fresh air CFM drops off and therefore the tons transferred to the fresh air drops off. The

top chart also shows the air temperatures illustrating the difference in the dry bulb temperature of outside air and the approximate 75.8F exhaust air drives the amount of energy available for transfer to the fresh air.

A building that operates more than one shift would have greater 24 hour transfer of energy to the fresh air.

Figure 11: 24 hour performance

BLD sq-ft = 498,600ALL ELECTRIC Peak day

Design 24hr BLD.24hr-kW= 10,096

(Fan)24hr-kW = 6,482(Duct)24hr-heat kW= 0

(FA)24hr-heat kW= 0Heat24hr-total kW= 0

Plant24hr-kW= 7,688SYST 24hr-kW = 24,267

(CCWS)24hr-kW= 14,170BLD.24hr-kW= 10,096

Total24hr-kW = 24,267People24hr Ein ton = 950.0Weather24h-Ein-ton= 6059.6SITE24h-kW-Ein-ton = 4715.2Plant24h-kW-Ein-ton = 2186.6Total24h-Ein-ton = 13911.4Pump24hr-heat-ton = -79.3

AHU Ex24hr-Lat-ton = -181.5AHU Ex24hr-sen-ton = -1247.9

Tower24hr-ton-Ex = -12696.4E24hr chg internal energy = 294.23

Total E24hr-out-ton = -13910.9ASHRAE

Figure 12: 24 hour performance without exhaust air energy recovery

Figure 11, 12, & 13 illustrates the exhaust air energy recovery has moderate effect on 24 hour energy consumption at peak design summer weather conditions.

Figure 13: 24 hour performance with exhaust air energy recovery

CONCLUSION FOR PEAK DESIGN DAY WEATHER CONDITIONS

Exhaust air energy recovery reduces the chiller kW about 9% for the conditions studied here.

Next we will consider average summer conditions.

TYPICAL SUMMER WEATHER

Figure 14: Summer weather

Figure 15 24 hour system kW demand

Figure 14 gives the assumed typical summer weather and Figure 15 gives the 24 hour system kW for the system with and without exhaust air energy recovery illustrating very little effect with exhaust air energy recovery.

Figure 16 System 24 hour performance with exhaust air recovery

CONCLUSION

For the conditions studied here exhaust air energy recovery has be shown to have very little effect on the total energy consumption of the system. This study showed that the kW size of the chiller is reduced about 9% if exhaust air energy recovery is installed in all 26 VAV fan systems.

ASHRAE Standard 90.1-2013 requirement for exhaust air energy recovery is at best questionable.

NOMENCLATURE (NOTE see other papers at this site for additional understanding of the system and nomenclature) Air Side System Nomenclature Each of the more than 100 variables of the air side system 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 buildingTstat-int = interior stat set temperature (F)Bldint-air-ton = supply air ton to offset interior loadBLD kW = total building kW demandBuilding perimeter space;%clear sky = percent clear skyTdry bulb = outside dry bulb temperature (F)Twet bulb = outside wet bulb temperature (F)Ex/Infillat-ton = latent load due to air infiltration or exfiltration (ton)Ex/InfilCFM = air infiltration or exfiltration CFM

Exfilsen-ton =sensible load due to 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 systemInterior 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 duct(ABS Bld Ton) = absolute building load on (CCWS)Coil(coil)sen-ton = sensible load on all coils (ton)(coil)cap-ton = LMTD * UA = capacity (ton) one coil(coil)H2O-ft/sec = water velocity thru coil (ft/sec)(coil)design-ft/sec = coil design water velocity (ft/sec)LMTD = coil log mean temperature difference (F)(coil)L+s-ton = latent + sensible load on all coils (ton) transferred to Plant(coil)gpm = water flow (gpm) thru one coilUAdesign = coil UA design valueUA = 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 coil(H)coil = air pressure drop thru coil (inches)(H)coil-design = design air pressure drop (inches)VAV 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 inlet

VAVret-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 plant

CENTRAL PLANT

Nomenclature will be defined by addressing each component of the plant.Primary/secondary pumping nomenclaturegpmevap = total gpm flow thru 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)Plantton = load (ton) from air side to plantPipesize-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 kWPlant kW = total kW demand of plantCondenser nomenclature:(cond)ton = load (ton) on one condenserTCR = temperature of condenser refrigerant (F)TCR-app = refrigerant approach temperature (F)(COND)ton = total load (ton) on all condensers(H)cond = tower pump head thru condenser (ft)(cond)ft/sec = tower water flow thru condenserTower piping nomenclaturePipesize-in = tower pipe size (inches)gpmT = each tower water flow (gpm)(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 on

tfan-% = percent tower fan speedtton-ex = ton exhaust by one tower

T# = number of towers onTton-ex = ton exhaust by all towers onTrg+app = tower range + approach (F)One hour performance indicesBLDkW = kW demand of building lights & plug loadsFankW = air side fans kW, VAV, return terminalsDuctheat = perimeter heat to air supplyFAheat = heat added to fresh airHeattotal = total heat added to airPlantkW = total plant kWSystkW = total system kWCCWSkW = air side + 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 ton

Tower 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 system airPlant24hr kW = plant 24 hour kW usageSyst24hr kW & therm = total system 24 hour energy usage(CCWS)24hr-kW = Central chilled water system (air side + plant) 24 hour kW usageWeather24hr-Ein-ton = 24 hour weather energy into systemSITE24hr-kW-Ein-ton = 24 hour energy into site, building & air side systemPlant24hr-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 building

Tower24hr out-ton = tower exhaust from system (ton)Total E24hr-out-ton = total 24 hour energy out of system