"Building Cooling Load Profile"
PROCEDURE load(T_ai: tons) {T_ai=dry bulb temp}
IF (T_ai>=558) THEN {Units of T_ai = R}
tons:=1000
Endif
IF (T_ai>=520) and (T_ai<=558) THEN
tons:=21.052*(T_ai-460)-1063.156
ENDIF
IF T_ai<520 THEN
tons:=200
ENDIF
END
"Gives tower coefficients, tower fan constants, and air flor rates for specific towers."
PROCEDURE tower (TNUM:c,n,FHPCA,FHPCB,V_a)
IF TNUM=1 THEN
n:=-.7907
c:=1.2581
FHPCA:=0.2150
FHPCB:=6.2501
V_a:=70800 {cfm}
ENDIF
IF TNUM=2 THEN
n:=-.7907
c:=1.2581
FHPCA:=0.2150
FHPCB:=6.2501
V_a:=80750
ENDIF
IF TNUM=3 THEN
n:=-.7907
c:=1.2581
FHPCA:=.2150
FHPCB:=6.2501
V_a:=88300
ENDIF
IF TNUM=4 THEN
n:=-.7907
c:=1.2581
FHPCA:=.2150
FHPCB:=6.2501
V_a:=95000
ENDIF
IF TNUM=5 THEN
n:=-.8068
c:=1.3209
FHPCA:=-.5028
FHPCB:=6.3801
V_a:=99400
ENDIF
IF TNUM=6 THEN
n:=-.8068
c:=1.3209
FHPCA:=-.5028
FHPCB:=6.3801
V_a:=108700
ENDIF
IF TNUM=7 THEN
n:=-.8068
c:=1.3209
FHPCA:=-.5028
FHPCB:=6.3801
V_a:=116550
ENDIF
IF TNUM=8 THEN
n:=-.8068
c:=1.3209
FHPCA:=-.5028
FHPCB:=6.3801
V_a:=123550
ENDIF
IF TNUM=9 THEN
n:=-.8167
c:=1.3184
FHPCA:=-.7495
FHPCB:=6.0872
V_a:=124450
ENDIF
IF TNUM=10 THEN
n:=-.8167
c:=1.3184
FHPCA:=-.7495
FHPCB:=6.0872
V_a:=133450
ENDIF
IF TNUM=11 THEN
n:=-.8167
c:=1.3184
FHPCA:=-.7495
FHPCB:=6.0872
V_a:=142200
ENDIF
IF TNUM=12 THEN
n:=-.8240
c:=1.4034
FHPCA:=-.9342
FHPCB:=6.3006
V_a:=143800
ENDIF
IF TNUM=13 THEN
n:=-.8240
c:=1.4034
FHPCA:=-.9342
FHPCB:=6.3006
V_a:=157550
ENDIF
IF TNUM=14 THEN
n:=-.8429
c:=1.3538
FHPCA:=-1.4302
FHPCB:=6.3567
V_a:=166050
ENDIF
IF TNUM=15 THEN
n:=-.8429
c:=1.3538
FHPCA:=-1.4302
FHPCB:=6.3567
V_a:=181800
ENDIF
IF TNUM=16 THEN
n:=-.8429
c:=1.3538
FHPCA:=-1.4302
FHPCB:=6.3567
V_a:=195000
ENDIF
IF TNUM=17 THEN
n:=-.7834
c:=1.4031
FHPCA:=-1.6379
FHPCB:=6.3624
V_a:=193800
ENDIF
IF TNUM=18 THEN
n:=-.7834
c:=1.4031
FHPCA:=-1.6379
FHPCB:=6.3624
V_a:=207800
ENDIF
IF TNUM=19 THEN
n:=-.7834
c:=1.4031
FHPCA:=-1.6379
FHPCB:=6.3624
V_a:=220150
ENDIF
IF TNUM=20 THEN
n:=-.6737
c:=1.3967
FHPCA:=-1.6823
FHPCB:=6.1870
V_a:=221550
ENDIF
IF TNUM=21 THEN
n:=-.6737
c:=1.3967
FHPCA:=-1.6823
FHPCB:=6.1870
V_a:=235000
ENDIF
IF TNUM=22 THEN
n:=-.7044
c:=1.3936
FHPCA:=-2.3084
FHPCB:=6.3769
V_a:=255400
ENDIF
IF TNUM=23 THEN
n:=-.7044
c:=1.3936
FHPCA:=-2.3084
FHPCB:=6.3769
V_a:=270700
ENDIF
IF TNUM=24 THEN
n:=-.7044
c:=1.3936
FHPCA:=-2.3084
FHPCB:=6.3769
V_a:=290050
ENDIF
END
"This procedure resets the temperature for the entering cooling water to 68F if the exiting tower water is less than 68F."
PROCEDURE setpoint (T_twrocalc:T_twro)
IF T_twrocalc>=528 THEN
T_twro:=T_twrocalc
ENDIF
IF T_twrocalc<528 THEN
T_twro:=528
ENDIF
END
"This procedure calculates the fricion factor for pipe flow."
PROCEDURE frictionfactor (Re_d,PipeD:f)
IF Re_d<2300 THEN
f:=64/Re_d
Else
AA:=(6.9/Re_d)+((.00015/(PipeD*3.7))^1.11)
BB:=log10(AA)/log10(10)
f:=(1/(-1.8*BB))^2
Endif
END
"The optimum cooling tower for the engine driven gas chiller unit was tower #22."
TNUM=22
CALL Tower(TNUM:c,n,FHPCA,FHPCB,V_a)
CALL setpoint (T_twrocalc:T_twro)
CALL frictionfactor(Re_d,PipeD:f)
"Cooling Tower Model"
Q_twr=epsilon_a*m_a*(h_swi-h_ai) {Btu/hr}
epsilon_a=(1-exp(-(Ntu*(1-m_star))))/(1-m_star*exp(-(Ntu*(1-m_star)))) {cool twr efectiveness}
m_star=m_a/(m_wcnd*(C_pw/C_s))
C_s=(h_swi-h_swo)/(T_twri-T_twro)
h_ao=h_ai+epsilon_a*(h_swi-h_ai) {Btu/lbm}
T_twrocalc=T_twri-m_a*(h_ao-h_ai)/(m_wcnd*C_pw){R}
Ntu=c*(m_wcnd/m_a)^(1+n)
deltaT_twron=T_twrocalc-T_twri {R}
"Fan Power"
FanHP=exp(FHPCA+((ln(V_a)-10.5)/2)*FHPCB) {hp}
TD=(deltaT_cnd-.1*deltaT_twron)/(.9*deltaT_twron){tower duty}
FanKW=((FanHP*.7457)/.85)*TD {kW}
deltaT_cnd=(T_twro-T_twri) {R}
"Water Pump"
TDH=H_piping+H_tower+H_cnd {total dynamic head}
"H_piping"
H_piping=(s^2/(2*g))*((f*L)/PipeD) {piping head loss}
PipeL=200
PipefL=450*PipeD
PipestrainL=250*PipeD
L=PipeL+PipefL+PipestrainL {equivalent length}
PipeD=d/12 {ft}
s=(gpm*.002228)/((3.1416*(PipeD^2))/4) {ft/sec}
Re_d=(s*PipeD)/8.64E-6 {Reynolds #}
epsilon=.00015 {ft}
g=32.2 {ft/sec^2}
"H_cnd"
H_cnd=30 {cnd head loss}
"H_tower"
H_tower=11 {twr head loss]
"PumpPower"
PumpHP=(gpm*TDH)/(3960*eta_pump) {hp}
eta_pump=.65 {pump efficiency}
eta_motor=.85 {motor efficiency}
PumpKW=PumpHP*.7457/eta_motor {kW}
d=12 {pipe diam - inches}
gpm=3000 {cnd flow rate}
"Property Relations"
h_swi=enthalpy(AIRH2O,T=T_twri,r=1,P=14.7) {Btu/lbm}
h_swo=enthalpy(AIRH2O,T=T_twro,r=1,P=14.7) {Btu/lbm}
h_ai=enthalpy(AIRH2O,T=T_ai,B=B_ai,P=14.7) {Btu/lbm}
"Inputs"
C_pw=1
V_wcnd=3000*convert(gpm,cfm) {cnd flow rate}
m_wcnd=V_wcnd*rho*(60) {lbm/hr}
rho=density(WATER,T=T_twri,P=14.7) {density, lbm/ft^3}
m_a=V_a*density(AIRH2O,T=T_ai,P=14.7,B=B_ai)*(60){lbm/hr}
"Design Cooling Load"
Tons_design=1000 {tons}
"Enter Outside Conditions"
{These weather conditions were listed along with the electric and gas rates in a paramtric table for each month.}
HRS=3
CALL load(T_ai: tons)
load%=tons/Tons_design {percent of design load}
A=lookuprow(#percent,load%) "A lookup table was
B=(.1*T_twro)-50.5 used for Figure 3.6 -
COP=lookup(A,B) calculates COP."
"Cycle equations"
Q_cnd=m_wcnd*C_pw*(deltaT_cnd) {Btu/hr}
Q_e+Q_cnd=W_cmp {Btu/hr}
W_cmp=eta_eng*Q_g {Btu/hr}
eta_eng=.30 {engine efficiency}
Q_g=-Q_e/COP {Btu/hr}
Q_e=tons*convert(ton,Btu/hr) {Btu/hr}
P_eng=-Q_g*HRS {Btu}
Therm=P_eng*convert(Btu,therm) {Therms}
"Calculates energy cost by applying rates to consumption."
EnergyCost_chill=Therm*Rate_gas {$}
EnergyCost_fan=FanKW*HRS*Rate/100
EnergyCost_pump=PumpKW*HRS*Rate/100
EnergyCost=EnergyCost_chill+EnergyCost_fan+EnergyCost_pump
"Heat Recovery"
Q_gcreditB=(((1-eta_eng)*(eta_whrec))/eta_boiler)*P_eng{Btu}
Q_gcredit=Q_gcreditB*convert(Btu,therm) {therm}
eta_whrec=0.65 {heat rec. fraction}
eta_boiler=0.78 {boiler efficiency}
"Gas rates are applied to the heat recovery credit and subtracted from the energy cost."
EnergyCost_withheatrec=EnergyCost-(Q_gcredit*Rate_gas)