"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
"UA Equations for Condenser"
PROCEDURE ua(tons:UA_cnd)
IF tons<800 THEN
UA_cnd:=2530664-756321.5*(tons/1000)+467446.3*(tons/1000)^2
Else
UA_cnd:=2224488
Endif
END
"Calculates friction 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
"Tower coefficients, tower fan constants, and air flow rate through tower are defined 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
"Resets value of temperature of entering condenser water to 68F if 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
TNUM=19 {Tower #19 was
CALL Tower(TNUM:c,n,FHPCA,FHPCB,V_a) optimum tower for
CALL setpoint (T_twrocalc:T_twro) 1000 ton electric
CALL load(T_ai: tons) chiller}
CALL frictionfactor (Re_d,PipeD:f)
CALL towerduty (TDcalc:TD)
"Cooling Tower Model"
Q=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)))) {effectiveness}
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}
"Calculates Tower Duty"
TDcalc=(deltaT_cnd-.1*deltaT_twron)/(.9*deltaT_twron)
FanKW=((FanHP*.7457)/.85)*TD {kW}
"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}
"Chiller Model"
W_cmpact=Q_evp+Q_cnd {Actual cmp work}
"Condenser Model"
Q_cndB=Epsilon_cnd*m_wcnd*C_pw*(T_wcndi-T_cnd) {Btu/hr}
Epsilon_cnd=1-exp(-NTU_cnd) {condenser e}
NTU_cnd=UA_cnd/(m_wcnd*C_pw)
Q_cnd=Q_cndB*convert(Btu/hr,kW) {kW}
CALL ua(tons:UA_cnd)
deltaT_cnd=T_wcndi-T_wcndo {R}
Q_cndB=m_wcnd*C_pw*deltaT_cnd {Btu/hr}
"Compressor Model"
W_cmpcarB=Q_evpB*(1-(T_cnd/T_evp)) {Btu/hr}
W_cmpcar=W_cmpcarB*convert(Btu/hr,kW) {kw}
W_cmpact=1.2194*(-W_cmpcar)+52.092 {Actual cmp work}
"Evaporator Model"
Q_evpB=m_wevp*C_pw*(deltaT_evp) {Btu/hr}
deltaT_evp=(T_wevpi-T_wevpo) {R}
Q_evpB=UA_evp*LMTD_evp {Btu/hr}
LMTD_evp=(T_wevpi-T_wevpo)/(ln(A))
A=(T_wevpi-T_evp)/(T_wevpo-T_evp)
Q_evpB=tons*convert(ton,Btu/hr) {Btu'hr}
UA_evp=629616.7+2268038*(tons/1000)-1174776*(tons/1000)^2
Q_evp=Q_evpB*convert(Btu/hr,kW)
"Chiller Input"
T_wcndi=T_twro
T_twri=T_wcndo
T_wevpo=504 {fixed chilled water
V_wcnd=3000*convert(gpm,cfm) supply temp}
V_wevp=2400*convert(gpm,cfm)
m_wevp=V_wevp*density(WATER,T=T_wevpo,P=14.7)*(60){lbm/hr}
"Constant Specific Heat"
C_pw=1
"Flow rates"
V_w=3000*convert(gpm,cfm) {cnd water flowrate}
m_wcnd=V_w*density(WATER,T=535,P=14.7)*(60) {lbm/hr}
m_a=V_a*density(AIRH2O,T=T_ai,P=14.7,B=B_ai)*(60){lbm/hr}
"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=20 {cnd head loss}
"H_tower"
H_tower=11 {tower 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}
"Inputs"
d=12 {pipe diamter}
gpm=3000 {waterflow rate}
"Weather Data"
{These values were put into a parametric table along with electric and gas rates for each month.}
"Total Work"
W_tot=W_cmpact+PumpKW+FanKW {kW}
"Total Power"
P_cmp=W_cmpact*HRS {kWh}
HRS=3 {Each run in the paramteric table corresponded to 3 hours.}
EnergyCost_cmp=P_cmp*Rate/100 {Rates were given in
EnergyCost_fan=FanKW*HRS*Rate/100 cents/kWh}
EnergyCost_pump=PumpKW*HRS*Rate/100
EnergyCost=W_tot*HRS*Rate/100