Chapter 7 : Air Conditioning¶

Example 7.1 Page no : 345¶

In :
# Variables
DBTo = 10.;			#Out door Dry bulb temperature in oC
WBTo = 8.;			#Out door Wet bulb temperature in oC
DBTi = 20.;			#In door Dry bulb temperature in oC
RH = 0.6;			#Re-Heat factor
a = 0.3;			#amount of air circulated in (m**3)/min/person
S = 50.;			#Seating capacity of office
BPF = 0.32;			#ByPass factor
ha = 25.;			#Enthalpy at point a from Psychrometric chart shown in Page 346 in kJ/kg
hb = 42.5;			#Enthalpy at point b from Psychrometric chart shown in Page 346 in kJ/kg
hc = 42.5;			#Enthalpy at point c from Psychrometric chart shown in Page 346 in kJ/kg
Wa = 0.006;			#Specific humidity at point a from Psychrometric chart shown in Page 346 in kg/kg dry air
Wc = 0.009;			#Specific humidity at point c from Psychrometric chart shown in Page 346 in kg/kg dry air
Tb = 27.;			#Temperature at point b in oC
na = 0.81;			#Specific Volume from Psychrometric chart shown in page 346 in (m**3)/kg

# Calculations
ma = (a*S)/(na*60);			#mass of air circulated per second in kg/s
Hc = ma*(hb-ha);			#Heating capacity of coil in kW
Ts = (Tb-(BPF*DBTo))/(1-BPF);			#Heating coil surface temperature in oC
C = (ma*3600)*(Wc-Wa);			#Capacity of humidifier in kg/hr

# Results
print 'Heating capacity of coil is %3.2f kW  \
\nSurface temperature of coil is %3.0f C  \
\nCapacity of humidifier is %3.2f kg/hr'%(Hc,Ts,C)

# rounding off error
Heating capacity of coil is 5.40 kW
Surface temperature of coil is  35 C
Capacity of humidifier is 3.33 kg/hr

Example 7.2 Page no : 346¶

In :
# Variables
S = 60.;			#No. of staff
DBTo = 30.;			#Out door Dry bulb temperature in oC
RHo = 0.7;			#Re-Heat factor at out-door
a = 0.4;			#amount of air circulated in (m**3)/min/person
DBTi = 20.;			#In door Dry bulb temperature in oC
RHi = 0.6;			#Re-Heat factor at indoor
Td = 25.;			#Heating coil surface temperature in oC
ha = 82.5;			#Enthalpy at point a from Psychrometric chart shown in Page 347 in kJ/kg
hb = 34.5;			#Enthalpy at point b from Psychrometric chart shown in Page 347 in kJ/kg
hc = 42.5;			#Enthalpy at point c from Psychrometric chart shown in Page 347 in kJ/kg
Wa = 0.020;			#Specific humidity at point a from Psychrometric chart shown in Page 347 in kg/kg dry air
Wb = 0.009;			#Specific humidity at point b from Psychrometric chart shown in Page 347 in kg/kg dry air
Tb = 12.;			#Temperature at point b in oC
na = 0.89;			#Specific Volume from Psychrometric chart shown in page 346 in (m**3)/kg

# Calculations
ma = (a*S)/(na*60);			#mass of air circulated per second in kg/s
Hc = (ma*(ha-hb))/3.5;			#Heating capacity of cooling coil in tonnes
Hh = ma*(hc-hb);			#Heating capacity of heating coil in kW
W = (ma*3600)*(Wa-Wb);			#Amount of water vapour removed per hour in kg/hr
BPF = (Td-DBTi)/(Td-Tb);			#By-Pass factor

# Results
print 'Capacity of cooling coil is %3.2f tonnes  \
\nCapacity of heating coil is %3.1f kW  \
\nAmount of water vapour removed per hour is %3.2f kg/hr  \
\nBypass factor is %3.3f'%(Hc,Hh,W,BPF)
Capacity of cooling coil is 6.16 tonnes
Capacity of heating coil is 3.6 kW
Amount of water vapour removed per hour is 17.80 kg/hr
Bypass factor is 0.385

Example 7.3 Page no : 347¶

In :
# Variables
RSH = 10.;			#Room sensible heat in kW
RLH = 10.;			#Room latent heat in kW
td1 = 25.;			#Inside temperature in oC
RH1 = 0.5;			#Inside Re-Heat factor
h1 = 50.4;			#Enthalpy at point 1 in kJ/kg
td2 = 35.;			#Out door Dry bulb temperature in oC
tw2 = 28.;			#Out door Wet bulb temperature in oC
CR = 4.;			#Cooling coil ratio
BPF = 0.1;			#Cooling coil bypass factor
tADP = 10;			#Apparatus dew point temperature in oC
RH3 = 0.55;			#Re-Heat factor at point 3
h3 = 58.2;			#Enthalpy at point 3 in kJ/kg
RH4 = 0.95;			#Re-Heat factor at point 4
h4 = 32.2;			#Enthalpy at point 4 in kJ/kg
RH5 = 0.81;			#Re-Heat factor at point 5
h5 = 36.8;			#Enthalpy at point 5 in kJ/kg
RH6 = 0.54;			#Re-Heat factor at point 6
h6 = 43.1;			#Enthalpy at point 5 in kJ/kg
td6 = 22.;			#Temperature at point 6 in oC

# Calculations
td3 = ((td2-td1)/5)+td1;			#Temperature at point 3 from Psychrometric chart shown in Page 348 in oC
td4 = (BPF*(td3-tADP))+tADP;			#Temperature at point 4 from Psychrometric chart shown in Page 348 in oC
td5 = td4+((td1-td4)/5);			#Temperature at point 5 from Psychrometric chart shown in Page 348 in oC
RSHF = RSH/(RSH+RLH);			#Room Sensible Heat Factor
QR = h1-h6;			#Total heat removed in kJ/kg
S = (RSH+RLH)/QR;			#Supply air quantity in kg/s
R = (S*(h6-h5))/3.5;			#Refrigeration load due to reheat in ton
D = (S*4)/5;			#Dehumidified air quantity in kg/s
T = (D*(h3-h4))/3.5;			#Total refrigerating capacity in ton
Q = (D/5)/1.2;			#Quantity of fresh air supplied in (m**3)/s

# Results
print 'Supply air condition to the room is %3.2f kg/s  \
\nRefrigeration load due to reheat is %3.2f ton  \
\nTotal refrigerating capacity is %3.2f ton  \
\nQuantity of fresh air supplied is %3.3f m**3/s'%(S,R,T,Q)
Supply air condition to the room is 2.74 kg/s
Refrigeration load due to reheat is 4.93 ton
Total refrigerating capacity is 16.28 ton
Quantity of fresh air supplied is 0.365 m**3/s