File:Psych1HeatCoil.EES
10/21/2003 3:41:38 PM Page 1
EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
"AREN 3010
In-Class Psychrometric Problem #1"
"
Moist air enters a heating coil at 40°F dry-bulb temperature
and 36°F wet-bulb temperature at a rate of 2000 cfm.
Barometric pressure is 14.696 psia. The air leaves the
coil at a dry-bulb temperature of 140°F. "
"Given information"
P_atm = 14.696
T_sa = 140
T_ma = 40
TWB_ma = 36
CFM_ma = 2000
TW_ent = 180
TW_lvg = 160
T_steam = 250
"Calculate properties of mixed air"
W_ma = HUMRAT(AIRH2O,t=T_ma, b=TWB_ma,p=P_atm)
h_ma = ENTHALPY(AIRH2O,t=T_ma, w=W_ma,p=P_atm)
v_ma = VOLUME(AIRH2O,t=T_ma, w=W_ma,p=P_atm)
c_p = SPECHEAT(AIRH2O,t=T_ma,w=W_ma,p=P_atm)
"a)
How much heat is added to the air?"
m_sa = CFM_ma/v_ma*CONVERT(hr,min)
h_sa = ENTHALPY(AIRH2O,t=T_sa, w=W_ma,p=P_atm)
Q_air = m_sa*(h_sa-h_ma)
Q_airT = m_sa*c_p*(T_sa-T_ma)
"b)
If the heat is provided by hot water that enters the coil at 180°F
and leaves at 160°F, what is the water flow rate?"
c_WATER = SPECHEAT(WATER,t=TW_ent,p=P_atm)
m_w = Q_air/(c_WATER*(TW_ent-TW_lvg))
"c)
If the heat is provided by a steam coil with saturated steam at 250°F,
what steam flow rate is required?
File:Psych1HeatCoil.EES
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
Assume that the steam leaves the coil as a saturated liquid?"
hfg_steam = ENTHALPY(STEAM,t=T_steam,x=1)-ENTHALPY(STEAM,t=T_steam,x=0)
m_steam = Q_air/hfg_steam
AREN 3010
In-Class Psychrometric Problem #1
Moist air enters a heating coil at 40°F dry-bulb temperature
and 36°F wet-bulb temperature at a rate of 2000 cfm.
Barometric pressure is 14.696 psia. The air leaves the
coil at a dry-bulb temperature of 140°F.
Given information
= 14.696
P atm
T sa
= 140
T ma
= 40
TWB ma
= 36
CFM ma
= 2000
TW ent
= 180
TW lvg
= 160
T steam
= 250
Calculate properties of mixed air
= ω
W ma
'AirH2O' , T = T ma , B = TWB ma , P = P atm
h ma
= h 'AirH2O' , T = T ma , w = W ma , P = P atm
v ma
= v 'AirH2O' , T = T ma , w = W ma , P = P atm
cp
= Cp 'AirH2O' , T = T ma , w = W ma , P = P atm
a) How much heat is added to the air?
CFM ma
min
m sa
=
h sa
= h 'AirH2O' , T = T sa , w = W ma , P = P atm
Q air
= m sa ·
Q airT
v ma
·
60 ·
hr
h sa – h ma
= m sa · c p ·
T sa – T ma
b) If the heat is provided by hot water that enters the coil at 180°F
and leaves at 160°F, what is the water flow rate?
c WATER
= Cp 'Water' , T = TW ent , P = P atm
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
mw
=
Q air
c WATER
·
TW ent – TW lvg
c) If the heat is provided by a steam coil with saturated steam at 250°F,
what steam flow rate is required?
Assume that the steam leaves the coil as a saturated liquid?
hfg steam
m steam
= h 'Steam' , T = T steam , x = 1
=
– h 'Steam' , T = T steam , x = 0
Q air
hfg steam
Unit Settings: [F]/[psia]/[lbm]/[degrees]
CFMma = 2000 [cfm]
hfgsteam = 945.5 [Btu/lbm]
msa = 9473 [lbm/hr]
Patm = 14.7 [psia]
TWB ma = 36 [F]
Tma = 40 [F]
vma = 12.67 [ft3/lbm]
cp = 0.2419 [Btu/lbm-R]
hma = 13.42 [Btu/lbm]
msteam = 242.4 [lbm/hr]
Qair = 229218 [Btu/hr]
TW ent = 180 [F]
Tsa = 140 [F]
W ma = 0.003532
No unit consistency or conversion problems were detected.
cWATER = 1.002 [Btu/lbm-R]
hsa = 37.62 [Btu/lbm]
mw = 11435 [lbm/hr]
QairT = 229162 [Btu/hr]
TW lvg = 160 [F]
Tsteam = 250 [F]
File:Psych2ZoneHeat.EES
10/21/2003 3:50:04 PM Page 1
EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
"AREN 3010
In-Class Psychrometric Problem #2"
"A building space is to be maintained at 70°F dry-bulb and 30% RH
when the barometric pressure is 14.696 psia. The total heating load
on the space has been calculated to be 60,000 Btu/hr.
Supply air is delivered to the space at a temperature of 120°F "
"Given information"
P_atm = 14.696
T_sa = 120
T_ra = 70
RH_ra = .3
Q_heat = 60000
Q_fan = 400*CONVERT(W,Btu/hr)
"Calculate properties of outdoor and return air"
W_ra = HUMRAT(AIRH2O,t=T_ra, r=RH_ra,p=P_atm)
v_ra = VOLUME(AIRH2O,t=T_ra, w=W_ra,p=P_atm)
v_sa = VOLUME(AIRH2O,t=T_sa, w=W_ra,p=P_atm)
c_p = SPECHEAT(AIRH2O,t=T_ra,w=W_ra,p=P_atm)
"a)
What is the volumetric airflow required for the space?"
m_sa=Q_heat /(c_p*(T_sa-T_ra))
CFM_sa = m_sa*v_sa/CONVERT(hr,min)
CFM_ra = m_sa*v_ra/CONVERT(hr,min)
"b)
What is the discharge air temperature?"
T_da = T_sa-Q_fan/(m_sa*c_p)
AREN 3010
In-Class Psychrometric Problem #2
A building space is to be maintained at 70°F dry-bulb and 30% RH
when the barometric pressure is 14.696 psia. The total heating load
on the space has been calculated to be 60,000 Btu/hr.
Supply air is delivered to the space at a temperature of 120°F
File:Psych2ZoneHeat.EES
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
Given information
P atm
= 14.696
T sa
= 120
T ra
= 70
RH ra
= 0.3
Q heat
= 60000
Q fan
= 400 ·
3.41214 ·
Btu/hr
W
Calculate properties of outdoor and return air
W ra
= ω
'AirH2O' , T = T ra , R = RH ra , P = P atm
v ra
= v 'AirH2O' , T = T ra , w = W ra , P = P atm
v sa
= v 'AirH2O' , T = T sa , w = W ra , P = P atm
cp
= Cp 'AirH2O' , T = T ra , w = W ra , P = P atm
a) What is the volumetric airflow required for the space?
m sa
=
CFM sa
Q heat
cp ·
T sa – T ra
v sa
= m sa ·
min
60 ·
CFM ra
hr
v ra
= m sa ·
60 ·
min
hr
b) What is the discharge air temperature?
T da
= T sa –
Q fan
m sa · c p
Unit Settings: [F]/[psia]/[lbm]/[degrees]
CFMra = 1110 [cfm]
msa = 4949 [lbm/hr]
Qheat = 60000 [Btu/hr]
Tra = 70 [F]
vsa = 14.72 [ft3/lbm]
CFMsa = 1214 [cfm]
Patm = 14.7 [psia]
RHra = 0.3
Tsa = 120 [F]
W ra = 0.004648
No unit consistency or conversion problems were detected.
cp = 0.2425 [Btu/lbm-R]
Qfan = 1365 [Btu/hr]
Tda = 118.9 [F]
vra = 13.45 [ft3/lbm]
File:Psych3CoolCoil.EES
10/21/2003 12:01:00 PM Page 1
EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
"AREN 3010
In-Class Psychrometric Problem #3"
"
Moist air enters a cooling coil at 78°F dry-bulb temperature and
50% RH at a rate of 2400 cfm. Barometric pressure is 14.696 psia.
The air leaves the coil at a dry-bulb temperature of 55°F and a
dew-point temperature of 53°F. The condensate leaves at a
temperature of 52°F. "
"Given information"
P_atm = 14.696
T_da = 55
TDP_da = 53
T_ma = 78
RH_ma = .5
CFM_ma = 2400
T_cond = 52
"Calculate properties of mixed and supply air"
W_ma = HUMRAT(AIRH2O,t=T_ma, r=RH_ma,p=P_atm)
h_ma = ENTHALPY(AIRH2O,t=T_ma, w=W_ma,p=P_atm)
v_ma = VOLUME(AIRH2O,t=T_ma, w=W_ma,p=P_atm)
W_da = HUMRAT(AIRH2O,t=T_da, d=TDP_da,p=P_atm)
h_da = ENTHALPY(AIRH2O,t=T_da, w=W_da,p=P_atm)
c_p = SPECHEAT(AIRH2O,t=T_ma,w=W_ma,p=P_atm)
"a)
What is the total load on the coil?"
m_sa = CFM_ma/v_ma*CONVERT(hr,min)
h_cond = ENTHALPY(WATER,t=T_cond,p=P_atm)
m_cond = m_sa*(W_ma-W_da)
Q_totExact = m_sa*(h_ma-h_da)-m_cond*h_cond
Q_tot=m_sa*(h_ma-h_da)
Error_Q = (Q_tot-Q_totExact)/Q_totExact
"b)
What is the sensible heat ratio?"
Q_sen = m_sa*c_p*(T_ma-T_da)
SHR = Q_sen/Q_tot
"c)
What are the supply air conditions?"
Q_fan = 1200*CONVERT(W,Btu/hr)
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
T_sa = T_da+Q_fan/(m_sa*c_p)
W_sa = W_da
AREN 3010
In-Class Psychrometric Problem #3
Moist air enters a cooling coil at 78°F dry-bulb temperature and
50% RH at a rate of 2400 cfm. Barometric pressure is 14.696 psia.
The air leaves the coil at a dry-bulb temperature of 55°F and a
dew-point temperature of 53°F. The condensate leaves at a
temperature of 52°F.
Given information
= 14.696
P atm
T da
= 55
TDP da
T ma
= 53
= 78
RH ma
= 0.5
CFM ma
= 2400
T cond
= 52
Calculate properties of mixed and supply air
W ma
= ω
'AirH2O' , T = T ma , R = RH ma , P = P atm
h ma
= h 'AirH2O' , T = T ma , w = W ma , P = P atm
v ma
= v 'AirH2O' , T = T ma , w = W ma , P = P atm
W da
= ω
'AirH2O' , T = T da , D = TDP da , P = P atm
h da
= h 'AirH2O' , T = T da , w = W da , P = P atm
cp
= Cp 'AirH2O' , T = T ma , w = W ma , P = P atm
a) What is the total load on the coil?
m sa
=
CFM ma
v ma
·
60 ·
min
hr
h cond
= h 'Water' , T = T cond , P = P atm
m cond
= m sa ·
Q totExact
Q tot
W ma – W da
= m sa ·
= m sa ·
h ma – h da
h ma – h da
– m cond · h cond
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
Error Q
=
Q tot – Q totExact
Q totExact
b) What is the sensible heat ratio?
Q sen
= m sa · c p ·
SHR =
T ma – T da
Q sen
Q tot
c) What are the supply air conditions?
Q fan
= 1200 ·
T sa
= T da +
W sa
= W da
3.41214 ·
Btu/hr
W
Q fan
m sa · c p
Unit Settings: [F]/[psia]/[lbm]/[degrees]
CFMma = 2400 [cfm]
hcond = 20.09 [Btu/lbm]
mcond = 17.58 [lbm/hr]
Qfan = 4095 [Btu/hr]
QtotExact = 77596 [Btu/hr]
TDPda = 53 [F]
Tma = 78 [F]
W da = 0.008539
cp = 0.2449 [Btu/lbm-R]
hda = 22.48 [Btu/lbm]
msa = 10452 [lbm/hr]
Qsen = 58866 [Btu/hr]
RHma = 0.5
Tcond = 52
Tsa = 56.6 [F]
W ma = 0.01022
No unit consistency or conversion problems were detected.
ErrorQ = 0.004553
hma = 29.94 [Btu/lbm]
Patm = 14.7 [psia]
Qtot = 77949 [Btu/hr]
SHR = 0.7552
Tda = 55 [F]
vma = 13.78 [ft3/lbm]
W sa = 0.008539
File:Psych4Mix.EES
10/21/2003 9:26:57 AM Page 1
EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
"AREN 3010
In-Class Psychrometric Problem #4"
"
Outdoor air is mixed with building return air in a mixing chamber
prior to conditioning. The outdoor air is at 90°F and 40% RH with
an airflow of 1000 cfm. The return air is 80°F and 67°F wet-bulb with
an airflow rate of 3000 cfm. "
"Given information"
P_atm = 14.696
T_ra = 80
TWB_ra = 65
cfm_ra = 3000
T_oa = 90
RH_oa = .4
cfm_oa = 1000
"Calculate properties of outdoor and return air"
h_ra = ENTHALPY(AIRH2O,t=T_ra, b=TWB_ra,p=P_atm)
W_ra = HUMRAT(AIRH2O,t=T_ra, b=TWB_ra,p=P_atm)
v_ra = VOLUME(AIRH2O,t=T_ra, b=TWB_ra,p=P_atm)
h_oa = ENTHALPY(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
W_oa = HUMRAT(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
v_oa = VOLUME(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
"What is the mixed air condition?"
m_oa = cfm_oa/v_oa*CONVERT(hr,min)
m_ra = cfm_ra/v_ra*CONVERT(hr,min)
m_ma = m_oa+m_ra
OA_frac = m_oa/m_ma
h_ma = OA_frac*h_oa + (1-OA_frac)*h_ra
W_ma = OA_frac*W_oa + (1-OA_frac)*W_ra
T_ma = TEMPERATURE(AIRH2O,h=h_ma,w=W_ma,p=P_atm)
v_ma = VOLUME(AIRH2O,T=T_ma,w=W_ma,p=P_atm)
cfm_ma = m_ma*v_ma/CONVERT(hr,min)
AREN 3010
In-Class Psychrometric Problem #4
File:Psych4Mix.EES
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
Outdoor air is mixed with building return air in a mixing chamber
prior to conditioning. The outdoor air is at 90°F and 40% RH with
an airflow of 1000 cfm. The return air is 80°F and 67°F wet-bulb with
an airflow rate of 3000 cfm.
Given information
P atm
= 14.696
T ra
= 80
TWB ra
= 65
cfm ra
= 3000
T oa
= 90
RH oa
= 0.4
cfm oa
= 1000
Calculate properties of outdoor and return air
h ra
= h 'AirH2O' , T = T ra , B = TWB ra , P = P atm
= ω
W ra
'AirH2O' , T = T ra , B = TWB ra , P = P atm
v ra
= v 'AirH2O' , T = T ra , B = TWB ra , P = P atm
h oa
= h 'AirH2O' , T = T oa , R = RH oa , P = P atm
= ω
W oa
v oa
'AirH2O' , T = T oa , R = RH oa , P = P atm
= v 'AirH2O' , T = T oa , R = RH oa , P = P atm
What is the mixed air condition?
m oa
=
m ra
=
m ma
OA frac
h ma
W ma
T ma
cfm oa
·
v oa
cfm ra
v ra
·
60 ·
60 ·
min
hr
min
hr
= m oa + m ra
=
m oa
m ma
= OA frac · h oa +
= OA frac · W oa +
1 – OA frac
1 – OA frac
· h ra
· W ra
= T 'AirH2O' , h = h ma , w = W ma , P = P atm
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
v ma
cfm ma
= v 'AirH2O' , T = T ma , w = W ma , P = P atm
= m ma ·
v ma
60 ·
min
hr
Unit Settings: [F]/[psia]/[lbm]/[degrees]
cfmma = 4000.005 [cfm]
hma = 31.14 [Btu/lbm]
mma = 17274 [lbm/hr]
OAfrac = 0.2459
TWB ra = 65 [F]
Tra = 80 [F]
vra = 13.82 [ft3/lbm]
W ra = 0.009743
cfmoa = 1000 [cfm]
hoa = 34.91 [Btu/lbm]
moa = 4248 [lbm/hr]
Patm = 14.7 [psia]
Tma = 82.47 [F]
vma = 13.89 [ft3/lbm]
W ma = 0.01031
No unit consistency or conversion problems were detected.
cfmra = 3000 [cfm]
hra = 29.91 [Btu/lbm]
mra = 13027 [lbm/hr]
RHoa = 0.4
Toa = 90 [F]
voa = 14.13 [ft3/lbm]
W oa = 0.01206
File:Psych5OneZone.EES
10/21/2003 9:28:52 AM Page 1
EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
"AREN 3010
In-Class Psychrometric Problem #5"
"
A building space is to be maintained at 78°F dry-bulb and 65°F wet-bulb.
The total cooling load on the space has been calculated to be 60,000 Btu/hr
of which 42,000 Btu/hr is sensible heat gain. Supply air is delivered to the
space at a temperature of 58°F. For acceptable air quality, 500 cfm of
outside air is required. Outdoor conditions are 90°F and 50% RH. "
"Given information"
P_atm = 14.696
T_sa = 58
T_ra = 78
TWB_ra = 65
T_oa = 90
RH_oa = .5
cfm_oa = 500
Q_sen = 42000
Q_tot = 60000
"Calculate properties of outdoor and return air"
h_ra = ENTHALPY(AIRH2O,t=T_ra, b=TWB_ra,p=P_atm)
W_ra = HUMRAT(AIRH2O,t=T_ra, b=TWB_ra,p=P_atm)
h_oa = ENTHALPY(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
W_oa = HUMRAT(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
v_oa = VOLUME(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
c_p = SPECHEAT(AIRH2O,t=T_ra,b=TWB_ra,p=P_atm)
"a)
What is the airflow required for the space?"
m_sa=Q_sen /(c_p*(T_ra-T_sa))
"b)What is the supply air humidity ratio?"
h_sa = h_ra - Q_tot / m_sa
W_sa = HUMRAT(AIRH2O,t=T_sa, h=h_sa,p=P_atm)
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
"c)
What is the capacity of the cooling coil?"
m_oa = cfm_oa/v_oa*CONVERT(hr,min)
OA_frac = m_oa/m_sa
h_ma = OA_frac*h_oa + (1-OA_frac)*h_ra
W_ma = OA_frac*W_oa + (1-OA_frac)*W_ra
Q_coil = m_sa*(h_ma - h_sa)
"d)
What is the sensible heat ratio of the cooling coil?"
T_ma = TEMPERATURE(AIRH2O,h=h_ma,w=W_ma,p=P_atm)
Q_scoil = m_sa*c_p*(T_ma - T_sa)
SHR_coil = Q_scoil/Q_coil
AREN 3010
In-Class Psychrometric Problem #5
A building space is to be maintained at 78°F dry-bulb and 65°F wet-bulb.
The total cooling load on the space has been calculated to be 60,000 Btu/hr
of which 42,000 Btu/hr is sensible heat gain. Supply air is delivered to the
space at a temperature of 58°F. For acceptable air quality, 500 cfm of
outside air is required. Outdoor conditions are 90°F and 50% RH.
Given information
= 14.696
P atm
T sa
= 58
T ra
= 78
TWB ra
T oa
= 65
= 90
RH oa
= 0.5
cfm oa
= 500
Q sen
= 42000
Q tot
= 60000
Calculate properties of outdoor and return air
h ra
= h 'AirH2O' , T = T ra , B = TWB ra , P = P atm
W ra
= ω
h oa
= h 'AirH2O' , T = T oa , R = RH oa , P = P atm
W oa
= ω
'AirH2O' , T = T ra , B = TWB ra , P = P atm
'AirH2O' , T = T oa , R = RH oa , P = P atm
v oa
= v 'AirH2O' , T = T oa , R = RH oa , P = P atm
cp
= Cp 'AirH2O' , T = T ra , B = TWB ra , P = P atm
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
a) What is the airflow required for the space?
m sa
=
Q sen
cp ·
T ra – T sa
b)What is the supply air humidity ratio?
h sa
= h ra –
W sa
= ω
Q tot
m sa
'AirH2O' , T = T sa , h = h sa , P = P atm
c) What is the capacity of the cooling coil?
m oa
=
OA frac
h ma
cfm oa
v oa
=
·
min
60 ·
hr
m oa
m sa
= OA frac · h oa +
W ma
= OA frac · W oa +
Q coil
= m sa ·
1 – OA frac
1 – OA frac
· h ra
· W ra
h ma – h sa
d) What is the sensible heat ratio of the cooling coil?
T ma
= T 'AirH2O' , h = h ma , w = W ma , P = P atm
Q scoil
SHR coil
= m sa · c p ·
=
T ma – T sa
Q scoil
Q coil
Unit Settings: [F]/[psia]/[lbm]/[degrees]
cfmoa = 500 [cfm]
hoa = 38.31 [Btu/lbm]
moa = 2114 [lbm/hr]
Patm = 14.7 [psia]
Qsen = 42000 [Btu/hr]
SHRcoil = 0.6208
Toa = 90 [F]
voa = 14.19 [ft3/lbm]
W ra = 0.0102
cp = 0.2449 [Btu/lbm-R]
hra = 29.92 [Btu/lbm]
msa = 8576 [lbm/hr]
Qcoil = 77720 [Btu/hr]
Qtot = 60000 [Btu/hr]
TWB ra = 65 [F]
Tra = 78 [F]
W ma = 0.01142
W sa = 0.008272
No unit consistency or conversion problems were detected.
hma = 31.99 [Btu/lbm]
hsa = 22.93 [Btu/lbm]
OAfrac = 0.2464
Qscoil = 48251 [Btu/hr]
RHoa = 0.5
Tma = 80.98 [F]
Tsa = 58 [F]
W oa = 0.01515
File:Psych6OneZoneOffDesign.EES
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"AREN 3010
In-Class Psychrometric Problem #6"
"
A building space is to be maintained at 78°F dry-bulb temperature.
The total cooling load on the space has been calculated to be 30,000 Btu/hr
of which 27,000 Btu/hr is sensible heat gain. Supply air is delivered to the
space at 58°F and 90% RH. The outdoor air mass flow rate is 25% of the total
supply mass flow rate. Outdoor conditions are 80°F and 55% RH. "
"Given information"
P_atm = 14.696
T_sa = 58
RH_sa = .90
T_ra = 78
T_oa = 80
RH_oa = .55
OA_frac = .25
Q_sen = 27000
Q_tot = 30000
"Calculate properties of outdoor and return air"
W_sa = HUMRAT(AIRH2O,t=T_sa, r=RH_sa,p=P_atm)
h_sa = ENTHALPY(AIRH2O,t=T_sa, w=W_sa,p=P_atm)
h_oa = ENTHALPY(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
W_oa = HUMRAT(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
v_oa = VOLUME(AIRH2O,t=T_oa, r=RH_oa,p=P_atm)
c_p = SPECHEAT(AIRH2O,t=T_ra,r=.5,p=P_atm)
"a)
What is the airflow required for the space?"
m_sa=Q_sen /(c_p*(T_ra-T_sa))
"b)What is the zone air humidity ratio?"
h_sa = h_ra - Q_tot / m_sa
W_ra = HUMRAT(AIRH2O,t=T_ra, h=h_ra,p=P_atm)
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"c)
What is the capacity of the cooling coil?"
OA_frac = m_oa/m_sa
h_ma = OA_frac*h_oa + (1-OA_frac)*h_ra
W_ma = OA_frac*W_oa + (1-OA_frac)*W_ra
Q_coil = m_sa*(h_ma - h_sa)
"d)
What is the sensible heat ratio of the cooling coil?"
T_ma = TEMPERATURE(AIRH2O,h=h_ma,w=W_ma,p=P_atm)
Q_scoil = m_sa*c_p*(T_ma - T_sa)
SHR_coil = Q_scoil/Q_coil
AREN 3010
In-Class Psychrometric Problem #6
A building space is to be maintained at 78°F dry-bulb temperature.
The total cooling load on the space has been calculated to be 30,000 Btu/hr
of which 27,000 Btu/hr is sensible heat gain. Supply air is delivered to the
space at 58°F and 90% RH. The outdoor air mass flow rate is 25% of the total
supply mass flow rate. Outdoor conditions are 80°F and 55% RH.
Given information
= 14.696
P atm
T sa
= 58
RH sa
= 0.9
T ra
= 78
T oa
= 80
RH oa
= 0.55
OA frac
Q sen
Q tot
= 0.25
= 27000
= 30000
Calculate properties of outdoor and return air
W sa
= ω
'AirH2O' , T = T sa , R = RH sa , P = P atm
h sa
= h 'AirH2O' , T = T sa , w = W sa , P = P atm
h oa
= h 'AirH2O' , T = T oa , R = RH oa , P = P atm
W oa
v oa
cp
= ω
'AirH2O' , T = T oa , R = RH oa , P = P atm
= v 'AirH2O' , T = T oa , R = RH oa , P = P atm
= Cp 'AirH2O' , T = T ra , R = 0.5 , P = P atm
a) What is the airflow required for the space?
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EES Ver. 6.867: #317: CEAE University of Colorado, Boulder
=
m sa
Q sen
cp ·
T ra – T sa
b)What is the zone air humidity ratio?
h sa
= h ra –
W ra
= ω
Q tot
m sa
'AirH2O' , T = T ra , h = h ra , P = P atm
c) What is the capacity of the cooling coil?
OA frac
h ma
=
m oa
m sa
= OA frac · h oa +
W ma
= OA frac · W oa +
Q coil
= m sa ·
1 – OA frac
1 – OA frac
· h ra
· W ra
h ma – h sa
d) What is the sensible heat ratio of the cooling coil?
T ma
= T 'AirH2O' , h = h ma , w = W ma , P = P atm
Q scoil
SHR coil
= m sa · c p ·
=
T ma – T sa
Q scoil
Q coil
Unit Settings: [F]/[psia]/[lbm]/[degrees]
cp = 0.2449 [Btu/lbm-R]
hra = 29.4 [Btu/lbm]
msa = 5513 [lbm/hr]
Qcoil = 34165 [Btu/hr]
Qtot = 30000 [Btu/hr]
SHRcoil = 0.8101
Tra = 78 [F]
W ma = 0.01031
W sa = 0.009226
hma = 30.16 [Btu/lbm]
hsa = 23.96 [Btu/lbm]
OAfrac = 0.25
Qscoil = 27677 [Btu/hr]
RHoa = 0.55
Tma = 78.5 [F]
Tsa = 58 [F]
W oa = 0.01204
No unit consistency or conversion problems were detected.
hoa = 32.42 [Btu/lbm]
moa = 1378 [lbm/hr]
Patm = 14.7 [psia]
Qsen = 27000 [Btu/hr]
RHsa = 0.9
Toa = 80 [F]
voa = 13.87 [ft3/lbm]
W ra = 0.009731