35
Table 30.
Conversion Factors (constant)
Water
500 = 8.33 lbs./gal. x 60 min,
– (Converts GPM to lbs./hr.)
Air
4.5 = 60 min
13.35 Cu. Ft./lb.
– (Converts CFM to lbs./hr.)
1.08 = 4.5 x 0.241 BTU/lb./ºF.
– (lbs./hr. x Sp. Ht. of Air)
0.68 = 4.5 x 1054.3 BTU/lb.
7000 gr/lb.
– (4.5 combined with heat
of vaporization of water
at 70ºF. and grains per
pound of water)
Water Heating, Cooling & Heat Reclaim Coils, Water Chillers,
Condensers, etc.
Q = 500 x GPM x T
= BTU/hr.
T = Q
500 x GPM
For brines, Q = 500 x GPM x T x (Sp. Ht. x Sp. Gr. of Brine)
Air Coils
Q Sensible = 1.08 x CFM x T
= BTU/hr.
Q Latent = 0.68 x CFM x SH
= BTU/hr.
Q Total = 4.5 x CFM x H = BTU/hr.
lb./hr. Condensate
= 4.5 x CFM x SH Grains
7000 grains/lb
SHR Sensible Heat Ratio = Q Sensible
Q Total
Heat Transmission
Q Total = U x A Surface x T
= BTU/hr.
Product
Sensible Heat in BTU/hr. = lbs/hr. x Sp. Ht. x T
Latent Heat in BTU/hr.
= lbs/hr. x Lt. Ht. in Btu/lb.
Heat of Resp. in BTU/hr .
= lbs x Heat or Respiration
in BTU/lb./hr.
All conversion factors used in standard calculations must be
corrected for other than standard properties
Properties of Water at 39.2 ºF.
Density of Water
= 62.4 lbs./Cu. Ft.
Specific Heat of Water
= 1 BTU/lb./ºF.
Latent Heat of
= 970 BTU/lb. at 212ºF. & Atm.
Vaporization
= 1054.3 BTU/lb. at 70ºF.
Specific Heat of Ice
= 0.5 BTU/lb./ºF.
Latent Heat of Fusion
= 144 BTU/lb.
1 Gallon of Water
= 8.33 lbs.
1 Pound of Water
= 7000 Grains
Nomenclature
Q = Heat Flow in BTU/hr.
T = Temperature in ºF. ( T = temp. diff.)
A = Area in Sq. Ft.
U = Coef. of Heat Transfer in BTU/hr./Sq.Ft./ºF.
H = Total heat of air at wet bulb temp. BTU/lb.
H = Enthalpy difference between entering & leaving air
SH = Specific humidity in grains of moisture/lb. of dry air
( SH = Specific humidity difference for entering
and leaving air)
CFM = Cu. Ft./min.
GPM = Gal/min.
W
I
R
E
I
2
X R
E X I
I X R
E
2
W
E
R
E
R
W
E
W
I
W
I
2
E
I
W
R
W X R
Table 31.
Single Phase Loads
Ohm’s Law for direct current
W = Watts
I = Current (Amperes)
E = Electromotive Force (Volts)
R = Resistance (Ohms)
To obtain any values in the center circle, for Direct or Alternating
Current, perform the operation indicated in one segment of the
adjacent outer circle.
3 Phase Delta Loads
3 0 Balanced Loads = P
1
+ P
2
+ P
3
Total Line Current = Total Power (Balanced Load)
If the phase are unbalanced, each of the phase will differ from
the others:
FORMULAE:
I
L1 =
I
2 +
I
2 + (
I
1 X
I
2 )
3 1
I
L2 =
I
2 +
I
2 + (
I
2 X
I
3 )
2 3
I
L3 =
I
2 +
I
2 + (
I
1 X
I
3 )
3 1
