T.D., C.F.M., B.T.U
T.D. = Temperature Difference
C.F.M. = Cubic Foot per Minute
B.T.U. = British Thermal Unit
F.T.D. = Fahrenheit Temperature Difference
C.O.P. = Coefficient of Performance
H.P. = Horsepower
K.W. = Kilowatt
G.P.M. = Gallon per Minute
Use any two of these to get the third number!
800 C.F.M. @ 20
°F T.D. = B.T.U.?
800 x (20 x 1.08) = 17,280 B.T.U.
or
17,280 B.T.U. @ 20°F T.D. = C.F.M.?
17,280 B.T.U. / (20 x 1.08) = 800 C.F.M.
or
17,280 B.T.U. & 800 C.F.M. = T.D.?
17,280 / (800 x 1.08) = 20° T.D.
Various Cooling Loads:
1-Person Light Work = 420 B.T.U.
1-Person Heavy Work = 1,800 B.T.U.
1-C.F.M. of outside air @ 95/78 = 59 B.T.U.
12 people (light work) with 10 C.F.M. per person outside air = 1 Ton
12 x 420 = 5,040 B.T.U.
120 x 59 = 7,080 B.T.U.
Total = 12,120 B.T.U.
1-H.P. = 2,900 B.T.U
1-K.W. = 3,412 B.T.U
1-Watt of incandescent lighting = 3.4 B.T.U.
1-Watt of fluorescent lighting = 4.1 B.T.U.
Approximate heat gain duct in attic:
R-8 insulation
250 feet of duct surface
55°F supply air temp
120°F attic temp
Heat gain = 1 / 8 = 0.125 B.T.U. per foot per °F temperature difference.
0.125 x 65° T.D. x 250° = 2,031 B.T.U. / hour
Note: If the insulation is compressed 50%, it reduces the efficiency 39%.
The Ocean Liner QE-2 uses one gallon of fuel to travel 128 feet!
To get the C.O.P. of a heat pump, you divide the heating capacity of the heat pump at 47°F by the K.W. input at that temperature x 3,413 (straight electric heat).
Example:
Heating capacity @ 47° = 36,000 B.T.U.
K.W. input = 4.22 K.W.
4.22 K.W. x 3,413 = 14,335 B.T.U.
This is the amount of heat you would get with electric heat.
36,000 / 14,335 = 2.5 C.O.P.
In other words, the heat pump is putting out 2.5 times as much heat as you would get using the same amount of energy with electric heat.
If a chiller is moving 100 G.P.M. of water and dropping the water temperature 8°F, what is the capacity of the chiller?
G.P.M. x 500# x 8° = 400,000 B.T.U.
The 500 converts G.P.M. to pounds per hour.
60 minutes x 8.33 pounds per gallon = 500
