Air Side
cfm x 1.08 x ΔT = btu
Duct velocity = v = 4004√Vp
Fan Laws: rpm2/rpm1 = cfm2/cfm1
(rpm2/rpm1)² = SP2/SP1
(rpm2/rpm1)³ = bhp2/bhp1
rpm fan/rpmmtr = MP/FP
Standard office spaces:
380 - 420 cfm/ton cooling air
350 - 450 ft² floor area/ton cooling
Interior zone: .75 - .90 cfm/ft²
North zone: .95 - 1.15 cfm/ft²
East zone: 1.20 - 1.45 cfm/ft²
South zone: 1.50 - 2.00 cfm/ft²
West zone: 2.00 - 3.00 cfm/ft²
floor area cooling
Cooling supply air:
54 - 58º F discharge temperature
Heating supply air:
110 - 120º F discharge temperature
Room exhaust:
75 cfm/water closet or urinal
Electric Room:
6 air changes/hr
Elevator shaft relief:
3ft² or 3 1/2 % of shaft area (which ever is greater)
Combustion air:
all air from outdoors - two (2) openings each
(one at floor, one at ceiling)
minimum 1 sq. in. free area per 4000 btuh equipment input
Louver free area = 45 - 55% face area
Refrigeration Side
Saturated suction temperature 38 - 42º F
Condensing temperature
air cooled 115 - 125º F
water cooled 90 - 95º F
Electrical Side
HP x 746 = watts
2545 btuh/hp
3.413 btuh/'watt
Heat gain from transformers 15 watts/kva
Multiply fluorescent watts by 1.25 (for ballast) to obtain heat output
Single phase bhp = ((amps)(volts)
(power factor)(efficiency))/746 = bhp
Three phase bhp = ((amps)(volts)
(power factor)(efficiency)(1.73))/746 = bhp |
Water Side
psi x 2.3 = ft. of head
gpm x 500 ΔT = btuh
Pump laws:
gpm2/gpm1 = rpm2/rpm1 = 12/1
ft hd2/ft hd1 = (rpm2/rpm1)² = (12/I1)²
bhp2/bhp1 = (rpm2/rpm1)³ = (12/I1)³
Cooling Water side
Condenser water:
3gpm water/ton @ 10º ΔT
75 - 90º F CT leaving water temperature
90 - 105º F CT entering water temperature
Chilled water:
2 gpm water/ton @ 12º ΔT
42 - 46º F CH leaving water temperature
53 - 56º F CH leaving water temperature
Heating Water side
Heating:
offices 15 - 45 btuh/ft² floor area
warehouses 40 - 55 btuh/ft² floor area
Hot water:
.08 - .20 gpm water/btuh output
175 - 190º F BL leaving water tmperature
155 - 170º F BL leaving water tmperature
Boiler hp: 33,500 btu/hp/hr
Natural Gas: 1 therm = 100,000 btu's
Steam: 1 lb steam = 965 btu/hr
Abbreviations
bhp - brake horsepower
BL - boiler
btuh - British thermal unit per hour
cfm - cubic feet per minute air
CH - chiller
CT - cooling tower
D - density F - Fahrenheit
FP - pitch diameter of fan pulley
fpm - feet per minute velocity
ft. - feet
gpm - gallons per minute water
H - head
I - impeller diameter MP - pitch diameter of motor pulley
SP - static pressure
rpm - revolutions per minute
ft² - squared feet area
sq. in. - squared inch area
v - duct velocity
Vp - velocity pressure |
