THE FOLLOWING FORMULAS MAY BE OF USE IN BUILDING SYSTEMS
ELECTRICAL
Footcandles =
lumens
area in ft2
Footcandles =
(lamp lumens) x (lamps per fixture) x (number of fixtures) x (CU) x (LLF)
area in ft2
Number of luminaires =
(footcandles) x (floor area) ,
(lumens) x (CU) x (LLF)
where CU = coefficient of utilization
LLF = Light Loss Factor
DFav = 0.2 x (window area/floor area) for spaces with sidelighting or toplighting with vertical monitors
watts = volts x amperes x power factor (ac circuits only)
Demand charge = maximum power demand x demand tariff
HVAC
Btu/year = (peak heat loss) x (full-load hours/year)
$/year = (Btu/year) x (fuel cost/fuel heat value) x (efficiency)
Btu/h = (cfm) x (1.08) x (T)
1 kWh = 3,400 Btu/h
1 ton of air conditioning = 12,000 Btu/h
Btu/h = (U) x (A) x (Td), where Td is the difference between indoor and outdoor temperatures
U = 1 / Rt
Uo = (Uw x Aw) + (Uop x Aop) , where o = total wall, w = window, and op = opaque wall
Ao
Uo = (UR x AR) + (Us x As) , where o = total roof, R = roof, and S = skylight
Ao
R = x / k, where x = thickness of material in inches
Heat required =
Btu/h
temperature differential
x (24 hours) x (DD °F), where DD = degree days
PLUMBING
1 psi = 2.31 feet of water
1 cubic foot = 7.5 U.S. gallons
ACOUSTICS
Sound = λ= c , where λ = wavelength (ft), c = velocity of sound (fps), and f = frequency of sound (Hz)
f
NR = TL – 10 log [S / AR],
NRC = a / s,
TR = K x
where NR
TL
S
AR
= Noise reduction (dB)
= Barrier transmission loss (dB)
= Area of barrier wall (ft2)
= Total absorption of receiving room (sabins, ft2)
where NRC = Noise reduction coefficient
a
= Total sabins (sound absorbing units)
s
= TotaI surface area in the room
V ,
ΣA
where TR
K
V
ΣA
=
=
=
=
Reverberation time in seconds
a constant of 0.05 when measurements are in feet
Room volume (ft3)
Total room absorption, sabins (ft2) at that frequency