Important Formulae

PERT- 

Te(expected time)= (O +4M + P)/6 where O=optimistic time, M= most likely time, P=pessimistic time.

V(variance)=( (P-O)/6)^2
Project variance= sum of variances along the critical path
Standard deviation = sq root of variance

LIGHT

1 lux = 1 lumen/sq meter
lux is the unit of illuminance
 Flux= illumination required(lux) x surface area(sq m)
Flux(lumen output)(received)= MF(maintenance factor) x UF(utilization factor) x Flux(installed)
depreciation factor = reciprocal of maintenance factor
lux=candela/d^2
cd(candela) = lm(lumen) / ( 2π(1 - cos(º/2)) )
for isotrophic light source(all directions), lumen = candela x 4x22/7
http://www.compuphase.com/electronics/candela_lumen.htm

Room Index(RI)= Lx W/[Hm x (L+W)]
Hm=mounting height

Spacing to height ratio SHR=  1/Hm x[ (A/N)^ 1/2]

Acoustics

T(reverbaration time in seconds)=  .161x V(volume in m3)/A(sound absorption power in m2-sabine = area x coeffcient of absorption)

Lp = 20 log 10(Prms/Pref) dB

Lp2 = Lp1 + 20 log10(r1/r2)

lp-sound pressure
sound level- 10 log 10(Prms/Pref) dB

Plumbing and Water Supply

Hazen -Williams Formula

used for pipes larger than 2" and smaller than 6' in dia

v = 1.32.Ch.R^0.63.S^0.54

v= average velocity ft/s

Ch=Hazen Williams Coefficient

R=Hydraulic radius of flow conduit(ft)

s=ratio of hL/L, energy loss/head lenghth of conduit(ft/ft)

in SI Units

v = 0.85.Ch.R^0.63.S^0.54

v= average velocity(m/s)

Ch=Hazen Williams Coefficient

R=Hydraulic radius of flow conduit(m)

s=ratio of hL/L, energy loss/head lenghth of conduit(m/m)

Volume flow rate Q= Av