GENERAL INDUSTRIAL VENTILATION


1. General dilution ventilation equation:

Rate of accumulation = Rate of generation - Rate of removal

    Or

VdC = Gdt - Q'Cdt

Where:
V is the volume of the room
G is the rate of generation
Q' is the effective volumetric flow rate
C is the concentration of gas or vapor
T is the time
At a constant concentration C and uniform generation rate, G

G(t2 -t1) = Q' C(t2 -t1)

Q' = (G/C)                                                                                                                                            Equation 1

Due to complete mixing, a constant value K is introduced thus making the equation

Q' = (Q/K)

This makes equation 1 as

Q = (G/C)* K
 

2. G = (Conv*SG*ER)/MW

Where:
G is the rate of generation
Conv is the volume in ft3 that 1 pt of liquid when vaporized, will occupy at STP
SG is the specific gravity of the volatile liquid
ER is the evaporation rate of liquid, pts/min
MW is the molecular weight of the liquid.

So, Q' in equation 1 becomes

Q' = (403*106*SG*ER)/(MW*C)
 

3. C1/TLV1 + C2/TLV2 + C3/TLV3 + C4/TLV4 + …………..+ C5/TLV5

is the equation when two or more hazardous substances are present.

TLV is the threshold limit value
C is the concentration of the hazardous substance.
 

4. The basic heat balance equation is

DS = (M-W) C R - E

Where:
DS is change in body heat content
(M-W) is the total metabolism - the external work performed
C is the convective heat exchange
R is the radiative heat exchange
E is the evaporative heat loss.

    Convection

    C = 0.65 Va0.6 (ta-tsk)

    Where:
    C is the convective heat exchange
    Va is the air velocity
    ta is the air temperature, oF
    tsk is the mean weighted skin temperature, usually assumed to be 95 oF

       Radiation

      R = 15.0(tw - tsk)

      Where :
       R is the radiative heat exchange
       tw is the mean radiant temperature, oF
       tsk is the mean weighted skin temperature, usually assumed to be 95 oF

        Evaporation

        E = 2.4Va0.6(rsk-r a)

        Where:
        E is the evaporative heat loss
        Va is the air velocity
      ra is the water vapor pressure of ambient air, mm Hg
     rsk is the water vapor of the skin assumed to be 42 mm Hg at 95 oF
 

5. WBGT (indoor) = 0.7tnwb + 0.3tg

Where:
tnwb is the natural wet bulb temperature
tg is the radiant or globe temperature
 

6. WBGT (outdoor) = 0.7tnwb + 0.2tg + ta

Where:
tnwb is the natural wet bulb temperature
tg is the radiant or globe temperature
ta is the ambient air temperature

7. Sensible Heat Rise can be determined by the formula

 Hs = Qs * ρ * cp *  ΔT * (60 min/hr)

Where

Hs = Sensible heat gain, BTU/hr

Qs = Volumetric flow for sensible heat, cfm

 ρ  =  Density of the air, lbm/ft3

cp  = Specific heat of the air, BTU/lbm-deg F

ΔT = Change in temperature, deg F

For air cp  = 0.24 BTU/lbm-deg F and  ρ  = 0.075 lbm/ft3;

Then the equation becomes

 Hs = 1.08 * QsΔT

 



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