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 V_a^0.6 (t_a-t_sk)

    Where:
    C is the convective heat exchange
    V_a is the air velocity
    t_a is the air temperature, ^oF
    t_sk is the mean weighted skin temperature, usually assumed to be 95 ^oF

       Radiation

      R = 15.0(t_w - t_sk)

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

        Evaporation

        E = 2.4V_a^0.6(r_sk-r _a)

        Where:
        E is the evaporative heat loss
        V_a is the air velocity
      r_a is the water vapor pressure of ambient air, mm Hg
     r_sk is the water vapor of the skin assumed to be 42 mm Hg at 95 ^oF
 

5. WBGT (indoor) = 0.7t_nwb + 0.3t_g

Where:
t_nwb is the natural wet bulb temperature
t_g is the radiant or globe temperature
 

6. WBGT (outdoor) = 0.7t_nwb + 0.2t_g + t_a

Where:
t_nwb is the natural wet bulb temperature
t_g is the radiant or globe temperature
t_a is the ambient air temperature

7. Sensible Heat Rise can be determined by the formula

 H_s = Q_s * ρ * c_{p *}  ΔT * (60 min/hr)

Where

H_s = Sensible heat gain, BTU/hr

Q_s = Volumetric flow for sensible heat, cfm

 ρ  =  Density of the air, lbm/ft³

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

ΔT = Change in temperature, deg F

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

Then the equation becomes

 H_s = 1.08 * Q_s *  ΔT

 Go to Dilution ventilation.