Latent Load Calc.

[lvaldez1350]

When calculating the Latent load portion of the heat load to a space, I have been using .68*CFM*(delta w). I know this equation is based on the formula Q=m*CP*(delta T), but can't figure out how it is derived. Can someone help out?

 

[smb168]

Hello lvaldez1350,

That energy equation is used to derive the energy equation for sensible heat load.

To Calculate the latent heat load, the energy equation starts:

QL=Mw*change in enthalpy=Ma*change in humidity ratio*latent heat of vaporization.

Mw=mass flow rate of water
Ma=mass flow rate of air
humidity is grain / lb of dry air

The constant .68 is the product of air density of 0.075 lbm/ft3, a latent heat of vaporation at approximate partial pressure of water vapor in the air 1061 Btu/lbm and 60 min/hr. the product then divided by 7000grain /lb of water.

i hope this help

smb168