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HVAC Formulas

Dehumidification Capacity

What is the dehumidification capacity of the supply air? Said another way; how much moisture can a known amount of air with a known humidity ratio remove from the conditioned space every hour?

Dehumidification Capacity

  CFM   Delta Gr/Lb    
4.5 *      *    = Grains/HR

Required Supply Air Humidity Ratio

If the supply air flow rate and the indoor humidity ratio are fixed, how dry does the supply air have to be in order to remove a known internal moisture load?

Required Supply Air Humidity Ratio

Gr/Hr CFM      
/ * 4.5   = Grains/LB

Required Supply Air Flow Rate

If the supply air flow humidity ratio and the indoor humidity ratio are both fixed, how much supply air is needed to remove a known internal moisture load?

Required Supply Air Flow Rate

Gr/Hr Delta Gr/LB      
/ * 4.5   = CFM

Mixed-air Humidity Ratio

When two air flows with different humidity ratios are blended, what will be the humidity ratio of the resulting mixture?

Mixed-air Humidity Ratio

  Airflow 1   Airflow 2    
CFM         
Gr/Lb         = Gr/Lb 3

Dehumidified Air vs. Bypass Air

A dehumidifier might need to dry only part of the supply air rather than its entire volume. How much of the supply air should be dried by the dehumidifier in order to bring the entire supply air flow to the required humidity ratio?

Dehumidified Air vs. Bypass Air

  Inlet Total Airflow   Bypass Airflow        
CFM        CFM 2        
Gr/Lb           = Gr/Lb 3

Sensible Heat Btuh

When there is temperature difference absorbed or transmitted that is not accompied with a change of state how many btus are being used?

Sensible Heat Btuh

Delta Temp   CFM      
* * 1.08   = Btuh

Latent Heat Btuh

When there is a temperature difference which is released or absorbed by a substance during a change of state ( i.e solid, liquid, gas) how many btus are being used?

Latent Heat Btuh

Delta Gr/Lb   CFM      
* * .68   = Btuh

Total Heat

How does one calculate the total amount of heat being used in a system?

Total Heat

Delta Btu/Lb   CFM      
/ * 4.5   = Btuh