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?
| 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?
| 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?
| 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?
| 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?
| Inlet Total Airflow | Bypass Airflow | ||||
| CFM | CFM 1 | CFM 2 | |||
| Gr/Lb | Gr/Lb 1 | Gr/Lb 2 | 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?
| 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?
| Delta Gr/Lb | CFM | ||||
| * | * .68 | = Btuh |
Total Heat
How does one calculate the total amount of heat being used in a system?
| Delta Btu/Lb | CFM | ||||
| * | * 4.5 | = Btuh |
