Rule of thumb
Rule of thumb
(OP)
I know already as a rule of thumb you need 450 cfm per ton of cooling.
How many cfm per 1KW (3412Btu) of heating ?
Thx in advance !
How many cfm per 1KW (3412Btu) of heating ?
Thx in advance !
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RE: Rule of thumb
RE: Rule of thumb
RE: Rule of thumb
So 450/3.48 = 129.3 cfm per kW
RE: Rule of thumb
RE: Rule of thumb
Air mass flow rate * specific heat * deltaT
It doesn't matter whether cooling or heating, just use consistent units
RE: Rule of thumb
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RE: Rule of thumb
RE: Rule of thumb
RE: Rule of thumb
Example: 1 kW heat load, room temp desired 70°F, supply air temp desired 120°F. That gives you a delta-T of 50°F. It's all sensible heat, so the air flow will be:
CFM = (1 kW * 3413 btu/kW)/ 50°F * 1.08 btu/°F/cfm)
CFM = 63 cfm per kW
So a good rule of thumb for those conditions might be 65 or 70 cfm/kW?
Good on ya,
Goober Dave
RE: Rule of thumb
Good on ya,
Goober Dave
RE: Rule of thumb
Also, you say 100% sensible, however the air does contain 35%rh. Is it really 100% sensible ?
RE: Rule of thumb
Heating adds no moisture to the air, nor does it remove any moisture from the air. It only changes temperature.
Good on ya,
Goober Dave
RE: Rule of thumb
However, it doesn't change much. For purposes of this discussion, it's best left alone. After all, we're talking about cfm of air, which nobody can measure to 3-digit accuracy in most building applications.
As pressure (and thus density of the air) rises, the 1.08 factor will go up. As humidity (and thus specific heat of the air) rises, the 1.08 factor will go up.
Good on ya again,
Goober Dave
RE: Rule of thumb
RE: Rule of thumb
If you are installing duct heaters, you need a minimum of 50 cfm per KW of heat. Other wise your ductheaters will overheat. So there is a minimum, or lower limit, you could work off of !
RE: Rule of thumb
RE: Rule of thumb
RE: Rule of thumb