Warm air return air arrangement & calculation

[PaulGreen]

I have been asked to carry out landlords certs on a series of properties which all have warm air units. The landlord has only just purchased the properties and wants a thorough top to bottom of the systems.

I have my warm air but havnt seen one for about 10 years (apart from in the acs centres, which to be fair was a very 'brief' assessment).

The question I have is regarding the return air arrangement and calculations. The return air grilles to each room are worked out at cm2/kw of heat (actually as btu/in2 for these units as quite old).

How do I work out the heat output to each room? I cand find any info on this in anything ive got.

My theory was, lets say its a 15kw max unit, to count up the number of registers (lets say 10 all the same size), divide the 15kw by 10 = 1.5kw per register. If there are 2 in a room, then 3kw of heat to use in the calculation.

Can anyone give me any more guidance on this please? Everything else im perefctly happy with or have managed to reference the information but this bit is proving difficiult to find.

 

[oz-plumber]

Basic calculations:

L/s = room volume (L x W x H) x air changes p/h / 3.6.

k/W = room volume x 0.042 - will give you general k/W allowance.
Very rough calculation but should meet your requirements.
We use this calculation for sizing warm air systems over here, but generally use l/s to size units.

As for return air vents - as long as the l/s requirement is met, you should have no problems.

 

[glenntaf]

What warm air unit are they? Lennox, J+S, Brink??