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Heat loss through ground floor

Heat loss through ground floor

Heat loss through ground floor

I am struggling with calculating the heat loss through the ground floor of an internal room.

Walls, roofs, windows etc. no problem as I have a design external temperature (I use -8C) and known u values and the infiltration rate. For the floor of an internal room I can calculate the PA ratio of the whole building, but don't know how this relates to an internal room. Also don't know what to set the ground (external) temperature at because it will be much higher than the air temperature in winter.

Is there actually any heat loss?

Can you help?

RE: Heat loss through ground floor

Why is your heat loss calculation that dependent on the floor loss?


Concrete slab thermal conductivity is only about 5x that of typical insulation materials.

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RE: Heat loss through ground floor

It's important because I don't know what it is. If I don't make any allowance for heat loss through the floor, the room(s) may be under heated(cool).

What I don't want to do is just guess it or put an allowance in. I'd rather know the theory/calculation behind it.

Can you assist?

RE: Heat loss through ground floor

Flag this thread to have it deleted and repost in HVAC/R forum. Wou will get more responses there.

RE: Heat loss through ground floor

Heat loss through basement floor Btu/hr = Sq ft floor area x U x TD
U for basement masonry If lights always on you can floor = 0.05 Btu/(hr - sq ft - deg F)
TD = indoor design deg F - ground temperature deg F
Outdoor design T deg F = -30 -20 -10 0 +10 +20
Ground T deg F = 40 45 50 55 60 65

From Carrier Handbook of Air Conditioning System Design Chapter 5 Tables 35 and 37.

If lights always on you can take credit for heat gain.

RE: Heat loss through ground floor

One might fully account for the heat loss to the floor and still feel cold due to radiation from occupant to the cold floor surface. If your interest is in comfort, then consider some type of in-slab heating.

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