Air Stratification



Question -

  I was wondering if an engineer could resolve a debate I'm
having with a friend. The debate is this: Is it more energy efficient (in
terms of cooling cost) to have a high-ceilinged house than a
low-ceilinged one? One view is that a high ceiling will allow the heat to
accumulate at the top of the house, be more comfortable at the floor
level, and require less cooling (lower cost for air-conditioning). The
other view is that a high ceiling (with the same floor space) would
result in a larger volume of air that needs to be cooled - that the air
will naturally circulate - and so drive up the cooling cost.

We have also argued over whether a flow through or vent at the top of the
house is energy efficient since the removed air would have to be replaced
and ultimately would have to be cooled.
The parameters you specified above are not complete enough to answer yes
or no. How well the ceiling and walls are insulated is going to be a major
factor. Whether by "cooling" you mean the entire room, regardless of
shape, is at the same temperature, or whether you are going to be
satisfied with a temperature gradient between the floor and ceiling (and
if so how large a temperature gradient). What is the temperature
difference between the outside of the house and the inside. What is the
air "turn over" between ceiling/floor and inside/outside, and  what is the
heat transfer between the floor and the ground (that is, does the room
have a basement below or is it sitting on the ground) and in that case
what is the ground temperature. You have not specified the relative
humidity. A significant factor in heating/air conditioning is controlling
the humidity in the room. This is very energy intensive. So there are a
lot of undefined parameters that could change the heat balance in room.

Want to keep up to date with all our latest news and information?
Subscribe to receive FREE TIPS, all new Radio/Podcast Episodes and Videos that will help you start Dropping your Energy Bill!
Enter your email below to join a world of new knowledge and savings!