energy used heating & cooling a volume of air?
energy used heating & cooling a volume of air?
(OP)
Hi all, this is my first post on the forum. I am a junior mechanical engineer and would appreciate if someone could clarify a problem I'm trying to logically think out.
I am currently using a building energy simulation software Virtual Environment from IES Ltd to run compliance check for CO2 production (Part L2 England & Wales Building Regulations).
The building has been modelled by a drafts person and they have created the internal space (which would be the occupied space to have HVAC) by including both ceiling and floor void as part of the space. Therefore the height of the room is 4.5 meters rather than 2.7 meters. I believe that the ceiling and the floor void should have been modelled in different zones.
What I would like to know is, would a larger room volume affect the energy consumption of the HVAC system? I have thought this out logically and my theory is that a smaller volume of air would mean that less energy is used to either heat or cool than a larger volume of air. Would anyone know how to calculate this?
I am currently using a building energy simulation software Virtual Environment from IES Ltd to run compliance check for CO2 production (Part L2 England & Wales Building Regulations).
The building has been modelled by a drafts person and they have created the internal space (which would be the occupied space to have HVAC) by including both ceiling and floor void as part of the space. Therefore the height of the room is 4.5 meters rather than 2.7 meters. I believe that the ceiling and the floor void should have been modelled in different zones.
What I would like to know is, would a larger room volume affect the energy consumption of the HVAC system? I have thought this out logically and my theory is that a smaller volume of air would mean that less energy is used to either heat or cool than a larger volume of air. Would anyone know how to calculate this?





RE: energy used heating & cooling a volume of air?
Steady state, no.
Would anyone know how to calculate this?
Yes, you should. It's a simple energy balance. They still teach that in school, yes?
RE: energy used heating & cooling a volume of air?
However, no room is perfectly insulated and presumably you'll have some air exchange (to keep the inside air fresh).
I agree that you'll probably have a higher a/c load since the total air turnover in the higher-ceiling room will probably be greater. Also, the higher room will have more wall area, so the heat transfer area to the outside will be nearly twice as large, all other things being equal.
It hopefully goes without saying that the selection and quality of installation of doors and windows (if any), insulation, ventilation, and the presence of heat producing devices in the room (computers, lighting, etc.) will all impact the room's a/c energy load.
Hope that helps. Dave41A
RE: energy used heating & cooling a volume of air?
I am not sure what "Transient" means would you be able to explain. Thank you.
RE: energy used heating & cooling a volume of air?
The energy used to heat or cool a room has to balance the loads.
Loads include things like:
Occupants, heat producing equipment, envelope conduction, solar, ventilation, and leakage.
Notice that none of these things contain a term for the volume of the room. Sure, some of them can be estimated based on the volume, but in a proper analysis they are not dependent on the volume of the room.
The only time you need to heat or cool the air that is already in the room is when you want to change the temperature of the room. Like if you turn the temperature down over night and in the morning you need to get the room back to a comfortable level.
RE: energy used heating & cooling a volume of air?
So as I'm using a building environment simulation software it would be best for the ceiling and floor voids be zoned separate to the occupied zone. I have done two test models and there is a difference of 5% in energy use, with the correctly zoned model having less energy consumption.
RE: energy used heating & cooling a volume of air?
Close the software and write out the equations yourself.
RE: energy used heating & cooling a volume of air?
If you are using non-air conditioned air to achieve this, this will add to your a/c load.