Last week, we received two incredibly similar inquiries related to the ruling in ASHRAE 90.1 from table G3.1.1a that “All conditioned spaces in the proposed design shall be simulated as being both heated and cooled even if no heating or cooling system is to be installed.”
Here is a sample of the question we received:
I have a space in the proposed that is heated only. It has a peak heating load of 12 Btuh/SF, but the baseline peak is 20 Btuh/SF. In this climate zone, heating is defined as conditioned when the peak load is greater than 15 Btuh/sf. Since the proposed is not conditioned and the baseline is conditioned, do I treat the space as unconditioned, semi-heated, or conditioned? If it is conditioned, how do I proceed?
That's a funny issue. To be clear, I'm assuming you are using 90.1-2007. In terms of heating for your climate zone, conditioned is defined as >15 Btu/h·ft2. Semi-heated is always defined as >3.4 Btu/h·ft2. By the way, semi-heated = a minuscule amount of heating. I have scarcely seen or heard of semi-heated outside climate zones 1, 2, or 3. Of course, the setpoint could largely determine that.
Since you have mentioned 15 Btuh/sf, that means your model is in climate zone 4 or 5.
In any case, the conditioned vs unconditioned should be based on the proposed value, which in your case, is not conditioned nor is it unconditioned. Therefore it is semi-heated. However, because of the climate zone, it is very possible that any small changes will move you into the “conditioned” definition.
You have two choices: