Unconditioned space in Trace Energy Model

4 posts / 0 new
Last post

How do you account for unconditioned space in a Trace Energy Model? I have a number of unassigned rooms that do not show up in the total square footage of the building.

That has come back to me in a LEED review comment. The comment says "the building area in the LEED Summary Report is inconsistent with the total building area indicated in section 1.1A of the form"

How can I get mechanical rooms, unconditioned closets, chases, elevator shafts, and interior stairwells to show up in Trace as square footage without assigning them to a system?


ebroemel's picture
Joined: 2011-05-06
Reputation: 0

That must be a lot of closets with no external envelopes you have. I'm assuming these spaces meet the requirements of ASHRAE 90.1 for unconditioned or semi-conditioned spaces? Look at the definition of "Space". Any space greater than 5 BTU/h*sf for cooling will require cooling. Any space greater than 3 BTU/h*sf for heating will require heating.

Let me ask this too, why did you change them to "Unconditioned"? Were you getting unmet hours with them? Would you be able to roll the SF into the adjacent space and just delete these closets? 

As far as the spaces you did mention above, do they meet the criteria of conditioned spaces in 90.1? Are you setting the t-stats for the space versus typical office temps? If they do require a system, say for example your mech rm...then you may need to create a unit heater, which may be in your design, but then you need a seperate cooling system, DX maybe. You cannot not have a cooling system per 90.1 and LEED if it IS a conditioned space. You'll need to work the problem till you see that the cooling plant never turns on, or maybe you have a fan that is used during the summer and you want just that component, but not compressors, pumps, etc...

Please post up a few of these unconditioned spaces that have no heating or cooling needs, let's talk numbers.

Be Sustainable -- Never let today use up tomorrow!.

Bobba_Fett's picture
Joined: 2010-10-01
Reputation: 229

I have an example of an unconditioned space in an existing building. It is a large storage area that has been built in on the side of the building. There are windows on the connecting wall. In the conditioned space, how do I represent that this wall is connected to the unconditioned space?

jasrael's picture
Joined: 2014-01-27
Reputation: 0

Simple, yet not so simple answer because of the windows.

You have to add a partition to the conditioned space. The difficulty is that you will need to determine a net U-value for the wall (with the glass), or add multiple partitions. (one for the U-value fenestration and area, and  one for the opaque material's U-value and area).

The next difficult thing is that there is is to define the partition type. Since a storage area sounds large enough, the conditioned space will probably not see ambient temperatures. I'd try to use Sine fit.

Finally, I assume that the "windows" are not going to have a solar heat gain impact on the conditioned space. This can happen though.

If you need to account for the solar heat gain from the "windows", you would want to add the said window to the conditioned area as a wall that is 100% glass. Set the net shading coefficient, but then the trick would be to set the U-value to 0 (since you already accounted for the U-value in the partition!)

You'd also need to setup some sort of overhang shading on the window as well. 

In general, the Solar heat gain is going to be near null, provided that the unconditioned space is of any size. 

Bob's picture
Joined: 2010-06-30
Reputation: 475