TRACE modeling question - Heating Only

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Hello, everyone.

I've got a question that I've never been clear on and figured I'd turn
to the experts (you all).

In appendix G, Table G3.1.1b, it's stated that all conditioned spaces
shall be modeled as being both heated and cooled, even if no cooling
systems exists, for both the proposed and baseline buildings.

We typically place Cabinet Unit Heaters in stairways and vestibules, and
don't worry about cooling those spaces. So, my question is, though
TRACE has a couple "Heating only" systems options, Appendix G says that
these cannot be selected. So, what is a common solution? The other
systems in the building are VAV, so, can those spaces just be grouped on
to there?

Thanks for any advice you'd have!

Martin Snarski LEED(r) AP

Snarski, Marty's picture
Joined: 2011-10-01
Reputation: 0

In my past experience, I had assigned those heated only spaces to VAV
systems for the baseline model. I think that's the most appropriate way
of complying Appendix G. And this way it went through without any
comments from the reviewer.



Fareed Syed's picture
Joined: 2011-09-30
Reputation: 0


I usually model heating-only systems in my proposed model as PTAC
systems for Appendix G. I use a high cooling thermostat temperature in
the proposed and baseline models to minimize cooling energy in those


William Bishop, EIT, BEMP, LEED(r) AP

Bishop, Bill2's picture
Joined: 2011-09-30
Reputation: 0

I think that requirement G3.1 (10-d):

"Where no cooling system exists or no cooling system has been specified, the cooling system shall be identical to the system modeled in the baseline building design"

plays also.


Demba Ndiaye's picture
Joined: 2011-09-30
Reputation: 200

What I did in Trace....

I have a mechanical room which I was going to cooled with exhaust fans and no
mechanical cooling. To do this, I set the infiltration equal to the exhaust
cfm in the Airflows tab. I then set the infiltration schedule and exhaust
schedule to be 100% whenever the mechanical room temp was above 80 degrees.
(You will have to create a schedule.)

Modeling the exhaust cooling as infiltration worked best since the air
travels from the outside directly to the room without going through any
mechanical divice. (Coils, filters, fans....)

I also made a coiling unit can called it "pretend" and had the set point 100
degrees. (So it would never turn on.

..... I then made the baseline without the exhaust system, so it would have
to mechanically cool the mechanical room to 100 degrees.

Jeurek's picture
Joined: 2010-10-07
Reputation: 0

I like your approach. Was this for a LEED job? If so, did the USGBC
reviewer like it? That's the important question that next needs


Clark Denson, PE, CEM, LEED AP

cdenson's picture
Joined: 2011-05-17
Reputation: 1

A heating only system is permitted in the baseline ONLY if the space(s) being served are categorized as semi-heated. 90.1 defines a semi-heated space as "an enclosed space within a building that is heated by a heating system whose output capacity is greater than or equal to 3.4 Btu/h*ft2 of floor area but is not a conditioned space."

So if it's more than that then it's a conditioned space. Conditioned spaces must follow the baseline system rules of G3.1.1 and must be heated and cooled.

An unconditioned space must follow Table G3.1 #12 for modeling exhaust fans to be the same between the baseline and proposed. In the Create Rooms, Rooms tab, the room type can be set to conditioned or unconditioned.

Bob Fassbender, LEED AP

Hintz, Scott F's picture
Joined: 2011-10-01
Reputation: 1