Residential Heating only/Ventilation system Modeled as PTAC per ashrae

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I have a residential building, heating only (radiators) with natural ventilation.  Per Ashrae I must model the baseline building as a Packaged terminal air conditioner (Ptac) system.  I've also been told I must model my proposed building as a Ptac system as well because I cannont take credit for  designing a system without cooling.

1) Does this make sense?

2) If that is how I am to model my system, I will have additional fan energy from the months trace is simulating cooling.  Can this additional fan energy be subtracted from my model?



dglenn9000's picture
Joined: 2012-08-07
Reputation: 0

I don't think it really makes since - no energy during cooling season will beat any mechanical cooling efficiency you will ever have.  However, that is the way they want you to model it.

The baseline system gets assigned per table G3.1.1A and B, which specifies the system type for heating and cooling.  Table G3.1.10 (HVAC Systems), letter d in the proposed column says where no cooling system exists the cooling system shall be identical to the baseline.  Since they are trying to keep the systems the same in both alternatives, I would think they want to account for everything in each case - including the fan energy.

FYI - I heard 90.1-2010 has some additional system types for no cooling spaces or no heating, which may be in some of the addenda for 90.1-2007 as well.  But I believe those are only applicable to certain types of rooms (vestibules, stairwells, mechanical rooms, etc.) which probably don't apply in your case.

Lancelot's picture
Joined: 2012-06-11
Reputation: 8

Lance is right.

And yes you have to have your fan energy included. The reason is that the LEED rating system is based on conditioned models. Otherwise, you could install highly efficient lighting in a heating only building and get say 15 points from that alone - because less energy in the baseline means that small savings will have a larger percentage impact. It would be too easy to score points in a heated only building. Now, semi-heated is different and does not require cooling in the baseline and proposed. However, semi-heated is reserved for near tropical climates when you do the math.

Bob F's picture
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Joined: 2010-06-30
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