[Bldg-sim] FW: Residential or Nonresidental? And sizing forPTAC units.

David S Eldridge DSE at grummanbutkus.com
Tue Mar 11 18:14:11 PDT 2008


For an 90.1, it asks you to separate the fan from the compressor.  This is because the standard will ask for fans to run constantly, however if you have a combined EER (entered as cooling-EIR) the fan power will not be calculated when the compressor cycles off.
 
That may be okay for non-App G analysis, particularly if your project will cycle with the compressor.
 
David
 
 

________________________________

From: bldg-sim-bounces at lists.onebuilding.org on behalf of Keith Swartz
Sent: Tue 3/11/2008 5:07 PM
To: Loren Appin
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] FW: Residential or Nonresidental? And sizing forPTAC units.



Loren,

 

I haven't had to get into that much detail for my energy models (not LEED), so I won't be much help on this. I suggest finding out from the manufacturer if the published EER includes fan power or not.

 

Sincerely,

Keith Swartz, PE, LEED® AP

Energy Center of Wisconsin

455 Science Drive

Suite 200

Madison, WI 53711

 

Phone: 608-238-8276 ext. 123

Fax:     608-238-0523

www.ecw.org <http://www.ecw.org/> 

The Energy Center of Wisconsin is an independent, nonprofit organization that seeks solutions to energy challenges.

________________________________

From: Loren Appin [mailto:lorenappin at gmail.com] 
Sent: Tuesday, March 11, 2008 7:30 AM
To: Keith Swartz
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] FW: Residential or Nonresidental? And sizing for PTAC units.

 

Thank you both Andrew and Keith,

Understanding the exceptions, and also correct calculations for the EER (didn't realize there was a limit of 15,000 BTU for the calculation until I read the small print!) are very helpful.  It brings up another question, now, though: 

When modeling a PTAC unit, and taking this EER value, would you use this to include the supply fan energy?  G.3.1.2.1 states that you should separate it into various components, which confuses me a bit.  I know this is getting down to minutia, however, just trying to make sure I'm doing this correctly.  If this is something that is common practice to look over, and just make sure to include the supply fan efficiencies within the EER for entire unit (something that would make sense to me as it is a packaged unit), also let me know.

Thanks again,

Loren

On Mon, Mar 10, 2008 at 6:35 PM, Keith Swartz <kswartz at ecw.org> wrote:

Loren,

 

One of the notes under Table G3.1.1A of ASHRAE 90.1-2004 states, "Residential building types include dormitory, hotel, motel, and multifamily. Residential space types include guest rooms, living quarters, private living space, and sleeping quarters. Other building and space types are considered nonresidential." The User's Manual also says, "If a building has both residential and nonresidential spaces, for instance a residential tower with retail and restaurants at the base, then the HVAC system type is determined separately for the residential and nonresidential portions."

 

I recently did an energy model for a motel that had first floor retail spaces, a swimming pool, an indoor parking garage, and a fairly large lobby. I used realistic systems for these spaces instead of PTACs or PTHPs. For a different motel I modeled, the nonresidential spaces were rather insignificant, so I used PTHPs throughout.

 

Regarding which capacity to use for the EER calculation, I would use realistic capacities. For example, for the space that needs 40 kBTU/h, I would assume that there would be two 20 kBTU/h units and use 20 kBTU/h for the capacity in the EER equation.

 

I think the decision to use an average EER for all the units is a judgment call depending on how complex you want your model to be. It's the usual trade-off between making assumptions to simplify the model or adding complexity to get more accuracy (presumably).

 

Sincerely,

Keith Swartz, PE, LEED® AP

Energy Center of Wisconsin

455 Science Drive

Suite 200

Madison, WI 53711

 

Phone: 608-238-8276 ext. 123

Fax:     608-238-0523

www.ecw.org <http://www.ecw.org/> 

The Energy Center of Wisconsin is an independent, nonprofit organization that seeks solutions to energy challenges.

________________________________

From: Loren Appin [mailto:lorenappin at gmail.com] 
Sent: Sunday, March 09, 2008 3:31 AM


To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Residential or Nonresidental? And sizing for PTAC units.

 

Hi All,

I'm modeling a 6 story hotel, and am confused with how I should classify the building.  The hotel is all guest rooms, and is not really mixed use.  So according to ASHRAE this seems that it would fall under the residential category, and I would be using PTAC or PTHP systems.  Under table G3.1.1A it specifically says hotels are considered residential building types, not just space types... so I assume I'm correct?   However, would I use a VAV or PSZ system for areas that are not technically guest rooms, or does this not matter as a hotel is considered a residential "building type"?


Also, when modeling a PTAC system it appears to me that you would get the EER information from 6.8.1D using the equation, however, sometimes it my system summary gives me a peak/capacity of a unit as 30KBtu or even 40 for one room and I know that PTAC units usually don't go much about 20.  So would the equation in this table still hold?  Finally, if I am getting varying capacities for each unit as would be expected, would you suggest taking an average of all the systems, and then use this capacity as the one to enter into the equation to get the EER and then apply this EER to all systems across the board?

Thanks so much for the help!


Loren Appin

Energy Engineer

Silpa Inc. 
s i m p l e  .  s c i e n t i f i c   .   s u s t a i n a b l e

AMERICAS | MIDDLE EAST | INDIA

www.silpa.com <http://www.silpa.com/>  | Mob: +971.50.9250895

 


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