[Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + Return Duct System

[Paul Diglio]

Cam:

Attached is an official interpretation I requested from ASHRAE concerning this 
issue. In my understanding, the supply fans that do not provide ventilation are 
not required to run continuously.

That being said, it is implied that the ventilation air is somehow distributed 
throughout the occupied space in order to provide air to all the rooms.  I was 
modeling an apartment building with two PTAC systems in each apartment of 4 
rooms.  The ventilation air was introduced via an outlet over the apartment 
entry door.  It would not be possible to distribute this air to the bedrooms or 
living room without ductwork.  So in this case the PTAC units (2) in each 
apartment need to run in order to distribute this air, especially if the 
interior doors are closed.  


Of course, in the real world the occupants would not leave the PTAC fans running 
continuously 24 X 7 to distribute this air.

Has anyone submitted a model to LEED cycling the PTAC fans when ventilation air 
is provided by another system?

 Paul Diglio, CEM, CBCP


87 Fairmont Avenue
New Haven, CT  06513
203-415-0082


www.pdigliollc.com




________________________________
From: Cam Fitzgerald <cam at energyopportunities.com>
To: Richard Ellison <REllison at southlandind.com>; James Hess <JHess at tmecorp.com>; 
Kathryn Kerns <kathryn.kerns at bceengineers.com>; 
equest-users at lists.onebuilding.org
Sent: Wed, February 27, 2013 7:40:30 AM
Subject: Re: [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + 
Return Duct System


Agreed…the conditioning fans can only be cycled if they are not required to 
distribute the ventilation air from the DOAS.
 
From:Richard Ellison [mailto:REllison at southlandind.com] 
Sent: Wednesday, February 27, 2013 7:35 AM
To: Cam Fitzgerald; 'James Hess'; 'Kathryn Kerns'; 
equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + 
Return Duct System
 
I agree with your comment that “…suggestion below that the DOAS should be 
modeled as a process load is inappropriate for the baseline case.”  However I 
have concerns on the final portion of your comment.  Most real designs that 
would be proposed don’t dump OA directly into the space and DO require the 
terminal fan be running to be operating to distribute OA from the DOAS into the 
building.  In this design you cannot assume the terminal unit is cycled in the 
proposed case and meet the 62.1 OA requirements.
 
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Cam Fitzgerald
Sent: Wednesday, February 27, 2013 7:27 AM
To: 'James Hess'; 'Kathryn Kerns'; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + 
Return Duct System
 
Good morning, all,
 
I inadvertently sent the following response only to Kathryn yesterday.
 
There is no fan power  correction available for the baseline residential systems 
type 1 (PTAC) and type 2 (PTHP). The baseline systems are standardized to 
establish a benchmark for demonstrating energy savings. If the dormitory 
includes non-residential spaces (lounges, corridors, and other common areas) 
with a total area of 20,000 sf or more, then exception (a) to section G3.1.1 
would apply and it is appropriate to used an alternate (non-residential) system 
type for these areas and if the proposed systems are fully ducted return systems 
with MERV 13 filters, then the adjustment factors for those devices may be 
applied in the fan power calculations for the non-residential systems.
 
In light of the suggestion below that the DOAS should be modeled as a process 
load is inappropriate for the baseline case. When DOAS supply tempered 
ventilation air directly to the space (e.g. not the return airstream of the unit 
conditioning the space) the ability to cycle the fans that condition the space 
to maintain the space temperature is acceptable (these fans are not required to 
provide ventilation so they do not need to operate continuously). In the 
Baseline case, the ventilation air is assumed to be delivered through the 
PTAC/PTHP units so these fans must operate continuously during occupied periods. 
The savings from cycling the fans in the residential units, the energy recovery, 
and air-side economizer generally compensates for the additional fan power 
required for the DOAS system. Note that if the DOAS system were modeled in the 
baseline case, it is possible that energy recovery would be required and some of 
the savings for this measure in the Proposed design would be lost.
 
Herein lies the value of energy modeling for design decisions…is the fan energy 
penalty for the DOAS system equal to or less than the potential savings?
 
Have a great day!
 
Cam Fitzgerald
 
Energy Opportunities/a 7group company
1200 E Camping Area Rd, Wellsville, PA 17365
 
 
 
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of James Hess
Sent: Wednesday, February 27, 2013 12:02 AM
To: Kathryn Kerns; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + 
Return Duct System
 
Interesting question about DOAS and the current fan power allowance for system 
types 1 & 2.  I think we very much need an update to Appendix G to account for 
the fan power requirements of the dedicated outdoor air systems that are (in my 
opinion) required for unitary type systems such as PTACs as well as the 
PSZ-ACs.  

 
I’m in the south, and so we cannot count on simply opening the windows to meet 
our ASHRAE ventilation requirements, at least not anymore J(we did exactly that 
through until ~ 1988 at the school in Louisiana I attending while growing up, at 
which point we finally got air conditioning and promptly shut the windows).
 
I would argue that a DOAS is necessary in the south to properly provide outside 
air, while maintaining acceptable building humidity conditions, for unitary type 
systems.  Anything less is negligent design, in our opinion.  However, at the 
present time, Appendix G assumes that PTACs (or PSZ-ACs) will bring outside air 
continuously into the zones and cycle the compressor to control room temp while 
ignoring humidity.  You can’t do that in real life.  Where we have seen that 
done, you get condensation and eventually mold, and eventually you get sued.
 
I think you have run into a gray area for which there is no good answer 
currently.  Assuming that you are working on a LEED project, you’ll have to hope 
that you run up against a LEED reviewer that will exercise good judgment and 
common sense, and understand that this area is not covered by Appendix G 
currently and that a reasonable allowance for DOAS fan power should work and 
should be allowed, since it can be argued that DOAS are required to meet the 
ASHRAE 62 ventilation requirements.
 
The issue is that the 0.3 watts/CFM is only enough fan power allowance to 
account for a motel “thru the wall” type unit.  No external ductwork (supply or 
return), barely a filter, and certainly no allowance for a DOAS.
 
My recommended solution would be to model the DOAS with the same fan power in 
the Baseline as in the Proposed.  

 
That’s conservative in my opinion.  You aren’t taking credit for any fan energy 
savings associated with the DOAS, but neither are you unnecessarily penalizing 
yourself either for something that is required for the Proposed Design.
 
Regarding AHRI fan power assumptions, I’m not sure about that question.  But I 
did a quick test in eQuest.  I built a quick sample model in the DD wizard, 
selected PTAC, and entered 11 EER for cooling efficiency.  I then went to the 
detailed mode and the EIR conversion was the exact same that eQuest does for any 
system àEIR = 0.2580 for EER =11.0.  Consequently, we know that eQuest is using 
the 365 watts/KCFM conversion.  But that’s eQuest. I don’t know what AHRI 310 
uses for fan power assumption, if anything.  I looked into this a while back and 
I don’t think that eQuest is on the same page with the AHRI fan power 
assumptions used in the ratings.  I could be incorrect, however.  Another thing 
is that the fan power assumptions used in the AHRI ratings have absolutely 
nothing to do with the Appendix G fan power requirements.  I do know that.  I 
think we need to let eQuest do its thing in the wizard/detailed interface 
transition, and then go to the detailed interface and change the EIR ourselves 
to whatever is appropriate, if we can figure out what AHRI is doing regarding 
fan power assumptions.
 
Hope this helps!  J
 
Regards,
 
JAH
 
James A. Hess, PE, CEM, BEMP
Energy Engineer
TME, Inc.
Little Rock, AR
Mobile: (501) 351-4667
 
From:equest-users-bounces at lists.onebuilding.org 
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Kathryn Kerns
Sent: Monday, February 25, 2013 5:57 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Baseline PTAC Fan Energy for a Proposed Merv13 + Return 
Duct System
 
Everyone, I have been modeling some dormitories with a proposed HVAC system 
involving a DOA with a full exhaust air HX and MERV 13 filters. The puzzle is 
what to do about the baseline PTAC fan power energy? If I use 0.3 w/cfm as 
Appendix G suggests, my PTAC baseline system does not account for a fully ducted 
return\exhaust or MERV 13 filters. The commercial fan power equation for systems 
3-8 accounts for this, but I am not supposed to use that formula for System 1 
and 2.
 
Another puzzle is if I develop an cooling EIR value for my baseline PTAC using 
the 365 w/kCFM conversion rule and equate that with 0.3 w/cfm, what happened to 
the other 65 w/kCFM? 

Maybe ARI 310/380 doesn’t use 365 w/cfm fan power?  I read it and didn’t find 
any statement regarding fan power requirements, but I assume it works the same 
as ARI 210/240?
 
I am wondering if a compromise of 
                        PTAC fan power = CFMs *0.000365 + A             where A= 
PD*CFMs /4131 and PD = 1.4
might be a reasonable solution?
 
                        PTAC fan power = 0.00063 kw/cfm
 
Does anyone else have experience with this puzzle?
 
Kathryn Kerns
Systems Specialist
BCEEngineers, Inc.
| Ph: 253.922.0446 | Fx: 253.922.0896 |
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