[Equest-users] PTAC vs WLHP Annual Energy Consumption

Wed May 6 13:18:09 PDT 2015

Morteza,

If you are looking for a relatively simple upgrade from PTACs (with electric resistance heat), consider packaged terminal heat pumps.

Keith Swartz, PE
Senior Energy Engineer | Seventhwave | Madison.Chicago.Minneapolis
(formerly Energy Center of Wisconsin)
608.210.7123 | www.seventhwave.org<http://www.seventhwave.org/>

From: David Eldridge [mailto:DEldridge at grummanbutkus.com]
Sent: Wednesday, May 06, 2015 11:45 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] PTAC vs WLHP Annual Energy Consumption

Some of the advantages of a WLHP system are related to maintenance and service life compared to systems with air-cooled condensers and requiring envelope penetrations. These concerns won’t show up in an ASHRAE 90.1 appendix G energy analysis. (Higher infiltration from PTACs?) Also I’d expect some efficiencies of scale from central equipment if your building is large, compared to the PTACs, this may not apply here.

But regarding your EAP2 questions…WLHP offers an energy savings when parts of the building are in heating while others are in cooling – depending on your building’s form and location, as well as modeling assumptions about setpoints, this may not be taking place. For a residential building it might be reasonable to assume that some portion of the residential units are set to different temperature ranges.

Conversely, if your location is cooling dominated all year, some of the advantages of WLHP go away. One thing to check here is the end-use demand components in your model. Is the WLHP using less at full load than the air-cooled system? If so, then you need to investigate the modeling assumptions about the controls of the WLHP system when operating at part load. Make sure that what you gained in peak efficinecy isn’t given back when the system is only partially loaded.

Verify that the WLHP control for the condenser loop is variable flow (if the proposed heat pump units have two-way control valves…if not, talk to your engineer about that!) and that there is a an adequate temperature range for the loop so that the towers and boilers don’t come on immediately. WLHP condenser loop which should be in the range where a condensing boiler will operate successfully, verify that the proposed case takes advantage of this compared to the baseline. Make sure that the condenser loop is operating on call for demand so that the model isn’t assuming continuous operation.

Regarding the DOAS, make sure that the baseline system has the same OA requirements at the PTAC units. Lastly, verify that the fan power for the WLHP units is entered based on the design pressure drop and not eQUEST defaults. Double-check that the fan run-times for the equipment are the same…which for LEED would be fans operating continuously. You probably have this in place already.

I see an interesting paper forwarded by Maria came through while I was typing. Note that the graphics in Figure 1 and Figure 2 are for CO2 emissions, and have non-zero axes, so there could be some variance for your specific case depending on the relative cost of utilities.

It is very interesting – if we take a proposed high-efficiency WLHP system from Figure 2 in Atlanta producing about 625 MTCDE compared to the Figure 1 ASHRAE 90.1 baseline air-source heat pump it is just under 650 MTCDE. In your case, by adding the DOAS and some other efficiencies and depending on your specific utility rates, it should be possible for a high-tech WLHP system to at least reach equivalency with PTACs if not surpass it. Additional savings should result if you are able to add efficiency from upgraded envelope, lighting, and DHW measures in the proposed design. Check the LS reports to verify that building heating and cooling loads are reduced in the proposed case compared to the baseline.

David

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Tim Johnson
Sent: Wednesday, May 06, 2015 10:26 AM
To: 'Morteza Kasmai'; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] PTAC vs WLHP Annual Energy Consumption

Morteza,
I took a quick look at your models and the one thing that sticks out to me is your pump energy.  The difference between PTAC and WSHP is huge.  I would expect some difference since the WSHP needs to run the pumps in cooling mode as well as heating while the PTAC only needs pumps in heating, but the difference in energy seems too big.  Also keep in mind that the heating and cooling efficiencies of the WSHPs are only for that piece of equipment, they don’t include the heat rejection required in cooling mode, the boiler input in heating mode, or the pumps.  For those reasons, I wouldn’t expect the WSHP system to be a lot more efficient than the PTAC.
Tim

Tim Johnson
Mechanical Engineer
o 208.336.4900 | d 208.577.5645
[CTA_email_graphic]

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Morteza Kasmai
Sent: Wednesday, May 06, 2015 7:54 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] PTAC vs WLHP Annual Energy Consumption

Dear eQUEST experts,
I am still struggling to find out the main reason(s) for high-energy consumption of WLHP system comparing to PTAC system and what can be done to make this system more efficient that the baseline system. In other words for complying with EAp2 requirements, for a mid rise residential building what types of HVAC systems (other than split system HP) can be selected which consume less annual energy than the PTAC.

I would appreciate it if you would share your experience on this and make some recommendation.

Morteza

[https://lh6.googleusercontent.com/Uuukta80GuFfvKouzA0mdSvUXqml7MtSwSiw-evuGMU=w147-h43-p-no]

On Mon, May 4, 2015 at 4:03 PM, <equest-users-request at lists.onebuilding.org<mailto:equest-users-request at lists.onebuilding.org>> wrote:
Send Equest-users mailing list submissions to
        equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>

To subscribe or unsubscribe via the World Wide Web, visit
        http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

or, via email, send a message with subject or body 'help' to
        equest-users-request at lists.onebuilding.org<mailto:equest-users-request at lists.onebuilding.org>

You can reach the person managing the list at
        equest-users-owner at lists.onebuilding.org<mailto:equest-users-owner at lists.onebuilding.org>

When replying, please edit your Subject line so it is more specific
than "Re: Contents of Equest-users digest..."

Today's Topics:

   1. PTAC vs WLHP Annual Energy Consumption (Morteza Kasmai)
   2. Re: PTAC vs WLHP Annual Energy Consumption (David Reddy)

---------- Forwarded message ----------
From: Morteza Kasmai <morteza.kasmai at gmail.com<mailto:morteza.kasmai at gmail.com>>
To: "equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>" <equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>>
Cc:
Date: Mon, 4 May 2015 12:04:23 -0400
Subject: [Equest-users] PTAC vs WLHP Annual Energy Consumption
Dear all,

This is a multifamily mid-rise building, 9 floors above grade. Per ASHRAE Table G3.1.1A the Baseline HVAC system is system 1 (PTAC with hot-water fossil fuel boiler) 9.3 to 11 EER.
Selected HVAC system for the proposed design is WLHP (3 Ton High efficiency HP by Daikin, 15.9 EER and 4.83 COP) with 2 cell cooling tower, DOAS unit (9.8 EER) and 2 Boilers (0.92 Eff.).

Although the efficiency of the selected HVAC systems is much higher than the efficiency of the baseline model, the simulation results indicate annual energy consumption of the proposed design is much higher than the baseline!

Am I missing something or did something wrong in the models? Please see the attached files of the both models
.
I would greatly appreciate it if anyone kindly gives some feedback on this,

 Morteza

[https://lh6.googleusercontent.com/Uuukta80GuFfvKouzA0mdSvUXqml7MtSwSiw-evuGMU=w147-h43-p-no]

---------- Forwarded message ----------
From: David Reddy <david at 360-analytics.com<mailto:david at 360-analytics.com>>
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Cc:
Date: Mon, 04 May 2015 09:39:44 -0700
Subject: Re: [Equest-users] PTAC vs WLHP Annual Energy Consumption
Hi Morteza,
I have not reviewed the results or detailed inputs of your model, but one thing to be aware is that depending on the rating conditions of your efficiency data, you may have to adjust the EIRs to be consistent with DOE-2 performance curves.  The default DOE-2 curves are normalized to the GSHP rating condition, so if using these and if your efficiency data is @ the WSHP rating condition, you will need to apply these adjustments.

Here is the table from the DOE-2 help provided with eQUEST.  There is a library of DOE-2 WSHP curves available from ClimateMaster that do not need these adjustments.

[cid:image002.jpg at 01D087E7.BEE13610]

- David
On 5/4/2015 9:04 AM, Morteza Kasmai wrote:
Dear all,

This is a multifamily mid-rise building, 9 floors above grade. Per ASHRAE Table G3.1.1A the Baseline HVAC system is system 1 (PTAC with hot-water fossil fuel boiler) 9.3 to 11 EER.
Selected HVAC system for the proposed design is WLHP (3 Ton High efficiency HP by Daikin, 15.9 EER and 4.83 COP) with 2 cell cooling tower, DOAS unit (9.8 EER) and 2 Boilers (0.92 Eff.).

Although the efficiency of the selected HVAC systems is much higher than the efficiency of the baseline model, the simulation results indicate annual energy consumption of the proposed design is much higher than the baseline!

Am I missing something or did something wrong in the models? Please see the attached files of the both models
.
I would greatly appreciate it if anyone kindly gives some feedback on this,

 Morteza

[https://lh6.googleusercontent.com/Uuukta80GuFfvKouzA0mdSvUXqml7MtSwSiw-evuGMU=w147-h43-p-no]

_______________________________________________

Equest-users mailing list

http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

To unsubscribe from this mailing list send  a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG<mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>

_______________________________________________
Equest-users mailing list
Equest-users at lists.onebuilding.org<mailto:Equest-users at lists.onebuilding.org>
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20150506/b36ffb2e/attachment-0005.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.png
Type: image/png
Size: 4443 bytes
Desc: image001.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20150506/b36ffb2e/attachment-0005.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.jpg
Type: image/jpeg
Size: 18892 bytes
Desc: image002.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20150506/b36ffb2e/attachment-0005.jpg>