[Equest-users] PTAC vs WLHP Annual Energy Consumption

Wed May 6 08:49:45 PDT 2015

Morteza and Tim,

Attached is a nice article from ASHRAE Journal discussing HVAC system selection for envelope-dominated buildings. It compares modeled performance of VRF, GSHP, boiler+chiller, and WSHP in a generic 9-story multifamily building in a variety of climates, and concludes that WSHP is the worst option. 

Maria

-- 

Maria Karpman LEED AP, BEMP, CEM

________________

Karpman Consulting

 <http://www.karpmanconsulting.net/> www.karpmanconsulting.net 

Phone 860.430.1909 

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Glastonbury, CT 06033

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Tim Johnson
Sent: Wednesday, May 06, 2015 11:26 AM
To: 'Morteza Kasmai'; 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
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

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On Mon, May 4, 2015 at 4:03 PM, <equest-users-request at lists.onebuilding.org> wrote:

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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>
To: "equest-users at lists.onebuilding.org" <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

Image removed by sender.

---------- Forwarded message ----------
From: David Reddy <david at 360-analytics.com>
To: 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.

- 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

Image removed by sender.

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