[Equest-users] Different cooling loads with different system types

[Walson, Kristy]

Thanks, Bruce.  I ended up figuring this out yesterday.  After going through everything and comparing different system types, I discovered that if I used the Equest system type "Packaged Single Zone", the software would add heating energy for the reheat used to control humidity, but did not add any additional cooling energy in order to overcome the additional heat from the reheat.  The cooling kWh was literally the exact same with or without the reheat.

I then changed my system type to "Packaged VAV", set the fan control to be constant volume, and the cooling energy responded more appropriately when I added reheat to the zones.  I hadn't run into this issue before, though I rarely use ASHRAE System Type #3 (Packaged single zone, CV, furnace), so it was a huge "aha" moment for me.  Equest doesn't operate well using the Packaged Single Zone system (similarly, it also does not operate well using the WSHP system type), so it's better to use the Packaged VAV option when your baseline is ASHRAE system #3 and you have humidity control.

I've been spreading this information like a public service announcement, but I'm sure others have run across this before.  Thanks again for your help!

Kristy M. Walson, PE, LEED AP BD+C, BEMP
Associate / Sustainability Consultant
407-487-1118

From: Bruce Easterbrook [mailto:bruce5 at bellnet.ca]
Sent: Tuesday, January 17, 2012 9:41 AM
To: Walson, Kristy
Cc: 'equest-users at lists.onebuilding.org'
Subject: Re: [Equest-users] Different cooling loads with different system types

Hi Kristy,
The explanation is the loads in the SS-D report are the coil loads of your system units not a full building load.  I ran into it on the SS-J reports on heating loads.  SS-J is a sub report of the SS-D.  The differences will probably be found in under heated or cooled hours and/or in your terminal units.  I noticed it because the low airflow in the ahu was not maximizing the amount of heat the unit could send to the zones.  As I increased the cfm/sf the heating peak increased on the SS-J report.  I assume it would have also increased on the SS-D report.  My underheated hours were decreasing as the peak heating was increasing.
The loads are there, just not on this report.  More information on the reports and what is in each one is in the Detailed Simulation Reports Summary in the DetailedUI folder of the Tutorials section of eQuest.
Bruce Easterbrook P.Eng.
Abode Engineering

On 16/01/2012 01:20 PM, Walson, Kristy wrote:
Hi All,

I am working on a model where the baseline system type is Packaged Single Zone with a Fossil-Fuel Furnace (System Type 3) and the proposed system type is Chilled Water VAV with a Gas-Fired Steam Boiler.  When I take the proposed model, save as, and then just change the system type to the DX CV system, the cooling loads in the SS-D report change.  They are less when the DX CV system.  How can the loads change?  These should stay the same and the energy used to meet these loads should change.  Has anyone run into this before?

Kristy M. Walson, PE, LEED AP BD+C, BEMP
Associate / Sustainability Consultant

TLC Engineering for Architecture
Your 2030 Challenge Partner

255 South Orange Avenue, Suite 1600
Orlando, FL 32801-3463

phone:

407-841-9050

fax:

407-425-7367

direct:

407-487-1118

website:

www.tlc-engineers.com<http://www.tlc-engineers.com>


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