[Equest-users] Unwanted Reheat hours in Baseline Model

Fred Betz fbetz at aeieng.com
Tue Dec 14 15:57:16 PST 2010


My only recommendation is to leave it as is if you are comfortable with the inputs reflecting reality to the best of your ability. Remember to make your temperature set points, schedules, and dead bands realistic for the client. If the client is ok with a few 65F hours at night, have the inputs reflect that. It just has to be the same in the Baseline and Proposed.

As long as the systems are the same, electric reheat, then you should be ok. I have had a few projects that utilize a strong passive design (shading, natural ventilation, etc.), which are meant to eliminate the entire heating or cooling system. I could easily see eliminating reheat in the Caribbean quite easily through a smart passive design and expanded thermal comfort range. If your passive design eliminates reheat in the real world, then the simulated design should mimic that for the most part in operation if not in inputs.

These passive features are missing in the Baseline, which is why it needs the reheat. In my mind the model is doing exactly what the design is supposed to be doing. If you have a poor Baseline design, you'll need reheat.

You'll have to decide if the Baseline model is realistic in its use of energy, and you can only really get that out of analyzing the hourly reports and referring to ASHRAE and your engineering experience.

Hope that helps,

Fred


Fred Betz  PhD., LEED AP
Sustainable Systems Analyst



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From: Walson, Kristy [mailto:kristy.walson at tlc-eng.com]
Sent: Monday, December 13, 2010 3:15 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Unwanted Reheat hours in Baseline Model

Hi all,

I am modeling a building located in the Caribbean that does not have any heat in the design.  Per ASHRAE 90.1-2004, even though the building has no heat, I am supposed to model both the Baseline and the Proposed model with electric heat (with all of the same properties between the two models).  My Baseline system is a Packaged, Constant Volume, DX system.  I find that the Baseline building is using a ton of electric heat for reheat because the system is constant volume and it seems to be overcooling without the reheat.  I was able to correct this in my Proposed model by reducing the Minimum Flow Ratio, but since my Baseline building is constant volume I can't reduce the minimum flow ratio to fix the reheat problem.

Does anyone have any suggestions on reducing this reheating?  Because the building doesn't even have any heat, I artificially inflated the heat in the Proposed to make the same as the Baseline because I was getting an imaginary benefit otherwise.  Thanks for the help.

Kristy M. Walson, PE, LEED AP
Mechanical Engineer / Sustainable Design

TLC Engineering for Architecture
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Orlando, FL 32801-3463

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