Crazy High Unmet Heating Hours on ASHRAE 90.1 Baseline Model

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Hi Dana,

The problem i am able to see can be the reason and alteration can be the
rectification many times during unmet load hours for heating in the case of
VAV with Reheat.

The thing that your are required to do is to change the Reheat delta T to
30-35 degree Fahrenheit . This might be able to successfully reduce the
unmet load hours to very less margins.

The place were you are required to change the Reheat delta is as an example
given below:

It is in the Air-side system-Heating tab.

*Thanks,*
Sharad.Kumar
Freelancer(Energy Simulation)
India.

---------- Forwarded message ----------
From: "Dana M. Savage"
To: "equest-users at lists.onebuilding.org" Cc:
Bcc:
Date: Mon, 30 Jul 2018 19:08:31 +0000
Subject: [Equest-users] Crazy High Unmet Heating Hours on ASHRAE 90.1
Baseline Model

Good afternoon everyone!

I am working through the process of creating an ASHRAE 90.1-Appendix G
baseline model and cannot understand where I?ve gone wrong in the design.
I have done a number of energy audits using eQuest but have never been
through the LEED process and thus this is my first attempt at dealing with
90.1 directly. Any help you may offer would be much appreciated and I am
more than happy to compensate any time spent.

The building is a System Type 7 ? VAV with Reheat ? and my cooling hours
are 0. However, I can?t seem to get my VAV terminal units to provide
enough heat at any time during the year. When I allow eQUEST to size the
capacities on their own, not enough heat is added and temperatures
throughout the winter and in all zones remain below 60F. But when I
specify a Maximum Heating Rate at the Zone Terminal the addition rate
doesn?t change! I?ve tired increasing the throttling range, which had some
effect. The only thing that had a significant effect on the unmet heating
hours was increasing the Heating Design Temperature for each Zone. But
this also had the effect of dramatically increasing the cooling unmet
hours! Finally, and most confoundingly, my heating energy consumption in
the winter is significant! Where is it all going?? I am at a total loss.

I hope I was clear in articulating my issue and again appreciate your
assistance.

*Dana M. Savage **::* Mechanical Engineer

CONTACT *::* DSavage at cfrengineering.com *::* C: 301.717.0003

ADDRESS *::* 20251 Century Blvd. Suite 120 *::* Germantown, MD 20874

*www.cfrengineering.com *

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Sharad Kumar2's picture
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Dana,
The heating setpoint is 70? F. 90.1 says to size the system based on a 20? F delta T between space temperature setpoint and supply air temperature. Base on that, I revised the A1Sys Heating tab:

[cid:image001.jpg at 01D42989.4E13B600]

This reduces the total unmet heating hours for that system from 40348 to 3148.

I would then increase the minimum flow percentage and reheat delta T in the remaining problem zones. Q = 1.08 * (cfm * delta T). To meet the heating loads either the supply flow or delta T have to be increased.

Christopher R Jones, P.Eng.
T+ 1 416-644-0252

[cid:image005.png at 01D42989.4E13B600]

Jones, Christopher2's picture
Joined: 2017-10-12
Reputation: 0

Thanks for the suggestions!

With this forum's assistance I've been able to bring the number of unmet hours to below ASHRAE levels - and find savings of around 37%!!

I sincerely could not have done it without everyone's assistance. Have a fantastic day all!

Many thanks,

Dana M. Savage :: Mechanical Engineer
CONTACT :: DSavage at cfrengineering.com :: C: 301.717.0003
ADDRESS :: 20251 Century Blvd. Suite 120 :: Germantown, MD 20874
www.cfrengineering.com
[cfr]

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