[Equest-users] VAV with Reheat in Summer

[Kathryn Kerns]

My only other advice is to identify which zones are requiring the extra cooling in the summer that the rest of the zones don't need. This is the cause of reheat.  Try setting all the process loads to 0.0 and if that fixes the problem, start adding the process loads back in a bit at a time.

I would also look at the hourly reports and see if you can identify the time of day the reheat occurs in the summer months. This might give you a clue as to the problem.

Kathryn Kerns
Systems Specialist
BCE Engineers, Inc.
| Ph: 253.922.0446 | Fx: 253.922.0896 |

From: Alireza Mohammadzadeh [mailto:ali.mo at rpeng.ca]
Sent: Monday, December 18, 2017 2:13 PM
To: Kathryn Kerns <kathryn.kerns at bceengineers.com>; equest-users at onebuilding.org
Subject: RE: VAV with Reheat in Summer

Thanks for the reply. Yeah I already set the cooling control to Warmest in the model. If I change it back  to "reset" (default in equest for VAV) my reheat load will be significantly higher.
Even with warmest in cool control, I have a lot of reheat in summer shoulder which doesn't make sense to me.

Ali

From: Kathryn Kerns [mailto:kathryn.kerns at bceengineers.com]
Sent: Monday, December 18, 2017 1:22 PM
To: Alireza Mohammadzadeh; equest-users at onebuilding.org<mailto:equest-users at onebuilding.org>
Subject: RE: VAV with Reheat in Summer

I was having the same issues and had difficulty explaining how the PVAV system works. After a lot of trial and error, I discovered one thing that affects the VAV reheat  in the warmer months and one thing that affects the amount of mechanical cooling in the cooler months.

  1.  The "Cooling Control" variable under the Cooling Tab affects the amount of reheat that occurs in the summer months. There is a great deal of difference in the amount of reheat if you use the ASHRAE baseline 5 delta F reset based on outside air temperature and using the "Warmest" option. Try it, and you will see.
  2.  The "Economizer Low Limit" function located under the Outdoor Air tab, if available, usually shows up as 45 F. Lowering this down to 35 F will reduce the amount of mechanical cooling used in the cooler season.

Hope this helps.

Kathryn Kerns
Systems Specialist
BCE Engineers, Inc.
| Ph: 253.922.0446 | Fx: 253.922.0896 |

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Alireza Mohammadzadeh via Equest-users
Sent: Monday, December 18, 2017 12:41 PM
To: equest-users at onebuilding.org<mailto:equest-users at onebuilding.org>
Subject: [Equest-users] VAV with Reheat in Summer

Hi eQUEST users,
I'm modelling a building that uses VAV with reheat for perimeter and interior zones. The min flow ratio at zone level can't be less than 1, and I set the design flow to match our design.
I get a lot of reheat in summer shoulder, and when I look at the hourly report it seems like my central coil is cooling down the intake and zone coil reheats it. I only have one thermal zone for each VAV at this stage, and I'm sure that summer reheat is not because of humidity control.
Any suggestion how I can get rid of the large should season reheat?

Thanks in advanced

P.S., I attached INP and PD2 files.

Ali Mo, EIT


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