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How to model DOAS Correctly using eQUEST?

asked 2014-10-08 00:59:45 -0500

yongqingzhao's avatar

updated 2014-10-09 00:40:15 -0500

In eQUEST,DOAS are usually considered as a dummy zone that a single zone with reheat system serves.But I am always confused if thermostat schedules are required for dummy zone.And I have ever tested the result difference between assignment thermostat schedules for dummy zone and not assignment.I found that the heating energy of the case that thermostat schedules were assigned for dummy zone was significant larger than the case that thermostat schedules were not assigned.

In addition,In my project,outdoor air from DOAS is processed to (temperature:64.4F,Relative Humidity:60 %).How can I implement it in eQUEST.

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It depends what kind of HVAC system you are using in eQuest? PSZ, PVAVS?

Julien Marrec's avatar Julien Marrec  ( 2014-10-09 02:25:24 -0500 )edit

My system is fan coil plus DOAS.I use single zone with reheat system to model DOAS.

yongqingzhao's avatar yongqingzhao  ( 2014-10-09 02:37:01 -0500 )edit

Am I understanding correctly that you have a PSZ with a dummy zone, and other spaces take outside air from the PSZ with OA-FROM-SYSTEM = nameofyour_doas?

Julien Marrec's avatar Julien Marrec  ( 2014-10-09 06:22:46 -0500 )edit

I kown that!But is the thermostat schedule required for dummy zone?And if Outdoor air is processed to (temperature:64.4F,Relative Humidity:60 %).How can I model it? It seems that the thermostat schedule determine the outdoor air tempertaure after which is processed by DOAS.

yongqingzhao's avatar yongqingzhao  ( 2014-10-09 06:34:00 -0500 )edit

This was simply a question, not an affirmation.

Julien Marrec's avatar Julien Marrec  ( 2014-10-09 06:51:11 -0500 )edit

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answered 2014-10-09 07:08:43 -0500

updated 2014-10-09 07:12:12 -0500

If you are using a PSZ for your DOAS system with a dummy zone, and having other mechanical systems taking outside air from it (OA-FROM-SYSTEM), yes, you definitely need to put a thermostat in the dummy zone. That's the entire concept of using a dummy zone, so you can assign a thermostat and define what the temperature the supply air should be.

For your humidity, define it in the PSZ system using Max humidity and min humidity (using min humidity will ask you what type of humidifier you want - if in your design you don't have one, leave min humidity as default (0))

I suggest you create a new hourly report block:

  • Variable type = HVAC Sytem
  • Building component = Your DOAS system
  • Select hourly results series, at least temp of air leaving cool coil - cold deck temp (deg F) and temp of air entering coil (deg F). I suggest also adding the outside air temperature (variable type = GLOBAL > outside dry-bulb temp (°F)) and for you, I'd add humidity as well.

Run your simulation, and then looks into the .HSR file and plot those temperatures. Then assign a schedule to your dummy zone, and do the same. You'll see the difference.

Here, I've got a DOAS with a dummy zone, without any thermostat, as you can see, the discharge air follow the outside air temperature: it's not controlled! PSZ And Dummy zone WITHOUT Tstats

Now, I've assigned a thermostat schedule to my dummy zone (here I wanted 55°F when Tout > 70°F, and 70°F when T < 55°F, and 125-Tout in between), and this is exactly what I'm getting: PSZ and Dummy zone WITH Tstats

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Thanks for your perfect answer!

yongqingzhao's avatar yongqingzhao  ( 2014-10-09 08:22:31 -0500 )edit

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Asked: 2014-10-08 00:59:45 -0500

Seen: 2,927 times

Last updated: Oct 09 '14