[eQuest users] packaged variable volume system

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I have a question regarding HVAC system types in eQuest. My baseline building is modeled as a packaged variable volume system (It is a System 5) while my design building is mostly modeled as a bunch of packaged single zone systems. For some reason I am getting a 70% reduction in gas consumption, even thought my efficiencies are pretty similar. This reduction seems unreasonable. Is there something about the packaged variable volume system in eQuest that I don't know about? What type of system do people usually use for a system 5?

- Thanks,

Scott Tomlinson, PE, LEED-AP

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Joined: 2011-09-30
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The first thing I would check is simultaneous heating and cooling. If it is a problem, check the reset temps and controls of the packaged system. The packaged unit may be cooling the air, then tempering it at the zone level.

Jeremy McClanathan, LEED(r) AP

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Joined: 2011-09-30
Reputation: 200

Scott:

If you are going from a constant volume system with reheat to a VAV system, you will eliminate a ton of excess heating. The % may be large as you may not have had much heating to begin with.

John Aulbach's picture
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Joined: 2011-09-30
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Here are some thoughts, not knowing anything about your building or your climate...

1. A central VAV system can have a lot of reheat, whereas your PSZ systems should have no reheat. That can be a big savings in gas use.

2. Did you check whether all of the zones are satisfied throughout the year in both runs (unmet hours)?

3. Are you modeling SAT reset in your baseline?

If all else fails, look at some hourly reports to make sure that the models are doing what you're expecting them to be doing.

Good luck!

Hwakong

From: stomlinson at smma.com
To: equest-users at lists.onebuilding.org
Date: Tue, 2 Mar 2010 11:42:14 -0500
Subject: [Equest-users] [eQuest users] packaged variable volume system

I have a question regarding HVAC system types in eQuest. My baseline building is modeled as a packaged variable volume system (It is a System 5) while my design building is mostly modeled as a bunch of packaged single zone systems. For some reason I am getting a 70% reduction in gas consumption, even thought my efficiencies are pretty similar. This reduction seems unreasonable. Is there something about the packaged variable volume system in eQuest that I don?t know about? What type of system do people usually use for a system 5?

- Thanks,

Scott Tomlinson, PE, LEED-AP

Hwakong Cheng's picture
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Joined: 2011-09-30
Reputation: 200