RE: [EnergyPlus_Support] How to explain the VAV SYS energy consumption?

Hi Gloria,

There are two variable outputs which might help you out with this, they are:

System Node Temp

System Node MassFlowRate

(these go into Output:Variable, put a * in the top row, those outputs in the next row and then "hourly" in the third row)

Put those into your model and rerun it, then open the ESO file, if you don't have a viewer it is easy to download just google ESO file viewer. These outputs will show you the temperature and the flow rates through all the nodes in your system. If you look at the temperatures and flow rates coming out of your fan, cooling coil and heating coil, you should be able to spot if there is reheat happening in the summer and hopefully be able to explain why, or change your inputs if the system is not performing as it should.

Annie

Dr. A. Marston, Ph.D. LEED® AP BEMP

Head of the Building Performance Group

Ebert & Baumann Consulting Engineers, Inc.

An Enterprise of the Ebert-Consulting Group

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: bankcommhr@xxxxxxx
Date: Thu, 18 Apr 2013 22:32:27 +0800
Subject: [EnergyPlus_Support] How to explain the VAV SYS energy consumption?

Dear all,

I now encounter a difficult problem. In the pursue of a LEED certificate, the reviewer question me on the VAV SYS energy consumption. But I really don't know how to explain, as I followed every procedure of modeling, and the results are there.

The question is: why the heating energy in the baseline case is higher than the proposed case through April to September?

The basic informations of the zone for VAV SYS1 are: lighting power density of baseline case is 11W/m2 higher than the proposed case; equipment capacity are the same in both cases,30W/m2; building envelope heat transfer coefficient is a little higher in the proposed case, but not much; the supply air flow rate is smaller in the proposed case than the autosized value in the baseline case. all other factors such as schedules are the same in both cases.

The VAV SYS energy consumption results screenshot are uploaded.

I think the heating need in summer is for reheat. It is a little wierd that the heating energy in the baseline is higher than the proposed one, as the moisture load in both cases should be the same (same outdoor air, same occupants).

I really need your opinions!

Thanks!

Gloria

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