[Bldg-sim] How to set the loop loss as 5 or 10%?

[Mitchell Dec]

Esmireta,

I've always provided a narrative to support this. The last two campus projects I've dealt with directly had two different resolutions.

1.       Project A: Modeled the virtual plant based on the equipment efficiencies following the District Thermal Modeling Guidelines. In this case, the heat loss from the campus piping distribution was assigned as a delta-T as loss to the tunnel. A narrative was provided to explain the total CHW & Steam consumption before adding the heat loss, and the consumption after applying the heat loss. I assume similar parameters, as you describe, by multiply the distribution DT by 10% for the tunnel losses - however, the results were much greater than a 5% or 10% increase in energy use for that component. I reviewed the summary of plant equipment reports and found the part load performance was completely different from the model without a DT factor applied. It appeared as though the plant was trying to accommodate for these loads so the equipment DT's were operating at higher ranges, thus changing factors for exiting CHW temperature and the LIFT. I didn't have much more time than to dig deeper, but adjust the DT down until the 5%/10% thresholds were achieved and explained this to the reviewer.

2.       Project B: Ended up using actual metered consumption of the CUP/CHP to build a spreadsheet of the total energy consumed for BTUs delivered. I was trying to model this approach, but it got very convoluted, and ultimately had a review with the GBCI review team and Gail Hampsmire from the GBCI. This was very productive and helped us forge ahead with a simple resolution of using a spreadsheet based calculation apportioning the real campus energy use meters to prorate kWh/therms for each building. Bottom line is if you are having a difficult time communicating with the review team, see about having a short call with Gail to help work through open issues and determine a path forward. She's been incredibly helpful for multiple items we've encountered.

-Mitch

From: Esmireta [mailto:e2fye2 at 163.com]
Sent: Wednesday, April 17, 2013 7:25 PM
To: Mitchell Dec; BLDGSIM
Subject: Re:Re: [Bldg-sim] How to set the loop loss as 5 or 10%?

Hi Mitchell,
Thanks for your reply!
I really don't know how the DT work. Why a little DT can give a huge rise in the energy consumption?
Further, will the GBCI reviewer question the way of setting DT to represent the loop loss? Did you give any specific explanation on the DT, or just leave it without narrative?
Thanks!
Esmi




At 2013-04-18 10:08:05,"Mitchell Dec" <mdec at glumac.com<mailto:mdec at glumac.com>> wrote:

I usually run with no loss, then adjust the delta-t until the additional consumption matches the % stated by the guideline.

Mitch Dec
Glumac
Energy Department Manager

Sent from my Verizon Wireless 4G LTE Smartphone

----- Reply message -----
From: "Esmireta" <e2fye2 at 163.com<mailto:e2fye2 at 163.com>>
To: "BLDGSIM" <bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>>
Subject: [Bldg-sim] How to set the loop loss as 5 or 10%?
Date: Wed, Apr 17, 2013 7:04 PM

Dear all,
As required by the district thermal energy guidance, the loop loss should be 5% for the cooling loop and 10% for the heating loop.
However, there is only DT input for the loop loss option panel. If the supply and return temperature difference is 40 F for the heating loop, the loss should be 4 F. But after I set the loss DT as 4F, the heating energy consumption will increase heavily, even 3 times of the orginal heating energy consumption.
So I wonder how it works. Does anybody have experience on it?
Thanks!
Esmi


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