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
How to set the loop loss as 5 or 10%?
Apr 17, 2013
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
I usually run with no loss, then adjust the delta-t until the additional consumption matches the % stated by the guideline.
Mitch Dec
----- Reply message ----- To: "BLDGSIM" Subject: [Bldg-sim] How to set the loop loss as 5 or 10%?
From: "Esmireta"
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
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
Dear Rut,
Thanks for your reply!
In my opinion, Q=m*cp*delta_t. During the transport of cold water, there is no mass loss, so m stay constant, and assume cp is constant. Assume the thermal loss=delta_Q, then, delta_Q=m*cp*delta_t1. Because delta_Q=10%*Q, then, delta_t1=10%*delta_t.
I think the above method is reasonable.
But why the delta_t1 will cause a lot of more energy?
Thanks!
Esmi
I've come across the same scenario before. I would say Mitchell's method is a reasonable way to go.
Additionally, the 10% loss in Temp (F) should be not equal to 10% in Thermal energy (Btu/h). This is most likely why you see huge spike in energy consumption. You'd have to identify the thermal property of the CHW and HW at the supply temp (in Btu/h), and determine the loss in Btu/h that is equal to 10%. If there is no loop loss Btu/h input, you could back-calculate the reduced Btu/h in water to determine the DT.
Rut
From:bldg-sim-bounces at lists.onebuilding.org on behalf of Esmireta
Sent: Wednesday, April 17, 2013 10:25 PM
To: Mitchell Dec; BLDGSIM
Subject: 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
I usually run with no loss, then adjust the delta-t until the additional consumption matches the % stated by the guideline.
Mitch Dec
Sent from my Verizon Wireless 4G LTE Smartphone
----- Reply message ----- To: "BLDGSIM" Subject: [Bldg-sim] How to set the loop loss as 5 or 10%?
From: "Esmireta"
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
Esmi,
I have made the same conclusion before, but the increase in energy consumption was unreasonably high, as you've observed; thus, prompting further look. However, in eQUEST I have the alternative in inputting Loop Loss in Supply Loss UA, in addition to Loss dT.
Without knowing how your model was set up, it's hard for me to speculate any further on the energy+costs increase.
If you can determine the energy consumption of the district/primary loop, then continue to adjust your Loop Loss deltaT until the additional 10% is met per Mitchell's suggestion. You can document the results to provide to LEED for supporting docs.
Good luck,
Rut
Hi, Rut,
Thanks for your reply!
I will try to document the results clearly, though it seems lack of logical support to do that.
Esmi
Esmi,
I have made the same conclusion before, but the increase in energy consumption was unreasonably high, as you've observed; thus, prompting further look. However, in eQUEST I have the alternative in inputting Loop Loss in Supply Loss UA, in addition to Loss dT.
Without knowing how your model was set up, it's hard for me to speculate any further on the energy+costs increase.
If you can determine the energy consumption of the district/primary loop, then continue to adjust your Loop Loss deltaT until the additional 10% is met per Mitchell's suggestion. You can document the results to provide to LEED for supporting docs.
Good luck,
Rut