Baseline system parameters with DES heating in LEED?

district-heating

asked 2016-04-22 03:48:29 -0500

markos
65 ●3

updated 2016-04-22 11:16:30 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hi everyone!

I would like to ask you for some help or guidance with DES heating modellling in baseline building especially with setting up a system parameters like energy efficiency, temeprature resets ect.

This is my first LEED-2009 CS project with DES heating and I'm already a little bit confused how to model it correctly. We chose an Option 1 (the building stand-alone scenario) and from what I have read in DES v2 Guidance it is not clear to me if the baseline heating source has to be modelled with exactly the same energy efficiency, the same temeprature resets and pump power like in Proposed building or it should follow the Appendix G with minimum efficiency requirements and resets stated in sections 6 to 9 of the ASHRAE 90.1 standard. To be more precise, is the Baseline heating source modelled exactly as the Proposed heating source with Option1 or not?

Thank you very much in advance for any help. I need it so much because now I'm not able to complete the simulation...

Martin

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answered 2016-04-22 10:37:15 -0500

Damien Tavan

311 ●2 ●5 http://linkedin.com/in/dtavan

updated 2016-04-22 11:02:54 -0500

When going for DES v2 Option 1, you need to model both the Proposed and Baseline buildings' energy sources as purchased energy, as explained in section 2.4.1.1 of the DES v2 Guidance.

The usual way to implement this option is to model a constant efficiency boiler with 100% efficiency on the hot water loop, and then apply a purchased heat energy rate to the estimated boiler energy. The exact implementation will differ depending on which modeling tool you use. Note that if your Baseline building uses the baseline system type 3, you will have to modify it according to Table 3 (page 11) of the DES v2 Guidance to make it compatible with a hot water loop.

Now, with regards to the actual hot water loop parameters, Baseline supply temperature, temperature reset and pump power should be based on actual Hot Water loop conditions in the Proposed Case. I can't find this exact reference in the DES v2 Guidance document, but these are the instructions written in the Revised Section 1.4 spreadsheet.

Also, keep in mind that when going for DES v2 Option 1 you have to calculate your purchased energy rate as outlined in section 2.4.2.1 of the DES v2 Guidance, under "District Hot Water Rate". Use these rates, which consider some default efficiencies for the District Heating plant, instead of those provided by your District Heating provider.

Finally, be aware that you can only claim a maximum of 12 EAc1 credit points when selecting this option with LEED CS v2009, as per Table 1 of the same document.

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Thank you very much for your reply. I appreciate that!

Yes, I noticed in the revised section 1.4 spreadsheet in helpful notes that Option 1 should be modeled something like that. But when I selected within "General HVAC" how the DES was modeled, helpful notes in "Water-side HVAC Details" has changed only when "ASHRAE 90.1-2007 Appendix G without addenda" was thicked and no change when DES v2 Option 1 selected. And it confused me. Have you noticed that in the 1.4 spreadsheet?

markos ( 2016-04-22 16:01:22 -0500 )edit

Ok, now I see what can be confusing, thanks for pointing it out. I checked the 1.4 spreadsheet, and it's not clear whether this might be an error or not. And since the only clear indication is Section 2.4.1.1 of DES v2 Guidance which states that "Any system parameters not specifically referenced in Table 3 are modeled as specified in Appendix G", I would follow this and model the hot water loop according to sections G3.1.3.3 through 3.1.3.5 of ASHRAE 90.1-2007 App. G.

Damien Tavan ( 2016-04-26 08:58:46 -0500 )edit

Also, bear in mind that choices of supply and reset temperatures for hot water loop won't have a significant impact on the results (I checked one of my projects using DH and observed less than 1% difference). However, the pump specific power for the baseline will indeed have a significant impact. Which is why I usually stick to the baseline power limit specified in G3.1.3.5 in all situations.

Damien Tavan ( 2016-04-26 09:03:38 -0500 )edit

Yes, you are absolutely right that supply temp. resets have not almost any impact on the results...

OK, so you are saying to follow App. G (temp resets, pump power) and heating source with 100% efficiency, right? The efficiency, I would say, is because G3.1.1.1 Purchased Heat where is stated "...on-site boilers shall not be modeled in the Baseline". I understand it correctly?

And thank you Damien for your previous replies...

markos ( 2016-04-26 10:20:38 -0500 )edit

Yes, exactly, because when modeling District heating systems, the heating conversion efficiency is already taken into account in the purchased energy rate. So you end up having to model a "virtual" on-site boiler with 100% efficiency, which is equivalent to having no boiler and getting all of your heating energy from the DH network. By the way, if you are happy with my answer, please mark it as correct. Thanks, and glad to help!

Damien Tavan ( 2016-04-27 07:24:15 -0500 )edit

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