We are dealing with the project served by DES. As client’s goal is to achieve Platinum we are proceeding with option 2 of modelling DES.
Our DES is served with mix fuel ( coal, biomass and oil) for which we calculated fuel mix price as 26,47 $/MWh. Our baseline system is on-site gas boiler for which fuel utility rate is 50,8$/MWh .
As DES guidance is super unclear we have a question in regard to the rates used for calculations:
should we use the same rates for baseline and proposed building equal to = 26,47 $/MWh (as calculated for the fuel mix)? Or maybe ,the same utility rates for base and proposed which are required in DES guide means that they must be consistent in both base and proposed building i.e. if DES will use gas it will be priced at rate of 50,8$/MWh - the same as baseline?
Any comments will be appreciated
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
June 2, 2014 - 10:41 am
Use the same rate in both models based on the rate calculated for the DES.
BH .
72 thumbs up
June 2, 2014 - 2:00 pm
But that don't make any sense, to price gas as fuel mix. Plus it's not giving any benefit of DES over standard boiler.
I found the guide which a bit clarifies the DES LEED guidance. Based on it I think we could use different energy rates for the base and proposed. Marcus could you look at it and comment that?
http://www.districtenergy.org/assets/pdfs/LEED/DES-User-Guide.pdf
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
June 2, 2014 - 2:23 pm
The gas price has nothing to do with it in this case since the DES does not use gas. Appendix G does not say that the Baseline is always gas. The Baseline uses the same fuel as the Proposed in Appendix G.
See G2.4 - the energy cost is determined using the actual rate. The rates applied to each model must be identical. Section 2.4.2.2 of the DES v2 states that the rates must follow the normal Appendix G and LEED protocol.
The DES guidance is set up to account for the impact of the DES. If the system is more efficient than the Baseline you show savings, if not you show a penalty.
In general Appendix G and LEED do not allow savings related to the comparison of different fuels.
The document is certainly not an official document so it does not really matter what it says but it is technically correct. If the DES used gas you use the building rate for the gas (not the DES gas rate) in both models. Since this does not apply to your case and 2.4.2.2 Exception a does apply, you use the central plant rate.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
June 2, 2014 - 2:29 pm
In the future please post your questions and comments in only one of the energy-related forums. I monitor them all and would prefer not to have to reply twice.
There is also a DES specific forum - http://www.leeduser.com/topic/new-district-energy-guidance-leed-released...
BH .
72 thumbs up
June 3, 2014 - 10:44 am
Marcus sorry if I double post it.
Still have doubts with the DES and rates which should be applied. I’ve looked at documents which you mentioned and:
G2.4 indeed defines that the energy cost are determined using the actual rates, but it not specified what rates should be applied to based and proposed.
As you mentioned Section 2.4.2.2 of the DES v2 states that the rates must follow the normal Appendix G and LEED protocol. I ‘ve looked at LEED Guidance and page 268 describes rates which should be applied for district CHP (our case) and describes them as follows:
The baseline heating and cooling plant uses the backup energy source of the design building (our case diesel fuel only for emergency electricity generation, no heating/cooling backup), or electricity if no backup source is present.
In case of the CHP we charge the fuel input, considering process energy related to DES operation.
That’s what ASHRAE and LEED states, unless I’ve missed something. Is that right ?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
June 3, 2014 - 10:36 am
CHP make it all a bit more complicated but the fundamental rules do not change. You need to use the same rates in the baseline and proposed. Since you are not using gas you apply the central plant rates. You cannot use a different rate between the two models.
BH .
72 thumbs up
June 3, 2014 - 10:46 am
But what about LEED guidance and info stated on the page 268 in regards to CHP ?
"The baseline heating and cooling plant uses the backup energy source of the design building (our case diesel fuel only for emergency electricity generation, no heating/cooling backup), or electricity if no backup source is present."
How to understand that in relation to what you wrote ?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
June 3, 2014 - 11:01 am
It seems to me that you are taking one sentence and trying to justify a comparison that uses different rates. You need to look at all of the applicable documents, not just the one that appears to give you the answer you want. I simply do not have the time it would take to figure this out for you. It is entirely possible that there are contradictory statements within the official LEED documents.
BH .
72 thumbs up
June 3, 2014 - 11:14 am
Yep that's the problem of DES, and it's LEED guidance. Simply not clear.
Sounds like the safest way will be use the same rates or do CIR
Thanks a lot for your time Marcus.