For LEED 2009, when modeling the proposed building which incorporates the DES (Method 2) how is the DES plant modeled?
As the central plant is huge in comparison to the proposed building load, is a fraction (say peak building cooling load / central plant cooling system) applied to each system? In other words, I scale down the DES plant to match the proposed building loads? Similarly apply the same methodology to the heating plant, pump size, flow rates etc.? I then apply the efficiencies of the plant that I have received from the DES operator?
Furthermore, the DES is a CHP plant. Does anybody have experience in modeling a CHP. I'm finding the guidance in Appendix D difficult to follow.
Your help is greatly appreciated.
Kind Regards,
Dónal
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
April 19, 2013 - 9:44 am
The answer to all your questions on how to model the DES plant is yes. Your approach is correct.
Modeling CHP is very similar, take it down to the building scale. How you model it is very software dependent.
Dónal O'Connor
April 25, 2013 - 11:23 am
Thank you Marcus!
Cheers
Dónal
Dónal O'Connor
April 26, 2013 - 12:56 pm
Hi Marcus,
Further to our discussion, I would like to know if my approach to assigning the tariff rates is correct, using Option 2. The DES is supplied by a CHP plant for the proposed building.
Annual metered electricity consumption shows that the campus uses 73% of the electricity generated by the CHP plant with the remaining 27% coming from grid supplied electricity. So, I intend to use this fraction and apply it to the total electricity consumption of the proposed building. Charge the 27% at the local grid supplied electricity rates and charge the remaining 73% CHP generated electricity based on Annual Fuel Input Cost to CHP ($)/Annual Electricity Generation (kWh).
Again from metered data, 67% of the heating energy supplied to the DES is from the waste heat generated by the CHP plant. The remaining 33% is provided by backup boilers using grid supplied natural gas. So 67% of the proposed building's heating energy will be "free" with the remaining 33% charged based on local natural gas utility costs.
The baseline building heating and electricity consumption will be charged at the local utility rates.
Is this methodology acceptable for LEED review?
Thanks
Dónal
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
May 1, 2013 - 10:19 am
You should follow the methodology outlined in Appendix D of the DES to determine the appropriate rates and how to allocate the CHP production. It varies from what you are describing.
Dónal O'Connor
May 7, 2013 - 1:55 pm
Hi Marcus,
I've determined the CHP Electric Output and CHP Fuel Input according to the formulas provided. However, I'm not entirely sure what to do with these numbers.
For CHP Electric Output it states "for CHP plants in which the recovered waste heat is used directly in the DES and that heat serves only heating loads in the connected buildings, the electricity generation assigned to each building is calculated as:
CHP_ELEC_bldg = (Xheat * BLDG_heat) * CHP_ELEC_total
Is the number calculated for CHP_ELEC_bldg considered free, with the remaining electricity (building electricity consumption is greater than CHP_ELEC_bldg) charged at the utility rate?
Similarly, how is the Proposed_BLDG_fuel value used?
Thanks
Dónal
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
May 22, 2013 - 10:47 am
Yes the CHP electric is free and is subtracted from the building electricity charged at the utility rate.
What you do with the fuel input value depends on how you have modeled the plant. If you modeled the virtual plant with an efficiency that only accounts for the hot water production (thermal efficiency) then you would add this fuel value to the building's consumption. If you modeled the virtual plant with an efficiency that accounts for both the thermal and electric production then the cost for the fuel input is already included so it would not need to be added.
Dónal O'Connor
May 28, 2013 - 10:15 am
Thanks Marcus!