Hi,
We are working with a building in Norway that has a ground-source heat pump as its main heating system and it is also connected to communal district heating as a back-up. The Central Plant is located in the building but there is a possibility that other buildings are going to use partially energy from this Central Plant.
That means we have a case of a Campus Energy System and we should use the guidance for Campus Thermal Energy in LEED. According to this document, the Proposed building should be simulated with a virtual on-site plant with average efficiencies. How should we calculate our average heating and cooling efficiencies since in our case the plant is located in the same building?
Anthony Hardman
Building Performance AnalystThe Green Engineer
16 thumbs up
February 20, 2013 - 10:16 am
First, I would try to determine if the system is designed to be a hybrid or if the district heating is truly only meant for backup (i.e. emergency) purposes. If the district heat is in fact only meant to serve as a backup, then you can ignore all the DES guidance and just model it according to 90.1.
Can you provide more details on your district heat (e.g. new/existing, fuel source, etc.)?
Therese Malm
WSP Environmental10 thumbs up
February 20, 2013 - 12:18 pm
The heat pump will cover up to 95% of the annual heating demand, and in cases of peak load the existing district heating will be used. That means district heating can cover up to 5% of the total annual heating demand. Is that a hybrid system that someone should handle as a DES or can it be ignored since district heating covers so little amount of the total heating?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
February 20, 2013 - 12:44 pm
That is a hybrid system and as such the baseline will be under the fossil fuel column in Table G3.1.1A assuming the district system uses some fossil fuel. Under the DES option 1 you simply treat the district energy as purchased heat. Under option 2 you would need to account for the system efficiencies. Use the actual efficiencies or the default values.
Therese Malm
WSP Environmental10 thumbs up
February 20, 2013 - 4:22 pm
If I understand correctly, in option 2 I should:
For Proposed building: replace the ground-source heat pump and the district heating with a virtual on-site plant with a boiler and a chiller. The efficiencies for the boiler and chiller can be either the actual ones (i.e. 95% of the GSHP and 5% of the district heating for the boiler and GSHPs COP for the chiller) ?? Or in the case of default values, the efficiency for the boiler will be 70% and the efficiency for the chiller will be COP=4.4?
For Baseline building: System 7, fossil fuel furnaces and chillers according to Appendix G.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
February 20, 2013 - 5:33 pm
You do not replace the GSHP since this part of the system is not DES. Model the proposed as designed. The virtual plant would be the district contribution only.
Therese Malm
WSP Environmental10 thumbs up
February 27, 2013 - 4:31 am
What if my GSHP and the district heating is the Central Plant that supplies more buildings than mine. Does that mean that I replace then the whole Central Plant with a virtual one? In case of default values that makes a very innefficient system in comparison to the actual one, i.e. virtual plant with total efficiency at 70% vs. a combination of GSHP with COP and a smaller part of district heating.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
February 27, 2013 - 9:22 am
I was under the impression that they were separate systems with the GSHP only serving your building. Since I do not understand the configuration of your system I can't say how it should be modeled within the DES.
If you don't like the default efficiency then calculate the actual.
Yoyo Shek
Allied Environmental Consultants Limited4 thumbs up
February 28, 2013 - 1:56 am
I am a bit confused with Option 1. What efficiency should we input to find out the amount of purchase heating/cooling?
Therese Malm
WSP Environmental10 thumbs up
February 28, 2013 - 3:13 am
My last question was not for my actual system rather than a general question. If someone has a Campus Energy System with a heat pump covering most of the heat demand and district heat for the rest does that mean I should replace the whole system with a virtual boiler? That is the impression i get from DES guidance.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
February 28, 2013 - 10:38 am
I don't think so Therese. The virtual boiler would only be for the portion of the heating supplied by the district system. The remainder of the baseline system would be determined by Table G3.1.1A. Since it is a hybrid system enter the table under the fossil fuel column.
The intent of the DES guidance is to account for the impacts of the DES on energy use.