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NC-2009 EAp2:Minimum Energy Performance

Energy cost for Baseline and proposed case CHP system

Profile picture for user simonsiva22
SAMY Chamy
Enginneer
T&T Green
LEEDuser Basic Member
9 thumbs up

Dear All

Our project uses a CHP plant where the heat form the natural gas generator (GG) is supplied to Exhaust Gas Boiler(EGB), from which the steam is supplied to VAM Chiller that is used for space cooling and the electrical consumption of project is less than CHP generated energy

Here the unit cost of design case electricity is calculated by dividing the total cost of natural gas by the total electricity produced by the generator. This cost is about 0.04 USD / kWh. Also REB is used as a back up source of electricity . Hence as per CHP guidelines market electricity cost is taken as baseline energy cost. However the market electricity cost is 0.124USD / kWh. This is 66% higher than the design case energy cost. In this case should we follow the CHP guidelines and use market cost as baseline or consider the design case cost (Gas cost/kWh) for both base case and design case? 

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Profile picture for user simonsiva22
SAMY Chamy
Enginneer
T&T Green
LEEDuser Basic Member
9 thumbs up

Fri, 09/28/2018 - 05:09

Awaiting for your reply
Profile picture for user DancingDavidE
David Eldridge
Energy Efficiency Ninja
Grumman/Butkus Associates
LEEDuser Premium Member
64 thumbs up

Fri, 09/28/2018 - 16:50

The difference in the pricing shouldn't be a variable (whether higher, lower, or the same) so you should follow the CHP guidance.  Was you question mainly that the benefit seemed to be too large from using the CHP system? One of the things to look at is the pricing for the natural gas to feed the generators. A grid-acquired electricity cost of $0.12/kWh would be high but within reasonable bounds.  Producing power on-site at $0.04/kWh implies a fuel input cost of $0.013/kWh if the power conversion efficiency is about 33%. That's $3.81/MMBtu for thermal fuel - on the low side, you'd definitely want to be able to support that pricing. But in the end, the virtual price doesn't matter - the baseline pays for conventional purchases, and the design case pays for fuel to run the generator, and the comparison isn't specifically about the efficiency but rather the input fuels for both cases. I'd have to refresh my memory how the CHP guidance covers the exported electricity, as that exported electricity will be included in your fuel inputs for the design case.   

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