Kim,

Do you have a seperate DHW loop set up? If so, this is your problem. Heat recovery from either jacket or exhaust can only go to a single loop each. If you are proposing to implement cogen then you want to put DHW loads on the heating loop as a process load with and appropriate schedule. This way you can assign the heat recovery to a single loop for simple modeling.

Good Luck,

Edward M. Allen, P.E. CEM

----- Reply message -----
From: "Kimberly Wiebe" To: "equest-users at lists.onebuilding.org" Subject: [Equest-users] Cogen heat recovery for dhw
Date: Tue, Jul 3, 2012 4:13 pm

Hello,

I am working on a project in which the heat recovered from the CHP equipment (1,416 kBtu/h) is able to meet the entire service water loop load (1,384.7 kBtu/h). Both the DHW and CHP run 24 hours a day. The building is both residential and commercial.

Net hourly loop load, including thermal losses and pump heat = Recovered heat or free cooling heat applied to this loop ... this is true for all hours in the hourly report.

However, there is still a consistent small natural gas load for the domestic hot water. It is flat for all hours of the day. What is this energy use going to? Standby losses?

I am thinking that it is a minimum energy use of the equipment if the equipment is operating. What is the minimum part load ratio for a gas fired storage service water heater? Where can I find the inputs/ outputs to confirm this?

Thanks!

Kim

Kim Wiebe