IES-VE User Forum

Hi!!

I am working on a care home where there is a central plant with CHP. The development consists of individual dwellings (assessed in SAP) and the communal area which are assessed in DSM (atrium so no choice). All part of one building.

The CHP has been sized, and it will provided 55% of heat requirements to the whole building. In SAP I enter this as 55% directly so no problem.

In DSM however, IES assesses when the CHP is running. The results are wrong as the DSM model does not incorporate the the dwellings, therefore the heat loads are not correct, therefore the running times of the CHP are not correct.

I don't want to put the system in as district heating as I don't get the BER benefit over the TER.

I am thinking that I should now adjust the CHP heat output so that the model accurately shows that 55% of the heat is form CHP. But how do I know what figure to enter? Can anyone point me in the right direction?

Many thanks in advance.

Hi,

I have had the same problem before. Sharing CHP between domestic and commercial is really messy.

Unfortunately in IES you can't model buffer vessels or include loads from other buildings. I don't think there is a way to get the CHP to follow the correct running times.

The approach used in the past is to use excel to properly model the CHP performance and get the calcs approved by building control.

Then set the IES CHP inputs to give the correct results for electricity generated etc. on an annual basis.

There are actually NCM templates for dwellings so you could make a case for doing the whole thing under one commercial assessment. You would possibly also need special permission from an accreditation board to do this for the EPCs.


I hope this helps.

Ross

Ross is correct, sharing CHP between commercial DSM and domestic SAP is horribly messy and frankly needs a lot of work under the NCM.

I think in the past I have set up a separate DSM model including the domestic areas and then used that to calibrate the CHP settings in the real model to get to the correct electric generation which is a hybrid of Ross' suggestions.

It's such a nasty situation that I would actually consider modelling it as a district heating system as long as I could still achieve all the required targets. But as you say, doing so comes with a rather unfair penalty to the result.

I've previously done it using a Bivalent systems, made up of two gas boilers (to ensure the Notional Building continues to use solely gas boilers). Once you're back in the main Apache System front page you can then edit to system's CO2 emission factor to represent the overall effect of the boiler, CHP's gas consumption and CHP's electricity generation.

You do of course need to do some sort of spreadsheet calculation to work out what the correct CO2 emission factor (and system efficiency) should be, but you may already have the bones of this if you've already worked out that the CHP is expected to contribute 55%.

I agree that it's a bit of a mess though!