CHP size affecting BER

[mlmJonathan]

HI

i am currently a little stuck with a model. I have built it and all is well, i am currently running the SBEM and working out where the energy is going and what can be improved.

i have intruduced CHP however i have found that even if its a 1kW CHP plant or its a 50kW CHP plant the BER does not change. Why is this ?

[Complex Potential]

Given that you are talking about inputting a kW rating for the CHP I will assume you are working in ApacheSim compliance rather than SBEM.

That being the case, I would say your problem could be one of a few thing:

1) you haven't linked your apache systems to the CHP by checking the relevant boxes.
2) your profile for heat matching strategy is set to off
3) your fraction of rated heat output on the CHP dialogue box is set to 1.0
4) your building has a negligible heat demand

Cant think of much else. Report back please.

CP

[mlmJonathan]

Given that you are talking about inputting a kW rating for the CHP correct I will assume you are working in ApacheSim compliance rather than SBEM using both apache (for systems)and SBEM (For BRUKL document).

That being the case, I would say your problem could be one of a few thing:

1) you haven't linked your apache systems to the CHP by checking the relevant boxes. All Boxes ticked Also worth noting, CHP is used to provide 100% DHW and not the heating
2) your profile for heat matching strategy is set to off The profile for the CHP is set to on continuously if thats what you meant
3) your fraction of rated heat output on the CHP dialogue box is set to 1.0 Heat to power is set at 1.8 (Probably should be around 1.6 on reflection)
4) your building has a negligible heat demand doubtful its a 14 storey student accomodation, only running one floor at the moment though

Cant think of much else. Report back please.

CP

[Complex Potential]

Are you defining your CHP in the Apache module or the VE Compliance module?

If using SBEM, I think that only the CHP dialogue box as brought up through VE Compliance will actually have any impact on the result. If you compare the two you will notice that the inputs are quite different when running via Apache or SBEM (for a start, the SBEM CHP dialogue box does not ask for a kW input).

This is one of those situations where I could probably spot your problem straight away if I had your model in front of me.

[mlmJonathan]

Are you defining your CHP in the Apache module or the VE Compliance module?

If using SBEM, I think that only the CHP dialogue box as brought up through VE Compliance will actually have any impact on the result. If you compare the two you will notice that the inputs are quite different when running via Apache or SBEM (for a start, the SBEM CHP dialogue box does not ask for a kW input).

This is one of those situations where I could probably spot your problem straight away if I had your model in front of me.

Yeah i see your point now, i am mixing the two which shouldnt be done. I see looking at the results in apache what the CHP is using and generating.

The problem i now have is with the SBEM then. I cant get my head round why the output in KW wouldnt have an affect in the BER. At the moment what size CHP plant is the SBEM basing its results on because a 1kW CHP cannot have the same BER as a 100kW CHP for example. ?

[mlmJonathan]

I have also just realised that i dont think you can model a CHP plant to do JUST the DHW. In apache it shows energy consumption as if its supplying to the heating system. So i changed the system for it to provide only to the DHW and i get 0kW energy consumption by the CHP.

What am i doing wrong, How does a DHW only CHP need to be set up in the systems ?

thanks in advance

[Complex Potential]

If you want to properly model the CHP then you need to switch away from SBEM to the ApacheSim methodology which is full dynamic analysis.

The problem with SBEM is that it doesn't actually use the dynamic engine, instead it works like a giant spreadsheet. As such, under SBEM, you don't get to input the kW rating of the CHP because it cant use that data, so it asks for you to estimate the proportion of the heating that it serves manually.

Unfortunately I don't use SBEM so I cant help you more on that side (someone else may be able to).

[mlmJonathan]

If you want to properly model the CHP then you need to switch away from SBEM to the ApacheSim methodology which is full dynamic analysis.

The problem with SBEM is that it doesn't actually use the dynamic engine, instead it works like a giant spreadsheet. As such, under SBEM, you don't get to input the kW rating of the CHP because it cant use that data, so it asks for you to estimate the proportion of the heating that it serves manually.

Unfortunately I don't use SBEM so I cant help you more on that side (someone else may be able to).

it makes sense what you are saying thank you. and i appreciate your help

[Complex Potential]

What I would say is that if you are using SBEM, all system inputs will also need to be via VE Compliance, so hunt around and see if you can find a mention of chp within those dialogue boxes.