Modelling CHP for Domestic Water Only

[mlmJonathan]

Hi

i have recently posted in the Part L2 part but that brought up another question which is relevant to this part of the forum.

So i have a building that is going to use a CHP system for the Domestic Hot Water only. Does anyone know or have a model in which this has been done successfully and has shown results in which reflect it working correctly.

I just ran my model and the graphs reflected results common with a heating type system, loads in the winter nothing in the summer, so i went back to my systems changed it around. Ran it again to simulate DHW only only to get 0kW CHP energy consumption throughout the year ??

[VirtualEngineer]

Hi

I would also be quite interested in an answer to this question, if anyone can shed any light on it?

Essentially I'm looking at introducing a CHP to produce a percentage of the DHW load in a hotel project we're working on. However it appears, when I run the SBEM to confirm a pass, the only improvement I can see on brukl is made by changing the fraction of space heating supplied.

I've got the below from the NCM, not quite sure how it fits into IESVE though?

Low and zero carbon systems
179. The following approach must be followed when calculating the impact of on-site electrical
generation for both Building Regulation calculations and EPCs as applied to non-dwellings.
a. Calculate the annual electrical energy used by the building irrespective of source of supply.
Multiply that energy use by the grid-supplied CO2 emission factor.
b. Calculate the electricity generated by the on-site system and multiply that by the grid-displaced CO2 emission factor, irrespective of the proportion of the electricity that is used on site and how much is exported.
c. The electricity-related CO2 emissions used to establish the BER is the net figure i.e., ‘a minus b’ above.
d. Any fuel used in generating the electricity (e.g., in a CHP engine) is added (at its appropriate CO2 emission factor) along with any other fuels used in the building (at their respective CO 2 emission factors) to arrive at the total building CO2 emissions (i.e., the BER).

Thanks for your help

[mlmJonathan]

I still havent worked this one out.

everthing i change or simulate comes out the same. For some reason the boiler takes priority serving the DHW and the CHP provides the heating.

No matter what i try there is no way to tell IES the CHP is providing the DHW demand also or even just the DHW demand.

[Complex Potential]

Are you sure the DHW is being served by the CHP system? Try setting up a separate system just for CHP (and make sure it is set to use CHP as well obviously) and then select this system under the systems tab in the templates where it asks for the DHW system.

The other possibility is that the CHP settings are somehow stopping the DHW load from being dealt with, either on max capacity or turndown ratio.

[mlmJonathan]

Are you sure the DHW is being served by the CHP system? Try setting up a separate system just for CHP (and make sure it is set to use CHP as well obviously) and then select this system under the systems tab in the templates where it asks for the DHW system.

The other possibility is that the CHP settings are somehow stopping the DHW load from being dealt with, either on max capacity or turndown ratio.

Yes i actually had it set up exactly as you said with a separate system for the DHW. However, even if you set up a separate system you have to select the CHP usage through the Heating tab don't you. I found this to conflict with the main system.

There isnt actually a way (or i dont know of one) to set up a system that does not serve a heating system and DOES serve DHW only via CHP.

This is where i got confused between the Apache and the SBEM tools, If only there was a way like in the SBEM part where you could specify how much of the energy goes to heating compared to serving DHW but you cant in apache.

[Complex Potential]

Yes, I see what you mean. It appears as though you can only get the CHP to link to DHW when running a full dynamic calc under VE Compliance. When working with a "normal" Apache model it seems not to work for DHW and CHP. This is rather odd.

When working in VE Compliance there is an drop down box in the DHW tab that says something like, heat source same as space heating, but it's absent outside of the VE Compliance module. Strange.

One for the IES tech support team I think because this feels like an oversight or bug.

[Terence]

Hi Guys,

I just tested this in VE 2015 and it was working the same in Apache and VE Compliance. Here are my inputs

DHW System



CHP



Room conditions in Apache (set up to be the same as the activity in VE Compliance)



System tab in room data



And here are the results for CHP

[Complex Potential]

Thanks Terence but I'm still on IES 2014. Any chance of adding a screenshot of the DHW tab under the system setup?

I can only assume this is a 2014 issue because I'm using the same settings as you and getting nothing.

[Terence]

The DHW tab was just defaults, the generator type was set to be "Same as space heating". I will try it in VE 2014 and post back.

[Complex Potential]

Now that's interesting because there appears to be no generator type option in the 2014 version. Methinks this could be it?