DHW solar collectors defined - but no effect on SBEM results

[Wasted Energy]

I'm probably doing something wrong here but I have defined a solar collector and tanks on the 'Solar Water htg' tab of my DHW system whilst in SBEM view. But whatever I define it has no effect on the SBEM calculation at all. Am I missing something?

Wasted

[Terence]

It depends on the values you have entered for the SES, the defaults are very poor. I assume you don't have design data?

Although I don't see any problems with experimenting with SES (or any other) inputs and recording the impact these changes have, the SBEM Helpline disagrees, and thinks that you should only ever enter design data, or use defaults if design data is not available.

"Please note that SBEM is not a design tool, and the most appropriate modelling tool for design purposes should be used. Once the valid design configuration has been set up using the appropriate modelling tool, the relevant parameters can then be input into SBEM to assess compliance. For e.g., the user should not be using SBEM to “experiment" with the performance parameters in order to make his building pass compliance. Even if a building passes compliance in SBEM, this does not prove that the design will work in practice."

In the past the helpline have recommended a SES tank storage volume based on an assumption of 5 litres storage per m2 of solar collector area. They also recommended a default of 130 W/K for heat transfer rate (assuming you don’t have the real data).

[Wasted Energy]

Hi Terrence

I am indeed working at a preliminary design stage and exploring possibilities. I had allowed 50 litres per m2 of collector, as this is what is suggested as a rule of thumb by CIBSE in a recent CPD. See http://www.cibsejournal.com/cpd/modules/2015-08/ but I had accepted the default value for the heat exchanger of 5.4 W/K which is very low.

Anyway using your suggested figures does indeed generate a result in the SBEM, and gives something to work with.

Thanks

Wasted

PS I am amused by the SBEM quote.

I am actually specifically employed to ""experiment" with the performance parameters in order to make this building pass compliance".

How else do they think it is done? Do they think design engineers are going to propose LZC technologies to clients without first knowing that they will achieve compliance? Has no one told them of the equipment sitting idle and unused in plant rooms across the land because someone like me specified it as the most cost effective way of passing the SBEM, knowing full well the client will eventually give up on it, and turn it off as soon as the first maintenance bill arrives? This is crazy of course, but if you make a 'rule', then people are going to design to that 'rule'.

[Terence]

Hi Wasted, good to hear (or read) that you're getting some outputs now.

The SBEM Helpline probably assume the approach would be to use a simulation tool like ApacheSim first, in order to validate a design. Such a tool is a more accurate predictor of performance than SBEM. You can experiment with that "design tool", and when you're happy, run the building through Part L Compliance using SBEM... Although I don't see why you would use SBEM method to show compliance after using ApacheSim for your design...