When setting up our DHW system in our models we have been setting the DHW delivery efficiency to 100% and then using both the storage and secondary circulation options to the take heat/pipework losses into account for flow & return or trace heating systems. Section 7.2.1 of the IES Compliance user guide states that this is the correct way for secondary circulation systems.
But if we untick the storage and circulation losses and set the DHW delivery efficiency to an ‘estimate’ for the overall system we are getting significantly improved results for our Section 6 compliance checks. Even taking a DHW delivery efficiency of 50% without storage/circulation losses selected was giving us improvements of more than 20% on our BER.
This is making a difference to our EPC ratings and can affect whether a building passes or fails Section 6 (2007) compliance.
Should we continue to use the storage/secondary circulation losses option as stated in the user guide, or in future use an overall ‘estimate’ for the DHW delivery efficiency to reduce our system loads and significantly improve our BER.
Thanks.
DHW System
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Complex Potential
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Re: DHW System
This is a bit of a necro post and I doubt the op will actually read it but it caught my eye as I was flicking through for the first time and others may find this handy.
I've looked into this and it appears that the NCM modelling guide 2010 does not specifiy that the software must calculate the DHW delivery efficiency from input variables. In fact, Tas does not have this option at all and it is just as accredited as IES for performing Part L calcs.
Therefore, if you have your own estimation on DHW delivery efficiency as a % then it is acceptable to use it, so long as you can back it up.
Care must be taken that you define your DHW delivery efficiency in the same way as is seen within the software. It should be the annual base DHW demand divided by the total annual demand seen by the boiler (ie, including secondary circulation loop losses and tank losses). You should probably still include the pump energy seperately to this % since it is likely it will need to be attributed to a different fuel factor, electric.
CP
I've looked into this and it appears that the NCM modelling guide 2010 does not specifiy that the software must calculate the DHW delivery efficiency from input variables. In fact, Tas does not have this option at all and it is just as accredited as IES for performing Part L calcs.
Therefore, if you have your own estimation on DHW delivery efficiency as a % then it is acceptable to use it, so long as you can back it up.
Care must be taken that you define your DHW delivery efficiency in the same way as is seen within the software. It should be the annual base DHW demand divided by the total annual demand seen by the boiler (ie, including secondary circulation loop losses and tank losses). You should probably still include the pump energy seperately to this % since it is likely it will need to be attributed to a different fuel factor, electric.
CP