Apache Systems Seasonal Efficiency

[R Tibenham]

When assigning the seasonal efficiency of a HVAC system, the figures for seasonal efficiency shown within the 'UK NCM system data wizard' differ from those shown on the Apache Systems 'Heating' tab.

eg, A seasonal efficiency of 4.25 with the 'UK NCM system data wizard' results in a seasonal efficiency of 3.1652 in the Apache Systems 'Heating' tab. The latter figurte is printed on the BRUKL document.

Why are two very different figures for the same parameter shown and which figure which should be used for the specification of equipment?

Given that air source heat pump manufacturers often provide the SCoP and not seasonal efficiency, this just adds another level of confusion to the process.

[Complex Potential]

Are you selecting "Yes, save and apply NCM paramters" when you close the wizard? If you are not, then that is probably why you are seeing a difference.

My understanding is that the seasonal efficiency you input in the wizard is the seasonal efficiency of the heat pump itself which is what is quoted by the manufacturer. Of course technically, the seasonal effiency of a heat pump is completely bespoke to the building it is connected to and so any such attempts by manufacturers to quote a general figure are mostly nonsense, but that's another discussion....

The other SCoP figure shown on the heating tab within Apache systems is derived by taking the heat pump seasonal efficiency and applying another factor (the greyed out delivery efficiency) to represent the losses from the system as a whole. This factor is dependent upon the UK NCM system type that you have selected (for example, a fan coil unit system will be more efficient at delivering the heat than a Central VAV). This is why the wizard asks you to apply NCM parameters and is in line with the methodology described in the NCM modelling guide 2010.

When I follow the above method, the Seasonal Efficiency shown on the heating tab is the same as in the wizard and is also quoted correctly on the BRUKL. This is using the ApacheSim - Compliance (DSM) simulation methodology.

Good luck

CP

[R Tibenham]

Thanks for that; I think like you say, altering the figure in the Apache HVAC field does not inform the NCM wizard, but visa versa does.

In the actual case in point I'd actually got a reduntant bi-valent contribution, which was copied over without my knowing when creating a new HVAC ystem type. Once this was removed the SCoP in both NCM and Apache System fields was the same.

Cheers for the help.

[Complex Potential]

Ah yes, a redundant bivalent setting would account for it. Glad you tracked it down.