Whilst end energy use is ultimately the most important (kWh/year) there are lots of variables that influence this which can be difficult to measure e.g. occupancy factors and weather. Instead a HTC is a very pure indicator of the fabric performance and its effectiveness in retaining heat. By extracting a HTC value from PHPP you can then compare this design performance value against a measured HTC using a measurement solution such as SmartHTC.
Deriving HTC from PHPP
PHPP does not total the losses in W/K but calculates the losses directly into kWh/year using a value G that accounts for the temperature difference (internal minus external). It is however very easy to extract the areas and U-values, thermal bridging and ventilation losses from the ‘Annual Heating’ or ‘Heating’ tabs in PHPP to derive the HTC based on the PHPP input data using the linked template.
Documentation and Tools
External Link
Calculation of HTC from PHPP TEMPLATE
Simple excel spreadsheet to extract a HTC from PHPP
External Link
HTC from PHPP worked example
Worked example of how to extract a HTC from PHPP
General Questions
A HTC is expressed in W/K and is the sum of all fabric losses arising from the U-values of the building components, thermal bridging, infiltration and ventilation. A HTC extracted from PHPP, SAP (field 39) and as measured using SmartHTC are all directly comparable.