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iPHA Fact Sheet  01 / 2019 

Comparison of heating energy demand according to the PHPP and consumption  

After the completion of a Passive House building, it makes sense to compare the actual consumption values with the calculation values that were previously determined using the Passive House Planning Package PHPP (PHPP). Such a comparison makes it possible to extrapolate the planned energy savings during initial operation and regular operation. A prerequisite for this is a realistic PHPP calculation performed during the construction process of the building as a whole (additional or modified thermal bridges, changes in insulation materials, airtightness, etc.) must be entered. In addition: 

• Differentiation between hot water generation and space heating is necessary.

• The consumption data must be adjusted for conversion, distribution and storage losses in order to obtain the actual useful heat (see Protocol Volume  No. 45, Research Group for Cost-effective Passive Houses "Accurate measurements in energy-efficient buildings" (currently only available in German)).
The actual weather conditions are required for the "Exterior temperature" and "Horizontal radiation" in the PHPP. This data has to be available in the form of monthly values for the investigated time period (identical to the measured energy values) of the building location or a nearby weather station (input in the PHPP worksheet "Climate"). 

The measured indoor temperature during the heating period (usually 1 October until 30 April) of the measured time period is entered in the PHPP (worksheet "Verification"; "Interior temperature winter"). This has to be the representative average temperature of the building. A single measuring point in a non-representative room does not provide any meaningful data. In an energy-efficient building the change in the heating energy demand is about 12 to 15 % per kelvin of increased indoor temperature (21 instead of 20°C / 71.6°F instead of 68°F ).

The actual electricity consumption influences the internal heat gains. These gains are assessed with 2.1 W/m² (planned) in the PHPP calculation for the standard case of a residential building. If the measured values for the actual electricity consumption are available, then these may also be taken into account. For this, the input in the "Electricity" 
worksheet has to be adjusted in such a way that the actual measured electricity consumption is obtained. Calculation of the actual internal heat gains (IHG) is only meaningful if a reliable estimation of all contributions is possible.  The actual occupancy rate, if known, can also be entered into the PHPP, "Verification" worksheet.
After these adjustments to the climate data set, indoor temperature and, if necessary, the internal heat gains (electricity consumption), the PHPP displays the heating energy demand of the building with the modified boundary conditions in the "Verification" worksheet.  This can then be compared with the measured value (heating energy consumption). 

It should also be noted that the maximum overall accuracy of the balance calculation is about ±3 kWh/(m²a). The overall accuracy of the measured data depends on the measuring devices used and cannot be stated as a general value. The size of the remaining deviations then indicates whether further investigations of the causes are necessary. 
To simplify the method, the Passive House Institute has developed a "Data preprocessing tool" which can be downloaded free from the following link:

Author: Søren Peper
© iPHA / Passive House Institute
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