Energy balance, PHPP calculations and verification: heating demand, primary energy, summertime and economics
The monthly balance in PHPP
PHPP solves a monthly balance: transmission and ventilation losses minus useful solar and internal gains, with a utilization factor accounting for the fact that gains cannot always offset losses, especially in summer and shoulder seasons. Heating demand is the annual sum divided by TFA. Verification checks demand, load, PER and overheating together; a building can pass on demand and fail on summer comfort.
Summer and economics
Summer is judged by frequency of overheating: no more than 10 % of hours above 25 °C, evaluated with the PHPP climate data, realistic internal gains and actual shading. Economics is normally a lifecycle comparison: extra envelope cost versus saved energy and, where relevant, avoided HVAC equipment.
Worked example: heating demand
Annual losses are 3,000 kWh. Useful gains are 1,800 kWh with a utilization factor of 0.95, so credited gains are 1,710 kWh. Net demand = 3,000 − 1,710 = 1,290 kWh/a. Over 150 m² TFA, that is 8.6 kWh/(m²a), comfortably below 15. If the utilization factor were 0.7, credited gains fall to 1,260 kWh and demand rises to 1,740 kWh/a = 11.6 kWh/(m²a) - still passing, but the sensitivity shows why gain assumptions must match the certifier's boundary conditions.
Traps
Double-counting gains or using unrealistic internal gains. Entering shading factors that do not match the built condition. Mixing PER and PE. And treating PHPP as a design tool rather than a verification tool: the inputs must describe the building as built, not the design intent.