PHPP energy modelling.
The energy model PHI certification is based on. We run it from feasibility to construction level, closing the gap between design intent and as-built performance.
What PHPP energy modelling delivers.
What it isPHPP is the Passivhaus Planning Package: a detailed monthly energy balance spreadsheet developed by the Passivhaus Institut. It models every heat loss and heat gain in the building: envelope transmission losses through walls, roof, floor and windows; ventilation losses through the heat-recovery unit; solar gains through glazing; internal gains from occupants and equipment; and the residual space-heating demand that remains after those gains are credited.
The output is the specific space-heating demand in kWh per square metre of treated floor area per year. For PHI Passivhaus Classic certification, this must be no more than 15 kWh/m²a. The model also produces the primary energy renewable demand, the summer overheating hours, and the peak heating load used to size the heating system.
The model is only as accurate as the inputs. At feasibility we use typical values to test the concept. By construction level, every input is replaced with a measured or certified value: window frame U-values from manufacturer test reports, insulation conductivity from product data sheets, MVHR heat-recovery efficiency from certified test results. This is how we close the performance gap.
Specific space-heating demand: max 15 kWh/m²a. Primary energy renewable: max 60 kWh/m²a. Airtightness: max 0.6 ACH at 50 Pa. These are tested in PHPP. Every component that affects the balance must be modelled with a measured or certified value for the certification submission. Estimated or default values are not acceptable.
Every construction element in the building envelope must have a U-value calculated to BS EN ISO 6946 entered into PHPP. Windows, doors and roof lights are entered with frame U-values to EN ISO 10077, glazing U-values and g-values to EN 410. Use our free U-value tool to check your constructions before the model is built.
How we build and maintain the model.
MethodAt feasibility we build a PHPP model with the proposed massing, orientation, treated floor area and indicative component values. The output shows whether the concept can meet the Passivhaus target and what envelope specification it will require. This is the point where the geometry can still be changed: the building depth, the orientation, the window-to-wall ratio. The feasibility model sets the design parameters for everything that follows.
At Stage 3, the PHPP model is updated with the developed geometry and thermal bridge values from the junction analysis. The model reflects the actual building layout, construction thicknesses and structural system. Window areas and orientations are entered from the architectural drawings. The Stage 3 model is the basis for the energy statement submitted with the planning application.
At Stage 4, the PHPP model is updated with specified values from product data: window frame and glazing U-values, MVHR heat-recovery efficiency and specific fan power, insulation thermal conductivity, and solar control factors for any shading. Thermal bridge values from the junction catalogue are entered in place of any assumed values. The construction-level model is submitted to the certifier for review and must meet the Passivhaus threshold before the project goes to site.
After the airtightness test, the PHPP model is updated with the measured n50 value. Any deviations between specified and installed components are entered. The as-built model is the final document submitted to PHI for certification, together with the test reports, component specifications and as-built drawings. The certifier reviews and approves the model before submitting to PHI.
Check your constructions before the model is built.
Use our U-value calculator to verify wall, roof and floor constructions to BS EN ISO 6946 before they are entered into PHPP. Accurate U-values are the foundation of an accurate PHPP model.
Common questions.
FAQWhat is PHPP?
PHPP is the Passivhaus Planning Package, the energy balance spreadsheet developed by the Passivhaus Institut (PHI) in Darmstadt. It models the annual heat balance of a building: heat losses through the envelope, heat gains from solar radiation and internal sources, ventilation heat recovery efficiency, and the space-heating demand needed to make up the difference. PHI Passivhaus certification requires a PHPP model submitted by a PHI-accredited designer or certifier, using measured or certified component values.
What is the difference between PHPP and SAP or DEAP?
SAP and DEAP are the UK and Irish regulatory compliance tools for dwellings, used to demonstrate compliance with building regulations. PHPP is a design and certification tool for Passivhaus buildings. PHPP uses the actual measured geometry and certified component performance of the building being designed. SAP and DEAP use simplified procedures and standardised inputs. PHPP and SAP or DEAP are used in parallel: PHPP for Passivhaus certification, SAP or DEAP for regulatory compliance. They produce different results because they use different methodologies.
When do you need a PHPP model?
You need a PHPP model if you are seeking PHI Passivhaus or EnerPHit certification. You also benefit from PHPP if you want to understand the real energy performance of a building before it is built: the space-heating demand, overheating risk, or the effect of different specifications. PHPP is most valuable when run from feasibility and updated at each design stage, because the early stages are where the decisions that govern performance are made.
What is treated floor area in PHPP?
Treated floor area (TFA) is the conditioned floor area inside the thermal envelope, calculated using PHI rules. It differs from gross internal area as measured for planning or rental purposes: stairwells above ground floor, storage areas below 1 metre head height and car parks are generally excluded or reduced. Getting TFA right is important because specific space-heating demand is expressed per square metre of TFA. We calculate TFA from architectural drawings using PHI rules for every project.
Commission a PHPP model.
Tell us the building type, target standard and stage you are at. We will confirm what the model will need and what the certification route requires.