What EnergyFlow simulates, and what it does not
EnergyFlow builds a model of your house, runs it through a year of weather, and reports what the heating, cooling, solar panels, battery and grid do hour by hour. You use it to compare options under the same assumptions: one heat pump against another, shading or none, a bigger battery or a smaller one. It is built for houses in France, Belgium, the Netherlands, Luxembourg, Germany, Austria and Switzerland.
A model answers the questions it was built for and no others. This page lists what a run covers, then what it is not.
What a run models
| Part of the model | What you describe | What the run does with it |
|---|---|---|
| Building and zones | Length, width and height of each floor, plus spaces that behave differently from the rest, such as an unheated garage or a basement | Each level is a thermal zone. A space with different conditions gets its own zone |
| Envelope | Construction year and house type give a starting point for how well each surface keeps heat in (its U-value) and how airtight the house is. You can review and change both | Heat flows through walls, roof, floor and windows, and leaves with air exchange |
| Windows and orientation | How much window area each outside face has, what the glass is like, and which way the house faces | Sun coming through the windows follows the real sun hour by hour |
| Shading | Adjustable external blinds, or none | Blinds close when the sun on the window passes a solar threshold and the outdoor air is warm enough, which cuts the solar gains through the windows |
| Weather | A typical year built for your coordinates, or one real year from a short list of recent years | Hourly temperature, sun, wind and humidity |
| Schedules | Household size, one of three presence patterns, yearly household electricity, thermostat settings by day and night | Heat from people, lights and appliances, and the temperatures the equipment tries to hold |
| Heating, cooling and hot water | Heat source, distribution, cooling, ventilation and hot-water mode | Hourly heat delivered, and the electricity or fuel the equipment uses to deliver it |
| PV and battery | PV capacity, roof face and tilt, battery capacity | Hourly generation after the effect of panel temperature and a default allowance for system losses, battery charging and discharging, and what is left over for the grid |
| Tariff | Fixed prices, or dynamic prices where we hold them for your country | Hourly grid import and export, and the annual electricity cost |
The equipment you can choose:
- Heat sources: air-source and ground-source heat pumps, four-pipe heat pumps (P4P), boilers and electric resistance.
- Boiler fuels: natural gas, heating oil, wood pellets, log wood or LPG.
- Heat distribution: underfloor heating or radiators.
- Cooling: floor cooling, split air conditioning, both, or none.
- Ventilation: mechanical with heat recovery (MVHR), extract only, or natural.
A four-pipe heat pump (P4P) is two machines in one. One side makes heat while the other cools, and the heat pulled out of the house during cooling goes into the hot circuit instead of being thrown away. That recovered heat is where it saves you money.
Natural ventilation means no fan at all: fresh air arrives through gaps in the building and when you open a window. For it, the model keeps a small steady flow of fresh air, about what you get by airing the house properly for half an hour a day. A leaky older house gets more on top through the gaps, and a house with no cooling also gets extra airing on summer nights.
The wizard checks your choices against the model’s rules. The glossary explains the abbreviations used across the library.
If you leave the schedules alone, the model assumes four residents on a typical weekday pattern, 4,500 kWh of household electricity a year (heating, cooling and hot water are counted separately), heating at 21 °C by day and 19 °C at night, and cooling at 24 °C. You can change each of these in the wizard: the number of residents and the presence pattern, the yearly household electricity, and the heating and cooling temperatures (the cooling ones appear when your house has cooling).
What a run is not
A result is a model estimate for the house, equipment, weather and schedules you entered. It helps you compare scenarios. It is not any of the following.
- An energy performance certificate, the official rating your country issues for a building. EnergyFlow does not issue one, and its output cannot stand in for one.
- A building permit, or a check against building regulations.
- A subsidy decision. Whether you qualify for support is decided by the body that runs the scheme, on its own rules.
- A site survey. We never see your house. The model works from what you enter and from stated defaults.
- A final equipment specification. Sizing, hydraulic and electrical design, product compatibility and commissioning belong to an installer or engineer.
- A safety assessment. Electrical, structural, fire and moisture risks are outside the model.
Results are also not a promise about your future bills or about how installed equipment will perform. Real use depends on the installation, the controls, the weather and how the house is used.
Use it to prepare, then ask a professional
Use EnergyFlow to walk into the conversation with an architect, an energy consultant or an installer with better questions and numbers to show them. It does not replace that conversation. Before you order equipment, build or sign anything, have them review your scenarios. They can check what a model cannot: the site, the products, the regulations and the installation.
We also do not sell equipment, so the comparison is not tilted toward a product.
Limits of the model
- Temperatures are averages. A floor is one thermal zone, so the indoor temperature is an average over that floor. It cannot tell you whether one particular bedroom stays comfortable at night.
- Interiors are not drawn. Partitions and furniture are represented by one thermal mass element per zone, with a medium-weight default. You enter the stairwell opening between floors as an area, which stands for air exchange between levels, not for exact air currents.
- Windows are entered per outside face, not by position. Where a window sits along a wall does not change how much sun gets in: what counts is the direction that wall faces and how much glass is in it.
- Schedules are part preset, part yours. You enter how many people live in the house and pick one of three daily patterns, then set your yearly household electricity and your heating and cooling temperatures. Hot-water use follows the number of people. What you cannot do is hand the model your own hour-by-hour profile.
- Equipment is a representative machine of its type and size, not a named product. Size is the part you will notice: a 17 kW heat pump and a 10 kW one behave differently in the same house, and a run shows you that difference. Two 17 kW machines from different makers differ as well, in how much their efficiency drops as it gets colder outside, which is what the performance curve on a datasheet describes. That difference is real, but it is smaller, and the model does not reproduce it for a particular product.
- Weather is a typical year or one reconstructed year. Neither is a forecast.
Two other articles go further: the simulation engine, and model assumptions and limits.