A building’s heat requirement need is calculated based on its estimated heat exchange with the surroundings and the building’s users.
The following parameters affect the heat requirement:
- Transmission losses
- Ventilation and infiltration losses
- Climate parameters: outside temperature, influx of sunlight, and wind factors
- Internal heat sources (additions): people, electrical appliances, lighting
- The building’s ability to accumulate heat
- Room temperature
The heat balance can be viewed as stationary, when heat accumulation and variations over time are disregarded. In the stationary case, the net heat requirement is calculated from the following formula:
Φnet = Φloss + Φventilation – Φadditions.
Performing dynamical calculations, where heat accumulation and variations over time are included, is a very complex task. Therefore it is most often carried out using computer software.