Understanding Heat Loss
Calculating the total heat load of a building is an essential process in designing and sizing a heating system effectively.
For low carbon heating systems such as heat pumps, these must be as close to meeting the specific needs of an application as possible, with a very slim margin of error. To achieve this, heat loss calculations must be applied on a room by room basis, taking into account a number of factors in order to get a more accurate picture, including:
- Building fabric
- Room dimensions
- Air change rates
- Desired internal temperatures
- Lowest external temperature during winter
Systems specified in this way will be more energy efficient, cost less to run and ensure end-users are comfortable in every room.
How do you calculate heat loss?
Heat loss is calculated based on the amount of heat energy transferring from the inside of the building to outside. It includes both heat lost through the fabric of the building (through external walls, floors, ceilings, windows and doors) and heat escaping through air leakage or intended ventilation.
Fabric heat loss
Fabric heat loss is calculated individually for each building element (wall, floor, ceiling, window or door) based on its U-value, area (in square metres) and the temperature difference between one side of the building element and its adjacent space. These factors are multiplied together to produce a fabric heat loss.
Ventilation heat loss
Ventilation heat loss is calculated individually for each room based on the internal air volume, expected air change rate and the temperature difference between the room and its adjacent space. These factors are multiplied together to produce a ventilation heat loss.
U-Values explained
A U-value is a measure of thermal transmittance and is used to quantify the rate at which heat transmits through a building element. The lower the U-value, the slower heat will transfer from one side of structure to the other. Therefore, smaller U-values will have less heat loss and are better from an energy performance perspective.