Calculating heat loss is an essential step when sizing a heat pump because it helps ensure that the system will be able to meet the heating demands of the building while operating efficiently. Heat loss occurs when heat escapes from a building through various structures such as walls, windows, roofs, and floors. 

    By determining the amount of heat lost, you can accurately size the heat pump to match the heat load of the building, which means the system will not be oversized or undersized. An oversized heat pump will operate inefficiently, leading to higher energy bills and increased wear and tear on the system, while an undersized heat pump will struggle to maintain the desired temperature, causing discomfort and potentially damaging the unit. 

    The total room heat loss value is calculated by adding heat loss from the natural ventilation and the heat loss from the fabric.


 

Total Room HL = Ventilation HL + Fabric HL


    For the ventilation heat losses, we have to calculate the product of the number of air changes per hour (which is a default value of each room and it can be edited in room details section – Step2.4), the air changes factor (0.33, constant) and the total room volume.

    The room volume is automatically calculated based on the floor plan uploaded/designed in the Step2.2 plus the inserted room height in Step2.4

Ventilation HL = Air changes per hour x Air changes factor x Room volume

   

    To calculate the fabric losses, we need to know the element area, its U value and the difference of temperature between the room the element belongs to and the outside

Fabric HL (for each room element) = Area x U value x ΔTemperature


    To get these calculations, we need to detail every room elements such as:

  • Exterior Walls
  • Interior Walls
  • Party Walls
  • Exterior Doors
  • Windows
  • Chimneys
  • Roof Glazing

 

    In Step2.1 and Step2.2 the layout of the property is defined. You can to identify all walls types in Step2.3, specifying the material and its U value (a default value is present according to the selected fabric material).


    The type of wall (interior or exterior) is automatically detected by the platform. You can convert any exterior wall to party wall, in which case a Uvalue of 0,50 and an outside temperature of 10ºC are considered.


    The remaining elements are added and detailed in step 2.4. When each element is added to a room, we need to specify, its material, dimension and the corresponding U value (default value according to the material).

The exception of this element characterization is the existence of chimneys, in which the only thing we need to determine is if the throat restrictor is fitted to flue.