The dynamics

The dynamics of the house can be a part of the model. The perceived temperature of the house is not fully consistent with the actual outdoor temperature. At colder temperature dips of for example -15°C, the house will not experience the real outdoor temperature, but experiences a temperature of -12°C instead (due to internal heat gains). Even the irradiance of the sun differs between the seasons (and different spots). The energy demand of the house is affected from those variances over the year, why it might be an idea to calculate the SPF over monthly periods. Also the use of a fictive outdoor temperature would be an alternative. The climate data can be adjusted (flattened out) depending on a number of inputs, but a temperature dip is still needed in order to make a proper effect dimensioning (this is dimensioning the entire system such as deep wells etc.). In a serious effort to evaluate dynamics, other factors have to e incorporated in a model, such as form factor, impact of building weight, window area compared to wall area, placement of windows, etc., which make such a model very complex.
 
 For ground source heat pumps, the temperature of the ground is varying during the year. The model should include a correction for this. This could be expressed as a function where the ground source temperature is a function of the outdoor temperature over the year.
 The model should contain a radiator heat curve where requisite supply temperature is calculated, an example of this can be found in the thesis of Fredri