This form extends a little on the simple calculations done on heat savings without looking at daily temperatures and also on the Temperature based form for calculating heat savings yourself. It is meant to be used to provide information enough to make buying decisions, but can also be used to try out and understand alternative choices and the effects of changing size on radiators or other factors affecting the heating water temepratures. The form, just like the temperature based, basically only needs three values in order to do meaningful calculations (where you live, how much heat the house needs, and what heat pump to model). Basically, in order to use the form, be shure to have pressed each read conversion and calculate button at least once, or that you have manually provided the data needed.
There is a lot of possible further extensions of detailing the calculations, a number of them defined below, but also with a lot of additions specifically to handle calculations based on the effects of having varying temperatures in the forward water, and predefined temperatures in the warm household water heating, defined further down. The calculations independent of varying forward temperatures are:
- Use outside daily temperatures to decide if additional heating will be needed
- Use outside daily temperatures to decide utilised COP for an Air-To-Water pump
- Use the house's energy need curve based on outside temperatures to decide needed heating energy
- Use the Air-To-Water input power and COP to determine if additional heating is needed, and then include that in the cost
- Use the Geothermal maximum Power to determine if additional heating is needed, and then include that in the cost
It delivers cost saving payback times utilising comparisons between the alternatives. The shown alternatives are
- Using an eletric heater only
- Using an Air-To-Water heat pump
- Using a geothermal heat pump, compared to an Air-To-Water pump
- Using the heat pumps with or without the production of hot water
The way the calculations are done are described here. An important assumption in the first part of the form is that all calculations assume that the radiators are large enough to deliver the needed heating without needing water temperatures above the heat pumps forward water temperature limits, and all calculations are done at the temperature for which the hea pump factors, like COP and powers, are defined. This can all be seen as calculations based on fixed condensation (in fact very strict fixed condensation, there are no varying of the forward water temeprature at all during the seasons of the year).
For the second part of the form, results are shown after including effects from varying the heat forward temperature need, decided hot household water temperature and adjusting for passingmax heat pump temperatures.
Extensions in calculations effects from varying temperatures in the forward water, and predefined temperatures in the warm household water
The results of these calculations are shown in the later part of the form. The calculations are based on the same information as is used for the rest of the form, plus:
- The forward water temperature is assumed to be varying with the outside temperature, thus taing into account that the radiators need to be warmer the colder it is outside, and that the heat pumps deliver lower COP and less power the warmer the forward water need to be.
- The hot household water temperature is assumed to be predefined, and at another level than the forward water. Thus effectively leading to a worse COP than for the forward water while heated
- The maximum temperature possible to produce with the heat pump is taken into account. Thus adding increased electrical heating need when the forward water exceeds what the heat pump can produce
There is a number of limitations in the calculations:
- The assumption is that the change of COP due to the change of water temperature is proportional to the distance from the known COP/Input/Output curve for the heat pump (which may be non linear). This assumption is good, but not exact
- If the hot household water temperature wanted exceeds the heat pump maximum temperature, assumption is that the hot water consumption empties and refills the hot water tub, or preheats the water to the heat pump maximum and then adds to that temperature in a second storage. No estimates are made of energy losses from the tank to the surrounding environment, or for germ fighting increases ot the hot water temeprature. Thus the calculations are using the heat pump for a part of the heating and eletric addition for the rest. In real world, this might not be the case, and the cost for heating the hot water when passing the maximum temperature for the heat pump will be higher than shown in the calculations. Maybe a future addition will add assumptions on the hot water tank size.
- If the forward water temperature needed exceeds the heat pump maximum temperature, the assumption is made that the water heating needed takes place in the heat pump up to its maximum temperature and that additional electric heating is used afterwards to achieve the desired temperature. It assumes the control system to work well and never stopping the heat pump (except when minimum outside temperature is passed) if the heat pump is not enough for the heating. It also assumes the electrically added heating to be well regulated (a fairly stable output temperature instead of the on/off behavoiur used in some heat pumps). The last means that the input temperature to the heat pump after its maximum temperature is exceeded will be the needed forward temperature minus the temparature drop over the radiators (assumed to be 10 degrees Celcius). A control system not behaving like described above will lead to higher costs than calculated when passing the heat pump maximum temperature. Also, not only the maximum output temperature but also the maximum input temperature of the heat pump could be considered in the calculations in the future.
The below input data is to define the outside temperatures to be used, some calculations are then provided to help understand how they affect the results.
- After selecting from which area to take the outside temperatures, outside temperatures and coming calculations will be based on that selection as soon as any of the below buttons are pressed
- The columns shown in the temperature table is described here