Calculating the house energy need correctly is not easy (there are so many factors affecting the need as well as the calculations). But as long as we know we are working on an estimate, and willing to accept the uncertainties that comes from the simplifications, there is a number of ways:
- The best way is to daily measure the energy need, and the temperature that were present at that need. When you have the result from those figures (either yearly hear energy needed, or the house energy needed per degree Celcius), savings from different usages of heat pumps kan be readily estimated.
- Second best way is to measure the same data during a number of very cold days. The colder the better. The rest of this page guides on the route for using such data to calculate your house need
- There are more ways. One is for example to know the energy consumption during a relative cold period of the year (say a month or so), and based on that data and the below available conversions methods, use that as a base for a rough estimate of the yearly need. In order to do the last thing, you can find the rough percentage of the house heating normally needed during certain months of the year.
Doing the data collection during many days, like a year, gives a very good knowledge of the heating need. But it can be done in shorter time. The shorter the time, the more likely errors are to creep into the calculations. One way to reduce errors is to do the measures at cold days (days needing high amounts of energy are reducing the errors by making the side factors less important).
So basically, one needs to do three things:
- Sum all energies used and wanted in the calculation, translating them all into one common factor.
- Measure the temperatures that were present during these measures
- Calculate the house energy need expressed as a function of the outside temperature (normally simplified as a simple dependency expressed as Watts per degree)
The simplest way to sum all energies is to convert them into a common factor before summing them. An easy way is thus to just tabulate them, summing the the total for all factors. To do this, below is a table allowing a simple addition of the most common sources, and using electricity kWh as the common factor. The cells marked with a green background in the below table is fields that can be filled in, but for which the current default value most likely is good enough, why a change is not necessary to get acceptable results.