Svenska Calculator
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Svenska rohi@kronwatt.com

Åtgärdskalkylen Prototype

Answer five questions about the house. The calculator shows which measures pay off, what they save and when they have paid for themselves.

The house

Shown in the as .

m²
Why do we ask?

The area sets how big the house is: how much roof, wall, floor and window it has. The calculator works them out from the area and the number of storeys.

The calculator starts from typical for the year. You can change them for each measure.

Why do we ask?

Houses from the same period were insulated much alike. The year gives typical values for how much heat walls, roof, floor and windows let out.

Pick the place nearest the house. The calculator has climate data for 9 places.

Why do we ask?

The place gives the house's climate. The calculator compares it with the energy the house buys, and works out what solar panels yield there.

Why do we ask?

The heating system decides what it costs to heat the house, and whether a heat pump can help.

All the energy the house buys in a year, counted in : all electricity, household electricity too, and for example district heating. Don't use the energy declaration's figure; it leaves out household electricity.

kWh
Why do we ask?

The calculator compares its model of the house with what the house actually buys. That way the savings follow this house, not a table.

More details

Hot water is counted as 1,000 kWh per person a year.

people

Electricity for lights, cooking and other appliances, per m² and year. Source: Sveby, Brukarindata bostäder, version 2.0. The calculator counts 70 % of it as heat in the rooms.

kWh/m²

%

years

    Show all details
    How we worked it out

    First the calculator takes away what is not heating: household electricity and hot water.

      saving = (U before − U after) × area × degree days × 24 ÷ 1000 × calibration ÷ efficiency or COP (for floors on the ground also × 0.5) annuity factor = r ÷ (1 − (1 + r)⁻ⁿ) cost per saved kWh = investment × annuity factor ÷ saving

      No rule says which discount rate to use. We worked 3.0 % backwards from eight published measures, from three independent sources. One possible reading is 4 % real interest minus about 1 % yearly growth in the price of energy. The rate also depends on the lifetimes assumed.

      Lifetimes follow Belok, Totalmetodiken, version 1.6, annex 3: 40 years for insulation and windows, 15–20 years for heat pumps and solar panels. U-values are typical values by construction period. Degree days are worked out from SMHI's and Boverket's climate data for 1991–2020, with 17 °C as the base. The energy price is a fixed value for each kind of heating, the same across Sweden. ROT is not deducted, since published figures are given before the deduction.

      The measures are worked out one by one. Done together, they affect each other and save less than their sum. The whole method is in the guide on cost per saved kWh.

      A prototype, not a finished service. It works in its own simple way, separate from Kronwatt's app. Think an assumption is wrong? Write and say so. It is the most useful thing you can send.