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Calcimator

Passive Solar Design Calculator

Thermal mass and window sizing for passive solar earthen buildings.

Inputs

Results

South glazing (sq ft)

114

Thermal mass (sq ft)627
Wall R-value3.6
Thermal lag (hours)18
Overhang depth (in)24
How to Use This Calculator
  1. Enter Floor Area (sq ft) and your site Latitude (degrees N).
  2. Input Wall Thickness (in) and Heating Degree Days (HDD) for your climate zone.
  3. Set South Glazing (sq ft) and Thermal Mass (sq ft) for the passive solar design.
  4. Enter the Wall R-Value to calculate heat retention.
  5. Review the solar gain and heat loss balance to verify the design meets passive solar guidelines (south glazing ~7-12% of floor area).

How the result changes with Floor area (sq ft)

Floor area (sq ft)South glazing (sq ft)
1,090124
3,565406
6,535745
9,0101,027

What each input means

Floor area (sq ft)
Total conditioned floor area of the building.
Latitude (degrees N)
Your latitude in degrees North (e.g. Denver = 39.7).
Wall thickness (in)
Earthen wall thickness in inches.
Heating degree days (HDD)
Annual heating degree days for your climate zone.

What each result means

South glazing (sq ft)
Recommended south-facing window area.
Thermal mass (sq ft)
Area of 4-in thick thermal mass floor/wall needed.
Wall R-value
Approximate R-value of the earthen wall.
Thermal lag (hours)
Time for heat to pass through the wall (flywheel effect).
Overhang depth (in)
South-facing overhang depth for summer shade.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Floor area (sq ft) = 1000, Latitude (degrees N) = 40, Wall thickness (in) = 18, Heating degree days (HDD) = 5500 = 4 input(s) provided
  2. Calculate South glazing
    South glazing = round(floorAreaSqFt * (glazingPct / 100))
    114 = 114
  3. Calculate Thermal mass
    Thermal mass = round(southGlazingSqFt * 5.5)
    627 = 627
  4. Calculate Wall R-value
    Wall R-value = round(wallThicknessIn * 0.2 * 100) / 100
    3.6 = 3.6

Engine last updated .

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