Renewable-Energy-Store

Sizing the Boiler

Please note that the boiler output specified can only be achieved under full load. To heat up the boiler will take approx. 30 mins until full load is reached. The boiler output is kept for a period of approx. 2 hours, after that the burn-out phase follows with reduced output for a period of approx. 1.5 hours. The residual glowing fire in the combustion chamber coasts the temperature for about one more hour, after that the fuel is completely used up. The duration of the burn cycle - approx. 4 hours.

The boiler will be heated up in the morning and in the evening, thus a burning time of approx. 8 hours is achieved.

Warning: This is imperative for the rating of the boiler to avoid that the boiler output is rated too weak.

Rough estimate of boiler size by means of living space:

e.g. building with 150 m² living space:

Boiler size required VIGAS 25 Kw

Old building     0.12 kilowatt per m²

New building                     0.08 kilowatt per m²

Low energy house             0.05 kilowatt per m²

Calculation of the daily output of the building

e.g. living space 150 m², e.g. new building => 0.08 kW/h per m²

            150 m² x 0.08 kW/h

            = 12 kW/h

The hourly output for the new building with an outdoor temperature of -16°C results in 12 kW/h

Daily requirements             24 hr x 12 kW/h

                = 288 kW

The heat output required at -16°C outdoor temperature is 288 kW per day.

Calculation of the boiler output: e.g. VIGAS 25:

Output        25 kW x 4 hours (full load)

                  = 100 kW

The burning-down heat output of a 25 kW solid fuel boiler at approx. 4 hrs full load results in 100 kW.

Daily requirements of the new building 288 kW : 100 kW (burning-down heat output)

                = 2.88 boiler fillings to achieve the necessary heat output of the building.

With this building you must fill the boiler around 3 times per day with an outdoor temperature of -16°C. Given an average annual temperature
of +7°C you can manage with about 2 fillings.

This calculation is for general information only and does not replace professional design!

If the boiler is dimensioned too small you will achieve boiler temperatures of 70 – 80°C, but the desired heating supply line temperature
will not be achieved.

e.g. building size 220 m² old building: boiler output 25 kW (wrong rating!), correct would be VIGAS 50kW.

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Last modified: 02/19/10