Climate control & energy > Burner / boiler
Combustion efficiency
To improve energy efficiency for greenhouse climate control, the first trick is to get the most heat out of the fuel and to transfer it as efficient as possible to the plants. Also important is to minimise the heat loss during combustion and transport. Important aspects are burner capacity and efficiency, boiler efficiency, water content, air supply, flue gas condensor, insulation.
Burner / boiler efficiency
Burner or boiler efficiency is a percentage indicating how much heat (e.g. in the form of hot air or hot water) is obtained from burning a fuel. The large industrial boilers that are used for heating large greenhouses have an efficiency ranging from below 80% to over 90%. This is more than 10% difference in energy costs. An old burner can waste a lot of energy, and can have problems such as a relatively high emission of pollutants. This is particularly undesirable when the flue gases are used for CO2 enrichment. Regular cleaning and maintenance improves the boiler performance.
Burner and boiler capacity
Heating systems that are dimensioned for standard conditions can be too small for extremely cold conditions. This can be due to all sort of limitations: limited burner, boiler, fuel supply, air supply, water content, radiation surface or pump capacity. Hence the temperature in the greenhouse can be too low in cold nights and mornings, which can cost production.
Air inlet & outlet
A burner draws a lot of fresh air from the surroundings for oxygen supply to the combustion chamber and out through the stack. This causes heat loss. The heat loss is larger when more air flows through the burner, and also when the incoming air is colder, or the air leaving the stack is hotter.
Solutions
The combustion efficiency can be increased by using a flue gas condensor (for gas boilers only). A condensor retrieves energy from the flue gases by cooling them down from over 200 °C to (possibly as low as) 40 °C. It also regains energy by condensing the hot steam in the flue gas. Another option related to a boiler is installing a buffer (see in menu).
Insulating the boiler & transport pipes
Energy can be saved by placing the boiler in a well-insulated boiler house. The combustion air is then pre-heated, which saves energy. But make sure there is always sufficient inflow of fresh air. Most boilers are pretty well insulated. A lot of heat can be lost from the heat transport pipes, which can be 100 °C. Lagging (insulating) these pipes reduces the heat loss.
Further reading
The Barton Soot Collector for coal boilers (2005)
Energy saving in the boiler house (2005)
Co-generation or combined heat & power (CHP) (2005)
Energy audits by energy specialist Peter Mos (2005)
