About Mechanical Cooling
Mechanical cooling is used in greenhouses in situations where the outside conditions (high humidity) do not permit the use of alternatives based on adiabatic cooling. Both CAPEX (investment) and OPEX (running costs) are higher than cooling based on adiabatic cooling.
The cooled air is usually blown into the greenhouses through ducts. Mechanical cooling can be used to control the temperature and humidity (dehumidifying) in the greenhouse.
Chillers create cold air powered by an electrically driven compressor. The coefficient of performance (CoP) parameter that indicates the efficiency of the installation, is usually 5. This means that 1 kWh of electricity generates 5 kWh of cold air. Chillers can generate air of relatively low temperatures.
Heat pumps work by pumping or transferring heat from one place to another using a compressor, an evaporator and a circulating circuit of liquid-gas refrigerant. A heat pump is often referred to as a “inverted refrigerator”. Heat pumps come with multiple advantages for your heat generation. The cycle can be reversed so the unit acts like cooler.
The coefficient of performance (CoP) is the parameter used to determine the efficiency of the installation. For example, a CoP of 4 indicates that the installation generates 4 kWh of heat while consuming 1 kWh of electrical energy. The CoP is influenced by the temperature and physical characteristics of the energy carrier and the outlet water temperature needed for the greenhouses. Heat pumps are generally applied in horticulture in combination with thermal storage in subterranean aquifers.
An absorption chiller produces chilled water using residual heat from sources such as steam, hot water or hot gas. Unlike heat pumps, the principle is based on two media: a refrigerant (often water) and an absorbent (often lithium bromide). The coefficient of performance (CoP) is the parameter used to determine the efficiency of the installation. For example, a CoP of 1 indicates that the installation generates 1 kWh of cold while consuming 1 kWh of heat. The CoP of an absorption chiller is low compared with a heat pump.
Absorption chillers are available in three different types: single effect, double effect, or the latest development - triple effect. Single effect systems have a single generator and have a CoP value of less than 1.0. Double effect systems have two generators and two condensers and are more efficient with typical CoP values of more than 1.0. Triple effect system include a third generator and condenser and are the most efficient with a typical CoP value of more than 1.5. Absorption coolers are generally applied in horticulture in combination with high grade, industrial waste heat.
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