Articles
ENERGY EFFICIENT HEATING WITH GAS ABSORPTION HEAT PUMPS AND LONG TERM HEAT STORAGE IN ORGANIC PROTECTED HORTICULTURE
Article number
1041_31
Pages
265 – 274
Language
English
Abstract
Conventional and organic greenhouse growers both face problems of high energy costs.
By using new technologies, like combined heat and power (CHP), growers are trying to control these costs; however, the use of CHP is not always possible for growers with a small production area and/or a diverse range of crop types, as is often the case in organic horticulture.
A semi-closed greenhouse with a gas absorption heat pump (GAHP) and short- and long-term energy storage might be a better solution for small scale companies.
For the purpose of this experiment, we used an insulated six-compartment greenhouse (1,250 m2) with three gas absorption heat pumps for a total heat capacity of 120 kW and a coefficient of performance (COP) of 130-170%. In this system, the CO2 released by gas combustion was available for use in the greenhouses for fertilisation.
Cold water produced by the heat pumps was used for dehumidification, thus allowing the greenhouse to remain closed for longer periods and reducing heat and CO2 losses.
Cold and warm water were stored for the short term in two 45 m3 water tanks.
Excess heat from heat pump operation for CO2 production on sunny days was collected during summer and stored long-term in a borehole thermal energy storage (BTES). In winter, stored heat was used by the heat pump to warm the greenhouse.
Two 400 m2 compartments were used to identify energy flows during the culture of organic tomatoes (Solanum lycopersicum) in 2012 and 2013. The crop was planted in January and grown until the end of November.
A COP of 140% was measured for the heat pumps.
The energy use for the 2012 season was 418.3 kWh m-2. With the COP of the heat pumps included, this resulted in a gas consumption (11.52 kWh m-3 gas) of 25.8 m3 m-2 with an average yield of 41.8 kg m-2. In 2013, energy use was 301.4 kWh m-2. With the COP of the heat pumps included, this resulted in a gas consumption of 18.54 m3 m-2 with an average yield of 36.1 kg m-2.
By using new technologies, like combined heat and power (CHP), growers are trying to control these costs; however, the use of CHP is not always possible for growers with a small production area and/or a diverse range of crop types, as is often the case in organic horticulture.
A semi-closed greenhouse with a gas absorption heat pump (GAHP) and short- and long-term energy storage might be a better solution for small scale companies.
For the purpose of this experiment, we used an insulated six-compartment greenhouse (1,250 m2) with three gas absorption heat pumps for a total heat capacity of 120 kW and a coefficient of performance (COP) of 130-170%. In this system, the CO2 released by gas combustion was available for use in the greenhouses for fertilisation.
Cold water produced by the heat pumps was used for dehumidification, thus allowing the greenhouse to remain closed for longer periods and reducing heat and CO2 losses.
Cold and warm water were stored for the short term in two 45 m3 water tanks.
Excess heat from heat pump operation for CO2 production on sunny days was collected during summer and stored long-term in a borehole thermal energy storage (BTES). In winter, stored heat was used by the heat pump to warm the greenhouse.
Two 400 m2 compartments were used to identify energy flows during the culture of organic tomatoes (Solanum lycopersicum) in 2012 and 2013. The crop was planted in January and grown until the end of November.
A COP of 140% was measured for the heat pumps.
The energy use for the 2012 season was 418.3 kWh m-2. With the COP of the heat pumps included, this resulted in a gas consumption (11.52 kWh m-3 gas) of 25.8 m3 m-2 with an average yield of 41.8 kg m-2. In 2013, energy use was 301.4 kWh m-2. With the COP of the heat pumps included, this resulted in a gas consumption of 18.54 m3 m-2 with an average yield of 36.1 kg m-2.
Authors
E. Eriksson, N. Vergote, J. Dewitte, K. Declercq
Keywords
energy efficiency, semi-closed growing system, organic greenhouse, BTES
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