Heat-pump dehumidifier as an efficient device to prevent condensation in horticultural greenhouses

• A heat pump dehumidifier was designed to avoid condensation on ornamental crops.
• A 4 W m−2 power consumption at the compressor sufficed to prevent condensation.
• Heat pump significantly contributed to greenhouse heating, reducing energy costs.
• Total operational cost was lower than estimated for ventilation with an exchanger.
• Device profitability is discussed for different countries according to energy cost.

In the context of increasing energy costs, alternative methods to the energy consuming venting-heating method must be considered for greenhouse dehumidification. In this paper the performance of a heat pump used as a dehumidifier is investigated. Contrary to the classical control aiming at maintaining the greenhouse air at a relative humidity set point, the considered device is designed as a preventive tool to avoid condensation on the crop and limit the energy consumption. The experimental set up was run during winter inside a 2350 m2 plastic greenhouse in the West of France for a set temperature of 16 °C. During the experiment, no condensation occurred on the plants with a mean condensation rate of 12 W m−2 and a mean electrical power of 7.62 kW, for an overall efficiency of 4.9. Moreover, the energy retrieved by vapour condensation was given back to the greenhouse as sensible heat, contributing to the total heating of the greenhouse. While dehumidifying the greenhouse air, the device reduces, or may even rule out the gas consumption. The total energy consumption of the heat pump during the season was compared to simulated values for venting-heating dehumidification, with or without an exchanger. The heat pump dehumidifier was shown to be 6 to 8.5 times less energy consuming than the former and 3-8 than the latter, depending on the exterior climate. Using the energy cost of several significant countries, a preliminary operative cost study was conducted and showed that the heat pump can be competitive as a dehumidification alternative.