ECONOMIC ASPECTS OF HEAT PUMPS IN GLASSHOUSE HORTICULTURE

J.P.G. Huys, W.P. Mulder
With a heat pump low-temperature water can be warmed up. The heat for this can be extracted from a low-temperature source. The amount of primary energy required for this is smaller than the amount of energy that is released. Application of the heat pump can therefore be one of the means to save energy, and with high energy prices it can be financially attractive.
  1. The peak load determines the capacity of the heat source that must be installed. Because this peak load is utilized for a short period of the year only, the capacity of the heat pump is generally such that it can meet only part of the heat requirement. In that case it is supplemented by a so-called peak-shaving facility fuelled by another source of heat. On the basis of the annual load diagram, which is rather linear, a heat pump with a capacity of 50 % of the maximum heat requirement meets 80 % of the total annual heat requirement. These calculations are based on the use of a gas-driven heat pump with a thermal efficiency ranging between 110 % and more than 200 %.

    For comparative purposes it should be noted that application of a flue-gas condensor can raise the efficiency of a heating boiler in glasshouse horticulture to 100 % related to the lower heating value.

    The figure shows the energy savings that can be achieved with various efficiency rates and various heat capacities.

  2. The efficiency of the heat pump is affected by the temperature of the heat source as well as the temperature at which the heat must be released. In glasshouse horticulture a specific heat output varying between 2.5 and 4 is retained.

    Outside air, which is available everywhere but maybe too cold for extraction of heat in winter, may be used as a source of heat.

    A second potential source of heat is spring water. Not everywhere in the Netherlands it is allowed to extract water from the soil, however. Better sources of energy are the ditches, rivers and canals, which are often used in the Netherlands to supply cooling water to industries and power plants. This enables them to release enough heat in winter, too.

    Finally there is the possibility of extracting heat from the soil, a method requiring an extensive pipeline system. This, too, is subject to restrictions.

  3. At the moment it is not yet clear how market prices will develop if the heat pump conquers the market. For gas-driven compression machines prices of Hfl. 600/kW released power are retained, and prices of absorption machines are estimated at Hfl. 1000/kW released power, while it is not easy to supply heat pumps of any capacity. For comparison, the price of a gas fired boiler is Hfl. 25/kW released power.

Here the question whether current and future energy prices offer any

Huys, J.P.G. and Mulder, W.P. (1981). ECONOMIC ASPECTS OF HEAT PUMPS IN GLASSHOUSE HORTICULTURE. Acta Hortic. 115, 511-516
DOI: 10.17660/ActaHortic.1981.115.57
https://doi.org/10.17660/ActaHortic.1981.115.57

Acta Horticulturae