The pressure control valve maintains a constant 5 bar inlet pressure to the system. Motorised valves connected to temperature controllers in the greenhouse then determine the flow of steam admitted to distribution headers, which in turn supply a network of 25mm diameter heating pipes. Condensate and residual steam from the heating pipes flow to atmosphere. The black steel heating pipes are installed above the crop, supplying heat to the air and radiant energy to the plants. Some comparison with other fuels is then possible.
Most heat is lost from greenhouses by air leakage and wind effects due to poor construction.
The new twin-skin plastic greenhouse achieves these low heat losses without loss of solar light transmission required for plant growth. Heat loss rates impact heavily on greenhouse profitability. Generally, higher crop yields are obtained at higher temperatures and the cost of supplying additional energy for heating must be balanced against the increase in yield expected. Low marginal cost forms of energy, such as geothermal, give higher optimum temperature conditions than high marginal cost system such as electricity. Most crops respond to 24 hour mean temperatures, provided the variation in temperature over that time is not too extreme.