"9% yield profits through cogeneration with heat pump"

High gas prices and a low fee for surplus electricity to the grid. This combination makes the financial efficiency of cogeneration (CHP) technology in Dutch horticulture uncertain on the long run. Consultancy Flynth and pepper grower Leo Hoogweg have developed an innovation that significantly increases the energy output of the CHP plant. The solution: a heat pump, extracting extra heat from the gases of the CHP.

The idea behind this innovation is that a lot of heat can be recovered from existing CHP gases. In comparison with a conventional boiler, a CHP uses a much larger excess of air. Although this is required for optimum combustion of gas, it simultaneously ensures that the condensation point of the gases is lower. By further cooling the gases and allowing them to condense, over 20% extra heat can be extracted from each m³ of gas.

Lower flue gas temperatures

For existing CHP plants, the exhaust gas is about 50°C when it leaves the chimney. With the interposition of a heat pump in a test at Leo Hoogweg, the temperature of the exhaust gas was reduced to as little as 20°C. The energy that would otherwise be lost, is now being utilized through a heat pump to heat up the water from 40°C to 50°C. The heated water of 50°C is used directly in the CHP as a means of heating the engine cooling water.

Simple installation, substantial efficiency gain

The existing exhaust gas condensers were found to be inadequate. However, A solution was found in the placement of an additional fume condenser behind the existing exhaust gas condenser. With a simple adjustment an efficiency improvement of 9% was achieved. Outside the addition of a heat pump, a second exhaust gas condenser, some pipes, valves and a small tank, nothing has changed to the existing heating system. Because heat pumps are available in various capacities, the project is extremely interesting for most horticultural companies working with CHP's.

The annual gas consumption decreases by more than 10%, and therein lies the chief financial profit. Thanks to the heat pump, the grower has to fire up the boiler less often, allowing the CHP to be turned off during certain hours of the day. The heat pump uses electricity, alternatively, to cool the flue gases and to heat the water. This should obviously be included in the calculation.

How the pump works

For more information please email us or contact Joel van Staalduinen, energy adviser to Flynth horticultural advisers and auditors in Naaldwijk: (0174) 637 100