If long generator runs are needed then combined heat and power or CHP could be the answer. For every Kilowatt of electricity generated using a diesel engine, you loose nearly 2 Kilowatts in waste heat. You have already paid for the diesel burnt so it makes sense to reclaim as much of the heat as possible. This heat can be used in many different ways. Domestic hot water and heating is the obvious one. We even use some of the heat to raise the temperature of our poly tunnel. This extends the growing season up here and allows us to cultivate apricots, grapes and many other delicious fruits and vegetables which we use in our cookery school.
A 5.0KW SDMO generator with jacket water heat exchanger installed.
Waste heat is split roughly 50/50 between the jacket water of the engine and the exhaust gasses. With water cooled units, a simple heat exchanger will work and give good results. On larger units the addition of an oil cooler as well will be beneficial and give good additional heat recovery.
The exhaust heat exchanger is the next vital piece of equipment. These are made by us to order and designed for the particular model of engine and the space available for installation. The one shown in the photograph below is long and thin because there was plenty of space availavle in this particular installation. It could, however be short and fat if space is at a premium. All exhaust heat exchangers are made of stainless steel. They are individually pressure tested and designed to give maximum heat recovery while still staying within the exhaust back pressure limits set by the engine manufacturer.
Exhaust gas heat exchanger for the engine above.
Diesel engine exhaust gasses are typically ejected at about 350 degrees centigrade. With this large temperature gradient, high temperatures for the heating water are possible. This make it particularly suitable for heating domestic hot water where high temperatures are normaly required.
When considering Combined Heat and Power, remenber that you have already paid for this heat with the diesel burnt in the generator. It is also, unlike most other forms of alternative energy, 100% predictable. If your generator is running, you know exactly what you will be getting out of your machinery.
All this heat reclamation can be retro-fitted to an existing generator. It will not put additional "strain" on the engine providing it is designed and installed properly. Water cooled machines are ideal to convert into CHP units. It is possible to reclaim heat from air cooled units as well although there will be a reduction in efficiency.
One of the slightly different ways of utilising that waste heat. The warm water is run through copper pipes, set in the raised beds of the poly tunnel which provides vital heating to both the soil and the surrounding air. This photo is taken in February where we still have many of last year's vegetables and are starting this season's produce even when the days are short and the nights are cold.
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