Buffer storage tank – the ideal way for efficient CHP heat utilisation

Buffer tank and piping in a CHP room

When planning a Combined Heat and Power (CHP) project, heat utilisation plays an increasingly important role in the UK. This is not least due to the Combined Heat and Power Quality Assurance Standard (CHPQA), which is becoming more and more important. It can only be achieved with a certain degree of efficiency and in many cases the CHPQA standard is very important for the profitability of the CHP.

Günther J. Schulz, director of the Kent-based company 4CleanTech has a very clear opinion on this: “Apart from cases where the heat can be fed in directly without a second heat source and without fluctuations on the consumer side, a buffer storage should be specified when implementing a CHP project.”

What exactly is a buffer storage tank?

A buffer storage tank is the water-filled heat storage tank of a heating system or a water heater.  It has the task of compensating for differences between generated and consumed heat. The buffer tank makes it possible to decouple heat generation from consumption. This means that it stores the generated heat temporarily so that it can be used as hot water or heating water at a later time. The result is better operating behaviour, higher efficiency and a longer life cycle of the gas engine.

How the CHP and a buffer tank work together

A CHP has its own circulation pump, which it uses to circulate the water needed to cool the engine unit and the exhaust gases at the coldest point in the entire system. After heating, the cooling water reaches the heat consumers via the CHP’s heating circuit distribution pumps. The buffer storage tank assumes the function of a hydraulic separator and – depending on its integration – enables, among other things, the decoupling of the volume flows of the heat generators from the heat distribution system. The pipes between the buffer storage tank and the connections of the CHP unit can be flowed through in both directions, depending on the operating state.

What exactly are the advantages of a buffer tank?

 If you use a buffer storage tank in combination with your CHP unit, you can benefit from a number of advantages.

  • The buffer storage tank separates heat generation from heat demand, which makes the operation of the CHP more efficient by minimising partial load times.
  • The buffer tank covers heat load peaks and avoids switching on the peak boiler during short-time peaks. This increases the running time of the CHP unit.
  • The buffer tank avoids intermittent CHP operation, which would lead to greater wear and tear on machinery and thus perhaps to CHP failure in the long run. It thus has a positive effect on the service life.

Dimension of a buffer storage

Accurate sizing of the buffer tank is a critical part of the CHP system design. In addition to this, the integration and control should be matched to the overall system, e.g. a heating system. Because it depends on this when the buffer steps in, i.e. when it stores and when it discharges. Another not entirely unimportant point is the issue of space requirements. Since a buffer storage tank can sometimes take on enormous dimensions, it should be ensured in advance that there really is enough space to avoid unpleasant surprises when it is installed.

Kent-based 4CleanTech uses buffer tanks for its CHP projects, simply to optimize the efficiency of the machines and to extend the life cycle of the engines.