tri-generation refrigeration; ammonia refrigeration

CHP: Combined heat and power - tri-generation refrigeration

Some sites that might consider installing CHP plant also have a large and continuous cooling demand, for example for process cooling or for air-conditioning. In this instance, it is worth considering absorption cooling (see below).

Furthermore, if a site is to maximise the financial benefits of tri-generation refrigeration and combined heat & power, all the heat output of the package should be used on-site. Where a site has a greater demand for electricity than for heat, it is often the heat demand that determines the size of the CHP unit, and the unit produces less electricity than the site requires.

The benefits of CHP refrigeration and cooling.

Where a site of this type also has a cooling requirement, absorption cooling offers two potential advantages:

 Most of the electricity used to meet the cooling demand is converted into a heat load, thereby reducing the site electrical demand and increasing the use of heat. This can materially alter the site’s heat to power ratio, perhaps turning a hitherto marginal case for CHP into a viable option. In some cases, it may even encourage specification of a larger CHP unit that will economically generate more electricity.

 The heat load for absorption cooling often arises when the site heating demand is at its lowest. Absorption cooling can, therefore,’ iron out’ some of the seasonal peaks and troughs in heat demand and extend profitable CHP running time. This can allow both new and existing CHP units to operate more efficiently.

Most CHP packages produce hot water at around 80-90°C, which is suitable for use by a single-effect absorption chiller.

Absorption Cooling

A site with a large and continuous cooling demand, and perhaps a declining demand for heat, may consider replacing a conventional electricity-based cooling system with absorption cooling – a system that uses heat instead of electricity for the cooling process.

Absorption cooling is a technology that allows cooling to be produced from heat rather than from electricity.

It uses an evaporator and condenser in the same way as refrigeration by mechanical vapour compression, but it replaces the compressor in the conventional system with a chemical absorber and a generator. A pump provides the necessary change in pressure. When a prime mover provides electricity, heat and cooling via an absorption chiller it is often referred to as tri-generation.

Converting an electrical load into a heat load in this way has several advantages:

 It reduces the site’s demand for electricity.

 It increases the options for heat use.

 It ‘irons out’ some of the seasonal peaks
   and troughs in the requirement for heat.

 In some cases, using heat for cooling
   can turn a marginal CHP case into
   a viable option.