Trigeneration

Trigeneration or combined heat, power and cooling (CHPC), is the process by which some of the heat produced by a cogeneration plant is used to generate chilled water for air conditioning or refrigeration. An absorption chiller is linked to the combined heat and power (CHP) to provide this functionality. Quadgeneration takes this process one step further with the addition of systems to purify carbon dioxide from the engine exhaust.

Benefits of trigeneration

There are a number of benefits to trigeneration including:

Onsite, high efficiency production of electricity and heat
Reduced fuel and energy costs
Lower electrical usage during peak summer demand
Engine heat can be used to produce steam of hot water for onsite use
Significant reductions in greenhouse gas emissions
No harmful chemical pollutants since water is used as the refrigerant

Combining a CHP or cogeneration plant with an absorption refrigeration system allows utilisation of seasonal excess heat for cooling. The hot water from the cooling circuit of the plant serves as drive energy for the absorption chiller. The hot exhaust gas from the gas engine can also be used as an energy source for steam generation, which can then be utilised as an energy source for a highly efficient, double-effect steam chiller. Up to 80% of the thermal output of the cogeneration plant is thereby converted to chilled water. In this way, the year round capacity utilisation and the overall efficiency of the cogeneration plant can be increased significantly.

Advantages Versus Conventional Refrigeration

Absorption based refrigeration technology offers the most established and economic solution for reduced emission, air conditioning systems.

Operated with heat, utilising relatively inexpensive ‘excess energy’
Production of electricity that can be fed into the power grid or used to cover the plant’s electricity requirements
During cold seasons, the heat can be utilised to cover heat requirements
Absorption chillers have no moving parts, there for there is no wear and maintenance costs are low.
Absorption system has noiseless operation
Low operating costs and lifecycle costs
Using water as a refrigerant replaces the use of ozone damaging substances.

Key Figures

Approximately 150-170 kW of cold output is required per 1,000m2 of office space
The term tonnes of refrigeration (TR) is generally used as the unit of cold energy 1 TR (metric) = 3.86 kWh, 1 TR (US) 3.52kWh
The term coefficient of performance (COP) is used for referring to the efficiency of an absorption chiller. For a hot water chiller, the COP lies between 0.6 – 0.8 and for a double-effect steam chiller between 1.2 – 1.3
Cold water temperatures down to 4.5°C can be achieved with lithium bromide salt
Temperatures down to -60°C can be achieved with ammonia