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Trigeneration refers to the simultaneous generation of electricity, heating and cooling. This tends to be a more energy efficient process than simple electricity generation because waste heat is captured and used in a heating, ventilation, and air conditioning (HVAC) system. Traditional power plants typically do not require large amounts of heat energy, so trigeneration systems can be best used as on-site generators. This can allow the power and HVAC needs of a building or large complex to be met all at once. Cogeneration is a similar process that harnesses waste heat but does not use it to power any type of absorption or adsorption chiller.
Traditional power plants typically have no use for heat energy, which is why little attempt is made to harness waste heat. Thermoelectric power plants use a variety of different fuels, including nuclear, coal, and waste materials, to heat water and create steam. The heated steam is referred to as a prime mover because it turns turbines and generates electricity. This process also creates a vast amount of waste heat. In certain circumstances, the process of trigeneration can harness otherwise wasted energy.
When the steam in a thermoelectric generator cools, heat can be captured for other uses. The heated water can be used directly in a HVAC system or stored in water tanks as a type of heat sink. Facilities that are operational 80 or more hours a week are often a good candidate for trigeneration due to the power savings of using waste heat rather than electricity to run the HVAC system.
Electricity generation tends to be a relatively inefficient process, depending on the method that is used. Most forms of electricity generation result in a large amount of waste heat that simply dissipates and is lost. Thermoelectric plants typically only capture about 30% of the total energy as usable electricity, leaving about 70% to dissipate into the environment. Cogeneration of heat energy and electricity can reduce that to about a 20% loss, depending on the fuel source. Trigeneration is not necessarily more efficient than cogeneration, but it does allow the heat energy to be used during warm summer months.
Unlike simple cogeneration, trigeneration can also be useful during warm summer months or in hotter climates. These systems typically include an adsorption chiller or other device that can cool off a facility using the hot water created by the power generation process. This isn't technically a greater efficiency, though it does present another use for the waste heat. Other facilities can find even more uses for the waste heat captured by cogeneration, such as the operation of a desalinization process.