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Technical
is circulated in insulated pipes to air-handling unit or fan coil unit equipment to keep the building cool in warm climate . Chillers are typically electricity-driven compression type . In tri-generation or quad-generation systems , cooling is provided by absorption chiller ( s ), which uses the recovered heat from the generator . The fact that the heat input to the absorption chiller is harvested makes a tri-generation or quad-generation system very efficient .
In principle absorption chillers operate on ‘ free ’ recovered thermal energy from natural gas-powered generators , thermal energy that would otherwise be wasted to the atmosphere . As long as the power generator is operational and there is a cooling demand , chilled water will be produced by the absorption chiller , independent of utility power .
Absorption chillers use Lithium Bromide ( a type of salty solution ) and distilled water as refrigerants , both with an Ozone Depletion Potential ( ODP ) of zero and a Global Warming Potential ( GWP ) of zero . By controlling the temperatures and concentrations of lithium bromide , it is possible to control the leaving chilled water temperature . Hot water from the generator will be pumped to the absorption chillers by means of a pump ( s ), situated in the generator plant room .
Absorption chillers have been commercially available for more than half a century and are now regarded as matured technology , and they gained acceptance due to their capability of not only integrating with tri-generation systems but also because they can operate with other industrial waste heat streams that can be fairly substantial .
Absorption chiller technology represents an optimal solution for a year-round efficient source of cooling and heat , especially when used in conjunction with a gas engine cogeneration plant .
HEAT OUTPUT Heat from the generator engine is recovered using multiple types of heat exchangers in various arrangements . The hot exhaust gas recovered from the generator engine can be used as an energy source for hot water or steam generation for an industrial process , or building heating system , or can be utilised as an energy source for a highly efficient , double-effect steam chiller . If steam is not required , hot water will drive the absorption chiller . The amount of steam , hot water or chilled water can be carefully modulated by facility management or control systems depending on the season ( cool or warm ) and industrial process ( cooling or heating demands ).
The ultimate heat recovery design depends on the client ’ s specific power , heating and cooling needs . A cost benefit analysis will be done by the MEP consultant to determine the best technical and optimal solution for the client . Some clients have a high steam or heating demand , while other clients may have a higher cooling demand or even require ice storage .
IMPLEMENTATION Tri-generation and quad-generation plants are a reasonably good solution for clients that require constant cooling , heating and power at their facility and have sufficient natural gas available but don ’ t have sufficient utility power . For clients that are looking to decarbonise or achieve a net zero energy building ( NZEB ), a tri-generation or quad-generation system is a great alternative to their existing or new facility .
A Net Zero Energy Building is a method of design and construction that aims to achieve an energy efficient , gridconnected building , enabled to generate energy from a zerocarbon emission or renewable energy sources to compensate for its own energy demand . As a result , these types of buildings boast a net zero energy consumption such that the total energy used by the building on an annualised basis is roughly equal to the amount of zero carbon emission or renewable energy created on the site or at a nearby location . Facility owners and developers have demonstrated awareness in developing net zero energy buildings to meet corporate goals and regulatory mandates .
Quad-generation plants are uniquely positioned in the industry in that they can provide reliable clean power around the clock – unlike solar or wind power plants which depend on the natural environment to generate power .
A key factor determining the optimal tri-generation or quad-generation solution is to determine the hourly base power , cooling and heating load demands / requirements in a building or industrial process .
Good examples of buildings with high power , cooling or heating base load demands include ( but are not limited to ) the following :
• Hospitals
• Universities
• Manufacturing plants
• Data centres
• Large hotel resorts
• Large international airports
As mentioned above , a cost benefit analysis will be done by the MEP consultant to determine the best technical and optimal solution for a client .
“ For clients that are looking to decarbonise or achieve a net zero energy building ( NZEB ), a trigeneration or quad-generation system is a great alternative to their existing or new facility .”
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RACA Journal I June 2023 www . refrigerationandaircon . co . za