Unlike conventional chillers, absorption chillers use the collection of waste heat from other processes or equipment to drive a thermodynamic process that allows water to be chilled and distributed for HVAC needs. In place of conventional refrigerants, water is usually mixed with either ammonia or lithium bromide, and lithium bromide is the more common one because it is not toxic.
Major considerations for installing an absorption chiller
Absorption chillers have the advantage of being free of electric compressors, which means that they can provide significant cooling capacity to a facility without contributing to the peak electric demand. The major consideration that must be made when assessing the applicability of such a chiller is that they do require a large and consistent stream of waste heat in order to function. Industrial manufacturing facilities are the most obvious candidates, but other settings such as university campuses, larger hospital complexes, or large hotels often present significant opportunity to benefit from installing an absorption chiller.
What are the benefits of using absorption chillers?
- The refrigerants primarily used in absorption chillers do not contribute to global warming and ozone depletion.
- An absorption chiller can reduce the cost of electricity, hot water, heating and cooling for the facility.
- Due to lack of compressors in the machine, the noise and vibration are significantly reduced in the building, providing a quiet environment with high reliability.
- An absorption chiller is powered nearly entirely by heat that was already going to waste
- It does not consume electricity for the production of chilled water and heat.
- It will not require nearly as much capacity to be allocated in an emergency backup power system.
The science behind absorption chillers
An absorption chiller normally has a condenser, a generator, an evaporator, an absorber, and a heat exchanger. First, the refrigerant, or the water mixed with lithium bromide, is stored in the absorber. It will be pumped through the heat exchanger and go to the generator tank at the top of the chiller. The heat generated from the outside or waste steam collected from other systems in the building will go into the chiller’s generator. Lithium bromide and water will then be separated under the heat. Water gradually becomes vapor and rises to the top, where the condenser located, and lithium bromide sinks to the bottom.
The lithium bromide will go through a pipe and flow back to the absorber, where it started originally. Then, the vapor in the condenser on the top will go through a cooling tower. The cooling tower pipe has a lower air pressure than the condenser. Thus, the vapor becomes water again as the air pressure decreases. The cold water then goes into the evaporator and waits to be mixed with the lithium bromide in the absorber again.
In short, the absorption chiller chilled water via sudden change of pressure. When the water heats up in the generator, the air pressure is high. Water releases the heat and becomes vapor. Then, a pipe leads the vapor to the evaporator, where the air pressure is low. The vapor will then cool down and become cold water again immediately. The outside temperature will drop as vapor absorbs the heat to become water.
The water evaporates and carries away all the unwanted heat. Then, as it goes through the cooling tower, the vapor cools down in a low-pressure environment and becomes water again. When the water mixed with the lithium bromide in the absorber, they are ready to go through the heat exchanger again and carries more unwanted heat with them.
When it operates, an absorption chiller produces chilled water while consuming just a small amount of electricity to run the pumps on it. And it will continue bringing out the heat from the building as it goes through the heating and cooling cir