Absorption air conditioning, also known as absorption cooling or absorption chiller, is an HVAC system that uses a heat source to provide air conditioning. Heat sources can include solar energy, waste heat, and natural gas. It can be an energy-efficient alternative to vapor-compression refrigeration systems, also known as direct expansion systems.
In this article, I’ve gone over what absorption air cooling is, the advantages of using this HVAC system, the various heat sources that can be used, and how it works.
What is Absorption Air Conditioning?
Absorption air conditioning is a cooling technology that uses mechanical energy and a heat source to function. Through chemical processes, it can change low-temperature and low-pressure vapor into high-pressure vapor.
Although absorption chillers are similar to vapor-compression refrigeration systems, vapor-compression refrigeration systems rely on electrically driven compressors to circulate refrigerants. Absorption cooling systems use the evaporation of a refrigerant and the absorption of the vapor.
This type of system used to be only available in commercial buildings. However, now they can also be found in large homes.
What Are the Components of an Absorption Chiller?
Water and ammonia or lithium bromide are commonly used refrigerants in an absorption air conditioners. The heat source can be steam, natural gas, liquefied petroleum, kerosene, solar energy, geothermal heated water, waste heat, or resistance heating that uses electricity.
Systems that use natural gas, the most common source of energy for absorption chillers, are known as gas-fired cooling or gas-fired heat pumps. One main advantage of this HVAC system is that it can be used in remote places or houses even when there is no source of electrical power supply.
There are four main components of an absorption cooling system:
- Absorber: The liquid absorbent solution absorbs the refrigerant vapor.
- Generator: Using a heat source, the refrigerant is regenerated from the absorbent solution.
- Condenser: The refrigerant vapor is condensed into a liquid and it rejects heat.
- Evaporator: Liquid refrigerant evaporates and it absorbs heat from the area being cooled.
How Does an Absorption Chiller Work?
The evaporator and condenser used in an absorption air conditioning system are similar to those of the compression system. However, the compressor is replaced by a generator, pump, and an absorber. Here’s a look at how the absorption cycle and system works:
In an absorption chiller, the heat source will cause the vapor refrigerant in the lithium bromide solution to boil. This increases in pressure, and the high-pressure vapor results in a higher condensing temperature. Vapor condensation happens at higher temperatures and pressures compared to the surrounding temperature.
Once the condensing temperature is higher than the ambient, the heat is transferred from the condenser to the surrounding area and removed. The high-pressure liquid is forced to go through a valve where its pressure drops.
This drop in pressure also causes the boiling point temperature to drop. It’s then passed through an evaporator where it’s boiled at a lower temperature and pressure. The liquid absorbs the heat energy from the conditioned air and causes the liquid to boil. The air is cooled and discharged to the room.
The vapor is then directed to the absorber, where it becomes a liquid lithium bromide solution. This solution is pumped into the generator. The lithium bromide is separated from the water via heat. Water vapor goes into the condenser and the lithium bromide goes to the absorber. This refrigeration cycle is repeated by the HVAC system to cool the room.
Advantages of Absorption Air Conditioning
There are several advantages to using absorption refrigeration system, including:
- They use waste heat or renewable energy. Absorption air conditioners that use renewable energy sources rather than electricity can be more energy efficient. It can also be a fantastic alternative if there is electricity supply.
- They require less maintenance than their counterparts. With less moving parts compared to compressors, they require less maintenance. They’re also quieter.
- They don’t use chlorofluorocarbon refrigerants (CFC). CFCs can break down in the upper atmosphere and deplete the ozone layer.
Final Thoughts
Absorption air conditioning systems can be a great alternative to vapor-compression refrigeration systems, especially in areas where electricity isn’t readily available. While they’re still most commonly used in large commercial and industrial buildings, homeowners in larger homes are starting to use this type of HVAC system.
Frequently Asked Questions About Absorption Air Conditioning
Are There Downsides to Using an Absorption Chiller?
Absorption chillers tend to be less energy-efficient than modern vapor-compression systems that use fossil fuels as a heat source.
Where are Absorption Air Conditioning Systems Used?
Absorption air conditioning systems are usually used in industrial applications and large commercial buildings. However, larger homes are starting to adopt these systems as well.
How Can You Maintain Absorption Chillers?
Absorption chillers need to be regularly maintained to extend their lifespan and prevent toxic ammonia leaks. They should be inspected for leaks, proper solution concentration, and levels, and alignments. They also need to be calibrated to make sure temperature, pressure, and flow controls are at optimal levels. This is not a recommended DIY project and maintenance is best left to trained professionals.
