There are many types of air conditioning systems being developed. But, some people want to use water to power their air conditioning system. So, what are the types of air conditioning systems that use water?
Generally, there are 4 types of air conditioning systems with water as follow:
- Evaporative Cooler
- Water-Cooled Package Unit
- Water-Cooled VRF System
- Chilled Water System
Air conditioning systems that use water for heat transfer are more efficient because water has a higher specific heat capacity than air. However, each of them has its own limitations and applications.
1. Evaporative Cooler
Evaporative coolers provide cooling using the principle of evaporative cooling which heat is rejected through the evaporation of water.
Evaporative cooler is also known as swamp cooler or air cooler in certain regions.
Technically, evaporative coolers are not air conditioners. They do not provide air conditioning which is a combination of temperature (cooling) and humidity controls. Evaporative coolers only provide cooling.
Evaporative coolers work by directing indoor air through infills that have water running on them. The infills increase the surface contact area of water thereby increasing the water evaporation rate.
As the indoor air passes through the infills, heat is transferred from the indoor air to the water. As a result, the temperature of the water increases which causes a small amount of water to evaporate.
Hence, evaporative coolers require a constant pour of new water as they “consume” water during operation.
The power consumption of evaporative coolers is significantly less than air conditioners. They only need a small amount of power to run the fan and the water pump that circulates water to the infills. So, a power socket and water are all that are needed to run an evaporative cooler.
Thus, many people find evaporative coolers convenient and they want to cool their house using evaporative coolers and save on electricity costs.
However, evaporative coolers don't work when the indoor humidity level is high.
Since water is constantly evaporating from the evaporative cooler, the humidity level in the house will rise as the temperature drop due to the cooling effect of the evaporative cooler.
As the humidity level in the house increases, less and less water is being evaporated from the evaporative cooler. Thus, the cooling effect of the evaporative cooler reduces.
At 100% humidity level, the evaporative cooler no longer provides any cooling.
Therefore, evaporative coolers are better suited for regions that have a very low humidity level. Even so, evaporative coolers are not suitable for long hours of cooling as the humidity level will eventually raise to 100%.
For outdoor applications, evaporative coolers work very well in mid to low humidity regions because water is constantly evaporating from the evaporative cooler. However, it also means that there is no temperature control, only the feeling of cool air.
2. Water-Cooled Package Unit
Water-cooled package units are compact air conditioners that use water for heat rejection. Hence, water-cooled package units usually work with cooling towers.
Cooling towers use the principle of evaporative cooling (just like evaporative coolers) to cool water. Since the water from cooling towers usually flows to the condenser of air conditioners, cooling tower water is commonly known as condenser water.
A water-cooled package unit comprised of a compressor, an evaporator, an expansion valve and a condenser. Just like air conditioners, water-cooled package units use the refrigeration process to provide cooling.
Hence, water-cooled package units are not the same as evaporative coolers as they can control both the temperature and the humidity level.
A water-cooled package unit is called a package unit because they don't have an outdoor unit like a split air conditioner does. Instead, the compressor and the condenser are packaged in a single unit together with the evaporator and the expansion valve.
Hence, water-cooled package units are relatively compact compared to other forms of air conditioners.
As opposed to split air conditioners that use the outdoor air for heat rejection, heat absorbed by the water-cooled package unit is rejected via its condenser to the condenser water. Later, the heat is dissipated to the surrounding air at the cooling tower.
Thus, a condenser water pump alongside a water piping system from the water-cooled package unit to the cooling tower is needed for the heat rejection process.
Furthermore, untreated water is corrosive which can reduce the lifespan of the piping system and the condenser of the water-cooled packaged unit. Hence, a water treatment system is needed as well.
Due to the need for cooling towers, condenser water pumps, a condenser water piping system and a water treatment system, water-cooled packaged units are not suitable for small capacity applications.
Generally, a water-cooled package unit starts at around 10 tons of cooling capacity.
Water-cooled package units can be found in large buildings where there is centralized condenser water supplied by several large cooling towers on the roof to multiple water-cooled package units.
3. Water-Cooled VRF System
A typical water-cooled VRF system is comprised of a single condensing unit that uses water for heat rejection and multiple evaporators that use refrigerant for heat absorption (cooling).
Water-cooled VRF systems need to work with cooling towers, condenser water pumps, a condenser water piping system and a water treatment system just like water-cooled package units.
However, water-cooled VRF systems offer a more flexible design.
A water-cooled VRF system has a condensing unit that handles the heat rejection process and a few evaporators that provide temperature and humidity controls.
The condensing unit is similar to the outdoor unit of a typical split air conditioner. But, the water-cooled VRF condensing unit uses water for heat rejection rather than air.
The water-cooled VRF condensing unit is connected to its group of evaporators via refrigerant linesets (just like a typical split air conditioner); two copper tubes, one for the liquid refrigerant and the other for the gas refrigerant and each set is joined by a specially made VRF Y-joint.
Since the evaporators are not attached to the condensing unit, the water-cooled VRF condensing unit can be placed far away from the indoor space to reduce the noise generated by the compressor.
Hence, water-cooled VRF systems can be quieter than water-cooled package units.
Water-cooled VRF systems can be found in luxury hotels where the water-cooled VRF condensing unit is placed in the hotel corridor and each of its associated evaporators is placed inside the hotel room to provide a luxury comfort experience.
Nonetheless, due to the high initial cost of the water-cooled VRF system, the smallest capacity based on the condensing unit is often around 6 tons. However, the 6-ton condensing unit can be connected to multiple different types of evaporators with different capacities.
For example, a 6-ton water-cooled VRF condensing unit can be connected to 6 units of 1-ton water-cooled wall-mounted evaporator or 3 units of 2-ton water-cooled ceiling ducted evaporator or other combinations.
Therefore, water-cooled VRF systems are very flexible. Compared to water-cooled package units, they are more suitable for relatively smaller capacity applications.
4. Chilled Water System
Chilled water systems are large air conditioning systems that use water for both heat absorption and heat rejection. Chilled water systems are the most common type of air conditioning system in commercial buildings.
A typical chilled water system has a “heart” which is the source that produces chilled water and it is known as the chiller.
The chiller of the chilled water system is what created the different types of chilled water systems.
Generally, there are three types of chillers as follow:
- Air-cooled chiller – Use the outdoor air for heat rejection.
- Water-cooled chiller – Use the condenser water for heat rejection.
- Hybrid chiller – Use the outdoor air for heat rejection via evaporative cooling.
Regardless of the type of chiller, a typical chilled water system has multiple evaporators that use chilled water to provide temperature and humidity controls. These evaporators are also known as air-side equipment.
There are many choices for the air-side equipment including ductless wall-mounted units, ceiling cassette units, floor-standing units and ducted air handlers (FCU or AHU) depending on preferences, capacities and indoor aesthetic requirements.
Since the air-side equipment is the same for all chiller types, I'll elaborate more on how each chiller type works in a chilled water system in the following.
An air-cooled chiller is comprised of a compressor, a condenser, an evaporator and an expansion valve. It uses the refrigeration process to produce chilled water.
However, air-cooled chillers don't need condenser water. They produce cold refrigerant to absorb heat and produce chilled water at the evaporator. Later, the hot refrigerant goes to the condenser and the air-cooled chiller has a fan to draw in the outdoor air to cool the hot refrigerant.
So, cooling towers, condenser water pumps and the piping system for the condenser water are not needed if the chilled water system is using air-cooled chillers.
However, a water treatment system is still needed to maintain the quality of the chilled water.
Therefore, chilled water systems with air-cooled chillers are more compact and cheaper. But, air-cooled chillers are not as efficient as the other types of chillers.
A water-cooled chiller has the same element as an air-cooled chiller. It also uses the refrigeration process to produce chilled water.
But, water-cooled chillers need condenser water for heat rejection. Similarly, they produce cold refrigerant to absorb heat and produce chilled water at the evaporator.
Later, the hot refrigerant goes to the condenser and heat is transferred to the condenser water for heat dissipation at the cooling tower, much like water-cooled package units and water-cooled VRF condensing units.
So, all the components associated with condenser water including cooling towers, condenser water pumps, the piping system and the water treatment for the condenser water are needed if the chilled water system is using water-cooled chillers.
Therefore, chilled water systems with water-cooled chillers are more expensive and occupy more space. However, they offer the best energy efficiency.
A hybrid chiller also has the same element as an air-cooled chiller. However, its condenser is much like a cooling tower, using evaporative cooling for heat rejection.
The condenser of hybrid chillers works like an evaporative cooler. It has infills that increase the surface contact area of water. At the same time, it is also a heat exchanger that the hot refrigerant can pass through for heat rejection.
Combined with a fan, hybrid chillers use the outdoor air plus the evaporation of water for the heat rejection process. Thus, water that is used for the evaporation process needs to be constantly replenished, just like evaporative coolers.
On a side note, those systems that involve cooling towers also “consume” water and need to be constantly replenished because cooling towers also rely on the evaporation of water for heat rejection.
However, because hybrid chillers are pouring water onto their heat exchanger, the material used for the condenser needs to be highly corrosive resistant like stainless steel.
Therefore, chilled water systems with hybrid chillers are very expensive but occupy less space. In addition, they are more efficient than air-cooled chillers thanks to evaporative cooling but less efficient than water-cooled chillers.
Regardless, chilled water systems are the largest air conditioning system that involves water as part of the cooling process. It is usually deployed in large commercial buildings such as hotels, shopping malls and hospitals.
Air conditioning systems with water are generally not suitable for homes and small capacity applications as the cost is too high. Thus, almost all of them started at a cooling capacity far greater than it is needed for a typical house.
Most of the time, the smallest air conditioning system with water is the water-cooled VRF system starting at 6 tons of cooling capacity which may be suitable for a house with around 2400 sqft of effective cooling space or more than 3000 sqft of total floor area.
However, a water-cooled VRF system requires a cooling tower which is usually large in the physical dimension in order to work. So, practicality is still questionable.
Instead, people who seek a high energy efficient air conditioning system may consider high SEER mini splits (maybe battery storage solar powered) or perhaps, a radiant floor/ceiling water cooling system.
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