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Heating Ventilation and Air Conditioning Full Course - HVAC Course (Part 14)

         This is part 14th of the full HVAC course. Access all previous parts at the end of this post below...

Chillers :

            A chiller is a term to describe a complete chilling package that includes a multi-compressor, multi-condenser, internal piping, other controls, and only one evaporator.
A chiller is a machine that removes heat from the liquid via a vapor-compression or vapor absorption cycle. In this AC system, Chilled water from the chiller is distributed to the heat exchanger or cooling coil in the air handling unit, and hot water is returned back to the chiller (Evaporator).

A chiller is used in the cooling system of HVAC (Heating Ventilation Air Conditioning). They work on principles of evaporation. Chillers are more efficient at higher temperatures and use water as coolant. Water is generally pumped from a river, lake, or sea via pipes through the evaporator coil into the house. As the hot air passes over the cold surface, heat is removed from the air and transferred to the water flowing through the coils. This heats up the water that then flows back out of the building. The outside air temperature has little effect on the chiller capacity.

In many areas of North America, outdoor air temperatures can easily reach 50°C / 122°F. Most people think of this as being too warm but actually, it's not. When you consider how much cooler the indoor environment can get when compared to the outdoors, it makes sense that chillers are more efficient. A typical residential home may have 4-6 rooms that need conditioning. These spaces could include bedrooms, bathrooms, laundry room, kitchen, and dining room. If we were to run these rooms using only electric space heaters, we would require 1-2 kW per person if we had 6 occupants. However, if we conditioned them using an 8-ton chiller, we would only require.8 kW per person! That means our energy bill would be reduced by 30%.

Capacity Range :

- 25 Tr to 420 Tr (Indian Market )
- 15 Tr to 3500 Tr (Gulf Market )

Advantages of Chillers over other Systems

- In Chillers, water is responsible to cool the air, and water is cooled by refrigerant. Whereas, in other systems refrigerant is directly responsible to cool air.

- In Chillers, water is circulated by using pumps, and water density are lesser than the density of refrigerant. Therefore, the circulation of water requires less power consumption compared with refrigerants. (80% to 90% saving of running cost in chiller).

Types of Chillers

There are two types of cooling systems in Chillers. They are
* Air Cooled Chillers.
* Water Cooled Chillers.

Air Cooled Chillers / Air Cooled Chilling Systems

In Air Cooled Chillers, condensing unit is cooled by atmospheric air by means of condenser fans or axial jet fans. In this chiller, when high pressure and high-temperature refrigerant comes out from the compressor it is passed inside the coils of the unit enclosed in the fins. Due to the high temperature of the refrigerant gas, the unit becomes hot, when the air moves over the unit it picks up the heat of the unit forces the gas to become liquid inside the coil. This change of phase from gas to liquid is known as condensation and the unit is known as condensing unit. If Air is the mode of heat transfer or heat pickup, then that condensing unit (Condenser) is known as Air Cooled Condenser and the corresponding chilled is known as Air Cooled Chiller.


- Air Cooled Chillers are mostly used for High rise buildings (Residential / Commercial).
- As Chillers are placed on the Roof Top of High Rise Buildings, Because of the higher altitude (height) wind velocity is also High. Because of this, they pick up the heat of the condensing unit quickly and thus make the condenser air-cooled.

Water Cooled Chillers

In Water cooled chillers, Condensing unit is cooled by water, and water gets cooled by means of the cooling tower. In this chiller, the condenser and evaporator look alike (same) and consist of a shell and a bigger diameter barrel and tube (coil) which we can commonly refer to them as the shell and tube type of heat exchanger. Water is made to move over tubes or coils using pumps, water comes out as hot water which is actually picking up the heat of the refrigerant and when the refrigerant heat is taken out it becomes a liquid. This change of phase from gas to liquid is known as condensation and heat is carried out away by water. Therefore, it is called water-cooled chiller.


- This type of chiller is mostly used for buildings having 1 or 2 floors (low-rise or medium-rise buildings) like Airports, laboratories, hospitals, campuses, etc. 

- These chillers are good in efficiency over outside temperatures above 120 °F also.

Chilled Water system (in short)

* Air-cooled chiller - Taking help from axial fan/jet fan.
* Water cooled chiller - Taking help from cooling towers.
- Change of temperature from 45 °F - to 55 °F in the evaporator.
- Here water is touching the refrigerant coil and Air is touching the chilled water coils.

Comparison between DX system and Chilled Water System

DX System.

- Refrigerant is directly responsible for cooling air.
- Usually, we use jet fan mode to cool the air.
- This is a non-centralized AC system.
- Initial Capital Cost is low.
- The life span of the DX system is short up to 5-8years.

Chilled Water System.

- First Water gets chilled by refrigerant and then chilled water is responsible to cool air.
- We use cooling towers and jet axial fans as a mode to cool air.
- This is a Centralized AC system. 
- Initial Capital cost is high, but it pays for itself later.
- Lifespan is higher. Goes for decades and decades.

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