In this article, I’m going to discuss how does a chiller works / how chiller plant works. Installed a new chiller plant for supply AC to the packing section where I work. There are three air-cooled chiller units that are installed to make chill water.
The main parts of Chiller plant
- Chiller units
- Air handling unit (AHU)
- Ac duct lines
- Chill water pipes
- Feed pumps
The chillers will produce “chilled water” which is pumped out around the building to the Air Handling Units (AHU’s) and Fan Coil Units (FCU’s) which remove the unwanted heat from the building and transfer it into the chilled water loop. The chilled water will enter the AHU’s/FCU’s at around 6°C (42.8°F) and by the time it leaves the heat exchanger within the AHU/FCU, it will have risen to around 12°C (53.6°F) and will then make its way back to the Air Cooled Chiller to dump this heat into the atmosphere before repeating the cycle.
The warm return “chilled water” only enters the evaporator where it passes along the outside surface area of the inner tubes, which contain the refrigerant, it then exits at the opposite end having given up its thermal energy. The refrigerant is the only fluid that moves around each of the components of the chiller. It changes its pressure, temperature, enthalpy, and entropy as it moves around the machine and transports the unwanted heat away from the evaporator chilled water.
The Air Cooled Chiller has 5 main components.
- The compressor – typically screw, scroll or reciprocating
- The condenser – a bundle of horizontal pipes that contain the hot refrigerant, these are surrounded by a number of thin sheets of metal in the vertical axis. This helps distributes heat away from the tubes and into the air which is blown across the tubes and thin sheets of metal.
- Condenser fans – These suck air across the condenser coils, entering from the sides, and then force this air out the top of the unit upwards into the ambient atmosphere.
- Expansion Valve – This expands the refrigerant before it enters the evaporator
- Evaporator – This is where the chilled water is produced and the heat from the warm return “chilled water” is extracted, to be sent to the condenser.
Refrigerant cycle in the chiller
- The compressor is the driving force of the refrigerant. The refrigerant first leaves the compressor as high pressure, high temperature, and superheated vapor and then enters the condenser.
- When the refrigerant enters into the condenser, it will run along the horizontal pipes and transfer its thermal energy into the ambient air stream which is forced by the fans on top.
- As the refrigerant transfers its thermal energy, it begins to condense into a liquid. By the time the refrigerant leaves the condenser, it will be high pressure, medium temperature, saturated liquid.
- Next, the refrigerant enters the expansion valve. The expansion valve meters the flow of refrigerant around the system. The most basic type is the thermal expansion valve which controls the flow of refrigerant by measuring the pipe temperature at the evaporator outlet and will adjust the flow rate to keep the temperature within the desired set point.
- The expansion valve holds back the refrigerant and maintains the high pressure of the condenser. Inside the expansion valve, a small orifice allows a restricted amount of refrigerant to continue to flow. As it flows through this restriction it reaches the low-pressure side of the valve. This sudden pressure drop allows the refrigerant to expand from a liquid into a liquid/vapor mixture. As this occurs it will drop in pressure and temperature. The same amount of refrigerant flows through, it just has more space so it expands to fill this gap.
- The refrigerant then enters the evaporator and will pass through a series of horizontal tubes which are surrounded by the “chilled water” and these will flow in the opposing, counterflow to each other. By the time the refrigerant leaves the evaporator, it will have picked up the unwanted heat from the return chilled water and will leave as low pressure, low temperature saturated vapor. The chilled water will have given its thermal energy up to the refrigerant and will leave around 6°C (42.8°F)
Air Handling Unit (AHU)
The air handling units (AHU) are installed in the various parts of the building that are to be air-conditioned, in the place called air handling unit rooms. The air handling units comprise the cooling coil, air filter, the blower, and the supply and return air ducts. The chilled water flows through the cooling coil. The blower absorbs the return hot air from the air-conditioned space and blows it over the cooling coil thus cooling the air. This cooled air passes over the air filter and is passed by the supply air ducts into space which is to be air-conditioned. The air handling unit and the ducts passing through it are insulated to reduce the loss of the cooling effect.
The AHU pumps the designed external air, which will be treated in temperature and humidity, as well as the quality of components with different types of filters. This treated air will be carried to respective areas by means of ducting.
For a dual flows AHU, besides the first objective explained previously, the AHU will extract the air from the areas that can’t be recycled back in the AHU (air too polluted or areas which require a percentage of extracted air), and will be rejected out of the structure.
Objectives of the AHU:
- Fresh air intake (which replaces the air polluted)
- Air treatment (by filtration)
- Humidity and temperature control of the air supply
- Structure easy to install in each type of architectural configuration
- Minimal surface facilities required (specification important due to the m² price today).
- Noise reduction (no need to open any windows)
- Integrated regulation with software adapted to health services
- Plug and Play unit.
- Reduction of the ductwork and installation – Important saving of time and money.
The AHU is used to control the following parameters of the space.
- Air Movement
- Air Cleanliness
In the site, we used it for AHU connected duct. Phenolic foam pre-insulated ducting panel compounded with an aluminum foil of high strength, which takes phenolic foam as the core material with reinforcing the aluminum foil on both sides. Duct line connects to Diffusers by using Glass wool flexible duct, wire ties & Silicon glue.
Advantages (How Does A Chiller Works)
- It is lightweight
- Pre-insulated duct installation saves time
- Installation less expensive
- Pre-insulated ductwork can save space
- The ductwork can be easily modified in the site