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Drinking water is the most essential requirement for every human being. If this water is available in a chilled form, it will be very nice to drink during summer. Water coolers are used to reduce the temperature of water irrespective of the ambient temperature. The water coolers also provide water at a constant temperature. They can produce cold water at about 7 C to 13 C.
This finds enormous application in our day to day life. For example, coolers are used in theatres, malls, hospitals, schools, offices, and so on. The thirst of the people those who are working in hot environment may be quenched by the cold water provided by these coolers.
It works with the help of a thermostatic switch which is set within the particular range. All coolers consists of basic parts that are the same as that of a refrigeration system such as compressor, condenser (usually air cooled), expansion device (thermostatic expansion valve or capillary tube), provisions are provided for water inlet and outlet. Basically there are two types of water coolers. They are:
- Storage type
- Instantaneous type water coolers
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1. STORAGE TYPE COOLERS
This type of cooler has all the parts that are used in a normal fridge that we use in our home. The basic parts being the compressor (usually a hermetically sealed compressor), condenser (usually air cooled condensers), expansion device, and an evaporator (the space where water is to be cooled). The refrigerant flows from the compressor to the condenser where the high pressure refrigerant vapor is converted into high pressure liquid refrigerant. From the condenser, the liquid refrigerant flows through the expansion device where the high pressure refrigerant is converted into low pressure, low temperature liquid refrigerant. The liquid refrigerant absorbs the latent heat from the water in the evaporator and gets converted into vapor refrigerant and flows to the compressor suction which completes one cycle.
In this type of cooler, the evaporator coils are soldered on to the outer surface of the walls of the storage tank. The water level of the storage tank may be maintained by a float valve. In this type of cooler, the disadvantage is that the time taken to bring the temperature down to the set value is more (i.e. the cooler will have to work for a long time since the mass of water in the tank is more). The thermostat senses the temperature of water and stops the machine when the set temperature has been achieved. When water is drawn from the cooler for drinking, an equal amount of water is being admitted in to the tank. When the temperature of the water increases more than the set point, the machine starts its cycle automatically.
This type of cooler finds a variety of applications such as in colleges, schools, hotels, etc.
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2. INSTANTANEOUS TYPE WATER COOLERS:
In general the instantaneous type of water coolers consists of two separate cylindrically wound coils. One coil is for the refrigerant and the other for water. They may be made of copper or stainless steel tubes. Usually both the coils are entwined and bonded together by soldering. The water is cooled by the refrigerant by conduction in the evaporator.
The instantaneous type coolers may be further classified as:
- Bottle type,
- Pressure type, and
- Self-contained remote type.
The water that is to be cooled will be stored in a bottle or reservoir. These are usually 25 liters bottles placed on top of the unit. A faucet is used to minimize the wastage of water. The drip receptor receives water that is not used and sends it to the drainage. When we operate the faucet, the water flows from bottle to the water coil through flow regulator. Now as the water travels through the coil, it loses its latent heat to the refrigerant in the evaporator coil there by reduction in water temperature is achieved. A thermostat is placed at the end of the water coil to the compressor start and stop according to the water temperature. This type of cooler may be used in hospitals, shops, home, etc. (The water cooler illustrated at left also provides heated water.)
In this type of cooler, water is supplied under pressure. The city water enters the cooler at the rear of the cooler. It is cooled initially in a pre-cooler. The waste water passing through the drainage line is also cool; hence this drainage pipe is wrapped around the fresh water pipe for pre-cooling thus reducing the cooling load for the cooler. The pre-cooled water is then taken to the storage chamber, where the refrigerant gains heat from the water. The outlet for water is taken from the bottom of the storage tank which may be a bubbler or a self-closing valve. A thermostat is used to control the temperature of water in the pipe to maintain a particular set point.
SELF-CONTAINED REMOTE TYPE:
This system consists of a mechanical refrigeration system, the water being cooled by the cooler which is remote from the desired drinking place. This remote cooler supplies cold water to the desired drinking place.
The thermostat is clamped onto water pipe at its outlet in an instantaneous type water cooler. The flow rate must be adjusted to match its capacity. If rate of flow is more, the cooler will not bring down the temperature of water to the set point and also it results in high evaporator temperature which in turn leads to high suction pressure of the compressor which may adversely affect the compressor motor.
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Bottle type cooler: http://en.wikipedia.org/wiki/File:Watercooler_Wikinews.jpg
storage cooler: http://www.homeshop18.com/homeshop18/images/product/krona/KRO14-KLL.jpg
Book reference: A text book of refrigeration and air-conditioning By R. S. Khurmi and J.K. Gupta