Function: Water coolers are used to give cold water having temperature, around 8°C to 16°C for drinking purpose.
Types of Water Cooler
The three types of water coolers are
- Storage type
- Instantaneous type
- Bottle type.
Storage Type Water Cooler
Figure 1: Storage type water cooler.
In storage type, tap water (water to be cooled) is stored in large size storage tank, surrounded by cooling coil (see Figure 1). It takes more time in the beginning to lower the temperature of water. It is generally used in schools, offices, hospitals etc.
Cycle used: Vapour compression cycle.
Refrigerant: R-134a.
The storage type water cooler has an evaporator coil soldered on the outside surface of the wall. The tank is made of stainless steel or GI sheet. The water level in the water tank is maintained and controlled by a float valve.
Construction:
Water cooler has a metal sheet cabinet. It consists of a hermetically sealed compressor, condenser, capillary tube, accumulator, refrigerant coil, water cooling coil, thermostat, relay, overload protection etc. Thermostat is provided to control the temperature of water. Separate inlet and outlet connections of water are provided to storage tank. Water level is maintained with the help of float valve to minimize the wastage of refrigerated water. A push type water tap is generally provided for drawing cold water.
Working:
When the vapour compression system starts to operate, the heat of water is taken up by the refrigerant flow through the evaporator coil and gets evaporated. This vapour refrigerant is sucked by the compressor, where it is compressed to high pressure, high temperature and is sent to condenser. In an air-cooled condenser, the heat content of refrigerant is rejected to atmosphere. A condenser fan placed in front of the condenser coils to produce artificial draught of air. This increases rate of cooling and refrigerant and condensation of vapour refrigerant into liquid refrigerant occurs in short time. From condenser outlet, the liquid refrigerant passes through a capillary tube to the evaporator coil and the cycle is repeated number of times, till the desired cooling of water occurs. As soon as, the desired temperature is attained by water in the storage tank, the compressor is cut-off by thermostat.
Applications: Used in offices, schools, hospitals, factories etc.
Instantaneous Type Water Cooler
Figure 2: Instantaneous Type Water Cooler.
Instantaneous type of water cooler gives cold water as and when required. The cooling coil is directly wounded on the tap water line. Therefore, as soon as water to be cooled enters the tap water line, it gets cooled instantaneously. The major drawback of instantaneous water cooler is slow delivery rate. This happens, when the cold water tap is opened more frequently and for long time. Here, water delivery rate is slow.
In case of instantaneous type of water cooler, evaporator consists of “two separate cylindrically wounded coils made-up of copper or stainless Steel”.
One coil is cooled as cooling coil and other one is water coil. In the Fig. 2, the cooling coil and water coil are shown separately for the illustration purpose. The liquid refrigerant received from capillary tube flows through the evaporator coil, whereas, water to be cooled is made to pass in the water coil through a filter and a flow regulator. Both coils are located closed to each other to permit heat transfer by conduction. Thus, the liquid refrigerant absorbs heat from the water by conduction reducing its temperature. Thermostat controls the ON/OFF operation of compressor to maintain the water temperature within the required limits. For this purpose, the feeler bulb of thermostat is located on the water pipe at its outlet end. In case of Instantaneous water cooler, it Is very important to control the flow rate of water as per the needed capacity of evaporating coil. If the rate of water is higher, the system will not be able to bring down the temperature of water to desired or required or set value. Therefore, high flow rate of cold water is required or desired, then high capacity evaporator should be selected.
Bottle Type Water Cooler
In bottle type, cold water is supplied from an inserted bottle, which is kept in the water cooler. Capacity of bottle is in few litres.
Capacity of Water Cooler
- Capacity of the water cooler is specified on the basis of volume capacity of the storage tank. It is specified in litres. For example: 50, 100, 200, 500 litres etc.
- Capacity of the water cooler is also specified on the basis of its capacity to cool a continuous flow rate of water at 10°C to 20°C from a specified temperature of the incoming water (say 32°C) under an ambient condition. In such cases, capacity of water cooler ranges from 45 to 190 litres of flow rate per hour.