Air Conditioning Installations PDF

___________________________________________________________________________ 10. AIR CONDITIONING OF OTHER INSTALLATIONS 10.0 WINDOW TYPE UNITS Air conditioners of the window type, are completely self-contained units, with the compressor, condenser, ev...

___________________________________________________________________________ 10. AIR CONDITIONING OF OTHER INSTALLATIONS 10.0 WINDOW TYPE UNITS Air conditioners of the window type, are completely self-contained units, with the compressor, condenser, evaporator, refrigerant piping and air filter, all assembled in a very compact assembly. The window units are usually of 1/2 to 2 tons capacity and fitted with 230 V motor upto 3 HP. Modern tendency is to employ sealed type motor-compressor units with the refrigerant piping system sealed-in with brazed joints, so that the leakage of gas is virtually eliminated and the unit may serve for long periods with hardly any attention. In these units expansion valve and liquid receiver are not provided. The refrigerant is controlled with the capillary system. The unit is so designed that it can be mounted on the window with small bracket from outside. Window units are particularly adopted when only few rooms are to be air-conditioned and they are widely separated. Window type unit has following advantages; Maintenance cost is less and very little, since the system is sealed. Ducts are not required. Occupy less space. Shaft seal is eliminated. No alignment problem. Better-cooling of compressor motor from the suction gas. The greatest disadvantage of the system is that since every thing is sealed, no repair can be carried out in field. The unit has to be repaired in workshop after cutting the sealed housing. The first cost of installation becomes 50 to 100% costlier than central unit when a number of units are employed for air-conditioning a large area. Periodic maintenance To enable the conditions of both of the atmosphere and unit to be healthy it is imperative to give a periodic maintenance to the unit. The period is to be fixed as per the experience gathered or as specified by the manufacturer. The following are the important aspects to be looked after during maintenance. Give attention to condenser coil, cooling coil and fan. 'Dust off these either by compressed air or brush it. CO2 may be used if available. ________________________________________________________________________ ___________________________________________________________________________ Hold the naked light in front to check the cleanliness in between. A hooked wire should be used to remove the foreign material Cooling coil need not be cleaned so frequently. Fresh air ducts should be cleaned and checked. Check the compressor mounting springs if external mounting is done. Replace them if necessary. Spring tend to loose its tension with age and this leads to noisy operation of the unit. Check the earthing connections. If necessary oil the dampers. View the unit slope. It should be 1/2 to 3/4" towards outside. Check the air fillers. 10.1 PACKAGE UNIT These units are functionally similar to the window models but are very much bigger in size and therefore arranged for floor mounting. These are available in several capacities i.e. 4,6, 8 and 12 tons. These units contain all the elements for cooling, dehumidifying, ventilating and circulating air and is quiet in operation. In larger sizes, the condenser is often water cooled and the necessary pipe connections will have to be made The compressor unit may be of the hermetically sealed, semi-sealed or open type. The control panel is conveniently located and provided with a 3 position switch marked 'OFF’, 'Fan', and 'Cool', in addition to a knob for setting the temperature at which the thermostat is to function. The disadvantage, however, is that the cost of installation is much higher than that of a central plant specially if large area has to be air-conditioned. 10.2 CENTRAL PLANT A central plant with full ducting is best suited for air conditioning of large buildings, theatres, halls and un-partitioned offices. In the central plant system, the airconditioning plant, comprising two or more heavy compressor units including the ancillary equipment like condensers and evaporators are located at a central point usually at the ground floor or basement. The conditioned air is delivered through a ducting system to all parts of the building. A duplicate ducting system is required to lead back the return air from inside, back to the central plant, to be dehumidified, cooled and recharged with fresh ventilating air to be circulated once again. The ducts are usually bulky and cumbersome as they have to handle large quantities of air. To accommodate them and keep them out of sight is a problem which often poses structural difficulties. In a large hall, network of ducting would be required to distribute the air uniformly to all parts. Individual DAMPER VANES are necessary to control the amount of air admitted at each outlet, as also at points where smaller ducts branch out. A considerable amount of adjustment and experimentation would be required to maintain the temperature variation within 1 or 2O C over all parts. ________________________________________________________________________ ___________________________________________________________________________ One advantage of this system is that the processing of air is centrally controlled and therefore a high standard of efficiency can be maintained. The compressor plant itself being large is sturdy and robust and could operate for long periods with little attention. Normally there should be at least two complete independent units, one a working set and the second a standby, Fig 1. SCHEMATIC DIAGRAM OF A.C. SYSTEM ________________________________________________________________________ ___________________________________________________________________________ Fig. 2 CENTRAL PLANT AIR CONDITIONING SYSTEM Apart from the objection of the large ducting, the other inherent disadvantages of the central plant system are: Adjustment of individual room temperatures, as required from time to time is not possible. Therefore, the system is definitely wrong for buildings which are spilt up into a number of small rooms, offices, hotel rooms and so on. It permits mixing of air, cigarette smoke, bacteria and odours between different areas and offices. The ducting occupies an appreciable space. ________________________________________________________________________ ___________________________________________________________________________ 10.3 DESERT COOLER The desert cooler works on the principle of evaporative cooling. A fan sucks outside air through a continuously wetted pad. The air in passing through the wetted pad gets cooled and humidified and this air is circulated into the room, where it picks up sensible heat and maintains fairly comfortable conditions as fresh air is continuously pumped into the room. The air from the room should be allowed to escape out through an opening at the farthest end of the room. 10.4 WATER COOLERS AND REFRIGERATORS 10.4.1 Refrigerator The majority of domestic refrigerators operate on the vapour compression system, the basic unit being a hermetically sealed electrically driven compressor unit which may be of the rotary pump type or reciprocating type. The unit is mounted at the base of the cabinet. The refrigerant commonly used is Freon22. The motor is generally of the high torque squirrel cage induction type using split phase design or employing capacitor start principle and operating on AC 230 volts 50 Hz supply. The usual expansion valve is done away with and replaced by one or more capillary The evaporator piping is fastened round and brazed to the freezer box. The condenser too is greatly simplified by laying the condenser tube to and fro over a single metal sheet and plate acts as a heat sink and dissipates the heat to air currents on the two sides of it. This type of construction eliminates the need for a condenser cooling fan. The top of the food storage space is reserved for the freezer unit for making ice cubes or storing foods for long periods at a low temperature. The rest of the cabinet interior gets cooled by convection currents of air set up by the freezer unit. The compressor unit starts and stops automatically under the control of an adjustable thermostat which in turn operates a relay. 10.4.2. Water coolers Water cooler is a machine working -on refrigeration system for cooling water for drinking purpose. The drinking water having temperature between 10OC to 13OC is preferred. As for the refrigeration system it is same which is utilized in airconditioning, refrigerators, etc. The water coolers can be classified into two main categories: Instantaneous water coolers Storage type water coolers It consists of a fabricated metal sheet work and the refrigeration equipments are installed inside. There is no storage tank for storing and cooling the water. The water is being cooled by the refrigerant no sooner the water flow starts. That is why, the name is given instantaneous water cooler. Here both evaporator coils and refrigerant coils welded together or one coil is passed inside the other coil (i.e. tube in tube arrangement) so that the maximum efficiency can be achieved. The evaporator unit is also insulated to avoid the flow of surrounding heat. The refrigerant takes away heat from water and changes to vapour. The ________________________________________________________________________ ___________________________________________________________________________ compressors used are normally hermetically sealed. The condenser is air cooled and a separate motor is provided for cooling the condenser. The capacity of this type of water coolers is small and another disadvantage is that in case of electric supply failure cooling of water will not take place. Storage type water cooler As the name employs, there is water storage tank depending upon the capacity of plant. The water is stored in stainless Steel tanks, G.I. tanks, or brass tanks. The evaporator coils are welded outside around the storage tank for heat exchange between the water in the tank and refrigerant passing through the evaporator coils. The condensing unit will continue to run so long the water temperature is not attained. The compressor used is sealed as well as open type. The refrigerant is being controlled normally with capillary in sealed units and. expansion valve in open type units. In some of storage water coolers the evaporator coils are directly kept in water as heat exchange will be good. But disadvantage is that the mineral salts of the water gets deposited over the evaporator coils and further heat exchange does not take place. In such cases the coil must be cleaned from the water, surface regularly. In addition to the above two types of water coolers, there are storage-cum- instantaneous type also. In this type, there is chiller of the cylindrical type in which a coil is inserted. First the refrigerant is expanded in the chiller coils, whereas water is flowing in the, chiller, as such the, water give heat to the refrigerant and then the same water flows in the tanks. The refrigerant, after passing through the chiller coils is again passed-in the outer tube of the evaporator coils fitted on the outside of the tank, that is why, it is called instantaneous cum storage type of water cooler. 10.4.3 Maintenance of refrigerators and water coolers: Small refrigerators, water coolers and domestic airconditioners employing sealed type units are designed to operate satisfactorily, for long periods without any-attention if used; with reasonable care. Leave well alone is an excellent rule to follow, tinkering should never be permitted. The insulation resistance of the wiring and bonding to earth of the body of the equipment should be checked at intervals of say once in 6 months to ensure safety. Defrosting the cooler unit and giving a general cleaning is necessary every now and then. ________________________________________________________________________