How to Install a package AC units?
Installation of package AC units (Air Cooled):
Purpose :- Now a days every Telephone Exchange requires Air Conditioning. The modern Telephone Exchanges install the Electronics Equipments. So, the installation of package A.C. units is one of the most important activities pertaining to the electrical wing.
Objective :- After discussion of this the trainees will be able to install the package A.C units in a proper &correct method, so that during their use there will be minimum complaints.
4.1 Co-ordination :-
The installation of package A.C. system in any building required utmost caution and coordination from the very beginning of the construction of the building/Exchange. After obtaining the working drawing the JTO(E)has to study the schedule of Accommodation thoroughly, specially the package room and the rooms which are to be air conditioned. During construction of the building following openings are to be made either in the walls or in the floors.
a) Opening for the delivery duct.
b) Opening for the return air duct/boxing.
c) Opening for fresh air fan in the package room wall.
d) Opening for refrigerant pipes and condenser cables.
e) Opening for main cable entry.
f) Opening for supply water pipe for humidification package unit and drainage pipe for condensed water.
4.1.1 Opening for delivery duct :-
If the duct drawing is available with the junior engineer, the opening is to be made as per that duct drawing. The openings are required in the package room, switch room or in any other room where A.C. ducts are to be provided. If approved duct drawing is not available with the JTO(E), the size of the opening is to be decided on the basis of permissible air to be delivered by the duct is to be known, and the number of package A.C. units i.e. their capacities are to be calculated.
As for example if two number of 7 TR capacity of package are kept as main and one number package A.C. is kept as standby, the approximate quantity of air to be handled by the main duct will be = 2 x 7 x 500 (500 CFM has been considered per TR) = 7000 cm. Now velocity of air to be delivered through the main duct is to be decided as per the recommended chart for duct design. As per this chart the maximum permissible velocity of air through main delivery duct is 500 meters per minute. Let us take 400 mtrs (1312 feet) per minute for this job. Now the cross section of the main duct will be 7000/1312 = 5.34 Sq.feet. the opening of the wall should be slightly more than the cross section of the duct, the opening may be 6 sq. feet (2 feet x 3 feet). In the same manner the opening for other branch duct etc. can be calculated.
4.1.2 Opening of return air duct/boxing :
In the same method as specified above the opening for return air duct or boxing can be calculated.
4.1.3 Opening for fresh air fan :-
Opening for the fresh air fan is kept in the package room. Generally the size of the fresh air fan ducting is 600mmx600mm. So the opening can be made as 610mmx610mm allowing the frame work for fixing the duct. The location of the fresh air fan should be such that the fresh air should not directly hit the delivery duct.
4.1.4 Opening for refrigerant pipes & condenser cables :-
This opening is also to be kept in the package room and the rooms through which the pipes are to be laid. This opening varies on the basis of number of package A.C. units. More the number, the opening should be more. For each package A.C. two pipes and one cable for condenser are to be laid. However for 4 Nos. package A.C. units the opening of 150 mm x 600 mm will be enough to accommodate 8 Nos. refrigerant pipes and 4 Nos. cables. The more the number of package unit more will be size of the opening.
4.1.5. Opening for main cable entry :-
Generally 3 Nos. cables are drawn from the sub station to the package room. The opening of size 150 mm x 300 mm will be sufficient. However, in place of that 3 Nos. holes of size 500 mm dia can be made in the floor or in the wall as per site requirement. It should be near to the main control panel.
4.1.6 Opening for supply water pipe :
The opening for supply water pipe can be decided after consultation with the civil engineering staff. The water supply can be taken from the nearest bath room or from the overhead tank. However, an opening of size 25 mm will be sufficient to provide 19 mm dia G.I. pipe for supplying of water for the humidification package.
4.1.7 Opening for drain water pipe :-
This opening is required to provide G.I. pipe to drain out the sweating water of the evaporator and over flow water from the humidification package unit. Generally 40mm dia. G.I pipe is provided for this purpose a hole of size 50 mm will be sufficient. The location should be to such a place so that water can be discharged either to the nearest bath room or the outside drain.
4.2.1 Receipt of Material & Inspection :
After award of work, the materials and equipments will be received by the Department specially, the package A.C. Units and condensers and the agency will ask for payments. As soon as the equipment reaches at site these are to be checked as per the technical specification mentioned in the agreement. Specially the motors, compressors etc. & their make, model No. etc. If any deviation in specification and the material/ equipments supplied is found, the matter is to be reported to the senior authority.
The equipment are also to be checked physically for the damages if any damage caused during the transportation, loading and unloading. If any damages are there, the details of the damages are to be intimated to the agency and to the senior authority for further necessary action at their end.
Damages of the condenser and evaporator fins reduce the efficiency of the unit. So the agency is to be asked to make the same good. If the damages are found to be heavy, the agency should be asked to replace the item i.e. condenser or evaporator.
4.3.1 Adherence to the specifications :
Before commencing the installation, the specification, package room layout plan and duct layout plan are to be thoroughly studied and match them with site condition. If there is any kind of difference, the matter is to be put to the higher authority. Materials brought at site by the contractor are to be checked as per specification of the agreement.
4.4 Location of the condenser :
Location of the condenser is to be decided as early as possible. While deciding the location following points are to be considered.
(a) Condenser is to be placed as near as possible to the package A.C. unit, so that the length of the refrigerant pipe is less.
(b) Sufficient fresh air should be available for cooling.
(c) There should not be any obstruction to flow of discharge air from the condenser or there should not be any short cycling of discharged air.
(d) Orientation should be considered. Fine or tubes of the condenser should not be exposed to direct sun rays.
4.5 Foundation :-
Foundation for the following items are to be made as per agreement.
a) Package unit
b) Control panel
4.6 Placement of the Equipment :
Before placing the equipment of foundation, JTO should be satisfied about the finishing of the foundation. Then ant vibration mountings are to be placed, specially for package units.
4.7 Ducting :
Generally G.I. sheets are brought at site and fabrication is done at site. So following checks are to be conducted specially besides the specifications.
a) Thickness as per aspect ratio.
b) Tie rods are to be provided from the ceiling.
c) Measurement of ducts before hanging.
d) Cross breaking are to be provided on the sheet to increase the strength.
e) Neoprene insulation is to be provided while making joints of two section of the duct.
4.8 Refrigerant piping :-
a) Refrigerant piping from the package unit to the condenser are to be laid on angle iron frame work.
b) Fixing of clamp should be done after wrapping that portion of the pipe with felt.
c) The route of the pipe should be decided in such a way so that the number of bends are minimum.
4.9 Brazing :-
a) brazing should be done with good quality of material and flux. If possible 3% silver rod may be used.
b) Acid should not be used at all as flux.
c) Before brazing surfaces of the pipes are to be cleaned.
4.10 Cabling :-
a) Cable should be laid on cable tray.
b) Two nos. loop earthing for each package unit.
c) Cable tray should be made in such a way that there should not be any sharp bend of the cable.
d) Cable tray should be made in such a way that there should not be any sharp bend of the cable.
4.11 Pressure Testing :-
a) After brazing the system should be cleaned by flushing with dry Nitrogen or dry air, so that the dust particles and carbon particles are removed from the system.
b) Now the leakage of the refrigerant piping system is to be checked. This is done by pressuring the system with dry Nitrogen.
c) On the high side i.e. condenser side around 350 PSI is to be given, whereas about 200 PSI pressure should be given to the evaporation side.
d) The pressure should be increased slowly. Now all the probable points of leakage may be checked by soap bubbles. Pressure and temperature are to be noted.
e) Keeping the system under pressure for 24 hours check the pressure again at the same temperature. If the pressure shows the same initial reading, it means that there is no leakage in the system. If the pressure is slightly decreased, observe it for another 24 hours.
f) If after 24 hours again there is further decrease of pressure, it means, there is minor leakage. Now the leakage is to be detected and rectified and get the system of vacuumisation.
After getting the system completely leak proofed we can put the system to the vacuumisation. For this purpose a good quality vacuum pump should be used which is capable of evacuation the system upto 5 micron. A two stage rotary vacuum pump is suitable for this purpose. The vacuum pump should evacuate at least vacuum upto 100 micron. However the pump should be run for 4 hours at least, so that the moisture content in the oil and in the system will get sufficient time to evaporate. Now let the system be kept on vacuum for 24 hours. Slight fall in vacuum may occur. This is due to the evaporation of moisture/water particles in side the system. After that vacuum should stabilized. If further fall of vacuum occurs, if means that there is some leakage in the system.
4.13 Purging :-
After leak test and vacuumisation we should do the purging. Purging means to break the vacuum with same type of refrigerant gas and have a positive pressure of 5 PSI. Again vacuum is to be done and purging is to be done again. After two nos. of purging the system should be vacuumised for gas charging.
4.14 Gas Charging :
Gas can be charged to the system from the high side as well as from the low pressure side of the system. If we want to charge the refrigerant gas in the liquid form, the gas cylinder is to be kept in inverted position and is to be connected to the high pressure side i.e. between the discharge line and expansion valve. However, during pouring gas, the compressor of the system can not be run. When the standing pressure of the system (for R-22 gas) reaches nearly 100 PSI the cylinder valve can be closed and the compressor can be run for a few minutes. Again gas can be fed to the system by stopping the compressor. In this process charging can be done till the operating pressure i.e. discharging and suction pressure match with the designed parameters.
Gas charging can be done from the suction side. However we should be careful enough so that liquid should not enter the compressor.
After doing the gas charging the compressor should run for a couple of hours to stabilize the system. Now check it up whether the discharge pressure and suction pressure are matching with the design conditions or not. Otherwise it will have to be checked that all the tubes of the evaporator are equally cooled. If so, it means that the unit is properly charged. If all the tubes of the evaporator are not equally, it means the unit is under charged and the reason is to be searched out.
4.15 Testing During Gas Charging :
During gas charging it has been seen that the system sometime charged with less quantity of gas. So far proper gas charging we should observe the following precautions :-
1. WINDOW AC UNIT:
a) The quantity of refrigerant gas is to be measured before charging. The quantity is specified in the technical booklet of the machine.
b) Suction pressure should match with the operating parameters of the machine or of the compressor.
c) Ampere taken by the machine should match with the rated ampere specified on the machine.
d) Charging should preferably done in the summer month.
e) Superheat i.e. the temperature difference between the ends of the Evaporator should be around 100F (5.60C).
f) We should also observed that most of the refrigerant ;tube of the evaporator should have equal temperature except the last tube, which is responsible for super heating.
2. PACKAGE A.C.
a) Suction and discharge pressure should match with the operating parameters. Where these parameters are not mentioned they should be obtained from the temperature.
b) Super heat i.e. the temperature difference between the ends of the Evaporator should be around 100F (5.60C).
c) Ampere taken by the machine should match with the rated ampere specified on the machine.
d) We should also observed that most of the refrigerant tubes of the evaporator should have equal temperature except the last tube, which is responsible for super heating.