Describe Operation and Maintenance Air Conditioning Units?
Operation and Maintenance Air Conditioning Units
Planning design and installation of the Air Conditioning units
Operation Air Conditioning Units :-
We have discussed various topics about planning design and installation of the Air Conditioning units. To get the best out of the air conditioning system we must keep the unit in healthy condition. Operation is the vital activity responsible for better performance of the air conditioning unit. Normally we use window A.C. split A.C and air cooled type package A.C. unit. Now we shall discuss the points to be observed for better operation. Through the operation and maintenance are interrelated we shall discuss these items separately.
A. WINDOW A.C. UNIT :Maintenance Air Conditioning Units
i) Proper connection of the electrical cable ;with the related switch gear is required.
ii) Proper voltage should be available. If low voltage or fluctuation prevails ;in supply source, voltage stabilizer is to be installed.
iii) In case of abnormal noise from the unit it is to be switched off and service man is to be called in.
iv) In case of malfunctioning of the unit the matter is to be put to the knowledge of the maintenance authority.
v) Once the unit is off it should be switched on only after elapsing of at least 3 minutes, so the pressure of both side of compressor is equalized.
B. SPLIT A.C. UNIT :- Maintenance Air Conditioning Units
i) Since the design and working of split A.C. Unit is more or less similar to that of window A.C. unit, same precautions are to be adopted. Only differences are that the compressor and condenser unit is installed outside of the building. To observe the abnormal noise and malfunctioning in the compressor – condenser unit the user is supposed to inspect this item occasionally.
C. PACKAGE A.C. UNIT :-
The design and function of the package unit are slightly different from that of window A.C. unit ;for proper operation we should observe the following points :-
i) Proper voltage should be available (3 phase)
ii) It should be 415 6%.
iii) Volume control damper should be open.
iv) After switching; on the unit we should observe the suction pressure is less, there will be less cooling, sometimes may be formation of ice just after the expansion valve. Under these conditions the plant is not to be operated.
v) In case of abnormal noise in the blower section/compressor the plant not be operated and the matter is to be reported to the maintenance staff.
Maintenance in Air Conditioning system is the main activity responsible for better performance of the system. Now we will discuss the method of servicing, repair i/c attending the defects.
1. WINDOW A.C. UNIT :-
In the Bharat Sanchar Nigam Limited normally we use 1.5 TR window A.C. unit, both in technical and administrative buildings. There are various manufacturers in the market. The basic principle of this unit is same. However, there may be minor design differences in electrical wiring and physical shape. The tentative wiring diagram is given below (Annexure –‘A’).
First we will have to operate the selector switch to switch on the blower motor. The blower motor may have two speeds or three speeds. On operating the selector switch further the connection is extended to the thermostat and then to the compressor through the over load. From the outgoing of the overload direct supply goes to the running winding and to the running capacitor. The other terminal of the running capacitor is connected to the starting winding. The overload has inbuilt coil as shown in the diagram, through which starting capacitor gets supply through a normally braking contact. The starting relay is provided to disconnect the starting capacitor after the compressor get started. The connection of the relay coil as well as breaking circuit has been shown in the diagram above.
After operating the selector switch it is observed that the blower motor functions well. As soon as it picks up speed the compressor should be switched on by further actuating the selector switch. Now the compressor should pick up the speed. If the compressor does not pick up the speed and gives humming abnormal sound it means that it has some starting problems and the matter is to be put into the knowledge of the maintenance staff.
If the compressor does give any kind of sound at all there may be the discontinuity in the connection ;of the compressor such as – in the thermostat, overload, and selector switch. In that case also the maintenance staff is to be intimated.
For purpose of maintenance of window A.C. Unit following points are mentioned.
1. Cleaning of Filters :-
Most of the complaints are occurred due to dirty filters. The filters may be of various types., viz – Coir filters, synthetic filters or metallic filters. These filters require regular cleaning. Normally cleaning once in a week may be sufficient. However in the dusty area the frequency of cleaning may be increased.
Accumulation of dust particles on the filters chokes it and reduces the air flow drastically. It may cause ice formation on the evaporator coil. This occurs due to insufficient air flow through the coil and liquid refrigerant does not get enough heat to vaporize. It may cause liquid flood back to the compressor and damage the compressor. The choking of the filter causes overloading of the blower motor. So, dirty filter is the major factor causing damage of the window A.C. unit.
|1.||Failure of compressor||i. Supply failure
ii. Selector switch faulty
iii. Failure of thermostat
iv. Disconnection in over
|i. Check the main supply
ii. Check the selector switch
iii. Check the thermostat for its continuity.
iv. Check the overload for its continuity
|2.||Compressor fails to start produces hum sound, trips on over load||i. Starting winding broken
ii. Running capacitor faulty
iii. Starting relay is not
iv. Starting capacitor faulty
v. Heating coil of the
overload may be broken
|i. Check the continuity of starting winding, resistance should be 3.8 ohms.
ii. Check the Run Capacitor
iii. Check the starting relay for its energisation .
iv. Check the starting capacitor.
v. Check the continuity of heating coil of the overload
|3||Starting relay burnt out||I . High Voltage
ii. Compressor short cycle
iii. Incorrect running capacitor.
|i. Voltage correction is required
ii. Check as per recommendation of the manufacturer
|4||Starting Capacitor burnt out||i. Compressor short cycle
ii. Relay contact sticking
|i. As discussed above
ii. Check the relay contact point for their proper functioning .
|5||Running Capacitor burnt out||i. High voltage.||i. Voltage correction is required .|
|6||Head pressure too high||i. Poor condensation
ii Unit overcharged
iii. High ambient temperature .
iv. Choking in strainer / capillary tube .
|i. (a)Condenser is to be cleaned .
(b) Air flow is to be checked
ii. Suction and discharge pressure is to be checked .
iii. Water splashing
arrangement is to be made
iv. Replace capillary tube / strainer .
Norms of Engine Alternators For Different Types of Telecom Installation:
In view of the present difficult power supply position, it has become necessary to provide suitable standby power plant equipment so that as far as possible the telephone exchanges work uninterrupted without having to shutdown either partially or totally. This necessitates provision of Engine Alternator in all the installations.
The following guidelines have been approved for provisioning of standby engine alternators.
|Capacity required for SMPS , Battery, Air-conditioning , DG set and MSEB Supply|
|0.5 K RSU||2K RSU||2K MBM||5K MBM|
|Qty||Cap.||Qty||Cap .||Qty||Cap .||Qty||Cap.|
|Bty.||2||200 AH||2||400 AH||2||1000 AH||2||2000 AH|
|PP(SMPS)||1(3+1)||25 A||1(3+1)||100 A||1(5+1)||100 A||1(9+2)||100 A|
|Inverter||Nil||Nil||1||1KVA||(2+1)||1 KVA||(3+1)||1 KVA|
|A/C||(1+1)||1.5 TR||(2+1)||1.5 TR||(2+1)||7.5 TR||(3+1)||7.5 TR|
|(1+1)**||1.5 TR||(1+1)**||1.5 TR|
|DG Set||1||10 KVA||1||30 KVA||1||75 KVA||1||100 KVA|
|MSEB Connection||5 KW (1- Phase )||25 KVA ( 3 Phase )||60 KVA ( 3 Phase)||80 KVA (3 Phase )|
|AVR (Servo type)||1*||10 KVA||Nil||Nil||Nil||Nil||Nil||Nil|
|Note :- * wherever supply fluctuation demands for stabilizer|
|** For A/C of PP room|
|At 2 K / 5 K MBM , Provision for 1 WLL , BTS has been met .|
These standards will broadly cover the requirements of most of the exchanges. However discretion will have to be exercised by the local officers regarding the capacity of the Engine alternators. In all cases, the Engine Alternator set must feed the total busy hour load of the local exchange/exchanges, the trunk exchange, the transmission equipment etc located in the same building and should also meet the load of blowers of A/C Plants and minimum lights and fans required for operation.
Provisioning of Engine Alternator may be treated as protective works and estimates sanctioned accordingly.
Maintenance Air Conditioning Units, Maintenance Air Conditioning Units
GUIDELINES FOR OPTIMIZATION OF ENGINE ALTERNATOR CAPACITIES.
- For the purpose of the calculating Eng Alternator capacity, following load and their peak demand may be considered.
Sl.No Type of load Load Peak Load
|E.I. & Fan
Administrative & General
|III.||Lifts||As per actual||100%|
|IV.||Pumps||As per actual||50%|
|V||Compound Light||As per actual||Nil|
|VI.||Fire Fighting||As per actual||Nil|
|VII||Air Conditioning Load (A/C Load – Essential only)||2.25 KVA/Ton||100% for main units and nil for s/by. (*)|
(*) This will include load on account of Window A/C also.
- Exchange Power Load
(i) C-DOT :- (As per information received from ADG(XT))
2K 2.5K 3K 3.5K 4K 5K 6K
7.5KW 8.5KW 9.25KW 11KW 11KW 12.75KW 15.65KW
** Add 0.75 KW for next 1 K each upto a total capacity of 10K
As per information received from ADG(ES-II)
10K 15K 20K
20.93KW 26.76KW 32.56KW
iii) Other new technology Exchanges :-
As per ADG(ES-II) U.0. NO. 40-18/94-ESL-II Dt. 15.4.97
|10K 20K 30K 40K 50K||20.93KW 26.76KW 32.56KW 38.38KW 44.19KW||O.8w/line O.8w/line O.8w/line O.8w/line O.8w/line||1SKW
|20.4KW 36.0KW 50.0KW 64.0KW 80.0KW||26.188KW 58.333KW
b) Rectifier efficiency 75%, Power factor = 0.7, Peak Load-100%
- Provision for unforeseen load may not be taken.
- For calculation of Eng Alternator load, telecom bldgs may be classified into three categories.
- G+1 bldg. at Tehsil For substation purpose, load may be taken for Taluka (H/Q) full A/C and ultimate capacity of switch room.
- G+2 bldgs. at For the purpose of Eng Alternator capacity for District (H/Q) * G/F – as per usage
* 1st Floor – Complete load including A/C for two switches of ultimate capacity.
* 2nd Floor -Only E.I. and Fans Load. When usage is not definite otherwise as per actual.
3. Multistoried bldgs (i.e. to be decided in consultation
more than G+2) Metro’s with all the concerned Telecom units.
and mini metros.
Annexure – I
Department of Telecommunications Engineering Instructions
Clause 3: Standard operating conditions:
The standard operating conditions are:-
- Mean barometric pressure 736 mm of mercury, corresponding to altitude of 300 meters above mean sea level.
- Intake air temperature 35º C
- Humidity – Water vapor pressure of 27.4 mm of mercury, corresponding to a relative humidity of 65 percent at 35º C.
- Intake air depression and Equal to that obtaining with intake and exhaust back pressure exhaust systems normally fitted to engine recommended by the manufacturer.
- The engine shall be driving all continuously running auxiliaries which are, in service, mechanically connected to it, and which are necessary for engine operation, such as coolant and lubricating oil pumps, scavenging blowers and, in the case of air- cooled engine only, the cooling fans.
Note:- For water cooled engines, in view of the wide choice of size and type of radiators available to meet particular site requirements, the Indian Standard rating specified in 4.1 shall be the power which the engine would develop if the radiator fan was not driven by the engine.
The normal power requirements of an engine driven radiator fan and a starter battery charging dynamo shall be stated for those engines which are commonly so equipped.
Clause 4 Rated Power Output and Speed
The Indian standard rating of the engine shall be the net output in brake horse-power of which it is capable of delivering continuously at rated crankshaft speed in revolutions per minute when working under conditions specified in 3.1 provided that the engine is in good operating condition.
When an engine is required to work under conditions which depart from the standard conditions specified in 3.1 the rated output of the engine at site conditions shall be determined as follows:
- For decrease in the atmospheric pressure, a deduction from the rated output of the engine shall be made at the rate of 1.4 percent per 100 metres of altitude about 300 metres. This de-rating is valid upto an altitude of 2500 metres above mean sea level. For higher altitudes, the de-rating shall be agreed to between the purchaser and the manufacturer.
- For any increase of the intake air temperature above 35% a further deduction shall be made at the rate of 0.25% per degree centigrade where combination of high atmospheric temperature and humidity occur, a further percentage deduction from the rated output of the engine shall be made in accordance with Table I which is based on a deduction at the rate of 1.75 percent/cm of mercury above 27.4 mm vapor pressure.
Percentage Departing For Atmospheric Humidity At Various Temperature:
|Atmospheric Temperature||Relative Humidity Percent|
|in O F||10||20||30||40||50||60||70||80||90||100|
Maintenance Air Conditioning Units, Maintenance Air Conditioning Units,
Note:- The reduction for humidity is related to the percentage (relative) humidity and the corresponding temperature of the surrounding atmosphere.
Care should be taken to use the percentage humidity actually corresponding to the maximum atmospheric temperature being considered. It is very rarely that high percentage humidity is combined with very high temperature of values which justify more than 6 percent de-rating for humidity in any part of the world, and this figure may normally be taken as a maximum.
Inlet air at actual engine intake is, in many installation heated significantly above the ambient atmospheric temperature, and this increase the reduction for temperature. The reduction for humidity should not be wrongly enhanced by applying a fitter for atmospheric percentage humidity to that locally elevated inlet air temperature.
Where the site conditions are more favorable to the engine than the standard conditions, an increased rating for the engine to suit the site conditions may be agreed to between the manufacturer and the purchaser.
Examples of de-rating for altitude, temperature, and relative humidity are given below:
Maintenance Air Conditioning Units,
Example 1 –
A kirloskar engine of 200 BHP is installed at a place whose worst site condition are given below . The engine is four stroke turbo charged without after cooling .
- Altitude – 500 mtr
- Maximum temp. in summer – 45 0 C
- Humidity –30 %
Calculate the output of the engine under above mentioned conditions.
A) Duration due to altitude = x 2.5 = 1.75 %
B) Duration due to temperature = x 3 = 8.1%
C) Duration due to humidity = 1% (After interpolation of the reading at temp 110 0 F and 115 0 F)
Total duration = 10.85 %
So , the output of the engine will be at site = x (100 x 10.85)
= 178.3 BHP
Maintenance Air Conditioning Units,
The engine manufacturer shall state the specific fuel consumption (SFC) at no load and the specific fuel consumption (SFC) at rated output under the standard reference conditions specified in section 1 of IS:- 10000(Part II) – 1980 for engines of all ratings . All engines above 20 KW , SFC shall also be declared at 110 , 75 , 50 and 25 % of the rated load . The consumption shall be stated in grams per brake horse power in the case of liquid fuel engines and in terms of heat units per brake horse power hour in the case of gas engines (based on the higher calorific value). A typical generating set will consume above 0.3 ltrs . of fuel per KWH generated .
Where site conditions are worse than standard reference conditions specified in section 1 of IS:- 10000(Part II) – 1980 , the specific fuel consumption at site will be higher than that under standard conditions and shall be increased at the rate of 3 percent for every 10 percent de-rating in the power output of the engine. A tolerance of 5 % on fuel consumption at full load shall be allowed unless otherwise agreed to between the manufacturer and purchaser. Maintenance Air Conditioning Units,