How many Types of Air Conditioning Systems?
Types of Air Conditioning Systems
There are various types of Air Conditioning systems and units are being used through out the work. Keeping in view the present needs and situations a few types of these units have been adopted in the Telephone Buildings.
In this lesson the discussion will be done regarding the types of the A.C units being used in the telephone exchange buildings, so that the trainees will be able to select them as per requirement of the buildings.
Now a days the Department is installing electronic exchanges which require constant air conditioning to maintain the desired temperature. These exchanges are generally housed in small buildings. So, following types of Air Conditioning units are found to be more suitable. These units are air cooled condenser type.
- Window Unit.
- Split Unit
- Package Unit.
1. WINDOW UNIT | Window AC : –
It is compact unit having air cooled condenser. The design of this unit has been done such a way that it can easily be installed or fitted in a window or a small hole made in the wall where sufficient atmospheric air is available for cooling of the condenser. That is why this unit is called Window unit. It is comprising of the following major parts
- Blower motor
- Electrical controls
All these components are fitted on a single bed plate. This unit has a constant flow liquid. This unit is made from 0.5 TR to 2 TR capacities. Mostly 1.5 TR windows A.C. are used in Telecom Department. It is compact unit, easy to maintain and install. This unit is factory charged and sealed.
It has some disadvantages also. It is operated on single phase A.C. supply. As such it can not sustain voltage fluctuations due its poor power factor. It does have humidity control. Since it required big opening in the wall, causes leakage and infiltration of outside dust particles.
This unit is used where small air conditioning load is prevailing, such as small exchanges administrative offices etc. it can reduce the humidity by sweating moisture, but can not increase the relative humidity.
It is also just like window unit. It is operated on single phase A.C. supply and having the similar components of window unit. The major difference of this unit from that of window unit is that compressor and condenser is put together on a bed place and installed outside of the building. The evaporator unit is made compact and can be installed at any place of the building. The compressor condenser unit is connected with the evaporator unit through two number of refrigerant pipes and control cables. It means we have splitted the window A.C unit in two portions.
It has the advantage of the window A.C. unit that it does not require any window for the installation, merely a small hole is required to draw the refrigerant pipes and cables. It decreases the infiltrations of outside air into the room. Other characteristics of this unit are more or less same to those of window unit.
It has some disadvantages over the window unit.
- Length of refrigerant pipe is more increasing the cost and decreasing the efficiency and effecting the performance of the unit.
- It requires separate platform for installation of the condenser compressor unit.
- More maintenance cost than that of Window unit.
The evaporator of split unit is very handy and compact and can be installed in horizontal and vertical positions. It is generally available in 3 TR.
PACKAGE UNIT | Package AC
The design of this unit is slightly different from that of window unit or split unit. It comprises of the following components :-
- Expansion valve
From the name it appears that all the items are packed in a single cabinet, but actually it is not like that, it is a split unit system. All these items are divided into two sections comprising compressor and evaporator I/c controls, is installed indoor. Like split A.C. unit both these sections are connected by the refrigerant pipes and cables.
The package A.C system can be provided with additional control system, such as :- Humidity control, fine filters, fire dampers etc. the package unit has thermostatic expansion valve with external equalizer which is capable of controlling the flow of liquid as per the load requirement with the help of the feller bulb clamped at the end of the evaporator. The package A.C unit is available in the market in various capacities. However, in B.S.N.L, we are using 5 TR, 7 TR and 10 TR. The 5 TR units are generally used in small exchanges ,7 TR and 10 TR units are used in bigger exchanges with plenum, fine filters and ducting system.
The packages units are having 3 phase A.C motors which can sustain more voltages fluctuations and better starting torque than single phase compressors used in window A.C and split A.C unit. For heavy duty purpose the package units are more suitable.
FACTORS AFFECTING AIR CONDITIONING LOAD
Air Conditioning is provided to maintain the temperature, humidity, and dust level, proper air circulation. Regular operations of the air conditioning system is required to maintain the above parameters. Why regular operation is required. Once it is cooled, it should remain cold. Since outside temperature is higher and causes changes inside the room. Heat is gained in room through various mediums. Following factors are responsible for quantum of heat gain.
- Orientation and location of the building.
- Type of the construction, materials, windows and doors.
- size of the room.
- telecom equipment etc.
- heat gain through delivery and return duct.
- fresh air.
1. TYPE OF THE CONSTRUCTION, WINDOWS AND DOORS :
we know that the intensity of Sunrays is on peak between 14.00 to 16.00 hours in day time when the Sun remains in the western sky. We also know that the latitude also influences the intensity of Sun rays. I.e.. heat gain. So, before commencement of heat load calculation we will have to mark the orientation on the working drawing of the space to be air conditioned.
- TYPE OF THE CONSTRUCTION, WINDOWS AND DOORS :
Type of building also affects the heat gain. Different materials have different co-efficient of heat gain.
- SIZE OF THE ROOM :
If the room is big, there will be more heat gain and vice-versa.
- OCCUPANCY :
In every Air Conditioned space there must be some persons who carry out the necessary work. Human body maintains a temperature 98.40 F which is much higher than the temperature of the room. So, there will be transfer of heat from the human body to the air of the room. Generally it is taken as 240 BTU/person/Hour, this is sensible heat. In the similar way in breathing every person expels moisture. It adds latent heat which is taken as 310 BTU/person/Hour.
- LIGHT :
Light adds reasonable quantity of heat load. The total wattage consumed by the light fitting/bulb is considered as heat load to the room. Now a day’s fluorescent fitting is provided. Generally one number 4’ (feet) tube consumes nearly 50 watts.
- TELECOM EQUIPMENTS :
In B.S.N.L, in the switch room only Telecom Equipments are provided with the computers etc. The heat load of the Telecom Equipments is to be taken from D.O.T. circular No. 3-1/Director/EW/97 dated 17.7.97 (Guidelines for Optimization of sub Station Capacities).
- HEAT GAIN THROUGH DELIVERY & RETURN DUCT :
Whenever the cold air passes through the duct it absorbs heat from outside air due to temperature difference. The heat gain through delivery duct is taken as 12.5 %, whereas heat gain in the return duct is taken as 5% of the total heat.
- FRESH AIR :
In a switch room fresh air is required to replenish the oxygen content for occupancy. So, fresh air is taken from out side. It contains moisture as well as high temperature. Means fresh air adds Latent heat and Sensible heat to the switch room.