Introduction to HVAC or Air Conditioning system

HVAC stands for Heating, Ventilation and Air Conditioning. It is a process of treating the air to control its temperature, humidity, filtering and distributing it to meet the comfort requirements of the occupant or people in the conditioned space (room). This article explains the components of an air-conditioning system, tips on selecting the right HVAC and the various types as well.

Temperatures at which people feel comfortable varies depending upon the season. In summer it will be 250C (780F) and in winter it is 200C (680F) with a relative humidity of 30% - 60%. The temperature can be measured in degree centigrade (0C = [(0F-32) x5/9)] or by degree Fahrenheit [0F =(0c x 9/5)+32]. Heat transfers from a hot body to a cold body through conduction in solid matters, through convection in liquids or radiation in gases. Heat also transfers through other ways or means i.e. Walls (exterior & partition), glass (windows/doors), roof, floor, people, lights (bulbs, tubes, decorative lights, etc) and equipment (computer, refrigerator, motor, mixers, etc.).

By using HVAC, we can control the temperature, humidity, filtration, and airflow. HVAC can be used in houses and villas (Residential), offices (commercial), hospitals and pharmaceuticals, Malls and theaters, Industries, Educational institutes (Schools, Colleges, Classes) and various others places( Aircrafts, etc).

HVAC unit
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Major Components of HVAC system

1. Compressor: It is known as the heart of the HVAC system which pumps refrigerant to the system. It separates the high-pressure system from the low-pressure system. If the compressor fails, there will be no cooling.

2. Condenser: It has coils which help to get rid of the heat from the space or room. It can be of two types, namely, Air-cooled type(located outside, in open) or Water cooled type(located inside, cooled with cooling tower). The condenser requires periodic maintenance and cleaning as dirt from air or water gets trapped in it.

3. Evaporator: It provides cool air into the room. This is located after the air filter. It helps in removing moisture from the refrigerant(air/water). As it filters dirt and dust from refrigerant(air/water), requires periodic maintenance.

4. Fan: The fan helps to intake fresh or ambient air from the atmosphere and helps to mix it across the evaporator coil. It is in front of or behind the evaporator coil.

5. Expansion Valve: It provides required refrigerant to the evaporator coil for proper cooling of the room. It separates the high-pressure system from the low-pressure system and is located at the evaporator coil. If the valve fails, it will cause compressor failure resulting in loss of cooling in the system.

HVAC - Basic working principle
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Refrigeration Cycle: The basic refrigeration cycle consists of 4 major components (Compressor, Condenser coil, Expansion valve and Evaporator). The hot air/water depending upon the system when compressed passes through the condenser coil, heat is rejected to outside(atmosphere), passes through the expansion valve, provides the required air or refrigerant for proper cooling and passes to the evaporator coil which helps in cooling of the refrigerant or liquid and sending the cool liquid or gas to the compressor. This is the basic refrigeration or cooling cycle. The refrigerant is normally referred in TR and 1 TR is the amount of heat to be extracted from the atmosphere(room) for melting one metric ton of ice in 24 hours or 1TR = 12000 BTU/Hr.

Selection of a proper HVAC system

1. Cooling load calculation: The factors to be considered while calculating the cooling load are, the space(Area) of the room, the glass exposed to sun and partition walls if any, the ambient temperature, the load due to light, equipment and occupancy, fresh air requirement, filtration and infiltration of outside air.
HVAC heat load calculation
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2. Equipment or system selection: The selection of the system depends on budget, need or purpose of HVAC, space and power availability, floor, beam and column layout, use of space and outside condition.

3. Air/Water or refrigerant distribution design: Depending upon the cooling required, system selection, one can design or select the type of refrigeration system, i.e. air, water or refrigerant system.

4. Evaluation of the system to be used: Once the above three is selected or calculated, we can evaluate the system with top-three selection for proper and accurate system selection.

Types of AC
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Types of Air conditioning systems

1. Direct Expansion (DX) system: A DX system has two types, Packaged and split type and are commonly used for houses, offices, etc. which directly cools the air supplied to the building as the evaporator is in direct contact with the air supply. It uses refrigerant vapor (expansion /compression) cycle to directly cool the air to and occupied room/office.

2. Chilled water/Air system: These systems are commonly used for large cooling capacity such as malls, factories, offices, hospitals, etc. Here Refrigerant act as the primary system and Water / Air to as its secondary refrigerant. Chillers (cooling tower) are used to remove heat from the water/air which is circulated through the system to absorb heat from the occupied space or room.

Depending on the system used, we will find many different types of Air Conditioning system. Some of the common types are:
a) Window AC - Window units are cheaper and make the most sense if it is for a small home or apartment and for the short run.
b) Split AC - Split air conditioner has 2 units (indoor and outdoor) which provide high efficiency and provide you more options.
c) Cassette AC - This is more appropriate for larger areas with limited space or no available walls to mount a split system or limited ceiling space for a ducted system and is cost-effective.
d) Packaged AC - An all in one unit which can be used for heating as well as cooling with the limited cooling area. This can be installed on the roof or on the wall of the building or home.
e) AHU (Dx & Chilled Water/Air) - An air handler is usually a large metal box containing a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers and is normally used in malls, shopping centers, theaters, hospitals, churches, schools, etc.

[Note: All the images used are from the internet free source and the souce of each image is given below of each picture.]


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