Imagine working hard on a very hot day outside and after finishing your task you are returning to your house. You are all covered with sweat, your mood is slightly irritated and you are drained. But when you enter your room with the air conditioner working, within a few minutes you are in a happy and much more comfortable mood. All thanks to WILLS CARRIER an American engineer who invented the first air conditioning unit. The number of methods experimented for cooling, heating, ventilation, conditioning of air. One such famous system is HVAC, which breaks into HEATING, VENTILATION, AIR CONDITIONING.


It is not like only people from the modern period started working on cooling systems; its roots are very deep in our past. Egyptian society is considered to be the first one to develop cooling systems. In Egypt, the climate is very hot and arid. ( temperature above 30oCand relative humidity less than 50%) They used to hang wet mats on the top of their doors so that heat is taken by water to evaporate and the evaporated molecule increases the relative humidity index. Romans used fresh water to circulate around their building using pipes. In ancient India, civilization settled along the bank of lakes or there were man-made lakes. Also, walls built by clay had a ventilation effect, and moisture within clay used to cool the air.


Imagine you are on a train journey from Novosibirsk (Siberian city of Russia) to Athens (capital of Greece) via Iran and Iraq. As Novosibirsk has extremely low temperature and low humidity, Iran and Iraq have a hot climate with less humidity and Athens with a hot and humid climate. As you start your journey, train coaches need to be well heated to raise the temperature to 25C and relative humidity up to 50%. As the train enters the terrain of Iraq coaches need to lower the temperature than outside and maintain 20C(air conditioning) and to increase humidity at 50%. Meanwhile, the fresh food supplies taken from Novosibirsk need to be stored in temperature below 0C so refrigeration is required. As the train enters Athens temperature needs to be lowered than outside temperature and humidity needs to lower at 50%. So for a comfortable journey at different terrain Temperature of 25C and relative humidity of 50% is required as it is termed as a comfort zone by ASHRAE (American Society of Heating, refrigeration, air conditioning engineers).

All the buildings are designed by using MEP aspects. MEP stands for the mechanical, electrical, plumbing aspect of a building. HVAC falls under the mechanical category and is responsible for taking 60% of total power input. The number of skyscrapers, residential buildings, hotels, shopping malls, trains, aircraft, ships, office complexes, hospitals is increasing. As they are in a nation’s growth and boosting the economy. They also attract people from abroad as workforce or investors. So it is necessary to adopt the best HVAC systems.

As electrical and electronic devices, the control system is widely used from all kinds of sensors to electronically controlled marine internal combustion engines. These components get heated up after use and their performance deteriorates due to heating and may cause complete failure of components followed by fire. So they need to be operated in a controlled environment of temperature and humidity. If humidity increases it can corrode the outer surfaces or cover.


The cooling system can be classified into two branches

1.Direct expansion system/DX: It is a system that uses refrigerant to cool the desired payload and reject heat to surroundings. This system consists of a compressor, condenser, evaporator, expansion valve. This is the most used in small apartments, refrigerators, surgery rooms, small server rooms, X-ray machine rooms. DX system is the most efficient system for cooling. it can produce a cooling effect instantly. But this system is only limited to small spaces because the distance between the condenser and evaporator can’t be too high. The system was held responsible for most of the CFCs (chlorofluorocarbons) emissions which were damaging the ozone layer. Refrigerants like R12, R22, R408 contain a huge amount of chlorine. But today HFCs are being used which are free from chlorine and do not harm the ozone layer Eg. R410a, R507,R134a.This system is best for refrigeration from 0.75TR TO 38TR*.

*1TR: TONNES REFRIGERATION, it is defined as cooling effect produce by 1000 kg of ice at 0oC for 24 hrs.

Direct Expansion
Figure- 1, Source: Internet, Courtesy:

2.Chilled water systems: It is a type of system where the refrigerant is used to cool the water and air is then supplied to FCU (fan and coil unit). This system is designed for big buildings, shopping malls, multistory buildings, hospitals, and industrial use. Refrigeration capacity varies from 15TR to 6000TR. This system consists of water chillers, AHU(air handling unit), and cooling tower. This system is not very efficient because energy input is higher due to the circulation of water to vertical and horizontal distances which require pumps. As chilled water has to travel from pipes, the temperature of water increases till the time it reaches AHU. This system is generally capable of fulfilling comfort conditions of 25C & 50% relative humidity.

Chilled Water System
Figure- 2, Source: Internet, Courtesy:


All the nations are working and seeking best HVAC systems for their transports, buildings, hospitals, schools, etc. it is one of the major subjects in town planning for countries with many climatic zones like U.S.A, China, Russia, INDIA, where climatic conditions are very different for each region. To keep the supply line, workforce, tourism, health, agriculture intact proper infrastructure with suitable requirements is required. In 2011 88% of new, single-family homes were equipped with HVAC systems. Today the Asia Pacific region is the dominating region for HVAC systems. In this region, China is emerging as the key player as it holds different climatic conditions and government laws are breeding the HVAC industry well.

India has focused to boost its HVAC industry by the foundation of ISHRAE in 1981(Indian society of heating, ventilation, and air conditioning engineers). Its main focus is to set standards for comfort zones, equipment, education, improving indoor air quality. Due to the true efforts today India’s HVAC market size is $3.9 billion and predicted to reach$5.9 billion with a 7% growth rate in 2024. As India’s infrastructure is improving and due to the availability of skilled mechanical engineers and technicians India could be the provider of the cheapest and efficient HVAC systems.

Authored By:- Cdt. Hardik Vats, TMI

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