Evaporative Cooling Technology

Low-energy cooling system

In India’s predominantly hot climate, space cooling constitutes nearly half of a typical commercial building’s energy demand. Modern evaporative cooling systems are great low-energy alternatives to conventional refrigerant-based systems. They are relatively inexpensive, clean, energy-efficient and highly versatile. In this webinar Mr. Shamkant Mirashi – Head of Arka Clean Technologies, discusses evaporative cooling technologies available in the market and their applications along with case studies.

The principle of evaporative cooling stems from several traditional Indian cooling techniques, like ‘matkas’ or earthern pots used for cooling water, and blinds made out of khus which when sprayed with water cool the surroundings due to evaporation. Evaporative cooling technology is conceptualized using the same thermodynamic principle. It is most effective in hot and dry climate since it adds humidity to the air thereby providing thermal comfort. There are two types of evaporative cooling systems used commercially- direct and indirect. Both systems use water as the refrigerant, are low-energy and highly energy-efficient.

In direct systems, the outside hot air is directly cooled when it meets a cooling media. Water is sprayed from the top of the cooling media thus cooling the outside air down due to evaporation. A blower then circulates cooled air in the room.

The second type is the indirect system. In this, hot outside air passes through one side of a heat exchanger plate while the other side is sprayed with water. Due to the indirect contact between the hot air and the cool plate, the hot air cools down and is then circulated in the room through a blower. This can be used in humid climatic conditions as it doesn’t contribute to the increase in the humidity levels.

An even better variation is the indirect – direct evaporative (IDEC) cooling system that combines both direct and indirect technologies to derive maximum efficiency. This system is capable of achieving a supply air temperature of 220C, even when the dry bulb temperature ranges (DBT) at 400C. The air is first cooled through the indirect system and then further cooled with direct evaporative cooling.

This system finds application in providing outdoor thermal comfort in regions where the temperature shoots up to 40oC during the summers. An example of a project using IDEC is Bihar Museum in Patna. For the same DBT, the supply air temperature by the IDEC system is 40C lower compared to the evaporative cooling systems. Moreover, the air quantity significantly reduces in IDEC allowing for smaller capacity sizes.

IEC-assisted HVAC, that combines the indirect-direct evaporative cooling system with a conventional HVAC, can very well be the future of low energy cooling. Take a scenario where the outdoor air temp at 400C is to be cooled down to 150C. A conventional HVAC would consume substantial energy to achieve this. Further, it would need to operate at full load, thereby reducing efficiency. However, if a two-stage IDEC is connected to the AHU, the outdoor air would first cool down by 10oC or more in the IDEC system and then be cooled further by the HVAC’s cooling coils. The overall energy consumption by the HVAC unit would thus reduce. The IEC-assisted HVAC system also presents unique latent heat recovery for additional savings. This technology finds application in many commercial establishments, star hotels, data centers, healthcare etc. where the cooling loads are high, fresh air is mandatory and conventional heat recovery could lead to cross-contamination.

The type of cooling system plays an important role in the overall energy efficiency, comfort, operational cost of a building and its environmental impact. To summarize, evaporative systems are a clean and low-energy alternative to conventional HVAC systems, especially in hot and dry climate. Modern systems can allow improved sensible cooling, control of humidity levels and fresh air supply.

This webinar was conducted on 17th July 2019.