The environmental benefits of evaporative cooling
According to a Eurovent Industry Monograph (1), the European evaporative cooling industry is made up of about 45 manufacturers, almost exclusively SMEs (Small and Medium Enterprises), representing about 1420 people. This industry has a direct yearly combined turnover of about 265M EUR.
Based on declared and reassessed data, the total aggregated number of installed evaporative cooling equipment (not including the field erected equipment) in EU28 is more than 3.900 units.
Eurovent stresses that the ecological footprint of mechanical refrigerating systems greatly depends on the technology used to remove the condensation heat. Compared to cooling with dry air (sensible heat transfer), evaporative cooling is more efficient; with 1 kilogram of water, the heat removed is about 2.200 kilojoule (heat of evaporation) per °C, while with 1 kilogram of air, the heat removed is about 1 kilojoule per °C. The evaporative cooling principle is used in wet cooling towers, where water is distributed over a heat exchange surface.
Eurovent has conducted an extensive study called “Evaporative Cooling 2030?, which has simulated, on a year-round base, the typical behaviour of a refrigeration system using an air-cooled condenser and a water-cooled condenser using wet cooling towers.
The refrigeration system using wet cooling towers is the clear winner when it comes to a year-round CO2 footprint. This study has resulted in average CO2 emission savings of about 15,5% for industrial applications and 16% for HVAC applications.
The average installed base of air-cooled chillers (cooling capacity > 1.000 kW) per year in EU28 is about 530 units. By converting these air-cooled chillers into water-cooled chillers, emission savings of about 56.000 tons of CO2/ per year is fully achievable. It corresponds to greenhouse gas emissions from 10.800 passenger vehicles driven for one year.
Furthermore, a recommendation paper by Eurovent (2) states that a traditional “rule-of-thumb” approach to estimating water consumption in wet cooling towers has led to a “myth of very high water usage”. The paper details how users of evaporative equipment can get a much more precise estimation of water consumption by considering climate data and load profile.
The growing interest in evaporative cooling is confirmed by the technologies addressed by the finalists of the Global Cooling Prize – an “international innovation competition to develop super-efficient, climate-friendly and affordable residential air-conditioning solutions” – announced on November 15, 2019 (3).
Four of the eight finalists have submitted technological solutions using evaporative cooling:
- Gree Electric Appliances Inc. of Zhuhai, China, with partner Tsinghua University, has presented an innovative hybrid solution designed to have an automatic, climate-smart operation in three unique modes – vapor compression refrigeration (R152a-based), direct evaporative cooling, and ventilation – which will switch between each other or operate the three modes in parallel to each other depending on the outside weather conditions to provide optimized indoor cooling. The solution has a small solar PV panel integrated into the outdoor unit to further lower the overall grid-electricity consumption of the system.
- U.S.-based Kraton Corporation, with partners Porus Laboratories, IIT Bombay and Infosys, has designed an electro-osmotic membrane dehumidifier with a water-based direct evaporative cooling system to achieve air conditioning without using any refrigerant. By applying a small voltage across the membrane dehumidifier system, water vapor from the indoor air is ejected to the outside air, thus making the indoor air dry in the process. The dry indoor air is then cooled via a direct evaporative cooling process, where the moving air loses its heat to evaporate the water, and in the process, gets cooled.
- M2 Thermal Solutions, a startup company based out of the United States, has developed a cooling solution that uses a combination of evaporative cooler and membrane technologies to independently cool and remove moisture from room air, and this technology requires no compressor or refrigerant.
- Godrej and Boyce Mfg. Co. Ltd., based in India, with partner A.T.E. Enterprises Private Limited, has designed an advanced R290-based vapor compression technology integrated with indirect evaporative cooling and solar PV panel.
(1) EUROVENT INDUSTRY MONOGRAPH 9/1 – 2019 The European evaporative Cooling industry in a nutshell
(2) EUROVENT REC 9/13 – 2019 Evaporative cooling Equipment: How to evaluate and minimise the water consumption: