HUMIDIFICATION & DEHUMIDIFICATION A cool recovery with humidifiers
Dave Marshall-George, sales director at Condair, examines how humidifiers can provide cooling to a building’s fresh air supply, in combination with energy recovery systems
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ecovering heat from a building’s extract air is a well-established method for reducing HVAC energy consumption during the winter. However, recovering thermal energy for cooling in the summer also offers huge potential. It is a greatly underused strategy and is currently nowhere near as well understood by building services engineers as its heat-recovery cousin. Now given the relative similarity in temperature between incoming and outgoing summer air, you might think that warm extract air from a room offers little potential for cooling incoming
air, other than on the hottest of days. And by itself, you’d mostly be right. However, by adding a low energy, evaporative humidifier to the exhaust airstream prior to an energy recovery system, the temperature of the extract air can be greatly reduced. This increases the potential for energy recovery from outgoing to incoming airstreams in the summer, allowing for up to 10K of very low energy cooling to be achieved. When water evaporates, it uses heat energy
from the air during the process. This evaporative cooling effect equates to around 0.68kW of cooling energy for every 1kg of water evaporated. A single evaporative humidifier can provide up to 1,000kg of water per hour
with a resultant 680kW of evaporative cooling, whilst consuming less than 1kW of electricity. So, by adding an evaporative humidifier to the extract airstream, an energy recovery system’s potential for providing cooling in the summer becomes significant. There are typically two main limitations for using evaporative humidifiers to cool in a HVAC system when used directly on incoming air. Firstly, the cooling capacity of the humidifier is dependent on the condition of the fresh air going on to the humidifier. Air with a high humidity prior to the humidifier will not absorb much water. So, without much evaporation, the resultant cooling can be
30 BUILDING SERVICES & ENVIRONMENTAL ENGINEER JUNE 2024
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