Hygroscopic Cooling Tower for Reduced HVAC Water Consumption
Dr. Christopher Martin | University of North Dakota Energy & Environmental Research Center
The overall objective of this project, EW-201723, is to reduce the water intensity of Department of Defense (DoD) facilities that use evaporative cooling towers to dissipate heat from air conditioning, data center cooling, power generation, and various other industrial processes. Cooling towers are intensive consumers of water, yet they are also potential energy-saving devices and can be important system components to meet combined energy- and water-saving goals. The technology under evaluation in this project attempts to strike a better balance between wet and dry cooling so that the benefits of wet evaporative cooling can be applied during hot summer afternoons, but the needless evaporation of water can be curtailed during cooler times when conditions allow for efficient sensible heat transfer to the air.
Under this project, two demonstration units of a novel cooling tower technology designed to restrict water evaporation will be field-tested at sites that are characterized by hot, dry and hot, humid summer weather. Annual performance data will be collected and will include water savings, cooling efficacy, and operational costs. The result of a successful project will be a methodology for DoD energy managers to 1) estimate the technology’s cost-saving potential, 2) understand its operations and maintenance requirements, and 3) identify potential integration strategies.
The concept behind this project is to use a hygroscopic cooling tower to seamlessly vary the amount of sensible versus latent heat transfer in response to changing ambient weather conditions. In this mode of operation, the maximum amount of water can be saved for any combination of cooling temperature set point and ambient air temperature value. Water can be saved when the ambient air is cooler relative to the temperature set point, but evaporative cooling can be invoked during peak air temperatures.
This technology is expected to greatly expand the potential for water savings in traditionally wet-cooled applications. Conventional hybrid systems are too costly to effectively span the full range of dry to wet cooling performance, and as a result, their economically feasible range yields modest annual water savings of up to 20%. Life cycle modeling of cooling an air conditioner with a hygroscopic cooling tower suggests that 50% water reduction is a feasible target to provide significant water savings while also being economically attractive at today’s water prices. Other applications that have year-round operation or high cost water will be even more attractive as savings opportunities.