The Great Debate: Water-Cooled versus Air-Cooled
A recent AHRAE Journal article by Omar Hawit, P.E. and Trevor Jaffe, P.E., addresses an ongoing debate about the efficiencies of water-cooled versus air-cooled HVAC systems. The authors note the historical idea of water-cooled condensers providing greater efficiencies when compared to air-cooled. However, they highlight some of the more recent considerations that should be used in a true comparison, such as geographical location, water trends, and fuel changes.
Areas with cool and dry climates may still see a more favorable difference in water-cooled machines, but for areas where resources, such as water and power, carry significantly higher cost, an air-cooled machine may provide significant cost savings. The cost of operation may be significantly higher on a water-cooled machine in those areas when an owner must pay for the water and the power for the cooling tower, in addition to the cost of maintenance to chemically treat the cooling towers.
The article doesn’t address an additional opportunity for efficiency gains and cost savings which is integrated free-cooling technology into air-cooled machines. The savings become even more significant in geographical locations with cooler winter months because of the automatic switching between mechanical cooling and “Free Cooling” in addition to reduced wear and tear on chiller components due to fewer running hours.
In summary, this will be an on-going discussion where there isn’t a right or wrong answer. There are too many variables to draw a conclusion on which option is best for a users’ operation without fully understanding the application, the geographic location and utility. However, air-cooled machines should be seriously considered as it may be more cost effective and provide greater energy efficiencies.
The full article, “Water-Energy Nexus: Heat Rejection Systems,” can be found in the September 2017 issue of ASHRAE Journal. Subscribers can view the digital issue here.