Improving Economizer Efficiency

January 16, 2015 By Karen Henry

rooftop hvac energy manageFor facility managers looking to save money on air conditioning electricity costs, an article in Buildings recommends adding an air-side economizer, which draws in outside air as a form of free cooling.

Here are some tips to maximize the cost-savings potential of an economizer:

1. Climate. Economizers are suitable for facilities of any size and type, but hot, humid climates are generally not a good fit since the outside air is typically not cool or dry enough to bring inside and could increase the risk for mold and mildew inside the building. An economizer works well in the winter because the air is typically cold and dry.

2. Installation.
 Economizers should fit within the existing HVAC footprint, so retrofits don’t require huge structural or mechanical changes. For an economizer that is installed alongside an existing HVAC system, the facility manager should plan for a larger outside air intake, a larger relief air opening, proper damper sizes and appropriate controls. A relief air fan may also be required. The HVAC system should be able to maintain the appropriate ventilation when the economizer is not running.

3. Parts. Components such as dampers should be made of robust materials like aluminum or galvanized steel so they can withstand the climate and the rigors of time. The enthalpy sensor should be calibrated properly so the economizer can compensate for the differential between the total heat content of the outside air and inside air. Fixed or differential dry bulb-based controls may be more appropriate than enthalpy-based controls.

4. Smart controls. A dedicated BAS monitoring system allows facility managers to monitor the economizer’s performance and receive alerts in the event of mechanical problems. It’s critical to program a set-point that disables the economizer if the temperature is too hot or humid.

Schneider Electric incorporates air economizers in one of its data center reference designs.

Photo via Shutterstock.

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