Improve Your Outdoor Economizer
Repair and improve your outdoor economizer. Economizers are outdoor intake dampers on most HVAC equipment that can be opened on mild days to use outdoor air to cool a building instead of running mechanical compressors. They can save a lot of money when they are working, and I don’t think many people would challenge me when I say most are not working. At the very least, you should inspect and test the operation of the economizer annually. Make sure the damper is not restricted and watch it open and close when commanded by the control sensors.
There are numerous ways to control an economizer with each giving incremental improvements in potential energy savings. Consider the following:
1) Dry Bulb Temperature: Open the outdoor air (OA) damper for “free cooling” when the OA is below 55 F. This is the most common method.
2) Enthalpy: Open the OA damper when the outdoor enthalpy (temperature plus humidity) is below a certain level. This method often correlates to the same 55 F setting on a humid day but a higher setting—such as 65 degrees–on a dry day, thereby allowing more economizer hours of operation.
3) Differential Enthalpy: This method compares the temperature and humidity of the OA to the indoor air. If the OA is cooler and drier than the indoor air, use the economizer damper and turn off the compressors.
4) Integrated Economizer: This method can be used in conjunction with any of the previous three. At certain temperature and/or humidity conditions, an integrated economizer is used in conjunction with the mechanical cooling. The economizer is basically the first stage of cooling and the compressor becomes the second, should the economizer not be able to achieve the desired level of comfort on its own.
On a tight budget, these improvements will have a large impact on your HVAC system and energy savings. In the coming issues of Retrofit, I will provide more strategies to improve the performance of your HVAC system to save energy and improve indoor environmental quality.
Other Resources
1. AEE’s Certified Energy Auditor and Certified Energy Manager, www.aeecenter.org
2. ASHRAE’s Advanced Energy Design Guides, $62 hard copy (or free download), www.ashrae.org/aedg
3. U.S. EPA and DOE’s Energy Star, www.energystar.gov
4. EPA’s Energy Efficiency and Renewable Energy, www.energysavers.gov
5. Your local utility’s Web site
Ryan Hoger, LEED AP, is a member of Retrofit’s advisory board and a product manager at HVAC Solutions Inc., a Chicago-based company. He is actively in involved in several local ASHRAE and USGBC committees and can be reached at [email protected].