Understanding HVAC Economizers
At Design West, we strive to bring energy efficient designs at competitive construction costs. One the most useful equipment options we can specify in meeting this goal is called an airside economizer.
An airside economizer basically looks at the outside air temperature (OAT) to determine if it is cooler than the return air temperature of the space. If it is, it makes sense to bring in outside air, instead of return air, because it takes less energy to cool down the colder air stream.
Generally HVAC systems function to produce ~55°F supply air. Return air temperature generally range from 72°F to 78°F. When the outside air is less than 72°F we bring in as much outside air as possible and supplement the cooling with refrigerant based compressors to maintain the 55°F supply temperature. This lowers the time the compressors are on. The compressors are the largest consumer of energy for a HVAC system, so keeping them off inherently saves energy.
At lower outside air temperatures, we can completely shut off the compressors, saving vast amounts of energy. The equipment then just modulates the outside air and return air dampers to maintain the supply air temperature.
HVAC Economizers & Title 24
The 2013 Title 24 code cycle included a prescriptive requirement for adding economizers to all units with 5 tons of cooling and above. This will continue into the 2016 code update effective January 1, 2017. This is not just any old economizer, the Title 24 economizer requires gear driven dampers, automated fault detection, and specific setpoints that can only be accomplished by a relatively advanced controller among other requirements. All of this drives up the cost of the overall unit and subsequently sometimes it may be advantageous to pursue other paths of compliance.
New Title 24 economizer designs have eliminated the maintenance issues of yesteryear. While they are more expensive, in most applications they pay for themselves quickly.
If you have any questions about HVAC economizers feel free to get in touch, we’re happy to help!