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And the metric is also radically different. Therefore, IEER is not an ideal metric for the DOAS product.ĪHRI 920 has drastically different test conditions that are more appropriate for DOAS applications (See Table 3). IEER test conditions and efficiency targets optimize the design of equipment for space condition applications and not DOAS applications. So, it doesn’t make sense to test, rate, and optimize DOAS equipment in conditions that will never exist.ĭOAS product without energy recovery also tends to use 200-cfm or less per ton of compression which is just another indicator that the type of loads is radically different than standard space condition units. Similarly, a 65☏ ambient condenser temperature at the 25-percent load and 80☏/67☏ on the evaporator coil also seems like an impossible condition. Since it’s 100-percent outside air, therefore, the evaporator and condenser air qualities should generally be the same. However, the associated condenser air temperature of 95☏ at 100-percent load doesn’t seem possible. For IEER, the air quality of 80☏/67☏ dry bulb/wet bulb for the evaporator coil is a reasonable and even an expected condition for outdoor air equipment. Unfortunately, we use AHRI 340/360 instead of AHRI 920 for DOAS calculations, according to Bent, who added that such a practice could possibly leave their DOAS ratings below the existing federal minimum efficiency requirements.Ĭomparing AHRI 340/360 and its IEER rating to AHRI 920’s Integrated Seasonal Moisture Removal Efficiency (ISMRE) rating clearly illustrates the former’s shortcomings for rating DOAS.įor example, looking at AHRI 340/360 Tables 1 and 2, how do the IEER rating points apply to an air-cooled DOAS unit conditioning 100-percent outdoor air? Why AHRI 340/360 Should Not Be Used For DOAS Specs Department of Energy (DOE) regulate DOAS via ASHRAE 90.1’s minimum efficiency requirements. The certification program will help the U.S. An AHRI DOAS certification program is expected to be ratified sometime in the next two years, according to Ned Bent, associate certification engineer, AHRI. And, ASHRAE 90.1–2016 sets minimum efficiencies for DOAS product. The current standard AHRI 920-2015 laid the groundwork.

For more on DOAS use in high-performance buildings, click here.

Thanks to AHRI 920 Performance Rating of DX Dedicated Outdoor Air System Units, these complex questions are now being addressed.ĪHRI’s forthcoming standard 920-2018 due out later this year, continues the process for certified DOAS testing and establishes a clearer definition of efficiency ratings.

What should consulting engineers use to compare DOAS products?.

Has ASHRAE 90.1 set a minimum efficiency level?.

Can AHRI 340/360 and its Integrated Energy Efficiency Ratio (IEER) work for DOAS units?.

In addition, the minimum efficiency has been well established by ASHRAE Standard 90.1, Energy Standard for Buildings, Except Low-Rise Residential Buildings. This conjures several questions: The industry has for years compared packaged unit efficiency utilizing AHRI Standard 340/360, Performance Rating of Commercial and Industrial Unitary Air-Conditioning and Heat Pump Equipment. However, the absence of a test standard, certification program, and an efficiency rating target makes it near impossible for engineers and contractors to compare brands, models, and features. Louis, MOĭedicated outdoor air systems (DOAS) have become a staple of HVAC specifications over the last 20 years. By JOHN McKISSACK, P.E., Nortek Global HVAC, St.