This article from Trane's Engineers Newsletter addresses the critical topic of rating standards for Direct-Expansion (DX) Dedicated Outdoor-Air (DOA) units. These systems are essential for delivering conditioned outdoor air to occupied spaces, often working in conjunction with local HVAC equipment.
Understanding the Need for AHRI Standard 920
Historically, a specific industry rating standard for DX DOA units was absent, leading to a lack of prescribed minimum efficiency requirements in standards like ASHRAE 90.1. The introduction of ANSI/AHRI Standard 920 in June 2013 marked a significant step, providing a uniform method to rate the performance of these specialized units, which focus on dehumidifying 100% outdoor air to a low dew point.
Key Differences: AHRI 920 vs. AHRI 340/360
The newsletter highlights the distinct differences between AHRI Standard 920 and the more general AHRI Standard 340/360. While 340/360 rates general DX air-conditioning equipment based on cooling capacity and IEER, Standard 920 is tailored for DOA units, focusing on moisture removal capacity and efficiency (ISMRE). This distinction is crucial for engineers specifying equipment that handles significant dehumidification loads.
Impact on Efficiency Standards
With AHRI Standard 920 in place, ASHRAE Standard 90.1 has begun incorporating minimum efficiency requirements for DX DOA units. This article serves as a guide for specifying engineers to correctly cite AHRI Standard 920, ensuring proper selection and compliance with evolving energy codes.
For more insights and resources on HVAC system design, explore Trane's Engineers Newsletter and other educational materials.
