Field Testing of Climate Appropriate Air Conditioning Systems

This project is a field study evaluating the potential and current DR capabilities of climate-appropriate air-conditioning (AC) systems. Targeted DR and EE programs can help reduce high peak demand caused by increased AC use and address uncertainties with respect to generation and consumption caused by extreme weather conditions. This field study will analyze how automated and optimized DR technology can build and implement accurate relationships between DR lead time, customer incentives, DR duration, external environmental conditions, and building occupancy by understanding a building’s heating, ventilation, and air conditioning (HVAC) capacity and thermal characteristics.

In commercial buildings, a heating, ventilating, and air-conditioning (HVAC) system conditions (heats or cools) the building space and provides fresh outdoor air (ventilation) to the building occupants. HVAC equipment in the building can be a primary contributor to overall energy consumption and peak power demand during both summer and winter periods. In recent years, manufacturers have begun to develop commercial HVAC systems with higher energy efficiency and greater flexibility, using variable load capacity technology. The Variable Capacity – Rooftop Unit (VC-RTU) is one of the most advanced vapor compression rooftop air conditioners currently available. This report examines variable capacity technology as applied within unitary packaged rooftop air-conditioning units, an HVAC configuration commonly used in commercial buildings in the United States. The purpose of this study is to provide a resource for evaluating and potentially implementing a program for variable capacity rooftop units to promote energy efficiency, peak electrical load reduction, and/or increased flexibility (such as for demand response) in commercial space conditioning equipment. This study provides new information to the growing body of documented performance for VC-RTU equipment. By mapping efficiency, capacity, power draw, and air flow rates, in every operating mode, and across a range of climate conditions, this study paints a clear picture of the VC-RTU’s characteristic performance capabilities. The study also presents an application specific assessment of performance for the installation observed to better understand the system’s advantages in a particular application that posed a number of unique challenges. An objective of this project was to document practical challenges associated with installation and operation of this new type of system. With seven distinct modes of operation and a number of variable speed components the VC-RTU is significantly more complex than a conventional rooftop unit. Engineers, contractors, and end users are not familiar with the capabilities and setup requirements for these systems. The lessons learned through this study broaden our understanding of the technology, and should support the evolution of design guidelines, industry standards, and technology function. Additionally, this project evaluates and demonstrates new potential for otherwise unrealized demand response capability from new-to-market variable capacity commercial HVAC systems in Southern California. Southern California Edison (SCE) and their customers will benefit from this effort by unlocking a new resource for both utility based demand response and customer directed demand management. The results of this study demonstrate VC-RTU systems achieve superior high energy efficacy at full and part-load conditions. Observations support a 30% reduction in energy usage at peak load. Given additional capabilities to respond to a demand response (DR) signal while optimizing its performance, overall average savings for energy efficiency may be enhanced with the DR functionality, providing a good fit for an integrated EE/DR offering in the future. The research team recommends the VC-RTU unit as an effective replacement to increase the performance of existing RTUs in both energy efficiency and demand response. The performance increase was most pronounced at hotter outdoor air temperatures, which demonstrates significant peak energy savings potential. The project demonstrates the VCRTU achieves better efficiency than a compliant RTU across the full range of operating conditions. Part load efficiency is improved most, and efficiency at peak operating conditions is improved modestly achieving approximately 19% reduction in kW/ton. The technological opportunity presented by this type of advanced rooftop air conditioner will become features made common for future HVAC equipment, but recognize that in the interim there is a significant need for market familiarization and for EE/DR programs to introduce the broader market application for these solutions.