Electrifying Large Commercial Central Plants: Demonstration of TIER and Program Delivery Solutions

Standard designs for large commercial buildings rely on separate gas-fired hydronic heating and chilled water loops. This technology has slowly been refined with incremental energy efficiency improvements over several decades. The HVAC industry has not yet had enough time to establish how to serve large commercial building heating loads effectively and energy efficiently with all-electric equipment. Many engineers lack the expertise and time to keep up with new and rapidly evolving equipment needed in order to overcome the novel design challenges to combine the plant equipment into functional systems. To meet the urgent need to rapidly decarbonize buildings, the HVAC industry needs targeted support to overcome these new design challenges and barriers around system complexity and integration.  The first generation of all-electric large buildings has relied upon air-to-water heat pumps (AWHP), an approach that has had difficulty meeting design objectives and is cost prohibitive for most building owners. AWHPs are inherently inefficient during cold weather, have limited operating ranges, and have a large footprint (making that approach infeasible for existing buildings with limited space). Heat recovery chillers can operate at higher efficiencies to generate both hot and chilled water but only when simultaneous heating and cooling loads are available. Many early projects have struggled with the misapplication of new equipment and critical design oversights.   Time independent energy recovery (TIER) is a revolutionary all-electric heating and cooling plant concept that integrates heat recovery chillers, thermal energy storage (TES), and AWHPs to overcome the shortcomings of alternative all-electric plant configurations. Traditional TES is used to shift or reduce peak cooling loads, whereas TIER leverages TES for heat recovery. The result is a cascading all-electric system that maximizes heat recovery and smartly deploys the plant equipment to maintain the highest system efficiencies. TIER is estimated to provide energy savings of 40 percent compared to the current state-of-the-art all-electric central plants.  Though TES can have large space requirements, when sized appropriately in a TIER plant, the heat recovered in storage allows for dramatic reductions in required AWHP capacity, significantly reducing plant footprint and first cost. In California’s mild climates, the energy recovered from cooling loads alone can satisfy heating loads for most of the year. The AWHPs only operate when needed and to an intermediate temperature, which allows for higher efficiencies. Overall, the TIER design saves space, improves energy efficiency, supports grid-interactive efficient building initiatives, and reduces first costs and operating costs compared to alternative all-electric plant approaches.   Each of the equipment types in a TIER plant are commercially available, however, the proper design and control of the built-up central plants is complex and challenging to implement. The purpose of this project is to unravel the physics and operational characteristics of a TIER system. This project will leverage an in-depth performance review of the first-of-its-kind TIER plant for a new 300,000 ft2 building and expected to begin operation in early 2024. The Project Team will demonstrate the benefits of the concept and develop resources for supporting broader application and technology transfer. This will include a case study, design guide, and recommendations for utility program design.