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

Commercial HVAC systems have long relied on gas‑fired heating paired with separate chilled‑water, but the industry has yet to establish a clear, effective pathway for fully electrifying large central plants. Engineers face steep learning curves with new equipment, and the complexity of integrating all‑electric components has slowed progress at a time when rapid building decarbonization is urgently needed.Early all‑electric designs have typically relied on air‑to‑water heat pumps (AWHPs), but these systems often struggle to meet performance and cost objectives. AWHPs have limited cold‑weather efficiency, narrow operating ranges, and large space requirements that make them difficult to retrofit into existing buildings. Heat recovery chillers (HRCs) can achieve higher efficiencies—but only when simultaneous heating and cooling loads are available—leading to common design oversights and misapplications on first‑generation projects.Time Independent Energy Recovery (TIER) is an innovative approach that integrates heat‑recovery chillers, thermal energy storage (TES), and AWHPs into a coordinated, all‑electric plant. Unlike traditional TES applications, which focus on shifting peak cooling loads, TIER uses TES to store and deploy heat recovery, enabling a cascading system that maximizes overall efficiency. TIER is estimated to reduce energy use by up to 40 percent compared with standard AWHP plants, while also reducing space requirements, first costs, and operating costs and supporting grid‑interactive building strategies.This project evaluated the first operational TIER installation, confirming that the system delivers higher performance than both conventional AWHP plants and its own modeled predictions. The installed system achieved an average combined heating and cooling COP of 5.5, compared to 4.0 for a comparable AWHP plant. These results reinforce TIER’s advantages in energy efficiency, compactness, cost-effectiveness, and grid support.Because current building‑simulation platforms cannot model complex central plants like TIER, the project team developed simplified spreadsheet tools to analyze TIER configurations using either hot‑water or condenser‑water storage. Modeling across three California climates and two building load profiles showed that TIER consistently reduces energy costs relative to chiller/boiler baselines, overcoming typical all‑electric “spark gap” cost penalties. Life‑cycle cost results did not produce a universally preferable TES medium or size; optimal solutions depend on site‑specific factors such as load profiles, part‑load equipment performance, utility rates, and opportunities to repurpose existing firewater tanks for storage.While TIER has clear performance advantages, system complexity remains a major barrier to widespread adoption. To address this, the project produced a design guide, example schematics, sequences of operation, and modeling tools to support engineers considering TIER systems. Lessons learned from early installations and from the analytical work included in this report can further improve implementation success.Finally, the report outlines a coordinated market transformation strategy to accelerate adoption. Interventions include workforce training, improved modeling tools, manufacturer engagement, design guidance, incentives, and supportive policy pathways. These actions focus on reducing perceived risk, simplifying design, and increasing industry familiarity—creating a roadmap for evolving TIER from an emerging solution to a mainstream, standardized approach for large all‑electric HVAC plants.