Lead Performer: National Renewable Energy Laboratory – Golden, CO
July 10, 2023
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Lead Performer: National Renewable Energy Laboratory – Golden, CO
Partner: Trane Technologies
DOE Total Funding: $1,400,000
Cost Share: $150,000
Project Term: January 1, 2023 – December 31, 2025
Funding Type: Lab Award
Project Objective
Decarbonizing the U.S. electric grid requires renewable power and storage options, widespread energy efficiency, controls enabling timely consumption, and a shift away from fuel-fired equipment. Many larger commercial and multifamily residential buildings use central boiler and chiller plants to provide hot and chilled water to distributed air handling units located in different zones within the building. In the U.S., 30% of commercial floorspace is heated with a boiler, and most of these buildings are larger than 50,000 square feet. Heat pumps allow these hydronic systems to be driven by clean electricity (from renewables onsite or the connected electric grid), yet less than 15% of commercial buildings utilize heat pumps for space heating, typically with smaller systems in warm southern regions. Three key barriers are preventing widespread adoption of air-source heat pumps for these central systems in cold climates:
- Significantly lower efficiency and heating capacity at cold temperatures, with backup electric heating elements lowering efficiency even further.
- The use of defrost cycles (heat pumps operating in cooling mode) to remove frost built up on outdoor coils, requiring backup electric-resistance elements to counteract cooling the building.
- Peak heating demand is in the cold early morning hours when building loads are highest and heat pump efficiency is lowest—but this does not coincide with peak wind or solar generation.
In this project, NREL and Trane will design, size, and develop controls for a heat pump + ice thermal storage system, improving heat pump efficiency and flexibility, and expanding the use of ice storage tanks from solely summertime cooling load shifting to winter energy recovery and flexibility. During the project's initial phase, the team will design the model and system for the heat pump + ice thermal storage system, guided by insights from an advisory group regarding buildings, climates, and HVAC systems, and formulate a commercialization plan. Subsequently, the team will determine the optimal thermal storage size for chosen applications and climates, while creating a model-predictive controller for efficient storage use throughout various seasons. The project will culminate in demonstrating the system and controller's performance in NREL's hardware-in-the-loop (HIL) lab.
Project Impact
The primary long-term impacts of this project are:
- Reduce energy use and peak demand for electrified heating systems, decarbonizing space heating in cold climates by removing fuel-fired equipment.
- Quantifying the barriers to efficient and load-flexible technologies like the heat pump + ice storage system to ensure its deployment throughout the United States, including in disadvantaged communities.
Contacts
DOE Technology Manager: Payam Delgoshaei
Lead Performer: Jason Woods