ET23SWE0071 - Field Evaluation of Ultra-Efficient, Compressor-less, Packaged Rooftop Unit with Integral Energy Storage
This project is an Emerging Technology Field Demonstration to evaluate the efficiency, cooling performance, and load shifting/demand flexibility, of a liquid desiccant- enhanced commercial packaged rooftop unit with integral energy storage. This tests a new class of equipment referred to by the US Department of Energy as a Separate Sensible and Latent Cooling (SSLC) air conditioning (AC) system on a commercial building. This technology uniquely brings high performance under extreme conditions. The project includes independent evaluation, measurement, and verification services.
The equipment is designed for use as a sustainable replacement for the ubiquitous compressor-based, direct expansion, packaged rooftop equipment, found on most commercial buildings under 300,000 square feet. For this project, the packaged rooftop design is sized to deliver 2,000 CFM of conditioned air with at least 30%, and up to 100% fresh air in the supply air stream. The unit can be used in dedicated outdoor air supply (DOAS) and/or return air unit applications.
One of the key differentiators is independent control of latent and sensible cooling. A novel conditioner core uses a low flow of non-corrosive liquid desiccant to dehumidify the mixed outdoor and indoor return air streams in combination with a dew-point-style indirect evaporative cooler that provides sensible cooling. The unit is designed to operate in all combinations of indoor and outdoor air, ranging from hot/humid through hot/dry. Integral thermal energy storage provides load flexibility with 6 hours of peak load shifting. The packaged unit includes a novel, electrically-driven, low global warming potential (GWP) refrigerant heat pump with small refrigerant charge to produce low grade heat which is used to regenerate the liquid desiccant. System cooling capacity and energy efficiency increases as ambient temperature increases, eliminating the negative impact of air conditioning load during heat waves and eliminating the need for equipment oversizing to meet design day cooling loads. The technology has a high turndown ratio, eliminating partial cooling load inefficiency.
The Project will install one unit on an existing commercial building and independently measure and evaluate the performance throughout the summer cooling season.
This report provides the results of a field demonstration of an ultra-efficient, dedicated outdoor air system with integral energy storage. The project evaluates the humidity, temperature, cooling performance, efficiency, and peak load-shifting capability of a novel emerging technology described as a liquid desiccant-enhanced dedicated outdoor air system with integral energy storage. At its core, the technology combines liquid desiccant with indirect evaporative cooling and thermochemical energy storage. This air conditioning technology fundamentally reimagines how buildings are cooled, dehumidified, and interact with the grid.
The host site for this project is a grocery store located in Gardena, California, in California Climate Zone 8. The unit operates 7 days a week for 18 hours per day, delivering 2,500 cubic feet per minute of conditioned 100 percent outdoor air into the main sales area at a 55°F dew point. The unit is comparable to a conventional 15-ton direct expansion dedicated outdoor air system.
An energy storage, liquid desiccant, dedicated outdoor air system achieves energy efficiency beyond the theoretical limit of a conventional direct expansion dedicated outdoor air system. However, energy efficiency alone is not the complete solution for achieving California’s deep decarbonization goals, because not all kilowatt-hours are valued equally, and therefore an important integral feature is dispatchable load shifting. The idea is to utilize excess renewable energy—for example, from 9 a.m. to 4 p.m.—and draw the energy from storage from 4 to 9 p.m., saving and shifting energy use.
An energy storage, liquid desiccant, dedicated outdoor air system helps futureproof buildings and electric utility distribution systems against weather-driven electricity consumption and associated peak demand from compressor-based air conditioners as the frequency and duration of heat waves with rising dew points increase. The efficiency of an energy storage, liquid desiccant, dedicated outdoor air system improves with rising ambient temperatures, while its supply air dew point remains consistent. The coincident peak demand of an energy storage, liquid desiccant, dedicated outdoor air system is not correlated with peak temperature, a key attribute for providing load flexibility and enhancing the resilience of California’s summer grid. The field data from this project were used to train a regression model for estimating the energy and peak-demand savings of the energy storage, liquid desiccant, dedicated outdoor air system compared to a baseline direct expansion dedicated outdoor air system. The regression models were applied to multiple locations in California (climate zones 8, 12, and 15) to evaluate the energy savings of the technology under different climate conditions. Those results are presented in Table 1 along with the energy saved during the peak period of 4 to 9 p.m.
The field test results showed that an ultra-efficient dedicated outdoor air system with integral energy storage has the potential to substantially increase distribution grid resilience during periods of extreme heat, futureproof buildings against the increased frequency and duration of heat waves with rising dew points, advance building decarbonization by storing and shifting excess renewable electricity, and reduce costs for ratepayers by lowering electricity use and peak demand, while shifting consumption to take advantage of time-of-use rates and utility-sponsored load management tariffs and incentives.
Recommendations
Study findings show that energy storage, liquid desiccant, dedicated outdoor air systems’ energy savings, peak-demand reduction, and load-shifting capabilities are substantial when compared to a baseline direct expansion dedicated outdoor air system. In the field study, only 8-16 percent of the total energy used by the emerging dedicated outdoor air system evaluated occurred during the peak hours of 4 to 9 p.m. It is recommended that additional field evaluation of the final commercial product be conducted to validate the energy savings determined in this project and provide additional data for measure development. Future efforts should both inform the development of new code requirements and identify potential barriers to broader adoption and codification of these advanced systems.
Feedback from diverse stakeholders—including building owners, tenants, architects, electric utilities, regulators, and the sustainability and engineering community—has been universally positive. Beyond its efficiency benefits, energy storage, liquid desiccant, dedicated outdoor air systems address the critical need for flexible building loads that can integrate as dynamic and predictable grid resources. Despite this widespread recognition of energy savings and load shifting potential, adoption rates remain low, primarily due to risk aversion associated with emerging building-integrated products. This CalNEXT project aims to reduce that risk and accelerate adoption for the benefit of ratepayers and society at large.