The primary objective of this project is to demonstrate a 30% improvement in the energy efficiency of a standard 10kW heat pump used for building air conditioning by utilizing the PowerPanel* SkyRadiance passive radiative cooling system. Rather than dissipating indoor heat in a heat pump to ambient air, the SkyRadiance system cools water by passively radiating the heat to the sky, both day and night, and uses the cooled water to improve the performance of the heat pump. A self-contained water-cooled system for heat pumps is particularly suited to reduce facility energy loads in a water-scarce hot/dry environment (compared to, for example, evaporative systems). The secondary objective of this project is to use the measured data from the demonstration to refine energy balance models for sizing 10kW heat pump systems augmented by passively cooled water storage to cool occupied buildings across a range of regional conditions. In addition, successful completion of the project should also allow the development of a transportable heat pump system for use in remote locations.

Heat pumps used for air conditioning currently leverage ambient air, evaporated water-cooling towers, or the ground to remove heat from a heat transfer fluid. Given this, increasing the energy efficiency of heat pump systems in hot zones is challenging: air-sourced heat pumps become less efficient as the ambient air temperature increases above 35°C [95°F]; ground-sourced systems are expensive due to the high cost of drilling wells or burying heat transfer tubing; and evaporative water-cooling towers are often not feasible in zones with constrained water supplies. Increasing the energy efficiency of heat pumps for cooling indoor spaces on Department of War (DoW) installations requires new strategies.

Radiative cooling is a well-known phenomenon: with clear skies, heat is emitted from exposed surfaces on Earth into outer space, lowering the temperature of the surface. 3M Company (3M) has pioneered the design, production, and use of polymeric passive radiative cooling films (PRCF) that have the required high reflectance in the solar spectrum to reject incoming solar energy combined with high emittance in the mid-infrared spectrum to radiate surface heat to space and the surrounding air. PowerPanel’s SkyRadiance system incorporates an array of heat transfer modules with 3M PRCF, which can cool water by radiating heat to the sky. The system achieves effective sub-ambient cooling at night, allowing the use of the stored cooled water to dissipate heat from the building during the day, significantly enhancing the energy efficiency of heat pumps compared to air cooling alone. A successful demonstration will yield immediate energy efficiency improvements at the hot/dry site as well as performance data that will allow researchers at the Lawrence Berkeley National Laboratory to generate an analytical model that can be used for further deployment of the system at DoW facilities in a broader range of zones.

The anticipated advantage of this technology is the demonstration of easy-to-implement, cost-effective air conditioning systems that use 30% less electricity or 30% less diesel fuel for essential installations. Another significant benefit is that these systems do not require water for evaporative cooling, which is particularly advantageous in areas facing water scarcity. The demonstration system is designed to increase the energy efficiency of a 10kW heat pump system used to air condition a 1000 ft² building in a hot/dry zones. In addition, the project will yield a model for use in identifying relevant sites in other regional conditions. A techno-economic analysis, based on the confirmed conservative values for the operation of the system and typical electricity costs shows a 3.6-year return on investment for the system. (Anticipated Project Completion - 2028)