Synopsis:

Variable Speed Solar Photovoltaic Heat Pump Compressor. Proof of concept to demonstrate a solar heat pump for advanced missions such as a lunar missions while at the same time, promoting commercialization of the technology for terrestrial applications.

NASA contract NAS-97113, Johnson Space Center

Shown here is Polar’s compressor with condenser and evaporator heat exchangers under test at NASA’s Johnson Space Center.

General Description (from the contract):

NASA JSC is investigating Solar Heat Pumps as a technology which will improve thermal control for future human space missions in hot environments such as the moon. Since this technology is very attractive for use on earth JSC's solar heat pump work has been structured as a dual-use development project. Vehicle solar air-conditioners and solar refrigerators are two commercial products which are potential outgrowths of developing this technology. JSC has completed a conceptual design for a solar photovoltaic (PV) powered heat pump which provides 50 kilowatts of cooling for a lunar base habitat (reference 1). Cooling is required from sun-up to sun-down with the greatest temperature lift required at noon when the thermal environment is the hottest. Studies have shown that a minimum mass system can be achieved by connecting a lightweight horizontal PV array directly to a variable speed compressor in a vapor compression heat pump. Heat pump power demand tracks PV power availability nicely, thus heavy and expensive power storage devices are eliminated. On earth, this type of variable speed direct-drive "solar compressor" would provide cooling in proportion to the amount of sunshine available and rely on thermal rather than electrical energy storage.

In order to demonstrate a solar heat pump such as the lunar base system described above (but on a small scale) and at the same time promote commercialization of the technology, JSC would like to procure a variable speed direct-drive solar PV heat pump compressor with motor and controller (hereafter called "solar compressor" The solar compressor will be installed in a solar refrigerator. A well insulated refrigerator cabinet of approximately 300 to 500 liters will be used and a cooling capacity of approximately 40 to 150 Watts is desired of the solar compressor. The refrigerator cabinet will incorporate a water/ice system to store thermal energy so that extra cooling can be done during the day to carry the system through the night. A nominal 12 or 24 volt PV panel with a maximum output of 120 Watts will be used as the only power source. The main challenges will be to overcome the typically high startup current of the compressor/motor without using a battery and to utilize the solar energy as fully as possible. An existing commercial PV panel will be used for testing at JSC (see Interfaces below) . The subject of this procurement is the variable speed direct-drive compressor with motor and controller (i.e. solar compressor) . The compressor must work with refrigerant 134a. A temperature feedback signal from the refrigerator will also be available for the controller to use.

Terrestrial applications include:

• Solar powered refrigerators in the 5 to 40 cubic foot range, freezers in the 3 to 20 cubic foot range, and dehumidifiers, ice makers, and beverage vending machines.
• Military applications include field portable freezers, refrigerators, ice makers, special freezing applications, and environmental control.
• Other commercial applications include: food and beverage dispensers for aircraft, bus, and train.
• Larger capacity compressors can be manufactured by Polar using the technology for solar air conditioning and larger freezers and refrigerators, etc.