Heat pumps of the future:smaller than a dime
September 02, 1994
RICHLAND, Wash. –
In the home of the future, tiny sensors may signal when a room is too hot -- and, in response, micro heat pumps embedded in the walls would immediately circulate cooler air.
Although this smart, energy-efficient house still is many years from reality, researchers at the U.S. Department of Energy's Pacific Northwest Laboratory are developing microscale technologies that may revolutionize energy use in homes, businesses and industry.
PNL researchers are creating a heat pump smaller in size than a dime -- so small that hundreds or thousands could be fabricated on a single sheet. Such sheets could be incorporated into the walls of homes and buildings and someday may replace conventional heat pumps, furnaces, air conditioners and ductwork.
These mini heat pumps could save much of the energy loss associated with conventional heat pump technology. No ductwork would be needed because the heating and cooling emanates from each individual pump. "Typically, 20 to 30 percent of the energy produced by a regular heat pump is lost in the ducts needed to carry air throughout the house," said Kevin Drost, project co- manager.
"Also, each time the heat pump cycles off and on, another 10 to 15 percent of its energy is lost," said Drost. With many heat pumps available, localized groups would turn on in stages, according to increased heating or cooling needs, instead of a single system turning on and off many times throughout the day.
And, since most homes have only one thermostat, some rooms get too hot while others are too cool. With the miniature heat pumps embedded in the walls, each room would have its own thermal control.
Like the conventional heat pump, the micro heat pump has three parts: an evaporator, a condenser and a compressor. PNL researchers have demonstrated successfully a micro heat exchanger that serves as a condenser and evaporator.
The heat exchangers are made by the same photoetching process used to make computer chips. Tiny channels, about the width of a human hair, are etched into a tiny piece of metal about the size of a dime. Much of the heat pump's work takes place in these channels. Refrigerant flowing through the channels evaporates or condenses, and heat is transferred to the outside.
"The smaller the channel, the more effective the heat transfer is going to be, due to the intimate contact between refrigerant and heat exchanger surfaces," said Bob Wegeng, project co-manager.
Efforts are focused now on miniaturizing the final compressor component, and PNL researchers expect to have a working heat pump ready in about three years. Once all three components can be miniaturized efficiently, they will be fabricated as separate layers and sandwiched together to make a sheet heat pump. Researchers say large-scale commercial development will depend on the efficiency of the micro heat pump and manufacturing costs.
The lessons learned by research teams in the process of miniaturizing heat pump components will be the foundation for developing other miniature technology systems -- perhaps small electric generators that produce power from a fireplace, wood stove or other heat sources in the home.
The micro technology work is funded by the U.S. Department of Energy.