The Lutfey Loop combines the efficiency of a ground source heat pump with the convenience of an electric water heater to provide heating and cooling needs. A highly efficient heat pump is configured to simultaneously heat and cool two tanks containing an antifreeze/water mixture. Heat is added or removed from the system through auxiliary tanks placed directly on the concrete basement floor. The hot and cold tanks provide the structure with hot water, radiant heating, air conditioning, and refrigeration/freezing abilities.
The Lutfey Loop consists of four 50 gallon tanks each filled with an antifreeze/water mixture. The bottom two tanks are sitting directly on the basement floor each with a pump to move fluid to the top tank (yellow hoses) and a drain back to the bottom tank (white PVC pipe). A heat pump is placed in between to top tanks and serves to transfer energy from the cold top tank to the hot top tank. Both sets of tanks are insulated to minimize unwanted heat transfer.
A Raspberry Pi takes input from temperature sensors and uses relays to activate the compressor and various pumps. A WeMo Insight switch measures energy consumption.
This setup provides all of the heating and cooling needs of a structure including hot water, radiant heating, air conditioning, and refrigeration/freezing.
Depending on the tank temperatures and the current heating/cooling demands, the system operates in one of four modes– heating/cooling, removing heat, adding heat, and standby.
The heating/cooling mode starts the compressor and moves heat from the top cold tank to the top hot tank. This would occur, for example, during initial setup when the fluid in all of the tanks is around 16 degrees Celsius. Here is data from this situation.
Summary: Duration: 4.199 hours Increase in hot tank : 49.187 - 16.312 = 32.875 degrees Celsius Decrease in cold tank: 16.875 - -4.625 = 21.5 degrees Celsius Total Kilowatt Hours : 1.8916 kwh
From this data the Coefficient of Performance (COP) can be charted for the hot and cold tanks. As a reference, the COP of an electric hot water heater cannot be greater than 1.
Coefficient of Performance hot tank : 3.8194 cold tank: 2.4978 combined : 6.3172
When the hot water demands are greater than the cold water needs, the system pumps fluid from the lower cold tank to the upper cold tank. The top cold tank heats up and the colder fluid in the top cold tank is drained into the bottom cold tank and is heated. This extracts heat directly from the concrete foundation.
This pumping can be done while the compressor is running (see chart) to maximize the rate of the temperature increase in the hot tank. This can also be done periodically based on expected heating needs.
When it becomes necessary to remove heat from the system fluid is pumped from the lower hot tank to the upper hot tank. A common example would be in summer months when the air conditioning needs are at their peak. When the hot fluid drains into the lower hot tank it passively is cooled by the concrete. The graph of this would be similar to the previous chart, but with the hot tanks increasing at a smaller rate.
All of the pumps and the compressor are shut off when the hot and cold tanks have reached their optimal temperature range. The only energy consumed in this state is from the processor periodically monitoring the temperature sensor for changes.
Inexpensive installation : The simple design of the Lutfey Loop serves to minimize the upfront cost of the system.
Low operating costs: By combining the heating and cooling into a single system and using the concrete floor as a massive heat sink the system provides a system more efficient than anything currently on the market. This eliminates two compressors in a structure (assuming it has an air conditioner, refrigerator, and freezer) along with a system to provide heat.
Low Maintenance Costs: The layout of the components allows for relatively simple replacement of the compressor and pumps when they fail.
Low Power Demands: This system could be useful in remote locations with limited power. A relatively small solar array could run this system.
Location: A concrete basement is required for this setup to function correctly.
New Equipment: Modification of a refrigerator and freezer would be needed to work with the Lutfey Loop. This would require removing the compressor and allowing for a mechanism to pump fluid from the cold tank through the radiators.
Existing Structures: Installing the Lutfey Loop in an existing house may require modifications to the HVAC system to achieve peak efficiency.