The Lutfey Loop water heater utilizes two water tanks located in the basement of a building. The first tank is not insulated and is placed in direct thermal contact with the basement floor. The second tank is insulated like a traditional hot water heater and is placed near the non-insulated tank. A heat pump is placed between the two tanks and moves heat from the non-insulated tank to the insulated tank. The foundation of the building adds heat to the non-insulated tank passively over time.
Version 1.0: I put this together with two 50 gallon water troughs, the inside of an air conditioner, some Styrofoam, two small water pumps, and two temperature sensors.
Version 2.0: Functionally the same as the previous version, but polished up. The cold tank is on the bottom and the insulated hot tank fits inside the 100 gallon water trough.
2.0 Fully assembled
Lutfey Loop Benefits:
- installation cost similar to electric hot water
- 5 times more efficient than electric hot water heaters
- 100 times less expensive to install than traditional geothermal
This configuration takes advantages of traditional geothermal heat pump configuration by extracting heat from the ground. Traditional geothermal systems have the drawback of having to bury a series of tubes underground to collect the heat. The Lutfey Loop doesn’t suffer from this drawback since the heat is drawn directly from the foundation floor.
The Lutfey Loop is also superior to traditional electric hot water heaters because it only concentrates the heat where electric systems heat the water purely from electrical resistance. This allows the Lutfey Loop to be 5 times as efficient as electric hot water heaters.
This data was collected with the setup shown above collected from the temperature sensors connected to a Raspberry Pi.
50 gallons of water was heated up 90 degrees Fahrenheit in 8 1/2 hours using 3.9 kwh of electricity. The data demonstrates that heat is added to the system even after the cold tank stops getting colder. The temperature increase in the hot tank appears to be linear. The slight drop off of the insulated tank (red) is attributed to heat loss through the Styrofoam as the temperature rises.