Modified Geothermal Heat Pump Furnace and Water Boiler

(This page is under construction!)

Some basics:

"Geothermal heat pumps (sometimes referred to as GeoExchange, earth-coupled, ground-source, or water-source heat pumps) have been in use since the late 1940s. Geothermal heat pumps (GHPs) use the constant temperature of the earth as the exchange medium instead of the outside air temperature. This allows the system to reach fairly high efficiencies (300%-600%) on the coldest of winter nights, compared to 175%-250% for air-source heat pumps on cool days.
While many parts of the country experience seasonal temperature extremes - from scorching heat in the summer to sub-zero cold in the winter - a few feet below the earth's surface the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 45F (7C) to 75F (21C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger."
More details are Here

Unfortunately, in my climate an efficiency of almost all flat plate solar collectors is close to zero during cloudy or snowy days, evacuated tube solar collectors are still too expansive. And my huge solar tank in the form of an indoor lap pool is not ready.
Nevertheless, during the heating seasons the ground temperature (temperature of the concrete slab in my basement) is VERY STABLE (about 52-57 degrees Fahrenheit). As a matter of fact, in my area almost all houses have basement with a concrete slab.

Evaporators of modern Heat Pump water heaters are installed about 4-5 feet away from the floor level and they absorb heat from the surrounding air. Therefore, efficiency of these water heaters is too low in the cold climate or cold room.
My approach is more efficient in the cold climate or cold room, because the evaporator of my heat pump is installed at the bottom of heat pump and my heat pump extracts virtually endless underground heat.
It's also very important to note that since the evaporator is so close to the concrete slab, utilization of cold air by concrete floor is faster. This is the major difference in our approaches.
In my case the source of heat and the main heat exchanger is the concrete slab and concrete footing of my basement.

My basement concrete slab (floor) is about 1,000 sq. feet and concrete footing is 12" X 16" X 130'.

It's easy to calculate a COP of your heat pump based on these facts:
- 8.34 BTU's are required to raise 1 gallon of water 1 degree Fahrenheit.
- The Coefficient of Performance - COP - is the ratio of heat output to the amount of energy input of a heat pump.
For example, if your heat pump delivering 15,000 Btu/h with a total input of 1 kW,
the COP of your heat pump is: 15,000 (Btu/h) / (3,413 X 1 (kW)) = 4.4

In order to test an ability of your slab to transfer heat you should to performed some tests - see below.


  How a Heat Pump Works
"The heat pump system contains a fan that forces air through an evaporator (1). The evaporator contains a liquid refrigerant. This refrigerant evaporates and extracts heat from the ambient air.
The now warm gaseous refrigerant is then compressed (2) by the compressor which is driven by an electric motor. As it goes through the compressor the pressure and temperature rises. The refrigerant turns back into a liquid which is now hot.
  The refrigerant then passes through the condenser (3), which in this case is wrapped around the water tank. The hot refrigerant loses its heat which goes into the DHW.
The now cooler refrigerant then passes through an expansion valve (4), where it goes back into a gaseous state and the process begins anew." More details are here:


  Evaporators of modern Heat Pump water heaters are installed about 4-5 feet away from the floor level and they absorb heat from the surrounding air. Therefore, efficiency of these water heaters is too low in the cold climate or a cold room.


  Modified Heat Pump - Test Unit #2


This unit works perfectly as a simple and reliable heat pump Furnace - the first ever presented Indoor Heat Pump Furnace, "powered" by heat from the basement slab as a heat exchanger!

Cold drawer (optional) contains: pipes, fan and differential controller with two probes/sensors.
Differential controller turns the drawer fan "ON" when the temperature around the Evaporator is colder than outside temperature.


  Frosted Evaporator
(when Evaporator fan turns Off)


  Switching Relay


To control your furnace/water boiler you have to connect your thermostat to a Switching relay similar to this.


  COP for a Two-stage HPWH at Various EWT (Entering Water Temperatures

"Low EWT applications can be much more efficient than high EWT applications.
This Figure shows the COP of a typical two-stage HPWH at various entering water temperatures"
From:http://www.wescorhvac.com/HPWH%20design%20details.htm#Designing HPWH systems


  To make a heat pump water Boiler I decided to use my old water tank from electric water heater.

You can install a condenser coil inside of your tank or you can wrap the tank with condenser coil all the way to the bottom to transfer heat into the tank and heat the water. as GE did it for the Heat Pump Water Heaters


Useful links:
Thermal Conductivity of some common Materials and Gases
Heat Pump Water Heaters: Design Details
US Geothermal Heat Pump Shipments to Double
Digital scroll compressor technology
How to add freon to your heat pump



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