Solarized geothermal heat pump describes our HVAC system.
I coined the terminology “solarized geothermal heat pump” to describe our own HVAC system. We utilize energy from both the sun (solar) and the earth (geothermal) to heat and cool our home.
A heat pump transfers heat to or from well water (which has direct thermal coupling to the earth). The solarized geothermal heat pump transfers the heat or cold from the well water into a holding tank next to the heat pump. The holding tank stores either hot or cold water from the heat pump. A circulation pump pulls cold water from the holding tank and distributes it through the radiant floor distribution network. The distribution network describes a grouping of radiant floor tubing along with zone control valves and of course the circulation pump.
Each of the zone control valves opens up to move water into its respective zoned tubing. The valves are in turn controlled by zoned thermostats that either call for heating in the winter or cooling in the summer. We usually change the heat pump heating or cooling modes back and forth twice a year. An internal heat pump jumper controls a reversing valve that changes the direction of heat transfer.
I have described the process of exploiting free geothermal energy for heating and cooling a building. Next I will describe a more complicated process, that of converting solar energy into energy the heat pump can use.
A solarized geothermal heat pump uses electrical energy derived from sunlight.
A heat pump does not make heat, but it does transfer heat. That heat transfer uses much less electrical energy than the heat energy it transfers. That same electrical energy is also used for powering all the other lifestyle conveniences in our home or shop. Now we will describe how the electrical energy is produced out of sunlight.
We convert the sun energy into electrical energy by using photo-voltaic solar panels and grid-tie inverters. Such equipment converts sunlight to DC electrical energy and ultimately to AC electrical energy. AC electrical energy is the form of energy our heat pump uses, not to mention all the other appliances that make our lifestyle possible.
The solar panels and their power optimizers convert the sunlight energy to a Direct Current (DC) form of electrical energy. The DC energy is not usable by either the heat pump or most other household appliances. We use grid-tie inverters to convert 350 volts of DC energy to 240 Volts of AC energy. Those same inverters conduct that energy onto the national energy grid utilizing very high tech electronics circuitry.
Consider purchasing a solarized geothermal heat pump as a financial investment.
The solar industry has made some very impressive technological breakthroughs in the past decade or so. Today you can purchase a very sophisticated and well-engineered solar panel system for prices people only dreamed of a few years ago. Most people in the US can now afford to purchase a solar system and pay back a loan is less than ten years. A ten year payback period is equivalent to ten percent interest paid to you in the form of energy savings. You can borrow money at six percent interest and make money off your purchase every month.
If you have money in a bank account, what are you waiting for? Where else can you get a risk-free ten percent return on your money these days? Energy costs seem to keep going up, so the investment is going to appreciate in value most years. I am only suggesting that some readers might have the right property and sun location to take advantage of these low prices. The US government has even sweetened the pie by offering a 30% tax credit for the purchase and installation of a solar system.
The mechanics of installing a solarized geothermal heat pump system.
The geothermal portion of our solarized geothermal heat pump system requires many functional components such as a well pump.
A well pump pushes our warm 60 degree well water up from the bottom of our 173 foot deep well. The pump only has to pump against a static head of about 60 feet. That is because the well water rises to only that depth below the ground surface. A 0.5 horsepower Grundfos submersible pump requires about 900 watts of power to lift the water to the surface. The pump also overcomes maybe 250 feet of resistance from 1.5 inch pipe and bends before reaching the mechanical room.
We use a 5 gpm pressure restrictor in the output (discharge) line from the heat pump primary. This keeps the water flow pretty constant compared to an adjustable water flow valve that was constantly changing. I decided to restrict the water flow through the heat pump to leave more water pressure and flow for the rest of the house.
Initially we started using a 1.5 horse power pump that used about 2000 watts of power. We then changed out that pump for a smaller 0.5 horse power pump that only drew about 900 watts of power. Instead of using a variable speed motor controller, I chose to use a Cycle Stop Valves mechanical device that is supposed to extend the life of the pump while it maintains pressure. The variable frequency motor controller did not reduce the energy load of the pump that I could detect, but it was sure noisy. The Cycle Stop Valve seemed to not change the energy requirements of the same pump, but it is totally noiseless and besides it is in the well.
A discharge well provides a place to exhaust the pure well water after heat has been extracted or added to it.
Geothermal heating people call a system such as our a “Pump and Dump” system. In our case, we pump the water out of a 173 foot deep well. Then we run it through the primary side of the heat pump and dump the water into a discharge well. The discharge well is also 173 feet deep and 100 feet downstream from the pumping well. The water returns to the same aquifer just as pure as it left. However we left the water either about ten to fifteen degrees hotter or colder than it started in the heating mode. The water leaves hotter than it started when the heat pump is in the cooling mode.
The discharge well can also serve as a spare well if anything ever happens to the primary well. It might be a good well for a manual well pump like our great grandfathers all used and there would be not other well pump restrictions to work around.
The heat pump is the most important part of the solarized geothermal heat pump system!
We chose the ClimateMaster three ton water to water heat pump for our solarized geothermal heat pump system. “Water-to-water” describes the use of water going through the primary of a heat exchanger. The other side of the heat exchanger intakes and expels water to and from the holding tank. Our radiant floor heating specialist specified a six ton heat pump for our size building. My calculations showed me that a three ton unit would do the job because of our exceptional insulating job. My estimates proved to be correct so far. The worst winter was this year when temperatures dipped well below zero with high winds for much of last December. Our heat pump ran much of that time but we never had temperatures drop below our normal comfortable levels.
A buffer (or holding) tank stores the heated or cooled heat from the solarized geothermal heat pump.
This tank performs a couple very important tasks for our solarized geothermal heat pump system. For instance it stores 80 gallons of either warm water for winter heating or cool water for summer cooling. The heat pump often increases the tank temperature from 60 to 11o degrees F in the winter. When we raise that much water 50 degrees F it amounts to 32,000 BTUs of energy being stored ( 80 gal X 8 pound/gal X 50 degrees F = 32,000 BTU). Hence our three ton (36,000 BTU/hour) heat pump takes almost an hour to heat our water to 110 degrees after being away for a few weeks.
A Grunfos computerized circulation pump transfers the conditioned water from the heat pump secondary ports to the buffer tank. Another identical pump forces water through any opened solenoid control valves through the radiant floor loops of Rehau tubing. A thermostat associated with each solenoid control valve determines when to open the valve to heat the associated zone. So room thermostats control the flow of water out of the buffer tank and through the various radiant floor heating zones.
This circulation pump is a part of the solarized geothermal heat pump system.
An aquastat which is thermally connected to the buffer tank water controls when the heat pump is activated to heat or cool the water. My electrician chose the Ranco brand aquastat. That unit comes with a temperature sensor that fits inside a standard buffer tank port. We set the programmable aquastat for temperatures we want the buffer tank to range between. When the aquastat reaches either of the two set points it will command the heat pump to either commence or stop operating.