Home Insulation First

Geothermal heat pumps work in a very green way, utilizing the steady temperature from the earth to offset the atmosphere extreme temperature variations. The house becomes the junction point between the ground and the air and part of a balanced system.
As such, insulation must be taken into account BEFORE you begin calculating loops and pump size in order to make the system as efficient as possible. The insulation of your home will affect the design of your pump and loops. There is no point in building a correctly sized geothermal heat pump with the right loops at the right depth if your uninsulated house is like a drainer, leaking heat from everywhere.
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his is also true for conventional heating, but what happens is that if you get your house properly insulated AFTER you have already built a ground source system, the previously correctly sized heat pump system for your uninsulated house suddenly becomes over sized, forcing the pump to run shorter cycles, working less efficiently and wearing too soon. This is not a problem for conventional heating, where you can do insulation before or after installation indifferently.
So in order to get the heat pump system correctly sized from the start, you must take into account house insulation first. Once done so, you can calculate pump and loop size. Now, the most obvious place where to start insulating is the roof or attic, since the heat goes up and there is where most dispersion takes place.
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n a scale of 1 to 15 R value, you should strive to get as high as possible an R value, since a 15 R means only 1/15th of the heat will go through a barrier as opposed to 1 R value, whereas all the heat goes through. Once the attic is insulated, you should not overlook windows, doors and even basement.
It is pointless having a totally sealed and super insulated attic if your windows and doors have frame gaps the size of a mail box slit. Close up all the gaps and fissures to maximize overall insulation. Also last but not least comes in the basement.

Ground Source heat Pump Soil Check

Generally speaking, the wetter the soil the better. You can make your system with any soil, clay, silt, gravel, sand, top soil, etc, but soils saturated with water work best because they are a close match to water, guaranteeing good heat transfer and temperature inertia, while dry or sandy soils have tiny pockets of air within, therefore transferring less heat to the liquid circulating in the pipes.

As a consequence of the different heat transfer capacity, a wet soil will require a certain loop size, while a dry soil will require a larger loop system for the same heating/cooling needs.

To check the soil you have to take samples, you have to excavate holes with a post hole digger at the right depth that varies depending on latitude and must be calculated before you start. But a digger is expensive to rent, a better solution is making a diy contraption with a DC motor and equipment you may already have laying around.
This will save you a lot of money in one of the most expensive parts of a diy ground source heat pump project. You can find all the information required for making your digging equipment and digging the trenches here (huge money saver).

Geothermal Heat Pump Loop Kinds

Once you have done home insulation and determined what type of soil you are dealing with, you can calculate the pipe loop system size and excavation depth.
Because you know the thermal diffusivity of your particular home soil, wet or dry, you can decide how big you pipe system will be. Saturated soil, where water sips in, will require the least amount of piping, about 400 feet per ton. Medium wet ground will require about 600 feet of pipe for each ton, but dry soil will need 1200 or more feet per ton.

Once the length of pipe loop has been calculated, you must make sure to adjust it depending on obstructing factors that may slow down the flow of the liquid into the pipe loop, forcing the pump to work harder and less efficiently. These factors are: friction inside the pipe determined by other pipes and fittings inside the house, the heat exchanger, the antifreeze viscosity inside the loop and the friction at the low temperatures in winter.

Diy Geothermal Heat Pump

If you have already sorted out the diy excavation and the pipe loops, then it’s time to think about the heat pump. The most important factor in building a heat pump is getting the right size in relation to the pipe loop system and the house insulation, this means not just avoiding a small under sizeded pump, but even worse making an over sized pump.

This may seem counter intuitive and against “the more the better” mind set, but what happens with an over sized pump is that it will run shorter cycles to heat up the house as opposed to running for longer cycles or even better continuously as in a right sized pump.

You may think that if the correctly sized pump runs for longer cycles or even non-stop to keep your house warm it should wear out more quickly and work harder. In fact the opposite is true, because it is the start up process which is the most stressing and wearing factor for a pump, much more so than running for longer or continuously. What happens is that an over sized pump will cut off and start again too frequently, leading to abnormal wear and inefficiency.

Every time the pump starts, it takes a great amount of power to get it moving, causing its metal parts to rub. Hence, the more start ups, the more wear and tear, the shorter the pump life and the less efficient the heating. It is a bit like comparing two cars with the same mileage, one with 100 miles trips on the log, the other with 10 miles trips.

The engine doing the shorter trips will have started the engine 10 times more frequently for the same mileage and will be more worn out than the long trips engine simply because it is when the motor starts that most wear and tear occurs, before the oil has had a chance to reach the the cylinders and pistons. So for a heat pump the same applies, the longer the cycles, the better the performance, efficiency and durability. The comparison has its limitations, but you get the point.

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A geothermal heat pump is in fact a ground source pump, not exactly geothermal. The difference is that ground source technology moves the naturally occurring warmer temperature from a shallow depth under the ground surface into a house, while the geothermic technology implies the boring of very deep holes, usually more than 100m (300 feet), to harness the very high temperatures found deep in the earth crust in order to generate electricity.

That’s why these kind of sustainable energy pumps are also called earth-coupled or geoexchange, because they can harness the underground even temperatures through the year to offset the extreme cold and heat variations above ground. Depending on latitude, at 20 feet down the temperature is a constant 50F to 60F, whether you are in the Death Valley or in Alaska, nicely sheltered from extremes.

o a geothermal heat pump carries that even underground temperature to warm the house in winter, when the outside air is colder than below ground, and vice versa push it back into the ground from a hot house in summer time in order to cool it down, using the earth like a sink hole, not unlike freezers.

In order to collect the heat from the soil, a system of pipe loops with an anti freezer running inside them is used to circulate back and forth to an heat exchanger and the pump. All components of the set up must be correctly sized to avoid poor efficiency due to mismatch. Even an oversize pump will cause inefficiency and wear out more quickly. Such pipe systems can be closed loops or open loops.

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losed loops can be set up horizontally, vertically or in a body of water like a lake or a pond, if the house is close to it. Open loops take in the warmer water from a body of water, run it through the house via the pump and release it back into the lake/pond as far as possible from the intake point.

For normal households, the horizontal loop is convenient and as it is normally half as cheap to dig shallow trenches than boring deep holes as in the vertical system (which is per se better because the deeper the pipe goes, the more uniform and warmer the temperature is through the year). In any case, a digger is very expensive to rent, but you could save a lot by setting up a diy geared DC motor and some hand built equipment to bore the holes for your loops, eliminating a big slice of the installation costs.

Ground source heat pumps can also be used in conjunction with other renewable energy sources like solar panels or wind generators (where suitable) to power the pump itself, making the system super efficient.
Even when powered from the grid, a geothermal heat pump is still 300% to 400% more efficient than conventional electric or propane heating systems. This is because the pump uses energy only to move the heat from one place (underground or in a body of water) to another (the house) , and vice versa for cooling, not to generate it.

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lso, in recent times these heat pump systems have become more efficient than in the past, with features like 2 speed compressors, low speed for fall and spring, high speed for winter and summer, and desuperheaters that help save more electricity by pre-warming the boiler water before heating it up.

If that is not good enough, some grid companies and governments are applying incentives for home owners to go the ground source way. There is just one caveat to all this goodness: installation costs. A normal household heat pump system can cost $15,000 upwards and take 5 to 10 years to pay off, while a large commercial building will take less, 2 to 5 years (still too long).

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he only way to go around these prohibitive costs (for most) is by doing it yourself. Until recently, only specialized teams could tackle the task of digging the ground or heat welding the polyethylene pipes, or making the compressor and the heat exchanger, but more and more diy projects by people with years of experience are successfully sprouting out as a solution to forbidding costs, sometimes bringing down the costs to as little as an unbelievable $1000, like this one.