Power With Nature (PixyJack Press, 2012), by Rex A. Ewing, is a practical guide for self-reliant homeowners planning to decrease energy costs and careless usage by harnessing the free energy of the earth. Ewing has written multiple books on renewable energy and powers his own residence with solar and wind energy. The methods he shares are effective and combine modern living with natural solutions. This excerpt talks about heating and cooling a home from underground by implementing geothermal pumps.
Most of the energy solutions in this book, Power With Nature (PixyJack Press, 2012), come from the great, untapped potential of the sunlight and breezes overhead. Mount a solar-electric array in the midday sun and you’ll have ample electricity. Or stick a wind turbine high up on a tower and let an unsettled solar-heated atmosphere toast your bread and run your stereo system. For hot water all you need are a few solar hot-water collectors on your roof where the sun can do what the sun does best. Firewood, which is stored sunshine, is a pleasant source of heat for anyone with a chainsaw and a ready supply of dead trees. It’s all quite elementary; the sky is where it’s happening.
And yet for home heating and cooling, there is another source of energy—largely but not entirely originating from the sun, that may be the best solution of all. It lies right beneath your feet. Say 5 to 8 feet down. That’s about the level where the effects of the different seasons are so gradual they barely fluctuate; where all the year’s hot days mix with the cold ones in a terra-firma stew that never really ever warms or cools. In the northern states the deep ground will stay a fairly constant 45 degrees – 50 degrees Fahrenheit all year long, while Southerners can expect constant ground temps of 50 degrees – 70 degrees.
But is this really good news for those of you living in the North Dakota hinterland, where winter heating bills rival the mortgage and cordwood procurement becomes a blinding obsession? Yes; especially you. It’s just a matter of changing the way you think about heating.
In many ways the Earth is like a magic battery capable of collecting the oppressive warmth of the summer sun and storing it until winter, when you really need it to heat your house. So efficient is this battery that with a properly sized and installed system you will never have to burn another gallon of propane, natural gas or fuel oil to keep your house warm, and — as an added bonus — the Earth also stores the waste heat from your home’s air conditioning until the mercury plummets and the snow flies.
Too good to be true? Not at all. Tens of thousands of people are proving every day that it is both practical and cost effective to heat and cool your house with the energy stored in the ground. It’s just a matter of moving heat back and forth using the same clever science that makes refrigerators and air conditioners possible: the common heat exchanger.
The Principle of the Heat Exchanger
How is it possible to heat your home cheaply and conveniently by extracting heat from soil that is only 15 or 20 degrees above freezing? By circulating through buried tubing water that is even colder than the earth itself. Since heat always flows toward where it’s colder, the water — mixed with an environmentally-safe antifreeze solution — picks up heat from the ground as it circulates. Thus it will be warmer when it returns to your house than when it left it.
The water is still cold, of course; no warmer than the earth it came from. So it has to give up its heat to something even colder — a refrigerant, such as liquid Freon, a substance so cold that it boils at subzero temperatures. Now we’re getting somewhere, though it may not seem like it yet. Inside a heat pump unit, the very cold Freon circulates in a double coil with the earth-warmed water, absorbing its heat and making the water cold again, relatively speaking. But even though the Freon has absorbed most of the heat the water gained from the soil (becoming a low-pressure gas in the process), it’s still no warmer than the ground outside. And we need to make it hot; hotter even than the air inside our house. How? By compressing it to a very high pressure. This concentrates the gas and raises its temperature to approximately 165 degrees. Then, by running the hot high-pressure gas through a second heat exchanger (either an air duct coil or a hot water tank), the heat is given up into your house. In the meantime, the gas cools to a liquid, runs through an expansion valve, and returns to a cold, low-pressure state, ready for the next go-round.
In summer the process is reversed: the excess heat inside your home is returned to the soil where, as I mentioned earlier, it will be available in a few months for winter heating. And in the process, it cools your home.
With three separate phases of heat exchange (ground to water; water to Freon; Freon to air or water), the use of a ground-source (geothermal) heat pump to heat and cool your home may not appear to be a very efficient process. But in fact it is extremely efficient — right in the neighborhood of 400%. This means that the ground surrenders four units of heat energy for every one unit of electrical energy you use to extract it. It’s like getting three free cords of firewood for every one you buy.
Types of Systems
There are two basic types of underground pipe systems — open loop and closed loop — with several variations. The one you use will depend on where you live, how much land you have, and the characteristics of the soil and ground water.
In a horizontal closed-loop system, loops of special heat-conducting polyethylene pipe (either in straight runs or the newer slinky coil method) are buried 6 to 8 feet below the surface. The length of each trench depends on the amount of moisture in the soil. In wet climates, for instance, three trenches, each 100 feet long, are usually sufficient for an average-sized house, while in an arid climate like Colorado’s an installer often has to go 200 feet per trench for optimal heat absorption.
Since many of us simply don’t have enough land for such a sprawling system, there are vertical closed-loop systems, in which loops of ¾-inch high-density polyethylene pipe are set in concrete in a series of 4½-inch holes. The holes are bored to a depth of 175 to 220 feet, and placed 10 to 15 feet apart. All the separate pipes converge at a manifold, where they are joined into two pipes — one in, one out.
A third incarnation of the closed-loop system is the pond loop. As the name implies, the tubing is floated over a body of water then fitted with ballasts and sunk to the bottom. If you’re lucky enough to have a lake nearby, it could spare you the cost of trenching or drilling.
In open-loop systems, ground water from a series of wells is used. Water is pumped out of one set of wells, run through a heat exchanger, and is then pumped back into a different set of wells. Since water conducts heat better than dirt, open-loop systems are very efficient and can be less expensive to install than vertical closed loops.
System Size, Cost and Applicability
In a temperate climate, a geothermal system will heat and cool roughly 750 square feet of space per each ton of capacity, which is equal to 12,000 Btu per hour. Installed systems range from $3,000 per ton for horizontal closed-loop systems in ideal soil, to $5,000 per ton for vertical closed-loop systems. If, on the other hand, you have adequate groundwater flow, vertical open-loop systems can save you money.
Are you building a new house? If so, the increase in your mortgage payment from choosing a ground-source heat-pump system over a conventional system will be more than offset by the savings on your utility bill, since a geothermal system will be nearly three times more efficient than any other type of heating and cooling system. If you instead plan to retrofit an existing house, the payback will take 10 to 15 years, depending on numerous factors. The good news is that the equipment should last for 20 to 30 years with little maintenance, while the underground tubing will perform trouble-free for at least 100 years.
Practically speaking, ground-source heat pumps work best with forced-air heating systems, but can also be made to work with hot water heating systems, including radiant-floor heat. When adapted to an existing forced-air setup, the system efficiency can be greatly augmented by sealing gaps and holes in the ducts, adding return-air ducts, and setting up multiple zones. With the addition of a desuper water heater, you can enjoy virtually free hot water in summer and more efficient water heating in winter.
When installed as a hot-water heating system, a geothermal system can only heat water to 110 degrees – 120 degrees, so for most homes it will require some amount of boiler-heated water on really cold days, though overall it should handle 80% – 90% of the heating chores over the course of a winter. Summer cooling with ground-source hot-water systems is accomplished by reversing the process. The heat pump unit produces cold water which is circulated to fan coil units which blow air past the cool coils. The cool air is then distributed through a separate duct system.
What is good for the planet is also good for your pocketbook. According to the EPA, geothermal systems are the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available.
There is one caveat: practically speaking, you will have to be connected to the power grid if you intend to install a geothermal heat-pump system. For although the overall efficiency of these systems is unmatched, they still use more electricity than an average house. What they don’t use is natural gas, propane, or fuel oil, the traditional fuels that take a bigger and bigger bite out of your energy budget every year.
How much will it cost to heat and cool your home on a yearly basis? I’ll give you an actual number: $800. Taking advantage of off-peak electric rates, this is the total annual utility cost incurred by some friends in 2004. And it’s not like they live in a small cottage in Texas or a trim little cabin in Georgia. They live with their four children in a 3,500 square-foot custom home in the frigid north woods of Minnesota. All the home’s heating and cooling is handled by a closed-loop system using a series of 13 vertical bore holes, while a desuper water heater provides nearly free hot water in summer and very inexpensive hot water the rest of the year. In 2005, when they decided to heat their 860-square-foot garage in winter and turn the house thermostats lower in summer (to appease their teenage daughters), their annual electric bill only went up another $190, in spite of a 3% increase in electric rates. This is about $82 per month for all of a rather large home’s considerable energy needs. They calculated system payback time at only three years, and this was before tax credits were available to pay for 30% of the system.
Solar Hot Water vs. Geothermal
Is it better to heat your home using solar hot water or geothermal technology? That depends largely on your circumstances, specifically on whether or not you plan to live off the grid. If you do, then a geothermal heat-pump system is in all likelihood beyond the generating capacity of your home solar and/or wind generating systems. But for those of you tethered to the power grid, my advice is to go with a geothermal heating and cooling system. There are two main reasons for this.
In the first place, it just doesn’t make sense to invest heavily in a technology that will only be useful during the time of year when it is least effective. Whether you install flat-plate collectors or evacuated tubes, their performance drops whenever the mercury takes a dive. And when the heavy clouds roll in, solar collectors enter into a somnolent state and hibernate — just when you really need them. A geothermal system, on the other hand, couldn’t care less whether it is warm or cold, sunny or overcast. You have to admire that kind of indifference in a system.
There’s also summertime to consider. For a geothermal system, summer cooling is child’s play: just run it backward. It’s a trick that doesn’t work with a solar hot-water system. But at least with solar you’ll get (almost) free domestic hot water, right? A geothermal system can do that, too, with the addition of a desuper water heater.
Secondly, to be truly effective, solar hot-water heating systems require lots and lots of collectors (unlike a domestic hot-water system, which takes only a few). Where are you going to put them all? The most likely answer is on the roof, but a sizable system can easily take up every inch of your home’s south-facing roof, and you may need to beef it up to support all that extra weight. You’ll also have to find a place for a hot-water storage tank, which can be several hundred gallons in a large system. Contrast this with a geothermal system: except for the heat exchanger, it’s all but invisible.
I have friends with both types of systems. Those heating their homes with solar hot water are proud of their systems, and they should be. But they often lament about how much money they have to shell out for supplemental propane. Those using geothermal heating and cooling, by contrast, are continually amazed by how little money they have to spend heating and cooling their homes; just a few bucks for electricity to run the pumps.
Using Solar Electricity to Supplement
A direct grid-tie solar system is a perfect accompaniment to a geothermal system, especially if you live in an area with Time-Of-Use (TOU) billing, where electric rates are cheaper at night than during the day. In this scenario, you will be able to sell your excess solar power to the utility while the sun is shining and the electrical demand is the greatest, and buy it back at night when demand lowest. With a large enough system, you can greatly reduce or eliminate your energy bills.
Reprinted with permission from Power with Nature: Renewable Energy Options for Homeowners (updated 3rd edition) by Rex A. Ewing and published by PixyJack Press, 2012, and available at PixyJackPress.com.