Tapping the Earth for home heating and cooling

Sue Butler decided it was time to cut the cord on fossil fuels. So when her aging gas furnace needed replacing, she turned to the Earth for a solution.

She installed a geothermal system--also called a ground-source heat pump, a water-source heat pump, or geo-exchange system--which recently started heating and cooling her Cambridge, Mass. home. Butler said she was motivated by environmental reasons and concerns over carbon monoxide from burning natural gas.

"It's not that much more expensive and I could manage it. And it means no more combustion and it gets the building off of carbon, which is urgent," she said.

Ground-source heat pumps have been around for decades but every year seem to attract more homeowners and organizations who are looking for alternatives to traditional space heating and cooling. They can hook into existing forced hot air and hot water systems but not steam heat.

Starting in 2006, nearby Harvard University installed six ground-source heat pumps as part of its Green Campus initiative. Administration buildings and athletic facilities are already online and two more buildings planned.

The pump room at an apartment building in Fitchburg, Massachusetts.

(Credit: MassInnovation)

One real-estate developer, MassInnovation, has made geothermal an integral part of its eco-themed housing and office buildings. Having equipped one senior living center with geothermal, it's now planning on converting what was once a giant 19th century factory into one of the largest geothermal installations in New England, according to CEO Robert Ansin.

People who go with geothermal are typically either interested in it because it's a clean energy technology or because they're looking to escape fossil fuel prices, said Diona Roberg, the director of operations at Water Energy Distributors, which distributes geothermal systems from ClimateMaster.

"Business is out of control--we can barely keep up with it," Roberg said. About half of the customers go geothermal to cut heating and cooling costs. But the other the half "don't care what it costs, they just want to do green," Roberg said. The family-owned business has doubled in size over the last four years.

Open and closed loop
Strictly speaking, what's often called a "geothermal system" is a misnomer because it implies tapping the heat in the Earth, something already done at large scale to supply electricity to utilities. This geothermal energy--and its offshoot enhanced geothermal--works only works in certain geographies and uses different technology.

Rather than use underground heat, geothermal heat pumps attached to buildings capitalize on the steady temperature of the ground or deep water wells. In effect, they treat the Earth like a giant energy savings bank, depositing or withdrawing heat depending on the time of year.

Two ground-source heat pump units stacked on top of each other. Heat is extracted or added to water which is pumped undergound.

(Credit: Martin LaMonica/CNET Networks)

During the summer, the systems pump indoor heat underground and draw on the lower temperatures of the Earth to cool a building. In colder months, the same process works in reverse, with heat from the ground being used to warm indoor air.

Indoors are box-shaped heat pumps that pull and and push either water or a working fluid, such as antifreeze, in and out of the ground. Using the same compressor loop mechanism that a refrigerator has, a heat exchanger draws energy from the circulating liquid to either heat or cool a building.

There are a number of different configurations for the liquid transfer loops--either water wells several hundred feet deep, which are said to be the most efficient, or coils which could be dug only a few meters underground. Others use a body of water like a pond as a heat sink.

Regardless of type, though, ground-source heat pumps are considered one of the most efficient forms of heating and cooling.

The International Ground Source Heat Pump Association, based in Stillwater, Oklahoma, said geothermal is 50 percent to 70 percent more efficient for heating than other systems. The U.S. Department of Energy says that a ground-source heat pump uses 25 percent to 50 percent less electricity than conventional heating and cooling systems.

Roberg said that the maintenance costs for geothermal are half the cost of traditional heating and cooling systems. The payback on geothermal systems, which used to be about seven years, is now typically four years, she said. Recently passed federal renewable energy incentives now include $2,000 per year tax credit.

Green Edge
But even with these benefits, geothermal heating and cooling still remains a relatively niche product, with about 50,000 units installed a year in the U.S., according to the Department of Energy.

One reason is the upfront cost. All told, a geothermal heating and cooling installation, including duct work, will be about 50 percent more expensive than fossil fuel-based system, Roberg said.

Drilling is typically the biggest portion of the bill because it can cost tens of thousands of dollars alone. The geo-exchange pumps themselves for homes can cost between $17,000 to $30,000, according to Butler.

A "vertical" loop of a ground-based, or an open-loop ground-source heat pump.

(Credit: WaterFurnace International)

Experts warn that installations of these systems are very site specific--poor installation of ducts, for example, can lead to an underperforming unit.

Also, certain regions appear to be better suited for geothermal-exchange technology; some developers have reported that pumps that spend most of the year pumping heat underground, and little time pulling heat out, don't perform as well over time.

In its analysis of its first six geothermal systems (click for PDF), Harvard identified a number of installation challenges related to the design of wells and understanding the water resources underground.

A more subtle challenge is the status quo. Homeowners who aren't aware of geothermal systems will install what contractors--also unfamiliar with the technology--will recommend.

Ansin of developer MassInnovation, encountered this institutional skepticism first hand while renovating an abandoned shoe factory in Fitchburg, Mass.

He was looking at spending a significant portion of his overall budget--about $500,000--on a standard industrial furnace and chiller when he had a chance encounter with a driller friend who suggested that geothermal heat pumps might be cheaper.

Ansin had never heard of geothermal, but once he looked into it, he realized that it could be both cost-effective and allow him to differentiate his buildings in a way other than just location. The facility, called Anwelt Heritage Apartments, is marketed as an eco-friendly building that uses a ground-source heat pump and a solar array.

The system is about half as expensive as the traditional set-up, said Ansin, who is now part owner of a drilling outfit. He passes the lower utility costs to people in the 86 residences, who pay less than a half of what they were paying in utility bills.

He's very enthusiastic about the technology but admits that the geothermal industry is immature compared to the traditional heating and cooling business.

"Even though heat pumps and geothermal space conditioning has been around for a while, it's still considered very much a new market and as such, there aren't nearly enough contractors and engineers," he said, adding that an installation can require coordinating different contractors. "Unfortunately, until you have a one-stop-shopping solution, it's not going to become nearly as ubiquitous as it could be."

[contentcreator--2008]

A "chord" is several musical notes played simultaneously. A "cord" is a string that you can cut.

[mlamonica]

thanks. fixed that.

[MadLyb]

It can also be a straight between two points on a curve.

[rfelgueiras]

We are currently completing construction of our 22-Floor head office using this process in conjunction with a solar tower for our heating and cooling needs. It's an amazing technology that more people should be looking into. The long-term savings and environmental benefit is ridiculous.

[EcarNahte]

My house is heated by this technology, works very well. I would suggest having a small propane heater in case the power goes out.
Only cost about $30,000.

[ArtInvent]

Combine a small geothermal system like this with the new German super-efficient building, insulation and ventilation systems that require virtually no heating and cooling input in the first place. If they can eliminate heating bills in Germany, I don't see why you can't do the same in New England or any other cold climate in the US.

See the Dec 27 story in the NY Times about 'Passive Houses' in Germany -
<http://www.nytimes.com/2008/12/27/world/europe/27house.html?scp=2&sq=German%20heating%20system&st=cse>

[mlamonica]

Thanks for the comment. Cut and paste this URL for an article on a super-insulation retrofit project, which is being done in New England. http://news.cnet.com/8301-11128_3-10123367-54.html?tag=mncol

[rfelgueiras]

We have.

http://www.hydro.mb.ca/projects/downtown/index.shtml

[starbuck2913]

For all the savings these systems promise, they are still PROHIBITIVELY EXPENSIVE. At a $100 a month savings, the least expensive sytem at ~$25000 would take 21 years to pay for the initial cost.
Now if you have the money just hanging around or a rich benefactor to front the installation, then lucky you!!

[rapier1]

I had looked into this some time ago when I was going to replace a furnace in my house. However, the estimated cost - close to $17,000 wasn't competitive with $5k for a new 95% efficient furnace. It simply wasn't economical.

[uglo]

In a few more years, mark my words, the eco people will be saying the pipes for the geothermal systems are destroying the planet and they have to be removed. Nothing will please them for very long because they have to have something to complain about or what good are they?

[LuvThatCO2]

Geothermal is great... but the initial costs can be very high. It can take many years to make back the investment, especially for a home.

[Endbringer]

It sounds great, but that initial, up-front cost is very steep. Besides, the eco-wackos will say that since some systems use anti-freeze, it hurts the environment more than it helps.

[rapier1]

That depends on the heat transfer fluid used. A significant leak of some types of glycol would be bad.

[Nevets77]

We invested $22,000 to go with geothermal ($15,000 premium over traditional). We are achieving actual savings around $300/year. We will never recoup our original investment and it was a poor choice overall. The marketing material suggested savings of $2000/year however this is a completely unrealistic expectation.

[delder]

Based on my recent underslab water leak, I think these systems would be okay until the first leak - then what?

[terrylweb]

This is a very complicated subject and the article misses a few key distinctions: There are big differences in efficiency/payback depending on the part of the country/world the system is located in, the size and type of building being heated/cooled, and what other fuel types are being compared. Although (for example) it is true that these systems use less electricity to provide heat than other ELECTRIC heating systems, they may not use less electricity than a gas furnace... which is what most Americans use to heat their homes. And switching from a low carbon fuel (natural gas) to a higher carbon fuel (electricity generated by burning coal) is not an environmental advantage. In the colder parts of the country, these systems must be very large to generate enough heat, and then the cost goes up. If they are undersized, then supplemental heating systems are required. Like with most things, results vary greatly, and if you rely on marketing materials to make your decisions, well...

[modjohn]

We built a new home in 07, 3400 sq ft including walkout basement. The home is very well insulated. We installed a 4 ton, dual speed geothermal system. The system required about 450 feet of piping for heat transfer. The piping is a very tough plastic with heat sealed joints, so in theory, it should never leak. Our system does not use glycol, it uses water with about 5 gallons of alcohol added to prevent algae growth. The system cost $16K, about $5K more than a propane fired system. It is all electric, so if the power goes out, no heat. And yes, most electricity comes from dirty coal fired plants, but our HVAC system uses less total energy than other systems. Not perfect, but an improvement.
Our highest total energy bill during the first winter was $105. That is for everything, heating, water heating, cooking, washing, lighting, etc. The highest summer bill was $157. The lowest bill with no heating or cooling was about $65. I figure we are saving about $1000 a year over a conventional system, so the payoff should be between 5 or 6 years when you included the financing of the higher initial cost. Plus, we do expect to have a longer life span with less maintinence.

[Dr_Zinj]

I currently use forced hot water for heating, using a oil furnace to heat on-demand. Only electricity needed is to run the igniter, the furnance blower motor, and the water pumps. My understanding is that geothermal would still require a booster heater for hot water to go from ambient ground temperature of ~50 degrees to the 85 to 90 degrees we like for showers, and higher for washing.

[MadLyb]

We have used a simple geothermal solution in my part of the world (Southeast US) for several decades that involves placing 4" PVC pipe (usually a couple hundred feet) below the frost line in a loop from the basement with fans at each end to move the air through the pipe.

Pretty much, no matter the temperature at entry, it comes out around 57 degrees. Some folks use it keep their basements regulated, but when I did it for my house, I used it warm/cool the external air feed to the heating/cooling system in my house. The result is I can provide fresh air to my house, but the cost of conditioning that air.

The total install was less than a $1000 including digging the line in the ground and the electrical costs are minimal. Only issue has been dealing with humidity, but the cost savings are significant.

[TennFarm]

Are you pushing air from inside basement thru 4" pipe underground a couple hundred feet and then pushing it back inside basement? What is humidity coming from?

[TucoS]

"Roberg said that the maintenance costs for geothermal are half the cost of traditional heating and cooling systems. " This has not been my experience. I installed a Water Furnace geothermal system in my 3,500 sq. ft. new house in 1996. The first two or three years were okay, then the problems began. It is now 12 years old and has been plagued with problems. Each more expensive than the next. In the past 12 months a pump went ($800 plus $400 labor), then a capacitor $400 plus labor, two weeks ago the compressor went (I've been quoted $2,500 to $3,000). These systems are highly dependent on maintenance and you should check out the cost service calls and replacement parts. Recently a malfunctioning sensor stopped the unit. The service call began with, "it'll be $98 a half hour.) I live in NY State and when it gets very cold the auxiliary electric heat kicks in, which gets quite expensive. I regret ever having made this decision and wish i'd installed a natural gas system.

[stanleey16]

hello tuco s..i to live in ny and had the same water furnace heater installed in my new construction house round 93...it is now 99 and i hate it . Not yhat ive had the problems u have but in the summer the unit never reaches a livable temp. while running all day..and in the winter forget about it the minute the temp drops down to the fifties the unit is constantly running. If it needs to pull more then two degrees at a time the emergency backup comes on (and so do the hi bills) My question to you is i cant find anyone with half a brain to work on this thing or give me some advice for an alternative option....have you? Im about an hour north of manhattan. If you know of anyone or have learned anything new about these crappy units id love to hear it.. ill do the same .thansk stan

[B_Safe]

We installed a ground source heat pump in our new 2,200 sq. ft. log house back in 1992 in Central Ohio. We used a ground loop, three loops 150 ft. long under one of the pastures. No natural gas available, just electric. Other options were propane and oil (or standard air-to-air heat pump). None of these were attractive due to the cost of the fuel and the cool temps from the a-to-a heat pumps of the day. We also made domestic hot water from it. We lived there for 10 years. Only issue we had was a pump bearing failure in year two (fixed under warranty). Being that it was a new build we had no comparison for operating cost but in A/C mode it was practically free, monthly bills with temp set at around 75 was under $80 a month (remember this is an all electric house). Monthly electric in winter was around $250 - 270. The backup source was just electric coils, not really adequate when really cold. In our new old house we have a new 13 SEER heat pump with the old oil-fired hot water system as the backup... we really miss the ground source heat pump, especially when oil hit $3.22 a gallon!