Geothermal Moves From the Ground Up – Part 2
Heat is being taken from the building and being transferred into the ground in summer. In winter, heat from the ground is transferred into the building.
An open-loop well is very much the same as a standing column. The only difference is that the open loop can be used in more applications, though it is the most common with the standing column scenario. With an open-loop well, water can be pumped from one well and returned to another, making this a recycling action as well as this being a total advective heat source.
For example, a contractor may drill a well 150 feet deep and come in to a vast amount of water. If this were to happen the contractor could drill a second well in hopes of encountering the same aquifer, in which case the driller would do a pump and dump. Thus the water goes into the building through the heat pump and then returns to a second well. If the user does not return any cool water to the well they are pulling from, then the well stays at a constant warm temperature. This situation makes this the most efficient of the options.
Another example of an open loop would be to discharge the water to some other sort of dry well. Users would want to make sure this is in an area that will accept the amount of water that will be discharged. This is not recommended if there is a chance of contaminating another water source or discharging of water into any lakes, streams, ponds, or other bodies of water without the state environmental protection agency’s approval. The open loop well is typically the most efficient and least expensive of options.
Many communities are considering, researching, or implementing microgrid solutions. The underlying rationale often involves complex business, operational, and economic issues. See our FREE Special Report: Understanding Microgrids
. Download it now!
Geothermal a Good Fit for New England
In Maine, Gagnon Heating and Air Conditioning Inc. has been installing Geothermal Heating & Cooling Systems since 2000. Owner Jeff Gagnon explains that in this region of the country often the area bedrock is relatively shallow which is a good thing in terms of less casing and easier installation.
“The only time bedrock is an issue is when it is so close to the surface that trenching becomes a problem,” adds Gagnon. “That is pretty rare.
“Open-loop systems are the preferred approach in Maine due to the fact we have very high static water level wells in Maine. In order for an open-loop ‘standing column’ well to perform well this is critical. In most of the country bedrock is deep and water tables are much lower. In that scenario open-loop systems are not preferred.”
In Maine, as in some other areas of the country with similar conditions, closed-loop systems are more likely to be chosen when there is risk of encountering salt water. Salt water will shorten the life of the heat exchanger in the geothermal heat pump.
“Open-loop systems can cost less to install and will be more efficient,” says Gagnon. “Closed-loop systems are very efficient as well, and have their place. Iron can be a bit of an issue, but not a big problem. Very high Iron can cause scaling of the heat exchanger. However, we have had to clean only one heat exchanger in the last 14 years.”
Gagnon considers the biggest challenge with geothermal to be how to adapt geothermal to existing structures that are not suitable for ductwork. There are two types of geothermal systems, including water to air, and water to water. Water to air uses ductwork; water to water uses radiant heat.
Add Distributed Energy Weekly and Energy Storage Solutions to your Newsletter Preferences and keep up with the latest articles stored and distributed power, battery storage solar microgrids, HVAC options, and smart energy systems and LED lighting retrofits.
“Existing buildings that have baseboard heat are not always the best fit unless ductwork can be installed throughout,” he says. “Some of the factors that make geothermal difficult in existing buildings include: a finished basement, no attic space, building on a slab, too small electrical service and lots that are too small. That said, we do a lot more residential geothermal work than commercial, some 95% residential and 5% commercial.”
When Limestone May Be an Issue
Cape Fear Drilling Services (CFDS) in eastern North Carolina has been in business since January 2006. Currently, 20–28% of their business is in geothermal. Chris Deal, vice-president, predicts that number will grow.
“The amount of geothermal work we are doing has definitely increased since 2006,” explains Deal. “As with most things that happen in this country, the Southeast tends to be one of the last areas to embrace new technology.”
Deal mentions both the environmental benefits and the cost savings of geothermal heat and air systems.“The tax incentives for geothermal installations certainly exist and are the first savings to be realized by energy consumers. As a company, we actually think the greatest benefit of geothermal HVAC systems is the decrease in electricity consumption, which provides great long-term cost savings. We frequently work with O’Brien Service Company [a local Heating and Air Conditioning service and system provider] in the installation, maintenance, and repair of geothermal systems. They use Trane, Bosch, and Water Furnace brand HVAC systems.”
The southeastern North Carolina soil is one of the many daily challenges faced by CFDS. This area of the coastal plain in North Carolina has a limestone formation. Once you go through that limestone formation, there is layer of a dense sticky mud known as Pee Dee Mud. It separates two different aquifers. The Pee Dee Aquifer is located at depths of roughly 60–200 feet. Some areas in this region contain limestone rock voids that can make drilling dangerously problematic. These voids can deter geothermal drillers due to the increased safety risks and costs incurred when a void appears during drilling. CFDS generally works in a six- to seven-county area. However, the voids are usually found in concentrated areas, rather than being spread evenly across the local geography.
Another local challenge is the over abundance of sandy soil, which can also pose drilling issues. “Other than that, work in our area involves pretty standard drilling,” adds Deal. “We happen to use top-head rotary equipment; everyone uses different equipment depending in their setting or situation. If voids are encountered, metal casing is used to enable the system to work properly. If casing is added, conductivity is reduced below what would be present without a void. For this reason, if you drill into a void, a lot of times you will end up adding depth to that borehole.”
A top concern for Deal is the grouting process. This includes the grouting product used and mixture formula. It’s important to make sure that the hole in which your pipes are placed is completely sealed by grout slurry. This prevents any contamination of the aquifer. Sloppy grouting and incorrect techniques in the drilling process can provide a pathway for contamination of drinking water.
“We are very environmentally conscious,” says Deal. “Our company’s president is super concerned with the protection of natural resources, and one of our team members is a specialist in environmental studies. We realize that we are tapping in to the earth itself in order to make use of the earth’s core heat for transfer to geothermal systems—a gift from the earth that should be honored. We feel the qualifications of any company, as well as the techniques used for this process, should be thoroughly researched. Our water source is very limited. As a well driller, clean groundwater should be viewed as something, which, once it’s gone, will never return. We’re grateful to have accessible natural resources and using geothermal energy as a heat and/or cooling source can be simply another way of doing that, if it is done correctly. It can be an awesome opportunity for environmental and cost-conscious energy consumers.”
Deal fears that it may become an industry tendency to jump on the geothermal bandwagon without proper knowledge and training. “How hard could it be to simply drill a hole and stick a pipe into it?” he asks. “It’s not rocket science, but at the same time you have to take care of the resources we have in our midst such as clean soil and water.
“Unlike fracking, nothing is being injected into the ground, which seems to be a common misconception regarding geothermal systems. All we are doing is accessing the earth’s core energy—the natural temperature found beneath the ground—to the maintain quality of life and comfort of our customers homes and businesses.”