Cold Ground* - Considerations for Geoexchange Projects in New Hampshire – Successful Projects and Cautionary Tales

This week we are following up on my last post on geothermal energy. In this article, I take a look at the successful implementation of a large geothermal project in New Hampshire. I also present a number of issues that impact the implementation of these projects here in New Hampshire that you should keep in mind when you get ready to harness the energy in the cold ground beneath our feet.  

In last week's post, I pointed out that what we call geothermal energy here in New Hampshire should more correctly be called geoexchange. We are not using the energy deep in the earth's crust to generate steam which can be used to generate electricity: instead, we are harnessing the moderate temperatures that lie six or more feet below the surface. Using ground-source heat-pump systems we can harvest this low temperature energy as a heat source to heat our homes in the winter and then, in the summer months, we use the earth as a heat sink by pumping the excess heat in our homes into the ground. It takes energy in the form of electricity to harvest this low grade energy, but with modern heat-pump devices we can draw more energy from the earth than we consume as electricity to run these devices. It is also necessary to remember that the actual source of this energy comes from solar radiation warming the earth's surface, so geoexchange is, in effect, an indirect form of solar energy.

Geoexchange systems are used in a variety of applications, from the heating and cooling of individual homes to large systems that are used to condition multi-building college and hospital campuses. It is a technology that is finally beginning to make headway even though it has been available since the 1940s. Twenty years ago the EPA noted that "Geothermal exchange systems are the most efficient, environmentally clean, and cost effective space conditioning system available." Millions of systems have been installed worldwide, and there are probably between 1000 and 2000 of these units installed in NH alone, most of them in private residences.


A great example of a large and successful geoexchange project is that installed near Boscawen, NH, at the Merrimack County Nursing Home. This is a long-term care facility that houses about 290 residents and it has a staff of 480. It is 235,000 square feet in size and it is a thoroughly modern, well-designed and sophisticated operation providing long term care in a positive caring environment. It is the largest facility of its type in New Hampshire. A picture of the facility is shown below.
  

Source:http://www.merrimackcounty.net/nursinghome/about.html

 
The whole building is heated and cooled by a ground-source heat-pump operation. When the design of the facility was undertaken in 2005, there was an early commitment by the design team that the facility would incorporate a geoexchange system to heat and cool the facility. The result was a well-designed building that uses water drawn from 16 standing wells on the property to circulate through 326 individual heat pumps which draw the energy out of the 60^oF well water in the winter. The well water, except for a small bleed stream, is returned to the wells at 55^oF. This same system is used to provide air conditioning over the hot summer months. There is a heat pump in each of the residents’ rooms, and the residents are able to adjust the temperatures in their rooms to between 68^o and 75^oF.

During the commissioning stage, the geoexchange implementation team, as on any large-scale project, had to deal with a slew of start-up problems associated with the heat pumps, reliable circulating water pump performance and electrical wiring issues, but over time these were all solved. The system now runs smoothly and maintenance issues are few and far between. The EUI number for the present facility is about 60 kBTU/sq. ft. The US average for equivalent nursing home operations is, according to the 2003 Commercial Building Energy Consumption Survey, 124 kBTU/sq. ft. which means this nursing home has an energy foot print one-half that of its peers. Impressive performance indeed!

I had the opportunity to take a guided tour of their operations with the administrator of the nursing home, Lori Shibinette, and her facility staff. Lori is a recent graduate of Franklin Pierce University's MBA program and she is justifiably pleased at what her team has been able to accomplish with the geoexchange operation. They have no back-up fossil fuel heating system and they are solely dependent on the geoexchange system for heating and cooling and keeping 290 residents comfortable. To ensure reliable 24/7/365 operation, the system incorporates backup pumps and wells. In the case of an interruption of the electrical supply, they do have a diesel fired back-up generator on site to keep the lights on and the geothermal system running. At the start, the maintenance team was a little skeptical of the operation but they are now big fans of geoexchange system. In contrast to most boiler rooms I have been in, the main geothermal exchange control hub was a quiet clean operation with a number of pumps, a large piping manifold, and a computer-monitored control network. A picture of part of the piping manifold is shown below.

 
Costs for the geothermal operation were approximately 3% of the overall investment for the new building, which is right in line with similar systems, and the calculated payback ranges between 2 and 4.5 years, depending on what assumptions one uses. Regardless, five years after the installation, the extra costs have been recovered and the facility will now for a long, long time benefit from their low EUI and the attendant energy and costs savings. This is clearly a well-conceived and -implemented project that has delivered on its performance.

Let's turn now to a topic that has been on my mind a lot the past few weeks: the installation of a geoexchange system for a stand-alone residence. In this case, the incremental cost of a ground-source heat-pump system is a larger percentage of a new home construction project, making the investment a little more challenging to justify. As a result, homeowners need to put a lot of thought and analysis into their decision whether to install a ground-source heat-pump system or not. That is exactly what I have been doing by reading and chatting to folks about geothermal systems. As fascinated as I am by the technology, I have learned that there are a number of crucial considerations to take into account.

One of the considerations is that here in NH we have a somewhat unbalanced energy load when it comes to conditioning our homes. In my post, A Hundred and Ten in the Shade, I wrote about heating and cooling requirements in NH as indicated by heating degree days (HDDs) and cooling degree days (CDDs) and I noted that in NH we have a heating-dominated energy load as we need much more heating than cooling. In Florida, the situation is exactly opposite. This is shown by the figure below which provides the typical annual HDD and CCD day requirements for New Hampshire and Florida.

These unbalanced winter and summer energy loads can cause problems with geoexchange systems. In the winters here in NH, a geoexchange system is constantly drawing heat out of the ground to compensate for the 6000 HDDs. As a result, ground temperatures around the ground loops drop, and in poorly designed systems the heat pumps can actually draw so much heat from the surrounding ground that the ground below the surface can freeze. In winter, ground temperatures can drop to below 32^oF in closed loop systems, which is why these systems usually use antifreeze as the circulating liquid and why they must be designed and sized to operate at very low ground temperatures.

In summer, the reverse happens and heat is drawn out of the building and pumped into the ground and, as a result, the earth around the heat-pump circulating system heats up and can run as high as 75^oF for closed-loop systems. The concern with a heating-denominated load is that the heat drawn out of the surrounding area in the winter will not be compensated by solar radiation and the heat pumped into the area during the summer months during the cooling cycle:  one could ultimately get a long-term drift to lower ground temperatures which will compromise the operation of the heat pump. A well-designed ground-source heat-pump system takes these factors into account by considering the thermal conductivity of the ground and surrounding rock and ensuring that the ground loop system is provided with sufficient volume to avoid long-term temperature changes in the surrounding rock.

 In warmer areas, such as Florida, where there is a cooling-dominated load, the reverse can happen. So much heat can be drawn out of the building during the cooling season and pumped into the earth that the ground temperatures rise. On top of this you have surface ground warming from the warmer temperatures all year round and in these systems one can see a long-term drift upwards of the temperatures in the ground which compromises the performance of these ground-source heat-pump units. The figure below shows the temperature fluctuation of a closed loop system over a number of years at Stockton College in New Jersey. This was an early large-scale closed-loop system, installed in the 1990s, that had a cooling-dominated load. Over time, the ground temperatures drifted higher and eventually a cooling tower had to be installed in the geoexchange circuit to relieve some of the heat build-up in the ground.

Source: http://www.neiwpcc.org/waterresourceprotection/wrp_docs/Stiles-GeothermalatStocktonCollegeNJ.pdf

These ground temperature drift problems tend to happen more with closed-loop systems. In standing well open-loop systems the temperature swings are more moderate, ranging from 45^oF in the winter to 65^oF in the summer. Open-loop systems rely more on the temperature moderating properties of the water table. Water conducts heat better than earth or granite and slow introduction of fresh water into an open-loop system by movement of the water table and the bleed stream helps to further moderate temperatures. However a good understanding of geologic characteristics and local underground water flow is required beforehand and for these systems a test well is often drilled.

Clearly, as you can see from the discussion above, there are many critical technical considerations involved in the installation of geothermal system. Installing a high performing and reliable system requires proper design and engineering, an experienced geothermal installer and a willingness to avoid "cost savings" shortcuts. Quite frankly, this is not something that you can just rely on your local HVAC contractor to install. Involve a geothermal expert in the design of your system to ensure the equipment you are installing is not undersized or oversized.

Design of a geoexchange system is a task that involves a compromise between the geological characteristics of the area, the heating and cooling loads, the specified equipment and a natural desire to keep installation costs down. Installation costs need to be managed and you need to be very involved but, before you even start, take a look at what you can do to reduce heat loss from your building. Money spent on better insulation and improving the building envelope will help reduce the size and cost of a geoexchange system. Installation costs can then be further reduced by taking advantage of the federal and state incentives. The Federal government provides a tax rebate of 30% for the cost of a geoexchange system and, if you are a customer, PSNH will contribute up to $4500 of the costs through their Energy Star program.

The installation of a ground-source heat-pump system is a complicated endeavor. Be willing to pay for expert advice and project management so that you will end up with a well-designed and -installed system that will, like the Merrimack County Nursing Home project, deliver on its design promises when drawing energy from the cold ground* beneath our feet.

Until next time, remember to turn off the lights when you leave the room.

Mike Mooiman
Franklin Pierce University
mooimanm@franklinpierce.edu
5/27/13

(*Cold Ground – This is a tune by a rather obscure group by the name of Rusty Truck which is fronted by Mark Seliger. Mark is better known for his famous photographs of celebrities and musicians including Bob Dylan, the Rolling Stones, Mark Cobain and others. His work has appeared on over 100 Rolling Stone covers. Even though he has been on the other side of the camera lens for most of his career, he clearly has made some friends in the process. On his first album, Broken Promises, he had Sheryl Crow, Jakob Dylan, Willie Nelson and Lenny Kravitz as guests, among others. Enjoy Cold Ground produced by T-Bone Burnett and featuring Sheryl Crow on backup vocals.)

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Burning Ground* - Geothermal Energy in New Hampshire

This week I am going to take a look at geothermal energy - the energy source that lies right beneath our feet. When we discuss geothermal energy we must be aware that there are essentially two forms of geothermal energy.

The first is the type that utilizes the high temperatures of underground rock formations in areas where there is a lot of geologic activity which is often indicated by the presence of hot springs and geysers. Places like Yellowstone immediately spring to mind. In this form of geothermal energy, water is pumped down deep wells, some as deep as 5 miles, to access rocks that have temperatures in excess of 212^oF. The water is heated by the rocks and is drawn back to the surface to produce steam which can be used to drive turbines and generators to produce electricity. The source of energy in these sites comes from the earth's internal heat which is produced from the decay of radioactive elements in the rocks or the heat flow from the earth's mantle where the earth's crust is thinner.

There are a good number of locations where we can access this energy, and as the US geothermal heat flow map below shows, these red colored areas lie largely in the western portion of the US. To generate electricity from geothermal sources, one needs rock temperatures in excess of 212^oF at reasonable depths. Interestingly, on close examination of the geothermal map below, one can see that there is a hotspot in NH located in the White Mountains area. At depths of 6.5 miles, rock temperatures in this area are in excess of 400^oF due to the abnormally high natural radioactivity of the granite in this area. This is a source of energy we might have to tap one day.

Graphic Sources: http://www1.eere.energy.gov/geothermal/pdfs/egs_chapter_2.pdf

The other type of geothermal energy we can access comes from the dirt beneath our feet. In many areas, the temperature of the ground, 4 or more feet below the surface, is a moderate 50 to 55^oF. We can utilize this property of the earth and draw heat from the ground in the winter or use the cooler ground temperatures to dump heat into during the hot summer months. This utilization of the energy in the ground beneath our feet is more correctly termed "geoexchange". Some like to call these arrangements earth exchange or ground source heat pump systems. This form of earth-based energy is very different from the "hot rock" type of geothermal energy as the source of energy in these geoexchange systems actually comes from the sun's warming of the earth surface. So, in essence, these geoexchange systems are indirectly a form of solar energy.

Because the ground temperatures are so low compared to the traditional geothermal systems which utilize the temperatures of hot rocks deep below the earth's surface to produce electricity, these geoexchange units cannot produce electricity. Instead we use the earth as a heat sink – we dump excess heat energy into the earth during the hot summers and we draw heat energy from the ground in the cold winter months to preheat the circulating air or water in our homes. But, and this is important in the understanding of these systems, it takes energy, in the form of electricity, to make these low temperature systems work. The electricity is needed to drive a device called a heat pump.

Most of us are familiar with heat pumps but we don't recognize them as such. The refrigerator in your home is a heat pump. What the refrigeration system is doing is drawing the heat from inside your refrigerator and pumping it into your kitchen. It does this through the compression and expansion of a refrigerant gas which provides the medium whereby heat is drawn out of the refrigerator and pumped into the kitchen. Because this device requires electricity to run the compressor pump and the warm air of the kitchen to work, it is referred to as an air-source heat pump. This is the same principal an air conditioner works on, which is pumping heat from inside the home into the warm outside air. With the geoexchange units we don't pump the energy into the hot summer air outside the home; instead we pump the energy into the cooler ground below our feet, which is why these units are called ground-source heat pumps. The fact that the ground is cooler than air makes these ground source units more efficient than the air-source units in typical air conditioners.

These heat pumps can also work in reverse. They can draw the heat from the air outside the house, or the ground, and pump it inside to warm up your home. You might be thinking that sounds awfully complicated when you can simply heat up the inside of your home with an electrical heater or your natural gas or oil burner. However because you are drawing energy from the moderate temperatures in the earth, you do not need as much energy as you would from an electrical or fossil fuel heater. In fact because you are drawing on the indirect solar energy stored in the earth, these heat pumps require only 25% to 35% of the energy you need to heat your home compared to an electrical heater. The ratio of energy needed to heat a space with an electrical heater to the energy used by a heat pump is termed the Coefficient of Performance, or COP, and is the basis of comparison between different heat pumps. For example, the COP value for a heat pump that requires only 25% of the energy to heat your home compared to an electrical heater is 4, calculated as follows

Coefficient of Performance = Electrical Energy required to heat home
                                               Electrical Energy consumed by heat pump

           = 100%
                25%           
            = 4.

Ground-source heat pumps range in performance with COP values of 2.5 to 4, with typical values in the 3.3 to 3.8 range. It must be noted that these values are highly dependent on proper engineering, the quality and efficiency of the mechanical device as well as the temperatures in the ground.

In geoexchange systems there are two main components, the heat pump and the circulation system that is drawing the heat from the earth. The circulation systems come in several different configurations. The most common, and the one most often used for homes, is the horizontal configuration in which the piping, containing an inert fluid, is buried in a shallow trench 4 to 6 feet deep alongside a home. The piping is made of plastic and is laid at the bottom of a trench in a slinky arrangement as shown in the figure and photo below.
 

These are referred to as closed loop systems as the circulation fluid, similar to antifreeze, is never directly in contact with the ground. Instead it is circulated between the heat pump and the ground through the piping. The heat pump draws the energy out of fluid, cooling it in the process and pumps the heat energy into the house. The cooled fluid is then circulated through the piping buried in the ground where it is heated up again to the ground temperature before returning to the heat pump.
 
Another type of closed loop configuration is a vertical system where the piping is enclosed in wells which penetrate deep into the ground as shown in the figure below. The advantage with these vertical closed loop systems is that, in these deep wells, the piping can come in contact with the ground water and water is a highly efficient medium for transferring the heat from the ground to the circulating fluid. These vertical systems also require a smaller surface footprint than the horizontal equivalents which can be crucial when space is limited or the heating loads are large, such as one might find in a school or apartment building.

A different type of system is the open loop configuration where the circulating fluid is ground water that is drawn from a vertical well and injected back into the ground via another well as shown in the diagram below.

 

There are many variations on these types of open loop systems including a standing-well system where the water is drawn from the bottom of a deep vertical well and is then returned to the top of the same well. With these standing-well systems, there is often a small amount of the circulating water, typically 5 to 10% of the water flow, that is not returned to the well. This bleed stream depletes the water in the well and this encourages the flow of fresh ground water into the well which promotes the maintenance of constant temperatures in the well and circulating water.

Most geoexchange units are, energy plant wise, relatively small scale units and are designed for specifically for individual residences or facilities such as hospitals, office complexes or nursing homes. There are also fair number of vendors of these systems that have been operating for a number of years in NH. As a result, it is difficult to get good reliable data on the total installed base of geothermal energy units in New Hampshire and my best guess is that there are many thousands of these units installed in homes and buildings throughout NH. In fact, some developers are building whole housing complexes and communities that make extensive use of geothermal energy.

In my chats with geoexchange system installers and folks who have these units in their homes, I have learned the following:

• These units are expensive to install and prices for a residential system, including the well, heat pump and circulating system, range from $20,000 to $35,000
• Because the installed costs are so expensive, sometimes the units are under-designed to save on upfront equipment costs. As a result, the systems are undersized and do not work well, particularly when temperatures are colder (or hotter) than usual. In these undersized systems, there can be an enormous draw on electrical backup heating systems which then significantly diminishes the savings.
• For the well-based systems, the choice between a closed loop and an open loop system is a difficult one and can be quite site specific. Each system has its own pros and cons and each has its advocates and detractors
• After installation, the owners either love or hate them. I have heard stories where owners are disappointed that the promised savings did not materialize or where there have been issues associated with the circulating systems or heat pumps. And then there are the owners who are delighted with their units and pleased to share with me that they no longer have fossil fuel bills.

I was interested in determining the financial return for installing a typical geoexchange system into a home with a pre-existing forced air heating/and cooling system so I ran some calculations based on my residence which is a typical New England home. Here are my assumptions

• Home Footprint: 2500 square feet
• Electricity Use: 12,000 kWh/year @$0.13 per kWh
• Oil Consumption for Heating: 800 gallons per year @ $3.75 per gallon.
• COP for Geoexchange System: 3.5
• Installed Cost: $25,000 with 30% federal tax rebate

With this data I determined that my annual savings would be $1800 per year which would yield a 9-year payback which is OK if I intend to stay in the house for more than nine years. However, I decided to do a more sophisticated calculation in which I assumed a 2% annual increase in the costs of electricity and a 4% increase in the cost of oil. On this basis, the payback period drops to 7.5 years and a single one-year long oil price spike would probably push that down to 5 years. Further calculations showed that the calculated rate of return for the project over 20 years is 14% which means I would be ahead of the game if I funded this project by borrowing for anything less than 14% which is pretty easy to do in these low interest days. Certainly food for thought and it looks like an option I might want to consider, however the best time to do so would be when I eventually have to replace my oil burner. In this situation I would be able to incorporate the costs of a new oil burner into the calculations and now the payback period drops to 4 or 5 years which makes a geoexchange system very attractive.
 
In NH we don't have the readily accessible hot rocks and burning ground* type of geothermal energy the folks out West do, but just 4 feet down we can access the solar energy stored in the cool earth. There are lots of opportunities for us to do so and I encourage you to consider a geoexchange unit when you build a new home or you have to replace the natural gas or oil burner in your home. Yes, it is a hefty investment but forward-looking, energy-conscious folks consider a 4 to 5 year payback to be a good return on an energy project.

Next week I will be discussing a large and impressive geoexchange project in NH I have recently visited plus I will share with you some geoexchange cautionary tales. I would be interested in your experiences with geoexchange systems so be sure to share them with us in the comment box below.

Until next week, remember to turn off the lights when you leave the room.
 
Mike Mooiman
Franklin Pierce University
mooimanm@franklinpierce.edu
5/20/13 

(*Burning Ground – A fabulous tune by Van Morrison from his 1997 Album "The Healing Game". One of those driving songs that makes you want to roll down the window, crank up the volume and sing along.)

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