Geothermal: Engineer Says Systems Can Lower Costs
Perry
Schools across the United States are turning to geothermal to heat and cool buildings, lower operating and maintenance costs, improve energy efficiency and provide classroom comfort.
Using a heat exchanger, schools can pull heat from the earth during the winter to raise indoor temperatures or pull heat out of the building and discharge it into the ground during the summer to cool interiors.
School Construction News spoke with Tom Perry, director of engineering services for Boston-based Shawmut Design and Construction, about the types of geothermal systems that are available, how much they can save schools on energy and maintenance costs, and some of the challenges facing schools when installing a new system. Perry has more than 27 years of construction experience, including 22 years of working with mechanical systems. He is the leader of Shawmut’s Green Building Committee and an active member of the American Society of Heating, Refrigerating and Air-Conditioning Engineers.
Q: Why is geothermal technology a good idea for schools?
A: It’s considered very cost-efficient, when compared to conventional HVAC systems. It’s the most efficient system out there. You will save money in operating costs, and that’s attractive to schools that have to both manage and minimize those long-term costs. It may have an initial investment that may be more than a conventional system, but the savings that you get from the operating costs and lower maintenance costs will quickly pay back that initial investment.
Q: How long is the typical payback period for a geothermal system?
A: Some of the initial costs to install geothermal wells and ground source heat pumps may vary from project to project. That payback period may range anywhere from five years to 12 years.
Q: Why is a geothermal system considered more cost-efficient than conventional heating and cooling systems?
A: It’s more efficient because you’re taking advantage of the relatively constant temperature of the earth. The system takes that medium, the Earth, to either extract heat from it in winter or to absorb heat in the summer. For instance, in the wintertime, you’re taking advantage of the natural heat of the earth and you’re taking that heat and transferring it to a building. In the summertime, you’re taking the heat out of the building and you’re using the earth as a big heat sink.
Q: Is there more than one type of geothermal system?
A: There are different types of systems. There is the kind that Shawmut is installing, which is a standing column design. It’s a 1,500-foot-deep column that is drilled into the earth and functions as a big heat exchanger in the earth. There is another type that is referred to as a closed-loop system, which is installed at a much shallower depth. It’s a loop of piping that goes up and down, and the surface area of the pipe acts as a heat exchanger.
You don’t want to confuse geothermal with high-temperature geothermal systems, and how they are being used. The word geothermal gets thrown around a lot and can mean several things. There is a type of geothermal system that takes hot water right out of the ground. It uses large plants to extract 300-degree water and use it for heating. Here, we’re not using high-temperature water. We are actually using the ground and a ground source heat pump.
Q: Can a geothermal system heat or cool individual zones of a school?
A: Yes. That’s the nice thing about a ground source heat pump system. The heat pump, which is the refrigeration machine that drives the whole system, can provide simultaneous heating and cooling — whatever is required. You could be heating in one room and cooling in another, depending on what is needed. There’s a thermostat on the wall that operates the heat pump, which will provide either heating or cooling.
The other nice thing about this whole system is that there is no on-site fuel or generation of emissions, which makes it pretty clean. However, we are using electricity to run the parts, so they are not zero-emission systems because we’re buying the electricity that is being produced somewhere on the grid, and that power plant is creating emissions.
Q: What do you do in cases of extreme temperatures? Are ground source heat pump systems suited to those kinds of situations?
A: Yes. You size the geothermal system to account for a specific building. Initially, we’ll do heating and cooling mode calculations to determine what the maximum loads are going to be and then we size the system based on that. We’re also looking at what the worst situation in winter might be: If it’s 5 degrees outside, how much heat do I need to heat my building? In the summer, if it’s 91 degrees outside, how much cooling do I need?
Q: It seems that certain parts of the United States, such as the Midwest and the Northeast, have more geothermal systems in place than others. Do you expect their use to become more widespread in the near future?
A: I think there’s been a lot of activity in the last five to 10 years. A lot of our clients are asking us about geothermal systems, so the word is getting out. Large universities in Boston and Cambridge and also in Connecticut have geothermal on their agenda for their buildings. In the Midwest , I think you’ll see the closed-loop systems grow more prominent. I’m not sure about the West Coast.
Q: Are ground source heat pump systems difficult to maintain?
A: Because you don’t have a boiler or a chiller involved, there is less equipment. It’s proven that the maintenance costs for ground source heat pumps are less than conventional systems, which improves savings and the bottom line for schools.
Q: Would it be difficult for an existing school to install a ground source heat pump system?
A: The system integrates quite well with existing buildings. With the standing column design, there is not a lot of space required. There is less mechanical equipment because there is no boiler or chiller, so a school’s mechanical room can be smaller. Structurally, there is not a lot of heavy equipment that has to be installed on the roof, such as a huge cooling tower that would require new structural upgrades.
Q: Do you have a rough estimate of how much a school can save on energy costs with a geothermal system?
A: It’s going to be all over the board. The Department of Energy and the Environmental Protection Agency endorse these systems and say they are 40 percent more efficient than conventional systems. We’re trying to do some historical logging of energy usage and compare that to conventional systems to see the savings because that’s good information for clients to have.
Q: Is geothermal technology used more frequently in K-12 or higher education projects?
A: We haven’t had a lot of K-12 projects that have used geothermal. We have a lot of preparatory and private schools that use it, as well as universities. It comes down to operating costs and educating owners about the selection of systems. It’s not going to be different from one building to the next.
One thing to consider is how the building is being used. For example, buildings that have a lot of cooling hours would do well with geothermal, as far as the payback is concerned. When you’re comparing geothermal to gas-fired heat in the wintertime and you match those two systems up, they might not do as well.
Q: What are some of the challenges you have encountered when installing ground source heat pump systems?
A: Shawmut is actually in the process of putting together a builders book that includes all of our experiences so we can share this information with others. One of the issues with geothermal installations is that water is generated during the drilling process. Being able to properly discharge the water back into the ground or into a stormwater system requires permitting and having a water management plan in place.
For instance, a project that we recently did for one of our larger clients required us to notify the National Water Resources Association about on-site procedure and how we planned to dump the water. We had a water management system on site that took the sediment out of the water that was coming up out of the well. When you are drilling down you’re cutting rock, so all of those rock cuttings have to come up with the water. You have to take the sediment out and then filter it, so we had sedimentation tanks and a filtration station and we discharged the water to a nearby catch basin, which allowed the NWRA to test the water to see if it was clean and filtered. You never know how much water you’re going to run into. On this recent job we had a tremendous amount of water. Our plan was flexible enough that it allowed us to keep our schedule.
Another important thing about these systems is the integrated acceptance testing, which is how we verify that the system is operating properly. Shawmut will go through a pretty stringent testing of the system and the sequence of operations to determine the system is operating at peak efficiency. It’s important to commission a system after it has been installed.