Perfecting Residential Geothermal HVAC Design, Installation
Better Training Leads to Fewer Problems when Installing Geothermal
Homeowner interest in geothermal heat pumps (GHPs) has surged in recent years due to increasing energy costs as well as generous tax credits offered by the federal government. This increased interest has prompted numerous HVAC contractors to start offering geothermal systems in an effort to help customers take advantage of the tax credits as well as provide them with an energy-efficient HVAC solution.
While many of these GHP systems have been designed and installed properly, there have been issues with others resulting in complaints of not enough heat in the winter and/or cooling in the summer. In most cases, the problems involve the loop field being designed or installed incorrectly or contractors using rule-of-thumb guidelines as opposed to actual calculations. Fortunately, more information is now available to help contractors avoid making costly mistakes when designing or installing GHP systems.
When GHPs first started to seriously generate interest more than 25 years ago, contractors and engineers did their best to accurately design the systems, but geothermal was not yet a perfected science, said Jay Egg, certified GeoExchange designer (CGD), EggGeothermal, Tampa, Florida. “A lot of research and development has taken place since then, and, over the last five years, it has really become a perfected art. If contractors don’t do it right these days, it’s because they have not taken the time to be properly trained.”
One area in which many contractors can use additional training is the design of the loop field, which is often undersized. “If you don’t calculate the load right, you’re going to have problems with not getting enough heating and cooling,” said Egg, who also serves as a geothermal speaker, trainer, and author. “Fortunately, loop-field design has been simplified significantly, as there are computer models and design software available that make it all a lot easier. Training is also readily available through IGSHPA [International Ground Source Heat Pump Association] or the GEOExchange.”
Even so, grossly underestimating the size of the loop field is one of the biggest mistakes that Jeff Persons, CGD, president, Geo Source One Inc., Plain City, Ohio, still sees. “Far too many contractors install loop fields based on hearsay information on the Internet and not by actual site, soil, or rock conditions. We often acquire these installations after the original installers either go out of business or fail to answer customers’ requests for service.”
Guy Wanegar, president, A&B Cooling and Heating Corp., South Windsor, Connecticut, agrees, noting that contractors often shorten the loop, believing they will realize a cost savings, but that does not usually work out well. “My very first geothermal job was through a utility program. The equipment representative and a utility representative said my loop design was too costly due to the footage required; however, after the first cold winter here, the utility had to add an extra bore hole. I have not compromised since.”
Another problem with system design is the tendency to size equipment based on the square footage of the area to be conditioned. While this does play a part in system design, said Persons, it can cause problems, particularly in larger homes that may use two units — one for the main floor and another one for the second floor. “Invariably, when we encounter a new customer with a comfort issue, it seems to be a result of the second-floor system being sized for the square foot load of that space without taking into consideration the warm air from the main floor will rise, adding dramatically to the cooling load on the second floor.”
To solve this type of problem, Persons sizes each system to accommodate about 70 percent of the combined peak load. For example, the block cooling load for a home may be 72,000 Btuh, but the finished square footage of the second floor may be 30 percent of the total finished area, however, the open area of the second floor may represent 50 percent of the area due to cathedral ceilings, a balcony, loft, or an open two-story foyer. “In this case, I would install a 48,000 Btuh system rather than a 24,000 Btuh system (70 percent of 72,000 equals 50,400 Btuh) for the second floor to help maintain a comfortable temperature in the summer and avoid customer complaints. In the winter, much of the heat provided to the main floor will rise to assist with heating the second floor.”
In new construction, Persons likes to address this issue right off the bat by discussing it with the homeowners, architect, and/or builder. “I prefer to use a single-zoned system where the entire capacity of the geothermal system may be dedicated to the upstairs or downstairs zone or shared between them. This avoids the added expense of installing two oversized systems to manage the disparity in loads between the upper and lower levels.”
For more tips, courtesy of Persons, check out his book, “Understanding Geothermal Systems.”
Installation and Training
Installation techniques have also improved over the years with drilling methods now available that minimize ground disruption. “With horizontal drilling, you can do almost all of your drilling from one location in certain applications,” said Egg. “And with pump to injection systems and standing column systems, you can provide conditioning for an entire building off a couple of bore holes in certain situations. Reduction of bore holes due to drilling types and techniques has helped significantly.”
Better foundation sealing techniques have also been devised, replacing the hydraulic cement or silicon rubber that were often used in early installations to seal around the loop lines entering the foundation wall. These seals often failed due to the thermal expansion and contraction of the polyethylene loop lines, resulting in foundation leaks and call backs, said Persons. “A flexible foundation seal is needed to allow movement of the geo lines inside a sleeve that is sealed to the foundation. We now accomplish this by using a 2-inch polyvinyl chloride (PVC) sleeve with rubber reducer couplings on each side. The sleeve is doped up with several bands of concrete adhesive sealer and inserted into the cored foundation. Additional adhesive is applied to the interior wall penetration before the interior fitting is secured to the sleeve. The 1.25-inch polyethylene loop lines pass through the fittings and are secured with band clamps to allow for flexing with temperature changes, yet they provide a water-tight seal.”
While the design and installation of geothermal systems may seem a little more complex, the key is to get the proper training, said Wanegar. “I went through intensive training at IGSHPA, and that taught me everything I needed to know — except the confidence to stick to my guns on that first job. In my opinion, you cannot properly design a geothermal system without this training. And you need to keep it up. I’ve continued my training to become a certified geoexchange designer, and I recommend that any consumer ask for references as well as IGSHPA-certification.”
Egg agrees that ongoing training is a must because the industry changes every year, and contractors need to keep up with all the latest trends. The good news is that many contractors seem to be heeding that advice, because Egg notes that he is seeing far fewer problems these days. “I would say complaints about improperly designed geothermal systems have gone down to about 10 percent of what we were seeing in 2010 and that’s all due to better education in the industry.”
SIDEBAR: Learning from Egg-sperience
Jay Egg is candid in noting there was a large learning curve when he first became involved in the geothermal industry, and he can chuckle now about one of the first systems he designed in 1990.
He had just finished his geothermal training at Oklahoma State University, and he installed a closed-loop system for a mansion in Tarpon Springs, Florida. The horizontal ground loop covered about 2 acres, and for three years the system seemed to work fine. Then, one day, Egg received a call from the homeowner, who wanted to know why his lawn was dead.
“It turned out that the loop had warmed up to the point where it had actually burned the grass until it turned white,” said Egg. “I learned right then that a closed loop isn’t always the best thing to install in a tropical climate. Fortunately, I was able to remediate the situation by putting in a Class V pump re-injection system to take out some of the extra heat, and it worked great. He hasn’t had a problem since.”
Egg is passionate about teaching contractors and engineers about the art of GHP design, which is why he wrote two books (“Geothermal HVAC” and “Modern Geothermal HVAC Engineering and Control Applications”) about the topic and gives regular workshops around the country.
“It used to be that people had to go to Oklahoma to get trained, but now they can go to regional workshops put on by IGSHPA, GEOExchange, and/or the American Ground Water Trust. These workshops provide continuing education credits to various professionals, and the information is up to the minute on industry hot points.”
Publication date: 7/28/2014