Snow melting systems require large amounts of energy for short periods of time, so they are generally not well-suited for geothermal heat pump systems.
In a hydronic/geothermal system, a water-to-water geothermal heat pump is used to deliver warm water to a building for a low temperature hydronic heating system, such as in-floor radiant heat. “They’re the ultimate in comfort systems. When we combine geothermal and radiant heating systems, customers get the best of everything - comfort, energy efficiency, and environmental friendliness. We have a hydronic/geothermal system in our office and warehouse, and we recommend it for our clients as well.”
While Landis is effusive in his praise of hydronic/geothermal systems, customers in his area have not yet tapped into his enthusiasm. Of the more than 300 geothermal system installations J.K. Mechanical Inc. performed last year, only about 5 percent involved a hydronic component. Perhaps that is due to the higher initial cost of these systems, but more likely it is because the current federal tax credit of 30 percent does not apply to most water-to-water geothermal units.
Regardless of the reason, Landis believes that hydronic/geothermal installations will grow in popularity as more customers experience the “unsurpassed comfort” these systems can deliver.
Contractors need to be particularly concerned with properly sizing the unit inside the house, as well as the outside ground loop. (Photo courtesy of WaterFurnace.)
MANY OPTIONS
The tax credits have definitely impacted the sales of standard water-to-water geothermal units, said Galen Betz, regional manager, WaterFurnace, Fort Wayne, Ind. “Sorting it out can be difficult at times. The way the tax credits work, the equipment has to have an Energy Star rating, and there is no system in place for testing water-to-water products.”That’s not to say there are no water-to-water geothermal systems out there that qualify for the federal tax credit; indeed, WaterFurnace recently introduced its Synergy 3D combination unit, which provides forced air cooling, forced air heating, and the water-to-water function for in-floor radiant heating applications. This particular unit qualifies for the federal tax credit, which is one of the reasons why the equipment is selling so well, added Betz.
Water-to-water geothermal heat pumps are most often paired with in-floor radiant heating systems to provide space heating, as well as other functions such as pool heating and domestic hot water. “Pool heating is a great application for geothermal heat pumps, since more heat is available in spring, summer, and fall to heat the swimming pool while the heat pump is also cooling the building,” said Lance MacNevin, Unit Manager – Rehau Academy, Rehau Construction LLC, Leesburg, Va.
A heat pump with a desuperheater option is also capable of producing domestic hot water most of the time, though perhaps not at peak heating loads. Snow melting systems require large amounts of energy for short periods of time, so they are generally not well suited for geothermal heat pump systems, added MacNevin.
Besides radiant heating systems, water-to-water geothermal heat pumps can be paired with other hydronic equipment, such as hot water baseboards or radiators. These applications may require supplemental heat - such as an electric heating element - to make the water hot enough for heating the space. As Landis noted, a hydronic/geothermal system will generally not provide the output needed for baseboards or radiators on its own.
“Hot water baseboard systems often require water temperature of 160°F or more, and geothermal heat pump systems operate more economically when delivering water in the 110° to 115° range,” said MacNevin. “Therefore, radiant heating is the most comfortable and efficient heat delivery option. Another benefit is that heat pump units may be able to perform 15 to 25 percent more efficiently when used with radiant heating.”
When supplemental heating is needed in a hydronic geothermal system, Bill Landis sometimes adds radiant panels to the floor or ceiling.
DESIGN DIFFERENCES
There are some pretty large differences between the design and installation of a more conventional water-to-air geothermal system and a water-to-water geothermal system, so additional training is required. As Landis noted, installing a water-to-air system is very similar to a conventional furnace or air conditioner installation, with the exception of the ground loop, of course.“For hydronic heating, you have to make sure you’re paying attention to floor coverings and R values underneath and above the tubing. Those are very important in the design phase, because you have to make sure you’re providing the right amount of heat to a home,” said Landis. The floor coverings factor into the equation, because carpet, for example, does not conduct heat as well as ceramic tile, and many homes have a combination of different flooring.
This combination of flooring requires a more comprehensive control system, as the temperature of water used in a tiled hallway will be different than that used in a carpeted bedroom. The advanced level of control is one of the reasons why these systems are so comfortable, though, added Landis, it is possible to put a thermostat in every room and have each set at a different temperature.
Outside temperature also plays a part when correctly designing a hydronic/geothermal system, as it is not necessary to make as much hot water when the outside temperature is 40° versus 20°. “The hydronic/geothermal system efficiency goes way up if you don’t heat the temperature of the water so high on more temperate days,” said Landis. “That is why outside air temperature monitoring is necessary, so the system can adjust accordingly in order to operate as efficiently as possible.”
Another issue that needs to be considered when designing a hydronic/geothermal system is correctly sizing the equipment, which is key to a properly functioning system. “Sizing is the No. 1 issue, not only of the unit inside the house but also the size of the ground loop. We can’t stress that enough in dealer training,” said Betz. “Unfortunately, a lot of contractors take the shortcut and do a rule of thumb when they figure the size of the house, rather than doing their actual homework.”
Indeed, relying on rules-of-thumb makes installers vulnerable to estimating errors, said MacNevin. “Proper heating and cooling load calculations for the building are essential to sizing all equipment correctly. Installers should make it a habit to ask distributors and manufacturers for training and support on specific products to prevent mistakes, especially when utilizing any unfamiliar technology.”
While hydronic/geothermal systems may not yet be as popular as their water-to-air cousins, Landis is confident that will change in the future. “We actively promote these systems, and we think the market will grow. Comfort is a big deal, and when customers find out how comfortable these systems are, they will definitely become more popular.”
Publication date:10/19/2009
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