Launch Slideshow

A Ground-Source Heat Pump for an Oceanside Home

A Ground-Source Heat Pump for an Oceanside Home

  • http://www.jlconline.com/Images/1356622639_Geothermal-1_tcm96-2159327.jpg

    true

    600

    A well drilling rig from Amherst, New Hampshire-based Skillings and Sons drills one of three 400-foot-deep vertical wells for the geothermal ground loop for a ground source heat pump (GSHP) heating and cooling system for a house on the Massachusetts shore north of Boston. Drilling three wells took the crew and rig two days on site. The truck carries sections of drill shaft in a rack; as the well gets deeper, the operators pause to attach new drill sections to the shaft. In the foreground, a water pump extracts groundwater flowing from the borehole.

  • http://www.jlconline.com/Images/525688149_Geothermal-2_tcm96-2159328.jpg

    true

    600

    Some geothermal wells are dry, but some produce water. This well produced 100 gallons per minute of fresh water after the shaft reached the water table, requiring a pump setup to extract the excess water as drilling continued.

  • http://www.jlconline.com/Images/1903266745_Geothermal-3_tcm96-2159329.jpg

    true

    600

    The drilling crew dug this sump trench to manage the overflow of fresh water produced by the ground loop well shaft. Homes in the area have fresh water supplied by a municipal water system, but many also have drilled wells that produce water for use in landscape irrigation. Despite the area’s location on the shore of the Atlantic Ocean, the wells produce fresh water.

  • http://www.jlconline.com/Images/1839418161_Geothermal-4_tcm96-2159333.jpg

    true

    600

    After the third well reaches the target depth, the crew withdraws its drill shaft from the borehole and stores the shaft sections in a rack on the side of the drill rig.

  • http://www.jlconline.com/Images/888996063_Geothermal-5_tcm96-2159334.jpg

    true

    600

    After completing the final well shaft, the crew pulls its drill truck away from the well, in preparation for inserting the geothermal ground loop tubing.

  • http://www.jlconline.com/Images/2011182533_Geothermal-6_tcm96-2159335.jpg

    true

    600

    The crew smooths the grade around the well head with the bucket and blade of a skid-steer mini-excavator.

  • http://www.jlconline.com/Images/1114867054_Geothermal-7_tcm96-2159336.jpg

    true

    600

    A crew member spins the top coupling off the well casing, prior to inserting the geothermal heat exchange tubing for the heating and cooling system’s ground loop.

  • http://www.jlconline.com/Images/510348880_Geothermal-8_tcm96-2159330.jpg

    true

    600

    The crew inserts the end of the ground loop into the top of the well shaft. The end of the tube is stiffened with several sections of rebar, lashed together with rubber tape.

  • http://www.jlconline.com/Images/2051691387_Geothermal-9_tcm96-2159331.jpg

    true

    600

    Two crew members guide the tubing into the well shaft while a third unrolls the tubing from a trailer-mounted spindle.

  • http://www.jlconline.com/Images/1748464608_Geothermal-9a_tcm96-2159324.jpg

    true

    600

    As the air-filled plastic tubing descends into the groundwater-filled well shaft, flotation becomes an issue and the crew has to fight against the buoyancy of the tubing. At that point, the crew connects the tube to a water spigot and fills the tubing with water to eliminate the buoyancy and equalize the weight, allowing the tubing to descend more readily into the shaft.

  • http://www.jlconline.com/Images/539285914_Geothermal-10_tcm96-2159332.jpg

    true

    600

    Once the full length of tubing has been inserted into the well shaft, the crew continues to run water into the loop in order to flush out any remaining pockets of air. When the spurts of mixed water and air change over to a continuous flow of water, the crew will disconnect the tube from the water supply and clip the ends.

  • http://www.jlconline.com/Images/377847608_Geothermal-12_tcm96-2159325.jpg

    true

    600

    A crew member clips the end of the plastic tubing.

  • http://www.jlconline.com/Images/1983700352_Geothermal-13_tcm96-2159326.jpg

    true

    600

    A crew member secures the tubing loop to the well shaft with an optic-orange comealong strap, and seals the ends of the tubes with rubber tape. The well head is now ready for the next step: connecting the ground loop to the house.

Energy upgrades for existing homes often focus on the demand side, and involve major modifications to the building envelope, such as improving the air-tight envelope, boosting insulation levels, and replacing windows and doors. But the supply side can be just as important — particularly in situations where upgrades to the envelope would be costly and complicated.

Coastal Connection is keeping tabs on just such a job in the town of Rockport, Massachusetts, on the Atlantic shore north of Boston. Treehouse Design, a design-build firm with decades of experience in the area, is handling the remodel of an oceanfront house that has just been purchased by new owners.

Company founder Tim Thurman says that the existing building, constructed in 1987, places difficult constraints on any effort to improve insulation or air-tightness. The footprint is complicated, with a multitude of boxy room sections, complex intersecting hip roofs, and cathedral ceilings. Adding insulation would require demolishing and replacing interior finishes that are still in good shape — and the intricate shapes involved would make that an expensive proposition. "We could do it," says Thurman, "but it would be so expensive that it would almost be cheaper to tear down the house and start over." Instead of that complex and risky endeavor, the new buyers have opted to install a more efficient heating and cooling system — in this case, a ground source heat pump (GSHP) with three 400-foot geothermal wells.

In two previous geothermal projects, says Thurman, he has figured out a way to hit a cost-effectiveness "sweet spot." Massachusetts has a heating-dominated climate, where houses need more energy for heat in the winter than for cooling in the summer. But Thurman has chosen to size his geothermal systems for the smaller cooling load, not the larger heating load. He makes up the difference with a backup oil boiler and indirect water heater — which also supplies ample domestic hot water for the home (sometimes an issue with geothermal systems). The result is an HVAC system that cools effectively all summer long, and meets the home's heating needs for all but a small number of winter days (when the standby boiler kicks in to make up the difference). The savings on the up-front cost of the geothermal ground loop (the heating system's biggest cost factor) is significant, says Thurman: "Basically, with the boiler as backup, we only have to drill two wells instead of three."

For this job, however, the new owners are adamant that the house should not rely on fossil fuels at all (ironically, they are engineers working in the coal and oil industries themselves). So Thurman has sized the geothermal ground loop to supply all the home's heat. An electric on-demand water heater will supply domestic hot water. This means forgoing the up-front cost advantage of the hybrid geothermal and propane setup Thurman has used in the past. But he says that in terms of the owners' wallets, this cost issue may be a wash. Current tax law provides a tax credit of 30 percent of the up-front cost of a geothermal heat pump system. "That tax credit is very useful to clients with high earnings," Thurman notes.

Coastal Connection will be following Thurman's job in coming weeks. For a look at the drilling of the three wells for the ground loop, see the slideshow.