Net-zero in West Tisbury: Wind Turbine and Geothermal



Nelson Mechanical Design, Inc. installed a geothermal heat pump system in a West Tisbury residence that was electrified by a 5 kW wind turbine.  The use of wind energy and geothermal heating and cooling led to a net-zero energy and carbon footprint for this home.  Since the project was finished over 5 years ago, the homeowners have had no service issues with the geothermal heat pumps.



The house has a six ton heating load so we installed two three ton water to air geothermal heat pumps.  Each heat pump is then split into two zones.






Each heat pump was served by its own loop circulator.  This made each heat pump independent and reduced the chance of losing heating or cooling in the entire building if there was an issue with a circulator.


Fielder geo ball slinkee before install Dec 2010

One important innovation was the use of “Geo-Balls” to reduce the size and cost of the geothermal field – when used in a horizontal geothermal field, a “Geo-Ball” reduces excavation costs by up to 30% compared to a conventional geothermal field.



Fielder geo trench w geo ball slinkee rolled out Jan 2011

Each “Geo-Ball” consists of 1000’ of ¾” plastic pipe that is configured in a “slinkee” fashion that shrinks its length to 130’. Manufactured in Bristol, NY, each “Geo-Ball” is shipped in its spherical form and unrolled on the site into a trench 6’ deep, 3’ wide, and 130’ long.  We installed 6 “Geo-Balls” at this project to meet the 6 ton heating load.



The use of “Geo-Balls” effectively shrinks the size of the geothermal field so that it can more easily fit within the permitted construction area, ensures uniform heat transfer between each of the loops, and reduces excavation and landscaping costs.

Our goal is to be Martha’s Vineyard’s premier plumbing and HVAC shop – we appreciate the opportunity to show you some of our work.