What’s what in green tech


Brian Nelson, an owner of Nelson Mechanical in Vineyard Haven, summarizes the pros and cons of various alternative energy sources, as follows:

Mr. Nelson says our Vineyard homes are getting more efficient, but we still expect to have more on-demand domestic hot water and typically have larger homes than most European and Japanese green equipment is designed to serve. One creative solution is the “retrofit hybrid” — use the green equipment for 80 percent of the heating load ( which works out to be around 90 percent of the heating season) — and use the existing fossil-fuel system for the really cold days. That’s the best mix, getting the value of what you have while operating most of the winter with the most efficient heating mode.

Geothermal requires land, and drilling is difficult in some places, but geothermal offers tax credits and great efficiency for larger systems. Geothermal offers great flexibility with pool and space heating and cooling and integration with solar, etc.

Solar hot water is great, but the sun’s contribution is smaller in winter, making heating more difficult. Great in the summer for domestic hot water and pools.

Air-to-air heat pumps, such as those made in Japan, have efficiency approaching geothermal all winter long and have the same operating cost (about half of fossil fuel) for half the install cost of geothermal. They work well with solar systems and are very easy to use in many small rooms/zones).

Air-to-water heat pump can be used for radiant heating and domestic hot water — using the same outside unit as the regular Japanese heatpumps, but with an inside “hydro box” that converts “stored solar energy” in the outside air into water hot enough for showers and heating. All that at half the operating cost of fossil fuel and half the cost of geothermal.

Pellet boilers and stoves. Some folks don’t mind combustion and like the idea of a carbon-neutral heating system).