U.S. homeowner installs CO₂ heat pumps to decarbonize

On his website (http://greencomfort.nationbuilder.com), Dave Sweet calls himself an “eco-friendly homeowner and builder” whose goal is to “use as little energy as possible while maximizing comfort for my wife, my daughters and I.”

Sweet, who has been building his own homes since the 1980s, described the steps taken in building his current (and ninth) home in Old Saybrook, Conn., in a series of videos on his website. One of the innovations was the installation of two Sanden CO₂ heat pumps outside the house to generate hot water and space heating.

He’s also using an induction cooktop and an electric fireplace, and generating more than half of his electricity from 42 solar panels (13 kW). “The idea was to totally decarbonize,” he said.

Sweet admires the efficiency of the Sanden units, derived from the large differential (from 60°F to 100°F) between the temperature of the return water from the house and the temperature to which the temperature is heated in the units. Sanden’s hot water temperature setting ranges from 130°F to 175°F.

The standard Sanden system that supplies space heating and hot water employs only water, a water tank and a separate heat exchanger. Sweet created his own design that employs a glycol solution. “I’m a tinkerer,” he said.

The heat pumps, each with a capacity of about 14,000 BTUs/hr, generate a hot glycol solution that is delivered to a 119-gal tank with a heat exchanger coil at the bottom, where potable water is heated and pumped out to the house. Separately, the heat pumps deliver heated glycol to the radiant heating systems in his home. He uses an electric element backup.

Though the Sanden units are more expensive than alternative heating systems, Sweet believes there is a good payback. “I can’t imagine a conventional piece of equipment being able to do space heating and domestic hot water; this is the only product in that classification.” He also recommends it as a domestic water heater only.