CO2 Heat Pump Water Heater in Madrona Passive House

PHIUS+2015 Certified on 9/13/2016

Hammer & Hand has built passive houses for five years, and is currently under construction of a 4,100 square foot passive house in Seattle for a client who shares Hammer & Hand’s commitment to both superior home performance and lowest environmental impact, including the most energy-efficient water and space heating equipment, ideally electric to make use of renewable energy and avoid combustion of fossil fuels. Sanden’s CO2 refrigerant heat pump water provides an electric alternative to a gas water heater, which is more efficient than a resistance electric water heater.  Although there are several heat pump water heaters on the market, the low global warming potential of CO2 compared to conventional refrigerants makes Sanden’s system attractive to both Hammer & Hand and its client.

Although Hammer & Hand might ordinarily consider installing a mini-split space heating system in addition to the DHW system,  the home is designed to be cooled by passive measures (solar reflective materials, shading, and night-flush ventilation) and does not need air conditioning.  Relying on the Sanden system for both DHW and hydronic heating completely eliminates the need for an additional mechanical system.

With the passive house’ superior thermal enclosure, it will be an almost-airtight building enclosure with balanced, mechanical ventilation with heat recovery.  However, it will still need a small amount of “active” space heating and domestic hot water, which Sanden’s system should be more than sufficient to do.  If on coldest days the Sanden system does not have sufficient heating capacity for both water and space heating Hammer & Hand may also install a high-efficiency tankless electric DHW system for additional heating capacity.

In the 1990s, Japanese engineers perfected high-pressure CO2 refrigerant heat pump technology (known as “Eco-Cute”).  Available in Japan since 2001, this technology has spread to Australia and Europe, but to date, it has not been available for North American homes.  Now, Sanden International is beginning to import its Eco-Cute system to North America. CO2 is an abundant, natural refrigerant.   CO2 has a GWP of one, far below the GWP of conventional refrigerants (1,000 or 2,000).

The Seattle Residential Code does not allow the installation of  a DHW system until it is tested to UL’s standard and listed by UL.  Although Sanden’s Eco-Cute is not yet tested by UL, the City of Seattle ITAC appreciated the environmental superiority of Sanden’s system and upon satisfying certain conditions, the ITAC has recommended Hammer & Hand be permitted to install the Sanden system.

Hammer & Hand is working closely with Sanden and its electrical and plumbing subcontractors to design and install the system

Benefits: Superior energy efficiency (high COP and reliable heat capacity even in cold weather) and environmental attributes (use of CO2 refrigerant substantially lowers the global warming from refrigerant leaks into the atmosphere).  Typically, refrigerants leak into the atmosphere both slowly during operation and quickly either upon an accidental release or at the end of the equipment’s use if the refrigerant is not carefully captured and either reused or destroyed.

Hammer & Hand is collecting information the City requested to meet the conditions of approval.  Sanden has made an application for testing and listing by UL, and it reported that it expects to complete the process by 2015.  The 2013 testing by Ecotope and Cascade Engineering for Washington State University and Bonneville Power Administration demonstrates that the Sanden system meets the first-hour test.   Sanden is providing proof that it meets the “lead-free” requirements in the Washington (State) plumbing code enforced by the King County Health Department (as the City of Seattle does not have its own residential plumbing code).