A super efficient heat pump with a GWP of 1
Dan Whitmore, project supervisor for Hammer & Hand, explains part of the mechanical system for a Passive House they recently completed: an air to water heat pump with en efficiency twist.
The technology is similar to a standard air-source heat pump: an outdoor unit extracts heat from the air and stores the heat in water. What is new about this Sanden unit is the refrigerant: R 744—CO2—which has a global warming potential of one.
One.
"Most heat pump water heater technologies use two other refrigerants, which have GWP of nearing 2,000 ...
This one has a global warming potential of one. It also has a significantly higher capacity. Because we are using CO2, the machinery can deliver energy from the outside air at a lower temperature and take it to a higher temperature.It's a wider range, so we do not end up needing the electric backup that the Altherma needs."
So we have this wonderfully efficient tank, it's going to deliver the space heating for the building, it is also going to deliver domestic hot water for the building, at a really high performance level, and purely from the air outside.
So it's going to take heat—even at negative five degrees, this unit has been demonstrated to take heat out of the air and put it in the water. We will be able to use it all year round here in Seattle, where it just does not go below zero degrees.
The actual demand for hot water, may outstrip the capacity for the system, because there are four bathrooms besides the kitchen and laundry. Because of this stretched limit, and the new technology, Hammer & Hand included an on-demand water heater backup.
—Dan Whitmore is a Certified Passive House Consultant (CPHC) and Project Supervisor for Hammer & Hand, a general contractor that specializes in high performance building with offices in Portland and Seattle.