- Hybrid-ductless heat pumps are a cost-effective option for heating and cooling.
- Average savings for seven houses in Tacoma, WA was 2,636 kWh per year.
- Proper installation and operation is critical for optimum performance.
Homeowners want a comfortable house no matter the outside temperature and they also want such comfort at an affordable cost. One option builders may want to consider for their next project is hybrid-ductless heat pumps (DHP), otherwise known as mini-split air conditioners.
Manufacturers offer numerous mix-and-match capacities and configurations to handle even the most difficult to heat and cool areas. Some units have a seasonal energy efficiency ratio (SEER) up to 21 and a Heating Seasonal Performance Factor (HSPF) of 10. Capacity ranges from 9,000 to 42,000 BTUs and high-performance air filtration is available.
In a study sponsored by the U.S. Department of Energy’s Building America program, DHPs were installed in seven Habitat for Humanity homes near Tacoma, Washington. In a
DHP/hybrid heating system, the DHP fan coil is located in the main living area in combination with electric resistance zone heaters located in the bedroom zones.
These hybrid systems, which have been used in Asia and Europe for years, have the following advantages compared to electric resistant heating:
- Cost less than central heat pumps
- Easy to install; thin copper refrigerant tubing in the wall or ceiling connects the indoor and outdoor units
- Two to four times more efficient, depending on outdoor temperature
- During cold weather, no supplemental heat is required
- Low maintenance; only filter cleaning every three months; change filters monthly or less
- Quiet operation; noisy compressors and condensers are installed outside
- Reduces heating bills by displacing large share of zonal electric heating
In a typical installation, the ductless heat pump provides the largest heating load, with the fan coil providing heat for the main living area. Electric resistance zone heaters are used in perimeter rooms for supplemental heat if required. The performance depends on the home size and efficiency. With a fan coil in every room, the cost increases and efficiency decreases. DHPs work well for one story homes, but not as well for multiple levels; a pump would be required on each level.
The Tacoma study showed:
- Average savings for the seven houses was 2,636 kWh per year (2016 average rate of 8.5 cents/kWh)
- Installed costs averaged $2,746 for a new home
- Life cycle costs: $3,690 benefit assuming 2,800 kWh/year savings for a 1,250-square-foot home
- Average monthly cash flow is positive
- 47 percent savings overall with an energy recovery (ER) system
- For heating, annual savings are 2.24 kWh/square foot; for cooling 2.19 kWh/square foot
With proper installation and operation, DHPs should only have to be replaced twice over the life of the home. They’ve lasted for 18 years in Asia and Europe.
Six out of the seven Tacoma homeowners chose DHPs because of the availability of cooling and better heating performance. They were more comfortable and were happy with the rapid heat-up. Indoor temperature and relative humidity monitoring helped maintain a comfortable environment. After the study, ten out of 11 homeowners decided to keep DHP.
However, homeowner education is critical to proper operation; some occupants turned off ER systems because they didn’t understand the controls. A two-hour homeowner orientation is recommended. Builders should also provide more information on savings and maintenance practices.
Equipment size is based on the load of the home. For heating, size to room or zone; in hot climates, size to the cooling load. If over-sized, units will short cycle and use more energy.
DHPs can work in other climates as well. A builder in Wilmington, NC installed such a system in a new home, reducing the average monthly cost of electricity from $200 to $50.