New Research Identifies Five Ways to Help Preserve Ductless Rebates
Dec 02, 2020
Many Northwest utility rebate programs for ductless heat pumps are not achieving their intended energy savings. Evaluators have found that rebated ductless installations on average are not producing the expected electricity savings. Insufficient energy savings from rebated installations could force some utilities to change their rebate program requirements. The five enhancements outlined below, when combined, can nearly double utility program savings. For many utilities, this savings increase could allow them to continue offering rebates.
In an effort to support utility ductless rebate programs, the NW Ductless Heat Pump Project commissioned a research project called Maximizing Mini-Split Heat Pump Performance. The research included: tests performed on ductless heat pump installations at the Pacific Northwest National Laboratory (PNNL); literature review of work performed by Energy Trust of Oregon and the Regional Technical Forum (RTF), along with roughly 40 other published papers; and interviews with 30 subject matter experts from all over the country.
Findings from the research identified five energy-saving enhancements that the Project shared with utility ductless program staff during a webinar in early November 2020. Now, those same energy saving enhancements are available to Project supply chain partners here.The following table shows the additional savings each of the five enhancements could achieve if implemented.
Read on for more information on the research that led to each enhancement recommendation:
Enhancement #1 - Target Homes with Large Electric Heating Loads
Research results show that utility programs would improve rebated savings by eliminating rebates offered on homes that currently use very little electricity for heating. Utilities would need to identify homes with large electric heating bills and ensure that rebate money is only (or primarily) available to those homes. Currently, most utilities allow contractors to offer a rebate for any home that has electric resistance heat installed, regardless of how much electricity it uses for heating.
It isn’t yet clear if or when utilities might change their program requirements or what they will ask contractors to do differently in response to this recommendation. However, most experts agree that programs will need to target homes with big electric heating bills for rebates. One low-cost idea would require contractors to check the home's electricity use during the winter heating months and compare it to the home’s shoulder season electricity usage. That kind of analysis could help identify if the home has the potential for any significant electricity savings on their heating loads.
Enhancement #2 – Designing Installations to Maximize Displacement
Field studies indicated that the indoor unit of a ductless heat pump system is not always located in a room that allows for the greatest electricity savings. In these instances, the ductless system becomes underutilized, and the homeowner relies more heavily on the original electric resistance heat. Ideally, installers should place the indoor unit of the ductless system in the living room, family room, or other primary living space where occupants spend most of their waking hours. The living room typically has a relatively large floor area, so it represents a larger percentage of the total heating load. If utilities decide to begin requiring this current recommendation for their rebate programs, a combination of increased site inspections and enhanced contractor training could help deliver improved savings.
Enhancement #3 - Use Recommended Installation Practices
HVAC installations are relatively complicated. They are subject to many requirements that, if not met, can result in sub-optimal equipment performance. Many rebate programs account for a certain amount of underperforming installations when forecasting their achieved savings. But, there are currently enough underperforming installations in the Northwest that a meaningful gap exists between the actual electricity savings and the savings that would be possible if all the ductless installations were performing as desired. This gap represents an opportunity for Northwest utilities.
Utilities could address this problem by increasing site inspection and quality assurance/quality control (QA/QC) activities on proper placement, head location, refrigerant charge, and control strategies, as well as improved contractor training. Utility researchers around the country are also developing a more advanced solution: a technology framework for remote diagnostics and post-installation QC that would be able to access the internal computer controls of nearly any ductless heat pump currently available to the market. Internet-connected heat pumps that provide remote performance data to a local utility could reduce or eliminate the need for onsite inspection and QA/QC. While still in the early stages of development, this technology framework has the attention of several leading heat pump manufacturers who are participating in joint research with utilities.
Enhancement #4 - Homeowner Education
The research also revealed that a significant percentage of homeowners don't know their ductless heat pump can operate in a heating mode. Therefore, many consumers are not using their system during the winter months. Without education from their contractors, many homeowners have purchased ductless systems for cooling only, despite receiving a rebate for displacing electric resistance heat. Homeowner education can have a major impact on energy savings.
Enhancement #5 - Integrated Controls to Coordinate Ductless and Electric Resistance Heating System
Lastly, the research found that requiring installation of lock-out controls on electric forced air furnaces can impact savings. The research showed that when a ductless heat pump is operating in cooling mode, it can trigger the thermostat of the electric forced air furnace, causing the furnace to heat the home while the ductless heat pump tries to cool the home. In the future, utility programs may ask contractors to install lockout controls. This type of control can prevent the electric furnace from operating at unwanted times.
In addition to lock-out functionality, a new class of master controls is emerging on the market that can provide a single interface for customers. The interface coordinates the operations of both the ductless heat pump and the electric furnace, so they work together to more efficiently heat the home. In fact, utility programs are already supporting these new controls in other areas of the country, including the Mass Save program in Massachusetts.