Maximizing Energy Savings for Ductless Heat Pumps

Sep 23, 2020

NEEA knows utilities continue to be in a state of uncertainty with the low savings rates and marginal (at best) cost effectiveness of many utility programs. To support utilities in the quest for improved measure savings, the NW Ductless Heat Pump Project commissioned a study to identify a set of ductless heat pump enhancements that utilities or contractors could use to improve the savings delivered by mini-split heat pumps. The research included reviewing literature, conducting interviews and surveying the market for products. The project built on work done by Pacific Northwest National Laboratory (PNNL), the Energy Trust of Oregon, and the Regional Technical Forum (RTF) and roughly 40 published papers and 30 subject matter expert interviews to identify and quantify the benefit of several “enhancements” that, when combined, can nearly double the amount of electricity saved by ductless heat pumps. NEEA staff will share the final findings of this study with utility and implementer parties during a webinar on Monday, November 2 from 1:00 PM to 3:00 PM PST.

The following table shows incremental savings identified (note, these are draft results and the final report may change). These are regional average weighted incremental savings values over the RTF’s 2019 published UES value of approximately 1709 kWh/year for zonal heated homes and 3,498 kWh/year for electric forced air furnace (EFAF) heated homes.

Max Minis Table

Enhancement #1 - Target Homes with Electric Heating Loads

Research found that a significant number of homes that receive ductless heat pump rebates have a relatively small electric resistance heating load. In these cases, the homes never could have achieved cost-effective electricity savings because they were not consuming the assumed electric load of a home their size prior to installing the ductless heat pump. A low-cost solution exists for this problem. Calculating a home's electricity use during the winter months and comparing it to months in late spring or early fall can reveal the heating portion of the home’s energy use. Targeting homes with high heat loads will produce the greatest energy savings.

Enhancement #2 - Strategically Locate Indoor Head

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 also typically has a relatively large floor area, so it represents a larger percentage of the total heating requirement. A combination of site inspection and/or enhanced contractor training could prevent installers from placing rebated ductless heat pump indoor units in sub-optimal locations within a home.

Enhancement #3 - Homeowner Education

In one of the more surprising research findings, the research uncovered that a significant percentage of homeowners don't know their ductless heat pump can operate in a heating mode to produce indoor comfort and savings year-round. Therefore, many consumers are not using their system during the winter months. Without education from their contractors, many homeowners have purchased ductless systems to only cool their home despite receiving a rebate for displacing electric resistance heat. The solution could be a combination of homeowner education and contractor training.

Enhancement #4 - Quality Assurance

HVAC installations are relatively complicated. They are subject to many requirements that, if not met, can result in poor equipment performance. Many rebate programs account for a certain amount of underperforming installations when forecasting their achieved savings. Currently, there are enough underperforming installations in the Northwest that a meaningful gap exists between the existing electricity savings and what would be possible if all the ductless installations were performing as expected.

This gap represents an opportunity for Northwest utilities. Utilities could address this problem by increasing their use of time-tested tools, including improved contractor training and more frequent site inspection and quality assurance/quality control (QA/QC) activities. 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. One concept under consideration is a new connected heat pump that could provide remote performance confirmation to a local utility. This could obviate 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 cooperating with utility researchers.

Enhancement #5 - Integrated Controls of Backup Heating System

The research looked very closely at what opportunities might exist to apply controls to homes with both a ductless heat pump system and an electric forced air furnace. The incorrect configuration of an integrated control system can lead to a costly error. 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. This problem occurs when the homeowner forgets to turn off their furnace thermostat in the summer months.

Contractors can help to mitigate this risk by installing lockout controls. This class of controls can "lock out" the electric furnace for outdoor temperatures at which the ductless heat pump can easily meet a home’s heating requirements. In addition, a new class of integrated controls 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 Mass Save in Massachusetts.

While these controls and strategies are seeing increased market adoption, research found lockout controls are expensive and produce relatively lower savings. Keep in mind this technology is still new and is improving.