Hydronic Heat Pump with Thermal Storage Solutions
Initial RFP (April 2022)
The Efficiency Maine Trust (the Trust) seeks a qualified contractor or team of contractors to identify and test a hydronic heat pump with thermal storage solution that can directly replace an existing heating system in a stick-built home with a hydronic distribution system. This heat pump system should replace 100% of the heat load of an existing structure currently heated by a delivered fuel. The project will include researching and proposing specific equipment that can be placed in stick built hydronic distribution homes, recruiting Maine installers and customers to implement the proposed technology, and monitoring and analyzing data collected from those participants.
The Trust will refer to this request as the Hydronic Heat Pump with Thermal Storage Solutions RFP.
Project is managed by Dan Mistro of The Trust
RFP was won by Ridgeline Energy Analytics
GridWorks provides open source storage heat software, hardware, design services
Paul Moscone Heating provides installations, design and HVAC service
Summer 2023 Progress Report
The flow control for the first system didn’t work, we didn’t have Paul on the team, the heat pump didn’t make hot enough water, and the distribution system was never able to fully heat the house. No pictures. Efficiency Maine decided to give it a second shot.
Summer 2024 Progress Report
Figure 1: Air-to-Water Heat Pump (AWHP) + Thermal Energy Storage (TES) space heating system in Maine.
Left: LG ThermaV AWHP. Center: Flow control and TES. Right: Simplified peration schematic.
What a difference a year makes. The first two systems in Millinocket are both a technical and economic success. Highlights for these two systems include:
Both are running on a Time-of-Use tariff with daily 5- and 4-hour on-peak periods;
Both have completely decarbonized existing fuel oil heating systems; and
Both have lower operating costs than the baseline fuel oil heating systems (see Table I-1.1).
While the above are seasonal estimates, they reflect the actual physical performance in terms of COP and capability of avoiding on-peak periods demonstrated by both houses.
A major concern of Efficiency Maine Trust, the primary funder for the Maine project (project EM-019-2022), was whether a heat pump would be capable of keeping a hydronic house in Northern Maine warm. This was answered with a definitive yes. On the coldest day of the year, the 2-stage heat pump in the first house consistently delivered 180°F water (with no resistive boost), and the thermal storage was able to ride through the on-peak periods.
One of the most surprising results of the season was that, despite the widespread expectation among industry practitioners, 180°F was not necessary to keep the first Maine house warm. The field-verified required source water temperature (SWT) on the coldest day was under 140°F, when the team had anticipated closer to 170°F. The optimal system design for a house with a maximum required SWT of 140°F results in significantly cheaper installation and operation, and likely allows for lower GWP refrigerant. The cost savings associated with the lower SWT would come from three primary sources: 1) cheaper heat pump, 2) fewer storage tanks, and 3) higher COP. This result is extremely preliminary and cannot be generalized at this point. However, evaluating the true SWT requirements in 6 Maine houses (as part of Efficiency Maine EM-019-2022) next winter will provide valuable data further investigating this preliminary result.
The financial success of beating oil on a simple time-based tariff was necessary for the continued support of the Maine site by Efficiency Maine Trust and is indeed a major achievement. However, the big win will be realized only as the true physical value TES can provide to the grid is monetized. Unlocking this hyper-local grid-balancing value, illustrated below in Figure I-1.7, requires the forward-looking grid-responsive controls being developed in this and other projects.
