The Bayview Tower project retrofitted an aging electric resistance water heating system in an occupied, 100-unit, affordable housing high-rise located in Seattle. The new commercial heat pump water heating system at Bayview Towers marked the first United States installation of Mitsubishi's HEAT2O (QAHV) system – the country's first large-capacity CO2 refrigerant-based domestic water heating system. It is also the first installation of a load shift capable commercial HPWH system nationwide.
Findings Summary:
In its first 18 months of operation, the system operated at a COP of 2.3 and saved about 180,000 kWh. The research team identified opportunities to improve COP on future installations.
During Jun and July 2022, the HPWH shifted electric load twice a day – 6- 9AM, 6-9PM – with 100% success. The HEAT2O is a valuable utility asset for shifting or shaping loads.
HPWH controls design and implementation are critical to load shifting. Utility programs should require proper controls on future installations. System thermal storage and heating capacity are critical for effective load shifting and utility programs should require proper sizing of both.
The industry needs specifications for testing the HPWH defrost to provide better information for designers on heating capacity reduction from defrost (defrost derate).
The industry needs additional load shift studies to develop best practices for load shift controls.
The Bayview HPWH system uses a Swing Tank design – defined in the Northwest Energy Efficiency Alliance (NEEA) Advanced Water Heating Specification (AWHS). The Swing Tank design includes a primary system for heating cold incoming municipal water and a temperature maintenance swing tank for trim heating the recirculation loop during periods of low water usage. The primary system which includes the HEAT2O, a heat exchanger assembly, and thermal storage tanks, was pre-packaged in a plugand-play, skidded assembly for fast, simple installation by Steffes in North Dakota. This skid-style design minimized the disruption of hot water supply to residents during installation.
The pre-retrofit system was a 93kW electric resistance system. The new HEAT2O, only draws 10 to 19 kW, and satisfies all the heating of cold incoming municipal water and most all of the recirculation heating. A portion of the existing electric resistance system was left in place to use as swing tanks and provide backup heat.
Depending on the season, the system achieved a Coefficient of Performance (COP) between 2 and 3, averaging a full system COP of 2.3. However, the project identified potential enhancements to elevate the system's average COP above 3 in Seattle's climate. Mitsubishi is acting on BONNEVILLE POWER ADMINISTRATION 2 these insights to advance its product offering. Bayview Tower has an atypical load shape. Instead of the traditional market rate multifamily load shape with a morning and evening peak, Bayview has a single morning peak and remains flatter throughout. The difference in load shape allowed the Bayview system to shift load more easily in the morning hours but made it more difficult for the system to sufficiently load up for an evening load shift.
The project team tested load shifting from March 2022 to June 2023. The yearlong testing revealed that: (1) during summer, the system performed exceptionally, and provided hot water through the shed periods each day without using electricity; and (2) during winter, the HEAT2O capacity was reduced more than expected by defrost, which, when combined with other factors, resulted in approximately a 35% capacity reduction. The capacity reduction prevented the Heat2O from fully charging the primary storage tank between shed periods and limited the evening shed. This meant that the HEAT 2O used more energy during the winter and could not complete shed periods. Despite this, the anticipated improvements and appropriate design controls can enable consistent year-round load shifting on future installations.
The research team used Ecosizer – an opensource HPWH sizing and simulation software – for simulating the load shift. The simulation results indicated that, contrary to common industry knowledge, the ability to load shift is not only correlated to storage volume. When well-designed load shift controls are included, significant load shift can be provided without adding additional storage volume.
The Bayview Tower project marks a significant milestone in market transformation of load shift capable water heating systems. The monitoring and studying of the system have yielded valuable insights, which will be used to improve the product and inform future large-scale implementation of load shifting HPWH systems. The findings prove that commercial HPWH systems can realize consistent load reduction during peak periods. This ability will play a role in supporting the transition to renewable energy, drive electrification, and help with grid stability