A central CO2 (R744) heat pump water heating system has been found to reduce the amount of energy used for hot water production at a 100-unit apartment building in Seattle, Washington (U.S.), by 55% compared to its previous electric resistance system, according to a study by local engineering firm Ecotope.

The CO2-based system consists of a Heat2O air-source heat pump from Mitsubishi Electric Trane HVAC US (METUS) and U.S. manufacturer Steffes’s plug-and-play electric water heating system, known as Origin.

The project was designed by Ecotope, and the packaged system was installed at Bayview Tower – a low-income public housing facility for senior citizens – in July 2021 as part of a demonstration project.

The engineering firm says this system is the first of its kind.

Energy savings

Domestic hot water production typically accounts for around 25% of a multifamily building’s energy use.

Once installed, the Heat2O-Origin system was found to reduce Bayview Tower’s energy use for water heating by around 135,000kWh annually. This corresponds to roughly US$15,000 (€13,663) savings each year in operating costs, said Ecotope.

The energy savings also correspond to reduced electricity demand and greenhouse gas emissions, it added.

With the ability to store up to 1,500gal (5,678l) of hot water at temperatures of 140–180°F (60–82°C), Steffes’s Origin water heating system is also capable of load shifting to be more flexible during times of high electricity demand.

As a follow up to the initial study looking at functionality and efficiency, Ecotope analyzed the demand response capability of the system and found that peak-time energy use for hot water production could be reduced to nearly zero when using the water tanks as thermal storage.

By preheating water to a higher temperature during periods of low electricity demand and storing it, the heat pump units could be turned off during peak periods, reducing energy demand while still enabling residents to access hot water when needed.

Minimum disruption

Origin – which Steffes showcased at AHR Expo in Atlanta, Georgia, February 6–8 – removes all complexity to make installation easier for contractors and customers, said Austin Krank, Product Engineer at Steffes.

“We provide everything they need,” he added.

The pre-assembled, plug-and-play unit offers a simplified connection between a heat pump and the building’s water supply and includes heat exchanger modules, water storage tanks and swing tanks.

For Bayview Tower, Steffes packaged Mitsubishi’s Heat2O heat pump into an Origin skid at its facility in North Dakota. The complete unit was then shipped to Seattle and installed on site.

Schematic of the fully packaged Origin system for Bayview Tower. (Source: Ecotope)

“This design minimized the disruption to tenants and only required hot water to be shut off for a few hours, not for multiple days of construction,” said Ecotope.

Building decarbonization

Origin works particularly well with CO2 heat pumps like Mitsubishi’s Heat2O, explained Brent Kovash, Engineering Manager at Steffes.

“We specifically like the CO2 heat pumps because of the nice [temperature] lift,” he said. “They can go from 50°F to 160°F [10 to 71°C] in one pass so that fits really well with what we’re doing.”

“We specifically like the CO2 heat pumps because of the nice [temperature] lift. They can go from 50°F to 160°F [10 to 71°C] in one pass so that fits really well with what we’re doing.”

Brent Kovash, Steffes

Origin is designed for multifamily building projects – whether new construction or retrofits – that have decarbonizations design goals, said Steffes.

It comes in three sizes and is suitable for buildings with 50 to 150 apartments, although systems can be combined to meet the requirements of larger facility, the manufacturer added.

Since the Bayview Tower installation, Steffes has reworked the design of its Origin water heating system, said Krank. Updates include making the unit more compact and easier to service.

The company has manufactured similar systems for industrial applications for many years, he explained. With Origin, Steffes is transferring its technology and experience to commercial settings, he added.

CO2 heat pumps at AHR Expo

CO2 heat pumps were a major feature at this year’s AHR Expo, with several exhibitors showcasing their products for the U.S. market, including Mayekawa, Lync by Watts, Transom and Mitsubishi.

Mitsubishi’s Heat2O heat pump water heater on display at AHR Expo.

According to John Brooks, Business Development Manager at METUS, its Heat2O heat pump water heater is relatively new to the U.S. market, with a few installations in Seattle.

“We want to make sure the contractor base knows about it,” he added.