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We are assessing high-efficiency electric heat pump water heating systems that use supercritical carbon dioxide as a refrigerant. CO2 heat pump water heaters (HPWHs) were first commercialized in Japan in 2001. Among heat pump water heaters, systems using a CO2 (or R744) refrigerant achieve a coefficient of performance (COP) greater than 3.2 compared to 2-2.5 for standard refrigerants. CO2 HPWHs have a broader range of operating temperatures, allowing the to maintain capacity at low temperatures, with a COP of around 2.0 at 17 degrees F. R744 also has a global warming potential of 1 compared to about 2,000 for typically used refrigerants (like R410).

Current Stage: Emerging Technology Assessment
ET Projects​​

​Field Test of CO2 Heat Pump Water Heater for Residential Pools

Abstract
This field test is to investigating the feasibility of using CO2 Heat Pump Water Heaters to pre-heat water for swimming pools using a electric resistance baseline heater to reduce overall energy use. This field test is focused on a residential application but has the possibility to be applied in commercial applications as well.
Project Team
BPA: Erik Boyer, Shane Ripley
Ecotope: Bob Davis, Ben Larson
 
Timeline
2016 – 2018
 
Reports

​Application of Combined Space and Water Heat Pump Systems to Existing Homes for Efficiency and Demand Response

Abstract
The Washington State University (WSU) Energy Program, with its partners, will conduct research on two types of combined space and water heat pumps in field and controlled experiments in existing homes of various efficiencies and climates.
One technology uses CO2 refrigerant and will be tested for performance at six field sites and at the PNNL Lab Homes for efficiency and demand response (DR) capability. The second technology uses a conventional refrigerant and will be field tested at five locations in the region’s hottest and coldest climates as well as in the marine coastal zone. Costs of system installation and energy use will be collected and analyzed. In as many cases as possible, monitoring will be installed prior to installation in order to establish a baseline.
 
Project Team
BPA: Janice Peterson
WSU: Ken Eklund

Timeline
2015-2017
 
Reports

​TIP 394: Small Scale Multifamily CO2 Heat Pump Water Heater Design & Pilot Study

Abstract
This pilot study will research, design, pilot, verify, and document a heat pump water heating system for small-scale multifamily buildings using CO2-based transcritical refrigeration cycles. The project team will conduct a general system design exercise to support specific building construction and create a system sizing tool. The tool will help contractors and designers find the right balance of output capacity and storage.
This project will add a remarkably low-energy water heating method to the multifamily market. The CO2 heat pump system could use 75% less electricity amounting to an energy savings of 1,444 kWh/yr for each unit served. BPA can incentivize this design concept to help reach its regional energy efficiency targets of output capacity and storage. Ultimately, the intent is to create a viable, cost-effective, high-efficiency alternative for water heating in the small multi-family residential market segment.
 
Project Team
Ecotope, Inc.
Northwest Energy Efficiency Alliance (NEEA)
Sanden International, Inc.
 
Timeline
2016-2018
 
Reports

Combined Space and Water CO2 Heat Pump System Performance Research

Abstract
This project conducted lab and field tests on a prototype combined space and water heat pump system using CO2 refrigerant in energy efficient homes built under NEEA’s Next Step Homes specifications. The research took place over 24 months. The main goal was to determine the performance of the prototype for both space and water heating through a wide range of temperatures and use patterns. Secondary goals include exploring the interaction between space and water loads and the impact on system performance, and logistical findings such as HVAC installer, builder and home occupant response to the systems. The field study began in the fall of 2014 with the installation of the prototypes and continued to collect a full year of data for all sites.
 
Project Team
BPA: Janice Peterson
WSU: Ken Eklund, PI
 
Timeline
2014-2016
 
Reports

Advanced Heat Pump Water Heater Research (TI Project 292)

Abstract
The Sanden GAU CO2 refrigerant, split-system heat pump water heater was tested in both lab tests and at four field sites representing the three heating zones in the Pacific Northwest. This report focuses on the field tests and the data and experience collected over almost two years of monitoring. The test data show these systems can provide the hot water needs of a family of up to seven without backup heat during a cold winter (with low temperatures ranging from almost -16°F in Montana, 2°F in Spokane, and the 20s°F in Portland and Tacoma). The energy needed to heat water in the field study averaged approximately 0.05 kWh per gallon used. This is half the energy needed by standard unitary HPWHs. When the final product is UL listed, it will be tested in the laboratory to confirm performance.
 
Project Team
BPA: Janice Peterson
Washington State University Energy Program
 
Timeline
2013 - 2016
 
Reports

​Assessment of Demand Response Potential of Heat Pump Water Heaters

Abstract
This project is a controlled field study and lab test that assessed the demand response (DR) potential of split system and unitary heat pump water heaters (HPWHs) that use carbon dioxide (CO2) refrigerant. The researchers included Washington State University (WSU), Pacific Northwest National Laboratory (PNNL), Efficiency Solutions, and Ecotope working with Cascade Engineering Services.
The controlled field test took place at PNNL’s Lab Homes Test Center in Richland, Washington. The configuration of the Lab Homes allowed simultaneous testing of the water heaters under the same weather, interior temperature, and loads. The tests conducted were: baseline measurement; balancing INC, which tests the response of hourly or sub-hourly changes in demand and the available dispatchable power/energy shift associated with it; and oversupply mitigation, which identifies the total dispatchable power, and resulting energy shift, that a noncritical load like water heating can provide during a 3- to 12-hour window. The Lab Homes tests reveal that both the unitary system and the split system HPWHs could provide water at the required temperature at an aggressive 130 GPD draw, and could perform balancing INC consisting of three 1-hour periods without a loss of delivery performance.
With the PNNL Lab Homes program exploring the extreme ends of the draw spectrum, the draw pattern selected for the lab tests was based on the regional average hot water use of approximately 15 gallons per person per day and with an average home occupancy of three. The goal of the lab tests was to identify the impact of DR on hot water delivery, HPWH performance, the dynamic energy storage potential, and controls needed for optimum DR implementation. The DR benefits revealed by these tests indicate that this is a highly efficient technology that can provide high-capacity storage for oversupply mitigation and can facilitate load balancing – in the same 24 hour period if necessary. This operation increases rather than decreases long-term efficiency.
Project Team
BPA: Janice Peterson
WSU: Ken Eklund
 
Timeline
2013-2015
 
Reports

​Assessment of Demand Response Potential of Heat Pump Water Heaters

Abstract
This project is a controlled field study and lab test that assessed the demand response (DR) potential of split system and unitary heat pump water heaters (HPWHs) that use carbon dioxide (CO2) refrigerant. The researchers included Washington State University (WSU), Pacific Northwest National Laboratory (PNNL), Efficiency Solutions, and Ecotope working with Cascade Engineering Services.

The controlled field test took place at PNNL’s Lab Homes Test Center in Richland, Washington. The configuration of the Lab Homes allowed simultaneous testing of the water heaters under the same weather, interior temperature, and loads. The tests conducted were: baseline measurement; balancing INC, which tests the response of hourly or sub-hourly changes in demand and the available dispatchable power/energy shift associated with it; and oversupply mitigation, which identifies the total dispatchable power, and resulting energy shift, that a noncritical load like water heating can provide during a 3- to 12-hour window. The Lab Homes tests reveal that both the unitary system and the split system HPWHs could provide water at the required temperature at an aggressive 130 GPD draw, and could perform balancing INC consisting of three 1-hour periods without a loss of delivery performance.

With the PNNL Lab Homes program exploring the extreme ends of the draw spectrum, the draw pattern selected for the lab tests was based on the regional average hot water use of approximately 15 gallons per person per day and with an average home occupancy of three. The goal of the lab tests was to identify the impact of DR on hot water delivery, HPWH performance, the dynamic energy storage potential, and controls needed for optimum DR implementation. The DR benefits revealed by these tests indicate that this is a highly efficient technology that can provide high-capacity storage for oversupply mitigation and can facilitate load balancing – in the same 24 hour period if necessary. This operation increases rather than decreases long-term efficiency.
 
Project Team
BPA: Janice Peterson
Washington State University
Pacific Northwest National Laboratory
 
Timeline
2013 – 2015
 
Reports
 
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