What is the measure?
A heat pump water heater of any size or configuration (packaged, split, or tankless) that utilizes CO2 (R744) as the refrigerant. Many building codes are pushing designers and developers to shift their projects from typical natural gas fired water heating systems to all electric designs. States, cities and local jurisdictions are banning natural gas and electric resistance heating elements for new construction and encouraging the adoption of heat pump water heaters for domestic use. These water heaters have many inherent benefits, but when they are integrated into a centralized design they can really stand out against the competition.
R744 is the refrigerant intended to replace traditional refrigerants with higher GWP, such as R134A. The indoor/outdoor unit flexibility is similar to a traditional heat pump water heater, but a CO2 heat pump water heater may require an additional swing tank, maintenance tanks and controls.
Sizing the system
A key part of the design process is to appropriately size the equipment with the building loads. As we have added more components and advanced control strategies it is critical that each component is selected to work together. A common tool for this is to use Ecosizer developed by Ecotope. Ecosizer is used for multifamily buildings and can help you determine the equipment size and capacities. The tool will look at several factors including apartment unit quantities, design temperatures, schematic layout, and can even look at load shifting strategies.
What are the benefits?
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CO2 is able to generate water at higher outlet temperatures than other refrigerants, which is particularly useful for applications such as heat reclaim and thermal storage
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Currently R134A HPWHs need additional electric resistance heating starting somewhere between 110-140˚F. In the case of R744, no secondary heating source would be needed but many installations would likely still have a backup method
What are the challenges/constraints?
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May require additional temperature maintenance tanks and additional controls to prevent scalding
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Premium pricing, more limited equipment availability and sizing than traditional refrigerants (R143A, R513A)
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CO2 operates at a higher pressure so there is need for more robust and expensive components
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May be limited to applications up to 2,000 kBtuh
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COP for CO2 HPWH ranges from 2-5
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Product durability is still being researched as it is a relatively new technology for water heating
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Indoor/outdoor unit flexibility similar to traditional HPWH
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R744 is non-toxic, non-flammable, has an Ozone Depletion Potential (ODP) of zero, and a low Global Warming Potential (GWP) of one, compared to other refrigerants, such as R134a and R410a, that have GWP of 1,430 and 2,088, respectively
