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The Custom Residential Architects Network (CRAN®) Knowledge Community develops knowledge and information to benefit architects who are engaged in, or who are interested in learning more about, custom residential practice. CRAN® presents information and facilitates the exchange of knowledge and expertise to promote the professional development of its members via discussion forums, national symposia and conventions, publications, and local activities.

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Global Warming Potential (GWP) in Heat Pump Refrigerants?

  • 1.  Global Warming Potential (GWP) in Heat Pump Refrigerants?

    Posted 12-21-2020 09:05 PM

    I need some advise on selecting the type of heating system for a small new home that will be all-electric.

    I am wondering about the common refrigerants used in small scale residential heat pumps and the concern about the GWP.

    Does anyone know the real world impact of this in terms of leakage? If the system is sealed and properly installed, does it leak over time?

    As far as I can tell, most of the common refrigerants in small scale residential systems have a GWP of around 1100-1400 (such as R-410A used in a Mitsubishi mini-split).  I know there is one company (Sanden) that makes an air-to-water heat pump that uses CO2 itself with a GWP of 1,but it involves some bulky equipment and produces a certain amount of noise, and vibration, which in a dense urban environments (like SF) is not easy to accommodate. Plus it involves a more costly water based radiant system, storage, etc. 

    A small mini-split system has somewhere between 2-4 lbs of refrigerant. My rough math indicates that a 1 lb leak of refrigerant equals driving about 1500 miles so want to be careful to consider the trade offs of the air-to-water using CO2 (using Sanden) or a more typical refrigerant system.

    I appreciate the perspective of the group. 

    Troy Kashanipour
    Troy Kashanipour Architecture
    San Francisco CA
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  • 2.  RE: Global Warming Potential (GWP) in Heat Pump Refrigerants?

    Posted 12-22-2020 06:38 PM
    I love your thinking Troy! If a mini-split has 2lbs of refrigerant, and it leaks 1lb a year, then that means its efficiency is worse than 50% at 1 year, and obsolete at 2 year. I'm not sure if all mini-split have such horrible leaks? In Asia, I don't recall repairing the AC so often. Checking out the EPA website and the Daikin manual, the refrigerant pre-filled in the mini split website is using the worse GWP. Good to note...

    Since I live in Southern California, I've considered electric wall warmers (not the coil types but the liquid kind), common place in Germany in bathrooms. And I am a fan of radiant heating. 

    Looking forward to other's input!


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