2 years ago just installed a 4 zone mini split into an 1100 sf 1920's bungalow in Sacramento. It is very quiet, performs well, and my energy costs are the same as my old gas wall mounted space heater bill even with AC. The biggest issues relative to leakage is with the installer. Not all fully comply with CA regulations for refrigerant capture. Adding shutoff valves on the line sets at the internal and external unit will reduce chances of leakage if maintenance is required at a later date as you can more easily isolate components. You can expect 25 years or better of service life in our climate. Buy from quality manufacturers and pay attention to coastal conditions as salt can quickly compromise the exterior coils.
You can do a co2e comparison of the old fossil fuel system and you will likely find that the full loss of refrigerant is much less than that of the fuel used if you stuck with gas, especially if you are adding PV and seeking a near or zero net energy solution.
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James R. Deane, AIA, CDT, LEED AP, PMP
Senior Supervising Architect
WSP
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Original Message:
Sent: 12-21-2020 09:04 PM
From: Troy Kashanipour
Subject: Global Warming Potential (GWP) in Heat Pump Refrigerants?
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.
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Troy Kashanipour
Troy Kashanipour Architecture
San Francisco CA
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