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Why cold-climate heat pumps are becoming more common

user-1137156 | Posted in Energy Efficiency and Durability on

It used to be, not so long ago, that heating by available reasonable cost heat pump alone was impossible throughout much of the US. What changed? Basically discovery and adoption of Enhanced Vapor Injection EVI. At first EVI was implemented in scroll compressors by injection of refrigerant into the scroll where it could, in effect perform as a 2 stage compressor. Mitsubshi pioneered a system where a low cost dual rotary compressor performed as 2 cascaded compressors with vapor injection between stages. The Mitsubshi approach essentially buried all of the EVI inside the sealed compressor. allowing a totally conventional refrigerant loop outside. Fujitsu soon folowed with their similar, even better performing products. The China clone makers couldn’t get the magical compressors. Enter Toshiba who developed a family of compressors with “hidden” EVI aimed at the clone makers of China. If not already, soon every brand will have a “hyper heat” family of models based on the different size compressors offered by Toshiba. All of which extend performance and allow rated heat output at 0c and 1/3 of minimum output at 47f. with a tiny cost penalty over conventional compressors. Some of the clones have better “tuned” hardware around the compressors and offer even wider performance range. Hidden EVI works by a single tube a “capillary” tube fed with some of the hot gas from the output of the compressor, wrapping around the vapor input to the compressor where the gas condenses and heat from the flow through the capillary is transferred to the gas going into the compressor. The same tube continues back around the compressor output where the liquid flowing through it is evaporated,cooling the hot gas coming out of the compressor and the flow through the tube becomes a vapor which is ” injected” between the two rotors. It makes for a very simple system requiring addition of only some tubing.

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  1. user-1137156 | | #1

    Sorry I quit typing too soon. Sophisticated compressor monitoring&control firmware is needed to "get the most "out of these compressors. Output gas temperature must be monitored and set an upper limit on compressor speed. The hidden EVI works well for a range of compressor speeds but the fact that refrigerant is a mixture with some oil can cause it's performance to suffer. At lower speeds the oil may reduce the capillary flow too much and COP will plummet. The onset of this situation determines how slow the compressor can run. Better firmware detects the performance hit and temporarily raises the lower speed limit. EDIT: In addition the built in EVI allows, since it's operation involves both a cooling and heating action on flowing refrigerant, a widened ambient temperature environment around the compressor . For example motor windings can be cooled and oil warmed. In well designed systems power can be shut off to resistance crank case heaters otherwise needed in cold ambient operation..

  2. calum_wilde | | #2

    Great post. Thanks!

  3. calum_wilde | | #3

    As the owner of two said systems, I'm all ears. Or eyes... You know what I mean. :)

  4. calum_wilde | | #4

    I love this site, but the mobile integration is lacking.

  5. user-1137156 | | #5

    Glad you liked it. I'm hoping someone will explain why Fujitsu systems,maybe not all but certainly some, acts differently? The Fujitsu systems performs more like a fully optimized scroll system delivering much higher COP during operation with smaller difference between IDT and ODT. (where running without EVI gives better COP).

  6. calum_wilde | | #6


  7. calum_wilde | | #7


  8. lance_p | | #8

    Is there a place to get detailed COP/output/temperature charts for both Mitsubishi and Fujitsu hyper heat ASHP products? Comparing the two based on published specs is very difficult for really cold climate applications.

  9. davidsmartin | | #9


    The Northeast Energy Efficiency Partnerships has a great web site with a spreadsheet that not only compares the data for many heat pumps but also shows information for low temperatures.


  10. lance_p | | #10

    Thanks David, I'll check that out!

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