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  1. #1

    Mitsubishi Heat Pump down to 0* ?

    I've heard that the Mitsubishi Heat Pumps operate down to 0*. Does anyone know how they make this happen?

  2. #2
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    Quote Originally Posted by David Lang View Post
    I've heard that the Mitsubishi Heat Pumps operate down to 0*. Does anyone know how they make this happen?
    Physics, there is heat in the air down to absolute zero 460 degrees bellow zero. As long as the refrigerant temperature is bellow the ambient it will be picked up and be rejected inside.

  3. #3
    True . . . But doesn't the COP drop off as the temprature drops?

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    Quote Originally Posted by David Lang View Post
    True . . . But doesn't the COP drop off as the temprature drops?
    Yes but in the end if the COP is higher than 1.0 then its still operating more efficiently than any electric resistance heat. Mitsubishi uses what they call a Hyper Heat module that helps the unit have rated capacity at 5F and work to 0 degrees.

    I assume you are talking about the MSZ-MUZ-FE12 or FE18 models right?
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  5. #5
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    Quote Originally Posted by David Lang View Post
    I've heard that the Mitsubishi Heat Pumps operate down to 0*. Does anyone know how they make this happen?
    It has an inverter driven variable capacity compressor.
    Several manufacturers inverter drive heat pumps are able to maintain their full heating capacity down to outdoor temperatures in the teens, and still be near full capacity down around 0F, because they are able to ramp the compressor and outdoor fan motor speed up to maintain capacity.
    If more government is the answer, then it's a really stupid question.

  6. #6
    Has anyone seen a COP curve for these units that run down to 0* ? I'd like to figure out when gas becomes more cost effective given my rates.

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    That doesn't really show COP and full speed. Of course that's the challenge with vairable capacity units. The efficiency will depend on both indoor load and indoor and outdoor conditions. You also have to multiple the frequency correction factor to the heating performance correction factor. But single speed units have a similar problem, because they can take 8-10 minutes to reach steady state rated effciencies. SO a unit that short cycles vs. one wiht long run times can have efficiencies vary by 30%.

    Sort of like EPA fuel economy numbers on passenger vehicles. They can vary dramatically based on driving conditions. I always liked how my BMW motorcycle was rated. It gave steady state fuel consumption numbers for a particular speed. THat seemd like a better way to comparatively gauge economy.

  9. #9
    This has a lot of great data. Thank you.

    From the table 7-1.3 it looks like this unit consumes 1.63Kw to produce 25,200Btu/h with an outdoor temperature of 55* and an indoor temperature of 70*. At an outdoor temperature of 5*, the unit uses 0.83Kw to produce 10,300Btu/h.

    So the unit keeps producing heat down to 5*, but the COP drops a little and the output drops by about half. Am I reading this correctly? Is this common across the Mitsubishi line?

  10. #10
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    Quote Originally Posted by David Lang View Post
    Has anyone seen a COP curve for these units that run down to 0* ? I'd like to figure out when gas becomes more cost effective given my rates.
    COP of ~ 3.5 near/above 25'F might be an economic balance point without too much drop-off in output.
    Gas $1.0/ therm (100,000 BTU)
    Electric ie., $0.12/ kw-Hr * 100,000/3412 / 3.5 = $1.00 per 100,000 BTU

    35'F
    Heat TPC --- 3,412
    _______ kW ---BTU ---COP
    12,000 0.93 --- 3,173 __ 3.78

    25'F
    0.84 kW
    3412
    2866. BTU
    10200 BTU
    3.56 COP
    Last edited by dan sw fl; 09-23-2012 at 11:13 AM. Reason: add TPC/ TC 35'F
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  11. #11
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    In fact, the Mitsubishi line will operate down to -13F before being shut off. The system ratings for their HP's are 47F and 17F just like all other HP's but certain Hyper Heat models will produce full rated output down to +5F, with outputs dropping below full capacity at temperatures under +5F. You should also know that the Hype Heat models operate at full output rating for the first 3-minutes of operation at the beginning of each heat cycle. For this reason, it's important to be sure the unit if properly sized for the room(s) or you could end up with short cycling.
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  12. #12
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    Quote Originally Posted by David Lang View Post
    Does anyone know how they make this happen?
    With the normal refrigerant cycle ...
    http://en.wikipedia.org/wiki/Heat_pump

    No, it's not magic, the output decrease is what one must pay address when selecting a heat pump and back-up in regards to the local environment/weather.
    Generally, the heat transfer balance point will be 32'F +/- ~6'F unless you're willing to signficantly lower your room temperature set point ( ~70'F norm)
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  13. #13
    I've been told that some units produce full output down to 0* or 5* (see below). Is that not correct?

    It seems like it would be pretty tough to pull off because as the COP drops the compresser would need to draw even more to keep the output up.

    The table in the spec sheet indicates a drop. I want to know because if it produces full heat down to 0* (or even 10*) then I wont need backup.

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