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?
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 0ºF, because they are able to ramp the compressor and outdoor fan motor speed up to maintain capacity.
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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.
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?
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
In fact, the Mitsubishi line will operate down to -13°F before being shut off. The system ratings for their HP's are 47°F and 17°F just like all other HP's but certain Hyper Heat models will produce full rated output down to +5°F, with outputs dropping below full capacity at temperatures under +5°F. 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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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)
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