Wednesday, July 25, 2012

Heating Capacity of Mitsubishi Mini-splits

Pursuant to my bleg the other day, the above (from this marketing brochure) shows the degradation of nameplate heat movement capacity for two current models of Mitsubishi air-source heat-pump as the outside temperature drops.

Indeed this would seem to be pretty viable for cold climates - such as mine in Ithaca, NY:

Here, a typical January night is 15oF and a really cold night is 0oF at which point the heat pump is only slightly degraded in its ability to deliver heat.  However, the above chart shows the record low as -25oF so I suppose a supplementary system would be needed to handle that.

Also of interest is this comparison of ground-source and air-source heat-pumps.  The ductless mini-splits seem to be getting a good reputation for being relatively fool-proof and reliable, and the upfront cost is much lower than ground source heat pumps.


sunbeam said...

I've got a tech question about the split units.

I tried (not very hard I guess) to find out exactly how they work.

I understand vapor compression and the thermodynamic cycle, that's not the issue.

My question is the compressor unit is outside. Now does the working fluid go inside the house to a condensor?

Or do they use a second fluid to go to the interior of the house and reject heat?

I ask this because I'd like to know if you have to braze copper tubing. Do you know if they use copper tubing to the interior of the house? or another type of line?

I kind of suspect the working fluid is being sent inside, and don't know how much of a performance hit you would take with an intermediate fluid. But if there were an intermediate fluid I think you wouldn't need an installer at all if you were so inclined.

Unknown said...

hmmm... heating performance seems almost independent of outside temperature.

Heat pump performance is governed by the limits defined by Carnot.

Nick G said...

These appear to be single room units.

I wonder if good air-air units are available as a central system?

Unknown said...

I've got four of the wall units and two outdoor units.

They do indeed send a single fluid to the indoor condensing unit. As far as I know the refrigerant needed to charge the unit will vary depending on the distance from the indoor to the outdoor unit as well as how many indoor units you install.

There is an ideal limit, but the W in the equation is very efficient in these units as it varies the amount of compression to meet the needs of the indoor unit.

They make multiple room units as well, there are even hidden ceiling mounted units. We are able to cool the entire 1st floor of our home (~900 square feet) with a single 1600 BTU indoor unit. The upside of having two indoor units connected to a single outdoor unit is that when running one indoor unit it can substantially surpass the number of BTU's it's rated for.

For heat it's great in the winter to set the house thermostat at 65 and heat single rooms to a desired temperature. My elderly father in law especially like this feature.

You would need a very well insulated house to rely on this as a sole source of heat, but these days it does seem possible if built to something like the passive haus spec.

Delia Abernathy said...

I have been using Mitsubishi Heat Pumps at WDS Green Energy for a while there much more reliable.