Are 1 heat pump with 3 multiple indoor unit Hyper Heat minisplits available from Mitsubishi yet?
DanVT
| Posted in General Questions on
I have a really simple question. I have installed a ductless mini split in my studio, but have been waiting for Hyper Heat units that can handle multiple zones to be on the market (1 heat pump w/ 3 indoor units) to be on the market to put them in my home. Mitsubishi website seems like they’re out now. Anyone know for sure?
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I had the same question so I asked online retailer "Younits" if they had these yet and they said that you could order them but wouldn't receive until later-early spring. If you check their online store, these units don't show in a normal search, but you can search for them using the search function on thetop right hand corner of the site and type in MXZ C. This should bring up the various units and prices for the outdoor unit.
Are you sure you really have the zone loads appropriate for a 3 head unit? It's important to run the heat load calculations to guarantee that the heads won't be super-oversized for the actual loads.
The smallest interior heads can still put out a lot of heat, and you need to size them correctly for the actual room loads. It's a common error to put a 6000BTU/hr head (7000BTU/hr heating) into a room with a design heat load of less than 2000 BTU/hr (and an average winter load of less than 1000 BTU/hr) which isn't great for either efficiency or comfort.
It can be better to use mini-duct cassettes and split the output between 2-3 rooms in very close proximity to one another to minimize duct lengths.
I am in the middle of building a house, We will be installing a 4-ton H2i Mitsubishi system, with I believe, 8 indoor units. Many of the heads are already installed, The heat pump is supposed to be installed in a month.
Jeff of Durango, CO
Four tons Hyper Heat would deliver more than 33,000 BTU/hr @ -13F, and something like 48,000 BTU/hr @+5F If that's a higher-performance house, it must be a big house to have a heat load that high. If the 99% heat load is only 25-30K and your outside design temp is only -1F (the 99% outside design temp for Durango) it means you probably have too much compressor and way too many heads. That's more compressor than you'd need for a decently thought out code-min 2500-3000' house, unless it's up in nose-bleed country, say Leadville (outside design temp of -14F.)
Dana, , I understand your point of view. Of course, sizing mini splits is tough for those of us who have standard houses like mine with average insulation and multiple bedrooms ( I have two floors of about 1600 ft in northern NJ). As you know, the problem is addressing a combination of sufficient heat, dealing with closed doors and distance down hallways and obtaining sufficient efficiency. In NJ rebates require 18 SEER and 13 EER. Even these new h2 Mitsubishi systems don't meet this criteria with ducted heads. Only some 9000btu single systems meet this criteria when ducted and they are not low temp (this winter we have had 20 days or so where the temp went to 5 F or lower at least some of the day). And when I have had HVAC guys in they all have recommended at least 5tons total. Thus it is hard to resist a multi head system like this. They seem to me designed for retrofitting regular houses. But if I could replace the 800 gals of oil I use to heat with 12000 kW of electricity at 11.5 cents a kw (60 pct natural gas sourced) , that may be a good trade.
If you're burning 800 gallons/year it means your whole house heat load at +15F (a typical 99% outside design temp for NJ: http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf ) is something like 28-30,000 BTU/hr. Five tons of compressor would be able to put out more than twice that at +15F.
With the efficiency & comfort hit you take from being more than 200% oversized with 5 tons of compressor along with on/off cycling rather than modulating, with much bigger room-temp swings, you'd be better off designing for the average winter load (maybe even breaking even @ +25F) backstopping any shortfall with resistance heating in the rooms you really care about. Even when it's below 0F the heat pump will still be delivering the majority of the heat. A 99% outside design temp means that only 1% of the time will the outdoor temps be under that. Specifying a modulating system to cover the load for the 99.9% condition means it never really modulates, undercutting efficiency slightly, but undercutting comfort by quite a bit. The comfort issue is less of a problem in super-insulated houses than it is in "standard houses".
Oversizing by as much as 1.5x would usually leave it in the modulation zone most of the season and provide some margin for lower temps, and run slightly higher efficiency than if exactly sized for the load. Above that it's pretty much down hill on both comfort & efficiency.