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Multi-Head or Pair of Singles?

tanzerson | Posted in Mechanicals on

I’m about to place an order for mini-splits to take over most of the heating in my house (two levels, both heated, 1500 sqft each, the bottom level is a walkout on slab).

Per my previous posts, I’ve satisfied my self that my total heating demand  at a design temp of -5f is about 44kBTU, this based on fuel consumption.   Loadcalc.net comes in about 15% higher.   Loadcalc estimates approximately event heating requirements on both floors.

I plan to put one head downstairs and one upstairs in large mostly open areas.  This mimics the current config where I have a NG insert in each of these areas , they work well except for the temperature swings between heat cycles and are almost 25 yrs old.

I will use the mini split heads mostly for heating (99% design temp of -5f) and cool maybe 2 weeks per year.   I would like to dehumidify downstairs when upstairs is off but the downstairs is already cool enough so I’m not counting on the drying mode to be effective without over cooling the downstairs

I’ve narrowed down to two options, both Mitsubishi.

1.  2 X 18kBTU H2i
2.  1 X 4C36 multi-split H2i with three heads (2X18 + 1X6).

Option 2 has the advantage of allowing an extra head (6k 75′ from the compressor), and has a bit more low temp capacity.  It will cycle at 47f as it’s minimum capacity is 22 kBTU vs a house load of 15 kBTU.

Option 1 should work without cycling at any heating temperature and it is just shy of the heat demand requirements at -5f.  It’s main advantage is the better turndown ratio and independence of operation on the two house levels.

Other than at high ambient heating (47f), the COPs appear to be about the same down to -5f.   Backup existing baseboard electric and NG inserts will remain so handling extreme lows isn’t a concern.

The way rebates are working in Canada, the cost of either option is almost the same.

Any thoughts on which option I should go with will be appreciated as have been the thoughtful and useful replies to my recent posts.

Thanks again

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Replies

  1. Walter Ahlgrim | | #1

    In my opinion you seem to have overlooked one of the biggest advantages of separate systems that is redundancy sooner or later something is going to fail and when to does having 2 independent systems one of the units will continue to be working while the other is being serviced.

    If the purchase price is the same as you say two systems seems like a clears winner to me.

    Will these be hyper heat type units?

    Walta

  2. prometheanfire | | #2

    I'm looking at a similar setup (size and system count wise). I'm planning to go with two systems for redundancy, lower startup load (looking at batteries), and ability to throttle lower.

  3. tanzerson | | #3

    Yes, Hyperheat. Redundancy isn't a huge concern as I have back up, but your point is valid.

    If I buy 2 units, I may now go Fujitsu XLTH due to better low temp performance and slightly higher COP. Same price as Mitsubishi installed.

    Anyone care to comment on Fujitsu XLTH reliability?

    Cheers

    1. mgensler | | #4

      We just had 3 ducted Fujitsu cold climate units installed a month ago. All 3 are one to one units. All started up fine and have been running fine. They seem well made and the installer said he rarely has service calls on them.

    2. Expert Member
      Akos | | #5

      Fujitsu has a lot of different units, make sure whichever model you pick comes with a drain pan heater, this is a must up here in the great white north.

      Also check out the engineering specs on the units, most Fujitsu units can deliver a fair bit more than their rated capacity, so might be able to get away with smaller units. With a one to one setup getting it right sized is not as important as with a multi split but could save you a couple of dollars on the install.

      You can search here, they post low temp data for most Fujitsu units down to -15F:

      https://ashp.neep.org/#!/product_list/

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