Mini split sizing question

[xman111]

Hey guys, great forum, hoping i can get a litte advice.

I live in Vancouver, Canada in a 3 year old 1430 square foot 1/2 duplex with floor heating (no ducts). Our portable air conditioner isn't cutting it anymore and we are looking into getting a mini split.

We were really mainly concerned about cooling our room but with pricing in Vancouver, $7500 for a single head seemed very expensive to just do one room. We were thinking about doing a single head above the stairs to try to do the whole floor, then $7500 doesn't seem so bad. It would be nice because our daughters room and our loft (which is currently the dog pen) would also get cooling. I am worried about spending the money only to find out that we were still hot in our room at night and the loft is ice cold. We just had a 45 degree heat wave and it was about 33 degrees upstairs in our house without using our air conditioner.

Our neighbour just got a Daikin 18,000 BTU single unit and placed it upstairs and they told me that it gets uncomfortably cold upstairs and perfect for downstairs. That being said, i don't know them that well and haven't been inside their place. It is a little different layout than ours as well.

The quote i got was $7400 CDN - $300 Lennox rebate, for a 18000 BTU Lennox mini split with 12 year parts warranty and 5 years labour warranty from a very well respected local company.

I attached a pic of our layout, wondering if anyone had the time to comment on it.

 

[Fitter30]

Surprised it did that good when design 23.2c and most ac units 37*c outside temp. Ac unit be must clean to run at that outside temp of 45*c. Also check with your electric company for rebate and energy audit that includes a blower ðoor test. A manual j is a load calculation that should be done instead of a guess.

 

[Sponsor]

 

[WorthFlorida]

Did the dealer make recommendations for the number and location of units? As stated a manual J is needed for your best sizing.

You done well getting a bid with a reputable dealer because service and support is getting more important. Mini splits they are a little more proprietary for parts than a conventional central air. Many use remotes for control and built in control boards that are unique to the manufacture. Going with one cassette usually won't work well. As you stated might get too cold in one location. Also you'll need to always keep the doors to the rooms open. For downstairs the one unit will dehumidify the air in the entire home that will make it a little more comfortable but the kitchen will be a hotspot and the first floor bedroom area. Did the dealer make recommendations for the number and location of units?

Another is condensate drain requirements. Sure there are pumps that can be installed but if the cassettes an be mounted on the exterior wall, the drain would just be plumbed right there. Another is multiple cassettes, decoration wise there be a high up on a wall and may distract the decor. There are cassettes that can mount below window level and easier to hide.

For the best comfort probably up to four units but two or three may do. With one unit you can always add cassettes in the future as long as the compressor can be expanded on. Some can, some cannot. As far as sizing, the dealer should have figured it out. Another advantage is all mini's are heat pumps so it you will benefit in the winter months. It may be less costly to use the heat pump for part of your heat load..

 

[Dana]

Surprised it did that good when design 23.2c and most ac units 37*c outside temp. Ac unit be must clean to run at that outside temp of 45*c. Also check with your electric company for rebate and energy audit that includes a blower ðoor test. A manual j is a load calculation that should be done instead of a guess.

That's right- without a load calculation it's nearly impossible to end up with the optimal equipment. Guessing usually causes one to oversize, at the expensive of COMFORT as well as spending too much up front.

For modulating heat pump equipment it's important to keep the oversize factors low in order to maximize comfort. The defaults built in to most Manual-J-ish tools such as the freebie online LoadCalc (dot net) or CoolCalc (dot com) are too conservative for this type of equipment,(though good enough numbers can be derived from either in the hands of competent people with experience.) An easier/better tool in the hands of newbies is the load calc part the BetterBuiltNW HVAC tool, with sufficiently aggressive default U-factors to get close without trying too hard. (That tool was developed by a consortium of utilities, targeted toward HVAC contractors in an effort to keep them from oversizing using their usual methods.)

A room by room load calculation would be useful in figuring out how to zone & size the system(s).

In Vancouver I disagree completely with WorthFlorida's assertion that "For the best comfort probably up to four units but two or three may do." At Vancouver's very modest 76F 1% outside design temp (with negative latent loads) multiple units would be suboptimally oversized, though a pair of separate (zoned by floor) half-tonners or 3/4 tonners might be workable. A single half ton Mitsubishi/Trane is good for 9000 BTU/hr @ 95F (35C), which is probably more than half the whole-house load at that temp, assuming you have an insulated ceiling and low-E windows. (The fact that you maxed out at only 33C indoors on a 45C day tells me you either have reasonably low-gain glass or good shading factors, and decent levels of insulation.)

Given the modest design temps and the rarity of temps substantially north of 35C it's worth choosing a model (like the Mitsubishi -FS06NA) with a relatively low minimum-output yet still high efficiency @ 82F (28C), otherwise it will almost never modulate, only cycle on/off at it's minimum output at potentially low COP. There are many minisplits that will drop to under 3000 BTU/hr at that temp, but many of those that do have abysmal COPs at their minimum output. eg: This pretty good LG can drop all the way back to only ~1000 BTU/hr @ 82F, which is good for comfort, but has a pathetic COP of 1.5 at min-mod @ 82F, compared to 6+ for the FS06 at ~1900 BTU/hr. It will cycle off less often but uses ~2x the power use per BTU of heat being pumped out than the FS06 would until there is a bigger cooling load.

A single 3/4 ton ducted mini-split mounted just below ceiling level in the Bedroom #2's WIC could easily serve both Bedroom #2 & #3 with ducts short enough to not matter, putting the coolth/heat where it matters most. You may have to use partition wall stud bays as jump ducts for the returns. This is more complicated than a simple wall coil, but a better solution overall for that floor. With the doors open to the loft & stairwell keeping the upstairs bedroom at 22C would provide substantial cooling for the lower level as well. The room by room load numbers for the first floor would tell you whether a single right-sized wall coil type in the living room would be adequate for serving Bedroom #1 as well.

For cooling-only if you have double hung or single hung windows you might be better off spending CDN$400-500/each on a couple of U-shaped Midea window units. The sash slides into the U-slot between the compressor & condenser side, isolating the indoors from the compressor and condenser fan noise. These things are essentially a "cooling-only mini-split in a can" in many respects, and are as quiet as many mini-splits. The smallest in the series is rated 8000 BTU/hr, but the 1-ton versions also have a very large turn-down ratio, and throttle back to about 100 watts when both blowers and the compressor are running at their lowest modulation levels. I have no idea how efficient they are at minimum-output (it's probably not all that great at min-mod) but under CEER test conditions they score 15.0, among the highest efficiency window units sold in the US. There has been price gouging on the 8000 BTU/hr versions- I ended up with the 1-tonner simply because it cost less than the street/internet price on the 8000BTU/hr version, and was more available at the point that I was buying. (Looking quickly online right now I see that the 1-tonner is now priced 50% higher than it was at June Jeff Bezos' online store, but at the Walton family's box store the 8000BTU version pricing has started to fall back to earth at ~USD$442- still $100 more than it was in April. Menards has them listed at USD$369 each, with a $28 rebate knocking some off of that.) Given the upfront price difference between these library-quiet better class window shakers and the CDN$7.5K estimate you are expecting (also a price gouge under normal market conditions) the difference in cost would never be made up in lower power use over the service life of the equipment.

They're a bit of a PITA to install and a bit awkward to handle compared with other small window-shakers, but from a quiet comfort point of view it's as good as it gets short of a true mini-split.

 

[xman111]

thanks for the replies guys.. i was hoping Dana would reply . I am going to go over this more thoroughly but just a quick comment. We have casement windows so the window AC won't work. I had the Midea U on order but cancelled it after thinking about the windows. We were going to replace my 1 window just for the AC but it was almost $2k just for the window, then the price of the AC.

 

[Dana]

thanks for the replies guys.. i was hoping Dana would reply . I am going to go over this more thoroughly but just a quick comment. We have casement windows so the window AC won't work. I had the Midea U on order but cancelled it after thinking about the windows. We were going to replace my 1 window just for the AC but it was almost $2k just for the window, then the price of the AC.

Have you considered DIY mini-splits? A 3/4 ton to 1 ton with a 16' lineset runs ~CDN$1000-$1500. With wall brackets and running the power etc the total cash outlay would still be under $2K. Even paying a refrigeration tech to pressure test & purge then pump down the linesets to check for leaks and do the rest of the final commissioning it would/should still be a <$1k cost adder. The overall reliability is usually a function of the competence & diligence of the installer properly purging & pressurizing with nitrogen to 500 psi+ for an hour (or a day) to test for leaks, then pumping it down to <500 microns and keeping it there for a half-hour or longer to ensure that any potential water contamination is truly out before releasing the refrigerant pre-charge in the unit itself. Taking shortcuts with a DIY unit without those additional steps can still work, but risks a shorter product life.

In your location you don't really need a "hyper heating" or cold climate version for heating, though hyper heating units usually have better turn down ratios even in cooling mode.