Seeking air conditioning advice for a mini-split ductless layout on ~10 year old home, which is well-insulated (R40ish SIPs and triple-pane windows) with in-floor heating (no air ducts, just low pressure HRV). Originally built to be passively cooled by opening windows wide at night, sealed tight during hot days, we're now considering adding AC to deal with increasing number of summer nights well above 15 deg C and also multiple smoky nights where windows must stay closed. I'm hoping to size a small AC system that will help keep the house at most warm (<= 24 deg C), rather than drift up to hot (28+ deg C) during multiple days of sealed windows. I'm not looking for fully sized AC solution that ensures each room is never over regular room temperature. Trying to keep costs down. Current plan is a single Daikin, Mitsubishi, or Fujitsu compressor on east (left) exterior side of the house, with line-sets up the window-less wall, leading to one wall-mounted unit near ceiling of the bonus-room upstairs and one wall-mounted unit near ceiling in the living room. Will a 3-ton unit outside, with 1.5 ton wall-mounted units (see attachments) do a decent job of cooling each floor, though perhaps not very evenly in all rooms? Any better ideas? Thanks in advance for advice.

You must first perform a cooling load analysis (e.g., ACCA Manual J, ASHRAE or equivalent) on a building before you can properly size the required cooling system. To accomplish this cooling load analysis, you must first select the design indoor and outdoor temperatures. The cooling indoor design temperature is typically 75F (24C) and the cooling outdoor design temperature is typically the historical Summer cooling 1% dry bulb temperature for the location of the building.

To maintain an even temperature throughout the building, you need to circulate and mix the cool air with the warmer air. If you don’t have a typical ducted ventilation system, you can leave doors open and use ceiling fans to accomplish this with some degree of success.

Thanks for the feedback. I'll wait to see what the various quotes I get back from local installers say. For context, I'm in Calgary, Alberta with following ASHRAE data (14 years ago): http://cms.ashrae.biz/weatherdata/STATIONS/718770_s.pdf

You may also want to look and see what you can do to mitigate passive heating (adding overhangs to your glazing, etc).
Also, double-check all of your air sealing in easily accessible areas as well (don't start ripping the facade off your home).

All replies ae very helpful no doubt.

Wow I didn't realize this post is a year old but.... since I already wrote it , here is my experience with a similar layout.

Your downstairs will be fine, because it is so open. The Den will probably not get very cool but probably tolerable.

Upstairs only the bonus room will truly be cool. The air will just not really flow into the bedrooms. Is there any way to get a head unit into the master bedroom?

I've got the 1 up 1 down setup and that is how it is. We use floor fans to try to get the cool air into the master and it just doesn't really work that well.