I wanted to update you guys on the latest. The last couple days I've been researching this issue from any angle i can think of. I've been talking with a lot of HVAC guys that deal with both mini splits and traditional. Getting bids and including the fresh air systems since we are going to make the exterior walls ICF. I even called a cousin and a friend (who is a hyper green builder in CA) that live on the west coast to get their unbiased opinion as they would not benefit from the install. Well, it looks as though mini splits may be on the chopping block. If it was a more open floor plan such as a loft, it would be a no brainer. It seems as though the efficiency I am craving is in large part lost when I go to a multi head system to provide air in each bedroom. SO, my friend (the green builder) suggested I look at the Rheem Prestige Inverter heat pump systems since they reach 20 seer and utilize an inverter technology. Combine that with burying my ductwork in the attic under an R60 blanket of blown in cellulose and the short runs my project will need since the air handler would be in the middle of the home, he thinks I would be happy with that system. So thats what I'm going now. lol. This build is gonna kill me. Thanks for the feedback and being the devils advocate. I appreciate the help as it helps me think thru my project and make the best decision I can for our home.

Seems you're still lettin' the cart get a bit ahead of yer horse by picking the equipment before better load numbers are known. The very SMALLEST of the line Rheem Prestige Inverter is a 2-tonner, which is probably more than 50% oversized for your loads, might even be 100% oversized. (Now you're thinking maybe ICF?) High performance houses twice your size rarely NEED a 2 ton heat pump.

This is a small house, with a small load, and the RA2024A is variable, but not infinitely variable. I couldn't dig up the turn down ratio in a quick search, but typically the 'merican variable speed heat pumps (Carrier Greenspeed, et al) only turn down to 40% of full speed, a 2.5:1 turn down ratio.

A variable speed heat pump with a 2.5:1 turn down that's 50% oversized for your design load at full speed it can only throttle back to 60% of your design load, which means more cycling, less comfort that something that's right-sized.

If it's 2x oversized at full speed it'll only drop to 80% of your design heat load, and will almost never operate in it's highest efficiency modulating mode.

No matter what it's SEER and HSPF number are, it won't meet them unless sized correctly for the (still unknown) loads.

Daikin makes a 1.5 ton ducted mini-split heat pump with a full size air handler and a 3:1 turn down ratio that's probably a better match. The FTQ18PBVJU marries nicely to their 1.5 ton mini-split compressors (as well as much bigger deal multi-zone compressors) to deliver SEER 20 and HSPF 12 performance.

http://www.daikinac.com/content/assets/DOC/SubmittalDataSheets/SDS%20FTQ18PBVJU_RZQ18PVJU9.pdf

https://cdn-tp2.mozu.com/11590-15709/cms/files/FTQ_PBVJU_Installation_Manual.pdf

If the load numbers come in even lower, Mitsubishi even has a 1-ton full-size handler, the MVZ-A12AA7 which are compatible with their 1.5 ton MXZ-2C20NA2, (but it's not as efficient as the 1.5 ton Daikin.)

If the configuration of the house can accommodate the Fujitsu -18RLFCD mounted central to the house, it has a 6.5:1 turn down ratio and would run nearly continuously for maximum comfort & efficiency.

http://portal.fujitsugeneral.com/files/catalog/files/18RLFCD1.pdf

It's only drawback is the comparatively lower power of the air handler, but in a house that size a competent duct designer could make it work.

I'd kill for this kind of knowledge. I am doing ok on most aspects of this build and have a good handle on it. That said, the HVAC system, and the people I have locally to choose from is making my head spin. Not one person has said anything even remotely like this and the only Diakin vendor near me hasn't bothered to answer the phone. If my head didn't resemble our lovable friend, the cue ball, I'd pull my hair out. I love living in the country except when it comes to stuff like this. Its when I see just how limited I am regarding qualified contractors. I REALLY appreciate your assistance walking me thru this, Dana. I had stumbled onto a few youtube videos of the attic manifolds that would marry the outside Mini split with an indoor ducted, and I wondered if the 4 vent manifold would work for my plan. I just assumed it would be cost prohibitive and didn't pursue it. I will make another call and see about the Daikin system you mentioned above. I do have one option that is slightly risky but may pay off. I have a friend, he used to be an HVAC guy but is now a Captain in the Fire Service. He still does some HVAC work and he has installed 2 mitsubishi units a few years back. He did tell me he'd install the system for me at a substantial discount, but he did admit he doesn't have the time to research what system would be best since he just adopted 4, yes 4, foster kids all under the age of 5. lol The guy is sharp and I don't doubt he could do it, just not sure how difficult these systems are to install. On the plus side, I am the best flash light holder you'll find so we have that going for us. lol

Posted By Dana1 on 05 Mar 2018 10:03 PM
Seems you're still lettin' the cart get a bit ahead of yer horse by picking the equipment before better load numbers are known. The very SMALLEST of the line Rheem Prestige Inverter is a 2-tonner, which is probably more than 50% oversized for your loads, might even be 100% oversized. (Now you're thinking maybe ICF?) High performance houses twice your size rarely NEED a 2 ton heat pump.

This is a small house, with a small load, and the RA2024A is variable, but not infinitely variable. I couldn't dig up the turn down ratio in a quick search, but typically the 'merican variable speed heat pumps (Carrier Greenspeed, et al) only turn down to 40% of full speed, a 2.5:1 turn down ratio.

A variable speed heat pump with a 2.5:1 turn down that's 50% oversized for your design load at full speed it can only throttle back to 60% of your design load, which means more cycling, less comfort that something that's right-sized.

If it's 2x oversized at full speed it'll only drop to 80% of your design heat load, and will almost never operate in it's highest efficiency modulating mode.

No matter what it's SEER and HSPF number are, it won't meet them unless sized correctly for the (still unknown) loads.

Daikin makes a 1.5 ton ducted mini-split heat pump with a full size air handler and a 3:1 turn down ratio that's probably a better match. The FTQ18PBVJU marries nicely to their 1.5 ton mini-split compressors (as well as much bigger deal multi-zone compressors) to deliver SEER 20 and HSPF 12 performance.

http://www.daikinac.com/content/assets/DOC/SubmittalDataSheets/SDS%20FTQ18PBVJU_RZQ18PVJU9.pdf

https://cdn-tp2.mozu.com/11590-15709/cms/files/FTQ_PBVJU_Installation_Manual.pdf

If the load numbers come in even lower, Mitsubishi even has a 1-ton full-size handler, the MVZ-A12AA7 which are compatible with their 1.5 ton MXZ-2C20NA2, (but it's not as efficient as the 1.5 ton Daikin.)

If the configuration of the house can accommodate the Fujitsu -18RLFCD mounted central to the house, it has a 6.5:1 turn down ratio and would run nearly continuously for maximum comfort & efficiency.

http://portal.fujitsugeneral.com/files/catalog/files/18RLFCD1.pdf

It's only drawback is the comparatively lower power of the air handler, but in a house that size a competent duct designer could make it work.

Adopting 4 kid is an act of extreme bravery and compassion! Kudos to your friend!

Getting to the "right" solution always starts with careful but aggressive load calculations, and when you're still in the design phase you have the option to reduce the loads dramatically. At some low load it's possible to heat & cool 1300' of space with one or two ductless heads/cassettes.

For now, forget the HVAC selection- just know there are options. Concentrate your efforts on designing-out unnecessary excess load. It's not all about R-value. At a whole-wall R of R25 or higher (a typical ICF, or 2x6/R20 with 2" of exterior foam, etc) it's usually more about window area size, and type.

A project I was involved with a handful of years ago was a deep energy retrofit on a 3 family house, in a location with a 99% outside design temperature of +5F. The load numbers indicated that a 1-ton Mitsubishi FE per floor (about 800-900 square feet per) could handle it, but the guy choked and with 1.5 tonners instead. They cycle a bit more than the 1-ton units would, but this place has sailed through -10F outdoor temperatures just fine. Key to getting the doored-off rooms to stay comfortable was minimizing the window sizes and using U0.18 triple pane windows. In your location you could do just fine with U0.20-ish double-low-E windows, that have a hard-coat pyrolitic coating on the surface facing the interior of the house.

That's more expensive than a code-minimum U0.32-ish window, but WAY cheaper than a triple-pane. Double low-E comes in both high SHGC and low SHGC types, depending on what they use on surface #2 (the inward facing surface of the exterior pane.) With reasonably designed overhangs on the south side you can use high SHGC glass on the south (and north) side to offset heating energy use, and low SHGC glass on the east, and particulary WEST side to minimize peak cooling load, since it's hard to shade the low-angle east & west sun. Cardinals LoE 180 + i89 double low-E glass runs an SHGC in the 60s, nearly twice the solar gain of a typical code-min window, but their LoE 340 on #2 + i89 on #4 SHGC down to the teens, a bit more half what a typical window has. Scroll down about 1/3 of the way on this page (under the heading " 3/4" 2 Pane LoĒ +i89 ") :

http://www.cardinalcorp.com/technology/reference/loe-performance-stats/

Other vendors have similar glass, but several of the nationwide window companies use Cardinal glass, and can build it with the double-low-E glass as a special order. the typical whole-window U-factors for double low-E can be as high U0.24 or as low as U0.20, but if you specify low-E on surfaces #2 & #4 you'll find the specs to be pretty good, and offered on at least some standard product.

If you specify different glass for different sides of the house, make the sizes or shapes of the high-gain windows dramatically different from the low-gain windows to ensure that only most AMBITIOUS idiots will install them on the wrong side of the house.