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Feedback on proposed new construction HVAC system design?

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mark johnson

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Discussion starter · #1 ·
We're having a new home built in the Portland OR area. Our architects are proposing a mini-split system, using a combination of ducted and ductless units. Since they are not HVAC professionals, I'm trying to confirm that this is the best approach for our 3500 sq ft home, as opposed to a conventional system, or a combination of the two. Obviously it'll be much more difficult to make any changes later, either after the design is finalized (without any provisions for ducts), or worse, after the house is built.

I don't know who to turn to for that kind of feedback - I tried some HVAC "consultants", but the ones I found are only commercial. And when I call residential HVAC contractors, they seem to be more in the business of installing, not designing.

Does anyone have recommendations for an HVAC professional in the Portland area who would be willing to review the proposed system - not to address the details, just to tell us if we're going in the right direction with the mini splits.

Below is a sketch of the proposed house layout and the mini split system.
 

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#5 ·
Is there no attic? Looks to be one way ceiling cassettes? What make/model system is being specified? What will have the southern facing walls? And about 10 other questions but im on the move right now so those will have to suffice for the moment.

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#6 ·
Fresh air ventilation? Most IAQ experts recommend a fresh filtered air change to purge indoor air pollutants and renew oxygen.

Regards Teddy Bear
 
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Discussion starter · #7 ·
I believe the plan is to use Mitsubishi ceiling cassettes. Single heads in most locations, except for a ducted system in the great room and other rooms in that area. As for window exposure, the plan shown above is drawn with North on top and South at the bottom, so we'll have lots of southern glass exposure.

The plans do show a fresh air intake in the garage area.

I just want to have some confidence that this system will work well for our house (as opposed to a conventional heat pump system), beyond the architects telling me that it will :).
 
#9 ·
My only concern is that you will only be able to use heat or cool on one condenser. Meaning what ever is connected to hp1 will only function in one mode. Same with hp2. To further explain this you can not operate one fan coil in heat and another in cool at the same time. So long as you understand this you will be fine. Then again its your house your dime. If you're not comfortable get what you want.

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Discussion starter · #10 ·
Zamoramax said:
My only concern is that you will only be able to use heat or cool on one condenser. Meaning what ever is connected to hp1 will only function in one mode. Same with hp2. To further explain this you can not operate one fan coil in heat and another in cool at the same time. So long as you understand this you will be fine. Then again its your house your dime. If you're not comfortable get what you want.
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Thanks for the warning on that aspect - I don't envision ever needing to cool one zone while heating another, normally we'll just want to heat (or cool) different areas to different temperatures. But not a mix of both heating and cooling at the same time.
 
#11 ·
mark johnson said:
Thanks for the warning on that aspect - I don't envision ever needing to cool one zone while heating another, normally we'll just want to heat (or cool) different areas to different temperatures. But not a mix of both heating and cooling at the same time.
Click to expand...
If you leave one in heat and turn one to cool it will not operate. Thats the biggest call we have. Then you remind people and they never bug you again.

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#12 ·
My 1st thought on using only mini-splits is look how many potential leaking evaporators there are. I used them and like them but on this size house it's split ducted units for the majority of the house but I'm too old to teach very many new tricks.
Also cost, wouldn't 2 systems be more cost effective even with zoning than all those units ? I don't know current pricing.
 
Discussion starter · #13 ·
Zamoramax said:
If you leave one in heat and turn one to cool it will not operate. Thats the biggest call we have. Then you remind people and they never bug you again.
Click to expand...
Understood, that makes sense. But that's no different than a central zoned system, so it's not like I'm giving up that option by going from central to mini-split, right?
 
Discussion starter · #14 ·
oldguy1949 said:
My 1st thought on using only mini-splits is look how many potential leaking evaporators there are. I used them and like them but on this size house it's split ducted units for the majority of the house but I'm too old to teach very many new tricks.
Also cost, wouldn't 2 systems be more cost effective even with zoning than all those units ? I don't know current pricing.
Click to expand...
Agreed that each cassette is a potential leak point, as well as a potential failure mode down the road. Then again, there's some benefit to a system that is essentially fully designed by one manufacturer to work as a system, with less opportunity for screw-ups compared to a conventional system, which is often assembled from components made by different manufacturers, where everything needs to be properly sized and matched, never mind all the potential problems with the duct system. Neither is obviously foolproof.

As for your cost question, are you asking about two zoned conventional systems compared to the mini-splits? Or two zoned mini-split systems?
 
#16 ·
Personally it looks like a nightmare. I have often heard from the guys on here who do a lot more minis than me that they should always be on outside walls and many say to avoid multi heads as much as possible. I don't know if I am seeing the pictures correctly but I thought I saw a branch box which is best to avoid using.
 
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#17 ·
I might be mistaken on the branch box I think thats an erv which is a great idea although if you are in a humid environment I would consider a ventilating dehumidifier instead.
If I'm seeing correctly one condenser is in a little slot between two wings of the house you need to make sure that there will actually be enough room for proper clearances to the unit and that it wouldn't cause recirculation of the condenser air.
 
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Discussion starter · #19 ·
R600a said:
Personally it looks like a nightmare. I have often heard from the guys on here who do a lot more minis than me that they should always be on outside walls and many say to avoid multi heads as much as possible. I don't know if I am seeing the pictures correctly but I thought I saw a branch box which is best to avoid using.
Click to expand...
Good point, I would also expect the heads to be towards the outside walls.

Can you tell me more about avoiding the multi heads - why?
 
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Zamoramax
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