I realize this question requires further evaluation based on the specifics of the home being built, but in general, is A/C 'necessary' to be comfortable in the summer in MN given the following build plans:

-2,500 square feet plus basement
-1 1/2 stories plus basement
-ICF Basement and Main Floor Walls (12")
-SIP Roof (10")
-As the home is 1.5 Stories the SIP roof provides the insulation of the '2nd' story (knee walls and ceiling built within SIP roof)
-<.25 U windows throughout
-In-floor radiant heat throughout
-HRV

Will the HRV provide enough dehumidification in the warm/humid months?  I can live with elevated temperatures in the summer and, I think, rely on air circulation via ceiling fans but the humidity, when present, is tough to overcome comfort wise. 

I have a south facing lot on Lake Minnetonka I'll be building on at some point, w/ good shade protection to the west. I talked to neighbors w/ similar lots and they only ran their A/C a few days last couple summers. Their homes are much older and less efficient but we've had cooler summers as well. You're right the humidity is the big factor in comfort.

Have you considered ductless mini-split heat pumps?  Something like this:

http://www.fujitsugeneral.com/wallmounted9-12RLS.htm#features

With these units, you could mount one of the smallest sizes on each floor to provide zoned supplemental cooling, dehumidification, and even heating.

These could be retrofited later as well; although, if you think you might install one or more of these units, it would be beneficial during initial construction to provide the necessary penetrations for power, refrigerant lines, and condensate drains.  It is a lot easier to put a 4" PVC pipe sleeve through an ICF wall prior to the pour than it is to later have to core drill a hole in the wall.

Yes, that's something I've considered, though I think I'd rather go to high velocity mini ducts rather than hanging those units in whatever rooms need them.  Anyone have input on these types of systems?

The answer probably lies with the windows - how much south facing glass ? Is it shaded in the summer? Do you have good cross ventilation? You should have enough insulation so that you don't need AC, but you could have significant heat gain which might offset that.

I'm a big fan of ductless mini splits. I personally do not mind the units hanging on the wall. I can't comment on your specific area's needs, but if your nieghbors useage is the norm and you have a very energy efficient house, would you even need a wall unit in each room? You may get away with 1 large unit in the main areas and spread that conditioned air with fans. Is your floor plan very open or cut up?

Doing a j calculation might give some insight.

Jboysen,

I live in Minnesota as well. My experience has been that A/C is not needed that many days during the summer months, however the days that it is needed, it’s really needed! Living in Minnesota is always a crap shoot during the summer if we get a hot streak and in the winter if we get a frigid cold streak. When I build, I am going to at least install an A/C unit (if I don’t go with a geothermal system) as a “just in case”.

I hate having to plug wall or window units in and finding places to store them. Perhaps it’s my military background, but I’d rather have and not need, than need and not have. It will cost less to install an A/C unit up front than it would to install one at a later date.

I assume that you are asking the question that in using ICF construction, would the thermal penetration during the summer months yield enough of a temperature increase to warrant the cost expenditure of the cost of an A/C unit? The answer comes down to a question of personal comfort. There will be a slight increase in indoor temperature during the hot days. This will also vary slightly if you open windows at night for fresh air or if you keep everything sealed up. Either way, you still have the nasty late July/early August humidity to deal with.

I would still personally install a smaller A/C unit for personal comfort though.

tlh,

You have no idea how sadly true that joke is! Guess that's what makes it so funny for us Minnesnowdans

= )

I think I've come to the conclusion that having A/C here is definitely a 'rather have than need' type of deal. We got off easy this last summer but that's certaily the exception to the rule. I'll be taking a very close look at mini-split systems, Fujitsu has some in-ceiling units that would circumvent having wall hung units.

Are you married? Because your "rather have" is probably "need" to the wife.. ;)

I think you hit the nail on the head about "need".  We spent 3 years in Wayzata in the mid 80's.  The first thing my wife wanted was AC.  In her defense, she suffers from allergies and we generally keep the windows closed.

Also, all of the major mini split manufacturers have ceiling cassette units available.

Bruce

jboysen,

I think I would at least prep for A/C just in case. How do you plan to have your HRV hooked up? You mentioned radiant floor heat through out, will you have forced air duct work through out the house? If you have duct work throughout you will have better air circulation and can connect the HRV to it... also connect a humidifier to remove humidity on the hot days. If you feel you still need/want A/C, add it then.

Hadn't really thought about how the HRV was going to be plumbed. I'd prefer not to have standard a/c ducting throughout the house, instead relying on a mini-split system. If there is no standard a/c ducting how is an HRV typically setup?

@jboysen: As an example, my contractor has spec'd a unit from this company which describes an HRV as "fully ducted" (in the top picture). So basically in a radiant-heated home with no A/C, the HRV would have it's own dedicated ducting.  Other diagrams on the page show how it can alternatively be connected to standard ducting in a forced-air heated/cooled home.  Hope this helps.

Would the 'fully ducted' ducting for just an HRV be less ducting than required for conventional a/c?

My understanding is that yes, the ducting for only an HRV (with no heating & cooling) is narrower and the air moves more slowly than standard HVAC ducting (wider with faster air movement).  My inquiries about central A/C lead me to believe that standard HVAC ducting is required to move enough cool air. 

That is exactly the issue.  For a hypothetical 4000sf house, you want somewhere between 0.5 and 1.0 air changes per hour for ventilation from an ERV or HRV, which is 300 to 600 cfm.  HRV/ERV are not really designed to provide "free cooling."

To heat or air condition with ductwork, a single large room may need >300cfm.  Accordingly, the ductwork must be quite a bit larger.

Bruce

In general then, is HRV plus requisite ductwork plus mini-splits for cooling going to be cheaper than HRV with conventional a/c and ducting? I would expect the former to be more efficient and economical to run.

Very good question, jboysen.  I'm currently pushing my builder to provide estimates on that exact scenario for my home with radiant in-floor heat; either:

1. Central A/C with full HVAC ducting also used by the HRV.
   
2. "Fully ducted" HRV (own separate ducting) and a set of mini-split ductless A/C units in rooms needing cooling.

My personal preference is also for the ductless (#2) approach as it should be more energy-efficient without cooling losses through the ductwork of option #1.  As well, it could be controlled on a room by room basis.

As for price difference, I'm still waiting to hear back from my builder.  I'll post once I hear in the next week or two.  If others have comments on pricing, I'd love to hear them.