Working on an ICF SFR in Western Washington. Would be very interested in opinions and thoughts on the following: Thoughts on the Daikin Altherma? Climate is well suited to air source HP. Radiant heat for most/all floors (still thinking through carpet for some rooms). Should the radiant heat be integrated with hot water? Want an ERV for air quality. Are the bathroom fans enough or is ducting required? Site has western exposure and there are enough hot days to justify air conditioning. Opinions on using chillers vs. an air handler? Thanks in advance.

Thoughts on the Daikin Altherma?

Get it.

Radiant heat for most/all floors (still thinking through carpet for some rooms).

With a pretty good envelope here you can go for a nice efficient low-temperature radiant system. You may not need radiant on the second floor here in W. WA

Want an ERV for air quality.

I think you probably want an HRV here.

Are the bathroom fans enough or is ducting required?

If you have the HRV, you will need ducting to deliver fresh air to the bedrooms and remove bad air from the kitchen and bathrooms. I still use bathroom fans as an extra boost to clear bathrooms of humidity quickly.

Site has western exposure and there are enough hot days to justify air conditioning.

You might be surprised how much of that late-afternoon westerly heat gain can be controlled using a good envelope and other passive defense techniques. You can get cooling with a mini-split situated in the bedrooms. On the few occasions you want the rest of the home cooled, just turn on the HRV boost and flush the cool air into the main living areas.

Thanks, ICFHybrid. What other passive defense techniques warrant consideration? The site has lots of western exposure.

BIG overhang on roof. Three feet or more. We have it on the South, because we have a passive solar, but even now, the big overhang on the West is keeping out afternoon sun. Also provides shelter because our weather comes from the southwest. Make sure the architect designs structure for the overhang. Sometimes they forget because it is relatively uncommon.

Low SHGC window glass on west for sure.

Screens that can roll down for the worst late summer weeks and roll up the rest of the year. You can get ones that you can still see through somewhat, but which intercept much of the radiation that comes in those West windows.

Typically, we need AC around here for three or four things

1) Having a very big crowd in the house on an otherwise warm day or evening.
2) Those 5-7 nights a year that are truly warmer than we are comfortable with so sleep is difficult.
3) Getting smoked by late summer sun.
4) Poor home design/construction/insulation.

Are you worried about any other?

Thanks. That is the same list I had in mind, We live nearby on a similar site and have use AC perhaps 15 to 20 days per year. We have the shades now and they help tremendously.

We are using the Altherma in Maine and love it.

Western overhangs have to be huge to do anything... sun is lower in the sky in morning/afternoon.

I wouldn't normally use bath fans AND an ERV/HRV exhaust strategy... but it depends on the fan unit you're using and how many bathrooms you have and how big a deal a little steam is for a short period of time. I would always advocate for a ducted ventilation strategy in multi-room buildings. you can ensure a lack of humidity problems with less, but you cannot ensure actual air quality in a room if you do not intentionally put fresh air in the room or at least pull stale air out with intentional pathways for fresh air makeup.

not sure why you'd want carpet though with radiant. best not to. it's possible, of course, but best not to. maybe consider radiant ceiling instead of floor if you're in love with a thick carpet.

Area rugs can be a good (and decorative) compromise over radiant areas.

Western overhangs have to be huge to do anything... sun is lower in the sky in morning/afternoon.

Yup. There was a huge debate with the carpenters (over) the overhang size. They felt it was a mistake on the drawings and were preparing to short it. Have seen other local builds where owners did not get the adequate overhang because the guy who ordered the trusses, the contractor, whatever, didn't believe what he was seeing either.

Fans + HRV is right, ERV has no additional benefit at PNW outdoor dew points (summer OR winter).

Dew points are low enough in summer, averaging in the low-mid 50s F that a chilled slab approach using the Altherma should work for cooling with zero risk of condensation on the floor. With some exterior shade on the west facing glass to take the peak loads down (even if it's a roll up outside shade) the slab likely would never need to drop even as low as 65F, and the slab surface would have to be several degrees below the dew point for awhile for visible films of water to form.

I am confused by your statement that AVERAGING low to mid 50's would mean cooling with zero risk of condensation would be achievable.

65 degrees surface on a floor is only about 10-12 BTU/sq ft of cooling. and the water temp required to achieve that would undoubtedly be condensing temperature a significant portion of the time.

condensation isn't just about slab surface temp.

Dew points above 60F are so rare in Seattle that it makes page-3 news when it does!   Pull up a dew-point history graph and zoom in & out around the summertime peaks- you'll see what I mean- it's a heluva lot drier out there than you might think, annual rainfall data notwithstanding.

Water temp of the PEX doesn't cause condensing puddles on the floor, only the floor temp does.  Adsorption of moisture by the slab when it's core is below the room's dew doesn't damage the slab, and is released when the slab warms back up.  Insulating related PEX & manifolds not embedded in the slab to keep them from dripping during cooling hours is appropriate/useful for the heating season efficiency too, and it's cheap relative to an alternate cooling solution.

Sensible cooling loads at the 1% peak  in western WA are usually well below 10BTU/ft even for current code-min houses, and (barring a HUGE amount of west facing glass) would be even lower in an ICF.  The 1000'/ton rule of thumb is extreme overkill there, and most people do completely without air conditioners or dehumidifers completely. Nighttime lows are reliably well below 70F even on days when it hits the 90s (the 99.9% condition) and nighttime ventilation schemes work pretty well even in not-so-massive houses.   Most of the time (maybe even all of the time) the floor temp won't have to be much below 70F, but it really depends on just how much west-facing glass there is.

If you zoom into the dew point graph for Tacoma in the link above you'll find that yes, it did hit 91F with a whopping dew point of 61F this year. That was once (August 5th), for a couple of hours, but the outdoor temp also  hit 59F  (with dew point 56F) less than 12 hours later.    In an ICF house the cooling peak load will lag the outdoor temperature peak by a few hours- three hours after the August 5th 91F peak the dew point had backed off to the mid-50s.  And that was the "worst" few hours of condensing hazard for the whole summer. Zoom in on August 16th & 17th you'll see temps bumping on 90F, but dew points in the mid-50s even at the temperature peak, which is pretty typical.

So sure, maybe the condensation risk isn't precisely zero, but from a practical point of view it is.  This is particularly true for a high mass house with higher than code R-values.  Move the same house to the mid-Atlantic or New England and it's a completely different dew-point vs. temp/cooling load story, where dew points are usually in the high 60s or low 70s at the 1% outdoor design temp, and the summertime dew point averages are well above western-WA peaks.

Good luck adequately insulating a radiant manifold and exposed pex. I would like to see what that detail looks like. only a minor snark there: if you have seen a good detail for it, I would genuinely like to see it. but I haven't yet... but if I can start breaking dew points with my radiant design supply water temp, that will radically change the radiant cooling game. typical methodology at this time is to mix a WATER temperature above dewpoint for radiant applications.

Spray polyurethane foam to the rescue! :-)

It's ugly, but a manifold wrapped with 3-mil poly (or sandwich wrap) hit with a nominal inch of 1.5lb FrothPak can be cut-free later if need be. (Haven't done it, but would I thought it was needed.)

I'd be curious to know what kind of cooling to expect per square foot with 55-58F water into the slab and a 75F-78F room temp? Just as a WAG I'd assume it's something on the order 5 BTU/ft or a large fraction thereof and slabs surface a bit over 70F, which would be enough for many PNW houses, but I've not done the napkin math on it. At 58F the number of condensing hours on any given day in Tacoma would be very few indeed, and not ultra-correlated with cooling loads.