it would be like debating whether you want 1/2" or 9/16" foam on the outside of your R20 wall cavity... negligable difference.

Would it improve heat loss by 9% - 20%?

I give up. When you can explain why the slabs I am involved with don't routinely have to go turn their supply temps up 10 degrees to match siggy's FEA analysis about what happens at the bottom of a slab, I'm all ears. as far as I'm concerned, he's debunked by reality on this one. His numbers say my designs shouldn't work. they do. I'm standing ten feet over one operating as designed right now. that's that.

as for the heat load, if you do the math you'll find you could offset any likely increase in heat load downward by putting the tubing on the bottom by doing jumping jacks in your basement for about a half hour every year, if you are insulated properly. If you are THAT concerned about your slab losses, adding another inch of foam would have a FAR greater impact. and once you do that, the downward loss effect of tubing position becomes EVEN MORE ridiculous to consider.

I'm new to HP operation. does do you run a HP on a rest? do you just adjust the target temperature and it cycles on and off? or can you actually control compressor speed?

the daikin has a modulating compressor and built in outdoor reset. for fixed speed compressors we vary the temperature of a buffer tank to ensure runtime but manipulate the average load water temp.

Posted By ICFHybrid on 18 Feb 2013 10:56 PM
Interestingly enough, the Rutgers study found a 9% improvement in upward heat flux when the tubing was placed mid-slab. Siegenthaler's FEA runs show maybe as much as 20%. Are you guys both saying that you have no interest in improving the upward heat flux by what may be 10% -20% simply through tube placement?

I am a bit suspicious at this point of the Rutgers experimental setup as they found essentially no difference in heat loss to the soil with tube placement. I wonder what happened to the upward flux deltas?

It shows up as a lower delta-T on the pumped water. It's not heat lost to somewhere else, but rather a lower rate of heat transfer out of the water and into the room.

Under-slab foam or even the R value of dry soil is far greater than that of concrete. That makes the minimal difference iR value of the 0-4" of concrete above it pretty much "in the noise" in terms of losses to the soil. since it's such a tiny fraction of the total. But the difference between R0.1 vs R0.2.5 of the concrete above the tubing is enough to makes for a measurable difference in rate of heat getting from the water into the room, so long as there are no insulating floor coverings.

As Rob correctly points out, as soon as you put a finish floor something with even R1 above the slab, the less that R0.1 vs. R0.2.5 delta in the concrete-R will matter, since it's an ever tinier fraction of the total R on the room side too.

Well, that makes sense.

Praise the Lord!

my delivery temp can be set at the minimum output for the altherma (86 degrees F)

I wonder if they didn't make some changes to some of the earliest models. I took delivery of my Altherma more than a year ago and just put it into service today at 77F.

NO, i don't think they did. I think I am just an idiot in this case, and you're absolutely right that the minimum temp is 77 not 86.

Bwahahahaha.......Finally get to ramp it (the Altherma) up!........now 78F going out, 71F in, 6 GPM. It's ...it's...ALIVE! BWAHAHAHAHAHAHA

Posted By ICFHybrid on 22 Feb 2013 07:58 PM
Bwahahahaha.......Finally get to ramp it (the Altherma) up!........now 78F going out, 71F in, 6 GPM. It's ...it's...ALIVE! BWAHAHAHAHAHAHA

What does one of these beasties cost (or should I ask)?

That's a question everyone asks and it is difficult to pin down. My best guess as a consumer is that you can get one for $10K - $14K. Installation extra, of course.

Some of the pricing confusion comes from the various conformations available. The units vary between a "split box" (outdoor compressor, indoor hydrobox) and a "monobloc", which is everything outdoors in one box. I evaluated a 30kBTU unit and a 54kBTU unit, but there seems to be some new size combinations now, so my numbers have to do with those first two. Keep in mind that these numbers include a stainless DHWS tank which is pretty much integral to the system.

AFAIK, units are still coming in to the states with British Standard fittings, so an adapter kit is necessary. Some places will try to sell you this, of course, and others will properly include it in the pricing.

I know that various sources have tried to paint the Altherma units with "sticker shock" labels, and I am usually more than ready to believe that sort of thing, but I just don't see it here. I've already mentioned the stainless domestic hot water tank, which, depending on size, can account for up to a couple thousand right there.
The quality is very impressive. I think this line is driven by the engineers and not the marketers. I can tell you that they delight in delivering MORE performance than promised.
The features are so deep that it is difficult to discover them all. One feature is the ability to control the unit with respect to different electricity tariffs so you can operate on the least expensive day/nite rates.

I am told there are now one thousand delivered units in the US. When I first evaluated them, there were literally, a handful.

the contractors that install them for us up here (Maine, not a hot market for construction) are generally quoting around $11-$13k installed for an 030 split (almost the only unit it makes sense to install up here!). Zoning, distribution and domestic hot water extra. That said, I know contractors that were quoting up to $30k installed in some markets, and the pricing on the units themselves did roughly cut in half for the smaller units around last june, before that pricing was higher.

we are usually seeing about 5-7 payback compared to a displaced propane or oil boiler. much faster if we're displacing cooling equipment as well. natural gas is a much harder comparison economically.