Hi, I have an older house in Seattle that's gutted and I want to install hydronic on the plywood subfloors.

I'll cut OSB into 12" strips to form the channels and use a jigsaw to cut the loop-ends.  Then over that 1/4" cementboard, 1/4" padding and carpet.  I want to use 5/8" O2 barrier PEX, as it flows more efficiently (thus I can use lower temps), but I can not find any aluminum heat transfer plates to fit it.  Does anyone know of a source?

The house has no gas service, and to me resistive water heating is a misuse of a high-grade power source like electricity, so I've been looking for an air-to-water heatpump which mounts outside.  I read that a "reverse-cycle chiller" is more efficient then even geothermal, but I can't find any info on the nature of this technology.  Can anyone advise?

I'll have about 4 zones, and I've been looking for an advanced thermostat which can control it.  Ideally it should have a temperature sensor in each zone, and each zone should be individually controllable.  Also it should be networked so I can access it on the computer and/or on an app.  In other words the most advanced system available.  Has anyone seen anything like this?

I need also hot water for the house.  I know that a hydronic heating system and domestic hot water would have quite different temperature requirements, so I was thinking a storage tank kept at say, 80 degrees, then a desuperheater for the hot water.  Is anyone familiar with such an arrangement?  Maybe this wouldn't work without solar evac tubes, as I'd need the heat on all Summer, but I can't think of a better idea.

And finally, a little off the subject, what is the point of having a domestic hot water recirculation which only comes on on demand?  Isn't the hot water going to get there about as fast anyway?

With regard to the hot water recirculation of course the heat is getting there at about the same time, for me that is not the reason I installed it. The advantage is that all that water is not going down the drain. I live on the high plains, and water is in short supply, so not wasting it is important. Of course YMMV.

You can look at www.chiltrix.com

I'm no professional, I would use closer tube spacing 6-8". Some aluminum heat spreading fins under the cement board. Carpet is an insulator.

Connexus is a system used by a Geo system designer that has the type of controls your looking for.

Blueridge is close to you and they seem to specialize in HR plate systems. While expensive and inefficient compared to a concrete slab system, plate systems are a viable HR option for remodels. To maximize efficiency by keeping required water supply temperature as low as possible, it is best to minimize the amount of R-value above the plates. John Siegenthaler's "Modern Hydronic Radiant Heating" is a great resource for all things HR. We have HR information and free HR design software on our website that you might find useful too.

Thanks all.

Dave, I don't understand how recirc saves water in this case? If it were on constantly it would, because instant hot water, but then there would be heat losses.

Jon thanks, Chilltrix (http://www.chiltrix.com/) is now on my radar, as are:
http://www.aermec.us/products-home/2015-06-11-14-07-23/ank
http://www.daikin.com/products/ac/lineup/heat_pump/index.html
It seems that those with a digital scroll compressor are the very most efficient, followed by those with an inverter-controlled compressor.

Chris I think you're right about the spacing. I'm aware that carpet is an insulator, so will be using 1/4" hard pad, which s the best I can do. Cement board rather than plywood overlayment is my own idea for efficiency.
I can't figure out what Connexus is? (http://www.connexus.xyz/) There's no detail. Looks like just an app from what I can see.

sailaway, that is a very nice set of tools you have there at http://www.borstengineeringconstruction.com/Calculators.html .  BlueRidge has exactly the right heat-spreader plates, but none for 5/8" tubing, which I would prefer to use to keep temps lower.  I can't find anyone making them for 5/8", so may be stuck with 1/2" tubing.  The heat-spreader plates are mandatory.

One reason I like using water so much is that it's directly supplementable by evac-tube solar. One reason I like reverse-cycle chillers is that they can also cool, through a water coil in an ERV.

Thanks and 1/2" PEX is more than adequate for your needs. Just keep the circuit lengths less than 300' to avoid excessive hydraulic friction and pump head. You appear to have things well in hand. Merry Christmas!

Deleted duplicate post.

You know, I have alot of respect for Uphonor, and their QuikTrak panels are just 1/2" plywood with a groove, and backed with an aluminum sheet!

I could do the same by getting aluminum sheeting from Everett Steel (http://everettsteel.com/3003-alum-sheet-p-1128.html) in .063" thickness (1/16"), laying it down, and laying down my OSB strips. Like Uphonor does, silicone down the PEX to the aluminum, then overlay with cementboard.

Apparently Uphonor believes that this will distribute the heat evenly, so what's wrong with this plan?

With the 1 GPM I shower at, a direct run of 3/8" tubing is fine in terms of pressure loss and heats up in < 20 sec (ie, 1/3 gallon of cool water down the drain).

The effectiveness of plate systems largely depends on how well the PEX is in thermal contact with the plates. Think thermal paste and close contact with heat transfer surface as is done for PC CPU installation... I suspect what you propose would work very well and perhaps be more cost effective too. I also suspect that continuous aluminum panel may be less susceptible to oil canning noise too. However, I don't have first-hand experience with this Uponor product so all pure speculation on my part. Blueridge might be good source for guidance on this sort of approach. We only do new construction and therefore we never use plate systems.

This is encouraging sailaway, thanks. I've requested a quote from Everett Steel for 1/16" 4'x8' AL sheets, so the floor cost would be these plus the OSB, to compare with QuikTrak. I must allow a gap between AL sheets to allow for expansion! Say, 1/4"?

Uh oh, fastening down the AL is undesirable except in the center.  Maybe I should silicone down the OSB rather than screw.  This might call for smaller AL sheets than 4'x8'.

I wonder if their plywood is denser than OSB? Denser would transmit heat better. I should compare the weight of OSB with plywood.

One thing I don't understand is Uphonor claims that silicone is a good heat transmitter.  I-hi don't think so.  But I can't think of any cost-effective adhesive that would be.

OSB R-value is 1.59 and plywood is 1.24 per inch. So yes, plywood is a slightly better heat conductor than OSB. Silicone adhesive, like silicon (a semi conductor) is indeed a good heat conductor. However, it is not a good electrical conductor...but you don't care about that...

aluminum-solar-absorbers.com they should have fin for 5/8"

Connexus-controls.com

A thin layer of silicone is certainly better than an air gap. Even where a plate has imperfect contact with pex tubing.

Greetings all,
Thanks for the good words Sailaway,
I will chime in briefly, have a quick look at our floor panel,
http://www.blueridgecompany.com/radiant/hydronic/527/rht-floor-panel-system-for-radiant-heat-systems
I am sure the clever person can bend there own plates and make the turns if so compelled.
The point to notice is our plate shape, plates are an omega shape that captures the pex pipe for heat transfer, further placement in the building when using these in the sandwich system as oppose to staple up places the fins on the plates much closer to the inner surface of the building envelope. Typical delivered water temp using the RHT floor panel system is in the 90 degree or less range.
I am not sure how effective laying the pipe on an aluminum panel and covering the bulk of the panels surface area with plywood would be.
If you do apply this method it would be interesting to hear the result re positing on this thread.
Good luck with your project,
Dan

Yes I considered your heat-spreaders and routed plywood Dan, but you simply do not make them for 5/8".

I do see the benefit of putting the spreader closer to the surface, but there's also the problem of the thickness of the spreaders when using a thin overlayment such as 1/4" cement-board, causing an uneven surface.

I am pretty sure at this point I'll be using 5/8" PEX as tests have shown a more even temperature dispersion and easier flow, allowing more efficient lower temperatures.

As to my heat source, I've mentioned that I'm considering reverse-cycle chillers, but these do require water storage of some kind to avoid 'quick-cycling'. I'll likely go with this:
http://www.americansolartechnics.com/products/heat-bank-storage-tanks/

So we design system, have been for some 25 years
Our standard residential is 1/2 pex to about 300'
Od of 1/2" pex is 5/8" Fits nicly in a 3/4" sandwich.
We find 1/2" much more versatile in smaller zones (1,500-2000 sq ft or less)
A grundfos alpha will drive quite easily a large (1,500-2000 sq ft) residential area offering sub zoning on the manifold or with zone valves.
Further there is a slightly thinner profile, a 3/4" sandwich.
We do sell 5/8" pex, love the stuff, but typical use is larger areas, shops , warehouse, manufacturing.
My 2 cents for what its worth.
Dan

As I said before, 1/2” PEX is way more than adequate for this project (i.e., both in terms of heat transfer and flow rate). Using 5/8” PEX would be far beyond the point of diminishing returns and the money would be much better spent on more insulation. HR required supply temperature increases with increasing building heat loss and decreasing HR emitter efficiency. So if you really want low required supply temperature, you need an energy efficient building (i.e., well insulated and well sealed) and an efficient HR emitter (i.e., high heat transfer coefficient and way more R-value below the PEX than above the PEX). So, don’t even think about putting carpet above the PEX. The engineering behind this subject is well detailed and documented in John Siegenthaler's “Modern Hydronic Radiant Heating” should you have any doubts and want further confirmation.

Alright, 1/2" it is. I'm doing all I can to seal the building, starting with foaming the stud cracks for the outside walls. The studs are only 2x4, and I'm a bit worried that R15 insulation won't meet current Code, and I'll have to fir the walls out for more thickness. But that's a different issue.

Unfaced batt insulation in the exterior walls, and 4 mil vapor barrier over that, then sheetrock. I know there are plastic pockets you can put around outlets, but no one's heard of them here in Seattle.

Dan I don't understand what you mean by 'sandwich' in "Od of 1/2" pex is 5/8" Fits nicly in a 3/4" sandwich." Or this whole sentence: "Further there is a slightly thinner profile, a 3/4" sandwich."