Remodeling the office (new floor, ceiling & adding insulation) passive house retrofit

[Daox]

Originally Posted by S-F

Can you get Polyiso which isn't foil faced? I'm all for not demanding that moisture stay in one place because you can end up with problems if there is too much of it. Talk to some local green builders to see if they can point you to recycled foam boards. Call all of 'em if you have to. This is going on all over the country.

I'll have to dig into this more. I've only seen foil faced in the big box stores though.

About your idea, if you later decide to outsulate you might be in a bit of a pickle. It's not advisable to have two vapor barriers in a wall. The moisture that inevitably gets trapped in there has no avenue of escape and you get rot and mold. Personally I think it's nuts that people sandwich OSB/CDX sheathing between spray foam and foil faced polyiso but there haven't been any disasters yet that I've heard of. Maybe in 30 years we'll see the truth. But none the less, putting fiber glass or cellulose between them is a no no. Also it's best to have your air barrier (polyiso and 1 part foam sealant) on the outside to minimize unconditioned air entering the cavity and convecting. All your insulation is next to useless if you have cold air cycling through there. The big advantage of the foil on polyiso sheets is that you can quite easily seal them together with foil duct work tape. Otherwise you need to seal boards together with spray foam. Some people say you can use tyvek tape but in my experience that stuff doesn't last more than a decade.

Oh, one more thought. You could put the foam boards on the inside if you air sealed the sheathing properly. This is effectively no different than putting it on the outside of the sheathing as far as moisture is concerned. You just completely eliminate the wall's ability to dry to the inside. Just don't make a vapor barrier sandwich and make sure that outside air doesn't get in. That's why I originally recomended the boards and 1 part foam. It's a relatively cheap (compared to filling the whole wall with spray foam or even filling it 1" deep) way of creating a fantastic air barrier. You kill two birds with one stone there. Oh and if you do try to dense pack the wall yourself you will have no way of knowing if you did it right. At first dense packing can be a little tricky. Even today I still am uncertain when dense packing a cavity I can't test. Well, at least I can't test it until the cold weather hits and the thermal camera shows me what a stupid job I did. :P

Thanks, I wasn't thinking about the outsulating. I would imagine that would be an issue, especially since I don't have A/C and my house gets incredibly humid during the summer months.

And your price on the spray foam looks berserk. I think that's about what I paid for the 600' kit. I think even on the Tiger Foam page they list it at $250 for the 200'' kit.

I was looking at their site just the other day and the 200' kit is $335 and $90 for shipping!

[S-F]

Call around to your local suppliers then. You might be able to have a lumber yard that sells green building products order one. Or you can see if you can get a contractor's account with Tiger Foam. Then you get a discount.

[AC_Hacker]

Originally Posted by Daox

I'll have to dig into this more. I've only seen foil faced in the big box stores though.(

I came across this very well written article on roof venting, but there is much in here that will apply to your remodel.

Oddly, it prohibits your being able to print it out... but we have ways...

-AC_Hacker

[Daox]

Originally Posted by AC_Hacker

I am very interested in how you approach this phase of your re-model.

As I recall, you already have fossil -fueled hydronic heating in part of your house.

And your solar panel rack and heat storage tank, both seem aimed at solar space heating... and may likely have lower temperature heat available to you.

I have experimented with Watts Radiant RadiantWorks and have found it very interesting and useful, especially when doing some 'what-if' trial runs. It has helped me understand how varying certain parameters can affect the system performance.

As for myself, I am beginning to favor the use of 3/8" PEX, spaced much closer than usual (3" or 4"), using a multi-tube spiral arrangement, as illustrated below.

...I am also favoring aluminum spreader plates like Gary's floor, topping the plates with 1/4" Hardibacker and finishing the floor with Marmoleum, which has very low R-value.

Best of luck with your project.

-AC_Hacker

I've been thinking more about how to do the hydronic floor and I'm looking for a bit more input. I'm definitely going to go the route of tubing with heat spreaders instead of a poured floor. I haven't yet been able to download the watts program and play with it. Is there a large benefit from going to the three 3/8" lines in parallel vs just a single 1/2" line?

[AC_Hacker]

Originally Posted by Daox

...Is there a large benefit from going to the three 3/8" lines in parallel vs just a single 1/2" line?

{some of this was covered here}

I came across a study by Siegenthaler (the guy who wrote the book) and he was comparing the effects of using several different PEX diameters...

As I recall, the bigger the diameter, the better the heat transfer, tube spacings being equal. However, the difference between 1/2" and 3/8" was very small... as I recall it was around 3% difference... pretty small, all things considered.

I've also seen studies, and learned from working with computer models (this is where RadiantWorks was so helpful) that the increase in heat transfer that results from decreasing tube spacing is large.

And the bending radius of 3/8" is favorably smaller, too.

When I first came across the concept of Low Exergy Heating (AKA: low temperature heating), I spent a couple of weeks on a massive google-blitz from which I learned that there was not much work that had done on Low-Ex heating in the US, and that the really important work had been done in Europe a decade+ ago. So that lead me to all kinds of installations and products that had been developed for this purpose. And there, over and over again, I found very closely-spaced tubing configurations... like around 3 to 4 inch spacing (or closer).

One of the most interesting studies I found was Chinese (they are graduating 400,000 engineers per year as opposed to our 80,000) where they experimented with an extruded plastic floor with small heated water channels, side-by-side. The material tests were very, very favorable.

Nowhere during my pursuit of Low-Ex heating information did I come across spacings of 9" and 12"... This is American fossil-fueled foolishness.

Back to wet system (poured concrete), one of the big determiners of spacing is a desire for even heating. The radiant-heating trade even has a term for cold spaces that result from tubes being spaced too wide. they call it 'striping'. Striping results in parts of the floor that feel cold to the feet, so it is to be avoided. So tubes are spaced more closely to avoid striping.

Thick slabs are less likely to stripe than thin slabs... Minimum thin slab thickness is about 1.5" before striping occurs... But in all these considerations, tube spacing was in the 8 inch range.

And again, if you look at Gary's thermal photos of aluminum plate spreaders, the heat falls off as you move away from the tube... closer tubes, less heat fall off.

So the heat that comes off a floor is the average heat of the surface of the floor. Floors that have a large variance in temperatures will need a higher feed temperature than floors that have a lower variance, to achieve a given heat output.

If you are using cheap fossil fuel (remember that stuff?) a difference of a few degrees is hardly worth concern. If you are going solar, it means more days that you can use 100% solar, if you are using a heat pump, the energy savings are very large.

I can certainly see that if you are a tradesman, installing radiant floors, you would want to get in, get the job done, and move on to the next paying job, and not fiddle around with a swarm of closely-spaced tiny tubes.

But then there's DIY...

Regards,

-AC_Hacker

PS: I think spending a couple of hours with RadiantWorks is much more educational than spending that time reading a book... and it's free.

* * *

[Daox]

Great info AC Hacker, thanks!


Just stashing info here for the time being.

BASSI,LLC

The R-value for a ¾" engineered bamboo floor is R=0.720, according to the Radiant Panel Association, RPA.

Since my flooring is only about 1/2" I'm guessing the R value is around 0.50.

[AC_Hacker]

Originally Posted by Daox

Since my flooring is only about 1/2" I'm guessing the R value is around 0.50.

RadiantWorks has a very interesting chart that will give you the water temp for the space you are working on...

It takes into account outside design temp, inside design temp, insulation of all surfaces and windows, etc.

You can change individual components (floor covering, for instance), do a re-calc and see what effect that has on feed temp.

Very informative.

-AC_Hacker

[S-F]

Originally Posted by AC_Hacker

RadiantWorks has a very interesting chart that will give you the water temp for the space you are working on...

It takes into account outside design temp, inside design temp, insulation of all surfaces and windows, etc.

You can change individual components (floor covering, for instance), do a re-calc and see what effect that has on feed temp.

Very informative.

-AC_Hacker

Is this software only for radiant heat?

[AC_Hacker]

Originally Posted by S-F

Is this software only for radiant heat?

Well, it is designed to support a radiant heating supplies company.

It does heat loss calcs so that you can select the appropriate equipment, which of course, they sell.

It does do a good job of heat loss calcs, so you could use that part of it only.

-AC_Hacker

[S-F]

Is it for mostly in floor radiant or does it also cover baseboards?