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

[Daox]

Well, it is being setup to work well with my solar hot water setup. So, I won't be feeding it super hot water temps. Thus the focus on efficiency and the close spacing.

With the parallel loops, it should act like the sum of the parallel lengths (because the flow rate is divided by the three legs). So in example 1 I have 345 feet of tubing, and in example 2 I have 430 feet of tubing. I just don't have the pressure drop penalty of the full length of the tubing.

[AC_Hacker]

Originally Posted by Daox

Well, it is being setup to work well with my solar hot water setup. So, I won't be feeding it super hot water temps. Thus the focus on efficiency and the close spacing.

I like it that you are thinking of using the floor for solar. With all your insulation, it should work.

What is your tube spacing & diameter?

Are you using aluminum spreader plates?

Was a spiral layout considered?

Did you use any kind of software to determine your layout & pipe spacing, etc.?

You are way ahead of me on your project. I had the insulation torn out from the room I'm remodeling, and a cold spell hit, and my little ASHP was unable to keep up with the house heat because heat was leaking out so fast through the back wall. So I went into overdrive to get enough insulation in to survive. Now reasonable weather is returning, so I can do it right. I got a pretty nice triple glass window to replace two that I am removing... window area is going down about 40%.

-AC

[Daox]

The two layouts in question are shown below. One has 6" spacing, the other 5" spacing. I am using aluminum heat spreader plates.

A spiral design was considered, but I think this should be easier, especially considering the non-rectangular room. I also don't think that uneven floor heat will be that big of an issue. The warmer end of the loop will be on the outer wall (the outer wall is the top of the images).

I did not use any software to design the floor besides the CAD for layout. I'm just trying to get the best most efficient design that is reasonable. I'm not trying to hit a specific heating load or anything. I just want to make the best use of what I do have (solar) which isn't going to be enough to do everything anyways. Perhaps this is flawed thinking, but it pushes me toward the extreme end anyways.

Originally Posted by Daox

The drywall and priming is done.

The hydronic floor work is ready to start anytime. This is the current tubing layouts I have laid out for the floor. I drew it up in my CAD software (SolidWorks). I'm looking for some feedback on which will be better and if the extra work will be worth it?

This is the easier one. The tubing is on 6" centers. Each parallel length is 1380 inches long, so flow will be equal through all branches. By using parallel runs, pumping losses should be minimized even for a small room.





Here is the second more preferred, but definitely more work. This is with 5" tubing centers. The parallel lengths are about 1720 inches each. I like this one because it really works into the irregularities of the room better. I don't see there being a huge benefit from going from 6" centers to 5" centers otherwise. My heat spreaders are 4.75" wide. I am wondering if bending my 1/2" pex tubing will be more of an issue with this spacing?




Feedback is very welcome!

[AC_Hacker]

Originally Posted by Daox

The two layouts in question are shown below. One has 6" spacing, the other 5" spacing. I am using aluminum heat spreader plates.

You might want to verify what the minimum bending radius of your selected PEX is specified to be.

Different brands of PEX seem to have slightly different bending radius specs.

For instance the U-turn of your 5" spaced floor would have a bending diameter of 5", so its bending radius would be 2.5".

One strategy to get closely spaced tubing, and not violate specified bending radius, is to use a serpentine layout. That way your corners will be have a liberal, minimum bending radius, your tubing can be as close as you want, and you will only be confronted with one critical radius. That would be the one in the center, which can be done so as to allow the minimum bend, and adjust by bringing the center tubes a bit closer.

Even at this late stage, I'd recommend Watts RadiantWorks. It's free, and very thorough.

If you modeled your room, with the insulation you have and the temperatures you want to work with, you'd most likely not change anything... but you would proceed with greater confidence.

-AC

[Exeric]

Originally Posted by AC_Hacker

I like it that you are thinking of using the floor for solar. With all your insulation, it should work.
-AC

I agree. One should always try to get as much solar bang for your buck as possible. Since you are using the solar for hot water in the other 3 (2.5?) seasons you can think of that use as partly subsidizing the somewhat inefficient use of solar in winter in your climate. That makes a lot of sense to me, just like solar PV in northern climates.

[AC_Hacker]

This quote from PEX Supply Company:

The Bend Radius of PEX Tubing
The bend radius of tubing refers to the inside curvature of the tubing. This measurement is the minimum radius that you can bend the tubing without kinking it. More flexible materials will have a smaller bend radius, allowing them to bend more before being damaged. Typically, with standard PEX tubing, you can expect it to have a bend radius of 6 times its outside diameter. Therefore, if you have 1/2" PEX tubing (which has a 5/8" outside diameter), the tubing will have a bend radius of about 3.75", making PEX tubing extremely flexible compared to other types of tubing.

This would mean that the center-to-center distance of 1/2" PEX laid out at the closest parallel distance allowed by minimum bend radius, as mentioned above would be 8.125" (3.75 + 3.75 + 5/8).

Serpentine would let you do tighter layouts.

-AC

[Daox]

I ended up going with the 5" centers layout. I'll post pictures a bit later on what I did to accommodate the tight 180 degree bends.

[gasstingy]

I noted that your design did not show bringing the tubing back near the point of origination. I suppose that means you have a manifold where the tubing runs begin and another manifold at the end of the run? Or, did I miss something.

My {unfinished} setup has a manifold to distribute and collect the water being circulated so the plumbing and valves to and from the tank are all close together.

[Mikesolar]

There is no problem having a 5" centre run and having a 180 bend a bit wider. It's done all the time.

[Daox]

Originally Posted by gasstingy

I noted that your design did not show bringing the tubing back near the point of origination. I suppose that means you have a manifold where the tubing runs begin and another manifold at the end of the run? Or, did I miss something.

My {unfinished} setup has a manifold to distribute and collect the water being circulated so the plumbing and valves to and from the tank are all close together.

There will be a manifold made out of tees to split the main supply and return line into the three parallel branches. I won't be using actual manifolds. This will be done under the floor so its not in the floor and will be accessible for repair if needed. The main supply and return lines will however go back to a home run manifold.