PEX Layout help Please!!!

[smuth10]

30 x 40 garage

Ran into a problem with my pex layout today. I obviously did not do my homework and in my rush to get this done before Saturday I ran into an immediate problem. I ran the first loop at the full 300' and then started running the second loop. We got half way done with the floor and had a lot of the second loop left. I know it is important to have equal lengths for the loops so I stopped for now.

My original purchase was based off of 1200 linear ft for a 1200 sq\ft garage, but the layout is not 1200sq\ft. The inside dimensions are 29 x 39 and then if you subtract the 12" all the way around you have 27 x 37 or 1000 sq\ft. To do it correctly I should have (4) 250' loops. Is this not correct? I am thinking I need to shorten the first loop and then take 50' from the second before I finish it up. Any help would be greatly appreciated as I need to finish this tomorrow.

Scott

 

[walrus]

30 x 40 garage

Ran into a problem with my pex layout today. I obviously did not do my homework and in my rush to get this done before Saturday I ran into an immediate problem. I ran the first loop at the full 300' and then started running the second loop. We got half way done with the floor and had a lot of the second loop left. I know it is important to have equal lengths for the loops so I stopped for now.

My original purchase was based off of 1200 linear ft for a 1200 sq\ft garage, but the layout is not 1200sq\ft. The inside dimensions are 29 x 39 and then if you subtract the 12" all the way around you have 27 x 37 or 1000 sq\ft. To do it correctly I should have (4) 250' loops. Is this not correct? I am thinking I need to shorten the first loop and then take 50' from the second before I finish it up. Any help would be greatly appreciated as I need to finish this tomorrow.

Scott

Each loop doesn't have to be exactly the same as other loops. I think 10% is the magic number or get a regulating manifold where you can adjust the flow in each loop

 

[engineer2]

If you just run a loop, the water will be cool by the end. The idea is to try to minimize temperature variations by using a correct layout, and put the most heat where it is needed like at exterior walls. Several ways to do it.
Multiple short loop. Requires a large manifold, but each can be flow regulated
Two parallel zig-zag loops hooked up to flow in opposite directions.
A spiral counter-flow loop.
Counter-flow serpentine.
Each has its uses depending on where the most heat loss is. Plenty of layout info on the Internet.

 

[smuth10]

Each loop doesn't have to be exactly the same as other loops. I think 10% is the magic number or get a regulating manifold where you can adjust the flow in each loop

Thanks Walrus that makes me feel a little better. At this point it will not be too much work to shorten the first loop a little and that way I can stay within the 10%

 

[Reflex]

Smuth,

In scanning your post and picture, I don't think you have too much to worry about. You're right that in an perfect world, your loop lengths would be identical....none of us live in a perfect world. A regulating manifold is probably the best solution for your piece of mind. While there is a tolerance for loop length differential, we'd still like the lengths to be as close to equal as possible. At 10% I'd be a bit uncomfortable.

It should be noted that a balancing manifold is not a "fix all", but it's close. Loop lengths still need to be within a reasonable length of each other (reasonable not defined here), but this type of manifold gives you a ton of latitude in loop layout.

There's a lot of talk on the board about temperature drop across the coil/loop. Much of this discussion seems to center around loop length. It should be noted that the temperature drop is dependent on several factors. It's true that a longer loop will have a greater temperature drop than a short loop, but the velocity of the liquid is the determining factor for temperature drop in a properly designed system. Identical loop lengths insure the same pressure drop though each loop. Faster velocities have less temperature drop than slower velocities. However, increasing the velocity comes at a cost (increased head = larger and more expensive pumps and operating costs).

A balancing loop effectively "chokes off" the shorter lengths to give a matching pressure drop to the longest lengths. In the end, Mother Nature thinks that all the loops are the same length resulting in the same flow for each loop.

In reality, the loops won't have exactly the same temperature drop as loops along an outside wall will have greater heat transfer than those away from the wall, however there are methods to compensate for this.

A couple of thoughts:

1) Looking at your picture, I'd want to make sure I spend a few minutes and a few dollars to insulate the perimeter of the building.
2) Find a balancing manifold that will work for your situation
3) 300' loops is the maximum recommended length for 1/2" tubing. Don't forget to add the leader length (pipe between the loop in the floor and the manifold) to the loop length!
4) I'd be happier with the first loop within 6" of the edge.

Best of luck!

Reflex

 

[brewchief]

Tighten the distance between the pex up a bit, if you are on 12" centers now adjust them to around 10", a little extra tube in the floor won't hurt a bit.

Sent from my SM-G900V using Tapatalk

 

[BadgerBoilerMN]

We use even loop lengths to facilitate fast and efficient installation without much balancing--the same reason we use a computer to CAD the layout before we start.

In semi-commercial layout such as this, the loop length simply doesn't matter in terms of performance as long as you don't exceed the maximum for a given application. 300' is well within the maximum and I defy anyone to discern the output of a 200' vs a 300' loop of PEX.

Balancing is easy and fast if you know what you are doing. We use various length circuits depending on the zones we have. I have 7 zones in this house, some as short as 55' and others over 300.

In these hobby garages tube spacing is not as critical as residential since the comfort targets aren't as hard to meet with fewer windows and a lower inside design temperature.

Variable tubing widths and placing PEX close the perimeter is a waste of time and money unless your build is pour and your climate severe.

Not to say a bit of planning isn't in order. Many vendors will give you a CAD layout and some even know what they are doing e.g. http://www.blueridgecompany.com/.

So DIY design isn't necessary.