Radiant slab help!

[Kubota king]

Well contrary to your suspicions it is 3wrap in 4" tile buried over 2ft deep and it's more like 11 something a ft and supplys are holding True to their advertised performance of no more than 1° per hundred ft loss. Cant ask for much better than that unless you feel the need to waste your money on 5 wrap for an extra 1/2°......Set of 3/4" for DHW flat plate, set of 3/4" for aquacoil coil on air handler, set of 1" for floor manifold and a single supply for boiler fillup.

 

[NSMaple1]

3 wrap pipe should only be in the $5-6/ft range.

The wrapped pipe stuff is notorious for getting moisture in between the layers over time & transferring heat from the pipe to the ground. Not saying it's happening here yet - just that it's been known to happen quite a bit.

 

[Kubota king]

Yes and for both tiles one 4 line and another 3 line was about 900 bucks for 85 ft and both ends were filled with spray foam and rubberized to minimize rodents and moisture.

 

[Marshy]

Interesting stuff, I'll have to come back and read it. The digram will help paint the picture. Maybe two pumps in series.

 

[Guswhit]

 

[Kubota king]

Here are a few quick pictures. This should give you a good idea what I have. If we have any "keyboard Professionals" please keep the criticism to yourself. Thanks!

 

[Kevin in Ohio]

Here are a few quick pictures. This should give you a good idea what I have. If we have any "keyboard Professionals" please keep the criticism to yourself. Thanks!

Not showing up for me. If you don't have a host pic site, email them to me and I'll try to post them for you.

 

[Kubota king]

Only part you don't see is the 85ft run underground.

 

[Kubota king]

I ran my loop calcs again last night and came up with heat loaf requirement was about 44,000 at 131° and head loss of manifold and loops only are 7.2 ft and required flow is 4.2 each loop needing 0.6-0.7gpm that is supposed to leave me with a DT around 20° give or take per loop . I can almost achieve 0.5 gpm thru the loops but my delta t is not where it should be. I tried different water temps but cannot get much change in supply/return temps. Maybe I'm not giving eadiquate time for acclimation.

 

[Kubota king]

CUTE

 

[Kubota king]

So no comments eh.

 

[dave_dj1]

Is the slab insulated? It looks to me like you are just asking too much from one zone if it's all on at once. Something is drawing the temp down.
I have never seen a set up quite like that. Not that I'm any kind of expert.

 

[Kubota king]

Thanks. And yes 2"xps on bottom and sides seems to hold heat well.

 

[Oxford]

I don't see any obvious installation issues that make me say "AH-HA!"

Worry about one thing at a time, and go from there. First, you are concerned that your flows are low. I see that you have an extra zone on your manifold. Either tie that together or use an old washing machine hose between the drains on your supply and return manifold, then use the drain valve to throttle flow between them while you monitor amp draw at your radiant circulating pump. This will tell you if you are flowing, and you can monitor flow at the same time. If the amperage is quite low and then increases when you bypass the radiant tubes, then I think it's a reasonable bet that you're air bound. If it doesn't, and your pump is at FLA, your flow meter is lying, and you've got the flow you're going to get. If it doesn't, and your pump is not at FLA, you've got more system head than you thought. Either let it run in that condition, or open your bypass a little and get the pump up on its curve, which will have the added benefit of decreasing your delta T.

Second, I also think that your head and flow calculations may be off a little, but I don't think it matters. You've got a cold slab on grade, insulated but not overly, and it's taking a lot of water to get that heated up. You're controlling the slab by the space temperature, which has its own set of consequences, not the least of which is that at low space loads the system isn't going to run long enough to warm the slab, which is going to keep the slab cold enough that your deltas are going to be high because the slab is sucking every BTU out that it can.

Third, I don't think the delta T matters nearly as much as you do. It's a matter of heat, not of temperature. Your return water is approaching your slab temperature because it's not running long enough to warm your slab. If you drop your supply temperature, your pump will run longer, your slab will warm, and your deltas will drop. Not as far as you think, but a little bit of cold return water in as much volume as that boiler holds isn't going to hurt anything, and will actually help.

Take home: drop the supply temperature to design and let the system run. Keep track of pump run time with a plug in timing device of some kind if you like. It's going to increase at lower temperatures to keep up with load, but unless it goes to 100% and the room cools off it won't hurt a thing.

 

[Kubota king]

Great read thank you very much I think you've eased some of my concerns. Alot of that makes sense now. The easiest way for me to lower water temp without effecting my other HX's is by setting mixing valve which is supposed to be "low head" but drastically slows my flows when activated any ideas here or should I let it be? That will cause longer cycles aslo.

 

[Oxford]

Good catch. The reason it's not "low head" in your application is that your system is open. As the mixing valve moves towards cooler water, the flow drops because it's shutting off flow from the pumped side of the valve. Put a little pump on your return before the mixing valve.

 

[Kubota king]

Oh ok nice thanks! As you can probably see I'm a little cramped for space between manifold and mix valve, so would there be any value added if a pump were placed on return line out at stove? Essentially pulling?

 

[Oxford]

I've been thinking about this as I've been working in the barn this morning, and I think your problem would be solved by placing your mixing valve before the existing pump. Pipe it in so that the hot inlet is first off the boiler, it can be installed in any position so vertical should be fine. Then pipe the pump suction to the valve outlet, and maintain the connection of the pump outlet to the feed for your radiant loop. Then tee the return from the loop, and pipe the bullhead of the tee to the cold inlet of the valve. Pipe the outlet of the tee to the boiler through a check, so that you really are feeding loop return to the mixing valve. Otherwise, it'll pull boiler water through both inlets. When it needs to cool the loop, it will move to feed more return to the valve, and the return from the loop will still have a clear path to the boiler to allow flow. I do believe that will do it.

 

[nywalleye]

I've been thinking about this as I've been working in the barn this morning, and I think your problem would be solved by placing your mixing valve before the existing pump. Pipe it in so that the hot inlet is first off the boiler, it can be installed in any position so vertical should be fine. Then pipe the pump suction to the valve outlet, and maintain the connection of the pump outlet to the feed for your radiant loop. Then tee the return from the loop, and pipe the bullhead of the tee to the cold inlet of the valve. Pipe the outlet of the tee to the boiler through a check, so that you really are feeding loop return to the mixing valve. Otherwise, it'll pull boiler water through both inlets. When it needs to cool the loop, it will move to feed more return to the valve, and the return from the loop will still have a clear path to the boiler to allow flow. I do believe that will do it.

Seems that have a minor misconfiguration somewhere in midst of your system. Try heeding oxfords advice and installing that mixing valve before the circulator pump. I just realized this was posted over a week ago, and i'm very interested in the outcome. Would be great if you can let us know if it all worked out or not.