Radiant slab help!

[Kubota king]

Hello all,
Needing some solid advice. My system is a Mahoning OWB 200 model with a taco 00R pushing 85' of 1"pex to a taco 5000 series 1" mixing valve with (3) 1" crimp elbows to reifing 6 loop manifold with 1/2" loop length 265' +- 5' and returning thru adjacent 85' 1" pex and a couple 1" sharkbite ball valves on each end and isolating pump. I ran head and gpm calcs. But something is wrong somewhere. Actual system performance is extremely low. With mixing valve opened all the way for less restriction (supply water to hot! 160) each loop is getting .4 gpm and delta t is about 60° at best! I need to speed things up but unsure of why! OWB is now very inefficient trying to recover low water returns. Any advice/ideas besides bigger pump? 00R is rated for 15 max head and 12.5 gpm at respective ends of curve. If all was as expected I should be seeing 6-8 gpm give or take rather than 2.4... floor is well insulated had has no problem maintaining 70° set point (doesn't kick on often) cold wv weather hasn't set in yet either!

 

[NSMaple1]

You've only got one pump on the entire setup?

And is there a bypass loop on the boiler or any kind of return temp protection setup on it?

 

[Kubota king]

No sir, I didn't elaborate on rest of setup didn't want to muddy the waters. I have 3 circs. 009 supplies coil in air handler. No problems there. Have an 007 continuously circulating a 14 plate DW exchanger. Both of these have manual bypasses. As for radiant setup no bypass only temp protection is 1- mixing valve 2- thermostat controls with min/max set points and 3 the boiler aquastat it's self... system is open.... thanks in advance for advice/support.

 

[Kevin in Ohio]

First I'm no expert on this stuff and my dealer helped with the set up and suggestions of what would work. Have you consulted with the people you bought the stuff from? Sounds like to me you are asking too much of one pump to do it all. Sometimes calculations and engineers can mislead a real world set up. Things like elevation of pump push and such get lost in the numbers.

My system runs with one main pump that runs 24/7.

It's in the basement of my house coming 100' from the boiler with a 20 ft drop. From there it goes through the sidearm on the hot water heater and then on the bottom line you see here to the heat exchanger. House needs heat? the valve opens and circulates past the heat exchanger. Water to the house is circulated via the old oil furnaces circulator pump which runs 24/7. I have a 36' x 50' garage that has 2 zones and radiant floor heat. If they need heat the pumps turn on via individual thermastats, first going through a mixing valve. Cold then can return via manifold on the right. Equal length runs for each run. Then back to the boiler.

Here is a close up of the floor pumps.

Is your mixing valve installed correctly? Is this a total new system or did it work before? When the slab is cold it always knocks the temp down on the boiler and it can't keep up for a while as you are basically sucking all the heat out on a large area for a while. It catches up within an hour but it's simply a lot of energy all at once.

 

[Kubota king]

Mixing valve installed,correctly. New radiant system in new basement/house piped into existing OWB. Plenty of btus available and floor has stabilized as fsr as maintaining heat as pump does not cycle too often inmy opinion. But there is a problem with head/flow causing an extremely high delta T of about 60°. Stove will supply heat demand without a doubt but in order to be efficient the water needs sped up to get more btu into floor and also lower delta T gap which should allow stove to (relax) not having to recover such low return temps. I've been leaving aquastat set to 160 so there is a slight fluctuation in temp but supply is entering manifold a degree or two different from actual boiler temp. Which is great IMO... only leaving manifold at actual floor temp no matter if I lower temp to 120 or raise to 160. Floor still sucks heat clear out. Simply put water is traveling to slow in theory. Btw floor bottom and sides are INSULATED with 2" xps r10. Should have minimal eacape. I'm no expert either only a determined mind that knows enough to be dangerous! Thanks to Lots of self education/research and soaking and sorting any advice given.

 

[Kevin in Ohio]

My dealer told me to set mixing valve at 140 degrees for the incoming concrete temp so that is what I did. He said any hotter than that was not a good thing to do. Don't know about a normal, wood floor. My baseboard heat runs the normal 185 degree water.

I'm a slow typer so didn't see your reply to the first poster till I was done.

 

[Oxford]

First, that's a really nice job, Kevin. Building a system on a wall like that is such a good idea for so many reasons- good for you!

To the OP: In any hydronic system, my troubleshooting always starts with isolation and an amp clamp. Turn off and isolate your air handler and DHW loops. Does the flow change to the radiant loop? If it does, by how much? Does the delta T change? If you really have .4 gpm in each of six loops at a 60 delta T, that's 2.4 gpm at 60 degrees, which calculates to roundabout 60,000 BTU/hour. That's a pretty big load in most residential applications. How are you measuring your individual loop flow rates? Now, shut off five of the six loops and give the flow a single path to home. Does the flow change now?

One of the most useful numbers in any "What's wrong with my pump?" question is the running amperage of the pump. Stick an amp clamp on the pump as you do the above and see what it's drawing. If it's at or near full load amps, it's moving water on its curve. If it's not, it's not. If this system is new, or if there are elevation changes in it- especially if the boiler is lower than the slab, my money would be on air in the loops- which, because the system is open, will be a chore to bleed. Not impossible, not even terribly difficult if the loops have isolation valves, but a PITA.

Get some numbers, and come back.

 

[Marshy]

Great advice by Ox. I use to love doing fluid dynamics in college but haven't used that stuff in a while. I agree with Ox, you need to figure out where your pump is running on the curve, near shutoff or maybe near runout. When you calculated the flow and required head to pick a pump did you factor in any safety margin or did you buy the exact same size pump you needed on paper?

 

[Kubota king]

Hey guys thanks for help so far! By my calcs. This pump should be satisfy 6 gpm easy and I'm getting2.4 as stated above. Air was one of my first thoughts. Oxford you are correct in saying boiler is slightly lower than floor but high point of system is manifold with air vent. I am in the process of cycling one loop at a time with return side of manifold drain going into a bucket to rid air to this point. Haven't gotten any bubbles yet. But I am seeing thst with all but one loop open I'm stI'll only reading 1.0 gpm max this is very disturbing seeing as I should be maxing the flow meter out with only one loop open.

 

[Kubota king]

Due to tacos forward thinking I'm considering switching out this 00R with my 009 to see if it makes a noticeable diffrence.

 

[NSMaple1]

No sir, I didn't elaborate on rest of setup didn't want to muddy the waters. I have 3 circs. 009 supplies coil in air handler. No problems there. Have an 007 continuously circulating a 14 plate DW exchanger. Both of these have manual bypasses. As for radiant setup no bypass only temp protection is 1- mixing valve 2- thermostat controls with min/max set points and 3 the boiler aquastat it's self... system is open.... thanks in advance for advice/support.

So the 00R is moving water the 85' and back between boiler and slab - and also circulating the 6 slab loops?

I think a diagram of your system might help.

How is the slab stuff hooked to the boiler loop? Is it in series? Or with close Ts? You only mention a HX for DWH - so there isn't one for the slab? Or air handler?

I did a quick google on pressure drop in 1/2" pex, and came up with each of your 265' loops at 0.4gpm presenting about 3' of head. 6 loops? That's 18' of head, just in the floor. Give or take.

 

[NSMaple1]

Looked at another chart and came up with 1.9' per loop at 0.4gpm.

Just going to 0.5gpm gave 2.9' per loop.

(Guess loss charts vary by pipe manufacturer & type).

 

[Kubota king]

You calcs are correct to me also but from what I've gathered you only use the length from your longest loop? Yes the 00r is pushing the 85 into house thru manifold with 6 loops. No need for hx on floor hot water comes straight from boiler. I'll try to squeeze in a sketch today. Thanks!

 

[NSMaple1]

Yes I think you're right there. Brain fart here.

Will wait for a diagram. But if your boiler flow is in series with your in-floor (thinking that is so if only one pump is involved), that means all the water has to go through the floor before it gets back to the boiler. Which you likely don't always want and I might guess is the issue. Thinking the boiler loop & the floor stuff should have their separate pumps, as the DW & HX legs have, and the circuits should be connected by close Ts, or a primary/secondary setup. Unless I am still misunderstanding - always a chance of that.

 

[Oxford]

If the supply and return manifolds have drains, tie the two of them together with a washing machine hose and isolate the radiant loops entirely, then see what your system does. I am not a fan of flowmeters, especially cheap ones. Put a clamp on the pump and see if it's actually doing any work.

Like @NSMaple1 , I would like to see a diagram of the system. I would also like to know the size of the slab and its location (house, shop, barn...?) If it's a design issue, you're not going to solve it with service.

 

[Kubota king]

Ok will get diagram asap ... I did swap out my 00R for my 009 and was able to get almost 1gpm per loop by simply switching pumps. How ever I did not leave it run long emough to see if delta t balanced out. It's not cold here at all todsy so floor is holding temp very well. Ie satisfying thermostat before return temps build up. This may be a design error but I sure hope not! Room and floor temps are easy to achieve just not real efficient at recovering such low return temps at owb. Slab is on grade basement 4"thick completly wrapped in 2"xps. 6 loops 1/2 pex 12"centers loops are 265 give or take a few ft.. Slab size is 62'×25'

 

[Oxford]

So, what's the actual slab temperature, and does it vary significantly throughout the slab? As I review this, I'm interested in that perhaps more than anything. Your slab's ability to heat depends on that one thing more than everything else. If your slab is the right temperature, everything else will come correct. I think your flows are probably low, in no small part because your PEX is one size too small. Also, it's worth noting that your boiler is rated at 200 MBTUh, so that when it's hammered out and you are running your DHW and your AHU, you're going to need high fire.

Regarding your return temperature, bear in mind that the return from the radiant loop is mixing with the return from the air handler and the DHW loop, both of which are likely warmer than the return from the floor. Return temperatures are a concern in traditional boilers to avoid condensation of flue gasses and resulting issues. In a "boiler" like yours, it's condensing all the time and then reburning the condensate, which is no small part of the reason that many OWBs are air pollution factories. Unless the manufacturer is wound up about return temperatures, I wouldn't be too worried either.

 

[Kubota king]

I'm not sure I csn properly answer your slab temp questions I only have one sensor dead center of room and it's staying Bout 4-5° above room temp which is set to 65 now. As for all returns mixing. Every supply has its own return port out at owb.I have a total of 7 lines coming and going to stove buried!

 

[NSMaple1]

Exactly what kind of pipe do you have running underground? That's a lot of pipe running underground and a lot of potential heat loss if not done using good pipe. And since 'good' pipe costs over $10/foot, I'm thinking it might not be that stuff.

Have you measured the temps on the pipes, all supplies & returns, at both ends? Like, just before the pipe enters the ground to return to the boiler, and where it comes out of the ground on the other end just before it hits the boiler again?

Should be an interesting system diagram, will watch for it.

 

[Oxford]