Radiant system air purging issue? Separate Manifolds for sloped loops?

JimN

Wow. Just found this site. Am putting in a new Snowmelt system, and part of the driveway is sloped requiring another 12' of elevation from my flat area. I've two questions to you guys.
1. Does it make sense to separate manifolds (SF of sloped = to that of flat) for the flat area of the driveway and another for the sloped? I was considering this and would use two Circ pumps, adding a second Taco 013 in series for the sloped area, and just the main one for flat area….and a total flow of 15 GPM.

2. Would there be any issue of air purging the higher zone by purging one loop at a time? Will be a 40% glyco mix. WHile i wil provide all air relief valves in the front end inside the house, I'm concerned that i should put in some kind of air relief assembly at the top but that would involve fittings under slab which is something i prefer not to do. Is there a way to know what kind of velocity i need to ensure i can push through the trapped air during purging? I don't want an air lock! Thank you for any input you can give.

EdTheHeaterMan

The slope has nothing to do with your air purging or pump sizing. Each loop will be purged the same way, forcing the air out of the tube with water (Glycol/Water) pressure until all the air is out of that particular tube. then move on to the next tube on the manifold. Think of it this way, If a slope would cause any issue, then we would have discovered that problem over a hundred years ago, when someone installed a wet system in a 2 story house.

I might suggest that you lay the tubing in the driveway slope across the driveway so each strait section is level with the horizon to minimize any air locks at the top of any vertically different loops. No high spots in the driveway that return back down to the lower part of the driveway.

hot_rod

I would add if you have a long driveway, doing loops across the with is a lot more work, generally you go down the drive 1/2 the length of the loop and return. With 3/4 pex you can run a very long loop.

Ideally you have a design built around the class of SIM you want and it will spell out loop length, GPM and supply temperatures.

The system is pressurized and after a proper purge, and the system under constant pressure, you should not have airlock issues.

Glycol solutions are tough to get all the micro air out. Use a good air separator, not an air purger.

GroundUp

Forget a second pump, especially in series, and don't bother with extra manifolds unless it's intended to be a separate zone. If that 12ft of lift is upward, just raise the system pressure high enough to accommodate that. If it's lower, there is nothing to change as long as the piping and circ are sized appropriately.

JimN

Thank you all for the comments. Makes great sense. ALso just found an article on purging as well. Indeed HotRod, putting all those horz turns in a 14' wide driveway is not practical but i certainly see the advantage if it was. Appreciate your experienced help guys!

JimN

That brings another question about is it the charged expansion tank that provides the pressure on closed Glycol system?

GroundUp

The fluid itself needs to be pumped in with positive displacement in order to create the pressure- the tank only cushions the expansion and contraction to maintain a constant pressure. I hope that you intend to hire a professional for the "meat and potatoes" part of this project?

hot_rod

The fill tank system, like an Axiom can work, but at a very, very slow rate. Better to buy a fill pump. A 1/2hp transfer pump in a bucket can work.

Pros often have a fill cart, dump the glycol in the tank and it does the work.

You would fill with site water, add a cleaner, circulate, drain, then pump in the glycol

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jumper

I've mentioned this before. Hydronic requires a high point where air can escape. And it really helps to evacuate air before filling. But that's not current practice so you have to listen to Ed.

hot_rod

A manual high point vent is a good option for first fills, after that a quality air sep at the boiler will do the job

The boiler is often the high point in SIMs

If the boiler is lower than the slab, a high point vent gets more involved

mikestooneat

I always purge all loops first then go back and if its a large manifold I’ll do two at a time.

Design should not be modified for height difference.

SKYPAINTER

Slope does not matter, it's a "closed" system, what goes up must come down as the circulator (which is NOT a true pump) creates a difference in pressure.

Lance

The pump in a closed loop system in simple terms is like the motor on a Ferris wheel. All the pump has to do is overcome the friction that is created when the water rubs against the pipes – and that friction has nothing to do with height. So, make sure the pump head pressure is calculated based on the friction to flow caused by size of pipe and fittings in each loop. Each pipe has two dimensions, length and diameter. The fittings and controls have listed specifications for their resistance. The only time height is a factor is when filling the loop to purge the air out of an open pipe. Once full and sealed, height is not a factor. And like all good designs, since air can show up in a loop, and add resistance to flow, proper piping to allow bubbles to rise easily to a vent point is a smart way to go. I may need 60 psi to fill a vertical loop to the top, but once full, I can reduce the pressure to 10 psi and all is good. So eliminate downward turns and all will rise smoothly. But if you have a drop that can collect air, put a vent at the top of it and never let those horizontal runs sag.

Glenn_Venco

I always load the slope section approximately 20-30 btuh/sqft higher, and designate the circuits/loops that address it, 20% shorter in length. This will automatically send more gpm flow, lower the dt, increase the average water temp, all to insure that section is getting more heat energy. Last thing I want is to hear about a car on the driveway when it slid uncontrollably into some other object or the street.

I do something similar at the foot of the driveway - 1st loop is horizontal, parallel to the street, usually at closer tube centers, and again a shorter loop. When the snow plow comes by, thats where the snow in street will be pushed. Last thing I want is the system to shut down, but we have a frozen speed bump at the end of the driveway . The shorter loop and tighter tube centers ensure that more heat is distributed there to deal with the uneven load.

Most importantly, I tell the customer about these modeifications. Usually they understand this and feel more comfortable about the job.