Air In System

ScottR

We have been out to this particular project a few times for no heat in one of the heating zones.  There is air in the system but only in one particular zone everytime.  You can hear the air in the pump upon arrival.  It is always the second zone in from the left for the first floor family room.  They use a wood stove in the room but that shouldnt have anything to do with this issue.  Every three weeks we are back there.  When purging the system, we never hear any air spurt from the vertical spirovent.  Usually you will hear some once in awhile but never on this unit.  We removed the head and everything was normal.  The rep says to change the head.  We have also tried adding a hi-vent on the return line but that didnt seem to help.  We never have any problems with air in the other zones.  Can anyone give me an idea what to look for?  I am scratching my head on this one. 

Charlie from wmass

With that room being satisfied most of the time.

at least with a wood stove I am assuming it is satisfied more than not it is acting as an air catch. I would recommend a pressure test and check for leaks and putting in a horizontal spirovent with a goose neck dropping to the circulator manifold. What is the system pressure?

ScottR

Air

I have tried different pressures ranging from 12-18psi, all the while adjusting the expansion tank accordingly.  We went with the vertical spirovent to save some room and were told by the manufacturer that it works the same as the horizontal unit.  Of course it is also more costly.  I was going to pressurize the system to test for leaks but the boiler pressure does not drop.  Recently we installed a hi vent with 6" nipple on the elbow on top of the spirovent.  That didnt work either.  Why is it only affecting the second zone in and not even the first one?

Mark Eatherton

Where's the barometric damper???

thought you had to have them even with oil.



Maybe you have an intermittent or bad pump there?



ME

icesailor

Air In System:

If you are hearing the water in the circulator, it is cavitating. It also sounds like there is high resistance to flow in the circuit. What kinds of emitters do you have on that zone? Is that a 007 circulator on that zone? Can you put a multispeed circulator on there to see if running on a slower speed will solve the problem?

Brad White

Some thoughts and observations

I do not pretend to have any answers here, so please bear with me while I gather more information.



I agree with Charlie regarding the zone seeing less use because it can be satisfied by the wood stove. Could be a factor and my inclination is to seek all factors of difference in the subject zone. That one at least stands out not to the exclusion of other things.



The branches seem to be the common 3/4" size and the main header, 1-1/4", as well as the Spirovent.  is that correct? Or might it be 1"?  1-1/4" is the most common, so will assume that.



The six zone circulators, are they all 007's? Is the DHW circulator larger, maybe a 0010? If they are all 007's and the circuits each 3/4" (serving fin tube, coils, panels?), the developed circuit lengths for each could vary from 50 to 250 equivalent feet of pipe, or more. With each circuit possibly moving 3 to 4 gpm, pressure drops could vary in each circuit from 1.5 feet to say 11 feet, with corresponding flows between 20 gpm to one or two gpm, depending on their balance point.



With any one circulator running, then another and another, your system pressure curve, especially on the return header size, will vary greatly. More to the point, the header could see flows between 1 gpm and 50 gpm, it not being inconceivable that a 007 can move 7-8 gpm against heads of 7 to 8 feet. Seven pumps at 7 to 8 gpm adds up fast.



The balance point, the pressure/flow gradient where they all settle when all are running, is yours to measure. But what might be a 5 foot head with one pump running will work out to an exponentially higher (^1.75) pressure drop with all running.



The 007's if that is what they are, peak at about 12 feet of head with nearly no flow. Whichever is your largest head-available pump, that one will win against all and could well stall the other pumps.



I was toying with the above dynamic,  I was going over what happens on the return side when one, then two, then three, then four... circulators are running. How that might climb and what would happen to any one zone that does not run, or at least not run often. I will have to sleep on this, but by putting it out there, it might trigger greater minds.. has not hit me yet.



Another observation- I note of course that the expansion tank connection-point pressure will not change, but the circulators are all at least 0.5 psig lower pressure there than at the expansion tank, because they are at least what seems to be a foot and a half higher in elevation. This is not enough to induce a vacuum, so the answer of where the air is coming from is still the mystery.



Sorry to ramble and no criticism of the design nor installation is intended. Just asking questions.



Brad

hot_rod

is it a baseboard system?

You could add a small hydroscopic vent on the return ell.



If the air is making it's way back to the header and Spirovent it should eventually come out. I too would suspect the vent is not functioning properly.



Ideally, as Brad mentioned those circs would have flowsetters and multispeed circs. Then they could be dialed in to the correct flow.



Increasing the pressure usually squeezes the bubbles and aids in removal, but only if the autopurger is on the job.



hr

clammy

check the system

I would shut off my water feed valve and see if my pressure drops there could be a small leak and the make up water is masking it up until you get the air in the pipes service call.I would also check the flow check and operation of that zones pump to make sure there are no issues there.I have in the past used vertical spriovents and found that they work just  as good as a standard ones .Nice looking job and of course buderus number one 3 pass oil fired in my mind but then again i'm german peace and good luck clammy

Ron Jr._3

Nice install Scott

How do you like the vertical Spirovent ? Wish I could get my supplier to stock them .



Sometimes you get those jobs where purging the zones out with even 25 psi pressure doesn't do the trick . On these we temporarily plug the relief valve port and power purge - 40 to 50 psi .



It could be like Clammy said too , a small leak somewhere .