Went to look at a problem a buddy is having and I’m confuzzled…
He has a 3 zone forced air heating system. The system ran without problems for 12 years but for the last four or so he has a recurring problem that I “think” is air getting into one zone only (the third floor). The inlet side of the line feeding the coil in the air handler gets hot (I am told) but the outlet side is only barely warm and of course there is no heat. The HVAC guys come and bleed copious amounts of air (we did the same this morning) which regains the heat but within a month or two it’s out again. There are many (I’d say easily 6) bleeders on the line most of which are newly replaced since this started, as well as a brand new expansion tank and purge valve in the system. I don’t understand A) How air is getting in and B) why the bleeders don’t purge it…
Any suggestions?
TIA
PaulB
Replies
You might need to give some more details.
As I first started reading this zoned air heat I was thinking of an individual furnace with zoning dampers to control the air flow.
Then I read COILS so I was thinking that you where talking about a heat pump system.
After readin the whole thing this is what I think you are talking about, but not sure.
A hot water heating system. In that system at least one zone is hydro air. That is a hot water coil in the air handler. And it is the one for the 3rd floor that is causing problems. The "apparent problem" is that air is getting into the hot water cirulation system.
Is that what it is?
Sorry Bill, I guess I didn't explain it well, but you are quite right... this is a "hydro/air" system with three zones, only one of which is a problem.
It seems as though air is getting into the loop somehow, probably making it to the coil it seems. What I don't get is how the air is getting in and maybe more importantly why aren't the numerous bleeders getting it out? Of course, a solution would please my buddy as well ;)
PAulB
On Ask This Old House they had similar problem.Said that it was due having the circulation pump in the return line where the pressure was the lowest.Moved it to the outputside of the boiler.Not really sure that I believe that. And that is about all that I know about HW heating systems.You might want to ask about this over at the Wall on heatinghelp.comThere are a bunch of "wet heads" over there.
Edited 10/29/2006 6:19 pm by BillHartmann
Not a bad idea Bill, thanks for reminding me of them... I guess I'm just used to all the answers to life's mysteries being available here ;)
PaulB
Assuming there is a pump in the system, about has to be. The pump could be sucking air in around the shaft, replace the seal.
"Pumping Away" by Dan HolohanGreat book (under $20.00), for anyone working on or paying someone to work on a hydronic system.GarettPS Bill beat me in refering you to "THE WALL" : another great site.
>>Said that it was due having the circulation pump in the return line where the pressure was the lowest.I thought they are always on the return????
Youth and Enthusiasm Are No Match
For Age and Treachery
"I thought they are always on the return????"
Only the ones done incorrectly. They are extremely prevelant, some manage to work, but all are still wrong.
Fintubes should have the pump on the return. Camus boilers will void the warranty if not. Helps to prevent steam locks.
ALWAYS pump away from the expansion tank.
Finned tube convectors do not have to have the return pumped. I have never heard of this. The logic behind such? It IS good practice to put the control valve on the return leg. I have never dealt with Camus boilers. I sometimes design system in which I put boiler circs (low head, in a primary/secondary piping configuration) on the return, but on a hydronic system of any size, pumping the return with the system circulators will more often than not lift the relief(s). Commonly, low pressure hydronic boilers will come with factory T&P valves, set at 30#. With the system pressurized to 12 or 15#, it takes less than 40 feet of head on the system pump to lift the relief. I deal with mostly non-residential systems, so my experience is obviously different than yours.
Lot's of commercial and resi, both steam and water.
Camus is commercial. The principals used to be RBI, also worked at laars. Apparently, the boiler design community is rather small.
Attempted to comission 2 - 2,000,000 today. Seems the gas regs are undersized. Some days it is nice to be paid by the hour.
I agree, you have to be very careful with pump design.
Munchkin wants the boiler pump on the return, but it is a high head hx.
More and more, the correct answer is, it depends.
Edited 11/3/2006 1:33 am ET by rich1
"...the correct answer is, it depends."
Absolutely. That's why I get paid. "Always" and "never" are only a guaranty that you'll be wrong some of the time.
I don't have the answer, but all of your details suggest a hor water heating system.
I will say it sounds to me like there's a leak somewhere and the ai9r is getting into the system as it comes out of solution from the repolacement water feeding into the system
I'd suggest trying a new boiler co, if they just bleed the system without looking for the problem.
Youth and Enthusiasm Are No Match
For Age and Treachery
If everything worked at one time, but now it doesn't, something has changed.
Perhaps the flow rate isn't able to push small amounts of air through the system, preventing large air problems, like it used to.
Beer was created so carpenters wouldn't rule the world.
My guess would be that that zone is drawing a vacuum when the zone valve is cut off, and there's an air leak on the supply line somewhere beyond the zone valve.
Replace the air bleeder. It's a cheap PITA part that finds the trash bucket about every 3 years or so.
Yes it's best to pump the supply side.
The line in question has about 6 bleeders all together, seems like d*mn near every elbow has a bleeder ;) , and they've all been replaced since this started. I'm thinking the leaking pump sounds promising... I'll let you guys know if/when we solve it.
Paul
FYI. Air travels to the high point.
If the water velocity exceeds 1.5 feet per second, and as a general rule it should, any air will travel with the water and go right past any air vent.
I manage 2 hydro air systems with main water line sizes of 1.5 and 2.0 inch pipe. For these systems air scoops were installed. Much larger units than the small air vents found on both of my own System 2000 units. We have never had a problem with the larger systems. Only once in 16 years have I had a problem of my own but... I'm a huge fan of PM. As such we look for and repair any possible problems before they come to the surface.
Thanks Rob... I did know that (of the little heating info I do know ;) )
Question: Is there enough water/pressure in the system? If the system lost water and didn't automatically refill you'd have trouble NOT pulling a vacuum somewhere.
Seems to be adequate Dan... this has been recurring for the past four or five years and in that time a couple heating guys have tackled it, including one I know well... I'm thinking the pump explanation sounds good... letchall know what happens!
PaulB