Boiler Plumbing Problem

Jbeees

Hi, I have a dual boiler setup, as I recently hooked up a wood boiler to supplement an oil boiler. The system works fine when the wood boiler temp is at or below approx. 190°. But when the temp goes above this and the thermostat calls for heat, the circulator pump comes on but barely is able to circulate hot water through the baseboards, specifically the baseboards hardly get warm. The obvious answer is there is air, and whenever I try to purge air from the system, bubbles do come out but it never stops. Like twenty buckets or so of water and still the same amount of bubbles. There is no noise from air in the baseboards upstairs and at lower temps, circulation is good. Also I have baseboard bleeders which were bled. I am thinking its cavitation but how do i know the source of the problem so i can fix it?



Here is another forum where i had some good info provided and there is more info and pics explaining my system:



<a href="http://www.plbg.com/forum/read.php?1,494338">http://www.plbg.com/forum/read.php?1,494338</a>

Ironman

A couple of things

As others have told you, the piping is wrong. you've got the wood boiler piped in series with the oil boiler. It should be piped pri/sec with 2 closely spaced Tee's above the oil boiler's circ on the return. That way it will inject heat into the oil boiler. Another circ would be required that would come on with the boiler's circ. Use an Electronic Temp. Control (ETC) for an aquastat and connect its sensor right at the outlet of the wood boiler. Use its contacts to either turn the oil burner on OR energize the wood boiler's circ. if the wood boiler is hot enough (170* - 180*). In other words, take the burner wire from the oil boiler's control ("B" terminal) and run it through the ETC so that it either sends power to the oil burner OR the wood boiler circ that you would install. The ETC would then choose either the oil boiler or the wood boiler to heat from depending upon the temp of the wood boiler.



The other larger issue is that a wood boiler needs buffer because a wood fire is difficult to regulate. Instead of turning on the circ when the water gets too hot and dumping the heat into the house, you need to install a buffer tank to absorb the heat. Depending on the btu rating of the wood boiler and how it's regulated, you need a large tank. Probably at least 200 gal. You could then use the house dump as a backup if the buffer tank over-heats.

Jbeees

Thanks

Thanks Ironman, appreciate your time and your response. I mentioned this in the other forum; can i make this system work as is for at least a year or two? And i can regulate the size of the fire/dump heat into the baseboards to control the size of the fire. If you think this would work, then what is the other issue i seem to be having? I am thinking it is cavitation but don't know the source of the problem...

Ironman

Cavitation

You're flashing to steam; that will cause all sorts of havoc. Parts of the wood boiler are probably much higher than the 220* gauge reading as a wood fire does not heat the surface of the heat exchanger evenly. I install outdoor wood boilers and have one myself. It's not unusual the hear boiling in the water jacket while the line temp is 180* or less because the logs get shifted and the fire is concentrated more in one area of the heat exchanger.



A properly sized buffer tank is not optional with a wood boiler. Without it, you have a potential bomb that could level you house.

SWEI

HOT fire versus HOT water

No problem having a 2000F firebox with 160F water leaving the jacket - it's a matter of circulation.  As noted above, a buffer tank is a required component when a batch solid fuel boiler is used.  Add an outdoor reset controlled mixing valve and you will have a safe system that provides maximum comfort and efficiency.

Jbeees

Buffer Tank

Thanks again Ironman, i say the following while acknowledging i am not experienced in this field but here goes; My father has the same wood boiler but as a standalone, in his house. He doesnt have a buffer tank and never had a problem......What would the bomb be caused by? To much pressure? The pressure in my system never topped 20psi max, even when the temp was 250* but it also has a blow-out valve and so does the oil boiler obviously..



Thanks,

Ironman

The Bomb

Obviously,

You've never seen the results of a failed relief valve that caused a boiler explosion. I have and it was devastating.

SWEI

separation of storage and distribution

Is the key to efficiency and comfort. You need sufficient storage to absorb all of the BTUs in a full load of wood, minus the BTUs consumed by the load during the burn (worst case, meaning a mild day with very little load.)  http://garn.com/ builds this right into their boilers, but most everything else needs a BIG tank in order to burn a full load cleanly (at high temperatures.)  Typical outdoor wood boilers (OWBs) choke off the air supply to lower temps, which turns them into inefficient creosote factories.



On the distribution side, you want to pull BTUs out of the tank at a rate sufficient to match the heat loss of the space.  The best way to do this is by using a motorized mixing valve and an outdoor reset control (you get both with a Taco iSeries valve, though the ODR control is limited.)

SWEI

the difference with oil

Is that the burner can turn off when the aquastat tells it the water reaches the high limit setting.  400 pounds of wood does not come with an off switch.

CMadatMe

Suggest You Read

The attached. Should help you out tremendously

Jbeees

need help

Thanks Everyone who replied, much appreciated.



I think i need to have an expert come out to identify why there are still air bubbles purging out of my system....I understand that my system may not be set-up ideally but i need it to run the way it is atleast for this season. Anyone know of a good person who can identify what is causing air in my system/cavitation and who can identify the fix to it?



Thanks again.

Paul48

Sure Do!

He gave you the cause and the fix already. You haven't asked about affordable ways to apply what he told you. I don't care if they have the same setup in the Vatican. It would still be wrong. It is always a chain of events that lead to a catastrophe.Are ya feelin lucky? Oh...your question....his handle is Ironman.

icesailor

And that's the way it is:

You found someone to tell you whats wrong, you didn't want to believe it. You asked us, we told you the same thing. You still don't believe it.

If you look long and hard enough, you will find someone that will tell you what you want to hear. Even if it is wrong.

Years ago, I had a friend who had a house with a hot water tank with a sidearm gas heater, no safety device (TPR Valve) or thermostatic gas shut off to stop the gas flow when the tank was hot. He came home from work one morning, took a shower at 10:30 AM and left for a wedding. He forgot to shut off the gas to the heater. The wedding was long but the wedding party was longer. Driving home carefully with many hours of indulging in adult beverages behind him, he pulled into his drive way to find his house gone. Well, the walls were on the ground but the roof was in the trees. The heater tank was never found.

Jbeees

Thanks

Thanks again guys, so my set-up in no way is good to leave the way it is. Understood, thanks for reaffirming. In the jensen manual for the wood boiler, however, it shows in series plumbing as an acceptable setup. Why is that?



To clarify, i am not trying to hear what i want i am just trying to find difinitive answers from multiple sources as i am obviously no expert.



Thanks again everyone.

CMadatMe

Guess

You didn't take a few minutes to read what I posted. Everything everyone is telling you is in there as well as proper piping diagrams. You can only lead the horse to the troff.

Paul48

Still?

We aren't looking at that manual. Is the boiler attached to a huge load? Have you looked at the article provided to you.? You are still looking for ways to make...wrong....right.You are still not asking any of the questions needed to get things changed. You've stated that the system has to run as it is. Under those limitations, who in their right mind would want to waste their time looking at the system.

Jbeees

cost

Thanks all, I just didn't understand why the manufacture would be ok with my setup. Anyway, any idea how Much the buffer tank and new valves would cost me if I was to hook it up like in the attachment provided? I plan on doing the work myself.

Ironman

Manufacturer

The manufacturer is mainly concerned with selling you his product. If he showed you all the ancillary equipment that's necessary (which he doesn't profit from) the cost might dissuade you from buying his product.

Also, most wood boiler manufacturers don't employ a hydronic engineer.

chapchap70

3/4" pipe?

The pipe coming out the top of the wood boiler seems to be reduced to 3/4" as it runs across the back and into the Peerless boiler return.  With the circulator where it is, the water from the system has to be sucked through a smaller opening which will cause issues. 



The diameter of the piping through the wood boiler and into the Peerless return must be larger than the piping to each of the zones.  From what I can see, that is your biggest piping issue(which will cause air problems); although not the only one.

SWEI

Cost, as usual, depends

Is the boiler pressurized or open?  How many pounds of wood does it hold when fully loaded?  How long does it take to burn that load?  What is your estimated building heat loss on the warmest day you would fire the boiler?

Jbeees

Pics

Anyone have pics of a dual boiler system that is hooked up?

SWEI

read the PDF

that Chris posted above.  Also available at http://www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_10_us.pdf