Cold return temps a problem for Biasi B10?

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Old 10-11-08, 12:24 PM
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Cold return temps a problem for Biasi B10?

I have an older house with large cast iron radiators, piped in a single zone monoflow system. It is heated by a fairly new oil-fired Biasi B-10 boiler that is not used for DHW. Because of the large amount of radiation and thermal mass in the system the circulating water rarely has to get very hot to heat the house. Do I have to worry about extended periods of cold return temperatures causing condensation in the boiler, and reducing its life?
 
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Old 10-11-08, 12:48 PM
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Have you measured the return temps? This is a tough time of the season for conventional boilers (while condensing boilers are in heaven).

Each firing cycle the return temps should get up to 113 or better. If they don't you should consider a boiler bypass if you don't already have one.
 
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Old 10-11-08, 01:32 PM
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For more info on boiler protection see this link
http://www.comfort-calc.net/Bypass_P...laination.html
 
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Old 10-11-08, 03:03 PM
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On a very cold day the return temperature might get up to 125 (boiler output around 155). Most of the time the temps are much less, probably below the 113 that you mentioned. Some sources talk about a 130-140 return requirement. That is unlikely to be met.

There is a "system bypass" connection with an adjustable valve. I have hesitated to leave it open, because any significant bypass decreases the flow in the system. This increases the temp diffential between the first and last radiators, and leads to uneven heating of the house.
 
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Old 10-11-08, 05:12 PM
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Yeah, I believe you will have troubles...

I know you've been reading the other posts on the subject, good on ya! Most ppl don't bother to do their own research...

You do want a boiler bypass...

For oil fired systems, the water can return a bit cooler than gas fired systems because the 'dew point' of the flue gases is somewhat less. I would venture to say that if the return temp doesn't get to say 120F within like 5 min or so, you are looking at a problem down the road.

Take a look at the ESBE Thermic Bypass valve... fully automatic, provides full bypass until boiler hits 113, starts to open, and is 'all in' at about 135... would probably be a good choice for your system. Kinda pricey... you could install it on the existing system bypass that you already have... in place of the tee on the return side.

Can you post pics of your system ? I'd like to see the install... free account on www.photobucket.com and a link here for us to view.
 
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Old 10-11-08, 10:15 PM
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Davis, the return temp depends on fuel type. Higher 130s for NG and 113 for oil.

You could try a really cheap experiment. Get one of those really cheap corded LED thermometers. Test if for accuracy at room temp and then take the lead on the cord and put it very close the return into the boiler and then wrap some insulation around where the sensor is. Get one with a Hi Low and from that you'll be able to see what the max temperature is between resets. Once or twice a day should tell you.

You could also try a Johnson A419 setpoint relay for less than $100 and then delay the firing of the pump until a setpoint temp is met.

That setpoint controller would be there to delay the pump until a certain (water supply outlet might actually be easier and safest, maybe 155?) temperature so that return temps will be above the condensing range on average is achieved. The pricy Buderus controller does that, however an A419 is less than $100 and is pretty rock solid from what I've gathered.

You add that and a delay on break relay to give you maybe 15 minutes of post purge, and you'd be well on your way to maybe the easiest way to the holy grail of the oil world. That being boiler protection AND full outdoor reset capabilities. Take the benchmark 260, indoor feedback to boot, set it to full ODR and for less than $100, the pump get delayed.

Could it be that simple?

http://www.universalmarine.com/pdf/j...19bulletin.pdf
 
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Old 10-12-08, 08:05 AM
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I don't think it can be that simple...

So you delay the circ until a certain temp... once the circ runs, the cold from the system is gonna 'dump' into the boiler... depending on how cold the return water is ... can you say STRESS ?

Then, the sensor will feel that dump, and shut the circ down... boiler heats up and cycle repeats...

No, I don't think I like it ... but I haven't yet looked at the PDF you linked, maybe there's more to it.
 
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Old 10-12-08, 11:39 AM
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NJ I have to agree with you. The biggest problems with return water to a cast iron boiler is as follows;
1. Extremely cold water returning to the boiler
2. Cool water at a high flow rate returning to the boiler
3. Heating the boiler up and turning on the circulator, it should run the entire call for heat
4. Going to high fire too early...Commercial only of course
Boiler protection can be as simple as a boiler bypass, 3 or 4 way valve, Thermic valve although I would suggest p/s piping with that, variable speed circ's set to a minimum return temp or checking delta "T" to name a few.
 
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Old 10-12-08, 05:35 PM
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I have posted a pic of the piping near the boiler.
http://i473.photobucket.com/albums/r...ler_Piping.jpg

As you can see, I now have several temperature gauges on the pipes. Unfortunately I won't get any meaningful readings until the weather gets much colder.

The thermic bypass valve looks like it would provide full protection for the boiler, by keeping the boiler return temperature higher. But the boiler output temperature would also be higher, probably higher than the system needs except on the coldest days.

I don't see any easy way to keep the boiler return temperature high for protection while keeping the output temperature low and the flow up for even heating. Adding a mixing valve, controller, and pump seems like overkill.

Unless somehow the Biasi is designed so it doesn't need the protection?
 
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Old 10-13-08, 12:46 AM
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can you say STRESS ?
ummm yes

STRESS

What do I win?

Hey... If there's a 2:1 bypass ratio, there wouldn't be too much shock when the pump starts because it would be quite mixed down.

How does the Buderus not shock the block when it's ODR delays the boiler circ while the boiler alone heats up, and then the pump starts up?
 
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Old 10-13-08, 03:26 PM
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If not stress what causes there cracks in the blocks sitting behind the distributors along with all the rest or us? You can try to design around the problem but nothing is 100% fool proof. They even show bypass piping in their diagrams for large water volume systems.
If it is cast iron you will see some stress cracks normally caused by bad piping. The problem of stress is a lot less on smaller water volume systems and multi-zone systems. You can't change physics.
The Thermic valve does a good job but if not piped p/s do we mainatin our 2 fpr flow in the system?
 
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Old 10-13-08, 04:31 PM
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The Thermic valve does a good job but if not piped p/s do we mainatin our 2 fps flow in the system?
I wouldn't think so, at least not until the TV is fully open. And, depending on the placement of the thermostat relative to the rads that are getting 'first heat', the call could easily satisfy quickly, leaving the farther rooms cold... or, the opposite may happen, if the t'stat is in a room near the end of the loop... rooms getting 'first heat' could easily overshoot, perhaps uncomfortably so.
 
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Old 10-13-08, 11:23 PM
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I noticed some new multi-colored debris on the floor under the vent pipe. I guess that this came through the cracks in the joints of the pipe. There is also some white stuff on the vent pipe. Does this indicate some problem? The vent pipe was installed when the boiler was replaced, as was a steel liner for the flue.

http://i473.photobucket.com/albums/r...oor_Debris.jpg
http://i473.photobucket.com/albums/r...ipe_Debris.jpg
 
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Old 10-14-08, 05:39 PM
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Sure looks like condensation in the flue pipe to me ...

Any idea what the stack temperature is ?
 
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Old 10-14-08, 07:52 PM
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The last service tag says 413F. I don't know how accurate that is.
 
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Old 10-14-08, 08:18 PM
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I know they may not be the most accurate things for the purpose, but those gas grill thermometers can be pressed into service as a cheapie flue temp thermo... a good one might cost $50 or so...

That 413 was probably after the tech forced the boiler to get hot in order to reach 'steady state' so he could take the readings.

In normal operation, you may not be getting that hot ... and if that's the pipe between the damper and the boiler, keep in mind that the temps may be as much as 100-150 degrees COOLER in the chimney itself.

I'd be concerned if the you were running much less than say 325 after the damper, for prolonged periods. When it's really cold, you may not have any trouble, but during this time of the year...
 
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Old 11-02-08, 06:12 PM
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I checked the stack temperature (before the draft control damper) using a grill thermometer. It stabilized at about 410F after 5 minutes. The chimney is lined, so I'm not too woried about the temp after the damper.

Then I happened to look inside the boiler and noticed a lot of red stuff at the bottom.

http://i473.photobucket.com/albums/r...g/DSCF0802.jpg

The boiler was cleaned at the start of the heating season, and the burner has run less than 100 hours since then. Any idea what this is, and if it is normal?
 
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Old 11-02-08, 06:46 PM
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It's a new breakfast cereal... Rasberry Corn Flakes ...

I can tell you that if you scoop a spoonful of that stuff into a jar, and add water, shake it up, the water will turn a very nice shade of cherry red ... and if you set the jar on a shelf for two years, that the water will still be the same shade of cherry red.

I can also tell you that they won't dissolve in Kerosene, which I found strange since the dye WAS disolved in fuel oil.

I'm certain that the red coloring is the dye, and after being burned for some reason only disolves in water...

more later ...
 
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Old 11-02-08, 07:32 PM
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Here's how I know about the red flakes... this photo is almost 2 years old. The jars are still on the shelf, and look exactly the same still.



My best guess is condensation... flue gases condensing on the inside of the boiler, then when the boiler finally gets above the 'dew point' the water evaporates leaving behind that mixture of red dye, sulphuric, carbonic, and nitric acid (and some small amount of iron that got eaten by the acid).

The residue falls off in flakes...

unless it gets trapped in a flue passage... if that happens, the flakes turn into rocks over time, like these:



You can tell how big these are by comparing them with the size of the rings the malt beverage left ... these were in the flue passages...
 
 

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