Oil fired boiler return temperature


  #1  
Old 10-11-13, 10:56 AM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
Oil fired boiler return temperature

I have a Danfoss TV valve on my Biasi oil fired boiler return. I'm using the 140 degree cartridge.

Lately I've noticed that the return temp has been running about ten degrees higher than normal, so I expect the old cartridge is either getting tired or clogged.

I'm thinking about replacing it... but I am not sure if I should stay with the 140 degree cartridge, or drop down to the 113 degree cartridge. Will the lower 113 degree cartridge provide ample protection against condensation in an oil fired unit?

Pete
 
  #2  
Old 10-11-13, 11:34 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
Uncle Pete! How the heck ya been?

I've seen the condensing temp for OIL to be stated as 115 or there about... and for gas to be 135 or so...

I don't know for certain, but I suspect that the reason Danfoss selected those two ranges is because of these numbers.

I would probably go for the 113 myself...
 
  #3  
Old 10-13-13, 12:18 PM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
Hi Trooper! Where the heck is Grady hiding? LOL!

I am going to have make a decision as to what cartridge to order... my return temp is over 150 degrees, and it was always rock solid at 140 F in the past. Looks like the valve thermostat is no longer fully opening.

I'd just like so more confirmation on the 113 degree return temp, since that is the temp that boiler return will stay at.

There sure isn't much definitive advice given on the thermic valve manufacturer websites. Am I safe in assuming that for a low volume boiler like the Biasi that the AVERAGE water temp in the boiler is more important than obsessing over the return temp?

Pete
 

Last edited by radioconnection; 10-13-13 at 01:08 PM.
  #4  
Old 10-13-13, 03:13 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
Grady is still here from time to time, but he's been taking some heavy duty courses that are keeping him busy!

If you say the magic word three times, and click your heels, like a genie from a bottle he will appear.

RIELLO RIELLO RIELLO! (click, click, click)

Let's see if it works.

Looks like the valve thermostat is no longer fully opening.
Sounds like it, or maybe there is a potato chip bag stuck in it... that's your basic automotive style thermostat with a wax capsule in it. Pretty common for them to get 'sticky' after a few years.

that is the temp that boiler return will stay at.
You mean once you get flow to the system the temp won't continue to increase during the heat call after the valve opens?

I'm fairly confident that you'll be OK with the 113...

the AVERAGE water temp in the boiler is more important than obsessing over the return temp?
I would say yes... and keep in mind that even though the return water is at 113 it doesn't mean that the cast iron on the fireside opposite that water is going to be 113 also.

Check out these charts...

Flue Gases - Average Dew Point for Typical Fuels

Not to change the subject... but to change the subject:
Did I happen to mention that I finally 'pulled the trigger' on a new boiler last year?

http://www.doityourself.com/forum/bo...n-finally.html
 
  #5  
Old 10-13-13, 03:23 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
They mention 'excess air' in reference to that chart, and this explains a bit more about that...

Optimal Combustion Processes - Fuels and Excess Air

IIRC, our oil burners run in the neighborhood of 30-40% excess air... sorta verified by one of the statements below the chart.

So, if it's true that we're typically running 30-40% EA, then the dewpoint of the flue gas is 115F or thereabout.

Here's another page with a bit more about EA...

Combustion Efficiency and Excess Air

I love Engineering Toolbox website!

One thing I've noticed over the years when taking 'smoke readings' is that if there's too much air, I start to get WET FILTER PAPER SPOTS, and the tube of the smoke gun has water in it. This sort of proves out that relationship between excess air and dewpoint.
 

Last edited by NJT; 10-13-13 at 03:51 PM.
  #6  
Old 10-13-13, 05:07 PM
G
Member
Join Date: Oct 2008
Location: USA
Posts: 2,590
Received 26 Upvotes on 25 Posts
Here's a link to flue gas due points vs. excess air for various fuels: Flue Gases - Average Dew Point for Typical Fuels

My problem is that while I can measure the flue-gas temp and the excess air at the boiler breach with a combustion analyzer, but I do not have a port to measure in the ductwork after the barometric damper. Maybe I should add a port.
 

Last edited by gilmorrie; 10-13-13 at 07:01 PM.
  #7  
Old 10-13-13, 07:08 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
but I do not have a port to measure in the ductwork after the barometric damper. Maybe I should add a port.
Whatsit gonna tellya? I guarantee it will be at least 100 cooler than at the breech, probably more.

I saw a Weber gas grill out for garbage a few years ago. I stopped and pulled the thermometer from it. It's nearly as accurate as my expensive FG thermometer, and only needs a 1/8" hole in the pipe.
 
  #8  
Old 10-13-13, 08:47 PM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
You mean once you get flow to the system the temp won't continue to increase during the heat call after the valve opens?

I'm fairly confident that you'll be OK with the 113...




Hi Trooper... yep, no matter how the system runs, the return temperature always stayed at 140 degrees, until I test fired the boiler the other day. Now she's running around 15 degrees higher, which would seem to indicate the TV thermostat is partially stuck. I'm pretty sure I got all the chip bags out of the system after I installed it, LOL! If you think having the return held a 113% is adequate, I'll give a try. The Danfoss TV cartridges cost around 100 bucks, so I want to get it right the first time.

Pete
 
  #9  
Old 10-13-13, 09:05 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
The Danfoss TV cartridges cost around 100 bucks
WHAT?!?!?!?! Seriously? HOLY you know what!

That's insane.

I was gonna say buy one of each... try the 113 and see what ya think... if not, throw a 140 back in. Uhhhh... no... you can buy a lot of 807's for that kinda scratch!
 
  #10  
Old 10-14-13, 08:10 AM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
Yeah, although I am hoarding 813s right now, LOL.

The ESBE TV is the most costly TV in the Danfoss litter. I'm doing my annual boiler maintenance this morning... charging the bladder tank, cleaning the low water electrodes, and in the middle of replacing the anti backflow valve and pressure regulator. These parts seem to be designed for 5 year life span. I remember replacing the old boiler and heaving 40 year old parts that were working good as new!

I just removed the cartridge and tested in water on the stove... I cleaned the black film off and I'm going to give it another shot. My IR temp gauge shows it maybe working now. I'll email ya and let you know the final prognosis.

Pete
 
  #11  
Old 10-14-13, 11:21 AM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
Grrrr! TV valve is leaking like a sieve!

Trooper, what do you think of this idea? Dump the cartridge, and just adjust the throttle valve on the return leg bypass to keep the return temp within reasonable limits. I'm being to think the TV valve is more trouble than it is worth. Adding the throttle valve was an afterthought, but maybe I can save a bit of money and simply the system (less failure modes) by going KISS. The TV valve body would just be a very expensive Tee fitting... LOL!

Pete
 
  #12  
Old 10-14-13, 03:21 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
I wish I could remember how your system is piped... but it's been a while and my remaining synapse is under the influence of alcohol...

Where is it leaking from? Maybe just needs a new gasket?

Sure you could use the bypass... it's a BOILER bypass, yes? You might find that you don't need it at all anyway. I piped one in on my system, but it's closed... didn't need it.
 
  #13  
Old 10-22-13, 04:56 PM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
Bypass won't do it, the Tekmar 260 doesn't offer boiler protection. Scratch Plan A.

Sooo, I splurged and spend the coin on a new Danfoss TV cartridge. Went with a 113 degree cartridge. That solved the return temp problems. I set the high limit for the boiler a bit lower, so maybe that will save some fuel too. Sure is good to see the boiler back up and ready for the cold WX coming in.

Pete
 
  #14  
Old 10-22-13, 06:34 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 19,710
Upvotes: 0
Received 8 Upvotes on 6 Posts
Good Deal Uncle...

You could always burn some electrons off tungsten to keep warm! I'm sure you've got enough of THAT around!
 
  #15  
Old 10-22-13, 09:16 PM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
I'm still a bit leery with locking the return temp to 113 degrees F. I've seen a few boiler specs where the manufacturers want the return kept above 140 degrees. I guess the real test will keeping an eye on the Delta T. Even with a 20 degree delta the supply will be under 140 degrees F. I'm being to second guess using a 113 degree thermostat.
I am also wondering if adding a blanket on the boiler floor would help with condensation?

Pete
 
  #16  
Old 10-25-13, 08:57 PM
R
Member
Thread Starter
Join Date: Aug 2006
Location: usa
Posts: 839
Upvotes: 0
Received 0 Upvotes on 0 Posts
I've been watching it run for a few days... the Delta T is running about 20 degrees, and the supply is getting up to 160 degrees. Since most cold start boilers are going to be condense when they start up, I'm not going to obsess about this any longer and I'm going leave the cartridge at 113 degrees. I'll check the boiler in the spring and see how crud is in the boiler passages. I'll get out of Trooper's hair for now
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: