Adding oil boiler

[GregMajecki]

I need advise how to change existing system to add oil boiler. Probably next year I want to move wood/oil boiler form the basement to the barn and add oil boiler in the basement. 500gal buffer will stay in the basement. Let me know what is the preferred way to connect oil boiler to the system.
see attached diagrams
light line is existing thick line is new
thank you for help

 

[salecker]

I put my oil boiler in the building with the wood boiler.
For the one simple fact that we didn't want a flame source in our home.
No worries about carbon monoxide poisoning,plus the no worries about house fires.No fire department where we live.

 

[Bob Rohr]

here is an example of the best way to pipe multiple boilers and distribution with a two tank connection. This attached drawing is a bit more complicated with an additional buffer on the mod con.

The key is to have all the boiler and load connections close to the tank on a large diameter pipe, at least 2"

That large pipe serves as a hydraulic separator and allows all the flows to work out without interfering of ghost flowing.

So of example if you have a 4 gpm load and the boiler is running at that flow or larger, the flow if from the boiler to the load, no interaction with the tanks.

The tanks will only charge when the boiler is suppling more gpm that the load requires.

The tanks cn unload without any flow through the boilers, it really simplifies and maximizes all the flows and energy transfer.

Download and read the Biomass Training PDF in the stickies above, it explains the two pipe buffer and how it works and pipes.

 

[leon]

I need advise how to change existing system to add oil boiler. Probably next year I want to move wood/oil boiler form the basement to the barn and add oil boiler in the basement. 500gal buffer will stay in the basement. Let me know what is the preferred way to connect oil boiler to the system.
see attached diagrams light line is existing thick line is new, thank you for help

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One of the many issues will be having the buried pipe or pex and buying the right piping as you cannot cheap out on that and unless you spend good money up front your going to be mowing the lawn all winter.

The simplest way to do this is put the oil burner in the barn and pipe both boilers in series. I am amazed that your pressure relief valve is not in the steam chest of the existing boiler, it is suppose to be there.

The relief valve for the new oil boiler must be in the steam chest of the oil boiler and moving it to another location will not be allowed by the insurance underwriter or the plumbing inspector. The relief valve for the wood boiler is supposed to be in the steam chest of the wood boiler as well.

You can pipe the oil boiler and the wood boiler in series and have the circulator on top of the oil boiler pumping away from the two boilers and pumping into the air scoop at least 18 inches away from the circulator with the bladder tank plumbed into the bottom of the air scoop with the automatic air vent in the top of the air scoop.

I will never go back to an air scoop and bladder tank as they are more trouble than they are worth.
I have a steel expansion tank in my system and operate my coal stoker at very low pressures.

With boiler drains coming off my single pipe loop I can power purge the air from the system and not have to crawl around on my hands an knees ever again to bleed air from my base board-I hate my baseboard heat and wish I had cast iron radiators.

You can have a single honeywell mechanical triple aquastat with the single thermocouple well to control both boilers from one tapping in the oil boiler steam chest and also have the relief valve in a second tapping in the steam chest. you accomplish this by having a second circulator to act as a temperature balancing circulator that would allow the oil burner to fire if the wood fire goes out.
You can use with L6006 strap on aquastats to control dumping excess heat in to a dump loop that is completely up to code.

You can have both boilers running on one triple aquastat with two circulators, one to to balance the temperature and the second circulator to feed the zones. it is not safe unless you install series parallel piping to segregate one boiler from the other with a second circulator and you will need a second air scoop and diaphragm for the second boiler. You will lose the ability to let your oil boiler take up when the wood boiler fire goes out and limit the ability to go on short trips or vacations etc.

 

[Bob Rohr]

I'd disagree with Leon on series piping, it turns the unfired boiler into a cooling tower, and a % of your oil dollars are going up the flue heating the great outdoors.

Again, the sticky above written by John Siegenthaler for NYSERDA has some excellent advise, piping and control logic examples. And it's free!

 

[maple1]

Related question - we know about 140 minimum return temp for a wood boiler.

What should it be for an oil boiler?

 

[Bob Rohr]

I've heard both 140 and 150 as the number? Although Buderus makes some models that they claim can take any return temperature.

 

[Bad LP]

Related question - we know about 140 minimum return temp for a wood boiler.

What should it be for an oil boiler?

My guy in Mass uses 135-140 on a modular 3 boiler set up as well as my System 2000. In Maine I'm using 140 out of past practice. Had problems a long time back lower than that with condensation running out of the flue pipes but it was due to an other issue.

 

[Bob Rohr]

The main goal is to get the conventional boilers out of condensing conditions as soon as possible. All cold start boilers condense until they reach the fuels dew point temperature. That temperature varies depending on the % of CO2 in the exhaust gases.

One rule of thumb is 10 minutes, or less to be out of condensing mode, after cold start. This is why boiler return protection devices are so critical, especially in high mass or large volume systems which could keep the boiler running cold for hours.

With solid fueled boilers extended condensing operation leads to a sticky mess And a big drop in efficiency when the HX surfaces become coated.

 

[leon]

Hello Bob,

please correct me if I have forgotten part of what Dan Holohan has always said but with the boiler bypass line installed it keeps more heat in the boiler reducing condensation to a bare minimum if at all when its operating right?

 

[Bob Rohr]

Correct you are Leon. Dan has shown some piping options in several of his books. Also some of the boiler manufacturers show bypass pipe/ valve and maybe a bypass pump in their manuals.

Remember however, unless that piping or pump has a way to actually measure and respond to a cold return temperature it is a guesstimate as to how to adjust or set them.

Large concrete radiant slabs or large volume buffer tanks will over power those "dumb" protection methods.

A thermostatic valve, or a pump tied to a temperature control are good 100% options.

 

[GregMajecki]

I am debating if I should move the 500 gal buffer tanks to the barn or not ?
It would be less work if tanks stay in the basement.