Getting OWB to run both heat and domestic hot water through existing boiler

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Old 01-18-13, 11:07 AM
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Getting OWB to run both heat and domestic hot water through existing boiler

Last year I hooked up an OWB system to my existing Bahama/Crown oil boiler with tankless heater coil, model BD-74, mainly to be used during the winter months and will use the oil during the summer.
The baseboard heat has been fine. I have the heat exchanger hooked up above the circulating pump for the baseboard heat and that all works great.
I am trying to figure out if there is a way to run my domestic hot water as well from the OWB. The other side of my Crown has the in and out for the domestic hot water that I assume works with the tankless heater coil. But I do not know the inner workings of the Crown to determine how to make the OWB work with this system.
Any suggestions or help would be greatful. The firewood is free - trying to eliminate oil use during the winter months.
 
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Old 01-18-13, 03:47 PM
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Not sure if I completely understand ...

I believe that you are currently using the tankless coil in your boiler for your domestic hot water needs?

I have the heat exchanger hooked up above the circulating pump for the baseboard heat and that all works great.
Can you describe how you have that hooked up? What do you mean by "above the circulating pump"? Don't forget that we can't see your system, you need to be a bit more specific, or take pictures or show us diagrams.

What you might need to do if I understand your goals correctly, is to set up the heat exchanger so that it pumps through the Crown in order to keep the indoor boiler hot all the time.

But let's get a better description of what you have, and what you want to do, and go from there...
 
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Old 01-22-13, 03:21 PM
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The original way this was hooked up is, I had the heat exchanger above the circulating pump on the indoor boiler. When it called for heat the pump kicked on ran the water through the indoor boiler. The return from the baseboards flows through the one side of the heat exchanger and back through the boiler. That allows for the hot water from the OWB to run into the indoor boiler.

I now have the system hooked up so that the circulating pump on the indoor boiler runs 24/7 and returns directly back through the heat exchanger. There is also a new pump inline with the supply and placed after the expansion tank to run through the baseboard when it calls for heat. This should be supplying the indoor boiler with hot water from the outdoor boiler 24/7. However, when I call for domestic hot water, the oil burner still kicks on. I have a couple of pictures, but do not see where to attach to this.
 
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Old 01-22-13, 06:05 PM
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Hi Pond, it is possible to attach pics here, but they get re-sized too small to see anyway.

Better for me (bad eyes) is to be able to see LARGE, HIGH RES pics...

Set up a FREE account at Photo and image hosting, free photo galleries, photo editing | Photobucket and upload your pics to a PUBLIC album.

Come back here and provide a link to your album.
 
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Old 01-23-13, 12:39 PM
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Above is the original set up. Just doing heat from the OWB. Circ pump kicks on when calling for heat. Oil burner fires when asking for domestic hot water.





Original circ pump running 24/7. New pump kicks on when calling for heat. Oil burner still fires when asking for domestic hot water.

OWB is set at 165-180 degrees. Indoor boiler high and low temps set at 160 degrees. I tried lowering the indoor temp, but that just gives me colder domestic hot water and the burner still fires.
 

Last edited by Hidden Pond; 01-23-13 at 12:51 PM. Reason: remove other links
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Old 01-23-13, 04:05 PM
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The first thing I noticed is the fact that it appears that you have 1/2" copper tubing in and out of that heat exchanger... that ain't right. You are 'choking' the flow by using 1/2". The SUPPLY out of the boiler appears to be 1" and that's pretty much what you should also have on the return.

Not gonna make a big deal out of the fact that the 'vent' pipe for your backflow preventer is doubling as a 'stand' for the piping... but that ain't right neither.
 

Last edited by NJT; 01-23-13 at 04:26 PM.
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Old 01-23-13, 04:08 PM
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Indoor boiler high and low temps set at 160 degrees
May not be an issue if you don't have any pumps connected to the C1 and C2 terminals in the boiler aquastat, but if you do, these settings would cause erratic operation of any pumped connected to them.

In NORMAL operation, they should be no closer than 20F from each other... says it right on the front of the white temp setting block in the aquastat.
 
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Old 01-23-13, 04:23 PM
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I still can't see where all the piping is connected... I think I have a general idea of your setup, but I need a solid idea in order to make any suggestions.

Either take more pictures from many angles so I can visualize the setup, or draw a diagram and photo that and post it. Unless the diagram is accurate, I would rather have pics... how about both?

Please also indicate pipe sizes.

I believe that to achieve what you are trying to do you will need to use some bigger pipes for starters. It's likely that the stuff in/out of the heat exch (HX from now on) is too small if it really is 1/2".

You will probably need to pipe the heat exchanger in parallel with the indoor boiler and there will be a check valve that will also need to be used.

Post up the info so that I can 'be there' in your basement and properly visualize the setup.
 
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Old 01-23-13, 04:24 PM
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What size, and how long are the PEX runs to/from the OWB?

What model is the pump that is pumping through the HX?
 
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Old 01-24-13, 08:25 AM
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All piping sizes and installation was done on the initial install. (Not me)
Pre OWB
1 1/4" from supply to expansion tank and then 3/4" to the baseboards.
Return from baseboards is 3/4" to circ pump, then 1 1/4" to base of boiler.
1/2" in/out for the domestic hot water side to 3/4" throught the house. Also 1/2"
for supply to the "heat" side.

OWB & HX (My install)
All I did was splice the 3/4" return above the circ pump to place the HX.
1" PEX from OWB. 135' boiler to boiler. Not sure of pump size. I do know it was larger than required. OWB company figured the pump and HX sizes required for my setup.

Existing setup - piping and eletric/controls (Installed by someone else)
Using 3/4" for the new loop that has the "old" pump running 24/7 through boiler.

I started this thread because I still do not know how this is supposed to work to supply domestic hot water without the oil burner firing. Will attach other pics.
 
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Old 01-24-13, 08:30 AM
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Old 01-24-13, 09:31 AM
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OK, great, I can see what I need to see now!

I would have 'up-sized' the pipe in the loop around the boiler through the heat exchanger. Probably gone to the same size as the pipes entering and leaving the boiler, but at LEAST 1".

Reason being that you need FLOW in order to move that heat out of the HX and into the oil boiler.

What you have done 'should' work though.

Basically what should be happening is that when the wood boiler is supply 180 water to the HX, that heat should be getting transferred into the boiler and maintain the oil boiler at 180.

Since the oil boiler is being maintained at 180, when a domestic heat call comes the burner should NOT fire...

UNLESS...

The domestic call causes the oil boiler temp to drop below the LO setting minus 10 on the aquastat.

This could happen if the wood boiler can't transfer the heat fast enough... or, if it had 'idled back' it's combustion because the system temp was satisfied... then it would take some time to respond and crank the fire back up to heat the water again.

In other words, your wood boiler needs to be capable of quickly replacing the BTUs that are being taken OUT of the oil boiler and into the home as central heating, or the water for domestic hot.
 
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