Domestic coil on WVO boiler

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Old 01-06-11, 10:04 AM
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Domestic coil on WVO boiler

I have a waste oil boiler installed in my basement burning WVO. It has a DHW coil installed, and the coil is currently plumbed to preheat the water entering my propane DHW heater (tee in cold water supply goes to coil, then back to another tee in cold water supply, with isolation valves.) I would like to shut off the propane and use a bronze circulating pump to keep the DHW tank at temperature. I assume I will need to relocate the hot water connection where the coil meets the tank, but I am not sure where to tee in and where to put the circulating pump. We have free electricity due to solar panels, so the additional electrical consumption is not an issue. The DHW tank has side inlet and outlet for space heating, so I may be able to tap in there to circulate the water. I have temerature controllers to operate the pump as needed. Any help is greatly appreciated, since I am currently unemployed and would like to minimize my propane consumption. The image is the current configuration. I think that if I add the bronze circulator and plumb it from the bottom space heating outlet through the coil to the upper space heating inlet, it should keep the tank at the desired temperature. I am running the boiler at 145 degrees F. Am I on the right track here?
 
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Old 01-06-11, 12:31 PM
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here is a better view of the current setup, it it helps.


errr, i suppose it looks the same.
 
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Old 01-06-11, 03:51 PM
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Am I on the right track here?
I don't think so, if I understand what you're planning...

Tell us the make/model of the propane water heater with the space heating coil in it.

Here's the problem with your plan:

I believe you intend to pipe the DHW coil in the WVO boiler to the space heating coil in the water heater. This will constitute a CLOSED system, and you will have problems controlling the pressure in that loop of piping. You MIGHT be able to do this if you install an expansion tank on the loop, but I still don't think it's a good idea.

IF the space heating coil turns out to be suitable for operation in 'reverse', that is, putting heat into the tank rather than taking it out, it would certainly make more sense to pipe it into the BOILER WATER circuit... treat it as an INDIRECT WATER HEATER... just another 'zone' off the boiler itself... abandon the coil in the boiler (do NOT cap the pipes! same deal with pressure build-up) ... you would not need an expensive bronze pump, an el-cheapo 007 would do the job.

What make/model is the boiler itself?

What is the other tank that you have shown in the drawing?
 
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Old 01-06-11, 04:32 PM
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Trooper's suggestion sounds good to me. But if there is any thought of going back to your original idea, you should disconnect the propane completely. You don't want it to be physically possible for it to fire.

Your drawing doesn't show a T&P relief valve on your "space-heating tank" or other appurtences that should be there (and maybe are). I'm leery of such simplified diagrams because we are left to assume what else is there in the way of controls or safety devices.

Are the two tanks shown on the left, one and the same tank, just different views? I'm confused. I'd like to see two system diagrams (not physical) showing before and proposed - with all the valves, etc.
 
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Old 01-07-11, 10:52 AM
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I appreciate your help. I will work on the diagrams. I am not quick with the paint program and was not sure of the symbols to use for the various safety devices. There are two hot water heaters, both 50 gallon high efficiency propane fired units. One was for DHW, and the other was for my in floor radiant heat system. Both systems are fitted with T&P valves and expansion tanks. The radiant heat system is fitted with T&P valves at the boiler, the water heater tank, and on the main system manifold. Both water heater tanks are currently unplugged and disconnected from the propane. The coil in the boiler is provided enough hot water for our needs, but stand by losses are causing the water temperature to drop to unacceptable levels if we don't use the hot water for an extended period of time. That is why I wanted to circulate the wter from the DHW coil in the boiler through the storage tank.

Here is a photo of the current setup. I will work on the diagrams asap.


The boiler is an AgSolutions B150 (Axeman-Anderson 87NPO boiler fitted with Kagi burner) The water heater tanks are Bradford White MIITW50T6CX12. There is not a space heating coil in the unit, it simply has connections for an open space heating system.
Here is a photo of the cold water going to the boiler coil, and back from the boiler coil, into the DHW tank.




Here is a link to my photobucket album. boiler setup pictures by forgedcu - Photobucket
 

Last edited by NJT; 01-07-11 at 05:09 PM.
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Old 01-07-11, 02:00 PM
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There is not a space heating coil in the unit, it simply has connections for an open space heating system.
In that case, YES, you can do exactly what you are planning.

An aquastat on the hot water tank would be wired to control the bronze pump to circulate water from the tank through the coil on the boiler...

In fact, you probably only need to re-plumb ONE of the pipes. You could probably leave the HOT side connected to the cold in to the heater... OPEN the bypass valve. The return to the coil in the WVO would come from the top port on the water heater.
 
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Old 01-07-11, 02:06 PM
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Awesome! Thank you for your help. Now I hope I can win the bronze Taco 006 on eBay today for $60.
 
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