installing open system owb to closed fhw system

[dlabrie]

For the last 15 years I have had my Central Boiler owb connected directly to my oil fired, FHW system in the house. This has left the entire system open to oxygen. When installed, I was led to believe that keeping the OWB chemicals in the system would be sufficient. Now I am planning on replacing the CB with a new gasification unit and I was told I would need a flat plate heat exchanger between the two systems.

I have two questions:
1- Does maintaining the anti corrosion chemicals allow installing the OWB directly to a closed system without harm to the system?

2- I understand how a flat plate HX works but after I hook up one side of the plate to the OWB, where do I splice in the other side to my 3 zone, oil furnace?

Thanks

 

[leon]

For the last 15 years I have had my Central Boiler owb connected directly to my oil fired, FHW system in the house. This has left the entire system open to oxygen. When installed, I was led to believe that keeping the OWB chemicals in the system would be sufficient. Now I am planning on replacing the CB with a new gasification unit and I was told I would need a flat plate heat exchanger between the two systems.

I have two questions:
1- Does maintaining the anti corrosion chemicals allow installing the OWB directly to a closed system without harm to the system?

2- I understand how a flat plate HX works but after I hook up one side of the plate to the OWB, where do I splice in the other side to my 3 zone, oil furnace?

Thanks

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Sorry to hear your going that route versus wood pellets or wood chips.


The same boiler chemicals are added to steam boilers for their
water supply as there is an air gap to the steam chest.

Your going to end up draining the indoor boiler water; you need to make sure that
you have plugs for the tapping's after you open the boiler back up.

Water PH testing and a few drops of Dawn Dish Soap help with
air bubbles and softening the water somewhat.

As far as your flat plate heat exchanger- If it were "Me" I would not use
that type I would use a very small shell and tube heat exchanger which
are used in swimming pools. They are easier to clean and have full flow at all times.

If you have two unused tapping's in your indoor boiler you can hook up your flat plate
heat exchanger or the preferred shell and tube type and use a very small circulator to
push the closed system water from the boiler sump through the heat exchanger and back
to the boiler sump in the opposing boiler sump tapping.

Saying that:

The feeder header for the zones should be moved to the top tapping of the boiler to enable
the use of the lower tapping's for the heat exchanger and a small circulator to strip heat from the new gasser.

 

[huffdawg]

As far as your flat plate heat exchanger- If it were "Me" I would not use
that type I would use a very small shell and tube heat exchanger which
are used in swimming pools. They are easier to clean and have full flow at all times.

I dont agree with that statement. I personally prefer to clean the flat plate over shell and tube any day. I have been cleaning both types at work for the last 20 yrs. Flat plate give better heat transfer also.

Also I think his decision to go with a gasifier is a good choice if he has access to lots of wood.

Why does he need a heat exchanger if he is installing a gasifier. Cant it all be pressurized?

Huff

 

[maple1]

As far as your flat plate heat exchanger- If it were "Me" I would not use
that type I would use a very small shell and tube heat exchanger which
are used in swimming pools. They are easier to clean and have full flow at all times.

I dont agree with that statement. I personally prefer to clean the flat plate over shell and tube any day. I have been cleaning both types at work for the last 20 yrs. Flat plate give better heat transfer also.

Also I think his decision to go with a gasifier is a good choice if he has access to lots of wood.

Why does he need a heat exchanger if he is installing a gasifier. Cant it all be pressurized?

Huff

Agreed, flat plate over a pool heater every day all day long. Just make sure you plumb in fittings & valves to make it easy for flushing it, if that ever becomes needed. A pool heater won't get & keep your indoor system water hot enough, especially a 'very small' one. And they are not immune to the same buildup a flat plate might see which diminishes heat transfer even more.

I think the gasifier being mentioned though must be an unpressurized outdoor one? Therefore the HX is needed?

As far as where/how to plumb the inside side - if you have an OWB tied in now, you should just be able to plumb the HX the same way inside? Don't know how things are now though.

Can't answer the chemicals question with any certainty.

 

[dlabrie]

Thanks for the responses.

I am sticking with the wood gasifier because I cut my own wood off of my property and I have a band saw mill and I burn the “waste” from that.

The original and the new OWB are both open systems.

Right now my owb is hooked directly to my FHW oil system. (I will post some pictures below noting how it is hooked up.) The oil furnace is a Buderus, cold start furnace. It only runs in the summer to heat my domestic HW via an indirect water heater(Boilermate), though it is set to come on if the OWB gets too low.

 

[maple1]

So based solely on those pics, or more exact the second one - I think I would plumb the 'OWB Feed' into one port of the inside side of the FPHX, and the 'OWB Return' into the other. With another circ pump add to that circuit to maintain the flow through it. Should be done either with copper, or O2 barrier pex. Can't tell if the pex in the pic is O2 barrier or not, but it doesn't look like the O2 barrier I have. The boiler mate feed/return lines should also be O2 barrier - and after looking at pics 3 & 4, they all should be also. If you were starting from scratch, you could likely plumb things so the extra pump wouldn't be needed (all flow through the HX) - but looks like a big job rearranging things there for that.

 

[Bob Rohr]

Do you have a buffer or storage tank involved? You do have an indirect to be heated by either source?

Do you want the switch from wood to the Buderus to be manual, or automatic?

Here is a rough drawing with a 3 way zone valve.

It shows the two modes of operation.

Ideally that boiler pump should be pumping away from the expansion tank. depending on how much repiping you want to get into. isolation valves, gauges, strainers left out for clarity.

 

[dlabrie]

Do you have a buffer or storage tank involved? You do have an indirect to be heated by either source?

Do you want the switch from wood to the Buderus to be manual, or automatic?

Here is a rough drawing with a 3 way zone valve.

It shows the two modes of operation.

Ideally that boiler pump should be pumping away from the expansion tank. depending on how much repiping you want to get into. isolation valves, gauges, strainers left out for clarity.

There is no Buffer or storage tank other than the 185 gallons in the OWB.
The Boilermate is heated by either source.


I don't think any of my PEX is oxygen barrier. I believe that was because when installed is was an open system and the chemicals were supposed to take care of the oxygen issue.

The owb boiler has a continuously running circulator. the circulator for the heating zones and boilermate only come on when needed. So is there a place in my system that I can connect the FPHX to maintain this setup without adding another circulator? Bob, from your drawings, it looks like it would go between the feed and return of the heating zones. I just can't figure out how to do that. I imagine I don't want too many elbows restricting flow.

 

[maple1]

The owb boiler has a continuously running circulator. the circulator for the heating zones and boilermate only come on when needed. So is there a place in my system that I can connect the FPHX to maintain this setup without adding another circulator? Bob, from your drawings, it looks like it would go between the feed and return of the heating zones. I just can't figure out how to do that. I imagine I don't want too many elbows restricting flow.

I think it could be done, sure, but would require some re-plumbing of that nice looking cast iron.

Example from your pics, looking at the second one:

If you put the load side of the HX, in the big return cast iron piping, below the fill water piping (between that & the IWB return inlet), then every time your heating circulator comes on it will draw heat out of the HX into the IWB & the rest of the system (as long as heat is being supplied to the supply side of the HX from the OWB). That would be the simplest setup I can see - aside from the re-plumbing job. But the re-plumbing would be confined to that short length of piping. (Plus perhaps replacing all the non-02 pex with 02 barrier). If heat stops coming into the HX from the OWB for whatever reason, then the oil burner would just cut in same as it ordinarily would. That would be a simple series setup.

The possible catch there, that I can think of, is that all your system flow would be going through the HX all the time - so you'd want to be sure the HX doesn't present too much head loss or restriction for what your max system flow would be. (I guess the bigger the HX the better). And also by having all the OWB heat go through the IWB, there would be a bit of added heat loss potential there - but the amount of heat loss may not be a concern, not sure there.

 

[dlabrie]

So the FPHX would be placed here in the system?

 

[maple1]

That's what I was picturing, more or less - but I'm no expert either.

(Also think your OWB lines there should be reversed - the two flows through the HX should be opposite each other. I think.)

 

[dlabrie]

That's what I was picturing, more or less - but I'm no expert either.

(Also think your OWB lines there should be reversed - the two flows through the HX should be opposite each other. I think.)

You are probably right about the flows being opposite. I just have to figure out the best way to hook it into the black pipe.

Thanks

 

[huffdawg]

That's what I was picturing, more or less - but I'm no expert either.

(Also think your OWB lines there should be reversed - the two flows through the HX should be opposite each other. I think.)

Your right Maple they should be counter flow for the best heat tranfer.