Central OWB hooked up to Pressurized Benjamin CC500 problems

[Kawliga]

Good Morning all...first post here and hope I can get some help from the experts...apologies up front for long winded post....

Background....3400 sq ft house, heat loss of 85000BTU, heating is all in floor radiant, both stories, pex in gypcrete slabs. Heating source is a Benjamin cc500 wood/oil combo unit, pressurized. System is 5 years old.

The system works very well on oil but sucks it back huge....approximately 1200 gallons year....however we do not use the oil unless really cold, only use the wood as we have 40 acres and a lifelong supply of wood. The benjamin is not designed and cannot keep up with heat load using just wood as it cannot get hot enough. We have managed for 5 years, but the fire has to be stocked every 2 to 3 hours and ashes removed every 2 to 3 days...a pain. The boiler is currently in our attached garage in a mechanical room.

Several neighbors have switched to OWB recently and love them so this year we invested in the Central boiler 6048, (397 gallons), we run 100' thermopex to the mechanical room. We put a sidearm HX on the hot water tank, (40Gallon), and then used a sheel and tube HX to tie in to the pressurized system. The HX is rated to 150,000 btu which is a little more than the oil output on the benjamin which is 125,000.

The central boiler unit is terrific...in -15 C weather we are filling twice per day....and it is putting 175 degree water into our mechanical room. Hot water is excellent, but we are not satisfied with the HX which ties into the existing pressurized system and radiant floors. In the past using the benjamin on oil....our supply lines to the radiant ran at 110 to 120 degrees....with the new system we cannot seem to get much over 100 degrees....(we had hoped that having a supply temp of 150 degrees minimum from the new central boiler we would just have to temper with cooler water). It appears that the return loops from our radiant system into the HX are cooling it down so that the supply temp is not getting as high as we hoped.

Ok questions:

1. Can we depressurize the Benjamin boiler, eliminate the shell and tube HX, and just tie new supply from the central boiler into our radiant floor system?
2. How difficult is it to depressurize and what are the pros and cons....?
3. Would we still be able to use the Benjamin boiler as our back up with the oil burner?
4. Would we be better to just sell the benjamin unit, tie into the radiant floor with the new boiler and go to electric baseboard etc...for back up?

We must have some form of back up heat for when we go away....

Thanks in advance for any advice

Mike

 

[bigburner]

if I understand you have a 70 F or C split across the heat exchanger, not good - sounds like it may be a sizing issue or install issue. Will need -- supply and Return temps on both sides of the HX?? Also the direction of the water moving threw it. Do you have the make model of the HX unit. Not similar with the como boiler, I would not remove the pressure, you will convert it into steam boiler in your not careful. If you have enough GPM of 150 degree water there is not reason the floor can't work in current set up.

 

[goosegunner]

If I understand what you are saying. You have a huge delta T on your boiler water leaving your heat exchanger.

Sounds like a gpm issue to me.

I had the same issue with my shell and tube exchanger for my pool. Not enough boiler flow caused large delta T. I have read it here many times. You can only flow X amount of BTU's through 1" pex. And Thermopex is 1" or .86 ID

What is that number again?

gg

 

[Kawliga]

Thanks bigburner and goosegunner or quick reply.

Big Burner: The Shell/tube exchanger is a Central Boiler item....Part # 151, 60 inches long, rated for boilers up to 150k btu. (the btu output on the benjamin with wood is 90k btu and on oil 118k btu).

I will work on getting you getting exact temps but here is an estimate:
Supply into HX from OWB: 170F, return to OWB from HX 150F.
Supply into Pressurized loop from HX: 95 to 105F
Return from pressurized loop into HX 85 to 90F.

The HX is mounted horizontally. My supply from OWB comes into a fitting that is part of the HX on top, likewise the return to OWB comes from a fitting on top of HX that is part of the unit, on the other end. The supply and return to my pressurized loop ties in at either end of the shell. The one end has the supply from OWB and the return from my pressurized, the other has return to OWB and supply to pressurized. Flow goes from supply from OWB.

From my OWB, 100', thermopex, (with 1" lines) to manifold in Mech room. From manifold I have 15 feet 1" dia pex to HX supply and 20' 1" pex from HX return to manifold. About 10', each of 1" pex to suply and return from HX to pressurized tie in. The pex is not insulated.

The specs on the shell HX say it may lose up to 20 degrees F. I really have a delta, (still to be confirmed upon temp checks at all points) of about 45 to 50F. This is based upon a 175F temp in the manifold from OWB, deduct another 5F for heat loss in pex, another 25 for HX and lines and radiation from shell, (shell is not insulated...but I like the additional radiant heat anyways in my mech room). This should leave me with 145F temp of water out of HX and into my pressurized loop. As i note I am only getting max 105....

The lad who put my boiler in is a little stumped, but anxious to try and figure this out. He says that my cool return into HX from pressurized system is greatly reducing what should be coming out of the supply end into pressurized from HX...I dont think so.

I have the circulation pump in the OWB running on high, and have the circulation pump on my Benjamin loop running on high as well. My radiant heat has 6 zones all with their own grundfos cic pumps....all are on high.

It sounds like my flow should be slower? I have already tried setting all pumps down to low, but it did not make any difference.

Central boiler has a part #177, 4 ft shell/tube HX for boiler up to 135K Btu....do you think he oversized the HX?? He thought bigger would be better. I shied away from the plate HX as I hear they can be a maintenance item....

If it would help to post pics I can do so....thanks

Mike

 

[goosegunner]

Just curious, but what are the size of the ports on the shell and tube heat exchanger?

gg

 

[bigburner]

This is out off the central parts book

Water-to-Water Heat Exchanger, Shell
& Tube
A water-to-water, continuous-flow heat
exchanger used mainly for boiler applications
Side ports are 1" FIP; end ports are 1-1/2" FIP
p/n Description
177 Heat Exchanger, Water-to-Water, Shell & Tube, 48

 

[bigburner]

Want a sketch of this layout! Want the pump make & model. It might be a piping issue. My current guess is you are experiencing the nice high temps of OWB because you are not moving the GPM and that's why the split on the unpressurized side looks correct more or less, but you aren't getting the BTU's on the pressurized side. The boiler looks great because it's not loaded.

"From my OWB, 100’, thermopex, (with 1†lines) to manifold in Mech room. From manifold I have 15 feet 1†dia pex to HX supply and 20’ 1†pex from HX return to manifold. About 10’, each of 1†pex to suply and return from HX to pressurized tie in. The pex is not insulated."

 

[Kawliga]

Want a sketch of this layout! Want the pump make & model. It might be a piping issue. My current guess is you are experiencing the nice high temps of OWB because you are not moving the GPM and that's why the split on the unpressurized side looks correct more or less, but you aren't getting the BTU's on the pressurized side. The boiler looks great because it's not loaded.

"From my OWB, 100’, thermopex, (with 1†lines) to manifold in Mech room. From manifold I have 15 feet 1†dia pex to HX supply and 20’ 1†pex from HX return to manifold. About 10’, each of 1†pex to suply and return from HX to pressurized tie in. The pex is not insulated."

I will get a few pics together and draft a layout of my system. I will detail from the OWB, to manifld to HX, including pumps/controllers and layout. Will also detail my prior existing pressurized loop and boiler etc...

GG, the connections on my Part #151 shell are the same as what BB listed for the 48" shell....my ends are reduced to brass fittings with a ball valve and 1" pex, (these are the loop into my pressurized system)

Really appreciate your time!....travelling for the next 36 hrs, will get data as requested together...

My goal with this sytem was to have 140 to 150 F in my pressurized loop and temper it down to run at 110 to 120 F 24/7.......maybe I was hoping for too much.....? Maybe my return loop from pressurized system feeding into HX is slowing heat transfer down?

Mike

 

[Kawliga]

OK, I am not great at photo programs etc....but here is a start.

I took a few pics and marked up supply and returns...mostly my existing indoor loop which was constructed 5 years ago and ran with the Benjamin wood/oil combo.

I did not bother to include pics of the DHW HX as it is working just fine.

Some other general info on system, (just modified 10 days ago with the addition of Central Boiler 6048 OWB.)
The OWB is approx 130 feet from my mech room which is in the attached garage to my house. Thermopex used. The OWB sits at an elevation roughly 68 vertical feet higher in elevation than the floor in my mech room....thermopex runs mostly above ground, all rock here, stuffed inside 6" non perf weeper. I have added this in case it is relevant although from what i understand static head is not an issue so the elevation change should be meaningless.

There is one Grundfos UPS15-58FC on the supply line of the OWB coming down to our mech room manifold. It is a 3 zone manifold....one zone to HX for DHW, 1 zone for HX to my existing benjamin boiler...and 1 future zone, (should we decide to use it), to go to HX for our hot tub.

On the side of the benj boiler there is a circ pump, same Grundfos as on OWB, (as a matter of fact all my pumps are this same 3 speed unit). This was prev. used by aquastat setting to come on to recirc water to boiler....before we installed OWB this pump pushed DOWNWARD. My OWB installer told me to reverse the flow on this pump so at present it is now pushing UP. (see the pics)
Both my original mech guy and the guy who installed the OWB and HX said this should cure the issue....but it is not giving me any more than 105 to 110F in my supply loops.

I have attached the Central Brochure method for tie in to pressurized system....looks diff than mine!!

The Installer of the OWB was unsure where to tie in to my press. system. He chose to install 2 1.25 dia Tees, with ball valve between, in the hot supply line that ran from my Benjamin boiler.

I have filled in both installers that there is a huge delta between temps coming into HX and what is dumping into my supply line....approx 40 to 50 degrees F. They are now suggesting to add another pump on the left side of the Supply tie in from HX, (to push into my supply for indoor loop)....I dont know if this will help or not.

We have 6 zones on my indoor loops....all 1/2" pex in Gypcrete or conc slab in garage....controlled by an "Argo 24v box, which activates an individual circ pump for each zone.

The larger pipes on my indoor loops are 1.25" dia copper and pare down to 3/4" copper where they feed into circ pumps and manifolds...

Well, I am sure there is more info required and prolly some clarity perhaps on my pics....let me know whatever other info I can provide and I will do my best to get it.

As a side note, it was always my plan to have the Benjamin oil as my backup....but now the way the circ pump has been reversed in flow, (and hardwired to run 24/7), I am not sure that it will do the job correctly. I only need the oil to be used when we take extended time away from home....

Mike

 

[Kawliga]

If I understand what you are saying. You have a huge delta T on your boiler water leaving your heat exchanger.

Sounds like a gpm issue to me.

I had the same issue with my shell and tube exchanger for my pool. Not enough boiler flow caused large delta T. I have read it here many times. You can only flow X amount of BTU's through 1" pex. And Thermopex is 1" or .86 ID

What is that number again?

gg

Are you saying that I dont have enough flow to keep up with my heat load? Since the HX is for boilers up to 150kBtu, (and my Benjamin is only 118K on the oil)wouldnt the greater surface area help in more and better heat transfer? The lad who installed the OWB has installed about 400 units, and only once or twice used the 1.25" dia pex...

Even if the flow is not enough how does that impact the actual temperature of the system, in terms of heat transfer to my pressurized system? If the HX is only supposed to lose approx. 20 degrees F in transfer, would I still not see at least 130 to 140 F temps on the pressurized side?

I also forgot to mention that I am running a glycol mix in the pressurized side....would this effect heat transfer thru the HX? or just the heat transfer to the slabs...?

Forgive me if my questions are ignorant on this subject!!

All we know from our previous setup was that if we could get contant 120 degree flow it kept up with the heat load just fine, even on the minus 30C days with -40 windchills.....we hope that at the least the OWB can achieve this...


Thanks

Mike

 

[bigburner]

Don't have time to think this threw now, but at first glance a few things some mind. The elevation difference does mean a little more when the water temps change, you are trying to push the coldest water [heaviest] up the hill. The pump should be looked at. I would like to see one with more head and mounted inside the boiler room. You are thin on pump performance now and it may be cavitating at the top of the hill making it pump even less. The other thing I would shut off every load but one and see if you get correct temps then, if so it's a flow issue. The other problem is that a little buffer tank in the boiler room wouldn't hurt either, when you have multiple loads cycling the, HX will struggle to give enough BTU"S and a low flow exasperates this problem!

 

[Kawliga]

Don't have time to think this threw now, but at first glance a few things some mind. The elevation difference does mean a little more when the water temps change, you are trying to push the coldest water [heaviest] up the hill. The pump should be looked at. I would like to see one with more head and mounted inside the boiler room. You are thin on pump performance now and it may be cavitating at the top of the hill making it pump even less. The other thing I would shut off every load but one and see if you get correct temps then, if so it's a flow issue. The other problem is that a little buffer tank in the boiler room wouldn't hurt either, when you have multiple loads cycling the, HX will struggle to give enough BTU"S and a low flow exasperates this problem!

Thanks, I will try as you suggest and shut down all but one zone to see what happens....will use a medium sized zone. I was told by my pump supplier that we could eliminate static head due to gravity, and that dynamic head should be the only calculation. I have sat and listend to the pump in the OWB for quite some time on a few occassions to see how it sounds....and it seems to be fine...runs just like my indoor zone pumps....and cannot hear any cavitiation or air in the pump....

If I understand you correctly, it would be better to push the cold up to the OWB?

Today is -30 C, coldest day of the year....the house is not as warm as I would like but keeping up...

I am kind of at a crossroads here as the whole expectation was to have higher temps for the indoor loop. I feel a little sick after investing 12K in the boiler and hookup and Tpex.

I am also investigating eliminating my old boiler and tying directly into my indoor loop from the Central OWB....do you think I would get higher temps this way?

I would lose my back up oil, but perhaps I could sell it for a few bucks and throw some EBB around the house for not much $ as a backup....

Thanks again for your time big burner...any other advice you can share is greatly appreciated...

Mike

 

[bigburner]

If I understand you correctly, it would be better to push the cold up to the OWB? -no that's not what I am saying, the water is heaver going up hill and lighter going down, so it's not a wash.

If the pump is in the boiler room there is a column of water on it that acts like a pressure system, this will help eliminate cavitation and minimize air bubbles.

You have about 11 to 12 ft of head from what I can tell, your pump will do about 7 gallons per minute @ 12. a split of 20 degrees gives you 70,000 btus, but if the GPM say is only 5 then the btu's are 50,000 - see the issue here.

Remember. these are only opinions.

 

[Kawliga]

If I understand you correctly, it would be better to push the cold up to the OWB? -no that's not what I am saying, the water is heaver going up hill and lighter going down, so it's not a wash.

If the pump is in the boiler room there is a column of water on it that acts like a pressure system, this will help eliminate cavitation and minimize air bubbles.

You have about 11 to 12 ft of head from what I can tell, your pump will do about 7 gallons per minute @ 12. a split of 20 degrees gives you 70,000 btus, but if the GPM say is only 5 then the btu's are 50,000 - see the issue here.

Remember. these are only opinions.

I understand...and don't worry, opinions are just fine. Would it be worth a quick try to just upsize the circ pump that is now in the OWB? This is an easy switch out and less of a plumbing issue. I did listen to the circ pump in the OWB with a stethoscope this am and it does sound a little noisy...almost like ball bearings being shaken inside a plastic cup, for lack of a better description. I shut off all zones except one, and yes the supply temp on my indoor loop went up to 120 degrees...

Mike

 

[bigburner]

I would try the UP26-99F it crosses to the 011 Taco or something very similar. The sound you hear is cavitation or at least that what it sounds like from here. LOL

 

[lkdiver]

I am certainly no expert... But before doing anything expensive, make sure that your HX is plumbed correctly. Counter-flow HX will have hot and cold lines on the same side, not opposite as shown on your second picture. So:
OWB water flows left to right (using the second picture)
House water should flow right to left - left side should be exiting the HX as hot.
IF I read the picture correctly, house water is flowing left to right, which is wrong...

 

[bigburner]

Oh ya - check the heat exchanger flow also, got distracted Sorry. It will lose some capacity hooded up wrong. But your splits will less, not more.

 

[Kawliga]

I am certainly no expert... But before doing anything expensive, make sure that your HX is plumbed correctly. Counter-flow HX will have hot and cold lines on the same side, not opposite as shown on your second picture. So:
OWB water flows left to right (using the second picture)
House water should flow right to left - left side should be exiting the HX as hot.
IF I read the picture correctly, house water is flowing left to right, which is wrong...

Thks Lkdiver

I dont know what "counter flow HX" is? Mine is part 151 60" shell....CB product...doesnt tell me in the specs that it is counter flow...

In my second pic, on left end of the HX: on the bunt(?), its the 90 degree connection port, is Hot from OWB, on the end of the shell is the return from indoor loop....just confirming this.

This concurs with your observation....and just so i am clear, on the left end where the OWB hot enters, the end connection here should be to my indoor hot supply?

You have read the pic correctly!

Can I reverse just the lines to and from the OWB? It will be easier than draining my pressurized system and then having to bleed a bunch of air...?

I am still reviewing all issues relative to my problem...as I think I may have more than just one issue going on here...and want to get a short list of diagnoses and then attempt to start trying the fixes...

I would think if mine is plumbed incorrectly I am suffering on the heat transfer....in addition to maybe some flow issues....If plumbed correctly I should certainly see some impact on my indoor supply temps..

thks

Mike

 

[Kawliga]

Oh ya - check the heat exchanger flow also, got distracted Sorry. It will lose some capacity hooded up wrong. But your splits will less, not more.

If LKDiver is correct then it indeed is hooked up incorrectly...want to be sure before I talk to my installer...Sorry BB, "but your splits will less, not more" ? Sorry, I am not clear....the split between Hot OWB to HX and Indoor Hot or the supply and return splits on each loop? From or at the HX?

No need for apologies sir....distracted,,,,yup know what you mean...and if you can hear my pump from there I better get it changed out quick ,LOL...

Appreciating everyones assistance on this....

Mike

 

[lkdiver]

Counter-flow simply means that primary and secondary flows are in the opposite direction. That configuration provides maximum heat transfer. From wikipedia:

There are two primary classifications of heat exchangers according to their flow arrangement. In parallel-flow heat exchangers, the two fluids enter the exchanger at the same end, and travel in parallel to one another to the other side. In counter-flow heat exchangers the fluids enter the exchanger from opposite ends. The counter current design is most efficient, in that it can transfer the most heat from the heat (transfer) medium.

Frankly, that HX does not seem to have enough surface area to transfer the BTUs you need - but correct configuration should help (some). If indeed configured incorrectly (as parallel flow), reversing one side will change it to counter-flow. It does not matter which side - if OWB side is easier to reverse, do that one...

 

[Kawliga]

Thank you everyone for your advice and opinions so far.

Murphy 2000 talked me thru some of the issues last nite and we have highlighted 3 issues to work on.

1. Flow, BB and others here have commented that my Grundfos UPS15-58 FC is pretty undersized for getting adequate flow thru the 1" pex from OWB , thru system and HX etc...so first step will be to switch out this pump or add another in line befre the boiler HX.

2. Even though it appears that my boiler HX is incorrectly hooked up I need to verify it is a counter flow spec on this Central Boiler unit...and then do the switch if it is installed incorrectly....don't expect to see major gains here, but it should be done right.

Hopefully these 2 should get me a higher temp output on my indoor, load, side.

Apparently my sidearm HX for my hot water tank is hooked up incorrectly as well. Hot from my OWB comes into my mech room into a 3 split manifold, 1 split goes to HX for DHW, (supply direct to HX and a return from HX to manifold....), one split goes to boiler HX, with return direct to manifold...other split is for future potential hookup to hot tub....

Does anyone else have this type of setup.....Most I have seen are in series...OWB to HX for DHW, then return from DHW HX to my boiler HX, then return to OWB....and this is what it shows in the CB brochure....

Will keep everyone apprised of how the fixes go....

Thanks

Mike

 

[lkdiver]

Another thought... I just re-read your description:

Hot from my OWB comes into my mech room into a 3 split manifold, 1 split goes to HX for DHW, (supply direct to HX and a return from HX to manifold….), one split goes to boiler HX, with return direct to manifold…other split is for future potential hookup to hot tub….

Splitting already marginal flow two (or three?) ways may not be the best idea. You may get better results going from OWB directly to house HX (using counter-flow orientation), than from HX output to DHW HX input and back to OWB (ignoring hot tub for a moment) - series hook-up. This may reduce DHW recovery time some, but if flow temperatures you listed are correct it still should be acceptable.

NOTE: There is nothing different about parallel and counter flow exchangers, just the way they are hooked-up.

 

[Kawliga]

Another thought... I just re-read your description:

Hot from my OWB comes into my mech room into a 3 split manifold, 1 split goes to HX for DHW, (supply direct to HX and a return from HX to manifold….), one split goes to boiler HX, with return direct to manifold…other split is for future potential hookup to hot tub….

Splitting already marginal flow two (or three?) ways may not be the best idea. You may get better results going from OWB directly to house HX (using counter-flow orientation), than from HX output to DHW HX input and back to OWB (ignoring hot tub for a moment) - series hook-up. This may reduce DHW recovery time some, but if flow temperatures you listed are correct it still should be acceptable.

NOTE: There is nothing different about parallel and counter flow exchangers, just the way they are hooked-up.

I do plan to eliminate the manifold....and will most likely plumb as you suggest...house heat is a priority, then the DHW. By the way Lkdiver, your concern that the HX for my boiler looks undersize mught be right on...another member suggested the exact same thing. Cannot find any specifications on the one provided by Central Boiler, Part 151....just thats its good for boilers up to 150k....it is only a 2.5" dia shell x 60".....I am going to change my primary circ pump first, (upgrade to 1/6 HP unit) and see how the HX performs...if it isnt any better I am going to switch out to a 60 plate HX....I shied away from the plate at first over concerns of maintenance issues, but now what the better heat transfer that the plate HX should give over the Shell/tube HX.

Mike

 

[bigburner]

Sounds like you are on the right track - except look up the DHW first -you need the hottest water here [greatest split] [we will add pumps on these also on domestic side "like a taco 006] -it will not drop the temp much and then on to the other loads. I wouldn't wing the pump thing either. [unless you have one laying there] Hook all loads in series figure the pressure drop and get a pump in the middle of the pump curve. I still think the pump should be on the bottom of the hill or if two are used one at the bottom and the other one on return at boiler if that is simpler - IMO PS went threw Murphy site interesting stuff. Have been thing about adding a waste oil gun on my system, but of course want to build one. LOL

 

[Kawliga]

Sounds like you are on the right track - except look up the DHW first -you need the hottest water here [greatest split] [we will add pumps on these also on domestic side "like a taco 006] -it will not drop the temp much and then on to the other loads. I wouldn't wing the pump thing either. [unless you have one laying there] Hook all loads in series figure the pressure drop and get a pump in the middle of the pump curve. I still think the pump should be on the bottom of the hill or if two are used one at the bottom and the other one on return at boiler if that is simpler - IMO PS went threw Murphy site interesting stuff. Have been thing about adding a waste oil gun on my system, but of course want to build one. LOL

Hey Bigburner...

My biggest problem before starting to make the changes to my newly installed system, (LOL), was just installed 10 days ago, (The OWB loop and HX that is), is I do not know how to calculate the pressure drop and flow requirements.

Last night I shut the DHW HX off at the 3 split manifold and lo and behold my supply temp on the indoor loop of the boiler HX output jumped 15 degrees! Is this because it increased the flow to my boiler HX?

You are right, I dont want to just wing the pump replacement on the OWB loop, (although I really want to get this system working correctly.)

So how do I really determine the head and flow requirements?...my installers are not capable of doing this for me....

Here is my proposed new layout:

OWB sits 70 vertical feet elevation higher than my mechanical room. The run of thermopex, (2 units of 1" diameter pex) is 130 feet, (260 both ways)

I am going to eliminate the 3 split manifold that is now installed.

Where it enters my mechanical room it will connect to the thermostatic valve, (this is used to ensure that a minimum of 150 degrees F returns to the boiler to prevent shock).

From the Thermo valve I will plumb to the DHW HX, then in series to the Boiler HX, then return to thermo valve and OWB.

For ease of plumbing, (I will most likely be retrofitting this work myself), my preference would be just to upgrade the primary circ pump that is already on the supply line of the OWB at the OWB. The flanges exist here with shutoffs so it is an easy switch out to a stronger pump. I just dont know how to determine the right pump size....and dont want to overdo it here and have a pump that is going to cost me 30$ a month to run....

My questions on this proposed redo are:

1. How do I determine the head and flow requirements so I get the correct circ pump at the OWB location?
2. Is there any major benefit to doing all the plumbing connections in my mechanical room with 1" copper as opposed to 1" pex?I estimate there is approximately 80 feet of 1" pex to connect the 2 HX and my indoor loops. A friend told me that the copper can handle a lot more BTU....but I would have to have a couple of 90 degree corners to plumb it...

Thank you so much for your help and advice

Mike