Greenwood 100 Again...

[bluecap24]

I am still working on my father's Greenwood 100 we installed back in 2007. We have learned a lot but still have a lot to learn. We just finished replacing all the panels and the inside heat exchanger. This will be the 3rd heat exchanger and 4th or 5th set of sides. SMH... Anyways I know we have a draft issue that I am dealing with but we have a draft inducer that keeps it around the .06 range. I have the return protection turned up this time so the return water doesn't get below around 145. My biggest observation is with the house furnace on and a water to air in the garage the boiler will still build up and cycle. Hmm..that should be around 100k btu or more draw so why does it still cycle? We have a LB31-20x heat exchanger separating the boiler from the house loop.

Could someone tell me if these temps are normal. Boiler output water 180 deg, boiler return water 155 deg, loop supply water at HX 166 deg, loop return water 111 deg. this is with no load on the system. When we put the load on it the loop supply will be 140-150 and the return will be 60-80 and the boiler will cycle. Is the HX too small? Could it be plugged up?

One thing I did notice is somehow this thing is plumbed up backwards but it is cross flowing. If you look at it the top left is the load supply, bottom left is the load return, top right is heat supply, and bottom right is heat return. According to the website the top left should be the heat supply, bottom left heat return, top right load supply, and bottom right load return. So even though I am cross flowing is this being hooked up backwards effecting is?

 

[Chuckcrj]

Loop temp supply 140 and return 60?? That indicates you have almost no flow in the loop. Heat exchanger is either undersized or scaled up also.

Pretty sure that being piped that way is OK, should transfer heat equally well.

 

[GENECOP]

Yes something is wrong with that 60 return.....Even the 166 - 111 seems way off....What keeps happening to the HX and side panels? Was this unit new in 2007?....

 

[bluecap24]

Thanks guys for the replies. The 60 return is after everything on the loop has pulled the heat from it. Shouldn't that be low? Yes the unit was new in 2007. The sides and HX have rusted through and leaked. We tried galvanized sides last time and they didn't last. This time we used steel and powder coated them with high temp powder. We made a stainless steel internal heat exchanger this time and powder coated it with high temp powder. I know the stainless might crack and it may have been a mistake. My brother owns a fab shop and I work at another fab shop so we are doing all this work ourselves. It just acts like it isn't passing off the heat to the main loop.

 

[GENECOP]

Each and every system is custom and unique, I am no expert, but I am heating over 3000 Sqft, mostly radiant except for one large hydronic zone in a second floor (forced hot air) my return temps are never more than 20 Deg lower, and most. Often 10-15 Deg lower...something does not sound right , to me. What do you mean "house furnace"....do you have two furnaces? Explain your dads system better.....

 

[bluecap24]

The system is two loops. One open loop on the back of the greenwood to the LB31-20x HX with the shunt pump to protect the return water back into the greenwood. The second loop (main) goes from the LB31-20x into the hose to a water to air heat exchanger in the gas furnace plenum. From their is goes out to the garage to a hanging water to air heat exchanger. It returns to the house and goes to a side arm for the DHW then returns back to the LB31-20x. The main loop is pressurized. It has a bell and gosset 3 speed pump that is running on setting two. Basically the temp starting the main loop is 140-160 but it returns at 60 or a little above when the house furnace and garage unit heater are on. Even without the house furnace cycling or the garage unit cycling it is going from 160 to 111. I was figuring that could be the DHW and just line losses even though all the lines are insulated and the line that runs to the garage is the expensive 1" pex encased in solid foam inside of a 5" black tube. I guess now it does seem odd that it is dropping that low. I was just surprised that the out going side of the HX wasn't closer to the greenwood temp. Just seems like it isn't passing enough of the heat to the loop. This thing has never seemed to run right and keep up so there is something fundamentally wrong with the setup I know but I can't put my finger on it. I don't have a flow meter on either loop so I really can't tell how well it is circulating. Could it be circulating too slow in the main loop? I have turned the pump up to setting three and it doesn't seem to help. It just makes the pump vibrate and on low it does seem worse.

Thanks again for taking the time to ponder this.

 

[maple1]

Sounds like not enough flow through the boiler side of the HX. That could be an issue with that pump, or a restriction in the HX, or too much flow in the 'shunt pump' arrangement. Or even something really out there like a valve partly closed. How long has this setup been in place? Has it always worked like this?

Gotta give some of you GW guys an A+ in perseverance - I would have lost patience & dug out the cutting torch long ago, I think. That is an obscene amount of maintenance over the years.

EDIT: After seeing what you posted you have for an HX again - I would also bet it is way too small. I think that's a 5x12, 20 plate? That's what I have just for my DHW.

 

[bluecap24]

On the boiler side of the HX the main circulator pump is brand new. We had to replace it Sunday as it was stuck to the housing when we started the boiler up after the "rebuild". It is a Taco 007. The shunt pump another Taco 007 is on an aquastat that only comes on when the return water drops to around 140 and shuts back off around 150. It has a check valve in the line. It is possible that the boiler side of the HX is restricted due to the rusted out tubes in the past and the stop leak that was put in it trying to nurse it to the end of the season.

As I am typing I see maple1 replied and the HX is the one that greenwood suggested and it does say it is for 100k btu but I suspect it is too small too.

Like I said since 2007 this system has never ran correct. Had it been mine I would have drug it out too, but since my parents spent 12k of their retirement to install this, my brother and I have to keep it going, which is coming at our expense. We have joked that we would be money ahead to pool our money and time we have spent and bought propane! My brother has a model 300 greenwood and hasn't had a single issue with his. I myself heat my entire home with a corn stove. Just a little background on why we are so persistent. Plus a 75 year old dad that has nothing better to do than watch this boiler and let us know when its not working...

 

[GENECOP]

Hopefully you will get some other solid suggestions here, as long as the Greenwood itself is up and running, doing its job, you just need to start at the beginning with the system design...hell, you are in this deep, there is no backing out now...My overall system is simpler in design, and even it has many things about the way it runs that I do not fully understand.....and I stare at it every spare moment......Hopefully with the input of some of the more knowledgable guys here, you can work through it...I'll keep watching and thinking...

 

[GENECOP]

Good for you sticking by your dad and helping to get it done...that Stop Leak stuff is disturbing....hopefully it
Did not clog anything up.....If the Greenwood is putting out 170-180 Deg water, then you at least know the problem is further down the line...

 

[maple1]

I would bet the HX is plugged some on the boiler side, after reconsidering the issues you've been fighting & potential for crud - and also since it's never worked right that it is also undersized. That is a pretty large load for a 20 plate HX. As far as what size to get, that gets into a whole mess of math starting with a heat load calc, and flows on each side, etc etc.. Or you could just get a big honking one that would make the math irrelevant - kind of my approach when I got my 20 plate for DHW. Flow meters would likely be nice but you should be able to narrow issues down by accurately measuring pipe temps in different spots - which I guess is what you've done here.

 

[mole]

You might consider removing the heat exchanger altogether. Unless your secondary loop is open to the air or contains non-O2 barrier pex, then you could probably cut the heat exchanger out and plumb it direct. I installed my Seton without a Hx. No issues.

 

[maple1]

Isn't the Greenwood an open boiler? I don't think I would risk exposing the rest of the system to what this boiler has been going through.

I may be wrong though....

 

[bluecap24]

Yes the Greenwood is an open system. We haven't had any issues with the other loop so I would kind of hate to mix the two. When we installed it we asked about just making one big loop connecting, but they said the return water would be too low and it would condensate. Well it did it anyways and rusted out. It would be nice if there was someone close to me that could take a look at it and maybe something would jump out at them. I guess we'll have to try and clean the HX when I can shut it down. Right now it is running fine on the greenwood side as far as heating up and maintaining temps so I don't think it is hurting the new parts its just not handing off the full amount of heat. As long as we can keep it from short cycling too much before we get it cleaned. So if we think it is plugged up on the boiler side of the HX could I just unhook that side and flush it without unhooking the other loop from it? We haven't broken into the other loop since it was installed in 07 with glycol. What do I flush it with?

 

[woodsmaster]

I'd bet money the Hx is way to small for that heat load.

 

[bluecap24]

I did some more tweaking an playing with the boiler last night. We have not shut it down yet to clean it, since it is chilly out dad doesn't want to turn it off. I was reading yesterday about the delta T for the heat exchanger and how it was related to the flow and this got me thinking. The main loop is all run by one NRF-36 pump on setting two. The temp difference between outgoing and incoming is running as much as 65 degrees, so that is likely not enough flow through the lines right? I am able to take the garage loop off of the system with some bypass valves so I did that last night and turned the pump up to 3. This changed my delta T to around 40 degrees after running for about 15 minutes. All of these are while the house furnace was blowing through the HX. I know this still isn't the 15-20 delta T that is ideal though. So does this mean that my flow is still too low through the main loop? If that LB31-20 HX is too small would it effect the delta T that much?

I am also relating this to the greenwood loop cause my delta T on it was around 20-25 degrees at the same time. So if it is plugged up I would be low on flow causing this. I really regret not putting in some t's with pressure gauges so I could at least calculate what the flow is by the pump curves and pressure drops.

So with all this do you think I need a booster pump on the garage portion of the main loop? Is the 007 pump on the greenwood too small? Is the NRF-36 pump too small? Would a larger plate HX change all this?

 

[maple1]

The next question that comes to mind after reading what you did last night, is how warm was the air coming out of the house furnace ductwork?

I still think first on my list would be put in a bigger HX - that is a really small one.

 

[woodsmaster]

the Hx your using is what most people use just for domestic hot water. Id just get a larger one and I bet your problem is solved.

 

[bluecap24]

So what would be a good brazed plate heat exchanger. Where is everyone getting them for a good price?

 

[bluecap24]

Had an opportunity to clean the heat exchanger since the temps haven't been too bad here lately. We hooked up a recirculating loop with an extra Taco 007 pump and some clear 1" hose. Wow was it dirty! I flushed it first with just water and it looked like dark chocolate milk coming out of it with some rust chunks. We then put an entire bottle of clr in it and let it soak for 15 minutes. That was also very nasty dirty. I was able to bleed off a little of the dirty water and inject clean water until it was running clean. Then we put an entire bottle of Johnson brand CLR type stuff in it. It also ran dirty again after a 15 minute soak. I then ran two tanks of clean water through it just to make sure it was running clear. After all this we fired it back up and it was transferring more heat than before but still seemed low on the return side. I then went down and turned off the garage loop to let it equalize with the smaller loop. It did eventually get to within 4 degrees of the boiler temp but would not recover very fast. So while inspecting the pump I had forgotten we installed a y strainer in the main loop..duh. I cleaned that which was almost plugged solid and the return water temps on the main loop are running much higher.

So I am satisfied with the main loop temps and recovery. They are back to what they were when we installed it at least. I still think I need to install a booster pump on the garage loop for the returning water.

What I am still noticing is the boiler temp can be 180 and the returning water back into the boiler is only 150. Does this indicate the flow through the greenwood loop isn't enough gpm? The pump we put on it is the same as what greenwood spec'd but we have rebuilt the inside heat exchanger and maybe it is creating more head?

I guess I need to install some pressure gauges to see what the flow actually is. Does this seem like a logical problem?

I found a replacement heat exchanger at Free heat 4 u that seems reasonably priced. Does anyone have any experience with them?
I am not going to rush out and buy one yet until I know for sure why the boiler is loosing 30 degrees running through the heat exchanger with no load.

 

[maple1]

How far is the HX from the boiler? What is in between them? Is there a chance some flow is circulating by convection on the load side of the HX?

 

[bluecap24]

The HX is mounted on the wall right next to the boiler. I attached a pic, don't pay attention to the wire mess. I don't think convection is doing anything here.

 

[GENECOP]

The HX is mounted on the wall right next to the boiler. I attached a pic, don't pay attention to the wire mess. I don't think convection is doing anything here.

Not sure if it is playing into things, but it looks like your exhaust steps down out of the back of your unit....then goes back to 6"....At least with my setup the rear exhaust is full width all the way.......I also have my Tee posistioned in the other direction with a cleanout on the left side, this lets me easily pop of the cover once in awhile depending on my wood type and usage....not sure what, if anything that Tee facing down does for you....

 

[maple1]

The HX is mounted on the wall right next to the boiler. I attached a pic, don't pay attention to the wire mess. I don't think convection is doing anything here.

Think you're quite right about no convection there.

Does flow stop all together on the load side of the HX when call for heat stops, or is the calling for heat just the turning off & on of fans on the load loop? Some run the fluid all the time & just regulate heat output by switching the fans.

 

[bluecap24]

Yeah the exhaust does step down to 6" per the greenwood manual. The masonry chimney is only 6" inlet too so I know that is all an issue with draft and that is why we have the inducer on it. It runs around .04 to .05 with the inducer running. That's a good idea with the Tee. Right now he can take the cap off and tap the pipe and the soot falls down.

The flow is constant on both sides. The heat is regulated by the forced air furnace fan and the garage unit heater fan. That's where I am seeing the differences. If I let it all equalize with no load draw the main loop will come close to being equal in and out within 4-6 degrees. The boiler side never does though. It is rare the return gauge goes above 155-160 even when the boiler is at 185. That's why I am suspecting too little flow on that side. I will temp it why my heat gun tonight to see if the gauge is accurate but I suspect it is.