Simple System, Impossible Problem.

NRT_Rob

thanks

for the kind words and the thoughts guys.



update will come as soon as I have one to give. enjoy your weekends!

icesailor

SS, IP:

Rob,

I installed a Munchkin a couple of years ago. My son needed some work so I let him pipe it up because I was busy. He had been working for a HVAC guy doing all his hydronic boiler installs. My install was exactly like you have except yours is radiant and I had three zones of baseboard with zone valves. I drew up a diagram of how it had to be done. There was no question about how it had to be done. There was no other way. He understood what to do and how to do it.

The owner mentioned that the water was very hot at times. I looked at it and found a tee on the wrong side of another tee. When the heat zone was running, it was sending hot water into the SuperStor. Sometimes, the only way to find a problem is to cast your eye upon it. It took me a while to find the tee. It took me even longer to take it apart and re-pipe it.

Mark Eatherton

THe OOHHhhh AHHHhhh test...

Eyes and hands on test during recovery will find it every time. It MUST be done while the whole system is coming out of a DEEP recovery, or you will burn your hand (DUHHhh).



I call it "Feeling Hydronics",



Warning: Hot metal pipes may be hotter than they appear in your hand held IR Home Depot thermometer. With laser :-)



Handle with EXTREME caution...



ME

eluv8

unknown problem

I do not see where you have a pump listed but I would suspect based on what I read that you need a bigger pump for the application. Are the manifolds opened up all the way? Is the PDBV working or set correctly, try closing the isolation valve forcing all flow through the loops? Have you ruled out any restrictions within the boiler coils?

CMadatMe

Piping

Rob,

I would say the boiler buddy is piped wrong. Your pulling from the bottom of the tank which is the coldest water. Tank sould be piped just like a low loss header. The radiant return should be coming back to the bottom of the tank not back to the boiler. You radiant supply should be coming off the top of the tank.



If your only supplying 6gpm from the boiler to the tank and only pulling 2-3gpm from the bottom you are always going to see that temp drop. Even if you piped it like a LLH your going to have a 6-10 degree temp difference betwenn the boiler supply water and the system supply water.



The ideal solution would be to get a sensor on the radiant supply side of the tank and get the boiler to satisfy the systems need not the tanks. Unfortunaltey that Munchkin doesn't have that capability like the Lockinvar, Viessmann and others. 



You may have to live with this unless you re-pipe.

 

NRT_Rob

eluv8

if you knew me at all you would know that I consider the phrase "bigger pump" to be about the worst insult you could throw at me



it's a 15-58 grundfos. medium speed is all we need, though it's on high at this point to try to jack up performance.



more soon!

Mark Eatherton

Details, details, details....

I down loaded the beautiful drawing that Rob posted, and was able to zoom in on it for better detail and drawing clarity. Try it yourself and see what you are missing.



THis is about as straight forward and simple an installation as it can be. Does it go against the manufacturers recommendations. Maybe, but knowing that Rob knows what he is doing, and has done this before, successfully, I don't worry about the design too much.



The tank is nothing more than a fat spot in the line. And one might think that by running fluid backwards through the tank goes against conventional wisdom, he's NOT trying to enhance stratification. In fact, keeping the tank thoroughly mixed, giving the extra BTU's a place to sit around, waiting to be used should work just fine in my minds eye. I really don't think that part makes any difference.



I think that what IS going to be found is that a check valve on the DHW pump has become fouled, is not seating correctly, and is allowing cooler water to mix with the boilers discharge water, causing a drop in temperature. Eventually, it will manifest itself with the DHW tank short cycling.



Remember, energy can't be created or destroyed. The buffer tank is not an energy consumer. The dilution is coming from somewhere, and there is really only one place it could be coming from.



If the boiler were underfired, it would not be capable of achieving the required discharge temperature.



This is not rocket science. It's basic hydraulics at its best.



Close a ball valve on the DHW circuit and see if your temps don't come up to par.



The oooh aaahhh test will prove it.



ME

Brad White

I agree with ME

The notion of an inadvertent T-mix is the only thing I can see causing a true temperature drop in that system. That is why we need to know temperatures right at the tank vs. at the boiler and out of the tank.



If the T-mix is happening at the DHW interchange, the temperature change would be happening upstream of the tank, even if detectable downstream of the tank.



I also agree, this is a great drawing and I would like to know what program you use to create it. Very professional, which is splitting an infinitive, I know. But it does set a high standard.

NRT_Rob

thanks Brad

we draw in a mac native CAD program, PowerCADD. Same one I think Siggy liked for a long time. though I have to gripe that a mac guy like siggy releases his own software for windows only!



I would prefer to use an active modelling software of some sort, but here we are.

NRT_Rob

Resolution

Well, we worked it out this morning.



When the contractor got to the site, he measured the temps at Boiler out, then radiant in (which is after a pass through the buffer tank), then radiant out.



-Those temps were 120 to 104 to 82... just about a 20 degree drop at each step.

-Flow meters read 4.2 GPM total for all the loops...

-so if this was real, we just exceeded the maximum output of the boiler (4.2 GPM x 500 x 40 dt = 84,000 on a Munchkin T80M)!

-Yet, boiler modulation was at a low level.



So it's conclusive: either my temperature readings are all bad, or the flow isn't what it says it is. Or, we just figured out how to make a 74k net output boiler put out an extra 10kBTUs/hr on low modulation! Can't wait to see what it would do on high fire !



So the contractor just opened up all the loops as much as possible. They were now reading a total of almost 7 GPM.



Within 15 Minutes the temperatures were now 119 boiler out 114 radiant out 94 radiant back. So the formerly 20 degree drop across the buffer tank is now nearly gone... just as it should be. I'm still not happy with a 5 degree drop, but we got impatient and moved on to another test.



Closed the bypass... within 4 minutes boiler out and radiant out were the same temp, within a degree or so, exactly as it should be in steady operation.





So, the problem is definitely flow, and my flow meters are definitely lying to me. They are reading much higher than they should. I would have called this impossible previously, but now I suspect that we have a batch of bad springs out there to deal with.



Bummer, but the system appears to be operating fine now even though I am running a higher pump speed than I wanted to and can't flow balance exquisitely until we replace the manifold.



Thanks for all the thoughts and consideration. This was a real head scratcher. But as my partner likes to quote from our hero, Mr. Spock, "When you have eliminated the impossible, whatever left, however improbable, must be the answer".



Enjoy your design days tomorrow (at least, those of us up in the northeast!)

icesailor

Impossible buffer tanks:

You know, that buffer tank, piped like it is is like a DHW heater is really piped. The dip tube on the cold inlet outs the cold water to the bottom and the heated water rises. If you feed the hot water in the top and take the hot water out of the bottom, the hot water rises to the top and as the hot water goes in, the hot level drops vertically to the bottom, there it finally comers out hot. Like ME said, it is like a bubble in the line.

What I have to say to you though is that no matter how experienced an installer is, they may have no idea how flow works. They just pipe by rote and follow the dots on the plan. Had you gone there, you would have started closing and opening valves. Like you did. Like I do. There's something about getting close to the beast and feeling it work.

My old boss used to say to never trust a gauge. It might be wrong. I always like to put gauges on either side of a circulator and take the differential pressure.

Glad you found it. 

NRT_Rob

Yeah

site time is good. But we are pretty experienced at remote troubleshooting... been doing it for more than ten years now... and it *usually* works out pretty well.



this was a real curve ball though, for sure. the idea that 9 separate gauges on 2 separate manifold bodies would ALL fail seemed pretty impossible. Unless there is a bad batch of flow meters out there!



certainly we do occasionally run into "yeah, you didn't really follow the plan, did you". and those are definitely real headaches. I think the calls for pictures were very sound, and if we were working with anyone other than the contractor I was working with, I would have required it too. But this one has all the trust we could ever muster to do a great and thorough job. and we did confirm critical details over the phone as well.



wild. I just hope there aren't too many of these flow meters out there!

Mark Eatherton

Uh.... I don't think you are done yet....

Having ONE bad flow meter, is a real possibility.



Having TEN defective flow meters on TWO different manifolds.... Nahhh... You're not done yet.



Keep looking :-)



Before you waste your fitters time to replace both manifolds, have him feel the system out during cold recovery and see where the dilution is coming form. Even the use of an Infrared camera probably wouldn't help much in this case. Too many shiny metal pipes.



Just my $0.02 worth.



ME



PS, I am sure you have all your tube flow dynamic numbers. Close off the PAB bypass and turn off the boiler, and see if the numbers you are seeing match the numbers you calculated to be able to select your pump. Easier than ripping and replacing manifolds...



ME

eluv8

no insult intended

You are right I know very little about you other than what I read once on your website. I have not frequented this site for some time and left the hydronics industry about a year ago and thought I would catch up a little and saw this post. I had no idea asking what pump you used, or if the DPBV had been checked would be considered insulting.



Based on the information you supplied I simply posted what I would look at first when troubleshooting a job I was unfamiliar with that presented the same concerns you stated in your post. It seemed to me like the thread was focusing in the wrong direction.



There are those who would say that a Grundfos 15-58FC in this application is no where near enough to be piped in this arrangement in medium or high speed. I have not seen your calculations, do not know the length or size of the tubing runs and am in no way in a position to question your methods. I am personally of the belief that in the areas that I have designed and troubleshooted for that a 26-99FC would be a better choice in this application but again I have not seen your calculations.  Again that is my own personal design criteria based on what I have seen in my own calculations.



It cant be fun when something you put your heart into and take much pride in doing does not work the way you intended and you do not understand why. I am glad you are getting things figured out. As  Mark E. I think the possibility of that many flow meters not working correctly at the same time is a stretch, unless they have proven to be inaccurate in the past. I personally never trusted or installed them. I always set up my systems by supply and return temperatures.



I wonder what the calculations look like when you remove the DPBV altogether in this application with a 15-58 in the system. You might find it to be beneficial as zones close....



I will go back to my lurking. By the way, you don't know my background either.......

NRT_Rob

I had a smiley face in there

because I was poking fun a little. I'm a small pump/minimal pumping fanatic. Telling me to add/increasing pump power is "fighting words" around this office. winky smiley



designing a loop field to 4-5 feet of head isn't that hard and allows primary pumping like this in many "typical" homes, like this one. we do it all the time. many times with some loops on a system closing in on 500 feet even... when you know you only need 0.2 to 0.3 GPM, the loop lengths can get kind of silly.

NRT_Rob

I thought the same thing mark

but I really don't see any other solution, and a bad batch of flow meters seems at least like it doesn't break the laws of physics.



if I'm really pushing 4 GPM of 120 degree water and it's 40 degrees colder coming back, and the only thing wrong is I'm pulling cold water and leaking it out somewhere, and even if I really do have the near 20 design dt I designed for (even nowhere close to design) in the loop field, then I would need more than 1 GPM of incoming ground water to dilute.



Also, the boiler modulation would be much higher. 40 dt at 4 GPM would be max fire on this boiler. but we were nowhere close.



I'm not sure what you're suggesting with the bypass though. we hit target flow rates with the bypass set more or less as specified, according to the flow meters. without trusting the flow meters I don't know how I would be able to gauge flow in a system with the boiler off?

Mark Eatherton

Sorry, I meant to say turn off the burner...

Keep the water at around room temp if you can, it is more dense at that point.



I don't think you have a hole in the system. Easy enough to figure out. Turn off the make up and see if the pressure drops. If it does, you need to find the leak and fix it, especially on well water.



You should be able to read the delta T across the boiler on the remote readout pad that came with the boiler. At least, I can on mine.



ME

Karl_Northwind

isolation

Just found this thread, and my first thought on looking at the diagram was to isolate system portions to reduce/eliminate interacting from different flow paths.   In this case, I think the only one you can is the DHW circuit.

you can also isolate the DPBP loop and turn on all the zones, and watch the temperature increases thru the system. 

Bad flow meters would be no fun, but at least they are on unions.

 I come from mostly a service (of all sorts of things) background, and that's my first thought on any system I have to service/troubleshoot.  Isolate whatever you can and test individually, and see if isolating any part fixes the problem.  I'm a hands on pipes kinda guy, and have the smooth fingertips to prove it.



karl

NRT_Rob

I don't follow

if the water is room temp I'll have a near zero delta T. what would that prove?



I think I see a way what you're alluding to could work though. If the flow was through the domestic circuit instead of the boiler, flow through the boiler could be very small, but present, while flow through the indirect would set the meters properly.



we will eliminate that possibility.... I think we already have, but I'll make double sure.



Thanks Mark.



edit: though this would not explain the temp drop across the buffer tank, as in that case we'd have a "primary secondary" circuit.. hot boiler, lukewarm everything else.

Paul Pollets

My 2C

I'd put a pump on the lower buffer tank outlet to the radiant manifold, and a check valve on the DHWT circuit.  If you can raise the temperature of the buffer tank, but not the manifold, it would seem to be a flow issue. Just my 2C.

Unknown

At the risk of sounding stupid...

A loooong time ago (like 25 years - almost before electricity) I experienced a similar mystery problem - drove me nuts and killed a massive amount of time.



Symptoms are the same but mine had a Phalen shell and mini tube heat exchanger (agreed a different animal than a buffer tank).  The solution after days of messing around - the exchanger was not piped for counter flow.  Switched and problem solved.



You guys think this might be a possibility?

pipe4zen

Steve

All of us here were guilty of overpumping at some point.

Thanks to Wilo, Siggy, and others, we now seem to be moving in a better

direction when it comes to properly applying pumps.



NRT however, IMHO, has taken the over pump issue to an extreme here and decided to under pump the system. Just as bad.



Maybe it is bad meters, maybe the math works, not fighting words, just seems fuzzy to me here without looking at the install hands on.



I, and others would have had a secondary ECM pump out of the other side of the tank, let the boiler pump load up the tank. The ECM will supply the micro loads. I doubt piping it that way, and using another pump would have added to , if any, more $$ spent on the electric bill vs. a pump on speed 3 operating as it is now.



My 2cents, not worth a dime.

NRT_Rob

Look, this is getting kind of old.

since we opened the flow meters further the system performed to expectations through a period of below design condition weather.



therefore, conclusively, it's not under-pumped. Never was. Case closed on the "under pump" theory, ok?

pipe4zen

not ok

This thread has generated a lot of hits, and all are welcomed to express their views, opinions, and comments, unless the moderator decides to close this thread, so far it has been civil, sorry if we hit a nerve.



Munchkin's preferred piping according to the manual has two pumps, one for the system, one for the boiler. Piped to the manual , the pump chart in the manual shows speed 2 on a 15-58 pumped into the boiler, not away. That is why I , and others here say you are underpumped.



Kudos to you for getting this to work. But professional installers are the ones getting the no heat calls, and are looking the owners directly in the eye. We don't have the luxury to experiment , not unless we are upfront. Like saying, hey Mr. and Mrs. Smith , I want to try to save you guys $2 a month on your electric bill so I'm going to use one pump instead of two, it may some tweaking, please be patient.

My guess is since they hired you through the internet, you furnished a pre-piped board, and you had flows, loops, etc all mapped out, everyone thought this would work right .



I'd rather not get that call, so I would have design-build the system per manufacturer preferred reccomendations, and used two pumps, and that is a fact, not a theory. What you had designed was based on theory. Now it's ok, good luck.

Gordan

See my reply from awhile ago.

Given where your thermometers are, you wouldn't seem to be in the position to say whether there is or is not a temperature drop across the buffer tank - or, at least, how much of it there is. If your flow through the boiler is lower than you think, then you are overestimating your BTU input. Also, the boiler is likely to be on low modulation, just like you say it is. Combine that with the thermal mass of the buffer, and you could be "recovering" that buffer for a long time, which would account for some temperature drop.



I also mentioned for the possibility of draining the heat from the buffer during a DHW call, further aggravating the "recovery." Isolating the DHW circuit completely, as Mark also suggested, would quickly identify whether your BTUs (and flow) are getting "lost" to the indirect.

Brad White

Munchkin with One Pump

I was told by HTP (Munchkin), that it is entirely possible to use a single circulator for the Munchkin (any Giannoni type for that matter), IF you do not vary the flow through the boiler. The problem occurs when you have TRV's or other means of varying flow through the emitters when this also varies the flow through the boiler.



HTP does highly recommend two circulators or at least one dedicated to the boiler, and do show this on their diagrams, sure.  But notice too how all of those diagrams have multiple zones with varying flows.



The HTP recommendation for P/S is because (my words here but paraphrasing), too many people do not understand the concept or cannot size a circulator. By promoting P/S piping, HTP has fewer calls into their help line. Also they cannot control someone modifying the system later, such as adding TRV's to radiators. No one  would recall the original simple design premise, they figure and they would have a flash steam boiler issue.



But a simple directly-connected constant flow system will not be a problem.

NRT_Rob

this is not experimentation

we do it routinely. as I've said plenty of times. You can have what opinion you want about how we design, but if you call this "under pumped", you're wrong, plain and simple. You might not do it this way, that's fine. But "Under pumped" is "the pump can't push enough flow to satisfy the load or the heat extraction needs of the boiler". That's a qualitative measure, not an opinion. Either a system has enough pump energy to do the job, or it does not. this one does. that's a fact, not theory.



Unfortunately, this job had some other issue we had to figure out and it's a weird issue. but the *same thing* would have happened if I had a 15-58 on speed two on a secondary circuit as is happening here. the pressure drop across the boiler just *isn't that big*. It did not cause this problem. I know this because I know the numbers behind what is happening there. They disagree with the flow meters. That would happen no matter what circuit the manifold was installed on.



those are the facts. Have whatever opinion you like, that's fine. You are more than welcome to prefer to do things to the manual. But you don't get to pretend that we're just throwing darts here.

NRT_Rob

exactly

we never void a warranty, and our design strategies meet manufacturer approval, even if they aren't in the manual.

NRT_Rob

some truth

but the pipe does not drop temperature at the domestic circuit connections, as it should if we were diluting hotter boiler output water with a cooler "domestic/radiant circuit". stays hot until it gets to the tank, cooler coming out, via touch test.

pipe4zen

one pump

Sure muchkin, TT Solo's, etc, can have a single pump. As shown. But the 800 pound gorilla is the 250 pounds of water in a buffer tank. That's a little more than just a "fat" spot in the loop.



I doubt if any maunufacturer or engineer would design a buffer tank in such a way. And while we are on the subject. Do we really need a buffer tank on a mod/con? Really?? I've yet to see one short cycle, even with a small , single load such as a panel rad. With reset, and low modulation , seems a little wasteful.

pipe4zen

Darts

I was'nt pretending to throw darts.



So let's agree to disagree on this one.



I also hope you compensated the contractor for his additional time.



Cheers.

NRT_Rob

at system flow rate

What does water mass have to do with pump size? I use the same pump on radiator conversions with hundreds and hundreds of gallons of water in them and it works just fine. it really it just a fat pipe. gallons in equal gallons out.



there are a few single loop zones in this system, bathrooms, and it's low mass. You can have a very legitimate argument about whether the buffer tank is cost justified, and neither of us would have any science behind us to prove it, but I know this boiler will probably have short cycling episodes at least some of the time, and the buffer tank ensures that will never happen. It's a "boiler protection insurance policy". I think it's worth it. You're free to disagree, and you might even be right.



Some others, including some who I have great respect for, disagree with me, so you wouldn't be alone.



Siggy and the boiler MFG's, if you ask them to put a number on an ideal target cycle time, say ten minutes! That requires buffer capacity in microzoned systems. I think that's crazy. But I don't mind hedging more in their direction.

NRT_Rob

what would you think is fair

if a manifold had bad flow meters on a project you installed?



fair question for anyone. this wasted an awful lot of my time as well.

Jean-David Beyer

Fair.

As a homeowner, and not a heating professional, I would expect at least         

that the manufacturer would replace the things free of charge. He might wish you to demonstrate that they are defective or have you return them for them to test. It would be nice if they would compensate you for your time, but that is probably too much to expect. Not too much to ask for, though. Maybe your distributer would consider this as a goodwill courtesy for a good customer.



It seems difficult for them to be bad; they are very simple devices. A weak calibrated spring, a slightly conical cylinder, and a slightly undersize piston. Were they erratic (e.g., dirt in the mechanism)? Or just calibrated wrong (wrong spring, wrong size piston)?

Leo_G

Now now NRT

Of course you're not under pumped. That would be impossible, because what you use are circulators! 

I like your thinking beyond the box myself.

NRT_Rob

it appears

they just read more flow than they really have. consistently. by perhaps 40% or more.



though, I have to own up, on a DIFFERENT job I thought this was the problem on, it does appear to be a problem, but on THAT one.... we are, in fact, underpumped, and the flow meters just hid that fact from us. That one was actually primary/secondary as well.



First time for everything! Bummer.

scott markle_2

P/S with ECM Vs. direct connected W/ DPBV

hey rob,



Sorry to revive this but I'v just noticed it.

I don't understand why the dpbv wasn't opening sufficiently to allow your buffer tank to come up to temperature.



With all due respect to your efforts at reducing Electrical consumption, I think you should be considering ECM pumps and P/S as an alternative to your direct connected system with bypass. The cost of a 15-58 and a good quality DPBV is close to an alpha. An alph eliminates the DPVB and uses significantly less energy even at it's highest output. In fact you can run two Alphas wide open for just a bit more energy than it takes to run one 15-58.



Finally if you are really committed to direct connected systems why use a boiler with such a high presure drop and strict minimum flow requirements. We've seen the pictures of overheated Giononni's , these HX's are beter protected from thermal stress when over pumped a bit. What happens if your DPBV is miscalibrated (as it seems to have been) what if it becomes stuck or needs adjustment? How do you confirm your boiler flow rates without yet another flow meter. How long could a flow sensitive boiler run before this problem is noticed? I'd save the direct connect systems for boilers that are more tolerant of low flow rates and or single zone systems that have consistent flow rates. BTW I have seen a stuck flow meters on new Viega manifolds, but this was easy to spot and came free with a bit of tapping. What kind of manifold are you using?

NRT_Rob

for the math we've done

unless you can ditch a PBV, it is not yet cost effective to use ECMs for constant flow apps.



having to use two alphas would be not at all cost effective compared to this setup. If we want to save electricity, we could trade the 15-58 for a single alpha, run constant pressure and keep the PBV and still be ahead by a couple hundred bucks and some electricity.



The Munchkin actually has one of the lowest pressure drops across the HE of any mod/con except the solo, but in this case, as in most cases, we use the boiler the owner/contractor wants to use and do what we have to to make it work. For most homes, you only need 3-6 GPM and we can handle that flow rate through almost any mod/con out there, honestly, with a single pump if you design your loop field well.



You make a decent point about not setting the PBV correctly, but on the other hand, it's not a complicated device and we do clearly specify what it should be set to. That's really a fair point though and I wouldn't fault someone for choosing the P/S instead of direct pump method, there are pros and cons. As long as they don't attribute all kinds of problems to direct pump systems that aren't real, either



our clients typically want it "done right" though, and are paying attention, and we allow them to reap the benefits of that. Cookie-Cutter or Dummy-Proof situations have benefit too, but also a parasitic cost in upfront and ongoing expense.



so it's a matter of what floats your boat, I think.



the manifolds we are using are the Mr. Pex Brand, brass. This appears to be one run of the manifolds as we have seen no other such problems in other years, just two on systems commissioned this year with manifolds shipped early last year.