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Bobcat boiler/Rad/Radiant System mixing valve issues (39 Posts)
Bobcat boiler/Rad/Radiant System mixing valve issuesHi there! First post but I have been a wallcrawler for quite some time, especially as I was planning out a re-working of my heating system in my 110 y/o home. Very appreciative of the knowledge and sharing that happens on this site!
Brief history: Moved into our old character home 2 1/2 years ago, major fixer-upper needing new electrical, plumbing, heating, etc. Before we moved in a contractor did asbestos remediation (pipe coverings) and installed a new boiler, S/F Bobcat B120, paired with an Amtrol Boilermate DHW tank. The home uses very large original radiators (2 storey + attic den + basement) on the main floor and 2nd floor. The boiler was piped into the original pipe scheme, therefore the whole house was on 1 zone (thermostat on main floor).
Of course because we gutted and insulated/vp'd/drywalled the entire 2nd floor (bedrooms, bathroom) during the winter it became unbearably warm upstairs with the only thermostat being on the main floor.
I decided that when it came time to finish the basement I would re-do the piping and add a bunch of zones to even things out, and I would also take out the low-hanging steel pipes in the basement to add head room.
Well I am now VERY close to completing that goal and just fired up my new heating configuration two days ago (not at all stressful!). Everything seems to be working relatively well as far as the thermostats (6 total now) calling for heat through the Taco 6 zone switching relay and the relay in turn actuating the zone pumps and firing up the boiler (minus some Bobcat ignitor issues which I know are separate and have had for a while).
My problem seems to be that the Honeywell AM102-US-1 mixing valve (see picture) is being bypassed or something, as the zones after it (4 radiant zones) are not getting very hot, max 80F or so. The pipe on the Cold side of the mixing valve gets super warm to the touch, basically as hot as on the Hot side of the valve, and the Mix pipe stays fairly cool. I have the mixing valve maxed to hot right now with no noticeable/measureable change. It basically seems like the hot water from the boiler is going straight through the mixing valve and creating a mini-loop (not seen on the attached picture is that there is another pump for the primary boiler loop), so my two full-temp hot water radiators are working great, but none of my zones after the mixing valve are getting hot enough.
I'm not a pro or engineer but have a lot of experience in the renovation industry and did about 3 months of research into my design/needs/components, so I'm really hoping I didn't miss something major here. I've seen several similar setups where the mixing valve is used like this in pictures online designed and built by professionals (or for sale as a pre-designed board) so I know I'm not really blazing new trails in terms of design.
Sorry for the long-winded post, hopefully there is enough background to get an idea of what my situation is. I will also attach a picture later of the actual setup, but for now here is my drawing I was working from (if the drawing doesn't come up right here in the forum, here's a link to it full-size: http://ilophoto.ca/blog/wp-content/uploads/2012/12/pipescheme.png )
Thanks for any help you can give!
-Grundfos UPS 15-58FRC pumps (including one for primary loop and another for DHW loop)
-1" copper piping (going to 1" pex in joists for rad loops, 1/2" pex for radiant loops)
-Honeywell AM102-US-1 mixing valve
-Temperature and pressure dials at points seen on picture
-Zones 3&4 are in-slab in basement (yes, I poured a new slab in the basement, this has not been a small job!)
-12" spacing between supply and return on primary loop as spec'd by Slant/Fin for the Bobcat and this type of setup
Disconnectthe supply and return to the left of circulator #6.The mixing valve is oriented hot to supply, cold to return?This post was edited by an admin on December 6, 2012 4:21 PM.
new picturesThanks Paul,
Cutting the loop to the left of #6 does make sense to me as then the pumps would be drawing straight through from the hot source, but then I don't think I have a primary loop for the boiler that I can see?
The mixing valve as it sits in the diagram has C on left, H on right, and Mix on bottom.
Here are two pictures now that I'm home (I also have two small leaks on solder joints, but I'll address that after I know what other fixes/mods I'll have to make before draining things).
nYou do reallize that none of that is piped primary/secondary. It looks like you have a boiler circulator in what would be the primary loop, except for the spacing of the tees.
so...if there was no mixing valve, would it then be a primary/secondary system?
I tried to follow the manual (pg 27 here: http://www.slantfin.ca/documents/479.pdf ) as far as the piping goes, changing things up by putting the last 4 pumps after a mixing valve.
I know that it should work fine if I do what you suggested and cut off the flow after pump #6 intake, as then it would be piped similar to how it was originally, with return and supply sides, so if that's what I have to do and makes sense, then I guess it's not a big deal.
I just for some reason am having trouble with why it's not a primary/secondary, however I definitely value your input and expertise so I may end up doing what you suggested.
Thereis many sources of info...this is just one. I'll save some typing this way.. http://www.comfort-calc.net/primary-secondary_piping_tutorial.html
ahhhWell I thought I had things basically figured out but definitely not. Thanks for the resource, I'll check it out more thoroughly later. I think for the time being I will put a valve after the 6th pump and close it; should be the easiest way to achieve a supply/return system. Thanks again, P!
Some Questions/ObservationsYour boiler has outdoor reset capability. Why would you instead run 180* all the time?
I believe that I understand your reasoning behind using the mixing valve, especially with the radiant, but you've taken an approach that's not gonna give satisfactory results.
Let me explain: Your rads need medium to high temp water (120 - 180*), but your slab needs low temp (80 - 110*). You're not gonna accomplish that with a single mixing valve. Also, a thermostatic mixing valve is not the correct device for a slab. Using it will cause the slab to over-heat due to its high mass. A smart valve or variable speed injection is the correct method.
Running the boiler at 180* continuously will make it much lees efficient and probably decrease its life expectancy.
I would recommend that you scrap the mixing valve, setup the outdoor reset curve properly, use the proper control for your slab and decrease the flow to your rads that are over-heating. If they still over-heat, you could use TRV's on them, but that shouldn't be necessary if they're on a separate zone.
If you're not familiar with these concepts, then I would recommend John Siegenthaler's book on Modern Hydronics from the book store on this site. It will be money well spent.
It's gonna require some re-piping, but now's the time to get it right. You'll thank yourself for years to come.Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
problemsis that returns 1 and 2 are on the mixing valve circuit. so their returns, which are presumably too hot for the mix circuit, are able to hit the mixing valve cold leg. not good. if you fix the mix header piping by cutting the loop, you'll probably start to see yourself pulling water that is way too hot whenever your high temp zones are calling.
Ironman is right as well, you definitely want to run this boiler with reset.NRT.Rob
A "for now" solution?Thanks so much for the responses, guys, definitely appreciated!
I obviously am new to this area of plumbing/heating but have really tried to wrap my head around the concepts. Looks like I missed the mark in a few areas but hopefully I can improve/rearrange things.
Do you think that for the time being (and Canadian winter) I could get by with doing as Paul suggested and putting an in-line valve to the left of pump #6 to cut off flow there? I'd prefer a valve because I have a bunch left over and it might help with future isolation/draining/maintenance (as opposed to cutting and capping the loop there).
I'm quickly running out of time and money with this basement reno (supposed to be done before family comes to stay for Christmas) and would like to re-visit things when I have more of both in the spring.
Right now the house is warm with the two "main" rad loops running similarly hot to how they used to with the old single-zone setup (coming back into the manifold where I have the temp gauges at about 110* near end of cycle), so the rest are kind of "bonus" zones and I can live with them being less efficient for the time being. I think I can also lower the boiler's temp manually (?) which might balance things out better for now.
I'll admit I didn't really know about the outdoor reset and am kind of annoyed the boiler company didn't mention or explain that option to me. Definitely seems like a no-brainer now that I'm learning about it. The boiler install was part of the real-estate transaction when we moved in and got lost in the shuffle a bit I think (as in, they were happy to lose it in the shuffle and just do their own thing; my wife wanted on-demand HW, they installed boiler-mate tank and told us "it's better"). I'm assuming the Taco PC-700-2 would pair well with my TACO SR-506-4 switch once I'm able to add that in?
Ironman, what models would you suggest (if the forum allows it) in place of the mixing valve in terms of smart valve or variable speed injection that you've had success with and might work well here? Or would I have to add it/them to the slab zones individually (pumps 3 & 4 on drawing)?
I want to continue to learn and research this project so that when I go in to do some changes next time I've got a decent road map to follow.
Thanks again for all the help!
How far apartare your water temp requirements for your high temp and low temp circuits?
If you don't know, what kind of radiant are we talking about for the mixed zones?NRT.Rob
3 different "kinds" of zonesBasically there are two radiator zones, two in-slab zones, and two in-joist zones.
-The two in-slab zones are about 250' (zone 3) and 175' (zone 4) 1/2" pex approx 2 1/2" from the surface of the slab on average. The old floor was very sloped toward the drain, so in some parts the new slab is almost 8" thick. I strapped down 6" grid rebar using tapcons and spacers to the old floor and ran my pex along the grids. Now on the slab I've installed Platon (like Delta FL) under 5/8" t&g OSB, and 5/8" engineered walnut goes on top of that. The top of the slab will then be about 1 1/2" from the finished height.
-The first in-joist loop is admittedly a quirky one that I'm not sure even makes sense (I installed it a couple years ago when re-doing the area it serves and left it disconnected until now). Basically it goes up to a Beacon-Morris kickspace heater, then hits another mixing valve and goes in the joists under the 2nd floor bathroom above it. I used those aluminum radiating panels to snap the pex into and secure it to the floor above, and foil-faced insulation below the pex to create a warm air pocket. The floor above is marble on plywood. I realize now that this loop doesn't need to be after the "main" mixing valve I have on the manifold, because the kickspace heater actually needs full-heat water. Dumb move on my part putting it after the mixing valve.
-The second in-joist loop (#6) just goes under the main floor kitchen floor, which I pulled back to the joists and installed 3/4" OSB, 1/2" plywood, ditra and silver travertine tile on previously. The pex is also run using the aluminum plates and foil insulation. It's a pretty short loop, maybe 125' to 150'.
I've heard (and correct me if I'm wrong) that radiant should be anywhere from 80-110* so I figured I could run them all in that range and the thermostats would call for heat appropriately as each zone has its own.
hmm.this is a complicated integration that really should be guided by a room by room heat load calculation and survey of your existing emitters. the following is NOT a substitute for actual math.
1. Slab could need anywhere from 80 to 140 depending on floor coverings and heat loads. usually it needs around 100 degrees.
2. joist could need anywhere from 90 to 160 degrees depending on floor coverings and heat loads. but it usually needs around 120-130.
3. radiators could need anywhere from 110-180. in existing homes it typically needs 140-160 unless very serious insulation upgrades have occurred.
4. kickspace heaters need a bare minimum of 110 and usually ship with an aquastat that requires 120 minimum or they just won't turn on.
also, your joist heat should really be insulated with real insulation, not just foil. If it's just foil, then you'll probably want even more water temp.
so you could be in any of the following situations:
- all emitters could comfortably run on one reset water temp, except the kickspace heater.
- your existing emitters may be appropriately assigned to mixed/unmixed, except the kickspace heater.
- Your joist radiant might be better suited to the unmixed temp
- Your joist radiant might be too high for the slab AND too low for your existing radiators to run properly.
problems that would indicate you need to do additional thinking here, once you've set up your outdoor reset and moved your high temp returns to the boiler side of the mixing valve cold leg:
A: radiator areas don't keep up or dont have even comfort through the rooms.
B: joist areas don't keep up, or have short demand periods of warm floors with long periods of cold floors in between.
C: Slab areas have "flywheel" problems with temperatures rising too much after heat demands.
D: kickspace doesn't run. honestly I hate those heaters... try to find something else to do there. otherwise, maybe you can run it off of your indirect water heater or something else that gives you fixed temp rather than ruining your reset curve.NRT.Rob
Up Against ItThe boiler is not a good fit for this application. One of the boilers that can handle at least 2 reset curves would have been a much better choice. I know......Too late in the game for that. You're going to have to do a lot of fenagling to get close to desired results.
okThe foil insulation in the joists is this stuff: http://www.homedepot.ca/product/reflectix-staple-tab-16x25/902357
It's made for that purpose so it should keep a lot of the heat up against the bottom of the floor (in theory, of course!).
Yeah, I know I might have some trouble with that kickspace heater. I think there is a low-temp switch I can get for it (which I'll have to if I keep it behind the main mixing valve). The reasoning behind using the kickspace is that this zone (#5 - back porch/powder room/upper bath) is on an addition on posts with no foundation.
Before I moved in it was a two-storey sun-porch kind of thing. I took it all down save the roof and two floors, re-studded/insulated/remodeled from basically nothing, and added a rigid foam>plywood>stucco skirt around the bottom. It was literally just on the two corner posts previously, but with adding the weight of laundry and two bathrooms I added another beam and centre post under it, then skirted it for more warmth.
All that to say when it gets wicked cold here (-40C not uncommon) any pipes underneath it will freeze. I had ice in one of the toilets the first year before I added the skirting with insulation. So in-floor hydronic wouldn't work. I was considering electric but the cost of operating my parents' 1200ft2 of electric on slab under tile turned me off of that. So now the line to the kickspace heater is in a bulkhead inside the insulated zone in the back porch. Then goes back up that bulkhead to the second story bathroom above.
I'm thinking I should remove the mixing valve I have after the heater (before the radiant loop) on this zone as it's probably a bit redundant and could hurt flow. After the trip up and through the heater it's not going to be burning hot under the floor anyways.
About the house itself: parts of our main floor is still original lathe-and-plaster with no insulation (just that old thick paper stuff). The entire second floor was gutted and insulated/vb'd/drywalled, still has the old original windows but with newer storm windows and perform pretty well. The attic has been converted to living space and is all new insulation and windows as well (no worries about heat up there!). The main kitchen was gutted and has new insulation and windows, and now the basement has been insulated/vb'd/drywalled, so all in all for an old house it's pretty tight.
I will try and re-route the rad returns to come in after the mix, that definitely makes more sense to me. Things you realize too late. Good thing copper's so cheap! yeesh...
foil is foilit's not really insulation. not very good insulation anyway, even though it has "radiant" in its name it's generally not adequate by itself. If you have access, add real insulation under it: R15 between heated spaces, 25 over tempered space, 35 over unheated space.
the point I'm making is you don't really know what your situation is. you can move stuff around and then find you are still in a problem zone, because you aren't planning this out with real information. real information in this case is a room by room heat load and analysis of the emitters. as long as you're fine with moving things around on that control panel "until it's right", so be it. but that's the price you pay.NRT.Rob
I understand...... that a more sophisticated approach would definitely yield more scientific results, but basically I lived in the house for two years and decided where I needed more (or way less) heat. Now it's just a matter of making some of the changes you suggested and living with it for a bit to note what's working and what's not. The control room will always be accessible so I'm not too worried if I have to take a week in the summer sometime and make some changes.
Thanks again for your help, a lot of the answers and suggestions you and the other guys gave had me smacking my forehead and wondering how I missed it, as it all makes so much sense after the fact.
-cut/close off loop after pump #6
-move rad returns to after mixing valve C stem
-add an outdoor reset
-pull out mixing valve after kickspace heater and get low temp switch
Should keep me busy for a while
noI don't think you should remove the mixing valve: you almost definitely need it here.
the only question is whether it should be on all radiant or just the slab zones.
the chances that those radiators will run at temps good for your slab are pretty small.NRT.Rob
Mixing ValveI agree with Rob. Don't remove the thermostatic mixing valve until you replace it with something better. It's not the right component for a slab, but it's better than nothing.
Again, a smart valve like Taco's "I series" that has built in reset or injection mixing with a Tekmar 356 are the best options. See the attached Tekmar essay for more info.
The boiler should have built in reset capability when an outdoor sensor is connected. You want to set its reset curve for the highest temp zone. Then set the slab's curve so it's parallel shifted to mirror the boiler's reset curve at a lower water temp. The slab's curve will be set on the device you choose (smart valve or injection mixing). Good directions come with either.Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
sorry, wrong mixing valveMy fault; sorry that was confusing, I meant that I might remove the mixing valve I have on the kickspace heater/upper bathroom loop (so not the main one on the manifold in the pictures). I installed this loop over two years ago when re-doing those spaces. So pump/loop #5 goes first to the kickspace heater then to a mixing valve, then to the radiant loop under the upper bath floor, then back down to the boiler room.
The mixing valve is behind the cabinet the houses the kickspace heater. That's the one I was considering pulling out for better flow and because I don't think the temp will be too hot for the radiant after it goes through the kickspace and up to the next floor (I could put in a temp gauge to verify, of course). Here's a very low-tech diagram of loop #5 attached.
Also I understand what you're saying Ironman about the curves and having them similar in shape but at a lower temp for the slabs, something I will deal with when I get the next set of components (outdoor reset, smart valve). All starting to make a lot of sense, thanks guys.
That can't workWhat is causing water to circulate through the mixing valve?
Add an ecocirc e3and turn the knob until you get the delta-T you need.
Yes, for sureMy point is, there has to be a circulator on the bathroom side of that mixing valve. It's not piped correctly no matter what; the floor mixed circuit should be piped with closely spaced tees off of the convector circuit and the mixing valve's "cool" inlet should be piped to the floor return, not convector return. The circuit as it is laid out now will not function properly even with a circulator on the floor side, as the mixing valve will restrict flow through the convector.
But you bring up an interesting point, and one I've been tossing about in my head for a while: are these highly efficient, adjustable pressure differential circs a good cure for the "loop too long" problem? In other words, just put them in series with the system circulator if you run into a situation with a loop or few considerably longer than others, and resulting flow issues. It's not zoning with circulators, it's more like an in-line booster.
added valve last nightI added a shut-off valve to the left of pump #6 last night as was suggested, but I'm not sure that it had the desired effect. It seemed like when that valve was closed, the temp gauge after the mixing valve still didn't move much past 70*. I played with the mixing valve's adjustment from coldest to warmest and in between, waiting a couple minutes each time to watch what the temp change was, but it really didn't do much. I was testing using pump #6 as it's just a plain short loop, but it was almost like it wasn't moving water at all; the pipe above its T wasn't warming up, nor was the temp gauge at the end of the loop.
Then when I opened the new valve to see where things were getting hot in the original configuration, I'm pretty sure #6 was drawing water somehow up through loops #1 and #2 (full-temp rad loops) and grabbing it from their return ends because #6 was the only pump activated but #1 and #2 were heating up and the pipe was hot to the left of #6.
So now my question is: could my mixing valve already be shot? It seems like water is going every which way to bypass it. The mix side of the mixing valve has not warmed up. Could the resistance going through it be that much that water would rather go up through 5 rads on loop #1 and 6 on loop #2 to bypass it?
Also the pipe between the return and supply is heating up to full temp. Now that I realize I don't have a true primary/secondary configuration but more of a supply and return, should I cut off the flow between those T's? Seems like during some of my testing/observing the boiler was utilizing its own mini-loop as the path of least resistance.
Anyways, after a true all-nighter the night before and 4:30 am last night, nothing much was making sense so I had to leave it be.
perhapsyou have installed the valve backwards. you would not be the first to do that.NRT.Rob
on pic aboveit shows the mixing valve installed. It's hard to make out but I'm 99% sure C is on the left, H on right and Mix on bottom. I'm at work right now so I can't give that extra 1% but I've looked at it enough that I'm pretty certain that's how it's orientated.
...unless that's not the right way of course!
wellhave H and C reversed, it would cause the kinds of problems you're talking about. you'd basically have a closed leg at that point. these valves DO have very significant pressure drops, so your behaviour when the valve is open is completely predictable (and is what I said was probably going to happen earlier in this thread, self pat heh)... but when that valve is closed if you are NOT pulling water through the valve at all, it's either busted, clogged, or backwards. Especially if you do get flow through that zone when the end of the header valve is open.
it's pretty unlikely that the valve is busted on a closed system. so that leaves clogged or backwards. Clogged would only be likely if this is a really scrungy system... existing cast iron radiators with really nasty water, maybe?NRT.Rob
didn'tsee this reply until now. Crossing my fingers that some of the nastiness from the old cast rads made its way into the valve and can be cleaned out.
And the self pat is approved, I'm certainly not giving myself any until I can right the ship a bit
personallyI'd cross your fingers that the valve is backwards. that's a one time fix.
really nasty water is a bigger issue for your boiler and all the other valves and such as well. then you want to consider dirt separation and maybe cleaning/treatment of the system.NRT.Rob
sorrydouble postThis post was edited by an admin on December 12, 2012 2:08 PM.
what do you thinkabout cutting off flow between the supply and return T's near the boiler? To me that would basically force the water to go through the mixing valve if pumps #3-6 are to move water at all.
I'm envisioning some repiping this summer it looks like. Closely spaced supply/return T's beside each other for each loop with separate mixes for each. The single mixing valve was an attempt which made sense to me to avoid having 4 such devices (one on each radiant loop).
onlyif you want to kill your boiler.NRT.Rob
I think...I should avoid doing that.
Do mixing valves get stuck often? It's on unions so if I took it out what would I look for or how could I test it? Just try another one?
you cantry purging through it with cold water and see if flow occurs.
or disconnect and see if you can see through it, blow through it, flush through it, etc.
they don't stick often IN CLOSED SYSTEMS, unless again you have really nasty water with gunk in it, typically from standing cast iron radiators or other "high particulate" sources.NRT.Rob
I willtry that. Some of the rads (all but 2, actually) were disconnected for quite a while while I removed the lines in the basement and replaced them with pex, so they may have had a lot of junk that had settled and was stirred up and passed along upon refilling. Hopefully it's as simple as that. The water coming out of my old pipes was very dark.
Update...Finally able to get online for any amount of time and fill you in (I know you've been on the edge of your seat!)
Looks like the two biggest fixes ended up being placing a cut-off after the 6th pump and bleeding the last two loops.
I removed the mixing valve from the 5th loop and installed a temp gauge in its place. I noticed that the Taco mixing valve I took out had the same dimensions as the Honeywell installed on my manifold, so I swapped it out (the Honeywell looked fine inside when I flushed it out).
Definitely the biggest problem however was air in the system. I finally read that the grundfos pumps I have don't really push air through, so I let some more pressure into the system and opened those lines and pushed (a lot) of air through. Let water come up through the pumps after disconnecting them from the top and a lot of bubbles came out (no bleed nipple/valve on these I guess).
Hooked it all back up and instantly had hot water going through all the loops.
Now I'm able to adjust the temp with the mixing valve and see the results within about 15 seconds on all the temp gauges, all the floors are warm when they should be (and the slab loops are amazing! stay warm very long after heat shuts off).
So basically it's all working really well (although I continue to monitor it pretty closely). Next step is to set the 5/2 thermostats and enjoy winter!
Thanks again for all the help!
I really like itWhen the original poster gives the details of the solution to their problem on these threads. Quite often the original problem comes up in a Google search, solutions are tossed back and forth, and then the thread dies with no resolution.
Like not having the ending chapter in a good mystery novel.
Like not having the ending chapter in a good mystery novel.This is my favorite example of one of those; by Mark Twain.
I also am frustrated when....that happens. Being a DIY'r who is waist-deep in a random project every weekend I know exactly what you're saying. Hopefully someone benefits from my outcomes, but really I just wanted to show as a new guy on the forum that I wasn't looking to use people in here for a quick answer and run off, I respect the time those above took to answer my questions.This post was edited by an admin on March 2, 2013 11:17 PM.