boiler protection with a variable speed circulator


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Old 01-09-11, 01:35 PM
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boiler protection with a variable speed circulator

I have an old monoflow system with big cast iron radiators, a single circulator, and just one zone. Until recently, the system was set up to cold start (no DHW involved). We were not very happy with it as there was typically a 5+ degree difference between the first and second floors. After getting some really expensive quotes to split the system into two zones, I gave up on that idea.

In a fit of boredom I changed the aquastat over to do a warm start with the hope it would help recovery time and maybe smooth out some of the swings. This ended up helping quite a bit, but not exactly for the reason I expected. I should have predicted that helping recovery time was pretty much a non-starter. With the huge amount of water in the system, keeping the boiler a bit warmer doesnt really change much. When there is a call for heat, the circulator kicks on, the burner fires, and the boiler temp drops very quickly due to the incoming cold water. So just like with the cold start aquastat, the system spends a lot of time trying to recover.

The difference though is that with the new aquastat the circulator shuts down when the low limit is violated. Since the flow of incoming cold water has stopped, the boiler recovers quickly. The recovery, in turn, causes the circulator to start up again. This cycle will repeat itself a couple of times until the water in the system is warm enough that it no longer cools the boiler to below the low limit on the way through. Eventually, the call for heat is satisfied or the limit set by the ODR is hit.

So now, instead of a typical burn lasting 30mins and everything ending up way too hot, the burns last about 10mins and everything comes up to temperature more slowly. The first and second floor have been staying within a degree of each other.

I'm tempted to just declare success and go back to ignoring this boiler. But now that I've seen how much time it spends with the burner running and the boiler temp below 140, I'm wondering if I can make things better still. Regarding condensation I figure at this point I am no worse off (and probably better off) than I was when set up for cold start. One question I'd like to ask here is: am I?

My other question is about improving things. I am not (yet) interested in hiring a plumber to come in and set up a proper bypass, though that seems to be the prudent thing to do. I was hoping for more of a do-it-yourself solution. The idea that crossed my mind was replacing the circulator pump with a variable speed setpoint equivalent. I currently have a Taco 007-F5. I'm assuming that the 007-VSF5 would just bolt right in.

If I were to set the pump to keep the flow leaving the boiler at 140 or so, the effect would be similar to but much smoother than what the low limit control of the L7224U is now doing. What could go wrong?
 
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Old 01-09-11, 02:16 PM
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Hmm. I think you are trying to solve your problem with over complicated solutions. I am by no means an expert here. However, I don't think a variable speed pump will be able to do what you want. The temperature of your system is going to vary based on load. On the warmer days, the water in your radiators is going to come to cool off much more than during colder days when your boiler is cycling more often. I have noticed that with my own system.

A few questions:

Is this an oil boiler?

Do you have copper or black piping? If copper, adding the bypass will be really easy for you to do yourself.

Do your radiators downstairs have valves on them? If they do, have you tried partially closing them to try and balance the upstairs and downstairs?
 
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Old 01-09-11, 02:50 PM
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Originally Posted by drooplug View Post
Hmm. I think you are trying to solve your problem with over complicated solutions.
I think you are right

Originally Posted by drooplug View Post
I am by no means an expert here. However, I don't think a variable speed pump will be able to do what you want. The temperature of your system is going to vary based on load. On the warmer days, the water in your radiators is going to come to cool off much more than during colder days when your boiler is cycling more often. I have noticed that with my own system.
What I'd like is for the boiler to not cool down so much when it starts up. From the perspective of comfort, it seems to be doing what I want it to now. The changes I am considering are about the longevity of the equipment. When I was ignorant of the temps inside the boiler I really didnt care much. Now it might just become an obsession.

Originally Posted by drooplug View Post
A few questions:

Is this an oil boiler?

Do you have copper or black piping? If copper, adding the bypass will be really easy for you to do yourself.
It is an oil burner. While the boiler is fairly new, the piping is quite old and almost entirely black pipe. There are a couple of radiator runs where short sections of black pipe have been replaced with copper, but the original monoflo loop is still intact.

Originally Posted by drooplug View Post
Do your radiators downstairs have valves on them? If they do, have you tried partially closing them to try and balance the upstairs and downstairs?
It's the upstairs that's too hot, but yes, the radiators all have valves on them. I've played with them a bit to to no affect. My oil guy says "that happens"... meaning that the valves stop working over time. He says I'm lucky they failed in the open position. I got the impression that if we were to start playing with the piping at all, going the zoning route would be best... but perhaps he was just looking for a project. My skills with copper are passable but I wont even think about playing with black pipe.

A few $$$ for some bolt-in protection sounds like a good deal to me. I realize that from a systems perspective it's a complicated solution with expensive parts. From a DIY perspective it's really pretty cheap. Of course if it wont help at all or even hurt, I'd rather not bother.
 
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Old 01-09-11, 03:29 PM
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What about the near boiler piping. Is that black pipe as well? That is where the bypass would go. A bypass will lower the water temperature in the system (the pipes and radiators on the other side of the bypass). That will require the pump to run longer and it will be more comfortable. I think the warm start concept is flawed as well. You are spending quite a bit of money doing that. Thats cash that could go towards fixing your problem.

Those valves can be replaced on the radiators. You could even put TRV's on the second floor. These can only be used if each radiator has it's own supply and return. Thermostatic Radiator Valves , Honeywell Thermostatic Radiator Valves , Danfoss Thermostatic Radiator Valves - PexSupply.com

Are you sure you have a monoflo setup? There is one loop with each radiator tee'd off of the main loop?
 
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Old 01-09-11, 03:49 PM
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Originally Posted by drooplug View Post
Are you sure you have a monoflo setup? There is one loop with each radiator tee'd off of the main loop?
Yup... I'm sure it's monoflo and yes it's all black pipe too.

One of the plumbers who looked at the system suggested getting rid of all the black pipe from the basement and doing home runs from the radiator feeds using pex-al-pex. The other mumbled something about breaking it into two loops and doing constant circulation. When I asked about fixing the radiator valves I got the ole "once you start messing with pipes that old..."

So yeah, the TVRs might do the trick, but for me, that's about as much of a DIY as replacing the monoflo loop... and honestly, I'd be more inclined to replace the monoflo loop myself. At least then all the "damage" will be confined to the basement!
 
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Old 01-09-11, 04:08 PM
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Getting rid of all the black pipe sounds excessive. If the radiators on the second floor all have pipes going to the basement, you just need to disconnect them from the current main loop and connect them to a new one. I doubt you would even need a new monoflor loop for them. Just pipe them all in series. That's what I had done in my home. The original system piping in my house is 80 years old and doing just fine. I have two reasons for why I want to replace it: more headroom in the basement and to reduce the amount of water in my system. The pipes get fairly large in diameter. Otherwise they are just fine.

I think you need to find a plumber with a higher skill level to replace those valves.
 
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Old 01-09-11, 04:17 PM
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Originally Posted by drooplug View Post
Getting rid of all the black pipe sounds excessive
I'm pretty sure that's why he only suggested getting rid of it from the basement.

Originally Posted by drooplug View Post
I think you need to find a plumber with a higher skill level to replace those valves.
That's interesting approach to DIY ...but thank you for the suggestion.
 
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Old 01-09-11, 05:34 PM
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What is wrong with black steel pipe in hydronic systems (in the basement or wherever)? Answer: it's perfectly OK, and less expensive to boot. Whoever said it wan't is either inexperienced or trying to sell you a bill of goods.

If he suggested replacing the black pipe just in the basement, I have a theory. He would charge you big bucks and just replace the easiest to do - when in fact, none of the black pipe needs to be replaced.

Good luck.
 

Last edited by Mike Speed 30; 01-09-11 at 06:17 PM.
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Old 01-09-11, 05:49 PM
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dbeau, why not post some pics of your system? Maybe we can come up with some alternate suggestions once we see what you are working with?

Free account / Image hosting, free photo sharing & video sharing at Photobucket / upload pics there / post a link to your PUBLIC album here...

I'm thinking that one option that might work for you would be to go to a primary/secondary setup... and it might not mean that much more piping than adding the bypass.
 
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Old 01-09-11, 06:13 PM
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The boiler should be cold start as it was, a bypass pipe and I believe the pump is the wrong size. There is a lot of resistance to flow in monoflo systems. Each tee is worth 23 - 25ft of pipe. I would bump that pump up to 0010. Without calculating it I don't think you have enough flow in the radiation.
 

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Old 01-09-11, 06:43 PM
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Originally Posted by rbeck View Post
The boiler should be cold start as it was, a bypass pipe and I believe the pump is the wrong size. There is a lot of resistance to flow in monoflo systems. Each tee is worth 23 - 25ft of pipe. I would bump that pump up to 0010. Without calculating it I don't think you have enough flow in the radiation.
The loop is about 70ft and feeds 11 radiators of various size spread over two floors... all one zone.

Am I correct to assume that spending all that time burning at such a low temp is going to be a problem. A higher flow pump will only make that worse, right? ...at least until a bypass is in place that is.

I think it was something you wrote that said boiler protection was all about controlling the flow through the boiler. You went on to describe a couple of different bypass methods. Is controlling the flow through the boiler with a variable speed pump really that crazy?

The cost of having the bypass installed plus the cost of a larger pump would likely exceed the $500 for the fancy pump, no?

The low limit circ lockout seems to be providing at least some protection. Is there any harm in keeping it warm start?





 

Last edited by NJT; 01-09-11 at 08:42 PM.
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Old 01-09-11, 08:46 PM
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Before you do anything else...

FIX THE BAROMETRIC DAMPER! The face of the damper MUST be PLUMB, and the shaft of the flapper MUST be LEVEL! It absolutely can NOT work properly the way it's installed...

And WTH is the story with that expansion tank? Not enough room to install it? So they BEND IT to get it to fit? terrible workmanship there...

In the one pic it looks like the damper is sucking the tank into it!
 
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Old 01-09-11, 09:05 PM
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Originally Posted by NJ Trooper View Post
Before you do anything else...

FIX THE BAROMETRIC DAMPER! The face of the damper MUST be PLUMB, and the shaft of the flapper MUST be LEVEL! It absolutely can NOT work properly the way it's installed...
A new chimney liner is on the way. I plan to get that taken care of at the same time.

Originally Posted by NJ Trooper View Post
And WTH is the story with that expansion tank? Not enough room to install it? So they BEND IT to get it to fit? terrible workmanship there...

In the one pic it looks like the damper is sucking the tank into it!
I'm still wondering WTH about using oil. The whole unit was replaced just a few years ago. Notice the gas hot water heater? The picture makes the expansion tank look a bit worse than it is. Another 1/8 turn on the connecting pipe and it would be plumb. Of course then, it would have zero clearance with the water heater.
 
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Old 01-09-11, 09:43 PM
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Yeah... I wonder why they didn't go with gas when they had the chance? I'm assuming this was done before your residency?

Using a VS pump with monoflo's is going to unbalance the whole system. You need a decent flow to get them things working properly. As rbeck said, there is a lot of resistance in monoflo systems.

I do think your cheapest solution would be to go with the boiler bypass AND a bigger pump.

Less cheap but perhaps a better setup would be to go with a primary/secondary setup. Have the bigger pump moving the water through the system. I think if you had your heart set on a VS pump, you could use one on the boiler loop.
 
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Old 01-09-11, 10:29 PM
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Originally Posted by NJ Trooper View Post
Yeah... I wonder why they didn't go with gas when they had the chance? I'm assuming this was done before your residency?

Using a VS pump with monoflo's is going to unbalance the whole system. You need a decent flow to get them things working properly. As rbeck said, there is a lot of resistance in monoflo systems.
The point of the VS in this case is *not* to supply a variable flow rate but rather to throttle the flow just while the boiler is heating up. It would be running full speed as soon as the outlet temp hit 140... less up to that point. To my untrained mind, this would have the same effect as a bypass in that it would keep things warm enough to prevent condensation. All of this, of course, assumes that during the time the boiler is heating up, we dont manage to heat just the second floor! But that's exactly why I'm asking these questions.

The problem I am having is not so much a lack of heat, but uneven heat. The second floor is usually 5F warmer than the first. All of the radiators get plenty hot. I havent measured their temps so I cant say much about how evenly they heat. If low flow can cause this, I'm all for bolting in a larger pump.

The 007 that is currently in place appears to have come with the boiler. So it seems likely that no thought was put into its selection. What are the potential problems associated with going with an oversized pump?

Originally Posted by NJ Trooper View Post
I do think your cheapest solution would be to go with the boiler bypass AND a bigger pump.

Less cheap but perhaps a better setup would be to go with a primary/secondary setup. Have the bigger pump moving the water through the system. I think if you had your heart set on a VS pump, you could use one on the boiler loop.
I can live with the system as is but if there was a quick fix I'd be happy to try it. The thought of going through the process of finding someone to do the work and then taking time off work to entertain them is not my idea of fun. Add to that the uncertainty of our still being here in five years, and you might get my drift. The VS pump does sound like a nice toy. If it doesnt help at all here, I do have another boiler in need of a bypass loop ...and that one I fully expect to still have in five years.
 
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Old 01-10-11, 05:49 AM
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As RBECK states, monoflows are restrictive and they demand flow to work efficiently.
I would do a Primary loop around the boiler, with a VS pump driving off a tekmar Tn2 house control, injecting into the monoflow loop.
Set the monofloow to run 24/7 or even better get you can get a timer that turns it off a period of time after the last call for heat.

The constant circa will help spread heat and even out room temps.
The variable speed will give you boiler protection and full ODR.
The Tekmar will give you indoor feedback to really improve recovery and comfort.
 
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Old 01-10-11, 05:55 AM
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What rbeck said. Install a bypass and a larger circulator.

VS is huge overkill. You would be adding two circulators (one for a boiler loop, one for the injection) in addition to a third for the heating loop, which already needs a bigger one anyway.

VS also requires $$ controls.

And put it back to cold start. Warm start in this application is a huge fuel-waster.

You could add a simple outdoor reset control (e.g., tekmar 256, Taco PC700) and get a lot better performance and comfort.
 
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Old 01-10-11, 09:35 AM
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So which pump would you suggest? The 007 is handling almost 10' of head would you go to 0012 for the nice long curve? But it only does 14' of head, the 008 does 16' and the 0014 does 23'. But I also guess the other thing to take into consideration would be the flange spacing. (007) is only $255.00, I would spend that as an experiment. (actually I would go with a bigger pump depending on actual head of the system and the a little oversize for good measure or future expansion)

Even cheaper and higher head then 007 http://s3.pexsupply.com/manuals/1252..._PROD_FILE.pdf

 

Last edited by grumpy_guy; 01-10-11 at 09:55 AM.
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Old 01-10-11, 10:06 AM
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Originally Posted by xiphias View Post
What rbeck said. Install a bypass and a larger circulator.

VS is huge overkill. You would be adding two circulators (one for a boiler loop, one for the injection) in addition to a third for the heating loop, which already needs a bigger one anyway.
I am only talking about replacing the one existing circulator with a VS setpoint circulator.

Originally Posted by xiphias View Post
VS also requires $$ controls.
The taco 00-VS line includes the controls... though the package is pretty expensive.

Originally Posted by xiphias View Post
And put it back to cold start. Warm start in this application is a huge fuel-waster.
I figured warm start was only a fuel-waster in the off season and that keeping it warm during the heating season would help protect the unit. The ODR does a warm weather shut-down... it disables the warm start in the off season.

Originally Posted by xiphias View Post
You could add a simple outdoor reset control (e.g., tekmar 256, Taco PC700) and get a lot better performance and comfort.
I did (L7224U +ODR module)... and it does. It's only been a few days, but so far the temp difference between the floors is much smaller.

Now I am just looking for "bolt-on" protection for the boiler. Of course all of these suggestions on how to really fix the problem are most welcome. The question of which circulator to get to replace the 007 certainly sounds worth exploring too.
 
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Old 01-10-11, 02:42 PM
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A VS circulator is not a good application in a monoflow system. Monoflows need a decent flow rate or things go kerflooey.

Glad you recognize that you are sort of reverse engineering this system....

You can get a good educated guess about what circulator would be appropriate using this:

http://www.taco-hvac.com/uploads/Fil...irculators.pdf

If you're handy with a spreadsheet, only takes an hour or so.

Grumpy if that question about what to choose is directed to me, then my response is to first pick a circ based on the desired flow characteristics. Typically 2-4 ft/sec. Maybe a bit more for a 2-story single zone monoflow system. For the single zone in question here, shape of the curve doesn't matter. Everything is constant, so match the circ to the target flow rate, trying to keep in the 60-80% range or so of the performance curve (i.e., not deadheading and not wildly overpumping).
 
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Old 01-10-11, 05:08 PM
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A VS circulator is not a good application in a monoflow system.
I don't think it's a good application for ANY primary system circulator. VS circs have very specific jobs that they were designed to do and this ain't it.
 
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Old 01-10-11, 05:10 PM
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My Head Hurts

Yes it was directed at you, sorry for not being clearer.

I thought the idea behind variable speed pumps was to help alleviate the math and keep the system at "best performance". The Taco pumps are pressure or Delta T controlled while Grundfos is pressure control or user choice. (guess Taco has user choice too)

Anyway with the op closing valves creating a greater pressure against the pump would a variable speed pump not be able to compensate. No matter the type of system.

One of the reasons this thread interest me so much is that I'm adding TRV's to 4 heat emitters. So I went out and put my money were my mouth is and bought a Grundfos ALPHA, my piping is 2 pipe direct without monoflow T's. (is this considered parallel?)
 
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Old 01-10-11, 05:22 PM
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There is a lot of energy saving with constant circulation, read up on it if you don't believe me.
Selecting the system circulator smartly and even getting the timer, will save you more fuel than the power required to run the circ.
A variable speed on a monoflow system, well an alpha is ECM so it's cheaper to operate but you will not gain anything from it's electronics. It may actually interfere with a monoflow system. Perhaps a Taco VDT set to maintain 10-20 degrees delta T, but thats pretty expensive for something a globe valve will do.

An alpha for a zoned system, that's a good choice. It will perform well in that application.

The additional 2 circus needed to do primary - secondary piping along with the controls is money well spent in my mind.
Sure it's capital cost but it will pay back.
 
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Old 01-10-11, 06:21 PM
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Grumpy, yer gonna get mixed up answers because we are focusing on dBeau, whose thread it is... you are welcome to read and comment, but please allow the focus to stay on dBeau's questions.

My comment was directed toward his issues...

In some cases a VS circ properly configured can operate as a system circ, and yours may well be one of those cases. But not in someone else's thread...
 
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Old 01-10-11, 06:37 PM
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My apologies if I seem rude, it's not my intention. If I really wanted my system fixed, I would just pay someone to do it (and then someone else to fix their mistakes). But since I am trying to learn about these systems, I have to call you on your unsubstantiated claims.

Originally Posted by xiphias View Post
A VS circulator is not a good application in a monoflow system. Monoflows need a decent flow rate or things go kerflooey.
Kerflooey as in bye-bye house and neighborhood kerflooey... or kerflooey as in damn it's chilly and/or hot in here kerflooey? What is it about a VS circulator that makes you think it's not capable of decent flow? It's my understanding that its just like any other circ with the same pump specs. The only difference is that it has a fancy control system that *can* based on sensor input change it's flow. Imagine for a second that the control was set to always pump full speed. I really doubt the monoflo system would know... please though, correct me if I'm wrong.

Originally Posted by xiphias View Post
Glad you recognize that you are sort of reverse engineering this system....
There's nothing reverse about it. I'm just looking at system's requirements and trying to put parts in place to meet them. It's basic engineering really. The hard part for me is determining the system requirements and that's where you guys have been very helpful. Thank you. But yeah, I get the feeling I'm heading into unexplored territory.

Originally Posted by xiphias View Post
You can get a good educated guess about what circulator would be appropriate using this:

http://www.taco-hvac.com/uploads/Fil...irculators.pdf

If you're handy with a spreadsheet, only takes an hour or so.
I'll take a look. Thanks.
 
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Old 01-10-11, 07:02 PM
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Originally Posted by TOHeating View Post
A variable speed on a monoflow system, well an alpha is ECM so it's cheaper to operate but you will not gain anything from it's electronics. It may actually interfere with a monoflow system. Perhaps a Taco VDT set to maintain 10-20 degrees delta T, but thats pretty expensive for something a globe valve will do.
Now we are getting closer to what I'm talking about. Imagine a system where you only have access to the circulator with no options for changing the plumbing on a boiler that has a condensation problem. If only we could keep the boiler temp above 140 we'd be all set.

What I am trying to explore is the idea of changing the circulator to a VS in reverse setpoint mode. With the sensor on boiler outlet and the setpoint around 140, the VS will operate at full speed so long as the the outlet temp is 140 or higher. Any lower and the VS will slow the flow through boiler to get the outlet up to 140. If things are really cold, it would be just like the aquastat shutting down the circs to let it recover. The flow through the system is likely to be slow only for the first couple of minutes of a burn... or not at all if the system was already up to temp.
 
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Old 01-10-11, 07:18 PM
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You are trying really hard to push your idea in the opposition of several very knowledgeable members here. I know you think it will be the easier solution, but it isn't. I don't know what your capability is when it comes to plumbing work, but I think you could fairly easily remove some of the near boiler piping and replace it with copper. Go back to cold start. This is will be far cheaper then trying this complicated method which probably won't work.
 
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Old 01-10-11, 07:23 PM
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Give this a read before you get too frustrated.
http://www.tekmarcontrols.com/litera...robat/e021.pdf

It will explain pretty much explain what I am talking about and how it protects the boiler, and allows full reset of the heating terminals.
 
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Old 01-10-11, 07:35 PM
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Originally Posted by drooplug View Post
You are trying really hard to push your idea in the opposition of several very knowledgeable members here. I know you think it will be the easier solution, but it isn't.
My apologies if I come across that way. What I am trying to do is to get some opinions on an idea that I had. I really do appreciate the knowledge here and the willingness of those who have it to share. It really has nothing to do with what is easier or what is cheaper. It does have a bit to do with what I am willing to with a couple of hours of my weekend time.

While I am sure I could learn, and someday I am sure I will give it try, I am not interested in doing any plumbing and even less interested in hiring someone to do it for me. Right now the house is comfortable and we'll likely sell it before the boiler rots. That said, I wouldnt mind making things better.

Originally Posted by drooplug View Post
I don't know what your capability is when it comes to plumbing work, but I think you could fairly easily remove some of the near boiler piping and replace it with copper. Go back to cold start. This is will be far cheaper then trying this complicated method which probably won't work.
Replacing a circulator seems pretty straightforward. If it doesnt work, I can put the old one back in with little risk. If I drain the system and start messing with the plumbing, there is a pretty good chance that something bad will happen that will leave me without heat. I'm not willing to risk the time or discomfort.

I do understand that the suggestions being made are the right way to go. I'm just interested in a low risk way that might not be wrong. At the start of all this I was half expecting that someone would say "oh yeah, we do it like that all the time". Now I get the feeling that it's never been done that way. Does that make it wrong? ...if so why? ...it's just how I learn.
 
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Old 01-10-11, 08:48 PM
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With the sensor on boiler outlet and the setpoint around 140
It's not ONLY the boiler outlet temp that you need to be concerned about. It's MORE so the RETURN temps, and to some extent the AVERAGE temp inside the boiler. If you are returning 70 degree water and the outlet is at 140, that gives an AVERAGE temp in the boiler of 105... and that means the 'c' word.

With a circ running slowly, you will probably be a lot longer waiting to feel any heat in the home. Especially with a monoflo system. It's all about pressure differences across the tees. With a slow lazy flow you won't develop the pressure difference you need to move the water out of the main and into the radiators... s l o w to heat. AND unbalanced... if you have 140 water moving slowly through the system, it will cool off by the time it gets half way around the system.

You want to MAXIMIZE the flow in the system. You want flow to all the radiators so that they start to heat. You want heat ALL AROUND the system. For that reason the flow in the system needs to be maximized.

A bigger pump and boiler bypass meets these requirements. The flow through the system is always maximized. The flow through the boiler is slowed to allow the average temp in the boiler to be raised by increasing the delta T across the boiler. Once the water starts to warm it is moved through the entire system quickly. The entire SYSTEM heats up at the same time, not just the first couple of radiators.

TO's (and my) suggestion of going P/S is obviously more 'spendsive but also meets the goal of even heating in the home, and boiler protection. Maybe even somewhat better protection than the simple bypass.

The flow through the system is likely to be slow only for the first couple of minutes of a burn
Maybe... if you only care about the supply from the boiler at 140 and no concern for the temp of the water returning to the boiler. You need to have a handle on that as well.

Now I get the feeling that it's never been done that way. Does that make it wrong? ...if so why?
I would say yes, it does make it wrong, for the reasons above. (and more I can't think of I'm sure!)
 
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Old 01-10-11, 09:56 PM
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Originally Posted by NJ Trooper View Post
It's not ONLY the boiler outlet temp that you need to be concerned about. It's MORE so the RETURN temps, and to some extent the AVERAGE temp inside the boiler. If you are returning 70 degree water and the outlet is at 140, that gives an AVERAGE temp in the boiler of 105... and that means the 'c' word.
Understood. I chose the outlet temp as representative because I felt the inlet temp would be less likely to change with no/little flow. Without a second well, there really isn't any other place to put the sensor. I agree though that it's not ideal.

Just to be clear, please note that I am not suggesting limiting the output temp to 140, I want it up at the ODR limit. I am just suggesting going slow until things heat up.

Originally Posted by NJ Trooper View Post
With a circ running slowly, you will probably be a lot longer waiting to feel any heat in the home. Especially with a monoflo system. It's all about pressure differences across the tees. With a slow lazy flow you won't develop the pressure difference you need to move the water out of the main and into the radiators... s l o w to heat. AND unbalanced... if you have 140 water moving slowly through the system, it will cool off by the time it gets half way around the system.
My system is currently running with the low limit circulator lockout keeping the circs off until 140. When they do kick on the temp quickly (30 seconds or so) drops below the low diff setting and the circulator turns off again. This happens just a couple of times at the start of each burn. Note that the burner stays running the whole time. I thought the VS approach would smooth out the start/stop of the circ. Once the temp is able to stay above 140, its full speed ahead until the call ends or the high limit trips.

At least in terms of condensation, I'd think this would be better than running in the 120-130 range for 5-10mins at a time which is the current state of things (when running cold-start).

Originally Posted by NJ Trooper View Post
You want to MAXIMIZE the flow in the system. You want flow to all the radiators so that they start to heat. You want heat ALL AROUND the system. For that reason the flow in the system needs to be maximized.

A bigger pump and boiler bypass meets these requirements. The flow through the system is always maximized. The flow through the boiler is slowed to allow the average temp in the boiler to be raised by increasing the delta T across the boiler. Once the water starts to warm it is moved through the entire system quickly. The entire SYSTEM heats up at the same time, not just the first couple of radiators.
...and this really seems to be the problem I am having. I'm going to take a stab at the math for sizing the circulator.

Originally Posted by NJ Trooper View Post
TO's (and my) suggestion of going P/S is obviously more 'spendsive but also meets the goal of even heating in the home, and boiler protection. Maybe even somewhat better protection than the simple bypass
If I decide to get a plumber in and make some changes, I'll certaintly go this way.

Originally Posted by NJ Trooper View Post
Maybe... if you only care about the supply from the boiler at 140 and no concern for the temp of the water returning to the boiler. You need to have a handle on that as well.

I would say yes, it does make it wrong, for the reasons above. (and more I can't think of I'm sure!)
Wrong it is. I can see where you are coming from. Now by implication, it's pretty clear that my current piping, with no bypass or protection of any sort, is also wrong... possibly more wrong? The thought of all that cold water currently going into my boiler makes me cringe. I was hoping for a "better than nothing" but it sounds like my idea doesn't even make it over that bar.

I really appreciate the analysis. It was quite helpful.
 
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Old 01-12-11, 07:58 PM
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it's pretty clear that my current piping, with no bypass or protection of any sort, is also wrong... possibly more wrong?
Unfortunately, in this industry continuing education seems to be sadly lacking. Many of the guys that have been doing this for years and years are not up on the latest stuff. The 'young blood' that comes into the field pretty much learns from the old timers... who have "always done it that way". So that's what they learn.

Then, most homeowners aren't going to know there's 'something wrong', because the home heats up just fine... so systems keep getting installed just like in the old days... and there's no 'driving force' pushing anyone to do anything differently.

Back in the old days, when boilers had big wide open flue passes, and the flue gas came out at a million degrees, there just weren't the issues with things like flue gas condensation (FGC), so nobody thought twice about it. Fuel was cheap, and boilers lasted forever.

When a homeowner goes out for quotes on a new installation, they aren't going to choose the guy at the top dollar mark... and maybe they shouldn't, but it's possible that HE is the guy that has done his homework, and knows that he has to repipe half the system to 'make it right'. Instead, they might choose the guy who will cut out the old boiler and simply hook it to the old pipes...

So, is it wrong? Yeah... but I would venture to say that MOST of the installers you talk to will tell you "NO, IT'S FINE! We've been doing it that way for 35 years!"
 
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Old 01-12-11, 08:06 PM
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I was hoping for a "better than nothing" but it sounds like my idea doesn't even make it over that bar.
Your idea for the Low Limit circulator control actually does have some merit... At a quick glance it does seem to meet some of the criteria for boiler protection, but what bothers me about the approach is that the boiler gets hot... the circ turns on... and glub, glub, glub, alla sudden the hot boiler is drowning in cold water. That CAN'T be good for it!

The idea of the VS pump has it's own detractions as already mentioned.

But, the GOOD thing in all this is that you are keeping an open mind, which means you will learn something! and IMHO, that is the BEST thing!
 
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Old 01-12-11, 08:36 PM
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I don't know if this has been mentioned?

HYDRAULIC SEPARATION

The beauty of the primary/secondary scheme is that there is a certain amount of hydraulic separation. You can achieve two distinctly different flow rates in the same connected piping, but one will not affect the flow in the other. In this way, you can have the full flow in the system at all times. At the same time you can have a different flow through the boiler. In effect, you will be 'injecting' heated water into the system loop while not affecting it's flow, and controlling the flow through the boiler to offer protection to it.
 
 

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