Avoiding Deadheading (low flow) in Mod-Con Boiler ???


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Old 12-19-09, 06:26 PM
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Avoiding Deadheading (low flow) in Mod-Con Boiler ???

OK, complicated questions perhaps, though it boils down to simple one I think.

I have a relatively new Triangle Tube Mod-Con boiler. The installer used a CH pipng system, with two circulators, both of which run much of the day, since my system has multiple zones. Zones are therms, with zone valves, not thermostatic heads.

I hate the idea of two circulators running all the time. Read Siegenthalers book (actually bought it) and found this ppt on the web as well. Great reading:

Siegenthaler Presentation Small


Talked to Triangle Tube re using a single system/boiler circulator. Their install manual describes this layout, and indicates that a pressure differential bypass valve should be used. The Triangle fellow noted that the boiler circ must run for a minute or so after the therm no longer calls for heat, to allow for cool down in the heat exchanger. There must be flow (ie no dead heading).

The TT rep was actually amenable to the use of the variable speed Grundfos Alpha as the main system/boiler circ, BUT, there must be a means of avoiding the deadhead issue.

Since the Grundfos Apha uses its own circuitry to maintain a constant pressure, useing a differential pressure bypass won't work. The TT Rep suggested perhaps a N.O. valve that would open during the cool down phase or a three way valve.

Both of those ideas seem reasonable, BUT!!!

Honeywell lists their N.O. valve as not for being "continuous duty" and since in cold months the system runs (one zone or the other) nearly continuously, I think thats out.

Honeywell has a 3 way, VC series valve that is listed as "15% duty cycle" --- But does that apply to just when the valve is changing positions, or ???? I need to call Honeywell, but finding someone to talk to a DIYer is tricky

Anyhow, ideas??? Thoughts??
 
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Old 12-19-09, 06:49 PM
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Pipe it primary/secondary and the boiler pump will always be able to circulate without deadheading.
 
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Old 12-19-09, 06:59 PM
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Belimo. They make a ton of great valves for all kinds of applications.
 
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Old 12-19-09, 07:13 PM
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Originally Posted by ZL700 View Post
Pipe it primary/secondary and the boiler pump will always be able to circulate without deadheading.
It IS piped that way. Works fine, but runs two circs RTC on cold days.

Whole point of some of the newest discussions in efficiency is to avoid unnecessary circ pumps. Even those "little" loads of 40w add up to big numbers after days/months/years.

That's the whole point of the Siegenthaler discussion. Bright fellow.....

I will try the Belimo valves. Any suggestions what to search for?

Thanks for the suggestions so far.

later....
 
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Old 12-20-09, 12:25 AM
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IIRC, they have valves that are N.O. and only draw power when opening or closing. Might have to find a distributor and ask if it's not obvious on their website.

You might also look at the Taco EBV. I think it has a N.O. flavor.
 
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Old 12-20-09, 06:43 AM
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It IS piped that way.
I don't understand... if it IS piped as primary/secondary, then how can you deadhead the pump?
 
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Old 12-20-09, 06:56 AM
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Originally Posted by NJ Trooper View Post
I don't understand... if it IS piped as primary/secondary, then how can you deadhead the pump?
I intend to change the piping, if I can solve the deadhead issue. Perhaps I didn't make that clear enough. Sorry.

I checked out Belimo. They DO have N.O. valves that have an end switch, which would be the ticket for my installation, but no clear indication if the switch can handle hours/days of operation. Thanks for the tip. I think I will try and call them -- I don't trust local shops or distributors to know the duty cycle answer.

The Honeywell zone valves do draw a little current when activated (obviously more when they are actually changeing position).

I'd love to get the guru himself (Siegenthaler) to give the answer to this one -- its right down his alley. This is really a simple problem that is created with the advent of the new, high tech pumps that control pressure automatically. They hold much promise for energy efficiency (read his ppt) but the "rules" for useing them are not yet perfect I suspect.
 
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Old 12-20-09, 07:10 AM
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I have been a Siggy devotee for several years. Check out Plumbing and Mechanical where he writes a monthly column, and does a 'glitch and the fix' column as well. Cool stuff.

The issue of assuring proper flow through modcons with direct piping and the new ECM pumps is fairly new.

There will be good strategies for this, but it might take a bit of manufacturer thinking and testing before they become really robust. My suggestion would be to watch for a while and look at this next summer/fall to see where everybody is.

One thing you might consider is just swapping out the two pumps for a Wilo ECO or Grundfos Alpha. The boiler circ could be set at fixed speed, and the system circ could be dP. Still two pumps, but the total draw would be half or less. (FWIW, when the Alpha is available with conduit wiring in a couple months, I'll probably put one on each of my zones. Not worth a total reconfiguration with ZVs, zone control, etc., but just swapping can reduce draw of this near-constant circ system to a pretty low level.)
 
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Old 12-20-09, 11:19 AM
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Originally Posted by xiphias View Post
I have been a Siggy devotee for several years. Check out Plumbing and Mechanical where he writes a monthly column, and does a 'glitch and the fix' column as well. Cool stuff.

The issue of assuring proper flow through modcons with direct piping and the new ECM pumps is fairly new.

There will be good strategies for this, but it might take a bit of manufacturer thinking and testing before they become really robust. My suggestion would be to watch for a while and look at this next summer/fall to see where everybody is.

One thing you might consider is just swapping out the two pumps for a Wilo ECO or Grundfos Alpha. The boiler circ could be set at fixed speed, and the system circ could be dP. Still two pumps, but the total draw would be half or less. (FWIW, when the Alpha is available with conduit wiring in a couple months, I'll probably put one on each of my zones. Not worth a total reconfiguration with ZVs, zone control, etc., but just swapping can reduce draw of this near-constant circ system to a pretty low level.)
Yes, you are right I think. I have already put an Alpha in the secondary loop. And the electrical savings of the Alpha when its in fixed speed (such as the boiler loop) is not that great so I am waiting there. $250 or so for the Alpha eats a lot of $$ saved (but I am doing this more out of principle and curiosity, than out of true $$ savings anyhow).

Of course, there is also the issue of why the boiler pump (also a Grundfos, but a 15-58) is on high speed even though the estimated head of the boiler loop is only 4 ft. With that head, even the lowest setting should maintain the proper flow (min 5 gpm on high fire) pretty easily. But that's another topic....

I will check out Siegenthalers columns.....
 
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Old 12-20-09, 12:28 PM
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what kind of electrical difference did you notice between alpha and non-alpha?
 
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Old 12-20-09, 01:17 PM
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Originally Posted by xiphias View Post
what kind of electrical difference did you notice between alpha and non-alpha?
Well, the alpha replaced a Taco 007, so its hard to tell, and I did not have a dedicated watt meter attached to the 007, although they are rated at .8 amp, so about 90 watts.

I have needed to run the alpha on constant pressure level 3 (the highest at about 12 ft head acc to the literature) to get one of my worst loops to flow adaquately. That means between 30 and 43 watts most of the time, acc to the alpha's digital display.

Still a pretty good deal, I think, compared to the 007.

I tried the Autoadapt setting for the alpha, but like I said, the one loop would show zero flow rates when it was calling for heat by itself. I used the fixed speed settings to roughly estimate my "bad" loop at 17 ft of head, including common piping.

Interestingly, although the loop flows zero on Autoadapt, it flows about 2 gpm on the fixed III (fast) speed setting and also shows 2 gpm on the highest constant pressure setting. I suspect that this only reveals the relative inaccuracy of the digital readout.

I bought the Alpha because the CH (boiler) circ is a Grundfos, as well as the DHW. I actually got the Alpha hopeing to reduce some flow noise in the house, which was only modestly sucessful. I think I am getting some flow noise from the CH circ still, which is a UPS 15-58F, set on its fastest setting.

I wish I had bought one of the new taco dT (temperature) sensing units in some ways, as I think for therm/zone valve controlled loops, the temp sensing (as opposed to flow) units might be better.

But you cannot argue with Grundfos reliability either....
 
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Old 12-20-09, 04:49 PM
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Not sure the dT approach is all it's cracked up to be, unless your system piping and emitters are set up to handle it. Series loop baseboard, for example, would need to have progressively more radiation along the loop (i.e., designed for it, not like a typical retrofit which probably wasn't). And even so, at warmer outdoor temperatures the end of the loop might be seeing non-useful temps. For example, if the dT is 20 and supply is 100, the end of the loop is down around 80.

There are other potential issues with TRV systems, etc. etc., but the above is probably the most concerning.

Home-run type piping set up for a dT=20 would be better, of course.
 
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Old 12-21-09, 02:31 PM
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Was able to have a useful conversation with a Belimo tech today.

He notes that all spring return zone valves require some small ammount of current to keep them open (or closed in the case of a N.O. valve) and as such, if the are called upon to remain "actuated" for long periods of time, they will likely fail prematurely.

He suggested that I try a CCV valve with a non-spring returning actuator. These valves have three terminals, C A and B and open or close depending on whether A or B gets current. They do not "fail" to one or the other position and once they have moved to a given (open or closed) position, they will stay there with no further current. If power is lost, they stay put.

For this approach, I would need an external controller (which I already have) which would make the control wiring less elegant (meaning more mesy) but it would work.

So I think I have found an approach to cause a valve to open to allieviate deadhead problems in a multiple zone system, during end of cycle cool down.

Thanks for Belimo suggestion. They were very helpful.
 
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Old 12-22-09, 05:02 AM
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Originally Posted by cdherman View Post
OK, complicated questions perhaps, though it boils down to simple one I think.

I have a relatively new Triangle Tube Mod-Con boiler. The installer used a CH pipng system, with two circulators, both of which run much of the day, since my system has multiple zones. Zones are therms, with zone valves, not thermostatic heads.

I hate the idea of two circulators running all the time. Read Siegenthalers book (actually bought it) and found this ppt on the web as well. Great reading:

Siegenthaler Presentation Small


Talked to Triangle Tube re using a single system/boiler circulator. Their install manual describes this layout, and indicates that a pressure differential bypass valve should be used. The Triangle fellow noted that the boiler circ must run for a minute or so after the therm no longer calls for heat, to allow for cool down in the heat exchanger. There must be flow (ie no dead heading).

The TT rep was actually amenable to the use of the variable speed Grundfos Alpha as the main system/boiler circ, BUT, there must be a means of avoiding the deadhead issue.

Since the Grundfos Apha uses its own circuitry to maintain a constant pressure, useing a differential pressure bypass won't work. The TT Rep suggested perhaps a N.O. valve that would open during the cool down phase or a three way valve.

Both of those ideas seem reasonable, BUT!!!

Honeywell lists their N.O. valve as not for being "continuous duty" and since in cold months the system runs (one zone or the other) nearly continuously, I think thats out.

Honeywell has a 3 way, VC series valve that is listed as "15% duty cycle" --- But does that apply to just when the valve is changing positions, or ???? I need to call Honeywell, but finding someone to talk to a DIYer is tricky

Anyhow, ideas??? Thoughts??
Probably a little late in on this one but...
Use a normally closed zone valve, then open it whilst the pump is on but no zone valves are on.

Use a 120vac x 24 vac transformer powered from the pump output to power the valve and a relay or two on each zone and use the NC contacts in series to connect the 24vac source to the NC zone valve actuator.
 
 

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