Indirect hot water : Oudoor Reset mode or Setpoint mode?

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  #1  
Old 01-06-09, 07:46 AM
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Indirect hot water : Oudoor Reset mode or Setpoint mode?

We recently replaced a very old (40+ years) Burnham oil-fired boiler with dometic hot water coil with a Peerless Pinnacle PI-140 gas-fired boiler and 40 gl indirect hot water tank.

As nearly as I can tell, if the indirect hot water tank circulator power and aquastat are connected to the relavant connections in the Pinnacle itself, the boiler operates in Setpoint mode whenever there is a demand for hot water.

On the other hand, if the indirect hot water tank circulator power and aquastat are connected as a third zone on the Taco Zone Control, a demand for hot water causes the boiler to operate in Outdoor Reset mode as it does for normal heating demand.

Question: which mode is preferred specifically in regards to DHW? If Setpoint mode, what would be appropriate settings for setpoint and differential?
 
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  #2  
Old 01-06-09, 10:27 AM
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You want the heat to be reset and the DHW to be setpoint. Depending on the piping of the Indirect it may be possible to connect to boiler. If piped to primary pipe instead of secondary boiler piping than it cannot be wired to the boiler.
See link
http://www.comfort-calc.net/ModCon/ModCon_wiring.html
Click on options under drawings and see if your piping matches one of the diagrams.
 
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Old 01-06-09, 11:37 AM
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Originally Posted by rbeck View Post
You want the heat to be reset and the DHW to be setpoint. Depending on the piping of the Indirect it may be possible to connect to boiler. If piped to primary pipe instead of secondary boiler piping than it cannot be wired to the boiler.
In my opinion, the installer grossly mis-wired the original configuration, but I won't get into the details here. Suffice to say, here is the way it is currently setup (by the way, in case it is not obvous, the Peerless Pinnacle has built-in Outdoor Reset Control functionality):

a) Indirect ("DHW") tank's aquastat leads are connected directly to the "DWH Sensor/Thermostat" screws on boiler's internal terminal strip. Power and ground leads for DHW tank's circulator are connected to boiler's internal terminals identified for that purpose.

When DHW temp goes below aquastat setting (125 deg F), boiler control energizes circulator and may or may not also fire up the boiler, depending on residual temperature of circulating water. Boiler eventually fires up in Setpoint mode, raises circulating water to setpoint + 7 deg (= 167 deg), then cuts out until differential (20 deg) is met.

b) Two heating zones (1st and 2nd floors) thermostats and circulators are connected to Taco SR503 zone control. Taco's X1 and X2 terminals are connected to boiler's central heating thermostat input terminals.

When any zone calls for heat, the appropriate circulator(s) comes on, boiler may or may not fire up immediately depending on residual temperature of circulating water. Boiler eventually fires up and operates in Outdoor Reset mode.


c) If simultaneous demand for DHW and Heat, both (or all three) circulators come on and boiler operates in Setpoint mode until DHW demand is satisfied, then continues in Outdoor Reset mode until heating demand is satisfied.

So, this is the current operation and I think it works well.

Comments are appreciated.
 
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Old 01-06-09, 12:05 PM
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Here's a quick & dirty sketch of the piping layout, done from memory. If I recall correctly, the expansion tank is connected to a riser off the end of the "boiler out" stub.

 
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Old 01-06-09, 04:01 PM
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You said:
the installer grossly mis-wired the original configuration,
and then you said:
this is the current operation and I think it works well.
Just so's I understand, I believe you are saying the the original installation 5ucked, and you either re-did or had it redone, and now it works great, correct?

I betcha that he had the indirect originally running through the SR panel set on priority, and as such, the water heater was running the boiler on ODR because the boiler had no way of knowing the diff between an indirect call and a space heating call, am I right?
 
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Old 01-06-09, 04:29 PM
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Originally Posted by NJ Trooper View Post
You said:

and then you said:


Just so's I understand, I believe you are saying the the original installation 5ucked, and you either re-did or had it redone, and now it works great, correct?

I betcha that he had the indirect originally running through the SR panel set on priority, and as such, the water heater was running the boiler on ODR because the boiler had no way of knowing the diff between an indirect call and a space heating call, am I right?
Almost! It was running everything on Setpoint, not ODR.

He had all three circulators connected to the Taco SR503. DHW circ and aquastat were connected to Zone 1, 1st floor circ/thermostat to Zone 2, 2nd floor circ/thermostat to Zone 3. The SR503 X1 and X2 terminals were connected to the DHW Sensor/Thermostat terminals on the boiler control. Therefore, any call for either heat or hot water resulted in the boiler running in Setpoint mode.

In fact, that is what caught my eye; I read the boilers manual from cover to cover and was curious about the Outdoor Reset programming. While monitoring operation, I noticed that with every cycle, the boiler would cut out at 187 deg (at that time the Setpoint was set at 180), instead of the much lower temp expected based on the outdoor temps of around 30-35 deg. My first thought was that something was wrong with the sensor, but investigation showed the real problem.

I (yeah, I know - I shouldn't do these things) re-wired it as described in my previous post and it now works as it is supposed to, I think.

One more thing - this one I just noticed a few days ago: inside the boiler, the yellow leads which are clearly marked "Supply Sensor" were in fact connected to the Return water temperature sensor and the blue leads, marked "Return Sensor" were, of course, connected to the Supply sensor. I have a feeling it may have come from the factory that way; I don't want to assume the installer did it.
 
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Old 01-06-09, 11:44 PM
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That piping diagram makes me wonder if your system is piped primary secondary. It doesn`t appear to be and it should be. The installer needs to better follow the manufacturer's I&O or your boiler won`t last long...
 
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Old 01-07-09, 04:40 AM
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Originally Posted by Who View Post
That piping diagram makes me wonder if your system is piped primary secondary. It doesn`t appear to be and it should be. The installer needs to better follow the manufacturer's I&O or your boiler won`t last long...
Looking at the manual (see image below), it appears that the piping is *not* done correctly. The heating loops, by the way, are of the "two pipe" variety - each of the radiators is tapped off a single large supply pipe and returns through an adjacent, equally large return pipe. Each of these two main "supply" pipes are plumbed to the boiler-out stub and the "return" pipes are plumbed to the boiler-return stub, as shown in my sketch.

What is the purpose of the primary loop? I am guessing it is to ensure that water can flow through the boiler regardless of whether circulators are running?

What are the dangers of the current arrangement? As it is now, I can tell you that I am getting good condensing action, good modulation, no unusual noises, and no errors reported by the boiler's control module.

I have to say that this exercise has resulted in lots of frustration for me as a homeowner who is trying to do the right thing. My contractor came well recommended by two co-workers, has a very good relationship with the local gas company reps and installers, and is listed on Peerless' web site using their "find a Peerless Installer near you" tool.

This page from the IOM manual shows the desired piping arrangement for my system:


 
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Old 01-09-09, 05:30 AM
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[bump]

Guys, I'd appreciate your thoughts on the last couple of posts in this thread.
 
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Old 01-09-09, 09:08 AM
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My opinion. If the boiler is not piped per the manufacturer's specifications, then it ain't right and needs to be redone.

The current configuration as you've diagrammed it is not per manufacturer specifications. Not even close. There is no way to ensure that the proper flow rate through the boiler's heat exchanger is maintained in this configuration. In fact, the required flow rate through the PI-140 is around 11 gpm. It is highly unlikely that the common-piping flow rate is anywhere close to that. This would be absolutely true when only one zone is calling for heat. No way. (But I will confess to being a bit confused by your description of how the heat emitters are piped, or what the heat emitters are, and that matters a bit -- baseboard? cast iron radiators? what size supply/return piping?) It's probably also true for the indirect. Most indirects, IIRC, typically specify a flow rate of 6-8 gpm to achieve rated performance.

You could even ask Pinnacle if such a configuration is acceptable.

I suspect they would respond with an emphatic "no," principally because the primary/secondary piping they require ensures a specific and constant flow rate through the boiler, which is necessary for the proper operation and longevity of this boiler's heat exchanger.

Not only does the piping need to be redone, but the installer will also have to ensure that the boiler loop pump is sized correctly. Refer him to page 7, table 3.4 of the manual (I'm looking at the Rev2 manual on the pinnacle site). A Taco 0010 or a Grundfos 15-58 set on speed 3 is required.

If he chooses another brand of pump, he will need to consult Table 3.3 on page 7 which shows the flow rate and pressure drop for the boiler. The pump will need to provide that flow rate (~11 gpm) at that head (8 ft) required for the PI-140.
 

Last edited by xiphias; 01-09-09 at 09:39 AM.
  #11  
Old 01-09-09, 11:38 AM
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I have to say that this exercise has resulted in lots of frustration for me as a homeowner who is trying to do the right thing. My contractor came well recommended by two co-workers, has a very good relationship with the local gas company reps and installers, and is listed on Peerless' web site using their "find a Peerless Installer near you" tool.
Had you contacted Weil-Mclain they may have said something like "We believe in the wholesale distribution model." (they did to me), implying that they keep a layer between them and their installers since they most likely don't want to stand behind their installers because of contractors who don't understand some of the technology. He piped your boiler like a conventional boiler and that was completely wrong for this particular type of boiler (as per the manufacturer).

That boiler needs more flow than your heating system. Just like Xiphias said, it's as simple as that.

That contractor effectively has ripped you off through incompetence or negligence. The boiler's operating life may have already been seriously jeopardized. Should that boiler fail, Pinnacle can simply say that it's piped incorrectly and then you're SOL.

Is that contractor aware yet that the boiler was piped incorrectly?

I'd actually insist on it being repiped AND a new boiler (unless the manufacturer puts it in writing that will stand behind this boiler down the road should it ever have an issue). I'm not sure how far you'll get, but yes it really sucks when you think you think have done due diligence about your contractor and then he doesn't know/care enough to read and follow the installation instructions.
 
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Old 01-09-09, 01:28 PM
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Originally Posted by Who View Post
That boiler needs more flow than your heating system. Just like Xiphias said, it's as simple as that.

...

Is that contractor aware yet that the boiler was piped incorrectly?
No, it's just in the last several days that I am beginning to realize the enormity of the situation. I haven't done anything yet because I am considering the options.

As to flow, each of the loops (two heating, one DHW) are being pushed by a Taco 007-F5 circulator. I am typically seeing 140'ish on the output temperature and 115'ish on the return temperature for the heating loops. The heating loops feed a number of old and quite large cast-iron radiators (the main pipes of each "two pipe" system are 2" I think), so there is a lot of water in each loop.

Sometimes life can be a real pain...
 
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Old 01-09-09, 02:54 PM
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So chances are very good that you do not have the necessary flow through the boiler.

For an old system like you describe, the contractor should also have installed a wye-strainer on the return so that all the old sludge and crud in the radiators and piping does not accumulate in the passageways of the heat exchanger. Those passageways are tight and can easily fill with crud which will definitely lead to the boiler dying a premature death.

I'm with Who on pursuing a new boiler or something in writing backing the current one.

At a minimum, you should insist that if the current boiler is reused, you get a wye strainer or some other form of robust dirt separation. You should also insist, absolutely and without compromise, that the existing heat exchanger be taken out, examined and cleaned according the manufacturer specifications. Preferably with a Pinnacle rep in attendance.

These are not your father's boilers. They are sensitive pieces of high-tech engineering design and electronics. There just isn't a whole lot of margin for error. Properly installed and maintained, they can be just fine. Not, is a different story.

Good luck and keep us posted.
 
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