Functions and/or features to look for in a new Aquastat

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Old 12-10-12, 08:07 PM
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Functions and/or features to look for in a new Aquastat

[editor note - this post COPIED to this thread as it was the seed of the discussion that followed in the other thread Mike mentioned below...]

The relays that Honeywell builds into these controllers are garbage. I would rather see you cannibalize the actual thermostatic switch from the controller and then build your own with a decent plug-in relay, control transformer and other components as necessary.

I have never used a stock aquastat for many reasons and chief among them is the lousy quality, but high cost of the standard units.
 

Last edited by NJT; 12-11-12 at 04:14 PM.
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Old 12-10-12, 09:30 PM
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[editor note - this and several posts following were MOVED from the previous mentioned thread]

Furd post a couple pics of what you prefer, please.
 

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Old 12-11-12, 01:06 AM
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Picture of what? An aquastat is merely an adjustable temperature sensitive switch with a control transformer and a relay. I use any common 120 / 24 volt control relay along with a 24 volt AC relay such as a Potter & Brumfield KRPA 11AG-24 which is an eight-pin plug in plastic cased general purpose relay.

Now if you want to get fancy I would use a digital meter with dual setpoint output such as a Newport Quanta Q2001 with a K thermocouple input. With this unit you get a digital panel readout accurate to about 1 degree with set point relays that can be configured to set both cut-in and cut-out temperatures with as wide a differential as you wish. Downside is that it costs in the neighborhood of $500.

Many different ways to do the simple job of starting and stopping the circulator and the burner.
 
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Old 12-11-12, 06:16 AM
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I know if I was to build an aquastat from scratch for my system, I'd set a delay between the time the circulation pump starts and the time the boiler fires. Something in the neighborhood of 1-2 minutes.
I'm not sure about other setups, but my boiler holds the heat a very long time. If I keep the t-stats set to a static temp (say 68'F), the circulation pumps might be able to satisfy the heat call without the need to fire the boiler. Would save some short cycling and some heating oil.
 
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Old 12-11-12, 06:49 AM
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a delay between the time the circulation pump starts and the time the boiler fires.
Temperature rather than time sensitive would make more sense I thing, as with the Burnham MPO (and other) current systems. They call it "Pre-Purge" whereby if the boiler is above 140 at beginning of heat call, pump only will run. If boiler then cools below 140, burner will fire.

I wish that 140 setting was user configurable. I would like to be able to go down to 120.
 
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Old 12-11-12, 07:19 AM
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Temperature rather than time sensitive would make more sense I thing, as with the Burnham MPO (and other) current systems. They call it "Pre-Purge" whereby if the boiler is above 140 at beginning of heat call, pump only will run. If boiler then cools below 140, burner will fire.

I wish that 140 setting was user configurable. I would like to be able to go down to 120.
You still have it better then what I have. Even with the cold start, my boiler never really gets below 150. This is probably due to the old, low efficiency rads I currently have and the fact my boiler holds heat really well if the water isn't moving.
 
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Old 12-11-12, 08:07 AM
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Furd

Picture of what? An aquastat is merely an adjustable temperature sensitive switch with a control transformer and a relay. I use any common 120 / 24 volt control relay along with a 24 volt AC relay such as a Potter & Brumfield KRPA 11AG-24 which is an eight-pin plug in plastic cased general purpose relay.

Now if you want to get fancy I would use a digital meter with dual setpoint output such as a Newport Quanta Q2001 with a K thermocouple input. With this unit you get a digital panel readout accurate to about 1 degree with set point relays that can be configured to set both cut-in and cut-out temperatures with as wide a differential as you wish. Downside is that it costs in the neighborhood of $500.

Many different ways to do the simple job of starting and stopping the circulator and the burner.
No--fancy isn't for me. Just wanted to see your scratch-built aquastat with hi/lo limits, adjustable differential & circulator control relay. Hopefully it's all in one box--my boiler already has enough cobbled-on gadgets already.
I could probably fab something up but why re-invent the wheel when you've already done it?
Thanks.
 
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Old 12-11-12, 01:22 PM
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Functions and/or features to look for in a new Aquastat

After one of the other threads went slightly off topic about what would be the perfect aquastat and it's features, I figured I'd start a thread about just that.

With my current system, I'm using running a Comet 145 Oil Boiler with a slightly modified L8124L Aquastat (cold start mod).
Currently running two zones (pump each) using a White-Rodgers Type 8A05A-101 relay box. No demestic Hot Water. May want to add third zone someday (basement).

Based on the other discussion, a temperature delayed boiler firing would be a feature I would want (turns on the circulation pumps as needed, but delays firing the boiler until a set temp).
Cold Start would be the other feature I'd want.

Anything else I should look for in the ultimate aquastat unit for an oil firing boiler?
 
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Old 12-11-12, 01:38 PM
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Turn LL off ( cold start) and adjustable high limit and High limit diff.


http://www.forwardthinking.honeywell...ll/69_1720.pdf
 
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Old 12-11-12, 03:57 PM
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My thinking is that you should have two separate switches for cut in and cut out. These are wired via relay so that you can have as wide a differential as needed to reduce short cycling AND the burner coming on every time the circulator runs. Also a totally separate high limit that requires a manual reset. I would not use any kind of timer circuit to delay burner operation.

Set the cut in switch to fire around 140 degrees and the operating limit to cut out at around 160 to 180 degrees F. The manual reset high limit would be around 200 to 220 depending on the setting of the operating limit.
 
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Old 12-11-12, 04:30 PM
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I like the setup trooper mentioned where if there is a call for heat, the pump for that zone starts, but the burner doesn't fire until the water temp hits a low value. This would solve a number of heat calls without the need to use oil.
 
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Old 12-11-12, 04:38 PM
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There are actually two approaches to 'getting the heat out'.

1. The 'pre-purge' we're talking about.

2. A 'post-purge' which I had on my old boiler for many years, Energy Kinetics I believe uses it, and my new MPO has a 0-10 minute timer one can configure in addition to the pre-purge.

The post-purge has been discussed at length in previous posts... see if you can come up with the thread in a search... (I'll look too later...) There were even complicated schematics worked up and posted... for a SINGLE zone system, it's a piece of cake though (what I have).

Found it (one of them), this isn't really aquastat related, but does sorta coincide with the discussion peripherally.

http://www.doityourself.com/forum/bo...-valves-2.html

And another:

http://www.doityourself.com/forum/bo...rge-mod-2.html

This involves allowing the circulator to continue to run on AFTER a heat call.

Downside is that you can end up overshooting a setpoint.
 
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Old 12-11-12, 05:00 PM
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if there is a call for heat, the pump for that zone starts, but the burner doesn't fire until the water temp hits a low value.
For an existing installation not needing a new aquastat from scratch (although that is fun too!), on a SINGLE ZONE system, I could envision this working with a single relay and a temp controller like the Ranco mentioned in the other threads (and the same one used on my oil preheater box).

If the relay were a DPDT part, once could wire so that a thermostat call would pull in the relay. One set of relay contacts could run the pump. The other set of relay contacts would be wired in series with the relay output of the Ranco controller in order to 'hijack' the heat call to the aquastat until such time as the temp in the system dropped to a setpoint.

It might not be a bad idea to use TWO relays though in order to keep the 120VAC circuit well separated from the 24VAC control to the boiler.

It might also be possible to use the 2 stage version of the Ranco to provide BOTH pre AND post purge functions.


All bets are off for this method if there is more than one pumped zone, or zone valves... lots more complications.
 
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Old 12-11-12, 05:17 PM
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I like the setup trooper mentioned where if there is a call for heat, the pump for that zone starts, but the burner doesn't fire until the water temp hits a low value. This would solve a number of heat calls without the need to use oil.


I dont think it will matter. The cold slug that comes around will trigger the burner anyway so its a mute point IMO.
 
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Old 12-11-12, 07:59 PM
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I haven't seem much action on the pre-purge on the MPO yet, think I witnessed it one time... but the weather hasn't been that cold yet and by the time another heat call comes the boiler is pretty much cooled below 140 anyway. That's why I wish I could lower it more...

BUT--- my home is WAY over-radiated, so the boiler doesn't ever get much above 150 or so in any case.

In a normally radiated home, with a probably oversized boiler, I could see a pre-purge saving maybe a percent or two because the boiler will get hotter faster, the home will warm slower, and more residual heat left in the boiler.
 
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Old 12-12-12, 06:19 AM
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Leave it to me to assume pre-purge and post purge was talking about the combustion chamber. Guess I need to brush up on the boiler (heating) terminology.

In a normally radiated home, with a probably oversized boiler, I could see a pre-purge saving maybe a percent or two because the boiler will get hotter faster, the home will warm slower, and more residual heat left in the boiler.
As you mentioned in the quoted piece, oversized boiler, under radiated home in my case.
If I set the t-stats to adjust only a few degrees I'd be lucky to see the boiler drop below 165'F (high limit set to ~170'F).
When heating season started and I did the aquastat/zone rewiring, I had set the t-stats very aggressive to drop to 59'F during the day (approximately 12 hour duration). The water temp would drop to 110-130'F with the boiler off for 12 hours. When the heat call was there to bring it back up to 65-68'F (depending on which floor at which time), the boiler would be back up in the 165-170'F.
I've since adjusted the t-stats to be less agressive with the main floor zone now only dropping to 63'F during the day. I may up this to 65'F once the weather gets colder out. The main floor zone is noticeably under radiated. This will be fixed come spring once I have the time and $$ to upgrade a few rads.

A temp or time delay between the circulation pumps starting and the boiler firing would probably add a measurable amount of savings. Both zone loops are 1 1/4" insulation wrapped copper pipe. Lots of water volume that holds the heat.
If I could hold the boiler from firing until the temp dropped down between 120-140'F, I'd probably cut out 2 to 4 boiler firing cycles while raising the temp from 65-68'F.
Might have to put a bit of thought into this...
 
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Old 12-12-12, 06:53 AM
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Your solution could be as basic as finding a way to increase the DIFF on the high limit.

That is after all, the net effect of what you are saying.

Is there a spare tapping in your boiler where a 4006 style aquastat could live?
 
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Old 12-12-12, 07:09 AM
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Troop why would he get the 4006? For the same price he can get the digital style.

Turn off LL and set diff as far as it will go off Hi limit.

No?
 
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Old 12-12-12, 08:28 AM
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Originally Posted by NJ Trooper
Your solution could be as basic as finding a way to increase the DIFF on the high limit.

That is after all, the net effect of what you are saying.

Is there a spare tapping in your boiler where a 4006 style aquastat could live?
I may be a bit slow out of the gate, but now it all makes sense.
I remember at the begining of heating season, you said you where going to go with a ~170'F hi limit. In the post I refferenced about your temp delay, you mentioned you could only go as low as ~140'F. I'm guessing your aquastat would have a high diff of ~30'F then.

From what I understand in the documentation of my current aquastat, the adjustable differntial only applies to the lower limit, which is useless on a cold start setup. That means I'm only using the 10'F builtin differential which would explain the numbers in post #16 (although it would be a 10'F span and not a 5' as I indicated).
 
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Old 12-12-12, 08:44 AM
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from what I understand in the documentation of my current aquastat, the adjustable differntial only applies to the lower limit, which is useless on a cold start setup.


The max diff I see on select aquastats is 30f.

The digitals are adjustable but it does not stat to what level.

The new 2012 doe compliant aquastats have all this pre/post purge stuff.

I guess you can go basic with the 4006 but for the same money go digital???

Possibly I am wrong in my statements...

 
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Old 12-12-12, 10:43 AM
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OK, let's see if we can get everyone up to speed here...

Mike NJ - N'Mike has already converted his old triple a'stat to COLD START... been that way for what, 2 months now? So the issue of turning the LL all the way down is out of the picture at this point... fuggeddaboudit.

why would he get the 4006?
I said " 4006 STYLE " ... meaning that I simply wanted to know if there are any spare tappings on the boiler into which an immersion well could be installed for the purpose of monitoring boiler temperature. Whether or not a 4006 is actually used remains to be seen...

The reason I'm 'going there' is because with the addition of another aquastat mounted on the boiler and wired IN SERIES with the high limit on the existing aquastat, one can use the adjustable diff of an 'add-on' aquastat to modify the operation of the existing one.

Since the existing aquastat is working fine, there's no need to replace it. But yes, economically it might make sense if one had to purchase a 4006 STYLE a'stat at retail.

For about $60 USD one can pick up a 4006 for this purpose... that's like a little less than half the price of a new digital a'stat.

you said you where going to go with a ~170'F hi limit. In the post I refferenced about your temp delay, you mentioned you could only go as low as ~140'F. I'm guessing your aquastat would have a high diff of ~30'F then.
I set the boiler HL to 170 because there appeared to be a 10 'offset' between the a'stat and the analog thermometers I installed. 170 at the a'stat gives me 180 out of the supply pipe...

I do have a digital and the diff IS adjustable to 30F and that is what I have it set at right now. Fact is though that if the boiler never even HITS the HL, the DIFF will never come into play anyway, and that is the case with my system. It will only hit 170 HL if I turn the t'stat all the way up and let the boiler bounce off the HL ( and this would be after many cycles because the BOOST in the ODR is set at 15 minutes, meaning that the first cycle would stop at ODR setpoint, then 15 minutes later boost ten to 155, then 15 minutes later boost ten to 165, then 15 minutes later boost another ten....)

So bottom line is that on MY system, the DIFF is a moot point...

BUT, I think you may be combining two functions we talked about...

On the MPO, the PRE_PURGE function... NOT any thing at all to do with the DIFF function... has a preset, non-adjustable setpoint of 140. This function has nothing at all to do with the HL or the DIFF, or anything else for that matter.

All this function does when turned ON is :

In the event of a heat call that begins when the boiler is ABOVE 140, ONLY the circulator will run to attempt to satisfy that heat call with the residual heat in the boiler. If it can, then fine... heat call ends, circ shuts down.

Chances are it WON'T satisfy, so when the boiler temp drops to 140, the burner will fire and run to setpoint as needed, (controlled by ODR, this time of year ODR setpoint is 145)

Hope this clears any confuzzlement!
 
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Old 12-12-12, 10:48 AM
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If you're getting so many heat calls that your boiler never cools down between cycles, don't you have the "System Type" or "cycles per hour" set wrong in your thermostat? Or left a window open
 
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Old 12-12-12, 11:01 AM
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That is of course a possibility, but it could also be that the 'standby losses' from the boiler aren't that great that the boiler cools appreciably between cycles.
 
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Old 12-12-12, 11:40 AM
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If you're getting so many heat calls that your boiler never cools down between cycles, don't you have the "System Type" or "cycles per hour" set wrong in your thermostat? Or left a window open
Its not so much many heat calls. Its the boiler firing up more than once during a single heat call. This would be attributed to an oversize boiler, inefficient rads and an aquastat that will fire the boiler once its 10F below the high limits (during the heat call).
Raising the temperature on the t-stat on my main floor (for example) from 63F to 68F will see the boiler fire about 4 times and shut off at the high limit.

I am also dealing with a 2900sqft 1937 former nun convent, so insulation upgrades over the years may not be perfect. It's on my many list of things to address.
That is of course a possibility, but it could also be that the 'standby losses' from the boiler aren't that great that the boiler cools appreciably between cycles.
Between calls for heat, the boilers standby losses are very minimal (~175F to ~145F over 12 hours of non-usage).
 
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Old 12-12-12, 12:00 PM
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IDK Mike.... I am over radiated with an over sized boiler. My boiler always kicks off on high limit.

Although I have a 15f diff non adjustable. I have since lowered my aquastat to 150f. It does soak up to 155f, 160f after the burner kicks off with the circ still going.

I only need 160f water for my heat loss.

Now it is a slower heat process. My boiler may hit high limit 2 or 3 times before the t stat is satisfied. ( when its cold) The circ will be running the whole time.

This relates to the constant circulation and lower temps therory.

IMO you need a A'stat with a wider diff is all. set it to the max if your running 180f water.

I dont want more then 15f diff with mine because I am at 150-155f water temp. So for condenstation issues I want the boiler to come on 130f minimum....

Just my thoughts.
 
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Old 12-12-12, 01:00 PM
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IMO you need a A'stat with a wider diff is all
Right... either an a'stat with a wider diff, or better yet, a less costly solution...

So, N'Mike, is there a spare tapping on your boiler, or no?
 
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Old 12-12-12, 01:08 PM
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Right... either an a'stat with a wider diff, or better yet, a less costly solution...

So, N'Mike, is there a spare tapping on your boiler, or no?
I am not sure if there is. I'll see if I can find one when I get home tonight. I have the manual for the boiler here in PDF format. Not sure if it'll indicated that there is or isn't one.
 
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