Downside to constant circulation?

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Old 03-29-10, 02:35 PM
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Downside to constant circulation?

My newly installed boiler is the buderus gb142/24. I also purchased the RC35 controller giving me indoor feedback to the system allowing me to run with constant circulation.

My installer does not agree about the approach of constant circulation. He says that my copper pipes will wear out with so much flow. Is this true? Should I be concerned?

I am completely sold on the energy saving benefits of this approach but question how much wear I will be putting on my system. From what I have read online, if I keep my ph above 7 (i have to being that its an aluminum boiler), the alkaline in the water will form a film on the copper pipes giving me some protection from wear.

Anybody have any other info to share?
 
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Old 03-29-10, 03:41 PM
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Hydronic systems generally run at a velocity of 2-4 FPS... I think you would have to run for about 50 years with that velocity to wear out the pipes.
 
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Old 03-29-10, 05:34 PM
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Constant circulation has been around for 50 - 60 years and has never been a problem. It is definitely an energy saving theory. The only downside is a slightly higher electric bill but the energy savings offsets the electric by far.
 
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Old 03-29-10, 06:41 PM
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Wear out the pipes? Good one. Maybe in 100-200 years or so.

The indoor feedback and constant circulation approach rocks. Finishing 3rd season with that setup. Never been more fuel efficient or more comfortable. Increased electricity is in the noise of typical monthly usage.
 
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Old 03-29-10, 08:03 PM
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Throw an Alpha or Wilo circ in there and enjoy the savings
 
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Old 03-30-10, 06:35 AM
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Being a devils advocate would those pumps take away from the whole idea of increased comfort for continuous pumping. If you are pushing a certain delta T which is what happens when you change pump speeds could that make the home less comfortable? I would think it will create cool spots instead of making the home heat more even. The idea of constant circulation is rooms that heat quicker when the heat is on will extract less heat on constant circ and the rooms that were cooler will extract more heat from the lower temperature water circulating. When you are forcing a delta T you end up with the same differences in room temp throughout the system. Yes, before I slammed that these are delta P pumps, I know those pumps work on delta P but the end result is delta T in the system when the flow changes.
 
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Old 03-31-10, 05:31 PM
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Rbeck this makes for good conversation
IF the zone valves are 2 way proportional valves then wouldn't it still be a continuous pumping? Or did you mean constant volume pumping vs variable volume pumping?
The higher the Delta T the more critical the zone control.
I haven't worked on any of these systems but sounds close to a commercial variable volume pumping system.
Are the zone controllers Proportional ? i would thing a 2 position zone valves would cause the little pump to constantly hunt. zone controllers with PI is what i would think they would be. Anyone know what kind of zone controllers are normally used with this system?
 
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Old 04-01-10, 09:47 AM
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They are just open/close valves for residential applications but he does not mention zone valves most constant circulation systems are just one zone otherwise why do constant flow?
 
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Old 04-01-10, 10:15 AM
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That is comforting to know that the constant circulation will not put any additional wear on my system.

And I have one zone right now but have set it up so I can add an additional zone in the future with zone valves.
 
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Old 04-01-10, 11:04 AM
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I havent worked on a Alpha pump but checked out the specs and how i think it works. It looks like a change in friction head or resistance to flow (zone valves closing off)
The pump senses a increase in head and decreases the RPM of the pump ( lowering the GPM and frictional head) So if this is how it works and there isnt any zone valves to change the system resistance why is Alpha pump used? Is it over kill? Good stuff thanks for the input rbeck.
 
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Old 04-05-10, 04:15 PM
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Originally Posted by rbeck View Post
Being a devils advocate would those pumps take away from the whole idea of increased comfort for continuous pumping. If you are pushing a certain delta T which is what happens when you change pump speeds could that make the home less comfortable? I would think it will create cool spots instead of making the home heat more even. The idea of constant circulation is rooms that heat quicker when the heat is on will extract less heat on constant circ and the rooms that were cooler will extract more heat from the lower temperature water circulating. When you are forcing a delta T you end up with the same differences in room temp throughout the system. Yes, before I slammed that these are delta P pumps, I know those pumps work on delta P but the end result is delta T in the system when the flow changes.
Well, would a manufactorer invest the time and money to develop a delta P pump with out knowing the advantages of it. If the you where to set the head of each loop to be equal than each flow path would cause the circ to change it's flow to what was needed for that flow path once the initial head / flow relationship was calculated.
At that point one would get near constant flow through the zone.
But, as you say devils advocate, if we want constant flow through each zone then the t/stat never really satisifies and each zone will always call. Why would you install a variable speed circ, as the flow will always be required. At the point a constant delta T circ would be required.

But this is real world and things aren't perfect, so the delta P circ came about.

Strayed off thought....
The Alpha is like an ECM motor, it can do a lot with out using much energy.
This is the point behind my comment, not about zone valves opening and closing...
I recently flowed a 14,000 Square foot warehouse with one alpha running 26 watts...
That kinda impressed me a bit.
 
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Old 04-05-10, 05:08 PM
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Silly me I thought it was due to the fact that the delta-P pumps are European and Europeans always talk resistance and the US talks Delta -T. The resistance changes as the water temperature changes so the pump would make charges as the boiler is running or off.
Never seen an Alpha in operation and must admit 26 Watts is impressive.
Question. What is the price difference between the Alpha used on that job site and the pump that would be used if a standard pump? If more $$ what is the length of payback and life expectancy of the Alpha?
 
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Old 04-05-10, 08:41 PM
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Originally Posted by rbeck View Post
Silly me I thought it was due to the fact that the delta-P pumps are European and Europeans always talk resistance and the US talks Delta -T. The resistance changes as the water temperature changes so the pump would make charges as the boiler is running or off.
Never seen an Alpha in operation and must admit 26 Watts is impressive.
Question. What is the price difference between the Alpha used on that job site and the pump that would be used if a standard pump? If more $$ what is the length of payback and life expectancy of the Alpha?
I think I was going to use a 15-58, which is about 100 watts I think. The circ runs all the time pretty much.
Europeans also like 15 Degrees C delta T as well.
Really how much pressure difference is there between say 80 and 110 F ?
 
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Old 04-05-10, 10:25 PM
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Pressure and Delta T are not the same thing. Pressure and gpm are the same thing, as one drives the other. When we talk about maintaining constant pressure, or altering pressure, we are not talking about altering temperature, we are talking about altering GPM. If you've designed a radiant heating system, you know that delta T and gpm are not the same thing.

There are many reasons to use an Alpha pump. For example, the electrical consumption is, compared to any comparable pump, next to nothing. If you can go from 100 watts to 25 watts, and your pump runs 24 hours a day, you can save almost 2kWh / day, 20 or 30 cents. How many years would it take, at $90 / year, to make up a $250 additional cost - 2.5? Seems like a good thing to me.

Or, no more differential bypass valves. Loops flow at the same rate regardless of the status of any other loops, which is not true with a non-flat pump curve. The advantages in terms of simplicity seem unrivaled.

Jeff
 
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Old 04-06-10, 06:12 AM
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A little dated but someone may find it interesting
Pump Tech - Archives - Reeves Journal. A few things i found interesting a Ecm motor draws the same amount of current on start up as it does running.
The Alpha i thought i read it had an inverter, they are talking about controlling speeds based on energizing ( for lack of a better word) motor poles. conventional motor 4 pole is around 1800 2 pole 3600 rpm Very cool, and i would think less costly then having an inverter. Downside i guess would be your limit to turn down is based on the number of poles in your motor.
Keep in mind the article was written in 2007 not sure what has changed since. Interesting the design of the pumps add alot to the efficiency and not just the ECM
 
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Old 04-06-10, 06:40 AM
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A D/P Circ Question

How does a D/P circ ie: Alpha sense pressure in a pipe. Also does Taco make a D/P circ or only D/T circs. Thanks
Rich Davis
 
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Old 04-06-10, 06:54 AM
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let me give you my 2 cents about my experience with constant circ. In Nov I had my boiler replaced with a Buderus G115WS, Logamatic 2107 with a room sensor w/ constant circulation and an Indirect. During the winter it was great. I always felt comfortable at a temp of 68. Never felt warm cold warm cold. However, with the weather we have right now my logamatic doesn't always go into Warm Weather Shut Down (WWSD). example: My room sensor is set at a temp of 68. The logamtic is reading a room temp of 72 but the circulator is still running because the outdoor temp is lower then what the WWSD is set to. If the boiler doesn't fire it is pushing approx 80 to 90 degree water through the loop because the room temp is satisfied. Now the problem is when the unit fires to make DHW, all that heat to make DHW in the boiler has to go somewhere and where do you think it goes? Through the house. Now I have 140 degree water being pushed through the house that is already overheated.

I really like constant circulation during the colder months but find it to be a nuisance with this type of weather. Right now I have to manually adjust the WWSD to halt the circ.

I hope that made sense Beer 4U2

John
 
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Old 04-06-10, 11:05 AM
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Johny, I'm thinking that something might be amiss with the piping if you are pumping hot water when you shouldn't be ...

This whole thread is getting a bit off the OP's topic, but let me ask you... you had posted some pics of the install a while back, didn't you? If so, why not start a new thread and point to the pics...
 
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Old 04-06-10, 11:13 AM
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Hi Trooper, I have been meaning to post before and after pics but have been to busy to find time. once I get a chance I'll post them.

With a room sensor the logamatic is set to constant circulation. Now from my understanding, the only time the circulator will shut off is during a call for DHW and during Warm Weather Shut Down.

[edit: Johny, I've copied these three posts into a new thread... you should see it in the list - NJT]
 

Last edited by NJT; 04-06-10 at 03:41 PM.
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Old 04-06-10, 11:52 AM
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Pressure and Delta T are not the same thing. Pressure and gpm are the same thing, as one drives the other
I totally agree they are not the same thing but one affects the other and the bottom line is Delta-T and Delta-P you end up with very similar results.
Water temperature will vary as thermostats call and systems start and start. When water temperature changes resistance to flow (pressure) changes, when pressure changes flow changes, when flow changes Delta-T changes. So the end result is similar just different highways to get there. You change flow as water temps change to maintain the same pressure or Delta-T. Boiler heats up some water flows easier and a Delta-P pump slows down as it has less resistance to overcome and the water cools off the resistance is greater so the pump speeds up. If the flow is changed at any given water temperature the Delta-T will be consistent. You cannot change any of the above without affecting something else.
 
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Old 04-06-10, 03:03 PM
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rbeck,
You are talking in circles. Delta T and Delta P are not the same thing, and they are not equivalent ways of handling changing heat distribution.
Jeff
 
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Old 04-06-10, 03:33 PM
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Jeff, he's not saying they are the same thing...

What he's saying is that the PROCESS VARIABLE is the same thing. The PV in this case is the FLOW.

The SETPOINT, and the MEASURED VARIABLE are both different things, but they BOTH affect the SAME Process Variable.

It sounds like a circle, but it's not.

He is further saying that the DT will CHANGE when the FLOW (the Process Variable) is changed even if that flow is under control of the pressure. and vice versa... no matter which parameter you hold constant.

One will always affect the other...

You could also say that they are both means to the same end, control of the flow.

Verschtenen?
 

Last edited by NJT; 04-07-10 at 04:25 PM.
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Old 04-07-10, 01:17 PM
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Thank You Trooper. The way you get there is different but the end result is the same.
 
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Old 12-16-10, 11:07 AM
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Cost for the RC 35?

bovineu (or someone else):

To revive this thread - I recently purchased the Buderus G115 with the Logamatic control/outdoor reset and have been able to set the system up as 95% constant circulation by adjusting the heating curves and using the main floor thermostat as a high limit on the indoor temperature. So far the system works great.

I was wondering if anyone knew the approximate price for the RC35? Is it worth the purchase based upon how I currently have the system setup?

It seems that the RC35 will allow for quicker recovery from a nighttime setback (on the Logamatic) and also allow for a finer tuning of the heating curve when the thermostat is at it's setpoint - any thoughts or opinions would be welcome.

Thanks
 
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Old 12-16-10, 06:14 PM
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You should check if there is DHW post purge to shed any remaining energy into the tank.
There may also be a setting to prevent the system circ or injection pump from running for a period of time unless there is a CH call.
Take a look at some of the more hidden settings.
 
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