Circulator pump question
#1
12-21-11, 06:09 PM
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Circulator pump question
Hey folks, I'm back with another question. This time about circulating pumps. I'm pretty sure the pump on my boiler came as part of the package, sizing not considered. I'd like to confirm whether I have the right pump. This is the pump I have. http://www.patriot-supply.com/files/...ett_103251.pdf
The height from the pump suction to the top of the cast iron radiators on the second floor is 15'. The oil fired boiler is piped in parallel, using 1" pipe, with an old unused gravity feed coal boiler which heats the basement. The 1" pipe tees off to two 3/4" lines feeding two headers. The supply and return headers are 2 and 1/2" a total of 36' long. There are 6 rads on the first floor and 6 on the second floor, feeds and returns are 1 and 1/2"X12' in the basement and 9' to the bottom of the upstairs rads . Each feed and return line has three 90 degree elbows and one 45.
So, based on this information can the proper pump be selected?
Here are some pics of how the boiler is connected:
Sorry for the coal dust in the pics...LOL...From many decades of burning coal.
Thanks to all the great people here for being so helpful.
The height from the pump suction to the top of the cast iron radiators on the second floor is 15'. The oil fired boiler is piped in parallel, using 1" pipe, with an old unused gravity feed coal boiler which heats the basement. The 1" pipe tees off to two 3/4" lines feeding two headers. The supply and return headers are 2 and 1/2" a total of 36' long. There are 6 rads on the first floor and 6 on the second floor, feeds and returns are 1 and 1/2"X12' in the basement and 9' to the bottom of the upstairs rads . Each feed and return line has three 90 degree elbows and one 45.
So, based on this information can the proper pump be selected?
Here are some pics of how the boiler is connected:
Sorry for the coal dust in the pics...LOL...From many decades of burning coal.
Thanks to all the great people here for being so helpful.
#3
12-21-11, 06:17 PM
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gravity feed coal boiler
I am just trying to grasp this one.... Although I have not read the original posts so possible I am alittle behind in whats going on here.
Mike NJ
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12-21-11, 06:19 PM
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#6
12-21-11, 06:24 PM
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Lawrosa, yep, filled with water, It was still burning coal up until 2 years ago when I bought the house. It keeps the basement toasty warm too. Not sure who installed the oil boiler or when. It is how I found it. The old coal boiler was made in 1957.
#7
12-21-11, 06:29 PM
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The coal and oil share the same flue too, I blocked off the coal furnace flue though. Coal is still pretty popular around here and very cheap compared to oil.
#8
12-21-11, 06:59 PM
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Drooplug, I guess one issue I see is that even though the boiler is maintained at 130 between firings, if there has been no call for heat for a few hours the boiler temp drops to below 100 degrees for quite a while as the entire system is reheated. Could that indicate a problem with the flow rate through the boiler or is it unavoidable?
#9
12-22-11, 10:05 AM
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I'm guessing the flow through the boiler may be too high causing the huge boiler temp drops and long recovery. Here is a picture of the piping. The bypass is connected from the supply to the return side of the pump. The bypass is wide open and I still see a huge drops in temperature when the boiler first starts and it takes a long time to recover. I've seen various methods of bypass installs, does this look ok? How should the valves be operated?
#11
12-22-11, 01:02 PM
The bypass is connected from the supply to the return side of the pump.
Knowing this is necessary to give instruction to proper setting.
In the pic it appears that the bypass line is smaller than the circuit piping. Is it?
Is that blue handle valve between the bypass and the boiler? In other words which direction is that return flowing?
#12
12-22-11, 01:14 PM
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Looks like a system bypass to me. The supply is going right back into the return. He would need to throttle the flow through the system with the blue andle on the supply to get the boiler up to temp quicker?
I just putting this out there and thats my take on it. Draw back is reduced flow on the system side.
In this case would not a boiler bypass be better?
Mike NJ
I just putting this out there and thats my take on it. Draw back is reduced flow on the system side.
In this case would not a boiler bypass be better?
Mike NJ
#13
12-22-11, 01:30 PM
Looks like a system bypass to me.
Yes, a boiler bypass is almost always a better choice.
System bypasses rob flow from the system and often result in lazy flow and unbalanced heating.
#14
12-22-11, 05:42 PM
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Ok, the pump suction is on the return side. Yes, the bypass is is 3/4" while the piping is 1". I would think they should be the same size but this is what was piped in. The arrows indicate the direction of assumed flow.
At the current setting, all valves wide open, the bypass keeps the pump suction side of the return piping much warmer than it is prior to the bypass piping just not at startup.
Given the size of the piping I am assuming the piping losses are pretty low when compared to more modern installations. According to the pump curve this pump is capable of up to 22 GPM. I'd like to calculate the total head so I can estimate the flow rate. Is there an online tool to assist me?
I updated the pic to show pump suction loacation.
As an experiment I closed the return valve. It is open 25%. Looks like I'm pretty close as the temps are now looking good.
It would appear that this boiler has been seeing low temps at startup since it was installed or someone opened the valve that was throttling the flow.
At the current setting, all valves wide open, the bypass keeps the pump suction side of the return piping much warmer than it is prior to the bypass piping just not at startup.
Given the size of the piping I am assuming the piping losses are pretty low when compared to more modern installations. According to the pump curve this pump is capable of up to 22 GPM. I'd like to calculate the total head so I can estimate the flow rate. Is there an online tool to assist me?
I updated the pic to show pump suction loacation.
As an experiment I closed the return valve. It is open 25%. Looks like I'm pretty close as the temps are now looking good.
It would appear that this boiler has been seeing low temps at startup since it was installed or someone opened the valve that was throttling the flow.
#15
12-22-11, 06:19 PM
Sorry... still not clear enough for my thick head to understand.
In the pic, the return pipe on the right side is coming back from the house, turning right, past the bypass tee, then to the pump, then to the boiler?
In other words, the bypass is on the SYSTEM side of the circulator?
If so, that's a SYSTEM bypass and you don't want to close that blue valve.
Yes, closing that blue valve will force more water through the bypass and into the boiler, BUT it will also rob that much more flow from the system. You do not want to limit the flow through the system.
All you will accomplish by closing the blue valve is possibly causing uneven heating in the home due to decreased flow in the system.
Exactly what is the return temperature? How do you know it was too cool?
In the pic, the return pipe on the right side is coming back from the house, turning right, past the bypass tee, then to the pump, then to the boiler?
In other words, the bypass is on the SYSTEM side of the circulator?
If so, that's a SYSTEM bypass and you don't want to close that blue valve.
Yes, closing that blue valve will force more water through the bypass and into the boiler, BUT it will also rob that much more flow from the system. You do not want to limit the flow through the system.
All you will accomplish by closing the blue valve is possibly causing uneven heating in the home due to decreased flow in the system.
the temps are now looking good.
#16
12-22-11, 07:37 PM
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Blue valve to the left is from the house. Bypass is piped from boiler discharge to the return/pump suction, circulating pump is on the return side if the boiler.
After a few hours of not running today the boiler started. The boiler temp gauge dropped from 130 to 80 in seconds before it started to slowwwwly warm up, not good for the boiler from a condensation standpoint.
I let the system cool down again, closed the return valve to 25%, the boiler temp dropped a bit but began to to recover quickly instantly, much better for the boiler.
It seems to me that the boiler cannot keep up to the return flow rate, even with the bypass wide open.
The system was originally designed to be a gravity feed so the pipes are big, 2.5" headers and 1.5" to and from the cast iron rads. That makes for a lot of water volume to reheat after a period of inactivity and I think I'm exceeding the recovery rate of the boiler.
I'm not sure how to calc the piping losses or what the flow rate should be so that I can use the pump curve to find the actual flow. Mine is the NRF-22, the upper pump curve.
I do know I have two 36 foot headers at 2.5" each, 6 rads on the first floor each with 13 feet of 1.5" pipe on the feed and return and 3X90 degree elbows on each of those. There are 6 rads upstairs, the top of the rads are 15 feet above the pump suction. Each upstairs rad has 22 feet of 1.5" pipe on the feed and return and 3X90 degree elbows on each of those.
I'm not sure what the return temp is exactly but the pipe is very cold to the touch and takes a long time to warm up, most likely it is close the room temperature since the system had not run for a few hours but it gradually warms up as the boiler does.
After a few hours of not running today the boiler started. The boiler temp gauge dropped from 130 to 80 in seconds before it started to slowwwwly warm up, not good for the boiler from a condensation standpoint.
I let the system cool down again, closed the return valve to 25%, the boiler temp dropped a bit but began to to recover quickly instantly, much better for the boiler.
It seems to me that the boiler cannot keep up to the return flow rate, even with the bypass wide open.
The system was originally designed to be a gravity feed so the pipes are big, 2.5" headers and 1.5" to and from the cast iron rads. That makes for a lot of water volume to reheat after a period of inactivity and I think I'm exceeding the recovery rate of the boiler.
I'm not sure how to calc the piping losses or what the flow rate should be so that I can use the pump curve to find the actual flow. Mine is the NRF-22, the upper pump curve.
I do know I have two 36 foot headers at 2.5" each, 6 rads on the first floor each with 13 feet of 1.5" pipe on the feed and return and 3X90 degree elbows on each of those. There are 6 rads upstairs, the top of the rads are 15 feet above the pump suction. Each upstairs rad has 22 feet of 1.5" pipe on the feed and return and 3X90 degree elbows on each of those.
I'm not sure what the return temp is exactly but the pipe is very cold to the touch and takes a long time to warm up, most likely it is close the room temperature since the system had not run for a few hours but it gradually warms up as the boiler does.
#17
12-22-11, 07:58 PM
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Why dont you cut that coal fired boiler out???? Less water to heat. Its not doing nothing but holding lots of water.
While you are it change the bypass to a boiler bypass and not a system bypass as you have.
I think others will add to this line of thinking.
Mike NJ
While you are it change the bypass to a boiler bypass and not a system bypass as you have.
I think others will add to this line of thinking.
Mike NJ
#18
12-22-11, 08:43 PM
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The coal furnace makes a nice rad for heating my basement and it would be a huge job to get it out, there are no shut offs so it can't be isolated. Might be a job to tackle in the summer.
#19
12-22-11, 11:23 PM
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Found this nifty calculator, it calculates the flow rate to attain various temp rise values based on boiler output.
WEA Online Engineering Calculators
My boiler uses 1 gallon per hour=138,500 btu/hr. At 86% efficiency=119110 btu/hr.
The outside temp is 32F, Hours go by between calls for heat. When my boiler starts, the return temp is low, I measured it tonight, it is 75F at the start of the cycle. So to maintain 130F in the boiler at startup I need a 55 degree temp rise. According to the table provided in the link the return flow would need to be 4-5gpm for my boiler's output. Since throttling the return valve the temp inside the boiler drops very little at the start so I assume I'm in the flow range.
The 55 degree temp rise may seem excessive but I have an outdoor reset control installed and now as the return temp rises the burner will shut off and the circulator will continue to run. When the supply temp falls to the ODR low limit the burner is restarted by the ODR. As the return temperature increases the burner on cycle gets shorter and shorter, but not short cycling, while the circulator stays on for the entire call for heat time. The burner used to stay on for the entire call for heat time because the supply temp would never get high enough for the ODR to shut off the burner and the temp in the house has less overshoot.
So far so good.
WEA Online Engineering Calculators
My boiler uses 1 gallon per hour=138,500 btu/hr. At 86% efficiency=119110 btu/hr.
The outside temp is 32F, Hours go by between calls for heat. When my boiler starts, the return temp is low, I measured it tonight, it is 75F at the start of the cycle. So to maintain 130F in the boiler at startup I need a 55 degree temp rise. According to the table provided in the link the return flow would need to be 4-5gpm for my boiler's output. Since throttling the return valve the temp inside the boiler drops very little at the start so I assume I'm in the flow range.
The 55 degree temp rise may seem excessive but I have an outdoor reset control installed and now as the return temp rises the burner will shut off and the circulator will continue to run. When the supply temp falls to the ODR low limit the burner is restarted by the ODR. As the return temperature increases the burner on cycle gets shorter and shorter, but not short cycling, while the circulator stays on for the entire call for heat time. The burner used to stay on for the entire call for heat time because the supply temp would never get high enough for the ODR to shut off the burner and the temp in the house has less overshoot.
So far so good.
#21
12-23-11, 07:08 AM
Originally Posted by imaddicted2u
o far so good.
One thing to worry about, is the return temperature to the boiler.
If it is below 115* for more than 4-6 minutes(?), then there is a good chance the boiler will, at some point, rot out from flue gas condensation.
Peter
#22
12-23-11, 08:20 AM
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Saves, the shortest run time of the burner is 10 minutes at the end of the ODR cycle, I read various times ranging from 3 to 10 minutes is considered short cycling based on various sites and literature, so I don't think 10 minutes is too bad. What do you think?
PeterNH, This issue has surely existed since the boiler was installed, long before I owned the house, so any damage is already done. As a homeowner I would not have thought to monitor the temp but thanks to you folks on this site I have learned the importance of the return temp and I am taking steps to correct it, better late than never.
The return low temp condition probably explains the half bucket of scale I found on the boiler tubes and in the bottom of the combustion chamber when I cleaned it. With the bypass wide open and the return valve throttled it is certainly better now, temp into the pump suction is always above 125 increasing in a few minutes to above 130, it used to get as low as 75-90 degrees and increased slowly over 20-30 minutes before throttling the return valve even after adding the bypass.
PeterNH, This issue has surely existed since the boiler was installed, long before I owned the house, so any damage is already done. As a homeowner I would not have thought to monitor the temp but thanks to you folks on this site I have learned the importance of the return temp and I am taking steps to correct it, better late than never.
The return low temp condition probably explains the half bucket of scale I found on the boiler tubes and in the bottom of the combustion chamber when I cleaned it. With the bypass wide open and the return valve throttled it is certainly better now, temp into the pump suction is always above 125 increasing in a few minutes to above 130, it used to get as low as 75-90 degrees and increased slowly over 20-30 minutes before throttling the return valve even after adding the bypass.
#23
12-23-11, 08:39 AM
Just to reiterate... you have decreased the flow to your radiation... in this mild weather you may find that the home still heats OK, but don't be surprised if when it gets colder you start to feel 'uncomfortable' in the rooms heated at the ends of the loops.
#24
12-23-11, 09:33 AM
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I agree, the flow has been reduced but I am convinced it was too high to begin with because the 2 and 1/2" and 1 and 1/2" pipes in my system present much lower head losses to the pump when compared to 1/2" or 3/4" piping used in today's systems, the boiler/pump was a retrofit to an existing system and the piping losses were not likely considered, in other words the pump came with the boiler. The lower head losses in my system allow the pump to flow more water through the system as shown in the pump curve I posted.
I am left with a decision to either allow the full flow or protect the boiler from condensation. The logical decision is to protect the boiler and the no cost, immediate solution is to throttle the flow.
The thermostat overshoot has reduced from 1.5-2 degrees to under .5 degrees and so far the comfort level throughout the house is better.
If the conditions change as the weather gets colder I'll open the return valve to compensate but my ODR will make the water hotter so I don't think that will be necessary. Time will tell.
Thanks for the advice, I appreciate it
I am left with a decision to either allow the full flow or protect the boiler from condensation. The logical decision is to protect the boiler and the no cost, immediate solution is to throttle the flow.
The thermostat overshoot has reduced from 1.5-2 degrees to under .5 degrees and so far the comfort level throughout the house is better.
If the conditions change as the weather gets colder I'll open the return valve to compensate but my ODR will make the water hotter so I don't think that will be necessary. Time will tell.
Thanks for the advice, I appreciate it
#25
12-23-11, 10:32 AM
I'm not sure we were aware of the fact that you also had an overshoot problem in the home...
Take a look at your thermostats and see if they have 'anticipator' adjustments on them.
You may be able to control the overshoot further by manipulating the anticipator for a 'shorter' cycle setting.
Depending on your piping overall layout, it's also possible that part of the overshoot problem could be caused by continued gravity flow after the heat call has ended... is there a 'flow check' valve on the hot supply out of the boiler?
But yeah, yer right... protect the boiler if possible even if it's after the damage has been done. If you benefit by added comfort in the home, then that's GREAT!
You could also throttle the supply side valve by the way... which one you throttle really makes no difference, the net result is the same.
The thing about throttling ball valves though... they are very sensitive to adjust if you are looking for precise adjustments (you aren't really), because the limited range of handle movement and the nature of fluid flow. The majority of the flow control, probably 90% or so, actually occurs in the first 10% of handle movement. It's a logarithmic function. So if you're only having to close the valve a small amount in order to raise the temp in the boiler, then it's not really limiting the flow all that much...
One other thing about BV throttling is that it can cause the valves to fail over time due to the increased velocity past the ball... it will eventually erode the ball and seals... but may take longer than the time we have left. So don't worry about it if it's working OK for ya.
Take a look at your thermostats and see if they have 'anticipator' adjustments on them.
You may be able to control the overshoot further by manipulating the anticipator for a 'shorter' cycle setting.
Depending on your piping overall layout, it's also possible that part of the overshoot problem could be caused by continued gravity flow after the heat call has ended... is there a 'flow check' valve on the hot supply out of the boiler?
But yeah, yer right... protect the boiler if possible even if it's after the damage has been done. If you benefit by added comfort in the home, then that's GREAT!
You could also throttle the supply side valve by the way... which one you throttle really makes no difference, the net result is the same.
The thing about throttling ball valves though... they are very sensitive to adjust if you are looking for precise adjustments (you aren't really), because the limited range of handle movement and the nature of fluid flow. The majority of the flow control, probably 90% or so, actually occurs in the first 10% of handle movement. It's a logarithmic function. So if you're only having to close the valve a small amount in order to raise the temp in the boiler, then it's not really limiting the flow all that much...
One other thing about BV throttling is that it can cause the valves to fail over time due to the increased velocity past the ball... it will eventually erode the ball and seals... but may take longer than the time we have left. So don't worry about it if it's working OK for ya.
#26
12-23-11, 10:56 AM
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The thermostat is digital set to 2 CPH, recommended for oil hot water systems. I have this one: THM501 Manual Downloads
Flow check valve is good, I have the one pictured on the left of this doc: http://completewatersystems.com/wp-c...011/03/607.pdf
Someone had monkeyed with it in the past and it was in the middle of it's range. It was siezed in that positon and I got it freed up, the stem started leaking but tightening the packing cured it. It is turned all the way clockwise now. I measure the temp after it when the circulator shuts off and the temp is dropping so it looks good.
I make small changes in the ball valve, I have worked with them before. I get good results with the valve open about 25% open.
Flow check valve is good, I have the one pictured on the left of this doc: http://completewatersystems.com/wp-c...011/03/607.pdf
Someone had monkeyed with it in the past and it was in the middle of it's range. It was siezed in that positon and I got it freed up, the stem started leaking but tightening the packing cured it. It is turned all the way clockwise now. I measure the temp after it when the circulator shuts off and the temp is dropping so it looks good.
I make small changes in the ball valve, I have worked with them before. I get good results with the valve open about 25% open.
#27
12-25-11, 08:39 AM
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Merr Christmas to all!
Hey NJ trooper, You were right....After the outside temp fell I had trouble maintaining temp at the edge of the loops, guess I declared success too soon.
My boiler is currently piped up with a system bypass. I'd like to convert it to a boiler bypass. Here is a pic of a boiler bypass from a link on bypass types posted in another thread. Also, here is a pic of what I have now. Will placing a valve at the noted location turn what I have now into a boiler bypass? The red arrows indicate the current flow direction. Will the added valve reverse the flow through the bypass as noted by the green arrows. My old cast iron radiators seem to satisfy the need for heat at lower temps. From what I have read on this site, a boiler bypass will allow lower temps to the system by mixing cooler return water with the hotter boiler water and could allow me to do full outdoor reset with my ODR.
This would be a simple valve install and seems to match the drawing but I want to make sure it will work before I start cutting pipe. Wouldn't throttling a valve in the proposed location reduce the total flow in the system and cause the same issue I ran into by throttling the currently installed return valve?
Thanks for your comments.
Hey NJ trooper, You were right....After the outside temp fell I had trouble maintaining temp at the edge of the loops, guess I declared success too soon.
My boiler is currently piped up with a system bypass. I'd like to convert it to a boiler bypass. Here is a pic of a boiler bypass from a link on bypass types posted in another thread. Also, here is a pic of what I have now. Will placing a valve at the noted location turn what I have now into a boiler bypass? The red arrows indicate the current flow direction. Will the added valve reverse the flow through the bypass as noted by the green arrows. My old cast iron radiators seem to satisfy the need for heat at lower temps. From what I have read on this site, a boiler bypass will allow lower temps to the system by mixing cooler return water with the hotter boiler water and could allow me to do full outdoor reset with my ODR.
This would be a simple valve install and seems to match the drawing but I want to make sure it will work before I start cutting pipe. Wouldn't throttling a valve in the proposed location reduce the total flow in the system and cause the same issue I ran into by throttling the currently installed return valve?
Thanks for your comments.
#28
12-25-11, 09:10 AM
could allow me to do full outdoor reset with my ODR.
Will placing a valve at the noted location turn what I have now into a boiler bypass?
A boiler bypass must be on the BOILER SIDE of the pump.
You would have to add the bypass tee and a valve BETWEEN the boiler and the pump.
Wouldn't throttling a valve in the proposed location reduce the total flow in the system and cause the same issue I ran into by throttling the currently installed return valve?
#30
12-25-11, 12:46 PM
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Makes sense, thought it would be too simple to just add a valve. I had overlooked the pumps in the graphic.
Since my pump is piped directly into the boiler base there is no chance for me to do boiler bypass unless I move the pump to after the boiler discharge, something I can't do without draining the system, no shutoffs downstream of the gravity flow preventer.
However, looks like if I put the pump where indicated in this pic, I will be able to re-use the current bypass piping. I think this would allow me to reset to lower temps while flowing less water through the boiler. Does the layout detailed in the pic look right? Is it ok to have the pump after the boiler in the supply line. The new valve I will add to the boiler inlet pipe will throttle the flow into the boiler forcing more flow through the bypass while the flow to the system should remain the same.
Since I will have to drain the system to install the pump after the boiler I will wait until the summer when I plan to remove the old coal boiler.
Thanks NJTrooper for being so helpful.
Since my pump is piped directly into the boiler base there is no chance for me to do boiler bypass unless I move the pump to after the boiler discharge, something I can't do without draining the system, no shutoffs downstream of the gravity flow preventer.
However, looks like if I put the pump where indicated in this pic, I will be able to re-use the current bypass piping. I think this would allow me to reset to lower temps while flowing less water through the boiler. Does the layout detailed in the pic look right? Is it ok to have the pump after the boiler in the supply line. The new valve I will add to the boiler inlet pipe will throttle the flow into the boiler forcing more flow through the bypass while the flow to the system should remain the same.
Since I will have to drain the system to install the pump after the boiler I will wait until the summer when I plan to remove the old coal boiler.
Thanks NJTrooper for being so helpful.
#31
12-25-11, 02:06 PM
If going to the trouble of moving the pump and all, you might want at the same time to make some other 'improvements'.
For example:
Set up the system to 'pump away' from the "Point Of No Pressure Change" (PONPC) which would be the connection point of the expansion tank...
Where is your exptank in relation to all this?
If doing a boiler bypass, it's advised to use a full size bypass... if the rest of the piping is 1", then the bypass should also be... but if it all works out to be easy and advisable to move the pump as you are thinking, then I don't think the 3/4" would be a real 'show stopper' if it turned out you could leave that in place.
Some might argue that it's sorta 'ghetto' to do this, I would consider buying another set of pump flanges and running a straight pipe between them to replace the pump. Might make a dandy spot to add a valve also.
If you do move the pump, use 'isolation flanges' to install the pump so that future pump work can be done without draining the system. Isolation flanges will also take the place of the system isolation valves.
I would also re-do and replace that relief valve. They should be mounted vertically, probably closer to the boiler, and the discharge should go almost all the way to the floor.
For example:
Set up the system to 'pump away' from the "Point Of No Pressure Change" (PONPC) which would be the connection point of the expansion tank...
Where is your exptank in relation to all this?
If doing a boiler bypass, it's advised to use a full size bypass... if the rest of the piping is 1", then the bypass should also be... but if it all works out to be easy and advisable to move the pump as you are thinking, then I don't think the 3/4" would be a real 'show stopper' if it turned out you could leave that in place.
Some might argue that it's sorta 'ghetto' to do this, I would consider buying another set of pump flanges and running a straight pipe between them to replace the pump. Might make a dandy spot to add a valve also.
If you do move the pump, use 'isolation flanges' to install the pump so that future pump work can be done without draining the system. Isolation flanges will also take the place of the system isolation valves.
I would also re-do and replace that relief valve. They should be mounted vertically, probably closer to the boiler, and the discharge should go almost all the way to the floor.
#32
12-25-11, 02:10 PM
Is it ok to have the pump after the boiler in the supply line.
#33
12-25-11, 03:47 PM
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Here is a twist that may explain much of my confusion around my boiler's temp:
ODR is a Honeywell AQ475A.
ODR settings Boiler Max Temp=160 Boiler Min Temp=130 Outdoor low= -10F
Aquastat=High limit=180 Low limit=120 Diff=10
Sequence of events:
1. No call for heat, boiler temp gauge = 130+
2. Call for heat- ODR starts ciculator but not burner
3. Measured Boiler discharge=130+
4. Discharge temp drops to below 120, aquastat fires burner on low limit, discharge temp continues to drop and gets below 100 before beginning to recover, ODR finally calls for burner to start according to the LED.
5. Next call for heat when the discharge temp falls to ~120 I turned up the Bolier min setting on the ODR so that it called for the burner to fire. Control setting at 160!
6. Next cycle ODR fires burner at 115. Tweaked up the boiler minimum a bit more.
7. Next call for heat the ODR fired burner at 128, Boiler min on ODR set to 180!
8. Next call for heat ODR fires burner at 129.
9. Set ODR boiler min to 175 on the dial. ODR fired burner at 125
10. Disconnected supply and outdoor thermistors converted Measured resistance to temp, looks ok. On the ODR scale 180=~130 175=~125 and so on. Probably a faulty boiler min potentiometer. I'll take it out and test it sometime. Right now it looks repeatable enough.
So, after all this time it turns out that the ODR was not even controlling the boiler min temp. The boiler aquastat was doing that job and too late to ensure recovery.
Now the question is, are the other controls wrong too? I guess I'll test them too....
ODR is a Honeywell AQ475A.
ODR settings Boiler Max Temp=160 Boiler Min Temp=130 Outdoor low= -10F
Aquastat=High limit=180 Low limit=120 Diff=10
Sequence of events:
1. No call for heat, boiler temp gauge = 130+
2. Call for heat- ODR starts ciculator but not burner
3. Measured Boiler discharge=130+
4. Discharge temp drops to below 120, aquastat fires burner on low limit, discharge temp continues to drop and gets below 100 before beginning to recover, ODR finally calls for burner to start according to the LED.
5. Next call for heat when the discharge temp falls to ~120 I turned up the Bolier min setting on the ODR so that it called for the burner to fire. Control setting at 160!
6. Next cycle ODR fires burner at 115. Tweaked up the boiler minimum a bit more.
7. Next call for heat the ODR fired burner at 128, Boiler min on ODR set to 180!
8. Next call for heat ODR fires burner at 129.
9. Set ODR boiler min to 175 on the dial. ODR fired burner at 125
10. Disconnected supply and outdoor thermistors converted Measured resistance to temp, looks ok. On the ODR scale 180=~130 175=~125 and so on. Probably a faulty boiler min potentiometer. I'll take it out and test it sometime. Right now it looks repeatable enough.
So, after all this time it turns out that the ODR was not even controlling the boiler min temp. The boiler aquastat was doing that job and too late to ensure recovery.
Now the question is, are the other controls wrong too? I guess I'll test them too....
#35
12-25-11, 04:00 PM
Join Date: Nov 2011
Location: Canada
Posts: 84
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The exptank is fed from the top left of the boiler next to the pump, opposite to the supply. You can see it in one of the pics below.
I'll take time to properly plan the job out with isolation valves a high priority.
Again thanks for your input.
Merry Christmas
I'll take time to properly plan the job out with isolation valves a high priority.
Again thanks for your input.
Merry Christmas
#36
12-25-11, 04:11 PM
Join Date: Nov 2011
Location: Canada
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The low limit on the aquastat is still in use to maintain the boiler at 130+, no DHW coil, good thing too because the ODR was not controlling boiler low temp. I planned on disconnecting the low limit and relying on the ODR to do its job. Glad I didn't do it yet because the boiler may never have started on low temp.
The last thing I expected was that the control in the ODR would be reading wrong. My boiler has been seeing temps as low as the mid 90's for 15-20 minutes at startup for who knows how long. I'm glad some of the things I have been reading here got me to looking and measuring or I would never have known!
The last thing I expected was that the control in the ODR would be reading wrong. My boiler has been seeing temps as low as the mid 90's for 15-20 minutes at startup for who knows how long. I'm glad some of the things I have been reading here got me to looking and measuring or I would never have known!
