the math of circulators

[Deleted User]

is the math doable for what's actually happening to the pressures in a system of this nature; ie, is there a practical explanation? and, the zone pumps may be larger but it's the only info i have right now

[Deleted User]

A pump is nothing more than..

a pressure differential machine. THe amount of pressure and related flow it experts is dictated by the pressure drop in the system at any given point in time.

Whether it creates positive pressure or negative pressure depends upon where the PONPC is connected in relation to the pressure differential machine. The machine does not care. Other system components do, however...


Tell you what. I will be up at the college this Monday with Lochinvar doing some high altitude testing. I will take a picture of the demonstrator we put together for a major court case because the opponent was trying to dispuste the PONCP. We tested it, and video taped it. When we shared the video tape with them during the "discovery" exchange period, they dropped their claim of insignificance like a hot rock, and it never came to light again...

I'll take a picture and post it here Monday PM.

Keep fighting, you will win.


ME

[Deleted User]

most excellent sir,

and many thanks. please post it monday

and while i have already 'won', as evidenced by the disappearance of the symptoms when the piping was changed to what we know here as the 'correct' way, my opponents still refuse to believe it. and while i can walk away self-satisfied at this point, for my mission to be complete, i want to show them the reality. whether they accept it at that point is up to them

again, thanks

Mark Eatherton

YOU'RE WELCOME

Understanding the PONPC and its relationship to pumps is one of the hardest concepts there is to see in ones minds eye. Hence, I came up with this demonstrator. I guarantee you that with the aid of this instrument, you WILL be able to impress upon them the concept.

Here's the drawing for the device.

Operating instructions: Fill system with water, completely flushing all air out of the system loop. OPEN THE BALL VALVE ON THE UNUSED PUMP's BYPASS. This is to avoid their misgivings about what it is you are about to show them. Eliminate all doubt. Turn on the pump that is pumping away from the expansion tank, close its bypass valve and partially close the bottom ball valve to exert a pressure drop on the system. The gage at the expansion tank will always stay the same, hence the title of PONPC. Now, let them see what's going on with the pressure gauges. The first gage down stream of the pumping away pump will show the highest pressure, and as you work your way around the loop, the pressure continues to drop until you get back to the PONPC, where it is the same as the fill pressure.

Now, turn that pump off, leave the ball valve on the bottom set wherever you have it set. Close the ball valve on the Pumping TOWARD pump, and OPEN the valve on the Pumping Away pump, and power up the pumping towards pump. What they will see is that the gage to the left of the pump is showing a significant drop in pressure, in fact could go sub-atmospheric if the fill pressure is dropped too low. As you move to the left looking at the gages, the gages become less depressed until you have worked your way back around to the PONPC, where the pressure is virtually unchanged. You have now visually demonstrated the PONPC, and the importance of the pumps location in relationship to the PONPC. What you were probably missing on your original demonstration was the pressure drop created by the system. You have to create this differential in order for the pump to do its thang.

Congratulations. Now, go pay it forward to your fellow hydronicians!

Attachment would not go from the LT, back ina second...

ME

[Deleted User]

JPEG of demonstrator is here...

Sorry for the cornfusion. Mac with Vista is confusing ME...

bob_50

Math

Mike, I am not real sharp with math however I count at least 27 different combinations of your 31' head pump and the 5 zone pumps. You have at least 27 different operating points on the system curve and 27 different flow rates. Each of the pumps will effect the performance of all the rest of the pumps. I wouldn't want to try to calculate the operating heads and flow rates for all the pumps at all 27 conditions. bob

[Deleted User]

yeah, without the pic

i was having a bit of a time picturing it in the eye of the storm in me mind. how high is high on the pump? in order to keep the cost down, can it be relative to the tank pressure?

and again, thanks. you sure did mean it when you said monday, as i didn't picture seeing it this early

today's 1st mission that i'm not looking forward to on a cold galv roof is to get a filter company some heat out of their cafeteria's heat pump. as i'd rather be in the shop building the model

[Deleted User]

27 combos?!

yikes! but there must be some simple math that dan has in one of his books. i think i have them all but i can't find an overlooked? formula

Bruce M

Pumpin Away

Mark, Is it safe to say that it is always beneficial to pump away or are there certain situations where it is best to pump on return? Are there any cases where it doesn't make a difference? What did the men who installed the hot water gravity systems know that we may have overlooked.

[Deleted User]

leaving out the names

to protect the innocent, would you detail the whys that took it to court?

Mark Eatherton

The real thing...

mike, I am not at liberty to discuss the case. However, the defendant was claiming that the air scoop was not an efficient means of air elimination, which we proved wrong, and that the location of the pump in relationship to the expansion tank did not make any difference, which we also proved wrong. This demonstrator never made it in front of the jury.

Bruce m, it doesn't really matter whether you are pumping towards or away from the boiler, so long as you are pumping away from the expansion tank. The only reason I can find for putting it on the return is for ease of shipping.

Back in the old days, when pumps had rag seals, it was thought that having the pump on the return extended the life expectancy of the seals. Todays pumps can handle 200+ degree F water all day long, so the only remaining reason is the ease of shipping the pump on the return.

ME

[Deleted User]

ah,

thanks for the pic. the pumps look like your basic off the shelf variety, but do you remember their specs?. and, what's the hose on the left side for?

[Deleted User]

mike

Use Grundfos 1542's or equal.

THe plastic tubing was to show the jury that we could make air go down hill, and also so show the effectiveness of the air removal unit. THe left hand cock of the fill and purge has a schrader valve on it. Once we got the unit purged, we would start the pumps, and then using a hand air pump, pump air into the stream. You could see it working its way around the clear flex tubing and then disappear, We had a ballon on the outlet of the autovent to show where it would go. Quite graphic...

ME

Alan R. Mercurio_3

Mark, thanks so much for sharing that information and the pictures to enable any of us to construct this great training simulator. I’m very fortunate that I’ve been given a very generous budget to put my classroom and lab together thanks to you I’m going to work on making this a part of the lab.

Your friend in the industry,
Alan R. Mercurio

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Bruce M

Mark, I need more information

Please help me understand this a little bit better. Let's use a "typical" boiler with the circulator mounted at or near the boiler on the return line. Where does the expansion tank need to be mounted in order to pump away from the expansion tank? Thanks for clarifying this.

jp_2

up stream

or near the inlet side of pump

archibald tuttle

circulators home and away

So forgetting the 5 circulators off diagram, if they just moved the water inlet with expansion tank, ergo no doubt PONPC, (what happened to the glossary link on the wall or am I dreaming, I figured that acronym out after a while but I thought there was a glossary where I once went to find out what a TRV was ) just to other side of the main system pump on the return they would be pumping away.

But that excepts that apparently the return pump serves as some kind of booster for feed pumps to individual zones that are on the feed side of the boiler but sort of qualify as pumping away excepting the drop of the boiler itself which is not capable of being simulated by the setup you have. Of course that depends a lot on what kind of boiler. My guess is that in the kind of system detailed there isn't too much drop across the boiler but maybe I'm mistaken. Your setup could simulate this with another valve between the airscoop/expansion tank and the pumping away circulator and then running both circulators. My guess is that the 24/7 circulator diagrammed is much larger than the zone circulators so you would have to maybe turn down the pump away if it is variable speed in order to simulate the diagrammed system.

What if the expansion tank and fill valve are on different sides, just as it is possible to have pumps on both sides can you have pressure buffers or sort of PONPC at more than one point in the system?

Finally on the construction of your sample. I'm guessing from the pencil diagram you posted earlier and from the best I can make out the circulator castings (it would be way easier to tell from the other side, maybe you can mount the next one on plexiglass) the grundfos is pumping away from the air scoop and the taco is pumping towards. Of course, if I've got this wrong then ignore all the following comments.

I can't see the schrader valve air introduction point, but if this is circulating the way I imagine then the air yould be bubbling up through the plastic tube. Assuming that the schrader valve were somewhere in the area of the grundfos, bubbles would have had to go down in order to come up.

I guess the one criticism of the model as metaphor is that in most cases the heating load would be up so the pumps would be on the bottom of the loop. It's a minor point unless you did some kind of myth busters thing and made the loop in a warehouse where you could run it up the wall 20 feet and down to simulate pressure circumstances resulting from height differences.

From a technical standpoint, this could be largely simulated by closing the load ball valve more, but my own version of this simulator was when I hooked up my baseboard in a hurry with clear pex, not too tall a rise over the boiler and PONPC, maybe 8 feet and in all likelihood wasn't pumping away but I can't remember where my temp. water input and expansion tank was, the rest of the configuration is lost in the sands of time -- too much eating out of aluminum pots -- but I watch the air bubbles circulating very slowly towards the pump and come to the down leg and slide backwards and do it again. It was my first actual vision of an airlocked loop. Then I raised the water pressure in the loop and it circulated. Maybe the up and down weren't really necessary for me to have seen or experienced approximately the same thing but clear pex for the whole loop might offer other insights. The main thing I haven't figured out is what you could put in that would help to observe the circulation of the liquid.


Thanks for posting all this stuff and any thoughts you have.

Brian

[Deleted User]

mark

the tubing idea is right on it. thanks again

[Deleted User]

Bruce M...

A lot of confusion stems from a book written by our gracious host. In that book, (Pumping Away and other cool tricks) Dan assumed that people would be dealing with conventional cast iron boilers. In that case, the expansion tanks are typically connected to the boiler, and the pump should be pumping away from the boiler and the expansion tank, hence the term "Pumping away from the boiler and the PONPC".

However, times and boilers have changed. Many of the new low mass high pressure drop mod con boilers require that the pump pump INTO the boiler to avoid nuisance lock outs due to pressure switches seeing a slight drop in pressure when the pumps first turn on.

Regardless of whether the pump is pumping into or out of the heat source, it is important that it pump AWAY from the PONPC, which is the place that the expansion tank is connected.

ME

[Deleted User]

You are welcome my friend...

I hope it helps open your students minds eyes as to the proper way to apply this equipment. Thank you for stepping up to the podium and helping to educate.

ME

Bruce M

Mark, I am a little slow today in Understanding

So if the circulator is pumping into the boiler (pump on the return side) does that mean the expansion tank should be on the return side before the circulator? I am usually not this slow in understanding things but it is a little dificult for me to visualize

[Deleted User]

Conditons that warrant pumping into the boiler...

Are dictated by the manufacturer. Pretty much all of the new class boilers pump awayfrom teh point of no pressure change, that being the expansion tank (PONPC), but towards the boiler.

In the case of the older, low pressure drop boilers, it is best to pump away from the boiler, AND the PONPC.

In a pinch, provided that the pumps added pressure and the fill pressure are no where near the relief valves release setting, you could pump away from the expansion tank, but into the boiler.

It is always best to follow the manufacturers instructions to a T. Most o fhte manufacturers I am aware of are aware of the pumping away strategy and incorporate it in thier I&O manuals. Some manufacturers still ship their boilers with the pump mounted on the return, but if you read their I&O manual, it recommends moving it to a pumping away position.

The only thing you really need to know is that the system will work BEST if you pump away from the PONPC. It allows the pump to ADD its head pressure to the system fill pressure, which causes air bubbles to become and stay small so they can be swept to the air removal device.

Will it work if your pump is pumping towards the PONPC? For the most part yes, except that there will be continuous air removal problems, and a host of other problems that raise their ugly head when you least expect/need it. Problems like water boiling, air bouncing through the system, low pressure cut off switches activating, pressure reducing valves feeding excess pressure to the system and so on and so forth.

Once you switch to pumping away, all these problems go away.

ME

[Deleted User]

the wm ultra's/tech support

want both to and away, like mark said, in order to keep a 'full' boiler