Two Tank Tango

ccstelmo

This two-story building with a basement is in Glenwood Springs Colorado. At 140 years old it has seen almost twice the changes in this world that I have, including, as you can imagine, a couple of boiler R and R's. The current iteration is a natural gas fired atmospheric boiler with electronic ignition installed about 35years ago by a guy who was my competitor at the time. (I say he was a competitor, but really, he was THE GUY when it came to heat back in those days and if he were alive today, he would smile at the notion that I was any competition to him.) He moved the boiler from the basement to the roof, leaving the pump, the bladder compression tank, and a gauge behind, orphaned. He did this because in commercial spaces square footage is directly related to income and the boiler was considered to be of second consideration to that. Makes sense.

A week ago, the tenants (commercial) in this building started complaining about being cold. People were cancelling their pizza orders, getting up, and walking out. Shops were closing early. Unhappiness set in.

The owner, responsive to the needs of his benefactors, responded by calling for help from the professional heating community of contractors in Glenwood Springs. None would come. He expanded his search to communities beyond, Vail, Avon, Eagle, Aspen --- alas, all were busy.

So, the owner, responsible beneficiary as he is, got into his private plane and flew to Glenwood Springs from his home in Santa Cruz, California. (Imagine the windshield time!)
He climbed to the roof and discovered that the wind had blown the flue, draft hood, cap, and all, off the boiler. It was lying in a corner of the roof. He also discovered the boiler was off on re-set. Surmising that hail, snow, and rain had entered the boiler's combustion chamber thru the uncovered flue he pressed the re-set button and - hey presto! The boiler fired, the building began to warm up, and the tenants withdrew their threats of withheld rent and legal action. Happiness regained a foothold, beer appeared, and toasts to the owner, a jolly good fellow, were the order of the day.

The owner sent me pictures. Pictures of the happy tenants and of the orphans in the basement and of the roof top installation.

In the basement, in a dark corner beneath a broken pull-chain light bulb (aren't they all broken?) a huge pump is pumping away. Really! "Pumping Away". Per Dan Holohan. The expansion tank is installed on the suction side of the pump. (See, my old competitor knew stuff. Thirty-five years ago, I didn't know squat about pumping away.) The tired old gauge, glass frosted and covered with grime and cobwebs reads 15 psi.

But wait! There's more!

On the roof too, there is an expansion tank (expansion or compression? I get confused). There it sits, showing signs of having been installed sometime after the boiler. Like the one in the basement it is 40 gallons and is a modern bladder type tank. A nearby gauge on the boiler manifold reads 0 psi.

I'm thinking that someone in the Glenwood Springs community of heating professionals arrived on the roof sometime subsequent to the original installation of the boiler there and said, without further investigation, "Hey, this isn't right! This boiler needs an expansion tank.

My advice to the owner was to shut off the valve to the rooftop expansion tank. He did. The nearby gauge did not budge off 0 psi.

But here's the deal - (and I'm quizzing you guys about this because my old competitor joined the Dead Men some years back. I can't call him. He's not answering). What's up with that 0 psi reading on the roof when the gauge in the basement is reading 15 psi. Is this the way it should be? I mean, the weight of the water should be irrelevant, right? I'm not getting my mind around this.

Thanks. I'm going to perch here on the edge of my chair while you guys gather your thoughts and reply. Don't take too long, would you? I need to use the bathroom. Old guys need to use the bathroom a lot.

ccstelmo

Larry Weingarten

Okay, I'll answer so you can then go to the bathroom.... not that I have a good answer.
The weight of water is relevant and it sounds like you have as much as thirty feet of height. So, with the lower gauge at 15, and taking into account that gauges can be somewhat inaccurate, or non-functional, the 0 psi on the roof isn't a big surprise. I'd use a gauge with a smaller range and see if you get any pressure on the roof. If not, bump up the pressure to 18 at the lower gauge as a test and see what the roof says then. It would be nice to verify the pipes high and low are connected somehow!

Yours, Larry

EdTheHeaterMan

I'll raise your 2 Tangos with a foxtrot and call with a Waltz,

There are two things to consider. (#1) The hight of the water in a column will have a direct relationship the the weight of the water at the bottom of the column. That is why we measure pressure in Pounds Per Square Inch. (PSI). Think of the water pressure in the city water supply. Many times that pressure comes from a water tower. Now if you were to measure the water pressure at the top of the water tower, you would expect to get the gauge to read 0 PSI just the same as tou would measure the pressure of the water at the top of a lake, or ocean or bucket of water. There is no "Gauge" water pressure at the top of the water surface. But if you were to place a gauge at the bottom of a column of that that was 50 ft in the air, you might expect to get a higher pressure reading. This is called Static pressure. Here are a few slides I used to convey this concept to the students in my Hydronics class.
Here is the same idea in a commercial building that is taller that the normal American home

The pressure at the top is much less than the pressure at the bottom. The higher the column of water is, the more pressure there is at the bottom. Think of a submarine that would get crushed at the bottom of the ocean as it sinks below the design pressure of the air chamber. The water pressure thousands of feet deep will crush the submarine. That water has all the weight of the water above it pushing on the submarine.

(#2) Now just because you took that boiler with 15 or 20 PSI water pressure to the top of the building, does not mean that the water pressure will stay the same as is was in the basement. I have doctored the last slide of the commercial 5 story building to have the boiler on the top floor. the top floor pressure is still the lowest pressure in the system and the basement pressure is still the highest pressure in the building.

So to test the theory, add 2 more PSI to the basement pressure and watch the boiler pressure rise as the water in the closed system becomes pressurized at the top.

Hope this helps your understanding of Static Water Pressure

Mr. Ed

kevink1955

That's quite a slide show. I agree with everything Mr. Ed said

ccstelmo

Ed:
I'm still having a hard time with it. I think I understand the math and the explanation seems almost intuitive. But ...... aren't the two columns (supply and return) that bear on the gauge in the basement sort of like two legs of a U manometer? On a manometer open to the atmosphere, the pressure (generated by atmosphere) is equal on both legs and the liquid levels in the legs are identical. It is with the introduction of external pressure on either of the legs (not both) that the liquid levels change, the pressured leg going down and the opposite leg going up the scale. Is it fair to say the height of the columns under a static (no pressure) condition is not relevant and they will be equal under any liquid height? Isn't it also true that if the manometer were filed at sea level and then brought to altitude the level would still be equal (but higher on the scale) in the legs?

Then add a pump. Close the manometer (the supply and return) at the top by connecting the legs together. Like inside of a boiler. Regardless of the height of the legs, nothing moves until the pump comes on and pressures one leg.

If you add a pressure tank in there, pressured so as not to move the legs one way or another (so that the levels of the legs doesn't move) isn't the whole system pressured solely by the pump when it is switched on?

Well, those are just thoughts. Seems like I'm supposed to know this stuff better, but I'm just not sorting it out

hot_rod

If two tanks are connected in different places, predicting the PONPC is a bit of a challenge. It would take a calculation of the pressure drop in the entire piping to come up with that point.

At the highest point you want at least 5 psi for adequate air removal. Maybe more if the boiler has a low pressure switch.
You also need to be aware of the circulators NPSHA. The higher the temperature, the more pressure you need on the circ. Maybe as high as 10- 12 psi at 200F. The pump manufacturers have that info, even for small wet rotor circs you need pressure at the circ.

They wanted more room in the basement, but left some of the old equipment in place??

EdTheHeaterMan

@ccstelmo. your understanding is very good. However, Pump head (or pump differential pressure) has nothing to do with Static pressure. They are 2 different measurements. we will tackle static pressure first.

The more water on top of the water pressure location you are measuring, the higher the PSI. When this pressure question came up in class I would explain it this way.
We take a trip to another Nation: the ImagiNation. If you have a 5 gallon bucket of water and it weighs 1 pound empty, when you put 5 gallons of water in it the whole thing weighs 42.65 pounds. Here is the math. I gallon of water = 8.33 pounds. So 5 gallons of water weigh 41.56 pounds. Add the weight of the bucket and you have to lift 42.65 pounds of bucket full of water in order to move it. Now you use your mind's eye to go to the ImagiNation.

If the bucket was 14” high and the diameter was about 10-¼” and you measured the gauge pressure at the bottom you would get ½ PSI and 0 PSI at the top. Use your mind's eye to imagine this. Suppose you had a container that was 1” x 1” square that went up almost 100 feet tall. Then suppose you put 5 gallons of water in that container. The container will fill up to about 97 feet high. If you read the pressure gauge at the bottom of the container of water that was 1” square, the gauge would read 41.65 PSI. Pounds per square inch. That is because all the water is in a 1 square inch column. Same water in a 5 gallon container, weighs the same amount. But the dimension of the container will result in different PSI at the bottom.


One more analogy is to use a different scale. Forget PSI and gallons. Think of a bucket of quarters. That makes it easy to imagine about 1 square inch. So we are now measuring the weight of quarters. I quarter weighs 1 unit in this example. If you put 5000 quarters in the bucket you have a bucket that weighs 5000 units plus the weight of the bucket. Now the bucket can hold about 50 quarters on the bottom layer so imagine that every quarter is laying flat in the bucket. There would be 100 layers of quarters. So the scale at the bottom of the bucket would read 5000 units but any one column of quarters would only weigh 100 units per column of quarters.

Now if you stack all the quarters in one tall column and place a scale under it, it would still weigh 5000 units. The difference is; since there is only one column of quarters , the weight is also 5000 units per column of quarters.


This all has something to do with Sir Isaac Newton and having an apple fall on someone's head. I think he called it gravity. It has nothing to do with how much head a pump can develop. Pump head is an entirely different animal when you are talking about a closed system like your boiler and radiator system. That is a discussion for after the coffee break.

EdTheHeaterMan

Here is the part about the circulator pump differential pressure or Pump Head. It turns out that the Circulator pump doesn't really need to be as powerful as you think. Here is why:

so of you were to look at this heating system from the prospective of the Circulator pump, all you need is enough pump head (or difference between the inlet and the outlet of the pump) to overcome the friction of the water moving past all those pipes, fittings, radiators and the boiler.


How high the pump needs to get the heated water has nothing to do with the Pump Head. (...the static pressure already did that) That means that this system will look identical to the one story system as far as the pump is concerned.



See how the longest pipe run is about 50 feet away from the boiler and the last radiator on the system has the same distance to and from the boiler on both systems?

So the pump pressure difference does not actually make a difference unless it is pumping towards the expansion tank... That is a whole other discussion.

ccstelmo

Thanks to all you guys. And Ed, I think we all agree that your math, examples, and diagrams really help to reduce the complexity of this stuff to levels that are intuitive. I feel like I'm on the same page with you guys now. But my story has a sequel because I got drawn into the solution when the boiler quit again. Yeah. It fired for a day then quit.

In trouble shooting almost anything, I learned years ago to be skeptical about the evidence. Mostly, to not be seduced by symptoms. (A detective told me once that he always looks for the "initiating event".) In this case, the flue sitting over in a corner of the roof was a symptom. It got replaced and the reset pushed. When the boiler fired the owner thought he'd figured it all out. He hadn't, and I ended up on the roof with him. The boiler wouldn't fire anymore so we started stripping the jacket off to find the controls. Very nice electronic control with an idiot light that said HSI failure. We went after that and found it to look relatively new from the outside but totally trashed at the business end. Crud all over it! Gently brushed and blew the crud off and the boiler began to fire predictably. Put everything back together and were leaving the scene of the crime when I thought about symptoms vs causes. I went back and stripped everything down because I wanted to look into that combustion chamber and see what those burners looked like.

AHA!

Sixteen burners, all of them with trash and crud plugging up the holes. The deflection trays sitting on top of the fin tubes were full of trash and products of combustion (white stuff). The fin tubes themselves were plugged up with white stuff. And on top of all that (or, actually, under all that) the floor of the combustion chamber (a 1-inch-thick semi-solid insulation material) was covered with a full inch of toasted debris.

I'm thinking the flue must have been off the boiler for years and a boatload of airborn crud and corruption (along with snow, rain, and insects) entered the combustion chamber and wreaked havoc. That every time those burners ignited, they stirred up all that stuff. I'm also thinking the fuel/air mixture is lean but did not see a way to adjust it without changing out the orifice sizes on the burners.

Scrubbed, scoured, vacuumed and buffed as much as I could and it's doing well now.
As I was leaving I checked the gauge. It's a 70 pound gauge and hard to read, but there seems to be about 2 psi at the boiler. The glycol level was at 15%, I surmise because someone put a feed valve on the system. (Never could figure out why people put water feed valves on glycol protected systems).*

* Actually, I'm of the opinion that automatic feed valves should be relegated to the dustbin of history. Back in the day, leaky old B&G bearing assemblies made them necessary but modern sealed bearing pumps make them antiques. To those who would say "Oh, there's always a little water loss somewhere" I say: Is this a closed system or not? If there's a leak, the solution is to fix the leak, not disguise it with an automatic feed valve.

I'm going to bump the pressure on the roof gauge to 5psi per hot rod.
I'm going to get rid of the roof tank because I think it makes no sense.
I don't know what I'll do with the glycol level. The owner's a cheapskate and won't stand for a 40% mixture at todays costs.

I'm still interested in continuing the discussion if anyone sees something I need to know.

ccstelmo

ccstelmo

Hello Ed:

You've got me hooked, now reel me in.

I can't ignore the comment "...the pump pressure doesn't actually make a difference unless it is pumping toward the pressure tank". I've got a whole book here called "Pumping Away" that has been my bible for some time now. I've always used the principle that pressure drives gas into solution to my advantage when piping systems and (especially) locating expansion tanks. Back in the day (the only days I have anything useful to say regarding heating) when cast iron was king, we'd get into lively discussions about how to capture that air and deal with it intelligently.

So please elaborate.

ccstelmo

leonz

I wonder if your building was originally a bottom fed gravity hot
water system that had air in the radiators to balance the system
and it was changed to a pumped system.
It really sounds like it was changed from a coal fired gravity hot
water heating system to a gas fired pumped system. BOOO, HIIISSSS.

EdTheHeaterMan

ccstelmo said:

Hello Ed:

You've got me hooked, now reel me in.

I can't ignore the comment "...the pump pressure doesn't actually make a difference unless it is pumping toward the pressure tank". I've got a whole book here called "Pumping Away" that has been my bible for some time now. I've always used the principle that pressure drives gas into solution to my advantage when piping systems and (especially) locating expansion tanks. Back in the day (the only days I have anything useful to say regarding heating) when cast iron was king, we'd get into lively discussions about how to capture that air and deal with it intelligently.

So please elaborate.

ccstelmo

There is a concept in a hydronic closed system called The Point Of No Pressure Change. Here is a summary of that concept. https://www.indoorcomfortmarketing.com/the-point-of-no-pressure-change/

Basically you can compress air in the expansion tank or the air can expand in the expansion tank. You can do this by heating the water causing it to expand. Since the water in the system can not compress we provide the air cushion in the compression tank or expansion tank. The air can compress and expand as the water volume changes. Likewise if you open the feed valve of the system to add more water, the air cushion will compress as the added water enters the tank. That added water can not go into the radiators or pipes or boiler because all those things are already filled with water. Since the water can not be compressed that water can only go into the expansion tank where there is room to compress the air. So the only way to put more water in or take water out of the expansion tank is by changing the water volume.

Since the circulator does not add water or subtract water from the system, the pressure difference between the inlet and the outlet of the circulator can only move the water through the system. It can not suck any water out of the tank. Where would that water go? Not to the boiler, or the pipes, or the radiators, they are already full of water. So the circulator will not remove any water from the tank. Likewise, if the expansion is located close to the outlet side of the pump, there will be no pumping of any water into the tank. Where would that water come from? The boiler? The radiators? The pipes? If that water was piped into the tank, what would be left in the void left by removing that water? You can not compress water or make the water expand to fill in a void. Therefore the expansion tank can not change pressure when the circulator operates. The Static pressure of the system with the circulator off is equal to the expansion tank pressure. Plain and simple.

Now that you have the system filled with water and the only air cushion is in the expansion tank you need to make a decision as to the location of the circulator pump in the system’s closed loop. If you have the circulator on the boiler return and the expansion tank is on the boiler supply, then the pressure differential of the circulator pump will be subtracted from the static pressure in the return side of the system. That subtraction of pressure may cause enough of a pressure drop on the return side of the highest point in the system to cause the static pressure at the top radiator valve to be lower than atmospheric pressure.

If you place the circulator on the supply side of the boiler, pumping away from the expansion tank, then you will be adding the pump differential pressure to the system static pressure. This will help drive tiny air pockets from the upper radiators out of the system and if you have a properly piped air cushion tank or a properly placed air vent near the expansion tank, that Air will never cause you a problem.

So that is the reason I added the Qualifier "the pump pressure doesn't actually make a difference unless it is pumping toward the pressure tank" to my statement about Static Pressure.

Now look at this system filled to 12 PSI static pressure.
when the circulator is on, let's say that the pump differential pressure is 6 PSI (that is pretty high for this system but it is only an example). When you pump towards the PONPC, The pump pressure can not increase the pressure on the outlet side of the circulator. So it MUST lower the pressure on the inlet side of the pump. If you were to place a gauge at different locations thru the system you could see how the pipe friction would lower the pressure incrementally thru the system.



This makes sense. Right?

Now look at the same system in a vertical application. Can you see how the top of the system might fall below the atmospheric pressure as the static pressure at the top of the system is lowered?



Look Closely at the pressure gauges on the supply and the return of the radiators. The ∆P is the same at each rad further from the boiler. The pump differential pressure is subtracted from the static pressure. At the top of this system there is only 2 PSI static pressure. But since the circulator differential pressure is about 6 PSI, and only 1/2 of that friction loss is used up as you get 1/2 way through the system (that happens to be at the top), only 1/2 of the pressure drop is 3 PSI. With only 2 PSI at the top, the top radiators are now lower than the atmospheric pressure by -1 PSI. In other words a slight vacuum (about 2" Hg). So if there was an automatic air vent somewhere up there, that air vent would suck air in. Or if there was a radiator valve with a leaking packing gland, air would enter at that point.

Also if the water temperature was over 200°F at that point. That water might boil at the lower pressure. What a racket that might make.

@DanHolohan Pumping Away goes over this in detail. I attended several seminars where Dan shared these concepts. Reading the book and hearing it in person makes a big difference... Hopefully reading my interpretation of his teachings gives you another angle to grasp on to.

I’m available for any questions you may have. As long as you can take a sarcastic comment from time to time.

Yours Truly
Mr. Ed

EdTheHeaterMan

I just had a funny thought when I read this paragraph.

@DanHolohan Pumping Away goes over this in detail. I attended several seminars where Dan shared these concepts. Reading the book and hearing it in person makes a big difference... Hopefully reading my interpretation of his teachings gives you another angle to grasp on to.

2000 years from now, would there be a Pastor at the pulpit saying something like: "This is a reading from the Holy Gospel according to DAN, Book of LAOSH, Revised, Chapter 23: Verse 3 thru 45." And the masses gathered to hear about the Dead Men. One of the followers of DAN proclaimed "There is no heat in my radiator” and the multitude chanted in unison "Do you have enough air vents?" This is the word of DAN.

Response: “Thanks be to DAN”

leonz

Dr. Mr. ccstelmo,

The first and foremost question I have to ask is:

Are there orifice discs in the first floor radiators?
It certainly sounds as if there are none.

I most certainly hope I am wrong in thinking there are no orifice discs.

If there are none in the first-floor radiator inlet's they desperately need them.

I hope the painters or THE PLUMBER BEFORE YOU did not throw them out
when they found them in the radiators if they messed with the radiators.

I hope that you can provide us with pictures of this system and one or more
radiator inlets on the first floor as it sounds as if there are no orifice plates.

Remember that water like electricity is lazy and go where it wants to go unless
it is controlled and regulated.

A big thank you goes out to the Dead Men and Mr. Holohan for his discussion of
orifice plates on pages 4 and 5 of CLASSIC HYDRONICS.

I hope you can provide us with pictures of this system as it needs work to improve it.

ccstelmo

Sorry about my extended absence on this system. (Life caught up with me, took me to the ground, cuffed me, and threw me in the hoosgow. But I'm out on good behavior now.) No news is good news, though, as they say, so you can assume it's back on track and you would be right. However .... there are still a couple of unanswered questions.

To Hot Rod - Yeah, they left the pump, a gauge, and a floor mounted 40-gal bladder tank behind in the basement. But it's tucked away in the corner so it's not taking up too much space. I can't imagine why Clem did that other than to say that if the pump was installed on the roof, then it'd have to be protected and there's no way to do that up there short of additional construction. Of course, the tank had to follow the pump. (But you're not going to get me to say anything bad about Clem. He was a hell of a heat man. Better'n me.) And I'm definitely changing out both gauges as you suggested. (The one in the basement was reading 25 psi, not 15 as previously reported (it was cloudy), and the one on the roof has a 1 - 100 range)

To leonz - You threw a curve at me with some of your comments. Your guess about the building originally being a coal fired gravity hot water system is right on. The pipe sizing confirms that. But what's all this about air at the top of the radiators providing accommodation for expansion though? Those air vents at the top of the radiators are for getting that air out. (Or don't they get ALL the air out?) I actually never thought about it before, but it's possible this was originally an "open" system, not a "closed" one. (In another part of town, I discovered an open system once, so they were not uncommon.)
Now, about "orifice discs". Actually, I never heard of them. It is intuitive, though, that since, as you observed "water is lazy", a designer would want to make it harder for the water to get into radiators closer to the boiler than those further away. Really, though, you don't want me to dump all the fluid in this system (400 gallons maybe?) to find out, do you? On the other hand, I will say this: in January and February the tenants on the third floor all leave their windows open and the tenants on the first floor all wear sweaters! (:
(The tenant and customer in the basement get heated by the big pizza oven down there.)o
And I'll get some pics of all this when I get back over there. (No one's complaining this year and it's a 200-mile round trip for me.

New news about the system: When I finally did get a flashlight that was bright enough to light up all the crevices in the basement, I spotted three 10" tall stand-up immersion thermometers Clem installed. One was downstream of the pump and the other two were on return mains connected to a tee, the branch opening of which feeds the suction side of the pump. Think this is how Clem monitored the system? This discovery was in the summer when the system was dormant. Any guesses what I'm going to see when I get back over there this winter?

Ed The Heater Man - Hallelujah! I'm a believer now. When I get over there (soon) I'm shutting off the tank on the roof altogether. I'm squirting some air into the basement tank (about 4-5 pounds) to bring the pressure on the boiler above up to about 5 pounds.

If any man present has any objection to this plan of action, speak now, or forever hold your peace.

ccstelmo

leonz

Hello and good morning Mr. ccstelmo,

I wonder if the landlord would consent to having a small shed or lean to with a sliding barn door placed over the boiler to protect it??

Please, quickly order copies of HOW COME and CLASSIC HYDRONICS from the Heating Help Bookstore, you need them to convince the landlord his system needs work to make him and his tenants happy.
I have them along with Pumping Away and What Hydronics Taught Dan Holohan, they are worth every penny and they will help you understand this system more easily.

The stand up immersion thermometers are like gold!!!!!!!! Please set up bear traps around then so no one takes them and floods the basement.
Actually, I think you may find that they are Dwyer vertical immersion thermometers. Still, please treat them like gold. Dwyer has a repair and testing offer for their gauges and it may well be time to have them tested and cleaned by the Dwyer folks if they are Dwyer Gauges.

Hint, hint installing a vacuum gauge on the inlet/suction side of the circulator is better than a crystal ball and a fortune teller when trying to find heating system trouble.

I have a vacuum gauge on the inlet side of my Bell & Gossett NRF-25 circulator and that helped my find negative pressure gradient(-Hg.) demon that said "Don't bother me I refuse to move water while squealing" in my coal stoker boiler system; eventually tracking it down to the packing nuts on the gauge glass of my 15 gallon steel compression tank that needed a 1/4 turn of tightening. Seeing a -13 inch Hg, Pressure gradient reading on my vacuum gauge when the system was off was the first clue in finding the problem and fixing it thanks to the wallies.

If there are no isolation valves that can be shut to remove the circulator when needed installing them in the off season would be a good time to install them.

I look forward to see your pictures when you have them. It would be a very good idea to suggest to the absentee landlord that he has a small lean too installed on the roof to protect the boiler and at the same time replace the flue stack piping with heavier flue pipe and a rain cap. A sliding barn door would allow for easy access to the boiler and help keep the boilers burners cleaner as well. Having 2 double gang outlet boxes installed at the same time would allow for more work lights and shop vacs as well at the same time.
making cleaning and tuning the boiler easier and allow for a faster repair if a small heater is needed while working in very cold weather.


Dwyer has nine inch Industrial thermometers with adjustable gauges that allow you to adjust them for the best viewing angle. I would mention the price but I don't want to get us yelled at.



Thanks for keeping me in the loop, I look forward to seeing your pictures.

Leon