What system pressure for 6,400ft above sea level?

OldSkool

As I have noticed lately, Taco now calls for 20psi system pressure for their pumps installed above 5,000ft.  I noticed this for the first time when looking into one of their newer #0015 models (replaces the 00R 3-speed).  Although the calculated volume of expansion water at my 180degrees is the same for both pressures (1.925gal), the difference in required tank acceptance is substantial.  For 12psi the tank can be 5.34gal total volume, for 20psi the required acceptance is 11.46gal.  Which means I need to install a big ol' fat model 90 instead of an 11" model 60.  It also means I can't use the HydroClaw mounting as planned because it won't fit the 15.375" diameter model 90.

Here is the question:  Is there a chart somewhere where I can look up just what the system pressure should be at a given altitude?  If this install was at say 5002ft altidude, it is obvious that the move up from 12psi to 20psi would be silly, so what are the actual pressure requirements for various high altitudes?  If say 16psi would work for my case at 6400ft a model 60 would satisfy the 7.29gal acceptance indicated by the attached Amtrol tank calculator (see bottom of catalog).

Zman

Try a different brand

There are countless circulators running at lower pressures and higher elevation. If Taco has decided there's cannot function at normal design pressures. I would chose a different brand.

Gordy

Missing something ?

Maybe I'm missing something but 12 psi on the gauge is 12 psi no matter what altitude. The only thing I can see is keeping air in solution may be a bit different.



Gordy

bill_105

That's just what I thought

Well, a while back the topic of elevation came up here. I was, and still am clueless. Could there be an effect on a relief valve?

Tire makers don't tell you to change tire pressure based on elevation.

Or, could a lower atmospheric pressure cause trouble with pump seals?

Still clueless. But still with plenty of crazy ideas!

OldSkool

Here's the quote from Taco



"CAUTION: Installations at higher elevations over 5000 feet must have higher fill pressure of 20 psi minimum to prevent pump cavitation and flashing. Premature failure may result. Adjust expansion tank pressure to equal fill pressure. A larger size expansion tank may be required." 

 

Taco puts the above warning on their instruction sheet for the current pumps.  The standard barometric air pressure on everything at sea level is 29.92 in/hg, which is 14.69 psi.  At 6400ft ASL the pressure down to 11.12 psi.  I believe this lower pressure at altitude is what they are talking about.  The lower ambient pressure reduces the net positive pressure available at the pump impeller, increasing the possibility of cavitation.  I'm no engineer but I believe they may be right on this. 

Zman

I agree

I agree that Taco appears to have invented a circulator that performs poorly at altitude. I don't know (or care) why. The question is, do you redesign your system or use one of the other fine circulators on the market.

Carl

OldSkool

Good point.

I'm looking today Carl into a couple of other pumps.  I just didn't want to penalize a company for perhaps just being the first to be honest on the subject.  I may have do two things this time...go with a different pump (without such a warning) and raise the pressure in the tank, regulator, and system a few pounds (up to say 15psi), but not the 20psi that Taco states.  At least that way I won't have someone asking me why I'm not complying with the manufacturers written requirement, if you know what I mean.  I have asked Taco for finer detail on this, and have not heard back from them just yet.  I'll post whatever I find out.  Thanks.

Gordy

Altitude and tire pressure

Altitude does effect tire pressure. If you go from sea level to 6000 feet it drops 4.6 psi.



But you would be filling a hydronic a system at what ever altitude to what ever operating psi. Not moving a 12 psi system from sea level to 6000 feet. If that we're true then yes the system would see a decreased pressure.



I think it has to do with keeping air entrained or in solution in the system by bumping up the psi a bit. Air comes out of solution more readily at lower pressure.



This would apply to any brand of circulator, and maybe this is something taco has figured out but no one else has, creating cavitation.



Gordy

Zman

Design

I think Gordy is correct. It must be a problem with keeping air entrained.

This is all related to the design of the circulators passageways. I suspect the newer taco circs have areas where low pressure occurs and air becomes trapped. I have seen countless circulators at 9,000 to 11,000 feet running at 12-15 psi. Never a circulator related air problem.

Carl

icesailor

Taco Cireculators:

I think that if you read the info on Taco circulators, they now say that if you want to mount them with the motor "up", you MUST raise the system pressure to 20# so you "squish" the bubbles and raise the boiling point.

If you air elimination like Taco 400 float vents and leave the caps open, you have less atmospheric pressure on the open float vent and a lower boiling point. Because of the controversy over leaving the fill valve (PRV) open or closed, a closed PRV can and will cause more problems.

There's nothing wrong with Taco pumps, they are just reacting to a problem with a solution. Raise the pressure. It really does seem to solve a lot of problems.

Zman

The manual

Ice,

Here it is http://www.taco-hvac.com/uploads/FileLibrary/102-433.pdf

There is no reference to "motor up".

I will be curious as to what taco comes back with. I like taco products but will not start resizing systems for them.

Carl

Gordy

Eye of the volute

I understand the reasoning because higher pressure raises the boiling point thus preventing water from flashing to steam in the volute, but in a closed system barometric pressure outside a closed system should not effect the psi of the system. Open systems yes.

OldSkool

NPSHA

No expert here .. by any means, but when I've seen Net Positive Suction Head Available calculated, ambient pressure is added to gage pressure, (I'll check again but that is what I remember anyway) as factors in the calculation.  In an open system, gage pressure contributes zero to the head calculation but ambient pressure is still in there.  Ambient pressure goes down as altitude goes up so there's your reduction in NPSHA.  The pump Net Positive Suction Head Required at some point exceeds available suction head and cavitation happens.  This helped me get some of the concept  -  http://www.mcnallyinstitute.com/11-html/11-12.html

jumper

absolute pressure

absolute pressure determines when cavitation begins. Absolute pressure is gage pressure plus atmospheric pressure. Both boiling water and gases coming out of solution can cause cavitation. Only industrial users are willing to pay for high level vacuum expansion tanks, but that at least minimizes the gases.

Zman

Pumping away

In a properly piped system, pumping away from your expansion system, you will never see pressures lower than your your design pressure. Your design pressure is relative to the atmospheric pressure.Once a closed system is purged, Altitude is simply not a factor.

icesailor

Pressures:

"Z",

The below link to Taco cartridges show that line 2, covers mounting "00" circulators with the motor "up" and raising the pressure to 20#.

I found one mounted with the motor "up" and thought it was wrong until I looked it up to see if it was wrong. Come to find out I was wrong, and it was right. But for some reason, I think I remember having to do something to the circulator and finding that it had a different O-ring gasket and that you could NOT use a red rubber gasket on it but would have to use the O-ring that fit it. And my supplier had to get one out of another circulator of the same type.

Its a personal thing. I use Will circulators because they use a fat, wide round gasket and you can't use red rubber gaskets on them.

icesailor

Pumping Away:

But "pumping away" will expose the rotating part of the circulator to the hottest temperature of the water being pumped. Increasing the possibility of cavitation due to the drop in internal pressures inside the circulator. The higher system pressures will overcome this.

IMO.

Zman

Ford,Chevy,Dodge?

Ice,

This certainly becoming on of those....

On one hand your point about heat and pressure are correct. On the other, the air eliminator, often mounted at the expansion tank will function better in hotter water.



I don't always pump away from the boiler. I like using a TT prestige with it's low head loss as a giant air eliminator. I then put the expansion tank and spirovent on the secondary (circulator pumping away). TT draws it this way and it works well.



Back to the subject. I suspect taco has discovered a design flaw in the pump or seal. Their solution is to raise the pressure. I am sure it works for the reason you describe.



Carl



I really like Chevys

And am partial to Grundfos

bob_46

Closed system

Carl, when you look at a gage on a closed system at sea level and the gage reads 12psi

absolute pressure in the system is 26.7 psi . When you look at a gage on a system in

Denver and the gage reads 12 psi the absolute pressure in the system is 24.2 psi .

Bourdon tube gages use atmospheric pressure as a reference just like a manometer.

Zman

Bizarre note

Bob,

You must admit it is a Bizarre note. The instructions say nothing about minumum operating pressures. They don't even require the system be closed. But if you want to install at altitude, 20psi.

I understand what you are saying about absolute pressure. I can't get my brain around how it effects a closed system.

Carl

icesailor

Wet Rotor's

As I remember (going back a while), Taco was the first wet rotor circulator I ever installed. To replace the Taco 110's and the B&G Series 100. Those old instructions plainly stated to NOT mount the pump with the motor up because you couldn't get the air out. I never read the instructions again. I never mounted them fanny up anyway. Only when I found this leaker that I fixed did I look into it and found the note about raising the pressure if you mounted it fanny up.

I crank all vent caps down tight. I left the one on top of my boiler open and I had to change it because of all the white crud from spitting water which evaporates and leaves white crud all over the top.. I should have left it cranked down like the one on the flow scoop.

paul_79

pressure

this is a question not of the pump itself but the gauge reading at higher altitudes

 this is why the refrigeration guys have a temp pressure chart for higher altitudes because your gauge is reading light at higher altitudes. So at 5000 feet your gauge will read a couple of pounds light. The fine folks at Taco have found that some of the pump installs at lets say ski resorts at 9 or 10000 feet then the pumps start to cavitate even though the gauge says 12 psi.  the real pressure is say 8 or so psi.   False gauge readings  that kill the pump from low pressure.

paul_79

pressure

 here is a good thing to remember your gauge from sea level gains appr, 1/2 pound for every 1000 feet of elevation. on my temp pressure chart that change is 2  pounds higher at 5000 feet than at  sea level.  so if i set my pressure at  12 then the real pressure  the system is at is 10  psi so at 10000 feet i would be at 8 psi the system  would see and the gauge would be at 12 psi.  so if the gauge is not corrected for altitude then the bladder tank pressure would also have to be addressed.

Gordy

Funny

As long as I have been hanging around here 11 years. Never has this been brought up as a problem , or as something that needs to be corrected for during installation at various altitudes.. There are people that hang here at those higher altitudes.





Referring to system pressure not combustion .



Gordy

icesailor

More on pressure:

Then, there is "pressure altitude" on aircraft. The altimeter on aircraft tells the pilot at what altitude the instrument is located. The baseline atmospheric pressure at sea level is 29.92". If the instrument at sea level is raised in height/altitude, and the atmospheric pressure stays the same, the instrument will show the elevation of the instrument. If the atmospheric pressure where the instrument was located at sea level drops, the indicated altitude will drop. The altimeter has an adjustment that is set to the current atmospheric pressure outside so that the instrument knows at what level it is at. When the aircraft and instrument is moved from a starting point to another place, if the atmospheric pressure goes down, the altimeter will read incorrectly. Through FAA area control centers or ATIS (Aircraft Traffic Information System), the correct atmospheric pressure can be found so that one can re-set the altimeter for the correct local pressure and correct the elevation read-out. There are many situations where a pilot was flying into IFR conditions into ascending/rising terrain and the outside atmospheric pressure was dropping due to deteriorating weather and because the pilot did not correctly adjust for drift, flew into the rising terrain. The altimeter showed enough altitude but because the outside pressure dropped, the instrument showed the aircraft at a higher altitude than was the true altitude.

The same thing happens in the heating system at higher altitudes. Like Paul points out, the pressure is dependent on the outside pressure in the system when it is filled.. Its the same as the mis-adjusted altimeter.

A closed heating system is just a closed mini atmospheric system.

Gordy

Aircraft altimeter

Ice I understand completely what you are saying as I took flying lessons for a summer until I figured out the cost of ownership, and how much I would actually fly.





Again I have to say while there are going to be differences is it enough to worry about? Maybe if the system was of considerable elevation. The higher the more effect.





So the next time a super low pressure system moves through I will be sure and bump my system pressure up as to avoid circulator cavitation;-).





Just having a little fun ice .





Gordy

OldSkool

That's the question

Gordy,

We've come back around to my original question.  If I'm installing a system at say 5002ft ASL do I really need to bump the system pressure, fill regulator, expansion tank size and operator instructions all the way up to 20psi?  Of course that would be a bit silly, but given that Taco has put in writing in their installation instructions to do just that, it makes the installation look less than professional if it doesn't even comply with stated manufacturers specific instructions.  It starts me off looking like some of the folks that I really don't admire.

I was hoping to get better written detail from Taco, but as of now have not.  It looks like, from reading this thread, that the calculation of the increased pressure required is simple enough...just taking into account the difference in absolute pressure between sea level and the altitude at the installation site and adding that amount to the gauge pressure.  (Although I have been, at times, really wrong in the past making such assumptions )  For just right now I think I'm going to use a pump that does not have such a warning  (15-58fc in my case here), and compensate as I just described. 





Bruce 

Zman

Yours is not...

Yours is not the only house above 6,400. I live with 2 -15-58s (5 years old) and a Taco 0014 (10 years old) My pressure is 15# and all circulators are dead quite.

I am at an elevation of 10,160 feet. As much as this is an interesting subject, the bottom line is that most circs have no trouble with altitude. Unless taco is willing to explain their position, I would just not use it.

Carl

icesailor

Missed points:

You guys are really missing the point. One circulator isn't any different than another one.

I gave you an example of going up because that's where you were going, up in elevation. Now, lets go down. In a submarine.

Submarines achieve neutral buoyancy by adjusting their ballast tanks with air. When they want to submerge, they flood the ballast tanks with water and the buoyancy air blows out. Not all air but some. As the boat submerges deeper, the air in the ballast tank is compressed, causing a lessening of buoyancy. Commercial fishing draggers are a boat in the water with a huge winch mounted on it to pull back nets. Submarines on the other hand, regardless of all the spooky stuff they can do, are really just a huge air compressor that can generate huge amounts of compressed air at tremendous pressure. Enough pressure to push the water out the bottom of the ballast tanks if the boat wants to change to a shallower depth. As they go lower, the air is compressed, and the boat becomes heavier because as the air is compressed, more water comes into the tanks. The air/ballast is carefully monitored.  A submarine that goes below the depth of where they can use the compressed air to raise them to the surface, sinks. When the boat ascends or rises, the compressed air bubble then expands causing an increase in bouyancy. They probably have a way to capture the compressed air rather than throwing it away. I'n not a submariner and I've never read anything about that air.

Everything that happens to a submarine, happens in a closed heating system. There is so much thrust in the propellers of a sub, that they will cavitate. If cavitation occurs, the boat can drop lower where the pressure is greater and enough to stop the cavitation.

In my opinion and not worth much, from a standpoint of physics, I think it is bad practice to mount a water lubricated wet rotor circulator with the motor pointed up. No mater what you do, you will always be dealing with air in the rotor chamber. And that can't be good.

Zman

Ice and others

I was rereading Modern Hydronic Heating, I get it!  Thank you for your patience. I must admit my mind is not as "pliable" as it once was.

I do believe the manual should have said "System pressure should be 15# at sea level, increase pressure .5 psi for every 1,000 feet.

Carl

paul_79

zman

better late than never