Euro-open system, point of no pressure change?

[Gooserider]

I have a couple questions on laying out a "European Open" (EO) style system where the system is "pressurized" by the weight of a water colum in a high mounted open overflow tank, as opposed to being tightly sealed and pressurized by the air pressure in an expansion tank like we are used to with closed systems...

1. I have seen numerous references by people here, and in articles on hydronics elsewhere by folks like Siegenthaler about the point where the expansion tank is attached to the system being the "Point of No Pressure Change" and the importance of setting up circs to pump away from that point in order to work best... I understand the science behind this, but am not quite sure where the equivalent point would be in an EO system - would it be the point where the overflow tank line connected to the system?

2. Does it matter where in the system one attaches the line to the overflow tank? It seems like most of the diagrams I've seen show the line as a dedicated line connecting down near the boiler, and essentially not being part of the main heating loop flow... However as I understand the physics, as long as one doesn't cut off the flow path to it, there is no reason the tank couldn't just connect to a tee off whatever heating loop was handiest to the tank location... Is this to preserve that point of no pressure change?

Gooserider

 

[Hansson]

Effecta has some schemes.Maybe you can get some ideas there
(broken link removed to http://www.effecta.se/images/hydraulicschemes.pdf)

this is a installation guide in English
(broken link removed to http://www.effecta.se/images/anvisningeng.pdf)

 

[julien]

And you lose the Oxygen Barrier with an opened system.

 

[chuck172]

The effecta installation guide speaks of a "automatic shunt valve"

"Automatic Shunt"
"It´s recomended to use an automatic shunt valve to control the
flue in the radiator circuit. It feels the temperature in a special
place in the house and regulates the temperature in the radiator
circuit flue. Using an automatic shunt will significantly reduce the
amount of wood needed during a year, and your indoor climate
comfort will also improve".

What is it, and how is it used?

 

[Hansson]

And you lose the Oxygen Barrier with an opened system.

I don't think much Oxygen goes to the water.My system was built 1957 and i still use the same pipe to expansion tank.
I check it when I change to a bigger expansion tank and it look fine.
If you are afraid of Oxygen you can put in some parafin oil in the to of the tank and you have a Oxygen Barrier.

Chuck a automatic shunt valve is used by everyone here. I put out the right temp to the radiators.Just enough to keep the house at the temp that you want.
This is one of the brands that we use
(broken link removed)

This is a photo of the one I use
(broken link removed to http://picasaweb.google.se/725hansson/Panrumsbilder#5020602465138459874)

U can see the circulating pump in the top of the photo


Sorry Gooserider if I came offtopic

 

[chuck172]

Thanks Hansson, I guess the automatic shunt valve is what we call a mixing or tempering valve. I don't think it be of any benefit to fin-tube hydronic heat. Probably more suited to radiant heat which can use lower temps.

 

[Gooserider]

Hanson, thanks for those links, they look very useful.

Julien - part of the problem that I have to deal with is that I live in the state of MA... MA codes are really stupid in some ways, and essentially say that if I want to run a closed system, I have to buy my boiler from either Econoburn or Wood Gun, and pay big dollars extra for an ASME "H-Stamp" version instead of their standard models...

If I go with an "open" system, I can use any boiler I like, with no requirement for an H-stamp, so I can get one of the standard model Econoburn or Wood Gun units, or any of the Euro-boilers, and avoid the hassles. By doing the "European Open" system I get nearly the same effect as a closed system, so it seems like a reasonable approach, as our house is tall enough to have such a setup work well (It wouldn't work as well in a single story house...)

Gooserider

 

[pybyr]

I have a couple questions on laying out a "European Open" (EO) style system where the system is "pressurized" by the weight of a water colum in a high mounted open overflow tank, as opposed to being tightly sealed and pressurized by the air pressure in an expansion tank like we are used to with closed systems...

1. I have seen numerous references by people here, and in articles on hydronics elsewhere by folks like Siegenthaler about the point where the expansion tank is attached to the system being the "Point of No Pressure Change" and the importance of setting up circs to pump away from that point in order to work best... I understand the science behind this, but am not quite sure where the equivalent point would be in an EO system - would it be the point where the overflow tank line connected to the system?

2. Does it matter where in the system one attaches the line to the overflow tank? It seems like most of the diagrams I've seen show the line as a dedicated line connecting down near the boiler, and essentially not being part of the main heating loop flow... However as I understand the physics, as long as one doesn't cut off the flow path to it, there is no reason the tank couldn't just connect to a tee off whatever heating loop was handiest to the tank location... Is this to preserve that point of no pressure change?

Gooserider

A couple of good articles-

(broken link removed to http://www.heatinghelp.com/article/11/Hot-Tech-Tips/260/The-Point-of-No-Pressure-Change)

http://www.google.com/url?sa=t&sour...p+away&usg=AFQjCNFEfoakAMs9ZP00UREQmDVMHpcDlQ

I expect the principles stay the same regardless of whether using a 'modern' diaphragm-type tank or an "EO" system. I believe the whole point is that you want any circulators pulling away from any expansion tank- and I'd tend to think, you'd also want the expansion tank tied into one of the fairly central, fairly large-diameter pipes (so as to minimize head/ pressure changes between those main parts of the system- and various circulators- and the expansion tank).

 

[Gooserider]

I agree, both articles are excellent, and a good explanation of the No Pressure Change Point concept, it is just that both are assuming a closed system, with a sealed expansion tank... It seems logical to me that an EO system would have a similar point, and that it would be where that high mounted colum/tank ties into the system, but I'm wanting to be sure...

One definite arguement in favor of it being the attachement point is that it would seem to me like if one had an EO system, you'd have a pressure reading at the attachment point - if you then cut off the pipe to the high tank and screwed an expansion tank in it's place, pressurized to the same reading, presumably the rest of the system would have no way to tell the difference...

Gooserider

 

[pybyr]

I agree, both articles are excellent, and a good explanation of the No Pressure Change Point concept, it is just that both are assuming a closed system, with a sealed expansion tank... It seems logical to me that an EO system would have a similar point, and that it would be where that high mounted colum/tank ties into the system, but I'm wanting to be sure...

One definite arguement in favor of it being the attachement point is that it would seem to me like if one had an EO system, you'd have a pressure reading at the attachment point - if you then cut off the pipe to the high tank and screwed an expansion tank in it's place, pressurized to the same reading, presumably the rest of the system would have no way to tell the difference...

Gooserider

At one point last year I gave a lot of thought to and read all I could find on the "semi-pressurized system" (now aptly dubbed the EO system)- I was definitely going to use it if I could have figured out a way to shoehorn a pressurized vessel down the bulkhead hatch into an old farmhouse basement. In the end, since I ended up needing to do an unpressurized tank, and since the only initial/ ongoing inspection where I live is me (though I do try to do things properly- and then some)(so I have no overzealous MA codes or inspectors) a small pressure tank ended up being easier and probably not more expensive than the EO approach.

Anyways, from the standpoint of the boiler and the circulators, pressure is pressure-- whether it comes from the 'head' of a vertical column of water or from some tank filled in part with fluid and part a pressurized gas. My household water comes from a gravity flow spring partway up the hill behind my place, and when it arrives in the cellar, it pushes just the same it would if it were coming from a reserve tank with an air charge (alas, but without quite enough push for modern items like a second floor shower). The pressure seems about what one would get from the standard calculation that every 10 ft of vertical water gives about 4.33 PSI

"Modern" diaphragm type pressure tanks are relatively recent creations, and old hydronic systems used a tank with air (and some way- sometimes automated) to maintain the proper amount of air (trouble was, they often gradually lost the air charge without the diaphragm barrier in the tank) ; some old, old US texts I ran across somewhere even did specifically refer to the "open tank high up" that we're now calling the Euro system.

There are only two factors that I think are really critical as far as pressure- one is that you have enough pressure to initially send the water up to the highest reaches of plumbing connected into your boiler system (and if you can locate the expansion tank higher than that point, you've accomplished that) and the other is to create enough "NPSH" at the inlet of the circulator that you'll avoid cavitation once the circulator begins pumping (thus the importance of putting the pressure reservoir on the inlet side of all circulators- the "pumping away" concept):
http://www.pmengineer.com/Articles/Feature_Article/9c6955c9ff298010VgnVCM100000f932a8c0____

(I re-read various articles on the cavitation issue once I decided to use an unpressurized tank and plate HX to make sure I'd have enough NPSH from my tank height to avoid cavitation in the circulators on the unpressurized side).

Long story short, as long as you have a proper sized 'Euro' type tank above the topmost part of your system, and tie it in towards the inlet side of all circulators, I can't think of any reason it would not work OK (subject to the question that your system is no longer completely sealed against oxygen- but it appears, as Hannson has noted, that many systems run OK this way, and presumably, not much oxygen makes its way down the narrow column to the working parts of the system).

 

[Gooserider]

Our house has a basement, two floors and an attic (actually 5 different attics, but for the heating system I'm only having to get into a couple of them) Doing the ball park estimate of 10' per floor, I am estimating that I'll get between 20 and 30 feet of height from the boiler to the tank, which will give me a system pressure in the boiler room of 10-15psi. Per the stuff I've read, that's plenty for the NPSHA requirements of pretty much anything in the small circ department...

The big challenge will be figuring out how to get all the plumbing into place... The design of the house is such that there is only ONE place where the walls line up for a chase area... Currently it is occupied by the almost unused gas furnace chimney - The gas DHW heater is still using it, but that unit will be going away, and the backup heat is the current gas furnace that is vented through the wall.

I am planning on replacing the gas chimney w/ a Class A pipe, hopefully 6", and next to it I'm going to have to run...

1. The already present network wiring to the 2nd floor, garage and demarcs, in 2 sections of 2" flex conduit.
2. Supply and return for the solar system
3. Supply and return for the 2nd floor radiant system
4. The plumbing for the EO expansion tank
5. Possibly supply and return for the garage heating glycol loop

Oh, and the side of the chase that would be easiest to expand is on opposite sides on the 1st and second floors... :coolmad:

Gooserider