location of de-aerator in boiler system

[EnergyProfessional]

De-aerators would best when water is hot and at low pressure. So ideally they would be downstream of the boiler, and upstream of the pump. but that puts the pump on the hot side of the boiler, which will degrade seals.

So since most of our hydronic system problems are degrading pump seals i put the pump upstream of the boiler (colder side). but that makes it impossible to have the de-aerator on the hot-and-low pressure side.

I can have the de-aerator on the suction side of the pump, which has it have lower return temperature. Or I can put it on the boiler supply side with hot water, but higher pressure. My question is, does high pressure, or colder water, have a worse effect on air removal?

I don't want to compromise on pump location, since whatever pump problems we have are seal problems. So I need to find out if the de-aerator on the high-pressure and high-temperature of the boiler is better than having it on the colder low-pressure side of the pump?

The boiler pressure drop is relatively small compared to the system, so the pressure downstream of the boiler will be close to pump discharge pressure.

Thoughts?

Edit: I found this graph of oxygen solubility vs. temperature and pressure. At the relevant temperatures (43°C - 60°C in my case) it seems temperature has little influence and increased pressure has a large influence. So if compromising, I'm better off locating the de-aerator at a low pressure and lower temperature location.
Example: typical system pressure of 12 psi at pump suction side (2 bar line approximated) and 43°C shows ~12 mg/l oxygen solubility. high pressure (4 bar, meaning 28psi pressure gain over the pump) and 60°C gives me over 20 mg/l. Even if I assume lower pressure, I still would be above 12 mg/l.

 

[Compositepro]

If you are talking about a hydronic heating system I think de-aerator is the wrong term for what you mean. A de-aerator is used to remove dissolved air from feed water to a steam boiler. An air vent is used to remove gaseous air from a hot water loop. An air vent should be placed at high points in the loop where air bubbles can accumulate.

 

[EnergyProfessional]

Air/Dirt Separator

 

[Compositepro]

"A properly placed Spirovent® air eliminator installed at the point of lowest solubility (see Figure B-2); that being directly after the boiler (highest temperature) and before the circulator (lowest pressure), will eliminate air most effectively based on the principles of Henry’s Law. However, in instances where high static pressure is present in the system, as is the case with high-rise buildings, directly after the boiler near ground level may not be the optimum location for any air separator."

https://www.spirotherm.com/sites/default/files/TechnicalData-AirElimination_3.pdf

 

[EnergyProfessional]

Yes, I know what they wrote. But that puts the pump on the hot side of the boiler, which degrades the pump seals faster. The air separator manufacturer is only concerned with the function of their device. As the designer I have to to integrate all components into one system and can't just make it perfect for component A, if component B suffers.

 

[immsk]

Maybe we don't need to worry about the high-temperature water damaging the seal. Take a look here:

https://bellgossett.com/2016/05/18/need-high-temperature-seal-condensate-pump/

What temperatures will the loop be running at?

 

[chicopee]

Bell and Gossett pumps have a good track history with circulating pumps. You must have bought cheap Chinese circulators.

 

[EnergyProfessional]

Higher temperature will degrade material faster. Maybe a higher quality seal will degrade in 17 instead of 20 years, and a cheap one will disintegrate in 5 instead of 7 years.
for systems I design supply most often is 140°F with temperature reset based on OAT and load. So it will be lower most of the year. I typically try to achieve a dT of 30°F. Some of our existing systems were designed for 180/160. However, we often run them at 160°f maximum supply.

We have Taco, Armstrong, B&G, and Grundfos for the most part in over 70 buildings. Taco and Armstrong are just garbage, we don't even replace seals when they leak, we just replace the pump with B&G or Grundfos. They just leak, especially in the off-season. In my designs I typically use Grundfos since they are a higher quality and often more efficient than B&G. But I also have used the B&G ECM pump where Grundfos doesn't cover the required flow and head. I also pay attention to spec the correct seal based on the fluid (some pumps have specific seals for glycol etc.). However, I don't have control over legacy or consultant-designs.
I don't think our issue is cheap pumps. Whoever bashed "Chinese" products doesn't know where B&G produces pumps.

Grundfos and B&G don't leak often, but with so many pumps there is a leak every once a while. So my goal is to give them the best conditions. Another thing causing leaks is dirt.

You can buy a 25 year old Lexus, Mercedes or other high quality car and even if that is the elusive "only driven by an old lady once a week" car, it will have leaks.