Removing expansion tank after system is hot 2

[BronYrAur]

What do you think of this one? On a hot water heating system, what if you removed the expansion tank after the system is hot? Everything has expanded and the pressure is stable. worse case, if everything gets cooled down, the pressure would drop. Auto fill would have to be isolated so as to not allow additional water.

The reason for this would be to utilize the floor space where the existing expansion tank sits. This is a temporary (less than 6 months) scenario using a rental boiler while the building boilers are replaced.

Can the expansion tank be removed once the system is hot?

 

[LittleInch]

All you really need is a vertical section of a pipe about 4 times the diameter of the ones coming in and out and a line off then end cap or flange or reducer and then a valve on the end of a piece of pipe to hold the air. you can make this out of simple standard components.

You really don't need anything fancy for your "temporary" system.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[GBTorpenhow]

A design more like an 'air scoop', i.e. 2 eccentric reducers and an oversized section of pipe with a branch connection looking up for the auto vent, might work as well. As long as you can get your fluid velocity low enough through the oversized section the air should de-entrain.

Not sure what your sizes and pressures are like or if anyone is in a position to come at you about this but I am always wary of inadvertently making a "pressure vessel". With the air scoop type configuration I would be more comfortable arguing that its just a wide spot in the pipe meant to temporarily to lower the fluid velocity.

 

[HVAC-Novice]

an air separator is designed to get micro-bubbles out of the system. Often it is combined with a dirt-separator.
The design includes a wider cross-section (for low velocity) some magical mesh inside to cause air to form bubbles, and are located at a low pressure/high temperature section of the system to facilitate air to become bubbles. Main reason is to remove oxygen.

An air vent just releases the air that collects at a high point. An air -separator typically has an air-vent as well. But you also have them in the piping system (at top) to let air out that collects. They don't actively dissolve air. Main function is to remove air that already is a gas, so the water can flow. There are auto-vents. You don't have to bleed them manually. In normal sealed systems we close the air-vent off with a valve after a time of operation to avoid any potential leaks. They should be opened up for a few days seasonally. In a system that constantly brings in new water (and oxygen), you need to constantly remove air.

 

[LittleInch]

Fair enough. Stick some metal gauze in there as well before you weld it up!

It's better than nothing and at that size with flow going through it doesn't become a PV IMHO, but I know others might not think that way.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Rputvin]

Most of the B&G rolairtrol separators we get in lack the mesh plate that serves as nucleation sites for the air to disentrain. Aside from the tangential connections, they are an empty vessel no different than a chunk of pipe. Create a low-velocity section like LittleInch describes and it will do the same function of allowing bulk separation of any air brought through the system. The accompanying B&G auto vents just have a calibrated ball check in them that will fall open when there's a sufficient amount of air below the check to no longer suspend the ball- that's why they spit and spurt during startup when they're actually working.

Your 6-month "temporary" setup includes seasonal changes that may impact usage of the system substantially, I'd be very hesitant to agree to "temporary" accommodations without seeing a year or two of thermal data to ensure with high confidence you'll only be seeing a small temperature change during the entire duration (and an additional 6 months of buffer time for project delays).

The safer bet vs. removing the tank would be to check that expected temperature change and size a tank at the absolute minimal to account for your corresponding volume change. You might be able to get by with a tank small enough to fit, and cheap enough to not run up the budget, which will avoid all of the issues presented in discussion already.

If you're taking sections of pipe offline for rework and putting them back into service an air separator should not be removed. The only way you'll get away with no air separator is if you can guarantee no leaks, no low pressure events, and no service valves being opened for the duration of the "temporary" work to ensure you're not introducing large amount of air into the system.

And I keep writing "temporary" in quotes because temporary solutions that work have a bad habit of being left in place, or worse, becoming normal practice.

 

[HVAC-Novice]

The B&G types are just a large tube. You could build those yourself (and paint it the same red!). B&G also don't tell you the removal efficiency for air and dirt... Spirotherm does.
For a permanent system I wouldn't cheap out on air/dirt removal. For this system, where someone talks about not even using an expansion tank, i wouldn't spend any money.

But you are right, those "temporary" solutions can be in for decades. which is why JHA likely treats them the same way as permanent systems.

 

[BronYrAur]

In my case temporary means temporary. It is for the rental boiler and chiller only. New permanent ones will be installed with the new equipment. I am just looking for solutions for the rental equipment.

 

[LittleInch]

In my case temporary means temporary.

That's what they ALL say.

10 years later.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BronYrAur]

@littleInch I get it but this is for a roll up trailer mounted chiller and boiler to serve the building while we gut and rebuild the plant. Temporary. I just need to get by for the duration of the rentals

 

[HVAC-Novice]

Isn't that how trailer parks became "legal"? They said they don't have to meet building code requirements, because they are just a camping trailer used temporarily. And then, 20 years later, the wheels are off, a little garden built around it and water and electricity hooked up permanently

 

[LittleInch]

In my opinion the word "temporary" should be banned from any serious engineering discussion or design as it encourages all these "it's only temporary" type arguments for not doing something properly or using inferior or lower pressure rated components.

One second, one minute, one hour, one day, one month, one year, one decade IT DOESN'T MATTER. Design it like it is going to be there for ever and very little will go wrong. IMHO.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[ChasBean1]

The air separator is all about minimizing corrosion and keeping you from having to burp the system. 6 months? Should be fine.

The expansion tank should not be ignored, even if you need a temporary location. If the system stays hot the whole time, all good. If the system cools down, might be good too. If make-up water is connected, and there is no expansion tank, just don’t heat the system back up again.