Closed loop heated slab questions

[slackdaddy1]

In a closed loop system, electro boiler, single zone (2 - 300' loops)

When filling the system, while you could force 99% of the air out, you will never get 100% of the air out.

When the "air eliminator" removes the "air",, what replaces the "air" ?

With that said, why don't closed loop systems have a small (1 gal) tank mounted as the highest point in the system, connected to the system with a tee fitting. This tank could be filled with additional solution that would keep the actual "loop" or system always filled.

Am I missing something ?

Nick

 

[Northislander]

Closed loop doesn't mean you don't have a feed system. You either connect to your domestic system with a boiler fill valve = (check valve and pressure reducing valve) or periodic manual top up or i personally use Axiom system fillers.

 

[slackdaddy1]

My last system was closed loop, and would have to be topped off occasionally or it would experience cavitation. This was do to poor placement of fill/purge valves.

I was considering placing a TEE at the highest point of the system, facing up. Running about 2' of 3" copper straight up with a boiler valve on top. This boiler valve would be the purge side of my fill procedure. The tube would also hold about 1/2 gallon additional fluid
at the highest point of the system, therefore ensuring the system is always "full" .
Dumb idea?

Nick

 

[Gooch]

Fill to your desires pressure. When the air is released the pressure will drop and you add more water to increase the pressure. Or you just get an auto fill that maintains a set pressure.

 

[forAK]

Fill to your desires pressure. When the air is released the pressure will drop and you add more water to increase the pressure. Or you just get an auto fill that maintains a set pressure.

Exactly. Don't over think/build it.

 

[slackdaddy1]

It's a closed system in a detached shop (no domestic water), cant do an auto fill.
Trust me, trying to keep it simple. Just don't want to have get out the bucket, sump pump, hoses, etc to top it off,, like my last system.
That's why I was thinking of adding a small "reserve" at the highest point, that can be filled from the top.

Nick

 

[hidollartoys]

To keep it "simple" you probably should have at least installed a freeze proof spigot so you could 'easily' top it off.

 

[yeldogt]

Interesting dilemma -- I have always installed where water is available? Normally they are filled to 12psi with a bladder tank maintaining pressure. You would need something able to supply water under pressure.

Must be some solution -- gizmo.

 

[walrus]

I've got a solar system heating my floor, closed loop,filled with water and no burst. pressure started at 18 PSI, down to 14psi after 4 years or so. Will probably recharge this summer, I have no reservoir

 

[slackdaddy1]

I do have a yard bib at the front, I meant no domestic in the shop.
I will be filling with Cryo-tek or similar, system will only hold about 7 gallons, So I will be filling with a sump pump in a bucket. Sump pump may get me to 5-10 PSI.
I could release some air from the bladder in the expansion tank, fill the system, then re-pressurize the bladder.

Nick

 

[Gooch]

They make auto fill resivouirs that you plumb in and fill a container and will 'top off' as needed

 

[bottom feeder]

It's always been my understanding that the expansion tank moderates the pressure. Air is contained on one side of the tank at a set pressure. The water on the other side of the tank (separated by a flexible bladder) is initially filled to a set pressure, which is really just compressing against the bladder in the tank and pushing against the air pressure on the other side. When the water heats it expands and pushes a bit harder against the bladder, compressing the air and providing somewhere for the extra water pressure to go.

As the small amount of air on the water side of the system works its way out via the air eliminator, the air pressure in the expansion tank equalizes the pressure with the water side automatically, unless there is a very large amount of air that burps out in which case the water side may need to be topped off.

 

[mygarageone]

If you have a pressurized system ( and you should with a closed loop system ) your expansion tank will accept a certain amount of water and it will maintain the operating pressure even if you lose a little water . As far as maintaining the pressure when you add glycol , you can rent a transfer pump which will pump,up to 12 # pressure .
So you would fill the system on one side supply side and allow the water to drain out the other side return side.
And you don't want all anti freeze , the container will give you the mixture ration you need to prevent freezing.
If your system is tight , once filled to pressure . You should not have any real pressure loss
And your Exspansion tank doesn't need to be at the highest point .

 

[BadgerBoilerMN]

The fill pressure (static) and the compression tank pressure (12#) should be the same. If you install a proper air eliminator on the low pressure side of you circulating pump AND your system is propylene glycol tight, you will never have to top-it-off.