Hydronic Accessories

[DuctHunter]

I'm trying to gain a little more knowledge on hydronic systems and at the risk of asking something obvious, Can someone please explain to me why we typically fill a hot water system (or chilled water)from the bottom of the system and not the top. It seems that if you fill it from the top you can eliminate the pressure fill valve and let gravity do the work. I know this is how it was done in the past.

Why fill the system from the bottom ? And why to you typically add another 4 or 5 lbs of pressure when filling the system.

Thanks for your answers.

 

[imok2]

It's all explained here:

http://wea-inc.com/pdf/system_p.pdf

 

[DuctHunter]

Thanks Imok2,

That was a great article and answered most of my questions. However I'm not sure if it answered the question as to why we can't fill a system from the top down. This way you don't need a 12 psi pressure fill valve. You only need to overcome the additional 4 lbs that you pressurize the system with.

Is the answer as simple as because the city water connections are down at the bottom of the building or is there something more to it ?

 

[ChrisConley]

I'm going to say that air is the primary issue. Filling at the bottom would push the air out the top of the system.

Having said that, I've filled many systems from the top (primarily because the boiler is in the penthouse) and not had any issues.

 

[ChasBean1]

To add, sometimes in new construction a CHW/HW fill is done before city water is piped (or filled) to the top. It's more of a function of construction schedule than mandating the fill be from the bottom...

 

[imok2]

The article states that you should fill from the bottom to remove air so filling from the bottom with a gate valve connected to a hose going to a drain from the highest point seems to me the best way to remove mosr of the air, and if I set the PRV to overcome the building height plus a few more lbs all I need to do is control the flow at the highest point until all the air is removed.