Home Page link

zoned hot water system problem

Home| Search | About
Login Password
Register Now! Lost Password?

HVAC Discussions - Heating, ventilation and air conditioning. 

Page 2 of 4       < 1 2 3 > last >> Bookmark this page:  YahooMyWeb Yahoo!  Google Google  Windows Live Favorites Windows Live  del.icio.us del.icio.us  digg digg  Add to Netscape Netscape
Subject Author Date
zoned hot water system problem RayV 11-01-2006
If you were  Registered and logged in, you could reply and use other advanced thread options
Posted by Steve Scott on November 2, 2006, 6:35 am
Manufacturers have for years installed circs on the return side which
is wrong. They should be on the supply side after the expansion tank.

Pumps on the supply side and return side usually indicates some sort
of half assed attempt at primary/secondary piping. You might use them
if you had a heluva pressure drop through the system.


>
>Steve Scott wrote:
>> Generally speaking, a typical residential system that's properly piped
>> and is in a standard series loop configuration w/o primary/secondary
>> piping will only have circs on the supply side after the expansion
>> tank.
>>
>> What makes you think not having a return circ would cause excessive
>> boiler temp?
>>
>This is the third house I've seen in this area (Eastern PA and NJ) with
>a pump on the return side of the boiler. One was a ranch with no
>zoning, the other had one pump with three zones with zone valves after
>the boiler (worked fine), and this crazy system with four pumps!
>
>Of course most of the houses in this area have the shingles overhanging
>the sheathing by 1.5" so they hang in the gutter but that isn't right.


--
My problem is drinking Coke in the
Pepsi generation





Posted by dd on November 2, 2006, 4:23 pm
I'm from eastern PA also and the circ on the return is real common here,
probably 90% are done this way, I have also done systems with the circs on
the supply as pushers and I really don't think it make a difference,
although I don't think as pushers you will have problems because of air in
the piping.
> Manufacturers have for years installed circs on the return side which
> is wrong. They should be on the supply side after the expansion tank.
>
> Pumps on the supply side and return side usually indicates some sort
> of half assed attempt at primary/secondary piping. You might use them
> if you had a heluva pressure drop through the system.
>
>



Posted by Steve Scott on November 2, 2006, 9:17 pm
Where are the fill valves located on the systems you see?

You're right about less air problems with the circ on the supply side.
Do you know why that is?

Where should the fill valve be? Why?

On Thu, 2 Nov 2006 16:23:42 -0500, "dd" <rtert> wrote:

>I'm from eastern PA also and the circ on the return is real common here,
>probably 90% are done this way, I have also done systems with the circs on
>the supply as pushers and I really don't think it make a difference,
>although I don't think as pushers you will have problems because of air in
>the piping.
>> Manufacturers have for years installed circs on the return side which
>> is wrong. They should be on the supply side after the expansion tank.
>>
>> Pumps on the supply side and return side usually indicates some sort
>> of half assed attempt at primary/secondary piping. You might use them
>> if you had a heluva pressure drop through the system.
>>
>>
>


--
'Do not meddle in the affairs of cats,
for they are subtle and will pee on
your computer.' Bruce Graham





Posted by RayV on November 2, 2006, 9:23 pm

Steve Scott wrote:
> Where are the fill valves located on the systems you see?

At the same level as the boiler inlet or lower.

>
> You're right about less air problems with the circ on the supply side.
> Do you know why that is?

Higher pressure from the hotter water raising the boiling point?

>
> Where should the fill valve be?

Close to the boiler inlet.

> Why?

Because it is easier to run the piping?


Posted by Steve Scott on November 2, 2006, 10:48 pm

>
>Steve Scott wrote:
>> Where are the fill valves located on the systems you see?
>
>At the same level as the boiler inlet or lower.

On the boiler return side? Same side as a lot of circs you're seeing?
Is the fill valve before the circ? Replace many expansion tanks?

>> You're right about less air problems with the circ on the supply side.
>> Do you know why that is?
>
>Higher pressure from the hotter water raising the boiling point?

The expansion tank is the point of no pressure change in the system.
The circ causes pressure differential. So, the expansion tank is the
point of no pressure change and the suction side of the circ is close
to the tank the circ adds to the static system pressure. That causes
the pressure to be as high as possible at the highest point in the
system.

If the circ is on the return side and the expansion tank is on the
supply side the highest points of the loops can be under negative
pressure causing air to migrate into the water...even from water tight
solder joints.

>> Where should the fill valve be?
>
>Close to the boiler inlet.
>
>> Why?
>
>Because it is easier to run the piping?

The fill valve should be near the expansion tank because it's the
point of no pressure change.

What we all commonly see is the expansion tank of the supply side, the
circ on the return side (cause the boiler manufacturer stuck it there)
and the fill on the suction side of the circ. This is a guaranteed
revenue stream as you will be replacing the expansion tanks regularly
and maybe the relief and fill valves trying to figure out what the
heck is going on.

The problem is this:
Fill valve and tank factory set at 12psi. Who changes them?
Virtually no one.

So the circ is off and the system is full there's 12psi at the fill
and at the expansion tank.

Let's assume the circ creates 6psi differential. The expansion tank
is the point of no pressure change so that stays at 12psi. There's
maybe 1psi loss through the boiler so the outlet side of the circ is
at 13psi (12psi at the tank + 1psi through the boiler). The circ
creates 6 psi differential so the suction side is 7psi. Which is what
the fill valve is seeing cause it's on the suction side of the circ.

Wait a minute. The fill valve is set at 12psi and now it's seeing
7psi? What's it gonna do?

Add water?

Yep.

Where's the water go?

The only place it can go is the expansion tank. The rest of the
system is already full.

What happens when the expansion tank has too much water in it?

The diaphragm ruptures.

And that's the short version of why in a correctly piped system the
expansion tank goes in the supply near the boiler with the feed near
the expansion tank and the circ right after the tank. With very few
exceptions.

If you're in the trade and want lots of good info on this buy this
book. http://tinyurl.com/wme2a Best $25 you'll spend.

--
'Do not meddle in the affairs of cats,
for they are subtle and will pee on
your computer.' Bruce Graham





Page 2 of 4       < 1 2 3 > last >>
Similar ThreadsPosted
zoned hot water problem resolved November 28, 2006, 8:23 am
Zoned heating system January 4, 2008, 8:11 pm
Gas Burner / Hot water system problem November 20, 2006, 9:56 am
Re: Intermittent high pressure in hot water heating system system February 3, 2007, 9:46 am
Re: Intermittent high pressure in hot water heating system system February 4, 2007, 3:49 pm
Re: Intermittent high pressure in hot water heating system system February 4, 2007, 3:54 pm
Re: Intermittent high pressure in hot water heating system system February 4, 2007, 3:43 pm
Re: Intermittent high pressure in hot water heating system system February 4, 2007, 3:06 pm
Re: Intermittent high pressure in hot water heating system system February 4, 2007, 3:05 pm
Re: Intermittent high pressure in hot water heating system system February 2, 2007, 10:20 am

Contact Us | Privacy Policy

XML SitemapXML Sitemap