Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building
"The most popular book on green building in the UK today."
New fourth edition in two volumes!

Order both books now for the combined price of just £9.95
and free delivery!

(free delivery applies to UK addresses only).

Or get both books for just £7.90 if purchased at the same time as a subscription to Green Building magazine





Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




    • CommentAuthorjamesingram
    • CommentTimeMay 16th 2016 edited
     
    ed , yes , just added the top cylinder to the existing feed as a simple way to expand solar pv heated water storage

    ringi, what djh said , i just stole that drawing to show the pipe and vent lay out ignore the thermal bit.

    So I just checked whilst running the kids bath, the vent on the top cylinder is the only one sucking .
    I turned the tap off. let the levels settle then blocked that vent and ran the hw bath tap.
    this solved the problem.
    I presume as Ed initially suggested the water is leaving the lower cylinder faster than it can leave the top cylinder and is therefore sucking in air also.
    the top cylinder is stainless steel (main presssure though used as open vented as mentioned ) so I presume this cylinder is less likely to collapses.
    Wouldn't blocking the top cylinder vent with a one way flapper valve just result in water being sucked in quicker from the header tank rather than cylinder collapse ?
    If I remove the top cylinder vent completely wouldn't it just vent and expanded through the lower cylinder vent ?

    Steamy , yes , I am suppose to know what i'm doing , but I admit when it comes to the finer points of hydrodynamic I'm a bit of a chancer :wink:
    • CommentAuthorEd Davies
    • CommentTimeMay 16th 2016
     
    Posted By: jamesingramI presume as Ed initially suggested the water is leaving the lower cylinder faster than it can leave the top cylinder and is therefore sucking in air also.
    Sorry if you read it that way, it's not what I meant. The pressure in the vent from the conventional cylinder will drop more than it would without the solar gubbins in its feed but it'd have to be a huge drop before it started sucking through its vent.

    Wouldn't blocking the top cylinder vent with a one way flapper valve just result in water being sucked in quicker from the header tank rather than cylinder collapse ?
    Yes, but only as long as the feed stays open. If the feed is blocked for any reason then the below-atmospheric pressure situation arises.

    Sorry, no idea if an unvented cylinder used like that could stand nearly a full atmosphere on the outside. My guess would be that it'd stand it better but make a bigger bang when it finally did collapse.
    • CommentAuthormike7
    • CommentTimeMay 17th 2016
     
    The saying "Measure twice and cut once" is especially valuable in what I imagine is an awkward working space, so if you haven't already started, the following info could be useful:

    The present height between the header tank water level and the tee on the upper cyl outlet.
    The length of the 22mm pipe run from the header to the cyl bottom flange, plus the bit from the cyl top flange to the vent pipe tee.
    Does air get sucked in at almost any flow rate, or can you measure/estimate at what fraction of the full flow rate air starts to get pulled in?
    Can the depth of water in the header tank be increased ie by tweaking the float valve? Every little helps.

    So far as I can tell, 10" or so head should be sufficient, but that is only for a steady flow. Momentary fluctuations due to taps turning on or off quickly are not allowed for!

    As you say, increasing the pipe size to 28mm will have limited effect with the cyl flanges at 22mm but could still be worth doing. If there's only 2 elbows in the run, the head reduction should be about 25%, more if there are more upgradeable fittings.
  1.  
    mike
    top of header tank water level to tee off upper cylinder = 240mm
    length of 22mm from header outlet to top cylinder inlet = 1470mm 2 bends, 1 x tight 90, 1 x pulled 90
    length of 22mm from top of cylinder outlet to vent pipe T =300mm

    I've adjust float to max level in header
    it doesn't suck on any 15mm outlets just the 22mm, 3/4" bath tap if on full.
    • CommentAuthormike7
    • CommentTimeMay 18th 2016
     
    Those figures give a head loss of 235mm for a flow rate of 0.3l/sec, amazingly close to what you have, so maybe not much increase in the head needed to be on the safe side if your flow rate is similar. The head loss increases with the square of the flow rate, so if you can restrict it below the tee just a bit eg. with a gate valve that might be enough. If not and you don't want to do the downward vent pipe thing, then my other suggestions, the easiest first...?
    • CommentAuthorjamesingram
    • CommentTimeMay 18th 2016 edited
     
    Mike thanks for that calc. I've got to drain down to blank a top immersion inlet at some point so I might do some adjustments then . I've got the potential to raise the header 70mm or so and I could easily switch the tight 90 to a steeped as it's in speed fit. So I'll do those things first.
    The only negative I can see of a down loop in the vent is air collection in that loop.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press