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

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




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.

The AECB accepts no responsibility or liability for any errors or omissions in the content of this site. Views given in posts are not necessarily the views of the AECB.



General: Should we be insulating cold water pipes in heated areas ?

Bottom of Page

1 to 26 of 26

  1.  
  1.  
    How much heat is lost into standing cold water in our pipes then flushed down the toilet/sink? Is it significant?
    • CommentAuthorDarylP
    • CommentTimeMay 1st 2013
     
    Mike......to avoid condensation... the answer is Yes!:smile:
    • CommentAuthorarnyj
    • CommentTimeMay 1st 2013
     
    I would have liked to but my plumber clicked back into normal mode when I took my eyes of him there is just enough room to insulate hot water pipes.

    I managed to get him to run both hot and cold water 6" away from outside wall so I could install internal insulation behind them and alongside them, then clad walls with ply to form my "Internal Shed"

    arny
    •  
      CommentAuthorfostertom
    • CommentTimeMay 2nd 2013
     
    It's a must in PH - consider also the cold-radiator effect of the WC cistern.
    • CommentAuthorrhamdu
    • CommentTimeMay 2nd 2013
     
    You need to be Stalinist about heat transfer: Anything that is not expressly permitted is forbidden.

    In practice this means looking wherever there is a temperature difference and asking "why would I *not* insulate there?"
    •  
      CommentAuthorfostertom
    • CommentTimeMay 2nd 2013 edited
     
    Posted By: rhamduAnything that is not expressly permitted is forbidden.
    I thought that was Switzerland? Or is that 'anything that's not forbidden is compulsory'?
    • CommentAuthortony
    • CommentTimeMay 2nd 2013
     
    The problem with insulation is that it does not stop heat loss or gain it slows it down.

    A cold pipe will over a long period ie a few hours warm up to room temperature and so will a WC cistern.
  8.  
    "I thought that was Switzerland?"

    And in some ways it's a very good approach. You can only park in marked bays which means a much much less cluttered streetscene. No need for yellow lines all over the place for a start...
    • CommentAuthorbarney
    • CommentTimeMay 2nd 2013
     
    If for no other reason, you'd insulate it for hygeine wouldn't you - as well as liking a hot shower I like my cold tap water to be cold (at a low enough temperature to limit microbial colonisation as well).

    regards

    Barney
    •  
      CommentAuthordjh
    • CommentTimeMay 2nd 2013
     
    Posted By: tonyA cold pipe will over a long period ie a few hours warm up to room temperature and so will a WC cistern.

    I wonder if anybody has ever calculated exactly how many hours, or better yet done an experiment to measure it?

    With a cistern, the other thing insulation does is to raise the surface temperature enough to stop condensation on the cistern. It's worth doing for that reason, IMHO. I guess the same is true for pipework although that is more out of sight, out of mind.
    • CommentAuthorEd Davies
    • CommentTimeMay 2nd 2013 edited
     
    The pipe will warm at an exponentially decreasing rate. Making a few assumptions I reckon the time constant (i.e., the time it takes to get about 2/3rds of the way to room temperature) would, for uninsulated 15 mm copper pipe, be about 25 minutes. For 22 mm, nearer 40 minutes.

    This surprises me. The slug of water in the cold hot pipe which seems to go uninsulated under the floor here gets pretty chilly in the time between me running some water for my shave and then running a bit more to rinse off afterwards.

    [Edit: I meant hot water pipe - which goes out into the cold weather]
    • CommentAuthorbarney
    • CommentTimeMay 2nd 2013
     
    A cold water shave ?

    I'd go along with those numbers Ed - bearing in mind we are only going up by about 10C in total.

    I've measured the time taken for a CWS pipe in ceiling void running near HWS pipes in a healthcare building to rise from approx 10 - 12C to about 22C ambient and it's not actually that long - half an hour wouldn't be unusual.

    regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 2nd 2013
     
    Posted By: djhI wonder if anybody has ever calculated exactly how many hours, or better yet done an experiment to measure it?
    It is in the units W.m^-1.K^-1

    W=J.s^-1
    s= time t
    K=T[1]-T[0]

    Follows dT/dt = -k(T[1]-T[0])
    This leads to
    T=e^(-kt) (Newtons Law of Cooling)
    Where k is the system properties, or the surface area of the pipe, the thermal properties of the material. Sometimes the surface area is put before the e

    I have 3 iButtons on my desk, I could do a test, shall use a bit of T-Towel as an insulator.
    • CommentAuthorbarney
    • CommentTimeMay 2nd 2013
     
    LoL - OK Ed, wearing the hair shirts OK - but a cold shave - now that's just barbaric.

    In a former life, we used to use mugs of hot instant coffee - and no soap

    take a few swigs and then when you just had enough to cover the razor - away you go - some guys used to drink the last drop as well after shaving - I couldn't face that myself

    similar to the cold pipe warming, your hot pipe is cooling exponentially (ST's newtonian cooling above) - from a much greater delta T - so it don't take long to get chilly.

    Not green to keep the hot tap running whilst shaving though - nor the cold tap running to brush teeth !!

    regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 2nd 2013
     
    Doing a test now, should be about an hour till I have some number.
    • CommentAuthorbarney
    • CommentTimeMay 2nd 2013
     
    Presumably you are going to run enough CWS to get the main at ground temp and then measure the room and the pipe wall ST - time stops when you are within say 1C ? of room and pipe wall

    Or are you actually going to measure the discharged water temp after x time

    Regards

    barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 2nd 2013
     
    Measured a hot pipe and see how it cools (was easy to get to and had insulation I could take off)
    Not really a long enough test, but can do some on the cold pipe and the cistern tonight as that is easy to get to.
    This is what I have so far.
    It is temp differences (from ambient) over time.
    Added two trend lines per curve, linear and exponential, though 20 minutes was not really long enough
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 2nd 2013 edited
     
    Test data looks like this, the pipe dip is when I took the insulation off.
    • CommentAuthorSprocket
    • CommentTimeMay 2nd 2013
     
    Yes, aside from the very valid condensation point, we have very few cold taps here that can actually produce properly cold water and at least one that seems to be very warm no matter what you do.

    If I could bear to rip up all the floorboards again I would definitely insulate all the cold pipes.
    I would also insulate the central heating pipes as well as the hot water pipes.
    • CommentAuthorEd Davies
    • CommentTimeMay 2nd 2013
     
    Doesn't really matter in this case as ambient is moderately steady (at least for first approximation results) but those difference from ambient results aren't very helpful. It's the change in actual temperature of the pipe that matters to find the heat loss. Then the difference is useful for working out how the heat loss is affected by the temperature difference.

    Still, the 22 mm seems it cools at about half the speed I estimated (16 °C to 8 °C in an hour where I'd have said 16 °C to 5 °C in 40 minutes).

    My assumption I'd be least confident in would be the heat loss coefficient. I assumed 10 W/m²·K but that's probably too high. Copper seems to have a pretty low emissivity, for starters:

    http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html

    Also, a relatively smooth surface would be less good at conduction, I'd have thought, than the sort building materials that 10 W/m²·K figure is typical for.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 3rd 2013
     
    Putting loggers on my bathroom wall, cistern and the cold pipe it took 400 minutes for the cistern to get within 1° of the bathroom temp (allowing for the half degree accuracy) and 90 minutes for the pipe.
    Quite amazed just how stable the temperature is in my bathroom overnight.
    •  
      CommentAuthordjh
    • CommentTimeMay 3rd 2013
     
    Posted By: Ed DaviesThe pipe will warm at an exponentially decreasing rate. Making a few assumptions I reckon the time constant (i.e., the time it takes to get about 2/3rds of the way to room temperature) would, for uninsulated 15 mm copper pipe, be about 25 minutes. For 22 mm, nearer 40 minutes.

    What about for an insulated pipe, though? (critical thickness insulation, before you ask!)
    •  
      CommentAuthordjh
    • CommentTimeMay 3rd 2013
     
    Posted By: SteamyTeaMeasured a hot pipe and see how it cools (was easy to get to and had insulation I could take off)

    I don't understand in your graph why the uninsulated case starts at a lower temperature at time 0?

    Surely the two lines should start at the same point, and then we'd expect the uninsulated one to drop more steeply.

    What am I missing?
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 3rd 2013 edited
     
    Posted By: djhI don't understand in your graph why the uninsulated case starts at a lower temperature at time 0?
    All I can think of is that an uninsulated pipe looses heat very rapidly, too fast for the 1 minute sampling to capture.
    It would account for an uninsulated pipe seemingly to loose temperature at a slower rate, but that is to do with starting at a lower temperature.
    So it seems to loose the first 15°C in under 1 minute, then near as damn it at the same rate.
    All I can think.
    • CommentAuthorbarney
    • CommentTimeMay 3rd 2013
     
    I'd go along with that ST - at least from my experienc of measuring pipes for investigations into water temperatures at sentinel outlets - Legionella compliance type of thing.

    The physics wuld support that as well - higher rate of heat loss with the biggest delta T

    regards

    barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 3rd 2013
     
    I shall try and rig up one of my RPis with some sensors and see if I can log every few seconds when I get some spare time. It is an interesting problem but with some spare pipe, insulation and a funnel, shoudl be able to sort it out.

1 to 26 of 26

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press