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    • CommentAuthorJoiner
    • CommentTimeOct 26th 2011
     
    OMG! :shocked:
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 26th 2011
     
    OMG
    Ordinary Midland Girl?
    • CommentAuthorJoiner
    • CommentTimeOct 26th 2011
     
    Now you're being silly. :tongue:
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 26th 2011
     
    SOS
    Silly Old Steamytea
  5.  
    Posted By: DamonHDYes, HDD Heating Degree Days and CDD Cooling Degree Days.


    Cheers Damon.
  6.  
    Quick question folks:

    I'm seeing 'K' come up in various formulae here. Am I right in thinking this is Kelvin?
    •  
      CommentAuthorDamonHD
    • CommentTimeOct 26th 2011
     
    K is kelvin, k is kilo as in kWh, if used correctly.
  8.  
    Posted By: palebluedotAm I right in thinking this is Kelvin?

    But only
    Posted By: DamonHDif used correctly.


    so quite often used as K for Kilo... :cry:

    J
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 26th 2011 edited
     
    Lower case (and often in italics) k is often used to mean conductance, or constant. All depends on the context. In my favourite formula it is the system properties and is a unit less number.

    SI units are in lower case:
    t=time (seconds)
    m=metres
    kg=kilograms (1000 grammes, it is the odd one as it should be grammes or a kilo should be called something else)

    Temperature is a scale and is a capital K (really should use K for all calculations but hard for many to envisage, especially the F people)

    Derived units such as Joules and Watts use capitals because they are 'made' from SI units.

    Joule (J)
    Watt (W)

    Prefixes below 0, such as pico, nano, milli, are lower case, above zero deci, kilo, mega, giga, tera are all Upper case.
    So mW is not the same as MW.
    •  
      CommentAuthorDamonHD
    • CommentTimeOct 26th 2011
     
    Prefixes less than 1, I think you mean ST...

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 26th 2011 edited
     
    Yes :shamed:
    It is the problem of using indices:
    ^1 and ^-1
    • CommentAuthorJeremy S
    • CommentTimeOct 26th 2011 edited
     
    ermmm... since we're being 'definitive': lower case for prefixes for 10^3 or less - sorry SteamyTea, but you contradict yourself, as d for deca and k for kilo are above 10^1

    doesn't hurt to refer to http://en.wikipedia.org/wiki/SI_prefix#List_of_SI_prefixes

    regarding PDB's query that sparked this tangent: formulae do not (usually) represent the parameters involved with their units, so if K is in a formula it should represent something other than Kelvin or kilo, e.g. K.E. = 0.5mv^2 (kinetic energy = half mass times velocity squared), not K.E. = 0.5 x kg x(m/s)^2 (= half kilograms times metres per second squared). Note that if units are used, anything that includes a prefix forces a symbol for multiplication, which may be x or .

    An exception is P=IV (power = current times voltage), where voltage is more correctly potential difference; this is frequently presented as W = A x V (watts = amperes times volts) and, of course, everyone says 'amps'. Again, note that derived units based on names of history's scientists are written out in lower case but abbreviated to upper case.

    it's something of a minefield, eh?
    •  
      CommentAuthorSteamyTea
    • CommentTimeOct 26th 2011
     
    Posted By: Jeremy Sermmm... since we're being 'definitive':lower case for prefixes for 10^3 or less- sorry SteamyTea, but you contradict yourself, as d for deca and k for kilo are above 10^1

    :shamed: again, easier when I just type it as I don't think about it. I try to just use the number, the language of science.
    • CommentAuthordjh
    • CommentTimeOct 30th 2011
     
    <pedantic_hat_on href="http://en.wikipedia.org/wiki/Thermal_transmittance">

    U-value is not about conductivity, its about conductance. Or more accurately, its about thermal transmittance rather than conductance.

    And by contrast, k *is* conductivity (W/m.K), rather than conductance (W/m2K), at least in the building trade.

    </pedantic_hat_on>
  15.  
    Hi djh.

    Perhaps I could put, 'Measurement of thermal conductivity of a material. (More strictly thermal transmittance - see http://en.wikipedia.org/wiki/Thermal_transmittance)'.

    I'm suggesting this, in case conductivity is what people mostly say, even if they know it's actually transmittance.

    Incidentally,


    And by contrast, k *is* conductivity (W/m.K), rather than conductance (W/m2K), at least in the building trade.


    So that's watts per metre times degree Kelvin? And watts per square metre times degree Kelvin? I apologise, but being new to these terms and formulae, and not being able to post properly formatted mathematical formulae in these forums, I'm a bit unsure.

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