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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.

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  1.  
    People always talk of the horrible damp cold in the UK. Since we've had heat recovery and ventilation, our house is bone dry. It also seems much more comfortable even when it's cold. We regularly tolerate 18-19°, whereas even 21° felt uncomfortable in our previous places.

    Is there some comparison of similar feelings of temperature at different humidity levels?

    Seems like it might be a good justification for insisting on heat recovery and ventilation in all new builds?
    • CommentAuthorbhommels
    • CommentTimeApr 11th 2019
     
    The influence of humidity on apparent temperature is a well known (and documented) effect:
    https://en.wikipedia.org/wiki/Heat_index
    and
    https://en.wikipedia.org/wiki/Humidex

    Have you got any data on the humidity in your house before and after by any chance?
    Our house sits between 50% and 70%, which is too high, and I can't wait to get on and finish the MVHR install job - halfway there.
  2.  
    I had some visitors from central Canada, where apparently it is quite nippy in winter. But they shivered outside in Aberdeen, they said the damp cold here 'gets in your bones' more than in their home city.
    • CommentAuthorgyrogear
    • CommentTimeApr 11th 2019
     
    We are by the sea, and I can confirm that in this dampish season, we are often lighting the woodstove of an evening not because of the cold, but because the damp air makes us feel cold in the bones ! LOL

    gg
  3.  
    Unfortunately, I don't have any data on the humidity inside, but I'd be interested to know how to test it.

    I think it could be a very persuasive argument for building better homes. Ie, if a dry home felt 1-2º warmer, this would be a huge saving (on top of efficiency savings through heat recovery).
  4.  
    I've had a look at the heat index, but this seems to assume that the 'real feel' is hotter, the more humid it is. This might work where it is unbearably hot, but I think an opposite effect occurs when it is cold. It may be that the same formula is inappropriately extrapolated to cold. Eg, this link: https://planetcalc.com/2089/

    Says 21º feels like 23º at 80% humidity, but
    21º feels like 19º at 30% humidity

    This does not feel right...
    •  
      CommentAuthorfostertom
    • CommentTimeApr 11th 2019
     
    This phenomenon is well known and precisely quantified in the psychrometric chart. The higher the humidity, the more a temp difference is subjectively felt: if it's hot in the room it feels hotter, if it's cold in the room it feels colder.

    Same goes for air speed; higher air speed has same subjective exaggerating effect.

    Similar effect again: the radiant vs convective ratio in the room.
  5.  
    Thanks @FosterTom. Do you have a link to the chart?
    •  
      CommentAuthorfostertom
    • CommentTimeApr 12th 2019
     
    Google gets dozens of hits
  6.  
    Thanks @Tom. Can you explain how to interpret it to work out the relationship between 'real feel' temperature of, say, 21º as the humidity changes?
    •  
      CommentAuthorfostertom
    • CommentTimeApr 12th 2019
     
    Oh dear, can't remember. Anyone?
    •  
      CommentAuthordjh
    • CommentTimeApr 12th 2019
     
    Psychrometry deals with various objective measurements of the properties of air-water vapour mixtures as far as I know. It doesn't deal with questions of human comfort. It is possible to mark up a psychrometric chart to indicate areas that are comfortable, just as it is possible to mark up other types of chart, but that's something different.

    Wikipedia has a comprehensive article about thermal comfort that has a brief section about temperature and humidity - https://en.wikipedia.org/wiki/Thermal_comfort#Interplay_of_temperature_and_humidity - and which indicates a degree of uncertainty about mechanisms.
    • CommentAuthorbarney
    • CommentTimeApr 12th 2019
     
    I'd suggest that the effect is principally that of conductive heat loss being higher to relatively wet air compared to relatively dry air - from a clothed body of course.

    Regards

    Barney
    • CommentAuthorgyrogear
    • CommentTimeApr 12th 2019
     
    https://www.rotronic.com/media/productattachments/files/h/o/how_to_read_psychchart_f_web.pdf

    gg
    •  
      CommentAuthorfostertom
    • CommentTimeApr 13th 2019 edited
     
    I stand corrected - but puzzled.

    I did learn, in student days - when Bath Univ School of Architecture housed with its School of Building Technology, Physicists researching in the basement, shared lectures etc - precise researched measures of subjective environmental comfort using the psychrometric chart.

    It turned out that the calibration data (like so much e.g. psychological research) centred on westerners i.e. student volunteers sitting or doing energetic tasks in climate chambers - and since then, the precision has continued to fuzz, as notions of Adaptive Comfort i.e. tolerance changing as the season progressed, have come in.

    But still, at any given season for any given demographic and task, the subjective comfort point on the psychrometric chart can be determined, and divergence quantified. Agreed, I see it's not one of the variables that can be read off the chart.

    Does anyone know what current practice is, to link subjective comfort to the chart?
    • CommentAuthorgyrogear
    • CommentTimeApr 13th 2019 edited
     
    A search for "subjective comfort psychrometric chart" threw up this link...


    https://books.google.fr/books?id=3FiQnjYAEKwC&pg=PA25&lpg=PA25&dq=subjective+comfort+psychrometric+chart&source=bl&ots=8z3rZqtmew&sig=ACfU3U15bwKYp9-VQ4fo1mMeqaySJiK24Q&hl=fr&sa=X&ved=2ahUKEwjTlsOp8MzhAhUKbBoKHWfvBhgQ6AEwBXoECAkQAQ#v=onepage&q=subjective%20comfort%20psychrometric%20chart&f=false

    wherein:

    "the relationship between the physical environment and the subjective comfort is blurred by all sorts of time-related factors"

    gg
    •  
      CommentAuthorfostertom
    • CommentTimeApr 13th 2019
     
    But still environmental engineers' job is to control the factors of the psychrometric chart, to achieve subjective comfort.

    Lately, Adaptive Comfort research has shown the engineers that there's more to it than their neat rigid target parameters, but that's just demanding more sophisticated use of the psychrometric chart.
    •  
      CommentAuthordjh
    • CommentTimeApr 13th 2019
     
    Posted By: fostertomenvironmental engineers' job is to control the factors of the psychrometric chart, to achieve subjective comfort.

    Another way of saying that is "environmental engineers' job is to control the temperature and humidity to achieve subjective comfort". The psychrometric chart is irrelevant; it's a convenient way to display or record the data, but there are other ways.

    The jury's still out on the validity of adaptive comfort, I think. It does demonstrate the need for a better understanding though.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 13th 2019
     
    Hm, perhaps I'm thinking of something else, includes e.g. air speed.
    Never had to make use of any of this - my clients can always open a window!
    •  
      CommentAuthordjh
    • CommentTimeApr 13th 2019
     
    Posted By: fostertomHm, perhaps I'm thinking of something else, includes e.g. air speed.

    Well yes, airspeed affects comfort, but the design rule for indoor airspaces is usually just 'keep it low'. I think there's a specific limit in PH methodology?

    Though Andy Simmonds piece about low-cost buildings in Africa (in the latest PH+ was it?) does point out that actively encouraging cross-drafts can be a valid technique in some circumstances. They figured out the value of a double roof in the tropics, but for some reason didn't quite get around to the notion of shading the walls. Some plants to keep the sun off can help a lot.
  7.  
    I think AccuWeather has an algorithm that accounts for 'real feel', including measures of humidity, so I wonder where they obtained the data to work out their algorithm.
  8.  
    BTW, our house is 45% humidity. Just got a cheap hygrometer.
    • CommentAuthorgoodevans
    • CommentTimeApr 16th 2019
     
    The most relevant wikipedia page is probably: https://en.wikipedia.org/wiki/Thermal_comfort

    However the statement "We regularly tolerate 18-19°, whereas even 21° felt uncomfortable in our previous places" may be more to do with wall/floor/ceiling/window surface temperature in your current house than humidity.

    I think in still air much of the heat loss/gain from the body is via radiation rather than conduction/convection to the air so lower air temperatures are more comfortable. But air temperature becomes increasingly important as the drafts increase (due to wind chill). And warmer air is required if the surrounding surfaces are cold as more heat is radiated from the body. Its complicated, emperical, subjective and messy.

    But I'm hoping that a lower humidity with MVHR ventilation in winter might allow my body to handle shorts bursts of activity in the house (e.g. hovering) due to the fact that perspiration will be more effective.
    • CommentAuthorgyrogear
    • CommentTimeApr 16th 2019
     
    Posted By: goodevansshorts bursts of activity in the house (e.g. hovering)


    sounds very good !

    on my polished floors, I tend to like a glide, personally ...

    gg
    • CommentAuthorgoodevans
    • CommentTimeApr 17th 2019
     
    oops - sometimes the spell checker doesn't save my inability to spell - obviously it should read "short bursts of activity - e.g. hoovering"
    •  
      CommentAuthorfostertom
    • CommentTimeApr 17th 2019
     
    my granny used to refer to Hoovercrafts
  9.  
    There are more subjective variables than just humidity. I would suggest:

    Effect of clothing on different parts of the body eg warm feet make one feel warmer throughout, just as a cold head has the opposite effect.

    Comfort of the chair one is sitting in.

    Attractiveness of the room furnishings.

    State of hunger.

    One's degree of happiness or misery.

    Absorbtion in a task, or idleness.

    Intense radiant heat in cold air feels much warmer than even temperate air.

    Ownership of the property - one's own house feels warmer than someone else's.

    Weekend approaching? Friday afternoons are warmer than Monday mornings.
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