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      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012 edited
     
    Been pondering this for a while (several years really since I finished my dissertation in a related area).
    We all know that when the sun shines things left out in it get warmer, what is not so easy to find out is how warm they will get above ambient temperature. This is the problem with weather, this leads onto that debate about low or high thermal mass, inter seasonal thermal stores, small or large glazed areas, overheating in the summer and extra heating needed in the winter.
    We also know that during the winter the sun is low in the sky, rises in the South East, sets in the South West, and is visible for only a few hours, summer is very different, it rises in the North East, Sets in the North West and hangs around in the sky for ages and goes high up (and if you live in Cornwall you get some great sunsets till gone 10pm).
    This means that there is a larger solar resource in the summer than the winter. Well almost, the weather then starts to play an important role. As we are at the tail end of the Gulf of Mexico weather systems, what happens down there takes a while to affect us here, but it does. This is mainly responsible for out mild climate, lack of extremes (I write this as people are stuck in snow on the M40 and M25).
    Without actively monitoring a building for several years to work out exactly how that one building responded I got to thinking was there a more generic way to estimate the effects of solar gain (which is really a function of cloud cover, azimuth and altitude angles, hours of daylight and temperature). Using some crude data from NASA and calculating the the azimuth and altitude of the sun along with the duration, I think I may have found a way to gauge what is going on. I currently, and some of you will laugh at this as I am going to use my least 2 favourite statistical methods, found a correlation based on the means of these values. It is only a starting point so these methods are perfectly valid. They also only show ground and air temperatures, they do not take into account the design of individual buildings, any technology used and cover a large geographic area (that's the get out of jail bit done).
    So what I did was find out the mean weekly azimuth and altitude angles, the mean hours of daylight, the mean kWh.m^-1 of shortwave and longwave solar radiation, air and ground temperatures and set about calculating an 'intensity' number. After much mucking about looking at correlations between angles,temperatures, solar radiation levels to confirm that there is less solar resource in the winter than the summer (obvious I know but it needs checking) I found that the best figures to use where hours of daylight and overall kWh.m^-2.
    By dividing the ground or air temperature by the sum of the radiation kWh.m^2, all divided by the hours of duration and then subtracting the ground or air temperature I think, and I stress think, that the figure represents the temperature gain caused by solar radiation on a common scale. This also allows for weather effects over a week.

    So
    Temperature Gain = (Temperature/(Solar Intensity / Hours Sunlight)) - Temperature

    Where
    Temperature is in degrees C
    Solar Intensity is in kWh.m^-2
    Hours Sunlight is in decimal hours

    This gives the unit of Degrees C per kW per metre square (C.kW^-1.m^-2)

    Thoughts anyone?
    When charted it looks like this:
      Solar Gain London.jpg
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    "summer is very different, it rises in the North East, Sets in the North West"

    Nick, you're in Cornwall, not Australia! :cry:
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012
     
    If North is 0 degrees, it rises at 49 and sets at 311
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    :bigsmile: You're putting a whole new meaning to the question: "Did the earth move for you?"

    The sun can't move above or below the tropic lines of Cancer in the northern hemisphere and Capricorn in the southern hemisphere.

    http://en.wikipedia.org/wiki/Tropics
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012
     
    • CommentAuthorborpin
    • CommentTimeFeb 5th 2012 edited
     
    Posted By: JoinerThe sun can't move above or below the tropic lines of Cancer in the northern hemisphere and Capricorn in the southern hemisphere.
    True, but the apparent angle of setting (because the earth' axis is tilted wrt the sun) moves North in the northern hemisphere in summer. How do you explain that the sun does not set in the Artic during the summer months?
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012 edited
     
    :crazy: I'm black and blue from pinching myself to check a) I'm still here and b) I'm not in some parallel universe.

    Do the exercise with Google Earth and, using azimuth tables, tell me if you manage to get (placing yourself anywhere in the UK) the line (use the 'rule' facility) to point ABOVE any point west or east of your location!

    Coincidentally, I did precisely that exercise to head-off a local anti-wind-farm campaign from making complete idiots of themselves over claims of flicker from proposed turbines, using dates in January, May, and September.

    :peace:
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012
     
    It is rather moving away from the point of the temperature caused by solar gain, which is not, in itself, effected by azimuth.
    But if you get a compass, note where the sun rises and sets over the year, you will find that in the summer it is towards the north and in the winter it is towards the south (in the Northern Hemisphere).
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012
     
    Posted By: SteamyTeathe effects of solar gain (which is really a function of cloud cover, azimuth and altitude angles, hours of daylight and temperature)
    Add to that, local horizon wrt to the object 'left out in the sun'. In summer prob irrelevent, but in winter is all-important.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012
     
    Posted By: Joinersummer is very different, it rises in the North East, Sets in the North West
    That's correct!
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012 edited
     
    Tom
    It is why I used the 'get of of jail card'.
    Each building will be different, and can be different every hour of daylight (every second in fact). Just using thermal blinds could make a very large difference to the energy use/temperature of a building.
    But without knowing the likely overall effect of solar gain on the local (well local in global geographic terms) it is hard to start to calculate an individual building. Picking London, for no other reason than it is on the Greenwich meridian could be a bit misleading as there is the urban island effect, but I was more interested in viewpoints of my methodology and whether they are valid.
    •  
      CommentAuthorted
    • CommentTimeFeb 5th 2012
     
    Steamy, isn't what you're doing producing the theoretical maximum possible solar gain figure, which would then be reduced to a 'real' figure by local conditions (horizon, etc)?

    How is an average person going to measure solar intensity? Or is this just a statistical average too?

    I also can't make out what is what on your graph as I can't see the colours in the key clearly.
    • CommentAuthorborpin
    • CommentTimeFeb 5th 2012
     
    Posted By: JoinerDo the exercise with Google Earth and, using azimuth tables, tell me if you manage to get (placing yourself anywhere in the UK) the line (use the 'rule' facility) to point ABOVE any point west or east of your location!
    Explain the sun never setting in the Artic during the summer months then?
    • CommentAuthorJoiner
    • CommentTimeFeb 5th 2012
     
    If the sun was north of you, then sundials would run anti-clockwise.

    Anyone else a member of the Flat Earth Society? :jumping:
    • CommentAuthorskyewright
    • CommentTimeFeb 5th 2012 edited
     
    Posted By: JoinerNick, you're in Cornwall, not Australia!

    Some figures I happen to have to hand...
    Here at Lat: ~57°N, Long: ~6° W, on June 21st at ~05:40 GMT the sun is ENE from here and already 14 degrees above the horizon (or would be if we had a sea view in that direction), at ~1910 GMT the same day it is WNW from here and again 14 degrees above the horizon (or would be if we had a sea view in that direction).
    • CommentAuthorGavin_A
    • CommentTimeFeb 5th 2012
     
    ST - Nasa already give you data for solar energy supplied on a vertical surface broken down by month. I presume you're already using the page that would have that data as an option.

    Posted By: JoinerIf the sun was north of you, then sundials would run anti-clockwise.

    Anyone else a member of the Flat Earth Society?http:///forum114/extensions/Vanillacons/smilies/happy/jumping.gif" alt=":jumping:" title=":jumping:" >

    you're obviously not outside much at 9pm or 3am in summer then.

    As steamy says, in the UK it rises in the north east, sets in the north west in summer, nothing flat earth about it, it's just to do with the tilt of the earth relative to the sun.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012
     
    Ted
    It is the mean figure from historic weather data for that area. So no need to actually measure anything if you can get hold of the data (I used the NASA site for this). Try copying the image into a graphics package, may make it clearer, does when I do it.
    But a quick explanation anyway.
    The two lines that rise the fastest and then decline the quickest are the mean temperature rise from solar gain (purple and green and use the secondary axis on the right).
    The other two lines (red and blue) are the mean ground and air temperature.

    What I think is happening is that I have disengaged the temperature elements that is caused by solar intensity that is above the mean levels, or when it is extra sunny (less cloudy). When and where this happens within a week is unknown, but using daily data does not allow that sort of resolution. It does not take into account the overall SHC properties of a building in any way, just the ground surface and the local air. I may try it over a patch of sea where I suspect that it is more stable, though there is greater air movement.
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012
     
    Gavin
    Yes, the NASA site does and for this it is what I have used, what I have tried to do is find the effects of that energy on the local climate at a better resolution,I find that weekly means are pretty accurate for the UK from previous work to do with cloud cover.
    • CommentAuthorborpin
    • CommentTimeFeb 5th 2012 edited
     
    Posted By: JoinerIf the sun was north of you, then sundials would run anti-clockwise.
    You are missing the point. During the summer, you are looking over the top of the Earth at the sun so yes it is North of you. :bigsmile:
    • CommentAuthorJanitor
    • CommentTimeFeb 5th 2012
     
    Wow... I'm a newbie and can already tell that this is a GBF classic! :bigsmile:

    It also highlights how brilliant and / or how wonderfully wrong lots of really technical stuff can be... no idea how the layman picks the bones out of it, but in some respects, I guess that could be the intent :wink:

    Interesting stuff nonetheless ST, thanks for starting to put it together :smile: Do you think there will be something conclusive at the end..? After reading a few comments across GBF, I'm trying to get a handle on the benefits of using south facing triple glazed windows as heat source, against what I gather to be a view which negates any gain by overall loss :confused:



    Loved this too:

    Posted By: JoinerI did precisely that exercise to head-off a local anti-wind-farm campaign

    Anyone who sticks it in the eye of a NIMBY get's my vote! :clap:
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 5th 2012
     
    Posted By: Janitoror how wonderfully wrong lots of really technical stuff can be

    I am well know for getting it totally wrong, why I post it up so I can have my mistakes highlighted.

    Posted By: JanitorDo you think there will be something conclusive at the end

    Who knows. What I can say, if my calculations are right, is that there is a reasonable amount to be had from passive solar gain in the beginning bit of the year, and some to be gained all year. We kind of know that this is true as we know, that even in mid winter that the daytime is warmer than the night time, I am just trying to put numbers on it. Once an expected temperature gain is known, different technologies can be compared (there are nice little statistical tests for this) to see if they really do make a difference.

    Posted By: Janitoron the benefits of using south facing triple glazed windows as heat source

    They would not really be a heat source as such, just a method of allowing solar energy in faster than letting it out.
    My views are very clear on this, insulation and airtightness, coupled with MVHR are the keys to really low energy use, see the 'Heating On' thread for some idea of what Tony's house does compared to the rest of ours. Give his house a few days and the heating will probably be off again. My house was cold yesterday (was wet and cloudy) , but the last two days it has remained above freezing, and today had some sun, not had to have any heating on since sunrise in my unheated kitchen/office today. My house tends to be between 3 and 5 C above ambient without additional heating.
    So fit triple glazing and get the insulation benefit and don't worry about the solar gain.
    • CommentAuthorpmagowan
    • CommentTimeFeb 5th 2012 edited
     
    Hope this works
    Sunrise and sunset throughout the year!
      anim.gif
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012
     
    Fascinating - why that sexy sideways hip movement?
    • CommentAuthorpmagowan
    • CommentTimeFeb 5th 2012
     
    The earth has a sexy wobble!
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 5th 2012
     
    Reely?
    • CommentAuthorpmagowan
    • CommentTimeFeb 5th 2012 edited
     
    yeah we have loads of wobbles. A regular moon wobble and a seasonal wobble as the earth tilts towards and away from the sun as its axis describes a circle like a spinning top when it starts to wobble.

    There are others too but they are not so large and related to our elliptical orbit and the other planets.
    • CommentAuthorGavin_A
    • CommentTimeFeb 6th 2012
     
    hi pmagowan, do you know what location that's from?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 6th 2012 edited
     
    • CommentAuthorborpin
    • CommentTimeFeb 6th 2012
     
    Posted By: fostertomFascinating - why that sexy sideways hip movement?
    It is not the wobble I think, but rather the inclination of the axis i.e The earth tilts towards the sun (summer / winter) but then also tilts left or right (not sure which) in relation to the orbit. That is why evenings (?) continue to get darker after the winter solstice even though the days get longer.
    • CommentAuthorborpin
    • CommentTimeFeb 6th 2012
     
    Posted By: pmagowanSunrise and sunset throughout the year!
    Brilliant!
   
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