I am asking this question in the context of evaluating solar beam irradiation on buildings at city scale.
I am wondering if those variations impact the amount of energy perceived by building, and therefor should be taken into account while evaluating how buildings are warmed up by the sun.
What do you mean under "from one season to another"? The meaning and the quantity of the solar irradiation in the summer and in the winter are very different.
Yes, it varies, but the quantity depends on your location and month you are referring (as said by Stoyanka). Irradiance has a difference value, month by month, however, you should also consider the Sun position and incidence angle, not just Irradiation quantity. To simplify, normally you can evaluate your building (considering Solar irradiation) just in each Season (Spring, Autumn, Summer, and Winter), in most cases evaluating the space for the coolest (winter) and warmer (summer) period is enough. If you can assure comfort in those extreme conditions, the building will accomplish its thermal goals.
If this is a research interest, and you have funding, you might want to consider buying a solar pathfinder, a small plastic instrument with a plastic dome and can be oriented and with templates, help to,quickly estimate solar radiation reaching specific sites. I have used this for assessing stream shading needs from adjacent trees several decades ago. Its a simple instrument, pricey now, but certainly a demonstration tool if sharing information with others in the field. There may be impove computerized or solar demonstration tools now that do just as good or better than solar pathfinder, so you may want to check for them first. Building material differences can also make a big difference.
Thank you all for your answers and questions. :)
My question concerned the fact that the earth is following an elliptical path around the sun... therefor the solar constant isn't really a constant from one season to another ... I mean, it has to change between summer or winter hasn't it ?
I'm working at a 47° North latitude.
Yes, the solar constant is not really a constant because the path the sun follows is elliptical.This "constant" refers to the quantity (of radiation) measured at the external part of the atmosphere, however, if we measured the irradiation on earth, it will never be equal to this value ( an average of 1365 w/m2). This value depends mainly on your location, and it would change as the "sun moves", I mean, the data would be different monthly and hourly. If you can´t measure irradiance there are many maps that can give you a monthly average.
https://www.altestore.com/howto/solar-insolation-map-world-a43/
http://pvcalc.org/global-irradiation-map
http://www.nrel.gov/gis/mapsearch/
https://maps.nrel.gov/swera/#/?aL=we1q1F%255Bv%255D%3Dt&bL=groad&cE=0&lR=0&mC=0.7031073524364909%2C78.3984375&zL=2
http://solargis.com/products/maps-and-gis-data/free/overview/
https://earthobservatory.nasa.gov/GlobalMaps/view.php?d1=CERES_NETFLUX_M
https://en.openei.org/datasets/dataset/nasa-sse-global-monthly-average-solar-ltr-data
https://purl.stanford.edu/xx487wn6207
solar pathfinder info if interested in a demonstration or site analysis tool. Relative quick, approximate..
http://www.solarpathfinder.com/PF
1365 w/m2 doesn't depend on your location, because it is average extraterrestrial irradiance. It varies with 3.344% because of the elliptical orbit or Earth.
See here - page 4 about Beam radiation, Eqs. (2) and (3):
http://www.ing.unitn.it/~Grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Hofierka_Jaroslav.pdf
Yes, I didnt´ mean that constant varies depending on location because as you said, I mentioned that it is measured outside atmosphere (extraterrestrial). I meant to say that Solar Irradiation measured on earth would depend mainly on location.
Maybe I didn't make clear that point. Thanks for completing.
Let me clarify a few things here.
- The "solar constant" (SC) is the average Total Solar Irradiance (TSI) over many solar cycles and for the mean sun-earth distance. It is really a constant within 0.2%.
- The extraterrestrial irradiance is the value of TSI (or for all practical purposes, SC) for that moment corrected for the actual sun-earth distance, which varies seasonally within about +/-3%.
- The irradiance incident on a building is a function of a lot of things: surface's tilt and azimuth, sun position, atmospheric conditions of the moment (clouds, aerosols, water vapor, etc.), site's elevation, ground albedo and shading. That's where you can spend a lifetime improving the modeling methods...
Dear Cecile,
As professor Chris said, You can concentrate more on the local parameters of building which includes weather conditions of that site, building orientation, is there any tilt or angle in which building and its components are inclined. In this you can find out the solar radiation that is incident on a building with few parameters as mentioned by Prof. Chris and me.
Suppose you consider a building with roof (its rise and run parameters for roof has to be calculated first, then find out the angle made by the rise to run). This angle will give you the tilt of the roof. Now you can use this value in the solar radiation mathematical models available in literature to estimate incident radiation on to building.
When you consider the season influence of incident solar radiation on to a building, you should consider parameters like temperature, cloud cover, relative humidity and intact sunshine hours. Based on these parameters you can again compute the solar radiation.
In this you can try to analyse the impact of these parameters on the incident solar raidation. Hope this information will help you.
All the best for your work.
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