SOLAR ENERGY. How much strikes the earth? How much can my building get? When is it too much? ENGS 44 Sustainable Design

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SOLAR ENERGY The sun: friend f fe? Drawing by Le Crbusier Hw much strikes the earth? Hw much can my building get?

ENGS 44 Sustainable Design Benit Cushman-Risin 13 April 2017 Renewable Energy Pssibilities Wind 2-4 TW extractable Tide/Ocean

$6 TW grss (US) (small fractin technically feasible) Hydrelectric 4.6 TW grss (wrld) 1.6 TW technically feasible 0.$

1 SOLAR ENERGY The sun: friend f fe? Drawing by Le Crbusier Hw much strikes the earth? Hw much can my building get? When is it t much? ENGS 44 Sustainable Design Benit Cushman-Risin 13 April 2017 Renewable Energy Pssibilities Wind 2-4 TW extractable Tide/Ocean Currents 2 TW grss Slar 1.2 x 10 5 TW n Earth s surface 36,000 TW n land (wrld) 2,200 TW n land (US) Bimass 5-7 TW grss (wrld) 0.29% efficiency fr all cultivatable land nt used fr fd Gethermal 9.7 TW grss (wrld) 0.6 TW grss (US) (small fractin technically feasible) Hydrelectric 4.6 TW grss (wrld) 1.6 TW technically feasible 0.6 TW installed capacity 0.33 grss (US) 1 TW = 1 tera-watt = Watts / Ttal human energy cnsumptin ~ 12 TW (Surce: Gerge Crabtree, Materials Science Divisin, Argnne Natinal Labratry) 1

Three mechanisms f heat transfer: - cnductin (mlecular agitatin in the material) - cnvectin (mvement f carrying fluid) - radiatin (electrmagnetic waves) Slar energy is carried acrss empty space frm

2 Three mechanisms f heat transfer: - cnductin (mlecular agitatin in the material) - cnvectin (mvement f carrying fluid) - radiatin (electrmagnetic waves) Slar energy is carried acrss empty space frm the sun t the earth by radiatin f electrmagnetic waves (infra-red, visible & ultra-vilet). Much f this radiatin is in the visible spectrum (47%), t which the atmsphere is quite transparent. UV = 5% and IR = 48%. Tw basic laws f heat radiatin Law #1: Stefan-Bltzmann Law All bjects emit radiatin. The htter they are, the mre they radiate. The emitted radiatin flux (energy per unit area and unit time), E, is given by: E T 4 where T = abslute temperature in degree Kelvin (= C ) = 5.67 x 10-8 W/(m 2.K 4 ) r where T = abslute temperature in degree Rankine (= F + 524) = 1.71 x 10-9 Btu/(ft 2.hr.R 4 ) 2

Law #2: Wien s Displacement Law The radiatin emitted by a bdy at abslute temperature T fills a spectrum, with peak at wavelength given by: max 2898 m. K T (in K) 5216 m.

3 Law #2: Wien s Displacement Law The radiatin emitted by a bdy at abslute temperature T fills a spectrum, with peak at wavelength given by: max 2898 m. K T (in K) 5216 m. R T (in R) Thus, the htter the bdy, the shrter the emitted wavelengths. Cnsequence f Law #1: One way t prvide heat t an bject is t expse it t a htter bdy. The htter, the better. Hence, slar expsure is much better than expsure t a warm piece f earth r even a fire. Cnsequence f Law #2: Because the sun is s ht (surface temperature T = 5750 K = 9,890 F), it emits mst f its radiatin arund = 0.48 m, which nt cincidentally falls in the visible range. The earth and ur huses are nt as ht (arund T = 72 F = 295 K) and emit their radiatin arund = 10 m, in the infra-red range. We need an infra-red camera t see this radiatin. 3

Radiatin frm sun and frm earth Atmsphere very transparent in the visible range Atmsphere very paque in infra-red range frm sun frm earth The atmsphere and windw glass are mstly transparent t visible

4 Radiatin frm sun and frm earth Atmsphere very transparent in the visible range Atmsphere very paque in infra-red range frm sun frm earth The atmsphere and windw glass are mstly transparent t visible light but quite paque in the infra-red range. Frm sun t earth: Being at 5750 K, the sun emits 6.2 x 10 7 W/m 2. Given the size f the sun (R sun = 696,000 km) and the distance frm the sun t the earth (d = 149,476,000 km), we can calculate the amunt f the slar radiatin arriving at the earth: at nrmal incidence W/m 2 = 435 Btu/(hr.ft 2 ) The preceding figure is the slar radiatin arriving at the uter edge f the earth, which is the upper atmsphere. What actually strikes the earth surface is smewhat less because f partial absrptin and reflectin by the atmsphere, especially cluds (in average, abut 60% left at grund level). A further reductin is caused by blique incidence (radiatin spread ver a larger area). 4

The angle f the sun abve the hrizn, at any given place and time, depends n 3 variables: - The latitude f the lcatin, (0 < < 90 ) - The day f the year, n (0 n 365) - The hur f the day, h (cunted + and

5 The angle f the sun abve the hrizn, at any given place and time, depends n 3 variables: - The latitude f the lcatin, (0 < < 90 ) - The day f the year, n (0 n 365) - The hur f the day, h (cunted + and frm lcal nn) The trignmetric frmula is: sin sin sin cs cs cs15 h in which is the slar declinatin (angle f sun abve equatrial plane): 23.5 cs360 n Lk fr key values f sin sin sin cs cs cs15 h Over the curse f the day, the sun is highest at nn (h = 0): sin sin sin cs cs cs( ) sin(90 ) 90 in which 23.5 cs360 n Spring equinx (22 March): n = 81 = 0 = 90 Summer slstice (21 June): n = 172 = = Fall equinx (20 September): n = 263 = 0 = 90 Winter slstice (21 December): n = 355 = 23.5 =

(http://www.irn-t-live-with.cm/ apartment/surce/4.

f summer sun. H H L H tan( 23.5 ) tan tan(113.5 ) H H D L H tan( 23.

6 ( apartment/surce/4.html) Overhang lengths and rm depths can be calculated t adjust fr this seasnal effect. Usually, we need t - maximize the uptake f winter sun and - eliminate the uptake f summer sun. H H L H tan( 23.5 ) tan tan(113.5 ) H H D L H tan( 23.5 ) tan tan(66.5 ) fr 23.5 S, if yu knw the height H f the ceiling, yu can calculate the length L f verhang and depth D f the rm. Wise use f verhangs t prvide shading against excessive slar intake 6

7 Htel in a trpical lcatin (phts by Lew Harriman) 7

Shading n suthern façade f the AVA Gallery in Lebann, NH Slar shades (http://www.

html) This huse under cnstructin in Durang, Clrad features straw-bale cnstructin

8 Shading n suthern façade f the AVA Gallery in Lebann, NH Slar shades ( This huse under cnstructin in Durang, Clrad features straw-bale cnstructin (excellent insulatin) and passive slar design. Nte the shade prvided by the verhangs. Clerestries (in-rf windws) prvide slar radiatin t the back f the huse. 8

Hw a clerestry windw wrks It brings daylight t the backside f a building.

sun electricity (http://www.regnlive.cm/envirnment/index.ssf/2008/04/27-week/) Imprtant Ntes 1.

The length f an verhang n an eastern r western wall wuld be prhibitively lng because the sun is lw

9 Hw a clerestry windw wrks It brings daylight t the backside f a building. Clever cmbinatin f clerestry windws and phtvltaic cells n rf belw: Winter sun heat int huse Summer sun electricity ( Imprtant Ntes 1. Shading with verhangs nly wrks fr suthern walls. The length f an verhang n an eastern r western wall wuld be prhibitively lng because the sun is lw when it strikes an eastern wall in the mrning and a western wall in the evening. Instead, vertical prtrusins shuld be cnsidered. Alternative slutins are - recessed windws, - vegetatin. 9

But by the time the sun shines in the late afternn n the western side, the building has been warmed by the mid-day sun and usually n lnger needs additinal heat.

10 Imprtant Ntes 2. There is n east-west symmetry. The reasn fr this is that when the sun shines in the mrning n the eastern side, the building is cler frm the previus night, and the sun is usually welcme. But by the time the sun shines in the late afternn n the western side, the building has been warmed by the mid-day sun and usually n lnger needs additinal heat. Thus, mre shading is needed n the western side than n the eastern side. The sun des nt just mve up and dwn in the sky, it als mves acrss the sky, rising in the East and setting in the West and ccasinally nt setting at all. Island f Lppa, 70 N, Nrth Nrway, July (Credit: Husm ft, Bks 231) Angle f the sun abve the hrizn: sin sin sin cs cs cs15 h Taking int accunt the azimuth angle (East-West sweep angle) int accunt is cmplicated. 10

11 The Passive Slar Huse, by James Kachadrian, Chelsea

12 Sun paths drawn n cylindrical sun chart. These are published. Adding the bstructins ( ), including the seasnal nes ( ) 12

Finally, blcking the undesirable slar incidences f the summer Fr a first estimate (nt adjusting fr vegetatin), ne simply distinguishes between east, suth, west and nrth facing walls f the structure,

13 Finally, blcking the undesirable slar incidences f the summer Fr a first estimate (nt adjusting fr vegetatin), ne simply distinguishes between east, suth, west and nrth facing walls f the structure, and use a s-called Slar Heat Gain Factr (SHGF) fr each side. Fr 40 N, SHGF values (in BTUs per ft 2 per day, fr average cludiness in the USA): In practice, use lcal cludiness factr Mnth # days East Suth West Nrth % sun January , % February , % March , % April % May 31 1, , % June 30 1, , % July 31 1, , % August % September , % Octber , % Nvember , % December , % Then apply a Shade Cefficient (multiply by 0.87) t accunt fr partial reflectin by glass if sunlight is captured inside f a windw. 13

One can ptimize the design by rienting the cllectin surface s that it intercepts sun rays at a better angle.

14 A small crrectin, ften skipped: Multiply previus values by this gegraphic factr t accunt fr atmspheric clarity: The previus calculated values were fr vertical surfaces (like mst windws). One can ptimize the design by rienting the cllectin surface s that it intercepts sun rays at a better angle. This is particularly imprtant fr slar panels placed n a rf. The suthern rf slpe can be chsen t face the sun rays perpendicularly. The basic rule: Nte: This rule will be mdified later in discussin f phtvltaic cells. 14

A well functining building needs t perfrm the fllwing three functins simultaneusly: 1. Capture the necessary slar energy - Enugh in winter - Nt t much in summer 2.

The preceding slides dealt with 1. The next cuple f slides give an advanced glimpse f 2. and 3.

15 A well functining building needs t perfrm the fllwing three functins simultaneusly: 1. Capture the necessary slar energy - Enugh in winter - Nt t much in summer 2. Stre heat during day fr delayed use thrugh the night, 3. Distribute the heat effectively thrugh the varius rms. The set f these three functins is called Direct Slar Gain. The preceding slides dealt with 1. The next cuple f slides give an advanced glimpse f 2. and 3. T stre slar energy fr later use: Have a cncrete slab as flr t absrb the heat and radiate it back at a later time. This is called using a thermal mass. Calculating the necessary thermal mass will be the subject f a subsequent lecture. ( 15

Sme alternative strage methds: (www.strawbalehmes.

rg/) water drums masnry walls r stne/brick

html) Distributin f heat by unfrced ventilatin (warm

16 Sme alternative strage methds: ( r why nt a pl? ( water drums masnry walls r stne/brick fireplaces ( Distributin f heat by unfrced ventilatin (warm air rises and cld air sinks under buyancy frces the chimney effect ) is tricky business. Effective designs prvide fr adequate passageways and exhaust penings. Estimating the airflw and temperatures at varius pints in the structure is best accmplished by cmputer simulatins. ( 16

17 A private residence in Straffrd, VT (pht by the prfessr) 17

Chapter 1 Notes Using Geography Skills

Chapter 1 Notes Using Geography Skills Chapter 1 Ntes Using Gegraphy Skills Sectin 1: Thinking Like a Gegrapher Gegraphy is used t interpret the past, understand the present, and plan fr the future. Gegraphy is the study f the Earth. It is