Information Job Sheet 3. Site Analysis. Solar energy

Transcription

1 Informtion Job Sheet 3 Site Anlysis Solr energy The rdint power from the sun for given re is known s solr irrdince, nd is commonly mesured in wtts per squre meter (W/m 2 ). On Erth s surfce, the rdint power from the sun is pproximtely 1 kw/m 2 in the middle of cler summer dy t se level. Pek solr irrdince (on Erth s surfce t se level): 1000 W/m 2 Figure 36. The Sun. Festo Didctic

2 The mount of sunlight tht reches the Erth s surfce over the course of dy is clled insoltion. Insoltion is typiclly specified in kwh/m 2 dy. Insoltion tht is mesured perpendiculr to the sun s rys, is known s direct norml irrdince (DNI). Dily sun hours for res in the world re shown in Figure 37. Averge dily sunshine hours <3.3 h h h h h h h >11.0 h Figure 37. Insoltion mp of the Erth. Solr collector position Proper orienttion of the solr collector is importnt to cpture the most solr energy possible, bsed upon the sun pth or solr window for given loction. The zimuth ngle nd tilt ngle re importnt fctors to consider when positioning nd mounting n rry of solr collectors. Azimuth ngle For exmple, in the United Sttes (in the northern hemisphere of the plnet), the optimum direction for pointing solr collectors is due True South (not Mgnetic South). The zimuth ngle is 0 when pointing True South, even though compss bering would be some vlue ner Festo Didctic

3 Tilt ngle Bsed on the solr ltitude ngle for the specific re, the optiml tilt ngle of ech solr collector is equl to the loction s ltitude. Subtrcting 10% from the ltitude cn ccount for locl climte vritions. The tilt ngle cn be djusted on sesonl bsis, lso. The verge declintion in summer is +15 degrees, nd the verge declintion in winter is -15 degrees, so the tilt ngle cn be improved by dding 15 in winter, nd subtrcting 15 in summer. Solr window Equinox Sun pth Zenith Summer Sun pth Est Winter Sun pth North South West Figure 38. Solr collector orienttion. Mgnetic declintion Mgnetic declintion is the ngle tht seprtes True North (locted geogrphiclly t the top of Erth s rottionl xis) nd Mgnetic North (where the north end of compss needle points). Mgnetic declintion vries over time nd loction. Isogonic lines on mp show the ngle where the declintion is the sme vlue. Negtive (-) ngles on n isogonic mp indicte tht True North is west of Mgnetic North (or counter-clockwise on compss). Positive (+) ngles on n isogonic mp indicte tht True North is est of Mgnetic North (or clockwise on compss). Finding True North True North is determined simply by dding the compss bering (in degrees) to the mgnetic declintion ngle (in degrees, with its signed polrity). Mny web sites propose isogonic mps to help find True North. Alterntely, True North is usully identified with str symbol on topogrphic mp. Mgnetic North is lbelled MN nd Grid North is lbelled GN. Festo Didctic

4 Solr collector rry plcement Nerby obstcles cn cst shdows on solr collector tht cn substntilly reduce therml output. Unobstructed solr ccess is criticlly importnt for the solr collector rry to mximize solr exposure time throughout ech dy. Current nd future shding conditions bsed upon mn-mde nd nturl obstructions, such s towers nd trees must be considered, before finl loction nd position is chosen for the solr collector rry. The rry should be plced nerest the therml storge or dump re to minimize het loss in the outlet pipes. This is especilly importnt for ground-mounted instlltions. Solr energy resources Most wether, climte, nd solr energy dt is vilble directly from the web. It is recommended to cquire the dt covering your geogrphicl re before instlling ny solr collector rry. Residentil systems The design nd instlltion of solr-powered heting nd/or cooling system in residentil home my be hndled differently, depending on whether the house is being built s new construction project, or if the home lredy exists. For new house construction, pssive system cn be designed into the rchitecturl plns well before ny building begins. For n existing home instlltion, n ctive system my be better solution. Different steps re recommended for ech type of job. New house construction (pssive system) In pssive solr energy system, solr collector converts light energy from the sun to therml energy s het. A verticl solr collector mde of blckened concrete nd glss, clled Trombe wll, or horizontl solr collector mde of concrete, clled solr slb floor, uses nturl convection to circulte sunwrmed ir throughout the household living spce. This process is clled thermosiphoning. At night, the reverse process cools the re. Pssive solr homes require creful blnce between the re of their glss solr collectors nd the volume of their therml storge mss. With too mny south-fcing windows or with windows tht re too lrge (overglzing), nd smll therml mss, the house cn quickly overhet during the dy nd become cold t night. Typicl bckyrd greenhouses exhibit this behvior. Conversely, if the therml mss cpcity is too lrge, nd there re not enough south-fcing windows or the windows re too smll, the house remins chilly during the winter months, during the dy time nd t night. Common tool sheds provide good exmple of this behvior. The home insultion nd ventiltion must be properly blnced lso. This technique prevents condenstion tht cn cuse mold nd mildew growth, nd llows fresh ir to enter the house, while thermlly isolting the indoor nd outdoor tempertures. Optionlly, thermo- shutters cn be instlled on windows to help trp het overnight. Exterior wlls nd the roof must be thermlly insulted with positive seled vpor brriers, s well. Often, 44 Festo Didctic

5 centrlized woodburning or col stove or smll conventionl (gs- or oil-fired) furnce or electric heter is used s bckup het source, nd smll ir conditioner my supplement cooling. Including conventionl heting nd cooling system helps to protect the resle vlue of the home, nd to mechniclly ssist the circultion of solr-conditioned ir throughout the house. Low-powered blower fns cn lso be used to help circulte wsted het from electricl pplinces nd lighting inside the residence. Existing home instlltion (ctive system) Active solr energy systems use electric wter pumps nd/or ir blowers, clled circultors, to distribute the therml energy throughout home. In order to mintin efficient opertion, mny of the nture-bsed design prctices tht pply to pssive system re lso used for ctive systems. Evlution tips nd building considertions. 1. Find True North on the property nd consider solr collector orienttion with reltionship to the sun during ech dy, month, nd seson. Idelly, the lrgest portion of the house should hve southern exposure. 2. Let nture help you, by designing the system performnce bsed on the loction s solr intensity (insoltion) over the course of n entire yer. Consider the ltitude ngle of solr noon (for south-fcing solr collectors) nd the pek sun hours per dy (zimuth ngle for est-fcing nd westfcing solr collectors) for ech of the four sesons. Situte most window nd door glss so tht the home is comfortble during both the summer nd winter months. The strtegic use of nturl plnts cn help lso. For exmple, in pssive solr energy system, deciduous trees cn be positioned ner house to block the sun during long summer dys, but their lefless brnches will llow needed sunlight to pss during the shorter winter dys. Consider other nturl conditions lso, such s breeze nd precipittion. 3. Use windows s solr collectors nd cooling devices, but do not overglze. Keep the squre footge of glss (on the est, south, nd west sides) between 10% nd 20% of the totl exterior heted wll re. Also, consider the shding effects from roof overhngs. 4. Include n effective therml mss to store the dily solr energy s het for nightly use. 5. Thermlly insulte the house exterior nd include positive seled vpor brriers, while permitting fresh ir to ventilte the living spce. 6. Be creful not to oversize conventionl heting or cooling systems, which cn be rted for smller cpcities in solr therml energy environment. 7. Mximize cost effectiveness by using conventionl building mterils in more energy efficient wys. For exmple, light-colored roofing mterils remin cooler in sunny conditions. Festo Didctic

6 Design process To pln n efficient solr therml energy system, the design process cn involve very detiled nlysis of ll solr, lnd, building, nd system component properties. Softwre is vilble to ssist with this complex process. In the upcoming SYSTEM SIZING Job Sheet, you will estimte the system sizing, by using generl rules-of-thumb. However, the following is list of some dt tht is required for more forml engineering nlysis. Solr/lnd physics Site loction (nme) geogrphicl loction must be predetermined. Coordintes (ltitude nd longitude, in degrees) look up vlue on web for the loction. Mgnetic declintion (ngle from True North, in degrees) use compss nd isogonic mp to find True North. Averge nnul (DNI) solr insoltion (in kwh/m 2 dy) look up vlue on web. Pek sun hours per dy (in h/dy) look up vlue on web. Averge solr irrdince (in W/m 2 ) look up vlue on web or clculte bsed on pek sun hours. Tilt ngle (in degrees) use protrctor nd solr pth chrt to determine vlue, or clculte bsed on ltitude. Azimuth ngle (ngle from True South, in degrees) use compss nd isogonic mp to find True North. Known solr obstcles (list) determine by observtion. Averge winter temperture (in C) look up vlue on web. Outside winter design temperture (in C) look up vlue on web. Averge nnul degree dys (heting nd cooling) HDDs nd CDDs find heting degree dys (HDDs) nd cooling degree dys (CDDs) for your re by visiting: Annul men sunshine (in %) look up vlue on web. Solr het gin fctor (SHGF) look up vlue for ltitude. An ASHRAE term used to determine solr het gin (in m 2 ). Shde coefficient (SC) look up vlue for glss. An ASHRAE term used to define reduction in solr het gin due to reflection. 46 Festo Didctic

7 Building physics Interior floor re (in m 2 ) crete or obtin initil floor plns of the house or building, then clculte the re bsed on the drwings. The system drwings should identify the loction of ll ir vents, return ducts, piers nd chimney bses, plumbing risers, nd wter pipes. Exterior glss re (of exposed windows, doors, nd skylights, in m 2 ) clculte re. Exterior wll re (of upper nd lower heted wlls, in m 2 ) clculte re. Insulted roof/ceiling re (in m 2 ) clculte re. Airspce volume (in m 3 ) clculte volume. Therml resistnce, R-vlues (for ech building envelope component/mteril, such s ll wlls, glss (windows/doors/skylights), roof/ceilings, nd floors, in W/m 2 K) rtings cn be found on the web, to determine het gin (in kj/ C dy). Therml conductnce, U-vlues (for ech building envelope component/mteril, such s ll wlls, glss (windows/doors/skylights), roof/ceilings, nd floors, in W/m 2 K clculted from R-vlues to determine het loss (in kj/ C dy). The ASHRAE (R nd U) fctors re inversely relted. You cn clculte one vlue simply by tking the reciprocl of the other vlue. R-vlue = 1 / U-vlue U-vlue = 1 / R-vlue Stndrds nd certifictions The Council of Americn Building Officils (CABO) Model Energy Code (MEC) is intended to help rchitects, designers, nd builders increse energy efficiency nd relize the potentil for energy svings in new homes. It includes three methods for designing, constructing, nd conserving energy: component performnce, systems nlysis, nd cceptble prctice. MEC complince helps to ensure tht building s therml envelope is energy efficient. The interntionlized version of this code is the Interntionl Energy Conservtion Code (IECC). Visit the Interntionl Code Council (ICC) website for stndrds nd building inspector certifictions. Free softwre is vilble online to check residentil code complince. Some countries lso hve their own building energy conservtion codes s well. The Ntionl Fenestrtion Rting Council (NFRC) provides energy performnce rtings nd certifiction progrms for fenestrtion products, such s windows, doors, nd skylights. Electricl power nd lighting must lso be reviewed during energy conservtion inititives. Festo Didctic

8 Job Sheet 3 Site Anlysis OBJECTIVE In this job, you will lern how to evlute loction for the effective instlltion of solr therml energy system. PROCEDURE Arry plcement 1. Strt by choosing loction for the solr collector rry, such s your home or school. 2. Complete ll of the informtion below regrding the chose site for the collector rry. To do so, consult reference books or serch for the informtion on the internet. Site loction: Ltitude: N or S Negtive ltitude vlues indicte South. Longitude: W or E Negtive longitude vlues indicte West. Mgnetic declintion (ngle from True North): W or E Negtive mgnetic declintion vlues indicte West. Averge nnul (DNI) solr insoltion: kwh/m 2 dy Averge sunshine hours per dy: h/dy 3. Is the vlue of pek sun hours per dy bout the sme or slightly higher thn the verge nnul solr insoltion (in kwh/m 2 dy)? Yes No 4. Multiply the verge sunshine hours per dy by to determine the verge solr irrdince vilble for your loction, nd record your nswer. Averge solr irrdince: W/m 2 Festo Didctic

9 Due to night-time conditions, the verge solr irrdince (in the U.S.) is below 33% of the pek solr irrdince (on Erth s surfce t se level). 5. Is this rdint power level (verge solr irrdince) below 33% of the pek solr irrdince (on Erth s surfce t se level)? Yes No 6. Consider ll nerby obstcles for ll sun directions to decide where to position the solr collectors nd how high the rry cn be plced. Use pen nd pper to drw (or computer to plot) nd dimension mp of your specific re. Keep in mind tht you re evluting three dimensions on 2- dimensionl drwing. Determine the optimum tilt ngle for your loction nd show the zimuth ngle (0 if pointing True South). Tilt ngle: degrees Azimuth ngle (ngle from True South): degrees. Known solr obstcles:. b For n ccurte shding nlysis, you cn use Trimble SketchUp to model prticulr home, school, or business. The View, Shdows nd Window, Shdows menu items will llow you to see shdowing for ny dte nd time. 7. Use the Internet to find the following dditionl informtion for the intended geogrphicl loction. If you cnnot find ll vlues, record t lest two of the vlues. Averge winter temperture: C Outside winter design temperture: C Averge nnul degree dys: HDDs nd CDDs Annul men sunshine: % 8. When the job is finished, ttch your completed mp drwing to this Job Sheet with dimensions nd obstcles lbelled. Nme: Dte: Instructor's pprovl: 50 Festo Didctic