( τα ) = Product of transmittance and absorptance

Transcription

1 Poceedings of the 010 Intenational Confeence on Industial Engineeing and Opeations Management Dhaka, Bangladesh, Januay 9 10, 010 Design of a Diect Gain Passive Sola Heating System Md. Tanbiuj Jaman, Md. Masudu Rahman, and A.N.M. Mizanu Rahman Mechanical Engineeing Depatment Khulna Univesity of Engineeing and Technology Khulna, Bangladesh Abstact The sola enegy that falls natually on a building can be used to heat the building without special devices to captue o collect sunlight in diect gain passive sola system. Passive sola heating makes use of lage sun-facing windows (south-facing in the Nothen Hemisphee) and building mateials. A well-insulated building with such constuction featues can tap the sun s enegy and educe heating bills as much as 50 pecent. Passive sola designs also include natual ventilation fo cooling. Shading and window ovehangs also educe summe heat while pemitting winte sun. In this pape, the heat enegy obtained fom sola enegy is stoed by themal mass floo which is used to maintain comfotable highe tempeatue inside the oom in day time as well as in the night. The themal mass floo was made of stone chips. The ovehang was also designed in simple, new, and effective way to educe ove heating duing summe. The low cost mateials used fo the study in ode to focus on low cost constuction with comfotable esult. Keywods: Passive Sola System, Diect Gain, Deteminants of Design Nomenclatue U L = Loss coefficient F -s = Receive Radiation View Facto F c = an enegy-weighted contol function ( τα ) = Poduct of tansmittance and absoptance H = Daily aveage total adiation fo the month H b = Daily aveage beam adiation fo the month H d = Daily aveage diffuse adiation fo the month =Gound eflectance F I =A special contol function T =Tempeatue inside the oom, ºC T a =Ambient tempeatue, ºC f i =Monthly mean faction of vetical eceive aea eceiving beam adiation as a function of elative ovehang dimensions R b =Ratio of the aveage daily beam adiation on the tilted suface to that on a hoizontal suface δ= Declination of sun φ= Latitude of sun A =Apetue aea S = Aveage enegy gain pe unit aea

2 1. Intoduction Sola enegy is efeed as enegy contained in the ays of sun. Sola enegy is available, only duing day time and if it needs duing night then some esevoi of enegy should be used. At pesent hanessing, stoage and use of sola enegy is becoming moe effective because of scacity of available conventional enegy (coal, oil, gas etc). Passive sola gain heating system is an impotant tem in sola enegy technology. A passive sola building is one that deives a substantial faction of its heat fom the sun using only natual pocesses to povide the necessay enegy flows. Themal conduction, fee convection, and adiation tanspot theefoe eplace the pumps, blowes, and contolles associated with active sola heating systems. The elements of a passive sola heating system tend to be closely integated with the stuctue fo which heat is povided. South facing windows, fo example, seve as apetues though which sola enegy is admitted to the building, and themal stoage may be povided by inheent stuctual mass. Sola adiation absobed inside the building is conveted to heat, pat of which meets the cuent heating load wheeas the emainde is stoed in the stuctual mass fo late use afte the sunset. The objective of the wok is to design a diect gain passive sola heating system with simplicity and low cost management. 1.3 Scope of the Wok: Passive sola design uses sunlight to ceate enegy efficient living and wok spaces that ae a pleasue to be in, and minimizes the use of fossil fuels and associated pollution. To top it all off, the pinciples of passive sola design ae easy to gasp and implement in new constuction. The pupose of these pocedues is to make the esults of ecent scientific eseach on passive sola enegy accessible to pofessionals involved in building design o design evaluation. By so doing, this new technology can be tansfeed fom the eseach laboatoy to the dawing boad and the constuction site.. Liteatue Review Diect Gain Passive Sola Heating System A diect gain passive sola heating system admits sunlight diectly into the space to be heated though windows o othe glazed apetues as indicated schematically in the Figue 1. The inteio mateials of the building ae capable of absobing lage amounts of enegy though adiation ad convection []. Figue 1: Schematic of Diect Gain Passive Sola Heating System Elements of Diect Gain Passive Sola Heating System: 1. Apetue (Window). Contol (Ovehang) 3. Themal mass floo

3 4. Distibution. Factos Impotant fo Diect Gain Passive Sola Heating System: 1. Building oientation. Window location 3. Sola window & calculated oof ovehangs 4. Heat tansfe mechanism. 3. Design of Diect Gain Passive Sola Heating System 3.1 Design of Diect Gain Window: In a diect gain passive system the window and the oom ae in effect, a vetical south facing flat plate collecto with themal capacitance. The methods fo estimating adiation incident on a shaded suface ae modified to account fo tansmittance of the glazing and absoptance of the oom to estimate diect gains. Loss coefficients ae in pinciple vey simila to those of flat plate collectos. But the use of movable insulation must be taken into account. The monthly aveage net gain o loss fom a diect gain system can be estimated by consideing the sola gain into the ooms independently of the themal losses though the window [1]. Net enegy gain The aveage daily adiation absobed in the oom can be witten as: ρh A S = AFc ( τα) HbR bfi + HdF s + The aveage themal losses fo a day: Ql = 4 AU L FI ( T Ta ) The net enegy gain: Q net ρh ( τα) H R f + H F + [ 4A U F ( T T )] ()` 1 = A Fc b b i d s Fo Decembe H b = MJ m, H d = 4.48 MJ m, H = = MJ m Fo w=1, e=0, g=0. and f i = 0. 95, F s = 0.39, ρ = 0., o o Fo single glazing window U L = 6.0W m C =.016MJ m C o Let, T Ta = 10 C L I a Now fom equation (1) net A Q = ( ) A ( 5.184) = 9.756A Fo, A = 1.5m Q net = MJ pe day fo the month. Fo, A = 1.5m Q net = 1.06MJ pe day fo the month. Fo, A = 1m Q net = pe day fo the month. 3

4 1.19m 1.19m Figue : Apetue Aea fo Poposed Sola Gain System 3. Design of Themal Mass: 1) Should be located in the same space that has the diect gain system. ) Optimum location is on floo diectly behind glazed aea. 3) A unifom distibution of themal stoage mass in conducive to a themally unifom living space. As geneal ule, a massive suface in the diect zone should be elatively dak in colo and low-mass suface should be elatively light in colo. This encouages absoption of sunlight on sufaces whee heat can be stoed [4]. Fo A = 1.5m Floo aea o themal mass aea Fo A = 1.5m Floo aea o themal mass aea Fo A = 1.0m Floo aea o themal mass aea A = 3 A = F 4.5m A F = 3 A = 3.75m 4 A = 3 A = 3m F Themal Mass: 8 inches of concete, stone, adobe, etc Insulation: inches closed cell foam Base: 4 6 inches of compacted gavel o sand 3.3 Sizing Ovehangs: Sizing ovehangs is a design that povides adequate potection fom oveheating in the fall may tend to educe the amount of sola enegy available fo needed space heating in late winte o sping. Since an ovehang does not povide potection fom sky diffuse o gound eflected adiation, it is often necessay to povide additional countemeasues to pevent oveheating duing the cooling season. Fo this eason, the cuently accepted design pactice is to size an ovehang such that the pefomance of the passive heating system is minimally affected, and employ additional countemeasues against oveheating as equied. The sizing pocedue intoduced [8]. Afte detemining the last month fo which total illumination of the apetue will be allowed, it is an easy matte to fix the ovehang geomety. The ovehang length is denoted by X and the sepaation is given by Y, as indicated in Figue 3. The atio X/Y is elated to the latitude (L) minus the declination (D) and this elationship is epesented gaphically in Figue 4 [8].

5 Figue 3: Ovehang Geomety Figue 4: Ratio X/Y Related to (Latitude-Declination)

6 4. Conclusion and Recommendation 4.1 Conclusion: The design is based on low cost analysis in diect gain passive sola heating system fo suppoting developing counties. The few tempeatue diffeence between oom and ambient is taken to be beneficial in cost fo model passive building. The way of sizing ovehangs is eally a new ea of simple and effective engineeing wold. 4. Recommendation: In diect gain heating system the length of the noth side walls should be lage than east o west side walls so that lage potion of the themal mass diectly exposed to the sun and moe enegy can be absobed by the themal mass. Night insulation should be povided to educe heat loss though the window. Double glazed apetue can also be povided to educe heat loss though the window. Black tile can be used as absobe plate to incease absoptance of the suface as well as to incease net enegy gain by the oom. Bette pefomance may be obtained by poviding pope insulation. Refeences 1. John A. Duffie and William A Beckman, Sola Engineeing of themal pocesses, John wiley & sons, New Yok.. Willam C. Dickison and Paul N. Cheemisinoff, Sola Enegy Technology Handbook (pat-b). 3. G.N Tiwai, Sola Enegy, Naosa publishing house, New Delhi. 4. John D. Myes, Sola Application in Industy and Commece, Pentice Hall Seies in Enegy. 5. Fank Keith and Jan F. Keide, Pinciple of Sola Engineeing, Hemisphee Publishing Copoation, Washington, London. 6. Renewable enegy netwok, Local govenment engineeing depatment (LGED), Bangladesh Unified Facilities Citeia (UFC), Depatment of Defense, USA. 9. Aizona Sola Cente (AZSC) 10. Depatment Of Enegy (USA)