Available online at ScienceDirect. Energy Procedia 48 (2014 )

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1 Available online at ScienceDirect Energy Procedia 48 (2014 ) SHC 2013, International Conference on Solar Heating and Cooling for Building and Indutry September 23-25, 2013, Freiburg, Germany Optimizing olar collector tilt angle to improve energy harveting in a olar cooling ytem Paolo Corrada a *, John Bell a, Lia Guan a, Nunzio Motta a a Quuenland Univerity of Technology, 2 George t, Bribane 4001, Autralia Abtract Solar cooling ytem are gaining popularity due to continuouly increaing of energy cot around the world. However, there are till ome factor that are hindering the intallation of olar cooling ytem on a larger cale. One being the cot aociated with the olar collector required to provide heat to the aborption chiller. Thi tudy demontrate the poibility of reducing the number of olar panel in a reidential olar cooling ytem baed on evacuated tube producing hot water at a low temperature (90 C) and a water-ammonia aborption chiller The The Author. Author. Publihed Publihed by Elevier by Elevier Ltd. Ltd. Selection and and peer peer review review by by the the cientific cientific conference conference committee committee of SHC of 2013 SHC under 2013 reponibility under reponibility of PSE AG of PSE AG. Keyword: aborption chiller; olar air-conditioning; olar cooling; optimum tilt angle in Bribane. 1. Introduction Air conditioning ytem are the larget uer of electricity in Autralia houehold in [1]. The amount of electricity ued in the cooling ytem i directly related to the heat load that need to be removed. Thi heat i trongly related to both the weather condition and un irradiation above the houehold. The contant increae in energy cot are making people increaingly intereted in reducing electricity conumption particularly airconditioning ytem. One poible olution i to reduce the ue of power from the grid by tapping olar energy, mot commonly produced by photovoltaic panel, to power a tandard plit ytem. The direct ue of thermal * Correponding author. Tel.: ; fax: addre: paolo.corrada@qut.edu.au The Author. Publihed by Elevier Ltd. Selection and peer review by the cientific conference committee of SHC 2013 under reponibility of PSE AG doi: /j.egypro

2 Paolo Corrada et al. / Energy Procedia 48 ( 2014 ) energy i becoming more popular in remote area where olar radiation i abundant [2]. Solar cooling ytem ue thermal panel to produce hot water at low temperature (90 C) combined with an aborption chiller. A limiting factor for the ue of thee ytem i the intallation cot, which i till too high to be compenated by benefit for a ingle houehold. The key component to improve, and o produce more affordable olar cooling ytem, are the olar collector and the aborption chiller [3]. Solar collector ued only for cooling are uneconomical becaue they are ued only for a part of the year, o it i neceary to ue the olar ytem for both heating and cooling all year round [4]. Optimizing of the number of olar panel by addreing the eaonal variation of the olar angle can be the key to achieve the economic viability of thi ytem. Nomenclature n day number of the day of year tarting from the firt of January of the ite angle with the horizontal unet hour angle for the tilted urface H b direct or beam radiation diffue radiation H r ground reflected radiation Q output power to the liquid circulating through olar panel F collector efficiency factor A a area of the olar collector () en effective tranmittance aborptance product at normal incidence G global olar irradiance U overall heat lo coefficient t m mean fluid temperature through olar field (t out -t in )/2 t a ambient air temperature efficiency of olar panel G on extra-terretrial radiation G c olar contant (1,367 W/m 2 ) H o monthly average daily extra-terretrial radiation on a horizontal urface K T clearne index diffue daily radiation 2. Heating and cooling load Thi tudy i baed on a 120 m 2 dwelling in South Eat Queenland (SEQ), Autralia, for which the predicted energy conumption for cooling and heating were etimated by a tandard commercial mathematical model [5]. The prediction for the cooling power required by thi dwelling i 12.2 kw wherea the heating power required i only 5 kw. The cooling power i upplied by the olar cooling ytem and the heating power i upplied directly by the hot water generated by the olar collector ued in the olar cooling ytem. 3. Solar thermal panel performance One of the parameter influencing the amount of energy collected by a olar panel i the tilt angle with repect to the horizontal, which i uually et equal to the latitude of the intallation location [6]. Other parameter influencing the performance of the olar panel are the ambient temperature and the hot water temperature required by the aborption chiller. Thi tudy found that chooing the tilt angle equal to the latitude of the intallation doe not maximize the energy collected by the olar ytem during ummer time when the cooling requirement i at the maximum. A mathematical model wa developed to addre thi calculating the bet tilt angle

3 808 Paolo Corrada et al. / Energy Procedia 48 ( 2014 ) for the SEQ. The dwelling optimum angle wa computed by earching the maximum average daily radiation on the collector urface for each month of the year. Etimation of the average daily monthly radiation for a ytem uing an inclination angle equal to 0 and equal to the latitude were alo performed. A Bribane i located at a latitude of degree thi value ha been ued in the calculation. The ame model include the ambient temperature variation during the day. Weather data wa made available by the Bureau of Meteorology [7]. 4. Methodology The firt tep i the mathematical modeling of the olar radiation on a tilted urface, where the olar declination and the mean unhine hour angle for the month ( ) were calculated uing the following formula [8]: δ = 23.45*in 360 * ( n day ) 365 (1) ω = co 1 * tanφ *tanδ ( ) (2) The value of the declination angle varie between ±23,45 degree which mean the earth axi weep a total declination angle of degree during the year. Thi variation of the declination angle i the caue of the cyclic change in olar radiation level. The etimated value of and are ued to calculate R b which i the ratio of the average daily direct radiation on a tilted urface to that on a horizontal urface [9]. co( φ β)*coδ *in ω + π * ω *in( φ β)*inδ 180 R b = coφ *coδ*in ω + π * ω 180 *inφ *inδ (3) where: ω = min aco( tanφ *tanδ) ( ) aco tan ( φ β)*tanδ (4) In equation 4, the firt line i the equation related to the horizontal urface and the econd i related to the inclined urface [10] The value of the extraterretrial radiation G on i then calculated a: G on = G c * *co 360 *n day (5) 365 where G c i the olar contant (1,367 W/m 2 ). The value of G on i ued to calculate the monthly average daily extraterretrial radiation on a horizontal urface a: H o = 24 π *G on * coφ *coδ*ω + π 180 *ω *inφ *inδ (6) Thi value i then ued to calculate the monthly average clearne index K T which i defined a:

4 Paolo Corrada et al. / Energy Procedia 48 ( 2014 ) K T = H H o (7) The fraction of the diffue daily radiation i a function of K T and it i etimated [11] a: For K T 0.13 H = (8) For 0.13 K T 0.8 H = * K T * K 2 3 T * K T For K T 0.8 (9) H = (10) The daily amount of olar radiation on a tilted angle (H t ) uing an aniotropic method i due to the um of three different input: Direct or beam radiation (H b ) Diffue radiation ( ) Ground reflected radiation (H r ) o that the total amount of radiation on a tilted urface i calculated a: H t = H b + + H r (11) The daily beam radiation i calculated a: H b = (H )*R b (12) The ground reflected radiation i calculated a: 1 coβ H r = H * ρ g * (13) 2 The total radiation on a tilted urface can be then calculated a: 1 coβ H t = ( H )* R b + H * ρ g * + (14) 2 The econd tep in the mathematical modeling i a imulation of the olar field where evacuated tube are ued. The choice of the evacuated tube i made becaue of the temperature required for the aborption chiller. The model i developed uing different required hot water temperature for cooling (90 C) and heating (60 C). That i a lower temperature i ued in winter where the efficiency raie and reduce the negative effect of a lower ambient temperature. The evacuated tube collector conit of heat pipe inide vacuum-ealed gla tube. To optimize the aborption of the olar radiation ome manufacturer intall a reflector in their product [12]. The mathematical model follow the tandard EN and [10] to pecify a reproducible methodology which aee the panel efficiency o that the reult are comparable. Two alternative tet method for the thermal performance characterization of olar collector are pecified, one ued for teady-tate tet and the other for quai-dynamic tet [10].

5 810 Paolo Corrada et al. / Energy Procedia 48 ( 2014 ) The ueful output power of a olar collector for a near normal incidence angle of the olar radiation during teady-tate operating condition, can be written a [10]: Q = F * A a *(( τα) en *G U *( t m t a )) (15) The efficiency i then calculated a the ratio of the output energy from the collector and the incident radiation on the area occupied by the collector: Q η = = F * τα G* A a ( ) en U * ( t m t a ) G (16) Introducing the variable T m * = (t m -t a )/G indicate the reduced temperature difference a: η = F * * (( τα) en U *T m ) (17) Heat loe are conidered a a function of two term, the firt i a contant and the econd dependent on the temperature difference between fluid and ambient (t m -t a ) The efficiency can be rewritten a: η = η o a 1 *T * * m * a 2 *G*( T m ) 2 (18) The value of o, a 1 and a 2 are uually provided by the manufacturer of the olar collector. The following collector have been ued for the modeling: Company: Thermomax Ltd Type: DF Serial number: Table 1 how the modeling reult for the average daily monthly olar radiation on three different loped urface: tilt angle variable with the month, tilt angle flat with the horizontal and tilted with an inclination equal to the latitude. Table 1 Average daily energy per quare metre collected by olar panel at different inclination angle Month Angle ( ) Daily monthly average energy (kwh) Angle ( ) Daily monthly average energy (kwh) Angle ( ) January February March April May June July Augut September October November December Daily monthly average energy (kwh) A olar array covering approximately 24 m 2 ha been ued to calculate the amount of energy collected by the olar collector with the different tilt angle.

6 Paolo Corrada et al. / Energy Procedia 48 ( 2014 ) Reult The cooling/heating capacity i maximized when the angle i varied monthly to follow the olar elevation. However, the optimization of a olar cooling/heating ytem alo need to take into account the amount of cooling/heating required a a function of the eaonal weather condition and the cot aociated with the ytem implementation. A the olar cooling ytem in thi tudy require a peak cooling capacity of 12.2 kw during ummer and 5 kw peak heating capacity during winter the propoed ytem need a dedicated area of 24 m 2 for the olar panel in order to collect thi energy. Figure 1 and 2 how the maximum cooling capacity obtained by the propoed ytem in ummer and the maximum heating capacity in winter uing three different inclination. The efficiency of the aborption chiller ha been aumed to be 0.7 [13] wherea the efficiency of the heating ytem i aumed a 0.9. The blue line in Figure 1 mark the maximum required cooling in ummer and the red line in Figure 2 mark the maximum required heating in winter. Spring and autumn requirement are well below thee line. Figure 1 Cooling production during ummer Figure 2 Heating production during winter The reult how that the propoed ytem can produce the cooling required during ummer only by adopting either a monthly variable angle or a fixed horizontal inclination. The calculation how that the olar energy collected during the ummer eaon by the variable or flat angle configuration exceed the one baed on the latitude angle by approximately 10%. Conequently, the number of panel needed for the ytem can be reduced by 10% with an equal aving in term of intallation cot. It hould alo be noted that the optimization of the angle by month achieve it bet reult in winter, when reduced heat i required. In fact the heating required acro the winter month i le than half that produced by our ytem. 6. Concluion The cot of implementing a olar cooling ytem can be compenated by uing the olar field of the ytem not only for a limited time for cooling purpoe but alo for heating during winter. Thi i poible by optimizing the

7 812 Paolo Corrada et al. / Energy Procedia 48 ( 2014 ) number of panel and their tilt angle to achieve the required cooling in ummer, a the winter requirement for heating i largely atified with the ame number of panel ued to match the cooling demand. The reult of the calculation ugget that the flat panel configuration i the bet olution for a olar cooling and heating intallation in the SEQ region conidering the cot involved in the intallation and maintenance of a variable angle ytem. Reference [1] Y. Strenger, "Air-conditioning Autralian houehold: The impact of dynamic peak pricing," Energy Policy, vol. 38, pp , [2] A. Demirba, "Global Renewable Energy Projection," Energy Source, Part B: Economic, Planning, and Policy, vol. 4, pp , 2009/10/ [3] V. Boopathi Raja and V. Shanmugam, "A review and new approach to minimize the cot of olar aited aborption cooling ytem," Renewable and Sutainable Energy Review, vol. 16, pp , [4] K. Sumathy, Z. C. Huang, and Z. F. Li, "Solar aborption cooling with low grade heat ource - A trategy of development in South China," Solar Energy, vol. 72, pp , [5] Trane. (2010). Trace 700 v Available: [6] K. Bakirci, "General model for optimum tilt angle of olar panel: Turkey cae tudy," Renewable and Sutainable Energy Review, vol. 16, pp , [7] BOM. (2013). Boreau of Meteorology. Available: [8] P. I. Cooper, "The aborption of radiation in olar till," Solar Energy, vol. 12, pp , [9] B. Y. H. Liu and R. C. Jordan, "The interrelationhip and characteritic ditribution of direct, diffue and total olar radiation," Solar Energy, vol. 4, pp. 1-19, [10] J. A. Duffie, William A. Beckman., Solar engineering of thermal procee., 3rd ed. ed. New York: Wiley, [11] A. De Miguel, J. Bilbao, R. Aguiar, H. Kambezidi, and E. Negro, "Diffue olar irradiation model evaluation in the North Mediterranean Belt area," Solar Energy, vol. 70, pp , [12] E. Zambolin and D. Del Col, "Experimental analyi of thermal performance of flat plate and evacuated tube olar collector in tationary tandard and daily condition," Solar Energy, vol. 84, pp , [13] S. A. Kalogirou, "Recent Patent in Aborption Cooling Sytem," Cypru Patent, 2007.