Available from Deakin Research Online:

Transcription

1 Thi i the publihed verion: Anderon, T. N. and Duke, M. 2008, Solar energy ue for energy aving in dairy proceing plant, IPENZ engineering TreNz, no , pp Available from Deakin Reearch Online: Every reaonable effort ha been made to enure that permiion ha been obtained for item included in Deakin Reearch Online. If you believe that your right have been infringed by thi repoitory, pleae contact droupport@deakin.edu.au Copyright : 2008, Intitution of Profeional Engineer New Zealand

2 Anderon T N and Duke M 2007, Solar Energy Ue for Energy Saving in Dairy Proceing Plant IPENZ engineering trenz ISSN Solar Energy Ue for Energy Saving in Dairy Proceing Plant 1. ABSTRACT New Zealand i one of the world larget producer of dairy product and ha a climate with high level of olar radiation; however, the ue of olar energy in the dairy proceing indutry ha received limited attention. An examination of hitorical record found that the annual peak in New Zealand milk production and proceing occur at a time when olar radiation level are increaing markedly. An F-Chart analyi wa ued to imulate the performance of large-area array of olar collector and to determine their uitability for heating and cooling in a dairy proceing environment. For the tudy four type of olar collector were analyed: glazed flat plate, evacuated tube, evacuated tube with CPC reflector and a building-integrated olar collector under development at the Univerity of Waikato (UoW). It wa found that of thee technologie, both flat plate and evacuated tube with CPC reflector could make ueful heating and cooling contribution. Furthermore, the olar fraction wa determined mainly by the collector area to torage volume ratio. Finally, it wa found that the UoW building-integrated olar collector could make a ignificant contribution to energy ue in dairie and may be an attractive future technology for the indutry. Key word: olar energy, dairy, heating, cooling, proceing 2. NOMENCATURE ω φ δ β ρg n Gc unet hour angle latitude declination collector inclination ground reflectance day of year olar contant o monthly average daily extraterretrial radiation monthly average daily radiation d monthly average daily diffue radiation b monthly average daily beam radiation T monthly average daily radiation on a tilted urface K T R b Ac FR U T a Δt τα N Tref Ti Ta G η f mean daily clearne index ratio of horizontal to tilted urface radiation collector area collector heat removal factor collector heat lo coefficient monthly average temperature econd per month monthly average tranmittanceaborptance product heating load number of day in month reference temperature inlet temperature ambient temperature incident radiation collector efficiency olar fraction (% of heating or cooling load provided by olar energy) 3. INTRODUCTION The New Zealand dairy indutry produce over 14 billion litre of milk annually (IC, 2006). A thi i far in exce of local demand, the majority of it i proceed for export market. To proce uch large amount of dairy product, it i neceary to upply a large amount of energy. To illutrate thi point, ovell-smith and Vicker (1983) found that the production of whole milk powder ued in exce of 14 GJ/t. Similarly, Vicker and Shannon (1977) found that ignificant amount of energy were ued for

3 generating hot water for cheee production and for cleaning in place (CIP) operation. A number of technologie have been propoed for reducing energy ue in the dairy proceing indutry, both in New Zealand and globally. ovell-smith and Vicker (1983) examined the feaibility of in plant cogeneration of heat and power (CP) in pray drying plant. They found that uch a ytem preented an economically viable olution to energy ue. The ue of CP wa alo invetigated by eal and Silveira (2002). They found that cogeneration uing molten-carbonate fuel cell technology wa both economically and technically feaible for ue in medium-ize dairy plant. Ozyurt et al (2004) explored the ue of heat pump in a pateuriation ytem. Their ytem wa baed on a liquid-liquid vapour compreion heat pump. Uing a heat pump ytem they achieved an average coefficient of performance (COP) of 2.44 from their ytem. They alo found that the heat pump could reduce their energy conumption by two-third compared to claical pateuriation ytem. Although reearcher have found way of improving energy efficiency through different technologie, the diadvantage of the CP, fuel cell and heat pump ytem mentioned i that they all require fuel or electricity to operate. To overcome thi hortcoming Benz et al (1998) and Benz et al (1999) examined the uitability of olar thermal proceing heating ytem for ome German food proceing plant. The Benz et al tudie found that evacuated flat plate and evacuated tube olar collector were uited to heating application in a milk pray drying factory. In their 1999 tudy they found that olar thermal ytem could upply heating, over a 20 year period, at a cot of $100 US/MWh. Furthermore, they noted that in a favourable climate, heat cot could be halved and performance doubled. Similarly, Schnitzer et al (2007) found that in the Autrian dairy indutry over 80% of the heating demand wa for temperature in the range from 60 C to 80 C, making olar energy ue ideally uited to heating in dairy proceing plant. Furthermore, they note that thi temperature i uitable for operation uch a wahing water in cheee production, preheating of cheee milk, outide cleaning, pateuriation, whey conditioning, and cleaning in place (CIP) operation. All of thee operation are commonly ued in the New Zealand dairy indutry. Given recent concern over the environment and the upporting evidence for the ue of olar energy, it wa decided to perform an analyi of how olar energy could contribute to heating and cooling energy reduction in New Zealand dairy indutry Solar Radiation in New Zealand New Zealand preent an ideal environment for the utiliation of olar energy, epecially when compared to ome northern hemiphere location. In New Zealand approximately 30% of all dairy farm, and a large number of dairy proceing plant, are located in the Waikato and urrounding region, to the outh of Auckland (IC, 2006). A Benz et al (1999) noted that olar thermal energy ytem for dairy plant could be improved in more favourable climate, a comparion wa made between the olar radiation in the Waikato region (EECA, 2004) and that of Stuttgart, a typical German location (Duffie and Beckman, 2006). In Figure 1 it can be een that the daily mean global radiation level in the Waikato are ignificantly higher than thoe in Stuttgart. Examination of the data correpond well with EECA (2001) uggetion that olar radiation in New Zealand i approximately 30% higher than that encountered in Germany. Baed on thi finding, it i poible that the New Zealand dairy indutry could produce thermal energy from olar reource more effectively than Benz et al were able to. In a recent tudy of energy ue in the European dairy indutry Ramirez et al (2006) noted that CIP account for approximately 70% of the energy ue in evaporator and up to 26% of the energy ued in dryer. They alo note that thee operation typically ue temperature in the range of 65 C to 75 C.

4 Daily Global Radiation (MJ/m 2 ) Waikato, NZ Stuttgart, D Month (Seaonally Adjuted) Figure 1: Mean daily global radiation for Waikato and Stuttgart. In addition to providing heating, olar radiation aid in the production of feed for dairy herd. A uch, with the onet of calving in early pring, and increaing level of olar radiation, there i alo an increae in milk production. Vicker and Shannon (1977) and Beneman (1986) howed that in New Zealand, thi peak in production occurred in mid to late pring before gradually reducing over ummer. In Figure 2 the trend in milk production i compared with the olar radiation level for a June to May year. From thi it can be een that milk production level and olar radiation exhibit a degree of correlation. The pinch method ue compoite heating and cooling curve a a viual repreentation of heat and temperature demand in proce indutrie. It how the point (ie the pinch ) above which it i neceary for heat to be added and below which cooling i required. The pinch method wa ued by Schnitzer et al (2007) to how that in a typical cheee production line the pinch point occurred at approximately 20 C. Thi confirm that the ue of olar energy i ideally uited to the dairy environment, a olar heating and cooling ytem would be able to deliver energy both above and below thi point. In order to integrate thi energy into the ytem it i poible to ue both direct and indirect integration. In Figure 3 and 4 two mean for the direct integration of olar heating are hown. The firt of thee how the olar array effectively acting a a inline heat exchanger preheating the water, or heating fluid, returning from a proce before entering the boiler or heat ource. In the econd the flow can be diverted o that, intead of uing the boiler or heat ource, the heat can be upplied by the olar array. Radiation and Milk Production Radiation Milk Production Month Figure 2: Qualitative relationhip between milk production and olar radiation level for a typical milk production eaon. Boiler (eat Source) Solar Array P-2 Proce Given the relationhip between milk production and olar radiation, combined with the energy ued in the New Zealand dairy proceing indutry, there i obviouly ignificant cope to utilie olar energy in the proceing of dairy product. Figure 3: Direct integration of heat from a olar array. 4. INTEGRATION STRATEGIES Perhap the mot common difficulty in uing olar energy in a continuou operation i determining where and how to integrate it. The pinch method i commonly ued to do thi.

5 Boiler Solar Array Proce Figure 4: Direct integration of olar heat into a proce. There are a number of argument for and againt uing a direct integration a hown in Figure 3 and 4. Typically the etup cot for thee ytem i relatively low; however, they do require continuou control and by their nature limit the ize of the olar array to enure that they do not provide energy at a higher temperature than i required by the proce. Furthermore, thee ytem will only function during the day. Thee hortcoming can be overcome by uing an indirect, torage-baed ytem a hown in Figure 5. By intalling an intermediate torage tank, heat can be added to the tank by the olar array and ued a required. The ytem doe not need to be continuouly controlled a with a direct ytem, and by adding a torage veel it i poible for heat to be tored and ued during period of low or no olar radiation. The main drawback of an indirect ytem i that it tend to have a higher initial cot and alo a longer payback time. Boiler Inulated Tank Proce Solar Array Figure 5: Indirect heat integration from a olar array utiliing a torage ytem. After examining the option for integrating olar energy into a proceing operation, it appeared that uing a torage-baed olution offered the bet olution given the continuou nature of New Zealand dairy proceing indutry. Thi would allow olar energy to be utilied with minimal diturbance to exiting ytem. It would require little control, and be able to be ued irrepective of prevailing olar condition. A imulation tudy wa conducted to determine the performance of large area array of olar collector coupled with thermal torage tank for ue in the indutry, uing the Waikato region a a cae tudy. 5. METODOOGY In order to determine the applicability of olar energy for heating and cooling, it wa decided that an F-Chart analyi would provide an adequate prediction of the heat that could be upplied by a olar heating ytem. Before the analyi of the heating ytem could be undertaken, however, it wa neceary to determine ome meteorological characteritic. NIWA (2007) provide baic data for the mean monthly air temperature and mean daily global radiation in amilton (Waikato) a hown in Table 1. In addition, the mean day for each month and declination on thi day are alo hown, a given by Duffie and Beckman (2006). Month Mean Day Air Temp ( C ) Declination (degree) Global Radiation (MJ/m 2 ) JAN FEB MAR APR MAY JUN JU AUG SEP OCT NOV DEC Table 1: amilton meteorological data. Thi data, however, cannot be directly applied in the F-chart analyi. Firtly, it i neceary to calculate the unet hour angle for each day uing Equation 1. coω = tan φ tan δ (1) By knowing the unet hour angle, it i poible to determine the integrated daily extraterretrial

6 radiation on a horizontal urface uing Equation 2. The extraterretrial radiation i the amount of radiation that would theoretically be received if there wa no atmophere G = SC 360n co π 365 πω coφ coδ in ω + in φ in δ 180 (2) aving determined the radiation to which a tilted olar collector i expoed it i poible to determine the olar heating or cooling fraction that can be obtained from a olar energy ytem uing the F-Chart method. The F-Chart method i commonly ued for the deign of active olar heating ytem and ha been developed from a large number of imulation of olar heating ytem (Duffie and Beckman, 2006). Subequently, by taking the ratio of the mean daily extraterretrial radiation to the meaured daily mean global radiation, we are able to determine the mean daily clearne index, a hown in Equation 3. K T = (3) 0 The clearne index allow u to determine the fraction of diffue radiation baed on Collare- Perreira and Rabl correlation, a given by Duffie and Beckman (2006), hown in Equation 4. For a typical liquid heating ytem, the olar fraction contributed by a ytem i given by Equation 7. Where: f = 1.029Y 0.065X 0.245Y X X Y = 2 ' AC FRU = A C F ' R Y ( τα ) 3 ( T T a ) ref T N Δt 2 (7) d = ( ω 90) [ ( ω 90) ] co115 ( KT 103) (4) Auming that the collector are mounted at an angle to the horizontal it i neceary for u to calculate the average daily beam radiation on the tilted urface uing Equation 5, for a ite in the outhern hemiphere. ' π ' co( φ + β ) co δ in ω ' + ω ' in( φ + β ) in δ 180 (5) R b = π co φ co δ in ω + ω in φ in δ 180 ' co Where: ω = min co 1 1 ( tan φ tan δ ) tan( φ + β ) ( tan δ ) Finally, it i poible to determine the monthly mean daily radiation on the tilted urface uing the Iotropic Sky model developed by iu and Jordan and a given by Equation coβ 1coβ T = brb + d + ρg (6) 2 2 Baed on thi method it i poible to determine the heating contribution provided by a olar water heating ytem. Similarly, olar energy can be utilied a the driving ource for an aborption cooling ytem. owever, thi require a number of modification to the F-Chart model. The olar fraction from a cooling ytem i given by Equation 8, a derived by Joudi and Abdul- Ghafour (2003). 2 f = ( X X ) 2 + ( X X ) 2 + ( X X ) Where: ' COPAC FRU X = ' COPAC FR Y = ( T T a ) ref ( τα ) T N Δt (8)

7 (COP i the mean coefficient of performance of the aborption cooling ytem.) By utiliing the F-Chart method it i poible to determine the olar fraction that i provided for ueful heating and cooling ytem. 6. SOAR EATING AND COOING SYSTEM For the purpoe of thi tudy three olar heating ytem were modelled. In the firt cenario it wa aumed that the olar heating ytem wa coupled to a water tank with a volume of 10m 3, in the econd a tank of 25 m 3 and in the third a tank of 100 m 3. Additionally, it wa aumed that the water in each of the tank would be heated from 40 C to 80 C over the period of a day. Thi would make it uitable for the application dicued by Schnitzer et al (2007) and be typical of the daily volume of hot water ued in mall, medium and large dairy proceing plant (CRES, 2008). Baed on the aumption for the olar collector ytem, it would be neceary to produce and tore 1668 MJ, 4170 MJ and MJ repectively. In each cae it wa aumed that the collector were in a clear north facing location and mounted at an angle equal to the location latitude, approximately 38 degree for amilton. A a general rule, olar water heating ytem require between 50 and 100 of torage volume per m 2 of collector area. For each tank volume, a collector array of approximately 50 /m 2, 75 /m 2 and 100 /m 2 wa modelled. Thu for thi tudy, array of between 100 m 2 and 2000 m 2 were modelled, although larger array are obviouly poible. For each cenario, calculation were baed on the gro aborber area uing efficiency equation from experimental teting by SPF (2007). Furthermore, for each tank volume and collector area, four olar aborber type were modelled. The firt wa a glazed flat plate collector with an efficiency given by Equation 9: ( t t ) a η = (9) G The econd wa an evacuated tube with an efficiency given by Equation 10: i ( t t ) a η = (10) G i The third wa an evacuated tube olar collector with a CPC back reflector with efficiency given by Equation 11: ( t t ) a η = (11) G i The final collector analyed wa a low cot building-integrated olar collector under development at the UoW. Thi collector i eentially a glazed flat plate collector; however, unlike the collector mentioned above it would be able to act a the façade or roof tructure of dairy proceing plant while having almot no viual impact. Although not in ma production, the collector ha been deigned to have an efficiency given by Equation 12. ( t t ) a η = (12) G i Uing the collector data in the F-Chart allowed the fraction of the heating load provided by the olar collector for each tank volume and collector type to be determined. For the olar cooling ytem, the collector efficiency equation remained unchanged, although it wa aumed that the cooling load would be 1668 MJ, equivalent to cooling a 25 m 3 torage tank from 20 C to 4 C. owever, becaue olar cooling ytem tend to be le efficient than heating ytem, two array, equivalent to a 25 /m 2 and 50 /m 2 torage ytem, were modelled. In both cae it wa aumed that the COP of the cooling ytem wa 0.4, typical of an aborption cooling ytem. 7. RESUTS From the analyi it wa found that the olar fraction provided by the olar heating and cooling ytem wa determined olely by the array area to tank volume ratio. A would be expected, the greatet olar fraction i achieved at a ratio of 50 /m 2 for all tank volume for the heating ytem. For the cooling ytem, the larger collector ytem, equivalent to a 25 /m 2 torage ytem, offered the bet cooling performance. For the olar heating ytem, an intereting finding wa that at low area to volume ratio, evacuated tube with a back reflector performed

8 marginally better than the flat plate collector and the ytem. owever, at increaing ratio the flat plate collector and the UoW building-integrated ytem began to perform better. Additionally, it wa found that the evacuated tube without a back reflector tended to perform approximately 25% le efficiently than both the flat plate and reflector tyle collector. Thi phenomenon i clearly illutrated in Figure 6 8. The reaon for the variation between the four type of collector can be explained by undertanding the propertie of the collector in the tudy. Firtly, the reaon that evacuated tube collector, without reflector, perform poorly relative to the other collector i that their optical efficiency i poor baed on their gro area. Eentially, although the collector may take up a certain area, the large pacing between the tube mean that a large portion of the radiation incident on that area i not aborbed during the period of the day when olar radiation i at it maximum. Thi hortcoming i therefore overcome by the addition of the reflector which allow a larger portion of the radiation to be captured. Solar Fraction Solar Fraction Flat Plate Evacuated Tube Evacuated Tube w Reflector Figure 6: Solar fraction for 50 /m 2. Flat Plate Evacuated Tube Evacuated Tube w Reflector Figure 7: Solar fraction for 75 /m 2. More intereting, however, i the fact that the UoW building-integrated ytem and the flat plate collector perform better at the higher area to volume ratio. Thi can be explained again by the optical efficiency of flat plate and evacuated tube olar collector. In Equation 9, 10 and 11 it can be een that the firt term in the efficiency equation, the optical efficiency, i higher for the building integrated and glazed flat plate than the evacuated tube. owever, the econd term, the heat lo coefficient, i lower in evacuated tube than in the other two ytem. A the area to volume ratio increae, the olar fraction decreae, meaning that heating i occurring at lower temperature. Thi i favourable for flat plate becaue at lower heating temperature their efficiency i higher relative to their heat lo. Converely, evacuated tube perform better at the lower area to volume ratio becaue depite having a lower optical efficiency, they are le enitive to heat lo. Solar Fraction Flat Plate Evacuated Tube Evacuated Tube w Reflector Figure 8: Solar fraction for 100 /m 2. From thi it can be een that both flat plate and evacuated tube with reflector offer the bet performance of the three olar heating ytem. owever, in a typical indutrial etting, higher area to volume ratio would typically be ued. Thi would, on a purely performance bai, tend to favour the ue of flat plate tyle collector a they perform better under thee condition. A with the olar heating ytem, it wa found that the evacuated tube with a back reflector offered a good olar fraction for the two cooling ytem. owever, the ability to ue olar energy for cooling wa le effective than for heating. Thi i becaue it mut be tranferred via an aborption cooling ytem. A wa hown, the olar fraction wa thu reliant on the COP of thi ytem.

9 The influence of the COP of the aborption ytem i clearly illutrated in Figure 9 and 10. In Figure 9 we can ee that the ytem contribute approximately 20% of the cooling load. owever, it can be een that by doubling the collector area that the olar fraction i improved dramatically. 80 C (CRES, It wa decided to model the ability of an array of 2000 m 2 coupled to a tank with a volume of 100 m 3 to provide a load of MJ, or 100 m 3 of 80 C-water per day. Thi water would be uitable for cleaning operation at the end of a day production, a uggeted by Worley Conultant td (1983). Solar Fraction Flat plate Evacuated Tube Evacuated Tube w Reflector In Figure 11 it can be een that during the ummer month, mot of the olar heating ytem are able to meet the heating load. owever, for early pring and autumn, it may be neceary to rely on auxiliary heat from a upplementary boiler Figure 9: Solar fraction for olar cooling ytem equivalent to 50 /m 2. Solar Fraction Flat Plate Evacuated Tube Evacuated Tube w Reflector Figure 10: Solar fraction for olar cooling ytem equivalent to 25 /m 2. From oberving the performance of the olar heating and cooling ytem it i apparent that both flat plate tyle collector and evacuated tube with back reflector offer the potential for ueful heating and cooling. The ue of evacuated tube without back reflector, although feaible, would require larger area for equivalent load. 8. POSSIBE ENERGY SAVINGS IN A ARGE DAIRY PROCESSING PANT To further highlight the advantage of uing a olar heating ytem, it wa decided to examine the magnitude of the energy produced by the four collector array in a large proceing environment. In a typical large dairy factory the hot water conumption i approximately m 3 per day, with cleaning operation occurring at up to Solar eat (MJ) Flat Plate Evacuated Tube Evacuated Tube w Reflector Figure 11: Poible olar heat production for a large dairy proceing plant (2000 m 2 array and 100 m 3 tore). A an alternative to a upplementary heat ource, it may be poible to increae the ize of the olar array. owever, it hould be conidered that for thi example the heating load ha been aumed to be contant over the year. Given the eaonal nature of the dairy indutry, it i likely that thi load would vary with production level and o the array may meet the demand outide the condition ued here. 9. DISCUSSION AND CONCUSIONS Examining meteorological data and hitorical production trend howed that olar energy offered the opportunity to provide a ueful amount of heating or cooling in dairy proceing plant. The reult preented how that flat plate and evacuated tube with back reflector tyle collector offered the bet performance in heating and cooling ytem. A noted, evacuated tube without reflector do not capture enough of the incident radiation falling on their gro area to compete with the alternative technologie.

10 Furthermore, it wa hown that the UoW building-integrated ytem appear to be able to compete well with the etablihed technologie. Given it ability to integrate directly into the building, it i poible that thi may be an attractive future technology for the dairy indutry. Baed on thee finding it i poible that large cale olar energy plant could make ignificant contribution to both heating and cooling load in the New Zealand dairy proceing indutry. 10. AUTORS' AFFIIATIONS T N Anderon i a PhD tudent in the Department of Engineering at the Univerity of Waikato. M Duke i a Senior ecturer in the Department. To contact the author, tna2@waikato.ac.nz 11. REFERENCES Beneman, B R 1986, Production planning in the New Zealand dairy indutry, Journal of the Operational Reearch Society, vol. 37, no. 8, pp Benz, N, Gut, M and Rub, W 1998, Solar proce heat in brewerie and dairie, Proceeding of EuroSun 98, pp , Portoroz, Slovenia. Benz, N, Gut, M and Beikircher, T 1999, Solar proce heat with non-concentrating collector for food indutry, Proceeding of ISES Solar World Congre, Jerualem, Irael. CRES, 2008, Solar Sytem Application in Dairy Indutry, m [cited 22/2/08]. Duffie, J A and Beckman, W A 2006, Solar Engineering of Thermal Procee, Wiley, New York. EECA 2001, Solar Energy Ue and Potential in New Zealand, Energy Efficiency and Conervation Authority, Wellington. EECA 2004, Code of Practice for Manufacture and Intallation of Solar Water eating Sytem in New Zealand, Energy Efficiency and Conervation Authority, Wellington. Joudi, K A and Abdul-Ghafour, Q J 2003, Development of deign chart for olar cooling ytem. Part I: Computer imulation for a olar cooling ytem and development of olar cooling deign chart, Energy Converion and Management, vol. 44, no. 2, pp eal, E A and Silveira, J 2002, Study of fuel cell co-generation ytem applied to a dairy indutry, Journal of Power Source, vol. 106, no. 1-2, pp IC 2006, Dairy Statitic 2005/06, ivetock Improvement Corporation imited, amilton. ovell-smith, J E R and Vicker, V T 1983, NZERDC Report No. 86: Cogeneration of heat and electricity in a pray drying plant, New Zealand Energy Reearch and Development Committee, Auckland. NIWA 2007, Climate Summarie, [cited 20/8/07]. Ozyurt, O, Comakli, O, Yilmaz, M and Karh, S 2004, eat pump ue in milk pateurization: an energy analyi, International Journal of Energy Reearch, vol. 28, no. 9, pp Ramirez, C A, Patel, M, and Blok, K 2006, From fluid milk to milk powder: Energy ue and energy efficiency in the European dairy indutry, Energy, vol. 31, pp Schnitzer,, Brunner, C and Gwehenberger, G 2007, Minimizing greenhoue ga emiion through the application of olar thermal energy in indutrial procee, Journal of Cleaner Production, vol. 15, pp SPF 2007, SPF Info, [cited 20/8/07]. Vicker, V T and Shannon, D V 1977, NZERDC Report No. 25: Energy ue in the dairy indutry, New Zealand Energy Reearch and Development Committee, Auckland. Worley Conultant td 1983, NZERDC Report No. 94 Energy Conervation and Oil Subtitution at a Dairy Company, New Zealand Energy Reearch and Development Committee, Auckland.