Heating or transporting? Energy use in greenhouse s aquaponics in continental cliate and the energy deand of transportation fro Mediterranean regions Márta Soogyvári 1 József Vada 2 Tibor Kiss 3 Viktor Kiss 4 Abstract: Greenhouse production in Mediterranean regions is a very profitable business. Nowadays European superarkets are full of agricultural products fro this area. The newest trend is cobining aquaculture and hydroponics: fish and vegetable production in one syste. It is also possible to produce these products in greenhouses in Continental cliate, but it needs uch ore energy. However, a question has arisen: which production type needs ore energy: produce products in Mediterranean regions and transport it to the heart of Europe, or produce it in Europe? This paper copares these two possible ways, building up a syste dynaic odel for an aquaponics greenhouse production in a Continental cliate. Keywords: location decision, aquaponics cliate siulation, energy deand of transport, heating deand, This work was carried out as part of the SROP-4.2.1. B-10/2/KONV-2010-0002 proect in the fraework of the New Hungarian Developent Plan. The realization of this proect is supported by the European Union, co-financed by the European Social Fund. 1 Corresponding Author: Márta Soogyvári, University of Pécs, Faculty of Business and Econoics, Departent of Business and Manageent Studies, Rákóczi Str. 80. H-7633 Pécs, Hungary, soogyv@ktk.pte.hu 2University of Pécs, Pollack Mihály Faculty of Engineering and Inforation Technology 3 University of Pécs, Faculty of Business and Econoics, Departent of Business and Manageent Studies 4 University of Pécs, Faculty of Business and Econoics, Departent of Econoics and Regional Studies 1
1. Introduction The production of agricultural products tends to break away fro the liitations through cliate, soil and sunlight. Huge glasshouses cover the rural regions of Spain; the plants grow in hydroponics without any soil or natural fertilizer, illuinated with artificial light. This trend reached the fish breeding branch, the aquaculture left the natural ponds and the ocean and oved into tanks. Aquaponics arises fro cobining the two systes. The waste water fro the fish tanks will be led into a hydroponic syste, where the bacteria in the biofil of the growing edia transfors the byproducts of the aquaculture into inerals, which will be used by the plants. The clean water will be recirculated into the fish tanks. Aquaponics is held to be the food-production of the future as a source of self-sufficiency. The sustainability of aquaponics syste needs a lot of research. One very iportant aspect is the energy-deand of such systes which is dependent priarily on the cliate of the particular location. 2. Proble definition: The aquaponics syste was developed in a tropical cliate, where all year round, intensive, low energy use production was possible due to environental conditions. Such systes are also operated in a colder cliate (with greenhouse technologies), but it is necessary to ensure the suitable inner cliate and light conditions, which we need energy for. Energy can be provided either with active or passive ethods. This paper investigates the energy use of such an aquaponics syste copared with the traditional syste, where vegetables and fish are transported to areas with a continental cliate (in our case Pécs) fro Mediterranean or subtropical areas, where heating is not required, but the greenhouse or screenhouse technology is used in order to protect the cultivated plants and fish fro weather s influences, pests, etc. If the energy needed to support the inner cliate of a greenhouse and the production syste is larger than the energy use for the transport of the sae product assuing that the energy use for running the syste without heating and the volue of production is the sae for both sites - than we can conclude that fro an energetic point of view it is not worth to install an aquaponics syste in the researched area. 2
3. The greenhouse odel with aquaponics The goal of a odel is a siulation of a greenhouse cliate in order to estiate the heat which is necessary to aintain an optial cliate in the greenhouse. The siulation of this hypothetical syste is based on functioning aquaponics and hydroponics systes (Rakoczy et al., 2006). The results of the siulation will be used to size experiental aquaponics greenhouses in Hungary. Table 1 The properties and diensions of the aquaponics greenhouse Length () 20 Width () 10 Gutter high() 4 Ridge high () 6.3 Area floor ( 2 ) 200 Area glazing ( 2 ) 321 Volue greenhouse ( 3 ) 1545 Volue air (3) 1030 Area plant beds (area gravel) ( 2 ) 150 Volue gravel ( 3 ) 40 Density gravel 250 Total surface area gravel ( 2 ) 13500 Specific surface gravel 2 / 3 300 Mass gravel (kg) 810 000 Volue fish tank( 3 ) 33 Deepness fish tank () 1.2 Area water ( 2 ) 27.5 Infiltration loss (l/h) 2 2.3 4.0 1.2 5.24 10.0 The production of the syste is estiated according to the data of Rakoczy (Rakoczy et al., 2006). In the first siulation we grow the fish tilapia and lettuce; this is a coon configuration in coercial systes. Tilapia is a war water fish, but it is cultivated in the USA in teperate cliate too, because it can tolerate crowding and the fish tank environent. If we succeed in ensuring the optial cliate in the greenhouse, we can harvest 92 kg tilapia and 600 lettuces (0.3-0-4 kg a piece) per week. The requireents for the teperature of the greenhouse plant beds are given not by the lettuce, but by the biofil. The bacteria in the biofil need a teperature of 25-30 0 C. The biofil perfors optially in filtering the waste of fish and ineralizing the toxic aoniu into nitrites and nitrates if the teperature is within this range. The lethal teperature of the biofil is 0 0 C, but the activity of the biofil is halved at 18 0 C what can lead to the collapse of the sall ecosyste. The optial water teperature growing tilapia is 28-30 0C, the lethal teperature is 16 0 C. The lettuce is the ost resilient, there are several sorts which can tolerate the teperature range between 6-25 o C, the iniu of the gravel bed for the is 6 o C. The source of the cliate data is the weather station of the 3
University of Pécs (http://oido.ttk.pte.hu/). Pécs is located in Central-Europe, latitude 46., it is in the 6. USDA cliate zone, the cliate is continental, with a little Mediterranean influence. External teperature and global radiation data were collected in Pécs, Hungary on a inute basis, and authors generated hourly data fro both. Figure 2. deonstrates the global radiation for 29. February 2012. in Pécs fro 0 to 23 hours. Figure 1 Global radiation (in W/ 3 ) on a winter day in Pécs, where the vertical axe is the tie variable fro 0 to 23. Source: Own elaboration. 3. Heat transport in an aquaponics greenhouse The heat transport fluxes in an aquaponics greenhouse are suarized on Figure 2. Figure 2. Energy and water vapor fluxes in a coon aquaponics greenhouse (without heating and ventilation) Air out Glazing Air in Plants Infiltration Global radiation out Condensation Evaporation Theral radiation Global radiation out Theral radiation Infiltration Conduction Evaporation Condensation Global radiation out Global radiation in Infiltration Condensation Evaporation Global radiation out Theral radiation Gravel Plant beds filled with gravel Theral radiation Plant beds filled with gravel Vater Conduction Fish tanks Concrete Soil Conduction Conduction Source: Fitz-Rodrígueza et al 2010; Zhou et al 1998 4
The goal of our current siulation differs fro the siulations described in various papers. We do not explore the efficiency of control echanis and heating-cooling systes in order to ensure the continuous production. We need only the global heating deand in order to copare the aquaponics production with the energy deand of transport. In teperate cliate the ain energy use is for heating. The greenhouse effect of a greenhouse, the overheating in suer which is a ain proble in war cliate can be usually solved in Pécs by proper echanical ventilation. We assue that the chosen lettuce sort does not deand artificial lightning. In order to decrease the heating deand we have redesigned and siplified the aquaponics syste: the fish tank is in the soil, the foundation and the fish tank is well insulated, the whole area is covered with gravel beds. We do not consider the heat loss towards the soil, the insulation akes it negligible. The heat loss due to evaporation will be considered in the energy balance of the gravel bed and the water in the fish tanks. The evaporated water condenses on the glazing of the greenhouse, ost of the heat will be lost due to the glazing, so we do not consider the condense heat in the energy balance of the greenhouse. Figure 3 The heat fluxes in the aquaponics greenhouse of the siulation Air out Global radiation out Conduction Glazing Infiltration Condensation Infiltration Condensation Air in Global radiation in Global radiation in syste boundary Evaporation Gravel Evaporation Vater Plant beds filled with gravel Insulation Fish tanks Soil If we consider the aquaponics glasshouse as a closed container (Roy et al., 2002), and do not consider the theral stratification of the heat storage asses, we can describe the theral interactions in an aquaponics greenhouse with a following energy balance equation. 5
l c 1 k k 1 t n t k 1 k 1 k 1 k 1 V gi A AU t i te AirVAirncAir t i te / 3600 (1) 1 1 The energy balance equation expresses the equilibriu of the heat flux (W) flowing in the tie into the various th heat storage asses with the equilibriu of the global radiation gain, the heat loss due to transission and infiltration (W). Table 2 Abbreviations c the specific heat of the th heat storage ass ( gravel or water), J/kgK density of the th heat storage ass heat storage ass ( gravel or water) kg/ 3 t k teperature of the th heat storage ass in tie step K t k-1 teperature of the th heat storage ass in tie step K-1 duration of the tie step, second V volue of the of the th heat storage ass, 3 g the coefficient of the pereability of the total solar radiation energy of the glass I A U ti k-1 te k-1 intensity of the radiation reaching the th glazing, W/ 2, (differentiation according to the orientation) area of the th glazing, 2, (differentiation according to the orientation) overall heat transfer coefficient of the th glazing), W/ 2 K, (differentiation according to the orientation) internal teperature in the tie step k-1, K external teperature in the tie step k-1, K Air density of air, kg/ 3 VAir volue of air 3 n infiltration rate, 1/h cair rwater xs X rwater specific heat of air J/kgK the evaporation coefficient of water kg/ 2 h latent heat vaporization of water evaporation absolute huidity at saturation at water surface absolute huidity of air kg water vapor/kg air evaporation heat of water The energy balance equations of the water in the fish-tank and the gravel bed as of asses with heat storage capacity and evaporation. t c k t k 1 V a gi level A level A k 1 1000 t t Air A x s x r Water 3600 (2) Where the index is the current ediu, the level index is the radiation intensity of the horizontal surface and the convection heat transfer coefficient. 6
4. The dynaic odel of the continental aquaponics syste AnyLogic 6.7.1 was used for the odel siulation. A syste dynaic odel has been created for the siulation of the greenhouse (aquaponics) syste. The odel consists of three ain odules: the gravel, water and air siulation. The teperature is the stock variable in each subodel. Flow variables change with the used ediu for heat change, which is influenced by the direct or indirect gain fro the global radiation and by the loss due to convection, evaporation, transission and infiltration. The gravel subodel is the following: Figure 4 The gravel subodel The heat change of the gravel is increased by the internal radiation gain. The heat will be decreased by the transission loss and by the evaporation loss, since the gravel is always wet due to the circulation of water. The gravel heating switches on when the gravel teperature goes below 25 Celsius in order to aintain optial cliate for the bacteria in the biofil. The teperature will be calculated fro the heat change. 7
The water syste odel is the following: Figure 5 The water subodel The structure of the water subodel is the sae as the structure of the gravel subodel. The water heating syste switches on if the water teperature goes below 25 Celsius. The accuulated heating quantity is collected in the accuwaterheat stock variable. The air subodel is the following: Figure 6 The air subodel 8
The heat gain of the air is equal to the transission and evaporation losses of the water and gravel. The heat of the air will be decreased by infiltration and convection. If the internal teperature of the air goes below 7 Celsius the air heating syste switches on. Total heating quantity is collected in accuairheat stock variable. 5. Results The total energy used 122,114 Megaoules for one year with a cold winter. The subodel s energy uses are the following: Gravel heating 109,290 Megaoule Water heating 12,823 Megaoule Air heating 0 Megaoule (did not switch on at all.) These are the first siulation runs. At this stage the gravel bed is not covered by plants (fro a siulation point of view.) At a later stages other vegetable fish cobinations will also be siulated. 6. Coparison of the energy needs In this section the energy need of the availability of the products in the case of local and reote (Mediterranean) production will be copared. It is vital for the coparison of the energy need for the two different ethods (greenhouse aquaponics in Mediterranean and Continental cliate) to know the transportation cost of Mediterranean goods to the heart of Europe do decide whether it is worth to plant an aquaponics syste in a given area. First, the transportation of one kilogra of goods (fruits, vegetables, fish, etc.) will be deterined. According to Speilann and Scholz (2004) the energy consuption (MJ/tk) of a vehicle involved in transportation varies between 1.54 and 3.08 MJ/tk. 9
Source: Spielann, Scholz (2004) p.x. We will use for the coparison with the energy use of an aquaponics greenhouse in Pécs the iniu energy consuption of road transport, which is 1.54 MJ/tk for 40t CH lorries. The distance between Aleria, Spain and Pécs, Hungary is roughly 3000 k (assuing that the lorries use the freeways). If the lorries are fully loaded (40t), the energy use for the 40ton lorry that transports goods fro Aleria to Pécs is roughly 184,800 MJ. For one ton of goods, that coes to 4620 MJ. There is an assuption, based on (Heidelberg, 2011) that a 40 ton lorry does not always carry 40 tons of coodity. This paper indicates that there is an average of 50% utilization (Heidelberg, 2011, p.21). To ake sure that our paper s results are not over exaggerated, we will use a 60% utilization rate. Therefore, the 184,800 MJ has to be spread to not 40 tons, but 40 tons 0.6 = 24 tons. The energy consuption (even with very conservative calculations) for one ton of good transported fro Aleria to Pécs is roughly 7700 MJ/t. Second, the Continental greenhouse energy consuption should be calculated. For the greenhouse exaple the yearly production of vegetable is the following: 10
For one week the salad is 600*0.35=210 kg. For a year: 210*52=10,920 kg. For one week the fish is 92 kg. For a year: 92*52=4784 kg. We do not differentiate the two types of produce, therefore we suarize the quantities: 10,920 kg + 4784 kg = 15,704 kg a year. 122,114 Megaoules are needed for one greenhouse per year. Since one greenhouse accounts for 15.704 tons of goods yearly, we can deterine that 7775.98 Megaoules are needed for the production of 1 ton of goods in a local greenhouse. This is practically the sae aount (less than 1% difference copared to 7700MJ/t) of energy that is needed for only the transportation of goods fro Spain. 7. Suary This paper analyses two different business odels for agricultural supply of a region. The first is a Mediterranean greenhouse production with transportation; the second is a Continental greenhouse production with heating energy usage. The place of the Continental production is Pécs, Hungary. International references were used for calculating the transportation cost in the first case, and a syste dynaic odel was created to siulate the total heating cost of the Continental greenhouse production. Our results support that fro an energy point of view practically there is no difference between the two cases. Additionally, it should be ephasized again, that this exaination does not consider externalities, energy and food independence, and other iportant factors. 9. References Fitz-Rodrígueza E., Kubotab Ch.,, Giacoelli G.A., Milton E. Tignorc S., Wilsond B., McMahone M. (2010) : Dynaic odeling and siulation of greenhouse environents under several scenarios: A web-based application. In: Coputers and Electronics in Agriculture 70 (2010) 105 116 11
Hedielberg, Ifeu (2011) Ecological Transport Inforation Tool for Worldwide Transports, Öko-Institut, IVE / RMCON. Rakoczy, J.E, Masser M.P, Losordo T.M. (2006) : Recirculating Aquaculture Tank Production Systes: Aquaponics Integrating Fish and Plant Culture. http://www.ca.uky.edu/wkrec/454fs.pdf Roy J. C., Boulard T., Kittas C. Wang S.(2002): Convective and Ventilation Transfers in Greenhouses, Part 1: the Greenhouse considered as a Perfectly Stirred Tank. In.: Biosystes Engineering (2002) 83 (1), 1 20 Spielann M., Scholz R.W.: Life Cycle Inventories of Transport Services, Background Data for Freight Transport, Swiss Federal Institute of Technology Zurich, Natural and Social Science Interface, ETH Zentru HAD, CH-8092 Zurich, Switzerland Zhu S., Deltour J. Wang S.(1998): Modeling the theral characteristics of greenhouse pond systes. Aquacultural Engineering 18 (1998) 201 217 12