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The integration of agricultural production systems into urban areas is a challenge for the coming decades. Because of increasing greenhouse gas emission and rising resource consumption as well as costs in animal husbandry, the dietary habits of people in the 21st century have to focus on herbal foods. Intensive plant cultivation systems in large cities and megacities require a smart coupling of information, material and energy flow with the urban infrastructure in terms of Horticulture 4.0. In recent years, many puzzle pieces have been developed for these closed processes at the Humboldt University. To compile these for an urban plant production, it has to be optimized and networked with urban infrastructure systems. In the field of heat energy production, it was shown that with closed greenhouse technology and patented heat exchange and storage technology energy can be provided for heating and domestic hot water supply in the city. Closed water circuits can be drastically reducing the water requirements of plant production in urban areas. Ion sensitive sensors and new disinfection methods can help keep circulating nutrient solutions in the system for a longer time in urban plant production greenhouses.
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AbstractThe integration of agricultural production systems into
urban areas is a challenge for the coming decades. Because of
increasing greenhouse gas emission and rising resource consumption
as well as costs in animal husbandry, the dietary habits of people in
the 21st century have to focus on herbal foods. Intensive plant
cultivation systems in large cities and megacities require a smart
coupling of information, material and energy flow with the urban
infrastructure in terms of Horticulture 4.0. In recent years, many
puzzle pieces have been developed for these closed processes at the
Humboldt University. To compile these for an urban plant
production, it has to be optimized and networked with urban
infrastructure systems. In the field of heat energy production, it was
shown that with closed greenhouse technology and patented heat
exchange and storage technology energy can be provided for heating
and domestic hot water supply in the city. Closed water circuits can
be drastically reducing the water requirements of plant production in
urban areas. Ion sensitive sensors and new disinfection methods can
help keep circulating nutrient solutions in the system for a longer
time in urban plant production greenhouses.
KeywordsSemi closed, greenhouses, urban farming, solar heat
collector, closed water cycles, aquaponics.
I. INTRODUCTION
HE cities of the world are growing. 54% of the world’s
population lives in urban areas and the most urbanized
regions are Northern America (82%), Latin America (80%)
and Europe (73%) [1]. The use of land by the urban spread
limits the agricultural area. On the other hand, in order to
secure food supply of an increasing urban population,
agricultural production must be move closer to the settlements.
Urban farming is a topic that has now been worked on
worldwide. Prior the millennium urban food production
estimates fifteen percent of the worldwide food production [2].
On one hand, questions about the ecology and economy of
urban food production systems must be answered and on the
other hand, the principles about technical integration of
agricultural production plants into the urban infrastructure
have to be developed.
Intensive vegetable production systems embedded in urban
building structures leads to a consumer-oriented production of
plant-based foodstuffs. Urban citizens can have a better
U. Schmidt, D. Dannehl, I. Schuch, J. Suhl, T. Rocksch are with the
Faculty of Live Sciences, Humboldt-Universität zu Berlin, Berlin, D-14195
Germany (corresponding author, phone: ++49 30 209346410; fax: ++49 30
209346412; e-mail: u.schmidt@agrar.hu-berlin.de).
R. Salazar-Moreno, E. Fitz-Rodrigues, A. Rojano Aquilar, I. Lopez Cruz,
G. Navas Gomez are with the Universidad Autónoma Chapingo,
Departamento de Ingeniería Mecánica Agrícola, Texcoco de Mora, México.
relationship with the food production process and are able to
learn more about process quality in the immediate vicinity of
the market.
Plant cultivation in the city can only be established if a high
areal production yield is generated and production systems are
operating with high energy efficiency. The energy and
material input as well as residual material remain should be
minimized. Therefore, closed production systems, well known
from intensive greenhouse horticulture, should be adapted to
an urban application. The closed greenhouse concept provides
a technology in which solar thermal energy can be produced
with the help of technical cooled greenhouses [3], [4]. For
more than 20 years, these systems have been technically
developed and scientifically investigated. In these
greenhouses, plants can be cultivated in hydroponic systems
under low energy consumption [5]. Thus, vegetables can be
produced with recyclable substrates (rockwool) or without
substrates (aeroponics). With these closed production systems,
agricultural production systems can also be combined to
generate synergies through intensive use of the area, as well as
energy and material exchange. An example of this is the
combination of aquaculture and hydroponics (aquaponics) [6].
The essential prerequisite is a precise management of liquid
fertilization and safe disinfection methods for the prevention
of plant diseases in long time circulating nutrient solutions
II. MATERIALS AND METHODS
Three innovative key technologies were developed to bring
greenhouses into combined urban and closed production
systems: A: A new cooling concept for a semi closed collector
greenhouses (SCCG) to maximize energy harvest and water re
condensation, B: new concept of heat storage in low-
temperature water tanks and C: new sensors for analyzing the
nutrient content of circulating nutrient solutions.
A. New Cooling Concept for SCCG
At the Humboldt University in Berlin, from 2010 to 2014,
experiments with a SCCG-system took place with tomato
production in hydroponics. Two experimental greenhouses,
307 each, were used for measuring the energy and water
consumption. One greenhouse was constructed as a SCCG, the
second greenhouse was operated as a reference greenhouse
with conventional technical equipment. With the SCCG a heat
pump integration and cooling concept to produce vegetables
and thermal solar heat has been developed. At the same time
the water consumption of the plant production can be lowered
by high water vapor condensation from the cooling system and
Closed Greenhouse Production Systems for Smart
Plant Production in Urban Areas
U. Schmidt, D. Dannehl, I. Schuch, J. Suhl, T. Rocksch, R. Salazar-Moreno, E. Fitz-Rodrigues, A. Rojano Aquilar, I.
Lopez Cruz, G. Navas Gomez, R. A. Abraham, L. C. Irineo, N. G. Gilberto
T
World Academy of Science, Engineering and Technology
International Journal of Agricultural and Biosystems Engineering
Vol:12, No:12, 2018
472International Scholarly and Scientific Research & Innovation 12(12) 2018 ISNI:0000000091950263
Open Science Index, Agricultural and Biosystems Engineering Vol:12, No:12, 2018 waset.org/Publication/10009868
reuse of this water for irrigation purpose (Fig. 1).
New finned tube heat exchangers are located under the roof
of the greenhouse to collect sensible and latent heat from the
greenhouse air (Fig. 2). Cooling is performed without fans
because the air movement is driven by density differences.
Caused by re-condensation of the plant transpiration water
vapor, the canopy itself is working as heat exchange surface
and thus integrated into the cooling concept.
Fig. 1 Technical Setup of the semi closed collector greenhouse
Fig. 2 New cooling technology for closed greenhouses using movable finned pipes (patented)
B. Concept of Heat Storage in Low-Temperature Water
Tanks
A concept was developed with above-ground water
reservoirs bivalent used for storage of rain water for irrigation
purpose and storage of solar energy. A conventional rain water
tank (1 water per greenhouse ground area) with
minimum isolation (500 mm expandable polystyrene on the
surface) was operated in a temperature range from 5 °C to 45
°C to save the heat from the SCCG. Higher tank temperatures
should be avoided in order to reduce the thermal losses and
still make the water applicable for irrigation purposes.
C. Key Sensors, Automation and Disinfection Methods for
Long Time Circulating Nutrient Solution in SCCG
Ion sensitive sensors have been developed for measuring
the concentration of single ion groups like nitrate, ammonium,
calcium, potassium and chloride. Because of compensation of
the inevitably drift of these kind of membrane sensors, a
calibration robot was developed. One time per day, the sensor
parameters have been corrected by the help of defined
calibration probes.
Software, hardware and precise pump technology are
available to control the ion concentration in the circulating
solution. With the micro injection of electrolytically produced
potassium hyper chloride in the circulating solution, the
activity of plant pathogens could be reduced (not shown).
III. RESULTS
A. Water Savings and Solar Heat Extraction from Closed
Greenhouses - Results from the Cooling Concept for SCCG
With the help of the SCCG-system consisting of the roof
cooling system, the heat pump integration and the low-
temperature storage, an energy yield of 1.76 GJ/m²a collector
World Academy of Science, Engineering and Technology
International Journal of Agricultural and Biosystems Engineering
Vol:12, No:12, 2018
473International Scholarly and Scientific Research & Innovation 12(12) 2018 ISNI:0000000091950263
Open Science Index, Agricultural and Biosystems Engineering Vol:12, No:12, 2018 waset.org/Publication/10009868
area could be measured in the closed greenhouse (Table I);
that is half of the global radiation impinge on the greenhouse
ground area.
While 0.53 GJ/m²a is used to heat the greenhouse, 1.39 GJ/
m²a can be used for other thermal processes in the city
(heating, hot water, drying)
TABLE I
HEAT ENERGY BALANCE FOR THE SEMI CLOSED COLLECTOR GREENHOUSE IN
GJ/M² YEAR
Quantity Value
Annual global radiation on the greenhouse surface 3.65
Overall stored heat energy 1.76
Electricity for heat pump cooling 0.32
Electricity for all electrical consumers for cooling 0.21
Electricity for heat pump heating 0.07
Electricity for all electrical consumers for heating 0.1
Electricity for the heat pump process 0.39
Thermal energy for greenhouse heating 0.53
Thermal energy for other thermal consumers 1.18
Fig. 3 Sensible and latent heat extraction from the semi closed
collector greenhouse
Fig. 4 Water use efficiency in different years with different tomato
varieties
With a maximum electrical power of 133 W/m² for the heat
pump, a maximum cooling capacity of 678 W/m² can be
achieved with a working number for the cooling of 5.1,
considering all electrical loads (COP = 3.6), the annual
cooling output was 478 W/m². This means that roughly half of
the global radiation input into the greenhouse can be
withdrawn.
Due to operating the finned pipe cooling system below the
dew point of the greenhouse air, a high amount of
condensation water was collected. The part of the latent
cooling by the canopy was about one third of the overall
cooling performance (Fig. 3).
The water quality was high enough to reuse the condensate
for the plant irrigation. Therefore, the water use efficiency was
27 to 82% higher compared to a conventional greenhouse
tomato production (Fig. 4).
B. Thermal Heat Storage: Results from the Concept of Heat
Storage in Low-Temperature Water Tanks
With the help of a water reservoir with a volume of 1 m³ of
water per of SCCG base area, a heat quantity of 0.36 GJ
can be stored at a temperature difference of 40 K. This means
that the store is suitable to heat the greenhouse at temperatures
outside of 5 °C for about two weeks without solar radiation.
With the help of the storage, the collector greenhouse could be
heated with solar energy from early March to late November
(Fig. 5). From April to September more heat can be delivered
than required for the greenhouse.
C. Analyzing Sensors for the Closed Recirculation Nutrient
Supply Systems for Hydroponic Plant Production
With a sensor stability of about 6 months for membrane
sensors, the daily slope of the ion concentration in the drain as
an essential prerequisite for a time oriented nutrient supply
strategy is now available. The first results had shown an
increase in the calcium and potassium concentration while
nitrogen concentration is decreasing (Fig. 6). Thus the
micropumps have to inject different amounts of nutrient
solution to work with a continuous ion concentration in the
tank. With the help of a sophisticated software algorithm, the
adapted amount of conventional nutrient solutions can be
calculated. From the point of nutrient balance with these
components a long-time circulation of the solution is now
possible.
IV. DISCUSSION AND CONCLUSION
The results from the closed plant production system
components had shown the ongoing progress in the key
components of this technology. An essential prerequisite for
system sustainability and a synergetic neighborhood of urban
living systems and plant production is the autonomy of the
plant production system. An additional added value may be
generated by thermal heat production in the SCCG and
absorption of gaseous urban CO2-waste from other technical
processes like heat production. With the ability and
technology of thermal storage in aboveground, low
temperature storage systems different possibilities for using
reservoirs in the cities are available [7]. Excess heat from the
SCCG can be used for service water heating or spa application
in the cities.
World Academy of Science, Engineering and Technology
International Journal of Agricultural and Biosystems Engineering
Vol:12, No:12, 2018
474International Scholarly and Scientific Research & Innovation 12(12) 2018 ISNI:0000000091950263
Open Science Index, Agricultural and Biosystems Engineering Vol:12, No:12, 2018 waset.org/Publication/10009868
Fig. 5 Heat balance and temperature of the 300 m³ heat storage tank
Fig. 6 Automatic 7 day measurement of temperature and ion concentration in the recirculating nutrient solution of the SCCG
The ion selective sensor technology is a key technology for
analyzing and managing closed nutrient circles. Against ion-
sensitive field-effect transistors (ISFET) [8] the developed
membrane sensors are working stable for a period of about 12
months. It is also the basic for coupling production processes
like vegetable and fish production (Aquaponics) or the
recycling of grew waste water from urban systems. The
question of the right location of plant production in the cities
(roofs, facades) is less interesting than the question of the best
interaction of plant production in an urban infrastructure. So
far from the point of view of non-expensive light conditions,
the production in high natural light transmitting greenhouses is
the more economical way.
For the docking of the closed plant production systems on
urban infrastructure more information about energy
consumption and mass flows of city supply and disposal
systems is required. Beside production purposes, plant
production systems should be considered as education and
social meeting center. Sustainability of plant production and
production technology hereby play just as important role as
production efficiency and costs.
ACKNOWLEDGMENT
The results from research on closed greenhouse production
Systems and ion sensitive sensors originate from different
research projects, supported by the German ministry of
agriculture and foods, ministry for environment, ministry of
Economics and Technology supported by different project
management organisations (BLE, AiF) and the German
Landwirtschaftliche Rentenbank.
REFERENCES
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475International Scholarly and Scientific Research & Innovation 12(12) 2018 ISNI:0000000091950263
Open Science Index, Agricultural and Biosystems Engineering Vol:12, No:12, 2018 waset.org/Publication/10009868
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[2] J. Smit, J. Nasr, A. Ratta, Urban Agriculture Food, Jobs and Sustainable
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2009 to 2014, the joint research program ZINEG is carried out in Germany. Its main aim is to reduce the consumption of fossil fuels and hence the CO2 emissions up to 90% for production in greenhouses. At Humboldt University the research is focused on using a greenhouse system as solar thermal collector with above-ground heat storage. During the tomato production in 2011, a seasonal energy efficiency ratio (SEER) of 5.1 and a heating seasonal performance factor (HSPF) of 4.4 was achieved using an electrically-driven heat pump utilized for cooling and heating in the collector greenhouse. Approximately half of the solar irradiation was stored into an insulated rainwater-tank. This corresponds to 1.76 GJ/m2. Twenty percent of this solar energy was collected by condensation (originally latent heat) on finned pipes in the roof zone. For heating the collector greenhouse, about 0.53 GJ/m2 of the stored heat was re-used. That means that additional heat might be exported or the cooling surface area can be reduced to one-third. Furthermore, the solar thermal collector greenhouse achieved a primary energy consumption of 147.6 MJ/m2 (considering a full re-use of the stored heat). Simultaneously, the conventional greenhouse achieved a primary energy consumption of 767.1 MJ/m2. That means that the consumption of non-renewable energies (fossil fuels) is reduced up to 81% with the collector system. In further studies an economic assessment regarding energy-saving in semi-closed greenhouses should be performed to estimate the potential of such facilities. http://www.actahort.org/books/1037/1037_20.htm
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World Urbanization Prospects: The 2014 Revision
United Nations, Department of Economic and Social Affairs, Population Division (2014). World Urbanization Prospects: The 2014 Revision, World Academy of Science, Engineering and Technology International Journal of Agricultural and Biosystems Engineering Vol:12, No:12, 2018 475 International Scholarly and Scientific Research & Innovation 12(12) 2018 ISNI:0000000091950263
Urban Agriculture Food, Jobs and Sustainable Cities. 2001 edition, published with permission from the United Nations Development Programme
  • J Smit
  • J Nasr
  • A Ratta
J. Smit, J. Nasr, A. Ratta, Urban Agriculture Food, Jobs and Sustainable Cities. 2001 edition, published with permission from the United Nations Development Programme