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Plant Production in Solar Collector Greenhouses - Influence on Yield, Energy Use Efficiency and Reduction in CO2 Emissions

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A semi-closed solar collector greenhouse was tested to evaluate the yield and the energy saving potential compared with a commercial greenhouse. As such, new algorithm for ventilation, carbon dioxide (CO2) enrichment, as well as for cooling and heating purposes initiated by a heat pump, cooling fins under the roof and a low temperature storage tank were developed. This cooling system showed that the collector greenhouse can be kept longer in the closed operation mode than a commercial one resulting in high levels of CO2 oncentrations, relative humidity and temperatures. Based on these conditions, the potosynthesis and associated CO2 fixations within the plant population were promoted during the experiment, resulting in a yield increase by 32%. These results were realized, although the mean light interception by energy screens and finned tube heat exchangers was increased by 11% compared to the reference greenhouse. The energy use efficiency was improved by 103% when the collector greenhouse was considered as energy production facility. In this context, the energy saving per kilogram produced tomatoes in the collector greenhouse is equivalent to the combustion of high amounts of different fossil fuels, where the reduced CO2 emissions ranged between 2.32 kg and 4.18 kg CO2 per kg produced tomatoes. The generated total heat was composed of approximately one-third of the latent heat and over two-thirds of the sensible heat, where a maximum collector efficiency factor of 0.7 was achieved.
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Journal of Agricultural Science; Vol. 5, No. 10; 2013
ISSN 1916-9752 E-ISSN 1916-9760
Published by Canadian Center of Science and Education
34
Plant Production in Solar Collector Greenhouses - Influence on Yield,
Energy Use Efficiency and Reduction in CO2 Emissions
Dennis Dannehl1, Ingo Schuch1 & Uwe Schmidt1
1 Humboldt-Universität zu Berlin, Faculty of Agriculture and Horticulture, Department for Crop and Animal
Sciences, Division Biosystems Engineering, Albrecht-Thaer-Weg 3, Berlin 14195, Germany
Correspondence: Dennis Dannehl, Humboldt-Universität zu Berlin, Faculty of Agriculture and Horticulture,
Department for Crop and Animal Sciences, Division Biosystems Engineering, Albrecht-Thaer-Weg 3, Berlin
14195, Germany. Tel: 49-30-209-346-414. E-mail: Dennis.Dannehl@agrar.hu-berlin.de
Received: July 16, 2013 Accepted: August 22, 2013 Online Published: September 15, 2013
doi:10.5539/jas.v5n10p34 URL: http://dx.doi.org/10.5539/jas.v5n10p34
Abstract
A semi-closed solar collector greenhouse was tested to evaluate the yield and the energy saving potential
compared with a commercial greenhouse. As such, new algorithm for ventilation, carbon dioxide (CO2)
enrichment, as well as for cooling and heating purposes initiated by a heat pump, cooling fins under the roof and
a low temperature storage tank were developed. This cooling system showed that the collector greenhouse can be
kept longer in the closed operation mode than a commercial one resulting in high levels of CO2 concentrations,
relative humidity and temperatures. Based on these conditions, the photosynthesis and associated CO2 fixations
within the plant population were promoted during the experiment, resulting in a yield increase by 32%. These
results were realized, although the mean light interception by energy screens and finned tube heat exchangers
was increased by 11% compared to the reference greenhouse. The energy use efficiency was improved by 103%
when the collector greenhouse was considered as energy production facility. In this context, the energy saving
per kilogram produced tomatoes in the collector greenhouse is equivalent to the combustion of high amounts of
different fossil fuels, where the reduced CO2 emissions ranged between 2.32 kg and 4.18 kg CO2 per kg
produced tomatoes. The generated total heat was composed of approximately one-third of the latent heat and
over two-thirds of the sensible heat, where a maximum collector efficiency factor of 0.7 was achieved.
Keywords: energy use efficiency, CO2 emission, tomato, fossil fuel, solar energy, climate change, energy saving
1. Introduction
Originally, producers transferred field grown tomatoes to greenhouses in order to improve yield, to reduce
phytosanitary problems and to extend the harvest season. However, this substantial progress is overshadowed by
the increase in fossil fuel prices, where the demand for energy used in greenhouses is significant high (Ozkan,
Fert, & Karadeniz, 2007; Rout et al., 2008). The energy consumption in Dutch greenhouses, for instance,
accounts for 79% of the energy used in the agricultural sector and 7% of the total energy use in the Netherlands
(Lansink & Bezlepkin, 2003). These dimensions show that the growth of greenhouse horticulture production
contributes to a large proportion of carbon dioxide (CO2) emissions, which are jointly responsible for the
predicted mean global temperature increase (WBGU, 2008). Based on these facts, scientists invested much effort
into the development of approaches for using renewable energies, in order to reduce the consumption of fossil
fuels for greenhouse heating. Esen and Yuksel (2013), for instance, found that various renewable energy sources
such as biogas, ground and solar energy can be efficiently used to heat a greenhouse during winter conditions in
eastern Turkey. They demonstrated that a combination of flat-plate water cooled solar collectors, a biogas
production plant and a ground source heat pump with horizontal slinky-type ground heat exchanger can be used
as a stand-alone greenhouse heating system. Near-surface and deep geothermal-energy are also important
alternative sources of energy for greenhouse heating, where the utilization of deep geothermal energy is not so
prevalent in Germany (Lund, Freeston, & Boyd, 2005; Sanner, Karytsas, Mendrinos, & Rybach, 2003). Another
source of energy is the solar energy, which can be collected in heated closed-greenhouses using cold water from
soil layers (De Gelder, Dieleman, Bot, & Marcelis, 2012). After absorbing the excess heat in the greenhouse, the
heat energy is stored in the aquifer, which can be reused in winter by means of a heat-pump (Bot, 2001). In this
context, the solar radiation sum impinging on the earth´s surface in Berlin (52°28´02´´N, 13°17´56´´E) was
www.ccsenet.org/jas Journal of Agricultural Science Vol. 5, No. 10; 2013
35
3992.4 MJ m-2 measured in 2011. This heat quantity per square meter is approximately equivalent to that
produced by the combustion of 99.8 m³ methane, 159.8 kg coal, 99.8 kg vegetable oils, 199.6 kg wood pellets or
87.9 kg heating oil (Demirbas, 2004; Fassinou, Sako, Fofana, Koua, & Toure, 2010; iwo, 2012; Telmo &
Lousada, 2011; Ulbig & Hoburg, 2002). Assuming that the light transmission of a conventional glass-covered
greenhouse is 85% (Dannehl, 2010), it can act as a solar collector, whereby large amounts of energy can be
collected and stored in summer, which would be available for heating during cooler periods. Therefore, the
objectives of this study were to improve the CO2 fixation within the crop, the total yield, the energy use
efficiency (EUE) and an associated reduction in CO2 emissions using a semi-closed greenhouse, which was
controlled by new algorithm for cooling and heating purposes initiated by a heat pump, as well as for ventilation
and CO2-enrichment.
2. Materials and Method
2.1 Experimental Set-Up and Calculation of the Energy Distribution, as well as Climate Parameters
During an annual production in 2011, energy cycles and their effects on tomato plants in a conventional
controlled four-span Venlo-type greenhouse (reference GH) (ground area = 307 m2, floor level heating < 17 °C,
ventilation opening > 24 °C, closed energy screen < 3 W m-2) were compared with those prevailing in a
semi-closed glasshouse with new algorithm for cooling, heating, ventilation and CO2-enrichment. Both
greenhouses were arranged on a north-south axis. The semi-closed greenhouse with a ground area of 307 m²
acted as solar collector, where 16 finned tube heat exchangers (4 per roof bar) were installed under the roof
region (Figure 1). These were used for cooling processes, whereby sensible heat caused by transmitted solar
energy and latent heat produced by plant transpiration were collected simultaneously. The total length of one
finned tube was 21.4 m, which was separated into 125 galvanised fins per meter of tube. The outer diameter of
the core tube was 48.3 mm and that of the fin was 100 mm. The thickness of one fin was 0.8 mm. These
dimensions lead to a total cooling surface of 684 m² resulting in a ratio of 2.23 in consideration of the total
cooling surface and the ground area of the greenhouse. As coolant solution it was used water containing 31%
glycol (v/v), which was pumped into the finned tubes with a minimum flow temperature of 7 °C. For this cooling
process and for heating processes, a system consisting of a reversible heat pump with 40 kW electrical power,
120 kW heating power and 100 kW cooling power, as well as one warm water tank (1 m3) and one cold water
tank (1 m3) was connected to this pipe system. In this context, a maximum cooling capacity of 390 W m-2 can be
achieved. While the ventilation was opened in the reference GH to lower the inside temperature, the cooling
process in the solar collector greenhouse (collector GH) was started at a temperature of 22 °C followed by the
ventilating at 29 °C to avoid plant damage. During cooling processes, large amounts of energy were collected
simultaneously. The generated heat was determined using magnetic inductive heat meters with a measuring
inaccuracy of 0.02 K and stored in a rain-water tank (300 m³), which is commonly used in practice for rain water
storage. The tank was additionally equipped with polystyrene insulation panels to suppress heat losses. This type
of energy harvesting was associated with the dehumidification of greenhouses, which was realized by the
removal of water vapour by means of condensation on the cooled finned tubes. The resulting excess condensate
water was removed using aluminium gutters, which were fixed below the cooling pipes (Figure 1). This water
was measured automatically with a precisely operating volumetric dosing system to calculate the latent energy (1
L is equal to 2.49 MJ) and to derive the sensible energy from the total energy that was removed from the
greenhouse. The collected energy dimension of this system was shown as an example for one week and
expressed as the daily amount of energy per square meter ground area of the greenhouse (MJ m-2).
The stored thermal energy above 30 °C was used directly for heating in the collector GH, whereas lower water
temperatures in the rain-water tank between 7 °C and 30 °C were increased to the required level by a heat pump.
At temperatures below 7 °C in the rain-water tank, a floor-level heating was used for the heat output in cooler
periods. Otherwise, the heat supply in the collector GH was realized via heat exchanger, i.e., using tubular film
blowers fixed under the channels (set = 16 °C) and a vegetation heating system (set = 17 °C). Additionally, the
reference GH was fitted with a daily energy screen, whereas the collector GH was equipped beside a daily
energy screen with highly aluminized energy screens in the roof and side wall regions to avoid energy losses. To
improve the conditions of plant production, the carbon dioxide fumigation was applied in both greenhouses up to
a level of 800 ppm for 12 hours, starting at 6 AM. In this context, the CO2 supply was interrupted when the
ventilation was opened above 10%. To obtain the desired environmental conditions in both greenhouses, all the
aforementioned set points for climatic conditions were controlled by different sensors arranged in the middle of
the growing tomato plants and under the roof. To provide accurate values of the experimental conditions, the
measurement uncertainties of the relative humidity sensors, temperature sensors and CO2 sensors were
maintained as low as possible, i.e. high precision sensors were used. In this context, the measurement
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uncertaint
i
calibrated
central c
o
operating
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In order t
o
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l
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A net-acr
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These we
r
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t
was cond
u
400) were
in terms
o
were addi
t
50 g) and
b
weekly to
number o
f
harvested
Prelimina
r
Plant Res
variation
o
et al., 201
3
measure t
h
exchange
s
ambient a
i
temperatu
r
were use
d
dissimilat
i
leaf area i
n
results w
e
harvest o
f
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et.org
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i
es caused by
at regular in
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ode of the g
r
o
show how th
e
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imatic data
w
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2
concent
r
d
-1
, respectiv
e
Figur
e
D
etermination
e
age of 200
m
r
e grown on t
h
t
summation
a
u
cted between
weighed wee
k
o
f both previo
u
t
ionally categ
o
losso
-end
r
calculate the
f
fruit of the i
n
d
uring the wh
o
r
y experiment
s
ponse Monit
o
o
f photosynth
e
3
). In the pres
e
h
e photosynt
h
s
ystem BER
M
i
r and the air
i
r
e (T
AIR
) and
d
to calculate
i
on processes.
n
dex for the r
e
e
re plotted cu
m
f
tomatoes be
g
the sensors
w
t
ervals to ens
u
e
r and recor
d
r
eenhouses w
a
e
different cli
m
w
ere sepa
r
atel
y
r
ation, relativ
e
e
ly.
e
1. Equipmen
t
and Calculati
m
² per greenh
o
h
e high chann
e
a
nd by the rec
i
February and
k
ly to compar
e
u
sly describe
d
o
rized into dif
f
r
ot fruit (BER
)
number of fr
u
n
dividual qual
i
o
le cultivatio
n
s
showed that
o
ring System
e
sis regarding
e
nt study, ten
l
h
esis every 30
M
ONIS. As su
c
i
n the chambe
r
a constant (2
9
GECO
2
(Eq
u
To evaluate t
h
e
spective gre
e
m
ulatively, w
h
g
an. The fix
e
Journal of
A
w
ere ± 3%, 0.
0
u
re scientifica
l
d
ed every 30
a
s developed a
t
m
ate control s
t
y
logged for e
a
e
humidity (R
H
t
for cooling a
n
on of the Fixe
d
o
use was use
d
e
l in roc
k
-woo
l
i
rculation of d
r
October 2011
e
the total yie
l
d
climate regi
m
f
erent weight
c
)
. As such, 10
0
u
it of the resp
i
ty characteris
t
n
period. The r
e
the photosyn
t
(BERMONI
S
two different
d
l
eaf cuvettes
pe
seconds as C
c
h, the volume
r
(DiffCO
2
), t
h
9
.93), derived
u
ation 1). The
h
e fixed CO
2
w
e
nhouse and t
h
h
ere the mea
s
e
d CO
2
was
e
A
gricultural Sc
i
36
0
2 K and ± 3
%
l
ly proven re
s
seconds, wh
e
t
the Humbol
d
t
rategies affec
t
a
ch greenhou
s
H
) and temper
a
n
d heating of
t
d
CO
2
Within
t
d
to cultivate
4
l
slabs and irr
i
r
ain water aft
e
. During this
t
l
d (kg
m
-2
) po
t
m
es. To deter
m
c
lasses named
0
tomato plan
t
ective weight
tic was extrap
e
sults were ex
p
t
hesis can be
m
S
). Under th
e
d
evices of the
e
r greenhouse
O
2
-gas excha
n
tric flow rate
o
h
e atmospheri
c
from the mol
amount of t
h
w
ithin the to
m
h
e molar mass
s
urements of
t
e
xpressed as
g
i
ence
%
, respectivel
y
s
ults. The me
a
e
re the softw
a
dt
-Universität
z
t
the microcli
m
s
e and subseq
u
a
ture. The res
u
t
he solar colle
c
t
he Tomato C
r
4
00 tomato pl
a
i
gated via dri
p
e
r each irrigat
i
t
ime, the harv
e
t
ential and the
m
ine fruit qu
a
as A-fruit (>
7
t
s (n = 100) o
f
class. At the
olated to the
t
p
ressed as nu
m
m
easured wit
h
e
same meas
u
same type w
a
were fixed at
n
ge (GECO
2
)
o
f the air (Q),
c
pressure (p)
,
ar mass and t
h
h
e GECO
2
w
a
m
ato crop, the
d
of CO
2
were
t
he GECO
2
s
t
g
ram CO
2
p
e
r
y
. Furthermor
e
a
surements w
e
a
re progra
m
f
z
u Berlin.
m
atic conditio
n
u
ently used to
u
lts were expr
e
c
tor greenhou
s
r
op and Light
D
a
nts (cv. Pan
n
p
irrigation, w
h
i
on cycle (set
=
e
sted tomatoe
s
total number
a
lity, parts of
7
0 g), B-fruit (
5
f
each greenho
end of the pr
o
t
otal number
o
m
ber of fruit p
h
high accura
c
u
rement cond
i
a
s not higher t
h
different heig
h
using the lea
f
the CO
2
level
,
the chamber
h
e specific g
a
a
s generated
d
d
aily quantity
included in t
h
t
arted one w
e
r
square mete
r
Vol. 5, No. 10;
e
, the sensors
e
re forwarde
d
f
or controllin
g
n
s, the mean v
calculate the
e
ssed as pp
m
d
s
e
D
istribution
n
ovy), respect
i
h
ich was cont
r
=
30%). This
s
s
of each plan
t
of marketabl
e
the harvested
5
0-70 g), C-fr
u
use were eval
u
o
duction cycl
e
o
f fruit, which
er square met
r
c
y using the
B
i
tions, the hi
g
h
an 1.9% (Sc
h
h
ts in the can
o
f
cuvette base
d
difference bet
w
area (ChA), t
h
a
s constant of
d
aily excludi
n
of the GECO
2
h
e calculations
e
ek before the
r
of the culti
v
2013
were
to a
g
the
a
lues
daily
d
-1
, %
i
vely.
olled
s
tudy
t
(n =
fruit
fruit
u
it (<
u
ated
e
, the
were
r
e.
B
erlin
g
hest
h
midt
p
y to
d
gas
w
een
h
e air
CO
2
,
n
g all
2
, the
.
The
first
v
ated
www.ccsenet.org/jas Journal of Agricultural Science Vol. 5, No. 10; 2013
37
net-acreage (g CO2 m-2). The GECO2 was specified as follows:
GECO
. (1)
To determine the light conditions in the passively cooled greenhouse, the spatial light difference ratio between
the reference GH and the collector GH was calculated. As such, 84 measuring points were located at a height of
4.60 meters for a uniform measuring distribution. The incoming light in both greenhouses was measured with
PAR-sensors at the same measuring points and at the same time on a sunny day in October 2011. Subsequently,
the spatial light difference ratio in the collector GH was derived, where zero is defined as 100% of the incoming
light in the reference GH. The results were expressed as percentage (%).
2.3 Calculation of the Energy Use Efficiency and Reduced Fuel Consumption
The energy use efficiency is defined as the amount of energy required to produce one kg of marketable fruit and
was expressed as MJ kg-1. The calculations were performed cumulatively, where the respective tomato yield and
the energy consumption of each greenhouse were used. In this context, variables such as the energy consumed
(EC) for the circulation pumps (CP) and for heat pump processes (HP), the primary energy factor for electrical
energy (PFEE) and the collector GH as heat producing system were considered to calculate the EUE for the
collector GH (Equation 2). The latter means that the excess energy (EE) stored in the rain water tank was
subtracted from the actual energy consumption in the collector GH, because the available energy could
theoretically be used elsewhere. Regarding the reference GH, the EUE was calculated in consideration of the
consumption of district heat (DH), the primary energy factor for district heat (PFDH) and excluding energy
generation (Equation 3). The EUE was calculated as follows:
EUE 
 (2)
EUE 
 (3)
The EUE was plotted weekly from the first to the last harvest date. In this context, the energy consumption from
planting to the first harvest date was added in equal amounts to each calculation of the EUE. An improved EUE
exists when less energy is required for the same amount of tomato fruit.
To evaluate the possible reduction of the fuel consumption per kilogram produced tomatoes using a collector GH,
the difference of the energy use efficiency between the collector and reference greenhouse was calculated at the
end of the experiment. This result and the heating value of a variety of fuels were set in relation, in order to
calculate the equivalent amount of the corresponding fuel and CO2 emissions produced by their combustion. The
heating values of natural gas, coal, vegetable oils, heating oil and wood pellets, as well as their properties
regarding CO2 release were used as reported by Ulbig and Hoburg (2002), Demirbas (2004), Fassinou et al.
(2010), iwo (2012), Telmo and Lousada (2011) and using a special software program named GEMIS version 4.8
(GEMIS, 2010), respectively. Depending on the heating material, the saved fuel was either expressed as cubic
metre or kilogram per kilogram tomatoes, whereas the reduced CO2 emission was displayed as kilogram CO2 per
kilogram tomatoes.
2.4 Statistical Analysis
The effect of the CO2 fixation within the crop on the yield increase was evaluated with SPSS, package version
19.0. In this context, the linear correlation between these variables was calculated via linear regression analysis
to obtain the coefficient of determination (R2) and to test whether the slope (m) in y = mx + b differs
significantly (p < 0.05) from zero. Comparisons regarding fruit yield and the number of fruit were calculated
using t-tests (p < 0.05). Asterisks or different small letters indicate significant differences. The mean variability
is pointed out by the standard deviation (±). All other calculations regarding CO2 fixation, energy distribution
and EUE were calculated with EXCEL, package version 2010.
3. Results and discussion
3.1 Generation of Energy Using a Solar Collector Greenhouse and Changes in Climate Conditions
During the warm period, the energy caused by the transmitted solar radiation and water vapour was captured
using a cooling fin system under the roof, which was connected to a reversible heat pump and a low temperature
storage tank. The graphs in Figure 2 present the behaviour of the removed energy depending on the transmitted
www.ccsenet.org/jas Journal of Agricultural Science Vol. 5, No. 10; 2013
38
solar radiation for seven days during the summer period in 2011. On the fifth day of the recorded data, a
maximum daily amount of energy (11.5 MJ m-2) was removed from the collector greenhouse, where a maximum
cooling capacity of 368 W m-2 was measured. The calculations showed that a maximum collector efficiency
factor of 0.7 was achieved on this day, when the removed total energy was considered in relation to the
transmitted solar energy. Comparable results regarding cooling capacity and collector efficiency were reported
by Grisey, Grasselly, Rosso, D´ Amaral, and Melamedoff (2011), who have used 9 FiWiHEx® heat exchanger.
This type of cooling is referred to as active cooling, which requires high amounts of energy for ventilators,
pumps and the cooling machine. In the present study, however, a passive cooling system only equipped with
cooling pipes and a reversible heat pump was used. Therefore, the construction of the collector GH can be
applied to reduce the energy costs compared with the FiWiHEx® system mentioned before. According to
Eisenmann, Vajen, and Ackermann (2004), as well as Kumar and Prasad (2000), the collector efficiency factor of
a thermal solar collector ranged between 0.7 and 0.9. Despite these higher values, the effectiveness of the
installed system in the solar collector greenhouse is comparable to a thermal solar collector due to the fact that
higher plate temperatures result in more heat losses, which lead to a lower value of the collector efficiency factor
(approximately 0.5) of such systems. Based on an annual production of tomatoes, this value corresponds to the
mean value obtained in the collector GH. In general, the captured total energy increased with increasing solar
radiation (R2 = 0.87) (Figure 2). This result was caused by low ventilation, a high ambient temperature and
higher levels of relative humidity. In relation to the total energy removal, the mean daily quantity of
sensible heat energy and latent energy was 71% and 29%, respectively. However, it was shown that the rate
of latent energy can be increased to 44% when a dehumidification system combined with a cucumber crop
is used (Campen & Bot, 2002; Campen, Bot, & de Zwart, 2003). Viewed over the year, a total amount of
energy of 50% of the impinging solar radiation sum was collected with the solar collector greenhouse,
although the emergency ventilation was frequently activated to avoid plant damage. In this context, it
should be pointed out that a high energy removal in the closed operation mode is accompanied by high
levels of temperature and relative humidity as shown in Figure 3. Based on the semi-closed operation mode
in the collector GH, a mean RH of approximately 92% was maintained during the production cycle,
whereas the RH in the conventionally controlled greenhouse varied widely from 64% to 92% (Figure 3).
Due to the later opening of the ventilation in the collector GH, a higher mean temperature and mean CO2
concentration were reached compared to the reference GH. A maximum difference in the daily mean
temperature (2 K) and CO2 concentration (233 ppm) was measured in spring. However, the calculated
levels of RH, temperature and CO2 did not differ significantly during the autumn period, which was caused
by cooler outside conditions and the associated ventilation set-point in the reference GH. These
characteristics may influence the plant vigour, e.g., the occurrence of Botrytis (Heuvelink, Bakker, Marcelis,
& Raaphorst, 2008) and can complicate the working conditions for the employees, especially in summer
time. Therefore, the challenge to producers is to learn how to work using the new system, including the use
of precise measuring technologies, to control dew points and plant physiological processes.
www.ccsenet.org/jas Journal of Agricultural Science Vol. 5, No. 10; 2013
39
Figure 2. Collected energy dimensions depending on transmitted solar radiation
Figure 3. Effects of different cliamte control stratgies on relative humidity, temperature and CO2 concentration
during harvest period
3.2 Effects of Prevailing Climate Conditions in a Solar Collector Greenhouse on Fruit Yield and CO2 Fixation
In comparison with the conventional climate control strategy, it was found that changing climate conditions -
caused by the collector GH - were responsible for a significantly increase in quantity of tomatoes (Figure 4). A
maximum yield increase by 32% was achieved at the end of the experiments. This extra yield was attained, even
though the mean light intensity in the collector GH was reduced by 11%. This result was computed from the
spatial light difference ratio as shown in Figure 5. The low values of these calculations were mainly induced due
to the cooling fins and energy screens installed in the roof region of the collector GH, where it meight be
possible that probably 3% of the light was intercepted by the cooling fins as shown by Campen and Bot (2002).
Light sinks especially occurred under the energy screens as detected at the measuring point one, four, seven, ten
0
2
4
6
8
10
12
14
16
18
2011-08-09
2011-08-10
2011-08-11
2011-08-12
2011-08-13
2011-08-14
2011-08-15
Daily amount of energy [MJ m
-2
]
Time [days]
removed total energy
removed latent energy
transmitted solar radiation
removed sensible heat energy
0
10
20
30
40
50
60
70
0
100
200
300
400
500
600
700
800
2011-05-10
2011-05-17
2011-05-24
2011-05-31
2011-06-07
2011-06-14
2011-06-21
2011-06-28
2011-07-05
2011-07-12
2011-07-19
2011-07-26
2011-08-02
2011-08-09
2011-08-16
2011-08-23
2011-08-30
2011-09-06
2011-09-13
2011-09-20
2011-09-27
2011-10-04
2011-10-11
2011-10-18
2011-10-25
Mean temperature per day [°C]
Mean CO
2
concentration per day [ppm]
Mean RH per day [%]
Harvest date
CO2 reference GH CO2 collector GH RH reference GH
RH collector GH Temperature reference GH Temperature colle ctor GH
www.ccsenet.org/jas Journal of Agricultural Science Vol. 5, No. 10; 2013
40
and twelve. Marcelis, Broekhuijsen, Meinen, Nijs, and Raaphorst (2006) reported that 1% less radiation results
in 0.6% to 1.1% less production of tomatoes. These results were not confirmed in the present study as previously
described. Rather, it might be possible that compensations for the light deficiency can be obtained by the
optimisation of other climatic parameters, such as temperature, relative humidity and CO2 concentration,
particularly in spring and summer. Based on the ventilation behaviour and associated changing climate
conditions, it was demonstrated that the calculated CO2 fixation within the crop was increased by 77% compared
to that observed in the reference GH (Figure 4). When a collector GH was used, 60% of the enriched technical
CO2 was fixed within the crop, whereas this amount was reduced to approximately 35% by the influence of the
reference situation. In this context, it is common in commercial practice that the CO2 enrichment remains
switched on in greenhouses, although the ventilation is opened. Compared to this case, the operation mode of a
semi-closed greenhouse leads to a reduction in CO2 emissions and costs of the technical CO2, because it can be
kept longer closed. Furthermore, a significant correlation and a significantly increased slope compared with zero
was found between the cumulative CO2 fixation and the total yield (R2 = 0.89; m = 3.55, p = 0.000). Regarding
photosynthetic activity, the results do not agree with those of other scientists. Besford, Ludwig, and Withers
(1990), for instance, found that plants did not maintain a photosynthetic gain with longer-term CO2 enrichment at
1000 ppm. However, plants in this investigation were solely exposed to different CO2 concentrations, while the
temperature and the relative humidity remained unchanged. Therefore, the evidence in the current study
indicated that a combination of higher levels of temperatures, relative humidity and CO2 concentration in a
semi-closed GH promoted photosynthesis, which resulted in an increased CO2 fixation and an associated
increase in total yield. This total yield was characterized by high quality fruit consisting of a significantly
increased number of marketable fruit (24%) when compared with the reference plants. This means in detail that
the number of A-fruit was increased and that of B-fruit was decreased by 45% and 8%, respectively (Figure 6).
Furthermore, the occurrence of BER-fruit was affected by the collector GH, because the number of these fruit
was reduced by up to 83% in relation to that of BER-fruit formed under conventional conditions. It is assumed
that the lower levels of RH in the reference GH led to high transpiration losses followed by a calcium deficiency
in plant cells during the summer period. In this case, the BER-fruit can spread throughout the crop as shown by
De Kreij (1996).
Figure 4. Effects of different climate control strategies on the cumulative total yield (n = 400) and carbon dioxide
fixation within the crop. The total was tested using t-tests, where asterisks indicate significant differences in total
yield at the end of the experiment (p < 0.05)
22.94
17.41
0
1000
2000
3000
4000
5000
6000
7000
8000
0
5
10
15
20
25
Fixed carbon dioxide [g CO
2
m
-2
]
Cumulative total yield [kg m
-2
]
Harvest date
fixed CO2 reference GH fixed CO2 collector GH
total yield collector GH* total yield reference GH
www.ccse
n
Figure 5.
T
Figure 6
tested
3.3 Influe
n
The EUE
EUE for
b
the rain
w
the results
as conseq
u
n
et.org
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jas
T
he spatial lig
h
d
6
. The effects
o
using
t
-tests,
w
n
ce of a Solar
is a useful to
o
b
oth greenhou
s
w
ater tank was
elucidated th
a
u
ence of
t
he r
e
h
t difference r
a
d
efined as 100
%
o
f different cli
m
w
here small l
e
Collector Gre
e
o
l to estimate
s
es was appro
x
not considere
d
a
t the EUE in
e
use of the st
o
Journal of
A
a
tio in the coll
e
%
of the inco
m
m
ate control s
t
e
tters indicate
s
experi
m
e
nhouse on th
e
the total ene
r
x
imately 40
M
d
to calculate
the collector
G
o
red energy. B
a
A
gricultural Sc
i
41
e
ctor greenho
u
m
ing light in t
h
t
rategies on fr
u
s
ignificant dif
f
m
ent (p < 0.0
5
e
Energy Use
E
r
gy use for gr
e
M
J kg
-1
p
roduc
the EUE for
t
G
H can be im
p
a
sed on the d
i
i
ence
u
se versus refe
r
h
e reference g
r
u
it quality (n
=
f
erences in nu
m
5
)
E
fficiency an
d
e
enhouse pro
d
ed tomatoes,
w
t
he collector
G
p
roved by 103
%
i
mension of t
h
r
ence greenho
u
r
eenhouse
=
400). The nu
m
m
ber of fruit
a
d
Reduced Fue
l
d
uction. In th
e
w
hen the exc
e
G
H (data not s
h
%
compared t
o
h
e cooling sys
t
Vol. 5, No. 10;
u
se (n = 84). Z
e
m
ber of fruit
w
a
t the end of th
l
Consumptio
n
e
present stud
y
e
ss energy sto
r
h
own). In co
n
o
the referenc
e
t
em in the col
l
2013
e
ro is
w
as
e
n
y
, the
ed in
n
trast,
e
GH
ector
www.ccsenet.org/jas Journal of Agricultural Science Vol. 5, No. 10; 2013
42
GH and using the equation to calculate the EUE (Equation 2), an energy input of -1.41 MJ had to be applied in
the collector GH, in order to produce one kilogram tomatoes (Figure 7). Therefore, an energy gain was achieved
in the solar collector greenhouse at the end of the experiment (Figure 7). Comparable values were determined in
Spain and in the tropics of Columbia as well (Elings et al., 2005; Medina, Cooman, Parrado, & Schrevens, 2006).
With respect to these countries, an EUE level of 1.97 MJ kg-1 and 1.11 MJ kg-1 was estimated, respectively,
where this low energy input for crop production was a result of unheated greenhouses. However, the energy use
efficiency in the collector GH was improved by means of the additional yield, collected solar energy throughout
the year and strongly aluminized energy screens. Due to the energy screens, the energy demand decreased with
increasing insulation up to 33% (data not shown). Similar results were reported by Tantau (1998) and Bot et al.
(2005) using thermal screens. Furthermore, the deteriorating energy use efficiency in the collector GH was
assessed as a disadvantage, which was observed over the harvest period (Figure 7). This result was a
consequence of the energy consumption for cooling processes in summer, whereas this procedure contributed to
the fact that large amounts of energy were stored in the rain water tank. Especially in summer, there was an
energy excess, which can be used primarily to cover the basic load for heating in other greenhouses or to provide
subareas in greenhouses with luxury heat. The stored energy can also be delivered to sanitary facilities in the
immediate vicinity or to postharvest processes, e.g., for drying of tomatoes. In this context, the collected heat can
be directly applied via heat exchangers to fruit, because a low drying air temperature protects the quality of
nutritional components in tomatoes (Hossain, Amer, & Gottschalk, 2008). Moreover, the water containing in the
low temperature storage tank had drinking water quality concerning microbiology criteria, although this was
circulated in cooling and heating processes for a year. Neither Escherichia coli ( 0 most probable number 100
ml-1) nor coliform bacteria ( 0 most probable number 100 ml-1) were detected in this water. Therefore, it can be
reused for watering without concern.
Figure 7. The weekly cumulative energy use efficiency depending on different operation modes of greenhouses
Finally, the energy saving per kilogram produced tomatoes in the collector GH is equivalent to the combustion of
1.04 m3 natural gas, 1.67 kg coal, 1.04 kg vegetable oil, 0.92 kg heating oil or 2.08 kg wood pellets when
compared with the conventional tomato production (Figure 8). Hence, this technology can be utilized to reduce a
substantial volume of CO2 emissions, whereby it is possible to produce tomato plants in a sustainable way. The
equivalent reduced CO2 emission ranged between 2.32 kg and 4.18 kg CO2 per kg produced tomatoes, where
these data depend on the fuel used (Figure 8).
-36.73
-1.41
146.10
40.21
-50
0
50
100
150
200
2011-05-10
2011-05-17
2011-05-24
2011-05-31
2011-06-07
2011-06-14
2011-06-21
2011-06-28
2011-07-05
2011-07-12
2011-07-19
2011-07-26
2011-08-02
2011-08-09
2011-08-16
2011-08-23
2011-08-30
2011-09-06
2011-09-13
2011-09-20
2011-09-27
2011-10-04
2011-10-11
2011-10-18
2011-10-25
Energy use efficiency [MJ kg
-1
tomatoes]
Harvest date
collector GH
reference GH
www.ccse
n
Figure 8.
S
4. Conclu
s
Due to th
agronomi
c
environm
e
radiation
w
p
rovided
f
energy sc
r
observed.
relative h
u
CO
2
fixat
i
should be
strategies
area in a r
greenhou
s
limited to
Acknowl
e
This feasi
b
Safety an
d
assistance
assistants
o
Referenc
e
Besford,
R
g
E
Bot, G. P
.
C
h
Bot, G. P.
s
o
n
et.org
/
jas
S
everal examp
collecto
r
sion
h
e results, it
w
c
approach to
e
nt can be re
l
w
as captured
u
f
or the heat e
x
r
eens and co
o
It is obviousl
y
u
midity and
C
i
on and more
y
sought in fu
t
could be achi
e
atio of one to
s
e productio
n
the closed gr
e
dgement
b
ility study
w
d
the Rentenb
a
of the Federa
l
o
f Division B
i
e
s
R
. T., Ludwig
rowing in hi
g
E
xperimental
B
.
A. (2001).
D
C
omputers
ttp://dx.doi.or
g
A., Van de Br
a
o
lar greenhou
s
les of a possi
b
r
greenhouse a
n
w
as conclude
d
produce a hi
l
ieved. On a
n
u
sing the cool
i
x
port to othe
r
o
ling fins in t
h
y
possible that
C
O
2
concentra
t
y
ields. Never
t
t
ure projects,
e
ved. In this
c
three is conc
e
n
while the li
g
eenhouse are
a
w
as funded by
a
nk managed
b
l
Agency for
A
i
osystems Eng
i
, L. J., & Wi
t
g
h CO
2
, phot
o
B
otany, 41(229
D
evelopments
and
g
/10.1016/s01
a
ak, N., Chall
a
s
e: State of t
h
Journal of
A
b
le reduction o
f
n
d fuel-relate
d
d
that a semi-
i
gh quantity
o
n
annual basi
s
i
ng fin syste
m
r
purchasers.
F
h
e collector
G
a reduced ve
n
t
ions can co
m
t
heless, a low
e
whereby pos
s
c
ontext, a co
m
e
ivable. As su
c
g
ht reduction
a
.
the Federal
M
b
y the Federal
A
griculture an
ineering.
t
hers, A. C. (
1
o
synthesis an
d
9
), 925-931. ht
t
in indoor su
s
Electronics
68-1699(00)0
0
a
, H., Hemmi
n
h
e art in energ
y
A
gricultural Sc
i
43
f
the fuel cons
u
d
CO
2
emissio
n
closed solar
c
o
f marketable
s
, a considera
b
m
. This energy
F
urthermore,
t
G
H did not in
f
n
tilation openi
n
m
pensate the li
g
e
r light interc
e
s
ibly higher y
i
m
bination of a
c
h, the excess
caused by c
o
M
inistry for E
n
Ministry of F
o
d Food. We
w
1
990). The gr
d
ribulose-1,
5
t
p://dx.doi.org
/
s
tainable plan
t
in
0
162-9
n
g, S., Rieswij
k
y
saving and
s
i
ence
u
mption per k
i
n
s released by
c
ollector gree
n
tomatoes and
b
le amoun
t
o
can be reuse
d
t
he mean ligh
t
f
luence the yi
e
n
g and associ
a
ght reduction
e
ption by mou
n
i
eld differenc
e
solar collecto
r
energy may b
e
o
oling fins a
n
n
vironment,
N
o
od, Agricultu
w
ould like to t
h
r
eenhouse eff
e
5
-
b
isphosphat
e
/Doi 10.1093/
J
t
production
w
Agriculture
,
k
, T., Von Str
a
s
ustainable e
n
i
logram produ
their combus
t
n
house can b
e
additional e
n
o
f energy of
t
d
for heating i
n
t
interception
e
ld adversely.
a
ted higher le
v
over the yea
r
n
ting parts (e.
e
s between b
o
r
and a conve
n
e
provided fo
r
n
d additional
N
ature Conser
v
u
re and Consu
m
h
ank all the sc
i
e
ct: acclimatio
n
e
carboxylase
J
xb/41.8.925
w
ith emphasis
,
30(1-
3
a
ten, G., & Ve
r
n
ergy supply.
A
Vol. 5, No. 10;
ced tomatoes
i
t
ion
e
recommend
e
n
ergy, whereb
y
t
he incoming
n
cooler perio
of 11% caus
e
The opposit
e
v
els of temper
a
r
, leading to h
g., energy scr
e
o
th climate c
o
n
tional green
h
r
the convent
i
energy scree
v
a
t
ion and N
u
m
er Protectio
n
i
entists and st
u
n
of tomato
p
protein
J
our
n
on energy s
a
3
), 151
r
lodt, I. (2005)
A
cta Horticul
t
2013
i
n the
e
d as
y
the
solar
d
s or
e
d by
e
was
a
tures,
i
gher
e
ens)
o
ntrol
h
ouse
i
onal
n
s is
u
clear
with
u
dent
p
lants
al of
v
ing.
-
165.
. The
u
rae,
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... Pahlavan, Omid, and Akram (2011) report an EUR of 0.001 MJ•MJ -1 in tomato production, where the inputs used were labor, fertilizers, herbicides, electricity and machinery. Likewise, Sepat, Sepat, Sepat, and Kumar (2013) In the second approach, the EUE is defined by Dannehl, Schuch, and Schmidt (2013) as the amount of energy required to produce 1 kg of commercial fruit expressed in MJ•kg -1 . The EUE, although it has the same units as the specific energy in the first approach, does not consider the energy consumed in the preparation of inputs such as fertilizers, seeds, herbicides, etc. ...
... The above figure is lower than that reported by Dannehl et al. (2013) for a solar collector greenhouse, but higher than that reported for unheated greenhouses in Spain. ...
... En el segundo enfoque, se consideró únicamente el consumo de electricidad de un motor monofásico, por lo que la EUE se expresó de la siguiente manera:(10)La cifra anterior se encuentra por debajo de lo reportado porDannehl et al. (2013) para un invernadero tipo colector solar, pero está por arriba de lo reportado para invernaderos sin calefacción en España. En relación con la mano de obra, durante el ciclo de producción de tomate se utilizaron 758 h de mano de obra para una superficie de 120 m 2 y producción de 2,288.94 ...
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Article
One of the advantages of controlled agriculture is the notable increase in crop yields. However, at high-tech levels, water use productivity has increased, while energy use productivity has decreased. Therefore, the objective of this study was to estimate water, energy and labor use productivity in tomato cultivation, for a low-tech greenhouse. The inputs used in the production process were recorded from April 24 (date of transplant) to October 16, 2016 (date of last harvest). The yields obtained were 19.07 kg·m-2. Water use productivity was 27.86 kg·m-3 (35.89 L·kg-1), which is within the range reported for unheated plastic greenhouses (30-40 L·kg-1). Energy productivity was 0.331 kg·MJ-1, and the energy consumed per unit area was 57.61 MJ·m-2, with Calcium nitrate being the input with the highest energy demand (49.49 %). During the production cycle, 738 working hours were used, 78 % of which were dedicated to cleaning and maintenance, with labor productivity of 3.02 kg·h-1.
... To date very few reports exist on heated greenhouses combined with energy production systems using RES to cover their energy needs for heating, cooling and electricity, but also to transfer excess energy to other facilities (Ramírez et al., 2015). In this context, a solar collector greenhouse (SCG) has been used to produce the thermal energy to cover its own energy demand as well as the basic load for heating other greenhouses (Dannehl, Josuttis, Ulrichs, & Schmidt, 2014;Dannehl, Schuch, & Schmidt, 2013). The SCG greenhouse equipped with efficient insulation can reduce the overall heat transfer coefficient (U) to 1.8 W m À2 K À1 (Schuch, 2014). ...
... Pannovy) were cultivated in each greenhouse from March to October 2011 (231 days). The detailed description of both greenhouses, the experimental design and the climate control strategy have been described in detail by Dannehl et al. (2013). Briefly, the SCG acted as solar collector, where finned tube heat exchangers (FTHE) were installed under the roof. ...
... The different climate control strategies affected the microclimatic conditions in each greenhouse, such as daily averages of CO 2 concentration, air relative humidity (RH), air temperature and ventilation (Figs. 2 and 3). The heat exchangers installed under the roof in the SCG reduced the light intensity by up to 11% compared to the RG, as described by Dannehl et al. (2013). Nevertheless, we have found that the photosynthesis was increased simultaneously, which was mainly caused by higher CO 2 concentrations (Fig. 2). ...
Article
Consumer and trade organisations demand year-round healthy diets including fresh, high quality vegetables from local producers. However, greenhouse gas emissions (GHG) of heating high-tech greenhouses in northern countries are higher than transporting vegetables produced in southern Europe in unheated tunnels. The aim of this work was to assess GHG emissions when renewable energy sources were used for heating and cooling a solar collector greenhouse (SCG) in comparison with a conventional greenhouse (RG). Thermal energy generated in the SCG from solar energy was stored in an insulated water tank and different strategies were examined: no reused energy; reused energy; reused energy and excess energy transfer. Based on the semi-closed climate control strategy set in SCG and associated higher CO2 concentrations, higher marketable yields were achieved (+22%) compared to the production in the RG. The results further showed that the cumulative energy demand of the SCG can be lowered by approximately 44% compared to that needed in the RG. The carbon footprint (CF) and the water use efficiency were improved by 24% and 28%, respectively. If excess thermal energy generated by the SCG could be considered as export energy, a negative carbon footprint of -0.7 CO2-eq kg-1 can be reached. The latter case shows that the CF can be reduced to levels of unheated greenhouses. As such, vegetable production in solar collector greenhouses can be more sustainable than in conventional greenhouses since energy and water, as well as fertiliser and associate CO2 emissions, can be saved.
... However, such greenhouses usually include more expensive equipment. Sometimes this equipment reduces the light transmission of the greenhouse cover [1,31], potentially reducing the plant's photosynthesis and yield. However, technical cooling and dehumidification of the greenhouse air may keep the greenhouse windows closed under increasing solar radiation and outside temperature [8]. ...
... CO2 concentration in the closed greenhouse was kept at 1000 µmol mol −1 , whereas it dropped to 450 µmol mol −1 in the conventional greenhouse at high temperature and solar radiation. Dannehl et al. (2013) reported a yield increment in tomato by 32% in a closed greenhouse with a 11% lower light transmission compared to Light reduction an otherwise identical conventional greenhouse. The CO2 target concentration in this closed greenhouse was 800 µmol mol −1 . ...
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Article
Concepts of semi-closed greenhouses can be used to save energy, whereas their technical equipment often causes a decrease in the light received by the plants. Nevertheless, higher yields are achieved, which are presumably triggered by a higher CO2 concentration in the greenhouse and associated higher photosynthesis because of the technical cooling and the longer period of closed ventilation. Therefore, we examined the effects of photosynthetic photon flux density (PPFD) and CO2 concentration on plant photosynthesis and transpiration in tomato using a multiple cuvette gas exchange system. In a growth chamber experiment, we demonstrated that a light-mediated reduction in photosynthesis can be compensated or even overcompensated for by rising CO2 concentration. Increasing the CO2 concentration from 400 to 1000 µmol mol−1 within the PPFD range from 303 to 653 µmol m−2 s−1 resulted in an increase in net photosynthesis of 51%, a decrease in transpiration of 5 to 8%, and an increase in photosynthetic water use efficiency of 60%. Estimations showed that light reductions of 10% can be compensated for via increasing the CO2 concentration by about 100 µmol mol−1 and overcompensated for by about 40% if CO2 concentration is kept at 1000 instead of 400 µmol mol−1.
... Our results show that the rate of truss initiation, production and partitioning of DM, and yield were not different in the treatments with or without a VTG, when the temperatures at the top of the canopy were the same. Higher yields were found when crops were grown in (semi-)closed greenhouses compared to conventionally ventilated greenhouses Hoes et al. 2008;Dannehl et al. 2013), mainly due to increased concentrations of CO 2 leading to higher rates of photosynthesis (Chapter 2). Furthermore, fruit quality and health-promoting compounds were increased by higher CO 2 concentrations in semi-closed greenhouses (Dannehl et al. 2012;, implying that semi-closed greenhouses can be beneficial to plant growth, yield and product quality. ...
... However, in our research, photosynthetic acclimation to elevated CO 2 was not found in the semi-closed greenhouse. Dannehl et al. (2013) neither found photosynthetic acclimation to elevated CO 2 in the closed greenhouse. This can be explained by the fact that the crops in the closed and semi-closed greenhouse had sufficient sink strength (high fruit load per m 2 ) to use the extra assimilates produced at higher CO 2 concentration. ...
... Another challenge for a greenhouse heated by lamps is the installation of the MCD unit of the heat harvesting system. In a previous trial, the MCD unit was installed above the crop, in a way that obstructed 11% of the sunlight coming into the greenhouse (Dannehl et al., 2013). In the current chapter however, shading by the MCD was assumed to be negligible. ...
... The revealed tomato fruit yields for aquaponics and conventional separate hydroponics were 23.7 kg m -2 and 26.5 kg m -2 , respectively, and were comparable to those gained by Suhl et al. February to October, respectively, using the tomato variety Pannovy (Dannehl et al., 2014a;Dannehl et al., 2013). ...
Article
The increase of global population causes rising food demand and concomittantly scarcity of resources. These facts including global warming need the further development of resource-efficient food production systems such as double recirculating aquaponic systems (DRAPS). This recent technology is suitable for intensive food production with minimal resource input and maximal reduction of emissions. In DRAPS fish water can be adjusted for plant growth (pH, nutrients) and both species are produced separately under optimum conditions. Primarily, the present study was conducted to investigate the improvement of DRAPS by implementation of an innovative suction filter device and, in addition, it is the first empiric investigation of combined African catfish (Clarias gariepinus) and tomato (Solanum lycopersicum L., cv. Pureza) production in DRAPS. Due to an immense loss of nitrogen caused by the primary sedimentation unit as connection between the fish and plant parts, the original DRAPS was modified by a new developed suction filter device to remove solid particles at minimal nitrogen loss. The nitrogen loss was significantly reduced by that system modification (≈43%) and thus resulted in a quite large reduction of greenhouse gas emissions due to the reduced need for manufacturing of nitrogen fertiliser. The combined production of African catfish and tomatoes in aquaponics revealed similar fruit yields of tomatoes as for the control using artificial fertiliser, while the overall fertiliser use in aquaponics was about 13.2% to 77.7% lower. However, fertiliser saving was highest after modification and replacement of the sedimentation unit by the new suction device. In addition, in comparison to already existing aquaponic systems, the total biomass output was significantly increased. The results were evaluated under consideration of intensive crop production in hydroponics.
... In the last years improvements related to renewable and sustainable based technologies which can save up to 80% of energy have been reported. These new technologies include photovoltaic modules, solar thermal collectors, hybrid collectors and systems, phase change material and underground based heat storage techniques, energyefficient heat pumps, alternative facade materials for better thermal insulation and power generation, innovative ventilation technologies using pre-heating and cooling and efficient lighting systems to achieve potential utilization in greenhouses (Cuce et al. 2016;Dannehl et al. 2013;Akyazi and Tantau 2012). On the other side, the environmental sustainability has become an important objective in the production of ornamentals in the last decades. ...
... There is great potential in reducing the environmental impact of horticultural production systems, especially in heated greenhouses (Mempel and Meyer, 2004;Torrellas et al., 2013), which result in higher environmental burdens than unheated greenhouse and open-field cultivation, by implementing renewable energy sources (RES). RES and energy saving systems (ESS) can be employed in greenhouses e.g., solar energy storage systems (Bailey et al., 2012;Ntinas et al., 2011Ntinas et al., , 20122014Schuch et al., 2014), PV systems (Chemisana et al., 2012;Sonneveld et al., 2011;Yano et al., 2014), use of geothermal energy (Torrellas et al., 2012b;Boughanmi et al., 2015) or high insulation techniques (Vadiee and Martin, 2012;Dannehl et al., 2013) and renewable biofuels like wood pellets (Meyer, 2011;S anchez-Molina et al., 2014;Bibbiani et al., 2016). ...
Article
The horticultural industry consumes increasing amounts of energy and water contributing to greenhouse gas emissions and global warming. The aim of this study was to investigate the energy flow and the environmental impact of different tomato cultivation systems when renewable energy sources are implemented in the production chain. Seven scenarios including heated greenhouses and open-field crops, in Southern and Central Europe, were examined in order to identify potentials to reduce energy costs, greenhouse gas emissions and increase water use efficiency along the cultivation phase. The environmental impact category applied in this work (carbon footprint) is related to global warming potential, which includes the basic emitted greenhouse gases contributing to climate change and uses CO2 as reference gas (CO2-equivalents). Additionally, an energy flow indicator (cumulative energy demand) and an inventory flow indicator (water use), both relevant to climate change, agriculture and energy processes were determined to assess the different scenarios. The main results showed that annual carbon footprint values varied between 0.1 and 10.1 CO2-eq/kg tomato. Annual cumulative energy demand presented values from 0.8 to 160.5 MJ/kg tomato. Water use efficiency values ranged between 25.6 and 60.0 L/kg. Hotspots for all seven scenarios were determined, with fossil fuel consumption accounting for most of the environmental impact, where applicable. Open-field tomato cultivation presented lower greenhouse gas emissions and cumulated energy demand, however water use efficiency values were smaller than in greenhouse scenarios. In greenhouse production, the use of renewable energy sources and an increased marketable yield reduced their greenhouse gas emissions drastically, even to the levels of open-field cultivation.
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Technical Report
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In the current context of predicted shortage of fossil energies and of reducing gas emissions, decreasing energy consumption in greenhouses is an important issue for the future. A glasshouse is a collector which can collect almost 80% of solar radiation: using systems to store this energy can be one of the solutions to reduce energy use in greenhouses. The objective of this trial is to use fine wire heat exchangers to heat and to cool a soilless greenhouse tomato crop in the climatic conditions in the south of France. The fine wire heat exchangers are installed under the crop gutters and are connected to a water basin to store energy collected by the greenhouse. This experiment showed that the system allows the greenhouse to be kept closed and a high CO 2 concentration to be maintained. The increase in yields in the closed greenhouse was 34% and energy savings of 20% were measured in the conditions of storage in this experimentation. The next step of this trial is to optimise electricity consumption which is more important with this concept in comparison with a traditional greenhouse. This trial will help to characterize a project of the semi-closed commercial greenhouse industry in the south of France using aquifer energy storage where the main goal is to obtain economic viability for growers.
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The interest in alternative or renewable energy sources for greenhouse heating is currently high, owing to the large heating loads and the relatively high price of fossil fuels. Important alternative sources of energy are solar collectors, heat pumps, biomass and cogeneration systems. This study experimentally investigates greenhouse heating by biogas, solar and ground energy in Elazig, Turkey climate conditions. The greenhouse (6 m x 4 m x 2.10 m) heated by mentioned alternative energy sources was constructed, and then required heating load of the greenhouse was determined. For this purpose, biogas, solar and a ground source heat pump greenhouse heating system (BSGSHPGHS) with horizontal slinky ground heat exchanger was designed and set up. Experiments were conducted extensively during the winter period from November 2009 to March 2010. During the experiments, 2231.831 of gas production by biogas system is provided. The experiments that are required for the growth of many plants need temperature of 23 degrees C, and conceivable success has been achieved in reaching this value by built systems. As a result, different energy sources have been successfully tested for greenhouse heating.
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The closed greenhouse is a recent innovation in the horticulture industry. Cooling by ventilation is replaced partly (in semi-closed greenhouses) or completely (in closed greenhouses) by mechanical cooling. Excess solar energy is collected and stored to be reused to heat the greenhouse. In temperate climates, this concept combines improved crop production with energy savings. This paper presents an overview of climate, crop growth and development, and crop yield in closed and semi-closed greenhouses. The technical principles of a closed greenhouse are described and the macroclimate and microclimate arising from this are studied. The consequences of the typical growth conditions found in closed greenhouses for crop physiology and crop yield are examined. Finally, the experiences of commercial growers are presented. In temperate climates, closed greenhouses can reduce the use of fossil fuel-derived energy by 25 – 35%, compared with open greenhouses. With high global radiation, the climate in closed greenhouses is characterised by high CO2 concentrations, high air humidity, improved temperature control, and a vertical temperature gradient. An annual increase in production of 10 – 20% is realistic, with reduced amounts of supplied CO2. The yield increase is primarily obtained through increased rates of photosynthesis due to the higher CO2 concentrations in closed greenhouses. To introduce this innovation into practice, knowledge transfer was a key factor for its implementation and the realisation of increased production levels. Future trends will require minimising the use of fossil fuels and increasing the level of control of the production process. Closed and semi-closed greenhouses fit seamlessly into this trend as they allow for a more controlled climate and higher levels of production, combined with savings in fossil fuel use.
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A prototype of a hybrid solar dryer was developed for drying of tomato. It consists of a flat-plate concentrating collector, heat storage with auxiliary heating unit, and drying unit. It has a loading capacity of 20 kg of fresh half-cut tomato. The dryer was tested in different weather and operating conditions. The performance of the dryer was compared with an open sun-drying method. Drying performance was evaluated in terms of drying rate, color, ascorbic acid, lycopene, and total flavonoids. Tomato halves were pretreated with UV radiation, acetic acid, citric acid, ascorbic acid, sodium metabisulphite, and sodium chloride. Sodium metabisulphite (8 g L−1) was found to be effective to prevent the microbial growth at lower temperature (45°C).
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Greenhouse cultivation in the high altitude tropics is an important economical activity and the interest to invest in greenhouse technology to improve yield and quality is increasing. The evaluation of the energy use and other burdens associated with protected cultivation have to be accounted for in order to increase sustainability. The aim of this paper was to make a contribution to the applicability of the life cycle assessment (LCA) methodology in high tropics tomato greenhouse production as tool to identifity energy use and some environmental impacts, studying a case in the Bogotá Plateau (Colombia). Overall energy costs for tomato production were calculated at 1108.7 MJ·ton-1, which is extremely low when compared to the energy use in northern Europe. The land use indicator was estimated at 38.5 m 2·y-1·t-1 and a water consumption of 28 L·kg-1. High potential emissions of N and P were estimated in relation with high concentrations applied in nutrient solutions and an elevated water use. Improvements in tomato yields and water use efficiency, enhancing the level of technology, are the key factors for reducing environmental impact. The adaptation of impact indicators will be necessary to apply LCA methodology in high tropical farming systems.
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An advanced prototype of a phytomonitor was developed at Humboldt University in the frame of the national ZINEG project for low energy greenhouses (www.zineg.de). Ten leaf cuvettes were allocated to different tomato leaves in the canopy to get a representative average of the gas exchange of younger and older leaves under shaded and non-shaded conditions. The cuvettes were constantly attached to several plants for the whole cultivation period, with a seven-day interchange period. Two instruments were used in two greenhouses with different climate control systems (semi-closed and a ventilated greenhouse as reference) to show the differences in the climate – canopy interaction. With the help of the Mollier Plot Analyzer software, developed at Humboldt University, the climate comfort zone of the canopy for maximum photosynthetic light use efficiency was found. With the calculation of the accumulated CO2 and transpired water, the differences in the yield expectation for the next four weeks and the plant consumed water was estimated. From the result of the light use efficiency evaluation with the Mollier Plot Analyzer, the comfort zone for tomato growing in the semi-closed greenhouse was estimated to be in a temperature range from 20 to 28°C, with a relative humidity of 75 to 95%. In the ventilated greenhouse most of the condition points with lower light use efficiency were found to have higher temperature and lower relative humidity. The difference in the yield between the semi-closed and ventilated greenhouse was shown by the difference in CO2 uptake measured by the phytomonitors and the difference in the photosynthetic light use efficiency of the canopy in both greenhouses. The calculated water consumption using the gas exchange measurement data showed a high correlation to the measured water consumption. With this result it should be possible to apply gas exchange measurement systems not only for climate control but also for irrigation control.
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Blossom‐end rot is not the result of a single factor, but from the interaction of several factors. To prove this and to get information on how to lower the detrimental effect of blossom‐end rot, a multifactorial trial was conducted. Tomato plants, grown in rockwool in a circulating system, were fed with 0.75, 1.25, and 1.75 mM phosphate (P) and two calcium (Ca) levels resulting in 4.0 and 11.2 mM Ca in the leachate. Two air humidity levels were maintained. The low Ca, P, and humidity resulted in higher levels of blossom‐end rot than the higher levels of these factors. The increasing effect of low P on blossom‐end rot could be the result of the fact that at low P, ammonium (NH4) addition was higher than at high P, because at low P, the pH tended to increase and pH control was done by adding NH4. However, it is possible that an effect of P remains. The combination of the factors at the low levels gave rise to 59% blossom‐end rot. In this treatment, plants suffered in course of time from severe leaf deformation and die‐back of the growing point. Therefore, the experiment had to be stopped earlier than planned. The cause of the deformation was the high amount of blossom‐end rot. Plants were not able to store assimilates in fruits. To avoid blossom‐end rot, growers have to maintain the P concentration in the root environment of at least 1.7 mM and a Ca concentration of 8 to 9 mM. Air humidity should be kept high.
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The collector efficiency factor F′, besides the collector heat loss coefficient UL, characterizes the thermal quality of a solar collector. As F′ is strongly influenced by the tube distance w and the absorber plate thickness δ, F′ is also correlated with the material content of absorber plus tubing. Due to the future mass production of collectors and to the restricted copper resources (in the literature, a range until 2026 is given), the role of material savings can be expected to become more and more important. This paper focuses on the correlations between F′ and the material content of absorber and tubing for flat-plate collectors with the fin-and-tube geometry. The correlations between w, δ, F′ and material content are presented in a new type of nomograph. This nomograph indicates the values of w and δ that minimize the material content (for a given F′). For a typical absorber with F′=0.90, material savings of 25% can theoretically be achieved without any deterioration of F′, by reducing the absorber plate thickness and the tube distance. The resulting plate thickness is below 0.1 mm; the respective tube distance will be about 7 cm. Practical restrictions are discussed. In a sensitivity analysis, the influence of different parameters on F′ is investigated. The most important parameters are w, UL,δ and the Reynolds number. The technique chosen for contacting tube and absorber has only a minor influence on F′.
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The objective of this study was to examine the energy use patterns and cost of production in greenhouse and open-field grape production. Data used in the study were obtained from the experiment conducted at the Akdeniz university research field. In the study, energy values were calculated by multiplying the amount of inputs and outputs by the related energy conversion factors. The results indicated that total input energy use in greenhouse and open-field production was found to be 24513.0 and 23640.9MJ/ha, respectively. However, the output energy of greenhouse grapes (73396.0MJ/ha) was lower than open-field grapes (120596MJ/ha). The output–input ratio for greenhouse and open-field grape production was found to be 2.99 and 5.10, respectively. The economic analysis revealed that production costs for greenhouse grapes were higher than open-field grapes but greenhouse grapes were more profitable than open-field due to premium prices for greenhouse grapes.