CO2 Enrichment

05 10 15 20 25 30

Mean daily temperature

Fig. A.5 Means of daily global radiation for Agadir (Morocco), Gafsa (Tunisia) and Almeria (Spain)

Annex B

Calculation of fuel consumption in Sect. 12.2.

1. Almeria, Spain (36°50’N).

tid = 16°C, tst = 2°C, u = 7 W/(m2 K), Ac/Ag = 1.33, see 12.5. Mean night temperature (°C)

tmmin according to Miiller (1996)

A tmaxd—tmind (Miller 1996)

£/n/(24-dj) Table12.3 (Hallaire 1950),

dj = mean daylight hours = /(latitude, month) according to Allen et al. (1998).

	tmmin	A	dl	S/n/(24-dl)	tmn
December	9.2	7.4	9.5	0.375	12
January	8	7.6	9.7	0.375	10.8
February	8.5	7.6	10.7	0.345	11.1
March	10.5	7.3	11.7	0.33	12.9

Fuel consumption tid = 16°C.

Qmonth (kWh/m2 month) = according to 12.5

	nd		nn = 24-dl	At	Qmonth
December	31		14.5	2	8.36
January	31		14.3	3.2	13.2
February	28		13.3	2.9	10.1
March	31		12.3	1.1	3.9
Yearly fuel consumption Qy	= SQmonth = 35.6 (kWh/m2 year)
2. Antalya, Turkey (36°53’N).
The same assumptions.
Mean night temperature
	tmmin	A	dl	S/n/(24-dl)	tmn
December	7.8	8.9	9.5	0.375	11.1
January	6.1	8.9	9.7	0.373	9.4
February	6.7	8.9	10.6	0.345	9.8
March	7.8	10	11.7	0.33	11.1
Fuel consumption Qmonth (kWh/m	2 month), tid =	16°C.
	nd		nn = 24-dl	At	Qmonth
December	31		14.5	2.9	12.1
January	31		14.3	4.6	18.98
February	28		13.3	4.2	14.7
March	31		12.3	2.9	10.3

Yearly fuel consumption Qy = SQmonth = 56.1 (kWh/m2 year)

3. Catania, Sicily (37°30’N).

The same assumptions. Mean night temperature

	tmmin	A	dl	Sfn/(24-dl)	tmn
December	9.4	6.3	9.5	0.375	11.8
January	7.7	6.4	9.7	0.375	10.1
February	7.9	7.2	10.6	0.345	10.4
March	9.3	7.3	11.7	0.33	11.7
April	11.6	7.4	13	0.31	13.9
Fuel consumption Qmonth (kWh/m2 month), tid =	16°C.
	nd		nn = 24-dl	At	Qmonth
December	31		14.5	2.2	9.2
January	31		14.3	3.9	16.1
February	28		13.3	3.6	12.6
March	31		12.3	2.3	8.2
April	30		11	0.1	0.3
Yearly fuel consumption Qy	= SQmonth = 46.4 (kWh/m2 year).

Annex C

Adapted calculation sheet for the reference evaporation ET0 in unheated green­houses, using the Penman-Monteith equation (Allen et al. 1998) and example for Almeria in middle of May (36°50’N, 7 m altitude).

Given parameters (Muller 1996)

Mean max temperature Tmax (°C) 22

Mean min temperature Tmin (°C) 14.9

Altitude z (m) 7

Mean daily global radiation qRS kWh/m2 (1 kWh = 3.61 MJ) 6.7

qRS = 6.7 x 3.61 = 24.2 (MJ/m2 day)

Latitude 36°50’N

Actual duration of sunshine hours (h/day) 9.9

Adapted parameters for unheated greenhouses

Mean max inside temperature Tgmax = Tmax + 4(°C) 26

Mean min inside temperature Tgmin = Tmin + 2(°C) 16.9

Mean inside temperature Tgmean = (Tgmax + Tgmm/2) 21.45

Inside global radiation qRSi = t x qRS MJ/(m2 day) 16.9

For single plastic film t = 0.7

Inside relative humidity RH = 75-80 (%) 80

Air velocity v = 0.3 m/s Slope of vapour pressure Д = /(Tmean), (kPa/°C), Table 2.4, Annex 2 (Allen et al. 1998)	0.3 0.157
Psychrometrical constant g = /(z), (kPa/°C), Table 2.2, Annex 2, (Allen et al. 1998)	0.067
Vapour pressure deficit eS—eA Saturation vapour pressure eS = (eSTgmin + eSTgmax)/2 (kPa), Table 2.3, Annex 2, (Allen et al. 1998)	(1.938 + 3.36)/2 = 2.65
Actual vapour pressure eA = eS x RH/100 (kPa)	2.12
Radiation Net radiation q^ = qRNS-qRNL (MJ/m2 day) Net solar radiation qRNS = 0.77 x qRSI qRsi = t x qRs (MJ/m2day)	13.01
Long-wave radiation: qRNL = (s x Tgmax4 + s x ^//2) x (0.34-0.14ffi) x (1.35qRSi/qRo-0.35) sT4, Table 2.8, Annex 2 (Allen et al. 1998) (s x Tgmax4 + s x Г„тіп4/2)	(39.27 + 34.75)/2 = 37.01
Clear sky radiation qRO = 0.75qRA (near sea level) or qRO = (0.75 + 2 x 10 5 x z)qRA Extraterrestrial radiation qRA = /(latitude) (MJ/m2 day)	40
Table 2.6, annex 2, (Allen et al. 1998) qRO (MJ/m2 day) qRSi/qRO (MJ/m2day) qRNL (MJ/m2day) Net radiation qRN (MJ/m2day)	30 16.9/30 = 0.56 2.1 10.91
Soil heat flux qRG can be neglected ET0 (L/m2 day)	3.16

20 c

CD

15

CD

10

[2] 0

A three-span round-arched plastic-film greenhouse, 6.4 m width of span, 12 m length, 2.5 m height to the eave, 4 m ridge height, 230 m2 floor area, has been investigated with two ventilation openings (Munoz et al. 1999):

G1: Half through roof flap vent on each span, linked to the ridge and opened 0.6 m at the gutter, maximum vent opening AV = 21.6 m2, AV/AG = 0.094.

G2: The flap vent was replaced by a rolling-up roof vent so that each span has vent opening of half roof area. AV = 128.5 m2, AV/AG = 0.56.

An anti-aphid insect screen of 0.4 x 0.4 mm mesh size and a porosity e = 0.45 was installed on all vent openings.

The CO2 concentration inside a greenhouse can drop significantly below outside level when a dense crop is growing, even if the greenhouse is well-ventilated. The concentration can drop to less than 200 vpm during winter in mild climate regions. As the CO2 concentration limits the photosynthesis of most vegetable species, the productivity decreases. The optimal CO2 concentration for growth and yield seems to be 700-900 vpm (De Pascale and Maggio 2005, 2008). The CO2 concentration should be kept to at least the outside level, but CO2 enrichment is not a current practice in mild climates up to now.

The production loss due to CO2 depletion may be higher than the production loss due to a reduced temperature through ventilation (Stanghellini et al. 2008). The enrichment of greenhouse air with CO2 leads to better plant growth, shorter cropping times, and higher quality. Therefore a combined control of ventilation and CO2 enrichment with low-cost CO2 sources may result in improved and economically viable methods for crop growth in greenhouses.

Production losses in greenhouses are influenced by two main factors:

• Sufficient ventilation to avoid CO2 depletion.

• Maintaining a higher temperature by heating on sunny, chilly days in spite of

CO2 depletion.

It is necessary to assess running and installation costs for CO2 enrichment or heating to find out the optimal strategy for climate control. The compensa­tion of CO2 depletion by increased ventilation or even by CO2 enrichment seems to be cheaper than compensation of production loss by heating. A good manage­ment strategy can be to ventilate as much or as little as necessary for temperature and humidity control, and to control CO2 concentration inside the greenhouse up to outside level when ventilation is being used, and to higher levels when no or little ventilation is required for temperature control (Stanghellini et al. 2008,

2009) .

C. von Zabeltitz, Integrated Greenhouse Systems for Mild Climates,

DOI 10.1007/978-3-642-14582-7_16, © Springer-Verlag Berlin Heidelberg 2011

The CO2 concentration can be raised as follows (von Zabeltitz 1999):

• Technical carbon dioxide from bottles or tanks.

• Exhaust gases from gas burner for CO2 enrichment with simultaneous heat production.

• Exhaust gases from directly fired air heater with gas burner.

• Straw between the plant rows, enriched with fertiliser and wetted. CO2 is released during decomposition, but the amount of CO2 cannot be controlled.

Exhaust gases from oil and coal heaters must not be used because of the content of sulphur dioxide.

Exhaust gases from gas burners can be led directly into the greenhouse (Fig. 16.1). Gas will be burned, and the CO2 is blown with the circulating air into the greenhouse. Special control systems are necessary, and care must be taken that no carbon monoxide is formed. It is practical to mix the exhaust gas with fresh air. The water vapour and heat production, as well as the maximum allowed concentra­tion, have to be taken into consideration.

CO2 from an air heater (Fig. 16.2) can only be produced while it is in operation and when heating is needed, which is normally necessary only at night in mild climate regions. Some of the combustion gases are tapped off and used for CO2 enrichment.