Scientific Papers Series Management , Economic Engineering in Agriculture and Rural Development Vol. 13 , Issue 1, 2013
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THERMAL CALCULATION FOR THE PRODUCTION OF VEGETABLES
GREENHOUSE
Ancu aăJURCO1, Dumitru MARUSCIAC1, Grigore ONACIU2, Eugen JURCO2
1
Tehnical University of Cluj-Napoca, Department of Civil Engineering and Fundations,
RomсnТКĽ PСonО: +40 0264599061
2
University of Agricultural Sciences and Veterinary Medicine, Cluj-Napoca, 3-5 Calea Manastur, Cluj County, Romania, Phone: +40 0264/596384
Corresponding author: jurco_eugen@yahoo.com
Abstract.
This paper presents the calculation regarding thermic transmision through the closing elements made for a greenhouse designed for salat production, pea, spinach and cabbage, D.M. greenhouse type, with medium and large openings (12...30m) having a light roof with spatial structure from bars and thin walls made from galvanized steel or aluminium and designed at the Technique University from Cluj-Napoca. The greenhouse opening is 15.90 m, the total lenght is 40.50m and 669.53 sqm surface with 643.95 sqm usable area. After analyzing the thermal calculations for the production of vegetables greenhouse show that the heat losses are insignificant, advantage is given by the light roof with spatial structure from bars and thin walls made from galvanized steel or aluminium.
Key words: greenhouse, roof with spatial structure, thermal calculation
INTRODUCTION
Greenhouses are constructions for extra-season production of vegetables, flowers or seedlings, having external surfaces made from glass or other transparent materials, in wich is realized an artificial microclimate favorable to crops, independently of season and the weather condition. The evolution of greenhouses construction led to different achieving conceptions of schemes for strength structure and closing elements, depending on the types of obtained crops and the local conditions, particularly for individual and block greenhouses [7].
MATERIALS AND METHODS
The calculation regarding thermic transmision through the closing elements was made for a greenhouse designed for salat production, pea, spinach and cabbage. At the Technique University from Cluj-Napoca was designed the D.M. greenhouse type, with medium and large openings (12...30m) having a light roof with spatial structure from bars and thin walls made from galvanized steel or aluminium (fig. 1). The new type of greenhouse is
equipped with all possible thermal energy saving technics and shading systems using a single or double screen etc.
RESULTS AND DISCUSSIONS
Calculations were prepared according to STAS 1907/3-97. The characteristic elements of the building location are:
- third climate area related to Romanian climate zoning map;
- orientation to the cardinal points: EV longitudinal direction, with the main facade to the west;
- the forth aeolian area related to settlements framing map in windy areas;
- the importance class related to P 100-2006; - seismic zone related to P100-2006:F, ag=0.08;
- corner period related to P100-2006: TC=0.7 sec;
Bearing structure and finishes:
Scientific Papers Series Management , Economic Engineering in Agriculture and Rural Development Vol. 13 , Issue 1, 2013
PRINT ISSN 2284-7995 , E-ISSN 2285-3952
192
Fig. 1. Greenhouse for the production of lettuce, peas, spinach and cabbage
Scientific Papers Series Management , Economic Engineering in Agriculture and Rural Development Vol. 13 , Issue 1, 2013
PRINT ISSN 2284-7995 , E-ISSN 2285-3952
193
The bearing structure made of rolled galvanized steel, will have 3 openings of 5.70 m, 4.50 m and 5.70 m and spans of 4.50 m, and as closing material will be used the glass, plastic foil and structured polycarbonate boards (Twinwall sau Triplewall). Prefabricated foundations have deep (from the natural field level) of -2.40 m and the socle level over the field at +0.30 m.
The envelope elements have the following composition:
- The exterior walls are made of glass, plastic wrap or structured polycarbonate boards (Twinwall or Triplewall) and metal frame. Glass, plastic wrap or structured polycarbonate boards must have the following qualities: great penetrability for sunlights, low reflection, high resistance at applications. Optimal thickness for lateral walls is 3 mm. - The roof is made from glass, plastic wrap or structured polycarbonate boards that have the following qualities: elasticity, flexibility, high resistance at applications, low specific weight, high optical transparency.
Land area on which is located the greenhouse: Sgreenhouse= 15.90m*40.50m= 643.95m2
Glass surface:
SFL=1.50m*40.50m*2+1.50m*15.90m*2=
=169.2m2
SFA= 17.81m*40.50m= 721.305m2
SF= SFL+ SFA= 890.505m2
Calculation of heat needed for greenhouse
Calculations shall be prepared according to STAS 1907/3-92.
So, is calculated:
50 . 0 : ) s (
for Sgreenhouse= 643.95m2
In the forth windy area (related to STAS 1907/3-92) "v" is the calculation speed for wind: s m 4 :
v
s m 35 . 6 v3 4
i, e superficial coefficients of heat transfer are calculated with the following relations: K m w 91 . 7 ) s ( v 63 . 1 65 . 4 : 2 i i
> 6.4 then n:=1.70
n
- penetration coefficient;
10 . 0 : n
for sealed greenhouses; n- leakage coefficient of the greenhouse; n:=1.70 for sealed greenhouses;
K / kg KJ t t i i : e i e i where:
ii- indoor air enthalpy (KJ/kg);
ie- outdoor air enthalpy (KJ/kg) or (Wh/m3);
- greenhouse is intended to produce salad ti:=
140C ui:= 70%
- greenhouse is placed in climate zone III te:=
-180C ue:= 80%
- ti- interior temperature of calculation;
- te- conventional temperature of outdoor air
according to climate zoning map of Romania;
3 i m kcal 118 . 9 : i 3 e m kcal 07 . 5 : i
K m kcal 443 . 0 t t i i : 3 e i e i
Kconv- global coefficient of heat transfer due
convection through glazed surface is determi
ned with the relation:
K m W 711 . 6
Kconv 2
c- coefficient that takes into account the occurrence frequency of hours with clear sky associated to conventional temperature of outdoor air, with the value c=0.10 regardless the climate area;
K m W 711 . 6
Kconv 2
K m W 10 . 0 :
c 2
ti:= 140C te:= -180C
Sgreenhouse = 643.95m2 SF = 890.505m2
n1
ET n ET
conv: K 1 K
Scientific Papers Series Management , Economic Engineering in Agriculture and Rural Development Vol. 13 , Issue 1, 2013
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Global heat demand "Q" of a greenhouse is calculated with the relation:
W x
t t c K
S S K m
W S
Q conv i e
greenhouse F greenhouse
5
2
10 618 . 2
26 . 3 35
. 0 26
. 1 :
CONCLUSIONS
After analyzing the thermal calculations for the production of vegetables greenhouse show that the heat losses are insignificant, advantage is given by the light roof with spatial structure from bars and thin walls made from galvanized steel or aluminium, model developed at the Technical University of Cluj-Napoca according to invention D.M. new type of greenhouse. The modern greenhouse has many new design with medium and large openings and with free spaces for the shielding installation under the roof and along the side walls. The energy crisis and the growth of fuel prices, from the last period, has generated interest in using new systems for the protection and use of heat sources, such as double-walled constructions to reduce heat loses, constructions with plastic closures without technique heating, using new sources of heating from solar, wind, geothermal energy etc.
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