Acta Horticulturae

Figure 1. Basic structure of a typical
energy-saving, greenhouse.
outside winter temperatures dip to -20° to -
10°C, even -25°C, in the north of China? The
answer is that the continental, monsoon climate
of China receives high solar radiation in
winter despite the very low temperatures in
northern zones. While winter sunlight intensity
is only 50%-60% of summer radiation, the
solar radiation provides enough heat that can
be stored by heat-conservation strategies
(Chen 2001).
A
B
C
Figure 2. China’s energy-saving
greenhouse ranges. A. Note straw
mat on ridges. B. A cluster of energy-saving
greenhouses showing
headhouses. C. Energy-saving
greenhouse in mountainous area.
walls for insulation against the cold outside
wind. The walls are constructed with bricks
and thermal-preservation materials. The front
roof has a transparent plastic film for receiving
sunlight. During the night, the plastic film is
covered by a mat made of insulating materials.
In the morning, once the air temperature
inside the greenhouse rises, the mat is rolled
up. In the afternoon, when the air temperature
inside greenhouse goes below 17°-18°C,
the mat is rolled down over the front roof to
prevent heat loss. A “cold-proof” ditch (0.5-
1.0 m deep, filled with insulating materials,
such as straw and manure) reduces heat
exchange through the soil between the inside
and outside of the greenhouse. The ridge of
the greenhouse is usually 3 to 4 m high, the
span is 6 to 8 m wide, and the length is 40 to
100 m long. The back wall is 0.5 to 1.2 m
thick. The unit area is about 300-800 m 2 .
The energy-saving greenhouse is a special
type of structure (Fig. 2). The heat energy
resource comes from the solar radiation and
depends on structural and heat conservative
technology (Sun 1993; Yang and Chen 1994).
Even in the severe cold winter season of north
China, air temperature inside the greenhouse,
even without supplemental heating, is sufficient
for cool-season leafy vegetables such as
celery and Chinese chive and also warm-season
vegetables such as tomato, cucumber,
sweet pepper, eggplant, and even watermelon
(Fig. 3). In general, capital costs and operational
expenses are much lower than that of a
modern multi-span greenhouse.
In the winter on a clear day, the greenhouse
can receive sunlight for 6 hours with light
intensity averaging 20-40 klx. The maximum
temperature inside the greenhouse can be
higher than 25°C, sometimes even up to
30°C, and can last 3-5 hours. Temperatures at
night are not lower than 10°C, and on cloudy
days, not lower than 6°C. Night temperature
differences between inside and outside of the
greenhouse can reach 30°C. In this microclimate
condition, certain cultural practices
improve plant growth. These include adoption
of low temperature resistant cultivars, grafting
to cold resistant rootstocks, multi-layer polyethylene
film covering, irrigation, and temporary
supplementary heating for warm season
crops such as tomato and cucumber. Leafy
vegetables perform well in the greenhouse,
even in unexpected cold and cloudy days.
Why can the energy-saving greenhouse without
a heating system grow vegetables when
STRUCTURE
In the earlier developing stage of the energysaving
greenhouse, the greenhouse was built
based on farmers’ experiences only, using
cheap and simple materials. In the Beijing district
the internal growing space of the greenhouse
was small with a span of 5.0-6.0 m at a
ridge height of 2.6-3.0 m. The wall was built of
dry earth, brick, and concrete; the front roof
frames were made of bamboo or wood, and
the outside covering mat made of straw or cattail.
Since the late 1980s considerable research
work has been conducted to improve heat
preservation and progress has been rapid. As a
result, horticultural crop production in the
energy-saving solar greenhouses is rapidly
increasing.
Dimensions. Based on 20 years of research,
the span of the greenhouse has been gradually
enlarged, based on local climatic conditions.
In Northeast and Northwest China, the span is
6.0-7.0 m where the lowest winter temperature
is below -17°C. In North China the span is
6.5-7.5 m where the lowest winter temperature
is between -17° to -12°C. However, if the
lowest temperature does not reach -12°C, the
span can be 7.5-8.0 m.
Greenhouse length is site dependent. The
back (north) wall is about 2.0-2.4 m high, the
ridge is 3.2-3.5 m high, which depends on the
span and local climate. At latitude 40°N, the
span can be 7.0, 7.5, or 8.0 m, and the ridge
2.9, 3.2, or 3.5 m, respectively. In warmer
locations, the span and ridge are wider and
higher.
Front Support and Wall Body. The front support
is made of bamboo or steel pipe covered
with 0.1 mm thick polyethylene film. The east,
west, and north walls of the greenhouse are
0.5 to 1.0 m thick and made of bricks. During
temperature warm-up during the day inside
the greenhouse, the wall is an endothermic
body, and during cool-down at night, the wall
body is exothermic. Therefore, the reasonable
structure of the wall is a double layer. Between
the two brick layers is a thermal-protective
insulation material such as perlite, coal cinder,
sawdust, or polystyrene in order to prevent
heat loss.
The Back Roof. The back roof of the greenhouse
is a multi-layered structure composed of
wood, straw, coal cinder, polystyrene, and
cement board. The roof consists of water-
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