Note: Descriptions are shown in the official language in which they were submitted.
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GREENHOUSE HEATING SYSTEM
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention generally relates to greenhouses and, more
particularly, to a greenhouse heating system.
Description of the Prior Art
United States Patent No. 4,790,478 issued to Sauvageau on
December 13, 1988 teaches heating a soil suitable for cultivation in a
greenhouse. An
immersed water-bed which acts as a heat radiator is provided underneath the
complete surface of the cultural soil.
The heating of the cultural soil causes at least part of the water
contained in the soil to evaporate, thereby giving rise to the generation of
mist or fug
1 S within the greenhouse. The lowering of the level of humidity in the
cultural soil is
obviously not suitable for growing plants. In addition, the ambient air in the
greenhouse also heat relatively slowly due to the low heat conducting
properties of
the soil.
Therefore, there is thus a need for a new plant growing environment
which addresses the above mentioned issues.
SUMMARY OF THE INVENTION
It is therefore an aim of the present invention to provide a heating
system suited for use in a greenhouse.
It is also an aim of the present invention to provide a greenhouse
heating floor system adapted to store energy in the form of heat and release
it over an
extended period of time.
It is a further aim to provide savings in greenhouse heating costs.
Therefore, in accordance with the present invention, a plant growing
environment comprising: a greenhouse defining a building envelope
circumscribing
an internal space having a surface area; a heating floor comprising a pool of
heat
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conducting fluid contained in a sealed enclosure, the sealed enclosure having
a top
surface extending over a major portion of said surface area, said top surface
providing a soil-less substrate for growing plants in containers, the plant
containers
being supported on said top surface, the pool of heat conducting fluid storing
and
releasing heat, and a heat source in heat exchange relationship with the pool
of heat
conducting fluid; a first temperature sensor sensing the temperature (T1)
inside the
building envelope; and a control unit coupled to the temperature sensor for
managing
the operation of the heat source as a function of T1.
In accordance with a further general aspect of the present invention,
there is provided a heating system for controlling the temperature inside a
greenhouse, comprising an enclosure containing a pool of heat conducting fluid
for
storing and releasing heat inside the greenhouse, a sun ray absorbing surface
atop of
said enclosure for receiving plants in pots, the sun ray absorbing surface
being in heat
exchange relationship with the pool of heat conducting fluid through the
enclosure, a
heat source connectable in heat exchange relationship with said pool of heat
conducting fluid, and a temperature sensitive control unit selectively
operatively
coupling said heat source to said pool of heat conducting fluid.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a schematic elevation view of a greenhouse having a floor
heating system in accordance with an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Now referring to Fig. 1, there is shown a greenhouse 10 having a
conventional skeletal framework including among others a number of vertical
supporting columns and transversal horizontal trusses. A light transmitting
membrane
12 is stretched over the skeletal framework to circumscribe an internal space.
The
structural membrane 12 can be made out of a polyethylene sheet or other
materials
such as polycarbonate, glass or other forms of plastic suited to form a
building
envelope. The construction of the greenhouse is conventional and not material
to the
present invention.
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The internal temperature (T1) inside the greenhouse 10 is efficiently
and economically controlled through the operation of a floor heating system
14. The
floor heating system 14 comprises a pool formed by a sealed enclosure 16
filled with
a heat storing mass including crushed stones, such as gravel 18, immersed in a
heat
conducting liquid 20. An insulating mat 23 is preferably installed underneath
the pool
to insulate it from the underlying soil. The gravel 18 provides a solid and
stable floor
base for the greenhouse 10. According to a preferred embodiment, the heat
conducting liquid 20 may be water. It is noted that the gravel 18 could be
replaced by
another solid heat absorbing material. The liquid level in the enclosure 16 is
equally
maintained with the upper area of gravel 18. A phase change material (PCM)
could
also be provided in the enclosure 16 to improve the heat storing capacity of
the pool.
The PCM is preferably chosen to have a phase changing temperature close to an
operational temperature of the pool. The sealed enclosure 16 preferably
extends over
the entire surface area of the greenhouse 10. It could extends over only a
portion of
the surface area of the greenhouse 10 but the heat distribution would be less
uniform
across the greenhouse 10.
The enclosure 16 is adapted to contain the gravel 18 and the water 20
while allowing heat to dissipate from the pool into the greenhouse 10. The top
surface of the enclosure 16 is preferably made of a black heat absorbing
material to
absorb the sun rays passing through the membrane 12 of the greenhouse and
transfer
the heat to the enclosure content. Plants in pots 24 are placed directly on
that black
membrane material. The enclosure 16 can entirely be made of a flexible
impermeable
membrane.
A drop-by-drop irngation system is preferably used to water the plants
in the pots 24. In this way, the enclosure 16 can itself contribute to heat up
the heat
storing contents thereof.
Alternatively, a plant growing mat 22, such as a sub-irrigation carpet,
can be laid down over a top surface of the enclosure 16 for receiving pots 24
or other
containers. In the case of sub-irrigation carpets, the pots 24 have a
permeable base to
allow water to pass from the carpet into the pots through capillary action.
The plant
growing mat 22 can be integrated to the enclosure 16.
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No layer of cultivation soil is provided over the enclosure 16, as taught
in US Patent No. 4,790,478. As described above, the plants are rather grown in
containers resting on the top surface of the enclosure 16. The presence of a
layer of
soil on top of the heat releasing enclosure 16 would result in the formation
of fog or
mist within the greenhouse 10.
The principal source of heat for the pool is preferably provided in the
form of a boiler 26 connected in heat exchange relationship with the content
of the
enclosure 16 via a closed piping circuit 28 extending through the enclosure
16. Hot
water from the boiler 26 is circulated through the circuit 28 via the
operation of a
pump 30. The hot water is preferably circulated along a serpentine path
through the
enclosure 16 to provide for maximum heat transfer from the hot water (the
working
fluid) to heat storing mass (i.e. gravel 18 and water 20) in the enclosure 16.
The hot
water is returned back into the boiler 26 through the return line of the
circuit 28, as
depicted in Fig. 1.
A valve 32 is provided preferably in the feed line of the piping circuit
28 at the outlet of the boiler 26 to selectively prevent hot water flow
through the
piping circuit 28 between the boiler 26 and the enclosure 16. The valve 32 is
operated
by a control system 34 responsive to a temperature change in the greenhouse
10.
According to an embodiment of the invention, the control system 34 will send a
command to open the valve 32 upon detection that the temperature T1 in the
greenhouse 10 starts to fall under a predetermined value. The control system
34 may
comprises a thermostat (not shown) coupled to a temperature sensor 36 sensing
the
temperature T1 in the greenhouse 10. According to a more elaborate embodiment,
the
control system 34 may be further coupled to second and third temperature
sensors 38
and 40 respectively sensing the temperature T2 within the enclosure 16 and the
temperature T3 of the ambient air outside the greenhouse 10. The temperature
data
(T1, T2 and T3) are fed to the control system 34 which according to an
algorithm
thereof determined whether the valve 32 should be opened or closed. Based on
the
temperature T1 inside the greenhouse, the outside temperature T3 and the
temperature T2 of the heat storing mass, the control system 34 will open or
close the
hot-water supply. The use a control system in combination with a valve permit
to at
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least reduce energy waste associated with passive circulation of hot water
through the
circuit 28 due to natural thermal siphoning phenomenon.
A fourth temperature sensor 42 is also provided to provide data on the
temperature of the hot water in the boiler 26. The fourth temperature sensor
42 is also
preferably connected to the control system 34, which processes the data
received on
T1, T2, T3 and T4 to manage the operation of valve 32.
According to another embodiment, the principal heat source could be
provided in the form of an electric heating system. In this case, the control
system
would control the operation of an on-off switch rather the operation of valve
32.
Various other type of heat source could be used as well.
The above described plant growing environment is advantageous in
that it requires less energy to maintain a stable temperature inside the
greenhouse 10,
while providing for an excellent plant growing environment. The above
described
greenhouse floor heating system when used in association with the cultivation
of
plants in pots (i.e. container growing) provides excellent plant growing
results as
compared to cultivation in standard greenhouse arrangements.
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