Method of and apparatus for reducing the heat load on a greenhouse

A method for controlling the condition of air in a greenhouse containing plants having a canopy, said method comprising:

• a) exhausting air from the greenhouse during periods of low light levels for controlling humidity in the greenhouse;
• b) replacing air exhausted from the greenhouse at a location below the plant canopy;
• and
• c) heating the replacement air by exchanging heat with the air exhausted from the greenhouse.

In combination:

• a) an enclosure having growing plants that provide a source of moisture;
• b) vent means for selectively exhausting air from the enclosure;
• c) a reservoir of brine;
• d) a first air-brine-vapor heat exchanger for contacting air in the enclosure with concentrated brine supplied from said reservoir and thereby dehumidifying the air and producing dilute brine;
• e) means for returning the brine form the first heat exchanger to the reservoir;
• f) a second air-brine-vapor heat exchanger supplied with brine from said reservoir for contacting air exhausted from the enclosure;
• g) means for heating the exhausted air before it is contacted by the second heat exchanger;
• h) said second air-brine-vapor heat exchanger being constructed and arranged so that the heated air evaporates water from the contacted brine for concentrating the same before the latter is returned to the reservoir and for increasing the humidity of the exhausted air.

In combination:

• a) an enclosure containing growing plants that provide a source of moisture;
• b) a reservoir of brine;
• c) a first air-brine-vapor heat exchanger for contacting air in the enclosure with concentrated brine supplied from a reservoir and thereby condensing water vapor thereby dehumidifying the air and producing dilute brine;
• d) means for returning brine from the first heat exchanger to the reservoir;
• e) a second air-brine-vapor heat exchanger supplied with brine from said reservoir and with air for contacting the air with brine;
• f) means for heating the contacted air in the second air-brine-vapor heat exchanger before the air is contacted by said second heat exchanger;
• g) said second air-brine-vapor heat exchanger being constructed and arranged so that the heated air evaporates water from the contacted brine for concentrating the same before the latter is returned to the reservoir and for increasing the humidity of the air contacted with brine in said second heat exchanger.

A method for using a latent heat converter to control the transpiration of plants in a greenhouse under low light level conditions, the method comprising the steps of:

• a) minimizing venting of the greenhouse during periods of low light level conditions;
• b) heating the greenhouse during such periods in a way that minimizes the rate of convective heat flow of air through the canopy of the plants;
• and
• c) using the latent heat converter to dehumidify the air in the greenhouse during such periods.

A method for operating a greenhouse comprising the steps of:

• a) insulating the structure of the greenhouse to reduce the transfer of sensible heat through the structure;
• b) heating the greenhouse during periods of low light levels in a away that minimizes the flow of air currents through the canopy of the plants;
• c) minimizing the venting of the greenhouse during such periods;
• and
• d) dehumidifying the air in the greenhouse.

In combination:

• a) a greenhouse containing growing plants defining a plant canopy within the greenhouse;
• and
• b) means for reducing the rate of flow across the canopy due to thermal air currents during periods of low light levels;
• and
• c) wherein the greenhouse includes vent means for selectively venting the greenhouse;
• control means for minimizing venting of the greenhouse at night;
• heater means for heating the greenhouse during said periods;
• and dehumidifier means for dehumidifying the greenhouse during said periods.

In combination:

• a) a greenhouse containing growing plants defining a plant canopy within the greenhouse;
• b) means for minimizing the rate of convective heat flow of air through the canopy during periods of low light levels;
• c) a first air-brine-vapor heat exchanger for contacting air in the greenhouse with concentrated brine supplied from a reservoir and thereby dehumidifying the air and producing dilute brine that is returned to the reservoir;
• d) means for exhausting air from the greenhouse to the atmosphere;
• e) a second air-brine-vapor heat exchanger supplied with brine from said reservoir for contacting the brine with air exhausted from the greenhouse;
• f) means for heating the exhausted air before it contacts the brine in by the second heat exchanger;
• g) said second air-brine-vapor heat exchanger being constructed and arranged so that the heated air evaporates water from the contacted brine for concentrating the same before the latter is returned to the reservoir and for increasing the humidity of the exhausted air;
• and
• h) heat exchanger means responsive to the humidified air for transferring heat contained therein back to the greenhouse.

A method for using a latent heat converter to control the transpiration of plants in a greenhouse under low light level conditions, the method comprising the steps of:

• a) minimizing venting of the greenhouse during periods of low light level conditions;
• b) heating the greenhouse during such periods in a away that minimizes the rate of convective heat flow of air through the canopy of the plants;
• and
• c) using the latent heat converter to dehumidify the air in the greenhouse during such periods;
• d) wherein the latent heat converter that dehumidifies the air is operated such that dehumidification is carried out under conditions of substantially constant enthalpy wherein the heat of condensation released when water vapor in the air is condensed is returned to the air almost immediately.

A combination comprising:

• a) a greenhouse containing growing plants defining a plant canopy within the greenhouse;
• and
• b) means for controlling the rate of convective heat flow of air through the canopy during periods of low light levels;
• c) wherein the greenhouse includes vent means for selectively venting the greenhouse;
• control means for minimizing venting of the greenhouse at night;
• heater means for heating the greenhouse during said periods;
• and dehumidifier means for dehumidifying the greenhouse during said periods;
• and
• d) wherein said dehumidifier means is constructed and arranged to dehumidify the air under conditions of substantially constant enthalpy wherein the heat of condensation released when water vapor in the air is condensed is returned to the air almost immediately.

In combination:

• a) a greenhouse containing growing plants defining a plant canopy within the greenhouse;
• and
• b) means for reducing the rate of convective heat flow of air through the canopy during periods of low light levels, said means for reducing including:
• (1) a first air-brine-vapor heat exchanger for contacting air in the greenhouse with concentrated brine supplied from a reservoir to thereby dehumidify the air and produce dilute brine that is returned to the reservoir;
• (2) means for exhausting air from the greenhouse to the atmosphere;
• (3) a second air-brine-vapor heat exchanger supplied with brine from said reservoir for contacting air exhausted from the greenhouse with said brine and thus concentrating said brine;
• (4) means for heating the exhausted air before it is contacted in the second heat exchanger;
• and
• (5) a heat exchanger for transferring back to the greenhouse heat contained in the exhausted air.

Apparatus for reducing the heat load on a greenhouse containing plants defining a plant canopy during periods of low light levels comprising:

• a) means for reducing the rate of convective heat flow of air through the canopy during periods of low light levels;
• b) said means for reducing including a first air-brine-vapor heat exchanger for contacting air in the greenhouse with concentrated brine supplied from a reservoir to thereby dehumidify the air and produce dilute brine that is returned to the reservoir;
• c) means for exhausting air from the greenhouse to the atmosphere;
• d) a second air-brine-vapor heat exchanger supplied with brine from said reservoir for contacting air exhausted from the greenhouse with said brine and thus concentrating the brine;
• e) means for heating the exhausted air before it is contacted in the second heat exchanger;
• and
• f) said second heat exchanger is constructed and arranged so that the heated exhausted air evaporates water from the contacted brine for concentrating the same before the latter is returned to the reservoir thereby increasing the humidity of the exhausted air.