Title:
Irrigation reservoir cooling system
Kind Code:
A1


Abstract:
A combined space-cooling and irrigation system and method of operation. The system is operated by an automated control unit specifically programmed to manage cooling and irrigation needs as follows. When irrigation water is needed, the system pumps cool water from a municipal water supply, a well, or a deep pond, through a heat exchanger on the way to a reservoir. The water pumped through the heat exchanger cools fluid in a separate closed circuit. The cooled fluid in the closed circuit is then used for cooling purposes, for example, to cool the air circulated through a house or building using a commercially available fan coil unit. The reservoir releases collected water for irrigation purposes at appropriate times.



Inventors:
Guglietti, Marco (Oakville, CA)
Del Greco, Raymond Paul (Beeton, CA)
Application Number:
11/889462
Publication Date:
01/22/2009
Filing Date:
08/13/2007
Primary Class:
Other Classes:
165/47
International Classes:
F25B27/00; F24F3/06
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Primary Examiner:
ZEC, FILIP
Attorney, Agent or Firm:
WELSH FLAXMAN & GITLER LLC (McLean, VA, US)
Claims:
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A space-cooling and irrigation system that utilizes ground water for cooling and irrigation purposes comprising: a primary heat exchanger; a water holding tank comprising a means of discharging water for irrigation purposes; a water conduit connected to a source of ground water and said water holding tank; and a closed fluid circuit operable to cool a space; wherein said primary heat exchanger is operable to exchange heat between said water conduit and said closed fluid circuit.

2. The space-cooling and irrigation system of claim 1 wherein said water conduit is provided with at least one pump operable to move water from said source of ground water through said water conduit.

3. The space-cooling and irrigation system of claim 1 wherein said water conduit is provided with an optionally usable first branch, said first branch passing though said primary heat exchanger; and said closed fluid circuit is provided with an optionally usable first branch, said first branch passing through said primary heat exchanger.

4. The space-cooling and irrigation system of claim 1 further comprising a means of controlling said system automatically, said means of control comprising a programmable controller unit

5. The space-cooling and irrigation system of claim 1 wherein said closed fluid circuit comprises: a heat-transfer fluid, said heat-transfer fluid filling said closed fluid circuit; at least one pump operable to move said heat-transfer fluid around said closed fluid circuit; at least one fluid chilling means operable to cool said heat-transfer fluid; and at least one space-cooling means operable to cool said space; wherein said heat-transfer fluid is cooled by at least one of said fluid chilling means and said heat exchanger; and wherein said space-cooling means uses said heat-transfer fluid to cool air and circulates said air through said space.

6. The space-cooling and irrigation system of claim 1 wherein said water conduit comprises an optionally usable second branch, said second branch passing though a secondary heat exchanger.

7. The space-cooling and irrigation system of claim 6 wherein said secondary heat exchanger is a dehumidifier.

8. The space-cooling and irrigation system of claim 6 further comprising: a tertiary heat exchanger; a second fluid circuit comprising: i) an outdoors heat exchanger operable to exchange heat between said second fluid circuit and outdoors environment; and ii) a pump operable to circulate a heat-transfer fluid around said second fluid circuit; wherein said tertiary heat exchanger is operable to exchange heat between said second branch and said second fluid circuit; and wherein said second branch optionally forms a water circuit operable to circulate water between said tertiary heat exchanger and said secondary heat exchanger.

9. A method of operating a space-cooling and irrigation system that utilizes ground water for cooling and irrigation purposes comprising the steps of: pumping water from a source of ground water through a water conduit, said water flowing through a primary heat exchanger and flowing into a water holding tank comprising a means of discharging said water for irrigation purposes; pumping a heat-transfer fluid through a closed fluid circuit operable to cool a space, said heat-transfer fluid flowing through said primary heat exchanger wherein heat exchanged between said heat-transfer fluid and said water cools said heat-transfer fluid.

10. A method of operating a space-cooling and irrigation system that utilizes ground water for cooling and irrigation purposes, said space-cooling and irrigation system comprising a primary heat exchanger, a water holding tank comprising a means of discharging water for irrigation purposes, a water conduit connected to a source of ground water and said water holding tank, and a closed fluid circuit operable to cool a space, comprising the step of: operating said space-cooling and irrigation system to maximize heat exchange between said closed fluid circuit and said water conduit when temperature of said space exceeds a predetermined temperature, when temperature of said ground water is lower than a predetermined temperature and when said water holding tank has water storage capacity, said operation comprising the steps of: i) pumping water from a source of ground water through said water conduit, said water flowing through said primary heat exchanger and flowing into said water holding tank; ii) pumping a heat-transfer fluid through said closed fluid circuit, said heat-transfer fluid flowing through said primary heat exchanger wherein heat exchanged between said heat-transfer fluid and said water cools said heat-transfer fluid;

11. The method of operating a space-cooling and irrigation system of claim 10 wherein said closed fluid circuit comprises at least one fluid chilling means operable to cool said heat-transfer fluid.

12. The method of operating a space-cooling and irrigation system of claim 11 wherein said step of operating said space-cooling and irrigation system to maximize heat exchange further comprises the step of actuating said at least one fluid chilling means to cool said heat-transfer fluid if additional cooling of said heat-transfer fluid is required.

13. The method of operating a space-cooling and irrigation system of claim 12 further comprising the step of: operating said closed fluid circuit as a stand alone cooling system when temperature of said space exceeds a predetermined temperature and when temperature of said ground water is not lower than a predetermined temperature or said water holding tank does not have water storage capacity, said operation comprising the steps of: i) pumping a heat-transfer fluid through said closed fluid circuit; and ii) actuating said at least one fluid chilling means to cool said heat-transfer fluid.

14. A method of operating a space-cooling and irrigation system that utilizes ground water for cooling and irrigation purposes, said space-cooling and irrigation system comprising: a) a primary heat exchanger, b) a water holding tank comprising a means of discharging water for irrigation purposes, c) a water conduit connected to a source of ground water and said water holding tank, and d) a closed fluid circuit operable to cool a space, comprising the steps of: a) determining whether temperature of said space exceeds a predetermined temperature, b) determining whether temperature of said ground water is lower than a predetermined temperature, c) determining whether said holding tank has water storage capacity, d) if temperature of said space exceeds a predetermined temperature and temperature of said ground water is lower than a predetermined temperature and water holding tank has water storage capacity: i) pumping water from a source of ground water through said water conduit, said water flowing through said primary heat exchanger and flowing into said water holding tank, ii) pumping a heat-transfer fluid through said closed fluid circuit, said heat-transfer fluid flowing through said primary heat exchanger wherein heat exchanged between said heat-transfer fluid and said water cools said heat-transfer fluid.

15. The method of operating a space-cooling and irrigation system of claim 14 wherein said closed fluid circuit comprises at least one fluid chilling means operable to cool said heat-transfer fluid.

16. The method of operating a space-cooling and irrigation system of claim 15 further comprising the step of actuating said at least one fluid chilling means to cool said heat-transfer fluid if additional cooling of said heat-transfer fluid is required.

17. The method of operating a space-cooling and irrigation system of claim 9 further comprising the step of periodically discharging said water in said water holding tank for irrigation purposes.

Description:

FIELD OF THE INVENTION

The present invention relates to a combined space-cooling and irrigation system.

BACKGROUND

Ground temperatures four feet below grade are a constant 50° F. to 56° F. from the east coast of North America to the west coast and from Atlanta Ga. to Sudbury, Ontario. This vast area has cool ground temperatures and hot summers with attendant cooling and irrigation requirements.

Cooling systems which make use of the relative coolness of underground water sources, such as wells or municipal water mains, are well known in the art. For example, U.S. Pat. Nos. 4,375,831, 4,946,110, 5,727,621, 6,041,613 and 6,688,129 disclose the concept of using the coolness of ground water to acclimatize living space. Also known in the art are systems for controlling irrigation, for example, U.S. Pat. Nos. 4,134,269, 4,393,890 and 4,693,419. However, none of the above patents combine a space cooling system, which makes use of underground water for cooling needs, with an irrigation system.

U.S. Pat. No. 5,140,829 to Barwacz teaches a space-cooling system using a heat exchanger for ground water that has been slightly chilled by a heat pump. The heat pump cools the incoming ground water and uses the return flow of warmed ground water, or at least a portion of the return flow, to evaporate the heat pump's refrigerant gas. The heated discharge water can be used as pre-heated household water, or discharged for irrigation or to a drainage system. Barwacz therefore discloses the use of ground water for heat exchange purposes and then using the water for irrigation or household uses. However, there is no disclosure of a closed loop cooling system that would allow for humidity control. Furthermore, there is no teaching concerning a balancing of irrigation needs and cooling needs.

SUMMARY

The present invention provides a system that makes use of the relative coolness of underground water for cooling needs when the water is needed for irrigation in any event.

It is an object of the present invention to provide a system that reduces electric energy consumption for cooling purposes by making use of the relative coolness of the ground water that is used for irrigation purposes.

It is another object of the present invention to provide a system that warms water to be used for irrigation purposes.

It is another object of the present invention to provide an integrated irrigation and cooling system that operates automatically.

It is another object of the present invention to provide a system that reduces electric energy consumption for cooling purposes by making use of cool external temperatures

It is yet another object of the present invention to provide a closed loop cooling system that allows for humidity control.

The above objectives are accomplished by a novel irrigation reservoir cooling system and method of operation. The system is operated by an automated control unit specifically programmed to manage cooling and irrigation needs generally as follows.

  • 1) When space cooling is needed, for example, during the solar heat gain of the day, the system pumps cool underground water (ground water) from a pressurized municipal (city) water supply, a well, or a deep pond, through a heat exchanger on the way to a reservoir. The water is pumped (transported) by providing the system with a water pump or by connecting the system to a pressurized municipal water supply.
  • 2) The water pumped through the heat exchanger cools fluid in a separate closed circuit. The closed circuit includes at least one fluid chiller, which is sufficient to provide cooling when irrigation water is not needed, for example, during the night, on rainy days or in the winter.
  • 3) The cooled fluid in the closed circuit is then used for cooling purposes, for example, to cool the air circulated through a house or building using a commercially available fan coil unit.
  • 4) The reservoir releases collected water for irrigation purposes at appropriate times, normally at night.

The irrigation reservoir cooling system is ideal for cooling buildings that use irrigation systems such as estate homes and golf and country clubs.

In one embodiment, the system is provided with a secondary heat exchanger to further exploit the low temperature of ground water for cooling purposes. The secondary heat exchanger can be any device or system that is operable to receive and exchange heat with a source of water, such as a dehumidifier.

In yet another embodiment, the system is provided with an auxiliary system that exploits cool winter temperatures for cooling purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described in greater detail and will be better understood when read in conjunction with the following drawings in which:

FIG. 1 is a schematical view of an irrigation reservoir cooling system according to an embodiment of the invention;

FIG. 2 is a schematical view of an irrigation reservoir cooling system according to another embodiment of the invention; and

FIG. 3 is a schematical view of an irrigation reservoir cooling system according to yet another embodiment of the invention.

DETAILED DESCRIPTION

With reference to FIG. 1, the irrigation reservoir cooling system 100 of the present invention generally comprises a water conduit 200, a cooling circuit 300, a holding tank 400, a primary heat exchanger 202 and a control unit 102. The direction of fluid flow through the system is indicated by arrowheads.

In the embodiment of the invention shown in FIG. 1, the irrigation reservoir cooling system is implemented for a building (not shown) with an external irrigation system (not shown). In general, water conduit 200 transports ground water, which is needed by the irrigation system, to holding tank 400. Cooling circuit 300 operates to cool spaces within the building. Water conduit 200 and cooling circuit 300 are thermally coupled to heat exchanger 202. Control unit 102 monitors and actuates the water conduit and the cooling circuit. Control unit 102 is programmed to fulfil irrigation and cooling needs and, at the same time, maximize the heat exchanged at primary heat exchanger 202.

A more detailed description of major components of the irrigation reservoir cooling system follows. Water conduit 200 is a water line that is connected to a water source 204. In the embodiment of the invention shown in FIG. 1, water source 204 comprises a pressurized municipal water supply. In alternate embodiments, water source 204 can be an underground well or a deep pond. In these alternate embodiments, water conduit 200 is provided with a pump operable to move water through the water conduit.

The water conduit extends from water source 204 to holding tank 400. Water conduit 200 is provided with a temperature sensor 206 and a first control valve 208. Beyond first control valve 208, water conduit 200 passes through primary heat exchanger 202

Generally, water flows though water conduit 200 as follows. Cool underground water flows into the water conduit from water source 204. The water flows to first heat exchanger 202, which exploits the low temperature of the water for cooling purposes. The water exits first heat exchanger 202 and flows to holding tank 400, which stores the water for use by the irrigation system.

Water conduit 200 is also provided with an optionally usable bypass circuit 210. Bypass circuit 210 provides an alternate route for water flowing through the water conduit. The alternate route bypasses first heat exchanger 202. Bypass circuit 210 is provided with a second control valve 212 operable to control use of bypass circuit 210.

Cooling circuit 300 is another major component of the irrigation reservoir cooling system. Cooling circuit 300 is a closed circuit provided with a first pump 302, a first temperature sensor 304, a second temperature sensor 306, a chiller 308, a chiller pump 310, a third temperature sensor 312, a second pump 314, at least one fan coil circuit 316 and a fourth temperature sensor 318. In front of first pump 302, the cooling circuit passes through first heat exchanger 202. The cooling circuit is filled with a fluid that can be water or any commercially available heat transfer fluid.

In the embodiment of the invention shown in FIG. 1, cooling circuit 200 is provided with four optionally usable fan coil circuits 316. Fan coil circuits 316 are connected in parallel to the cooling circuit downstream of second pump 314. Each of the fan coil circuits is provided with two control valves 322, 324 and a fan coil unit 320. Control valves 322, 324 are operable to control the flow of the fluid through their respective fan coil circuits 316.

The fluid is pumped through cooling circuit 300 by pumps 302, 310 and 314. Generally, the fluid flows through cooling circuit 300 as follows. The fluid is pumped through first heat exchanger 202, where the fluid is cooled by water flowing though water conduit 200. The fluid is then pumped from the first heat exchanger to chiller 308. Chiller 308 is operable to further reduce the temperature of the fluid. The fluid is pumped from the chiller to fan coil units 320. Fan coil units 320 are located proximate to spaces in the building that can require cooling. Fan coil units 316 are operable to cool air and circulate said air through the spaces that can require cooling. Next, the fluid leaves the fan coil units and flows back to first heat exchanger 202.

The cooling circuit is also provided with an optionally usable bypass circuit 326 that bypasses first pump 302 and first heat exchanger 202.

Holding tank 400 comprises a water level sensor 402, an overflow conduit 404, and a low level float 406. The capacity of the holding tank can vary depending on irrigation needs. In the embodiment of the invention shown in FIG. 1, holding tank 400 has a capacity of 5000 gallons and water level sensor 402 is a commercially available ultrasonic level indicator. The holding tank supplies water to the irrigation system.

Water flows into holding tank 400 from water conduit 200. In the embodiment of the invention shown in FIG. 1, the holding tank is filled by water supplied by water conduit 200. In alternate embodiments, water can also be supplied to holding tank by rainwater or thaw water. If the holding tank is ever filled to overflowing, the overflow water is directed by overflow conduit 404 to a drainage culvert 408. In alternate embodiments, the holding tank comprises an emergency drain provided with an emergency pump operable to rapidly pump water from the holding tank into the culvert or a storm system.

Control unit 102 is a programmable unit with multiple signal inputs and output. In the embodiment of the invention shown in FIG. 1, control unit 102 is a commercially available TAC Xenta™ 300 controller. Control unit 102 is in electronic communication with the above described sensors, pumps, control valves, chiller and irrigation system. The control unit is additionally in electronic communication with an external temperature sensor 104, which measures outdoor temperature, and at least one thermostat (not shown) located within the building. In the embodiment of the invention shown in FIG. 1, the control unit is connected to the sensors, pumps, control valves, heat exchanger, chiller and irrigation system by point to point wiring (not shown) easily accomplished by a competent electrician. The electronic connections can be either line voltage or 24V low voltage connections.

A description of the operation of the irrigation reservoir cooling system 100 according to the embodiment of the invention shown in FIG. 1 follows. A user of the irrigation reservoir cooling system inputs (sets) a desired temperature for a space within the building at a thermostat located within the space. When the temperature detected by the thermostat exceeds the desired temperature, the thermostat signals a need for cooling to control unit 102. In response to the signal, control unit 102 executes steps to reduce the temperature of the space to satisfy the temperature setting of the thermostat.

First, the control unit actuates chiller pump 310 and second pump 314, which operate to pump the fluid throughout cooling circuit 300. Next, the control unit executes one of two set of steps based on the availability of cool ground water and storage capacity in holding tank 400. Control unit 102 determines whether cool water is available based on the temperature of water from water supply 204 at first water temperature sensor 206. Cool water is available when the temperature of water is below a predetermined temperature, 12° C. in the present embodiment, that represents a water temperature that is sufficiently cool to warrant using the water as a coolant. Control unit 102 determines whether storage capacity is available in holding tank based on input from water level sensor 402.

If cool water is not available or storage capacity is not available, control unit 102 operates the cooling circuit as a stand alone cooling system. To this end, the control unit executes the following steps. First and second control valves 208, 212 of water conduit 200 are closed. Control unit 102 actuates chiller 308, which is operable to cool the fluid in cooling circuit 300. The fluid is pumped to the chiller, where the fluid is cooled, and from the chiller to a fan coil unit 320 operable to cool the space where the thermostat is located. The fan coil unit uses the fluid to cool air that is then circulated though the space. The fluid leaving the fan coil unit is pumped back to chiller 308, thus completing a loop of cooling circuit. If the temperature of fluid at third or fourth fluid temperature sensors 312, 318 falls below the desired temperature, additional chilling of the fluid is no longer needed and control 102 unit deactuates the chiller.

Alternately, if cool water is available and storage capacity is available, the control unit operates system 100 to maximize heat exchange between water conduit 200 and cooling circuit 300. To this end, the control unit executes the following steps. Control unit 102 opens first control valve 208, closes second control valve 212 in the water conduit, and actuates first pump 302 in the cooling circuit. Opening first control valve 208 allows water from water supply 204 to flow through primary heat exchanger 202. Actuating first pump 302 pumps the fluid of cooling circuit 300 through primary heat exchanger 202. Within the primary heat exchanger, the fluid of the cooling circuit is cooled by the water of the water conduit. The water leaving primary heat exchanger 202 flows to holding tank 400 wherein the water is stored until the next irrigation operation. The fluid leaving primary heat exchanger 202 is pumped through the cooling circuit, to a fan coil unit 316 operable to cool the space where the thermostat is located. Fan coil unit 316 uses the fluid to cool air that is then circulated though the space. The fluid leaving fan coil unit 316 is pumped back to heat exchanger 202, thus completing a loop of the cooling circuit.

If the temperature of the thermostat continues to rise and exceeds a predetermined threshold temperature, 1° C. above desired temperature in the present embodiment, and control valve 208 is fully open, the control unit actuates chiller 308, which is operable to cool the fluid in cooling circuit 300. Chiller 308 and heat exchanger 202 then work in concert to cool the fluid in the cooling circuit until either the temperature of the thermostat is lowered below the threshold temperature or the temperature of the fluid at third or fourth fluid temperature sensors 312, 318 falls below the desired temperature. If either of these conditions is met, control unit 102 deactuates chiller 308.

If the temperature of the fluid at fourth fluid temperature sensor 318 falls below the temperature of water from water supply 204, heat exchanger 202 is no longer capable of cooling the fluid and the control unit closes first control valve 208 of the water conduit and deactuates first pump 302 of the cooling circuit.

For both sets of steps, described above, when the temperature of the thermostat reaches the desired temperature, cooling of the space is no longer needed and control unit 102 closes first control valve 208 and deactuates the cooling circuit by deactuating the pumps and the chiller.

Control unit 102 also actuates the irrigation system to perform periodic irrigation operations using water from holding tank 400. When the above described cooling operations do not fill holding tank 400 with sufficient water to perform a scheduled irrigation operation, the control unit calculates the time needed to fill holding tank 400 based on input from water level sensor 402 and operates water conduit 200 to fill the holding tank in time for the irrigation operation. To this end, the control unit can open second control valve 212 in bypass circuit 210 so that ground water bypasses first heat exchanger 202 and flows directly to holding tank 400. Control unit 102 will not actuate the irrigation system when low level float 406 communicates to the control unit that there is insufficient water in the holding tank.

FIG. 2 is a schematic diagram of another embodiment of the irrigation reservoir cooling system. In this embodiment, cooling circuit 300 comprises an optionally usable chiller circuit 328 provided with a second chiller 330 and a second chiller pump 332. Second chiller 330 and second chiller pump 332 are connected to cooling circuit 300 in parallel with chiller 308 and chiller pump 310. As with chiller 308, second chiller 330 is operable to reduce the temperature of the fluid in cooling circuit 300. Second chiller 330 and second chiller pump 332 are in electronic communication with control unit 102. In operation, the second chiller and the second chiller pump are actuated when chiller 308 is not able to adequately cool the fluid in cooling circuit 300. In the embodiment of the invention shown in FIG. 2, if chiller 308 cannot provide sufficient cooling after 20 minutes of operation, control unit 102 actuates second chiller 330 and second chiller pump 332 to provide additional cooling. Control unit 102 deactuates the second chiller and the second chiller pump when additional cooling is no longer needed.

The roles of chiller 308 and second chiller 330 can be alternated on a weekly basis to equalize their run time. For example, every other week, second chiller 330 can be actuated first by control unit 102, and chiller 308 actuated only to provide supplemental cooling.

Also with reference to the embodiment shown in FIG. 2, water conduit 200 comprises a third control valve 214 and an optionally usable secondary branch 500 provided with a secondary heat exchanger 502. As with primary heat exchanger 202, secondary heat exchanger 502 is operable to exploit the low temperature of ground water from water source 204 for cooling purposes. Secondary heat exchanger 502 can be any device or system that is operable to receive and exchange heat with a source of water. In the embodiment of the invention shown in FIG. 2, the secondary heat exchanger is a commercially available dehumidifier. Secondary branch 500 also comprises a first control valve 504 and a first water temperature sensor 506. The secondary branch connects to the water conduit downstream of primary heat exchanger 202 and bypass circuit 210. The secondary branch extends from water conduit 200 to holding tank 400. Control unit 102 is in electronic communication with secondary heat exchanger 502, first control valve 504, and first water temperature sensor 506.

In operation, control unit 102 functions as described above with respect to the embodiment of the invention shown in FIG. 1 and also determines if secondary heat exchanger 502 requires cooling for dehumidifying air that is being pumped through heat exchanger 502. If the secondary heat exchanger requires cooling, the control unit opens first control valve 504 of branch conduit 500 and closes third control valve 214 of water conduit 200. In this configuration, water that has passed through either primary heat exchanger 202 or bypass conduit 210 will flow to secondary heat exchanger 502. The water flows through the secondary heat exchanger and then flows to holding tank 400.

FIG. 3 is a schematic diagram of another embodiment of the irrigation reservoir cooling system. In this embodiment, the irrigation reservoir cooling system additionally comprises a snowmelt circuit 600. Generally, snowmelt circuit 600 provides cooling to secondary branch 500 during winter months, when there is no demand for irrigation water Snowmelt circuit 600 passes through a tertiary heat exchanger 510 and is provided with a snowmelt pump 602, a heat exchange panel 604 and a fluid temperature sensor 606. Heat exchange panel 604 functions as a heat sink and is positioned outdoors, preferably in a location where unwanted snow accumulates, such as in a driveway. Snowmelt pump 602 circulates a fluid through the snowmelt circuit. The fluid can be any commercially available heat transfer fluid that remains in a liquid state when exposed to winter temperatures.

In the embodiment of the invention shown in FIG. 3, secondary branch 500 passes through tertiary heat exchanger 510 downstream of secondary heat exchanger 502 and is provided with a first water temperature sensor 506, a second water temperature sensor 508, a freeze sensor 512, a second control valve 514 and an optionally usable closed circuit branch 516. Closed circuit branch 516 is provided with a closed circuit pump 518 and a one-way check valve 520. Control unit 102 is in electronic communication with snowmelt pump 602, fluid temperature sensor 606, first and second water temperature sensors 506, 508, freeze sensor 512, second control valve 514, and closed circuit pump 518.

Control unit 102 operates the snowmelt circuit 600 when there is no need for irrigation water and cool external temperatures can be used to fulfill cooling needs. When these conditions exist and secondary heat exchanger 502 signals a need for cooling, the control unit executes the following steps. Control valves 208, 212, 214 of the water conduit and control valves 504, 514 of the branch conduit are closed. In this configuration, secondary branch 500 forms a closed water circuit that passes through secondary heat exchanger 502 and tertiary heat exchanger 510. The control unit then actuates closed circuit pump 518 to pump water through the closed circuit as follows. Water is pumped from tertiary heat exchanger 510, wherein heat is exchanged with snowmelt circuit 600, through one-way check valve 520 of closed circuit branch 516, to secondary heat exchange 502, wherein the water cools the heat exchanger. The water is then pumped back to tertiary heat exchanger 510, completing a loop of the closed circuit.

Control unit 102 also actuates snowmelt pump 602, which pumps the fluid around the snowmelt circuit. The fluid is pumped from heat exchange panel 604, wherein the fluid is cooled by the outdoors environment, to tertiary heat exchanger 510, wherein the cooled fluid exchanges heat with secondary branch 500. The fluid is then pumped back to the heat exchange panel, completing a circuit of the snowmelt circuit. In the embodiment of the invention shown in FIG. 3, the snowmelt circuit is provided with an optionally usable waste heat circuit 608, which further exploits the heatsink capacity of heat exchange panel 604. The waste heat circuit directs fluid that is flowing from heat exchange panel 604 to a boiler or other waste heat source (not shown), and returns the fluid to snowmelt circuit 600 upstream of the heat exchange panel.

If water in secondary branch 500 at freeze sensor 512 is in danger of freezing, the irrigation reservoir cooling system reverts to using water source 204 to provide cool water to secondary heat exchanger 502. To this end, control unit 102 opens control valve 212 of water conduit 200, deactuates snowmelt pump 602 and closed circuit pump 518, and opens first and second control valves 504, 514 of secondary branch 500.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and sub combinations of the various features described hereinabove as well as variations and modifications which would occur to persons skilled in the art upon reading the specification and which are not in the prior art.