CA2638235A1 - Recovery storage and conversion of waste heat from an ice rink using a concentric borehole heat exchanger system - Google Patents

Abstract

This energy management system is designed to be controlled by a microprocessor unit to recover and transfer waste heat from an ice arena to a concentric borehole heat exchanger storage unit for transferring on demand to a heat pump for transfer to a district energy system or a single demand application. The heat pump may also convert the heat energy to cold energy to be transferred to demand points. A heat dissipation unit is available in the system to purge excess heat energy to maintain system thermal stability. The system also enables cold energy from an underground concentric borehole heat exchanger to be pumped directly to the arena or be pumped via a heat pump to a district energy system.
In addition, the system may scavenge heat or cold from inside or outside the energy management system to transfer to demand points or borehole energy storage.

Description

RECOVERY STORAGE AND CONVERSION OF WASTE HEAT FROM AN ICE RINK USING A
CONCENTRIC BOREHOLE HEAT EXCHANGER SYSTEM

The present application relates to an energy system for recovering heat and cold energy, specifically from a rink, an energy management system or a district energy system for storage or usage within said energy management system or said district energy system.

BACKGROUND OF THE INVENTION

It is well-known that the earths dwindling supply of finite fossil fuels has been creating major initiatives and activity in the waste recycling industry. The recycling of waste heat from various residential, commercial, institutional and industrial complexes has thus shown great promise for saving huge amounts of energy for extended use on a global scale. Several practices and technologies have been employed to enable arenas and curling rinks to reduce energy consumption and associated greenhouse gas (GHG) emissions and associated use of synthetic refrigerants. The technologies are based upon;
(a) employing secondary loops instead of refrigerants to transfer energy, which reduces the use of refrigerants and (b) recovery of waste heat from the refrigeration system to use for heating demand points along with hot water for other uses. Several possible options include environmentally friendly fluids, geothermal heat pumps and thermal and cold storage systems. An important element to utilize resources in ice arenas and curling rinks is to realize appropriate use of energy sinks and the various parameters affecting energy consumption.

Energy management systems are usually devices used to monitor, control and optimize energy-consuming equipment in commercial, industrial and institutional facilities.
Computer-based monitoring permits immediate or scheduled adjustments of electrical and mechanical equipment, remote diagnostics and control and control and logging. EMSs generally consist of sensors, controllers, actuators, software and a communications network. Systems are designed according to specific site requirements such as utility type, operation and number of systems to be controlled. More complex systems can perform more sophisticated procedures and can command many energy-consuming systems simultaneously. In addition, advanced systems can adjust for seasonal changes, generate reports and evaluate problems in mechanical and electrical systems.

Ice making plants normally produce ice on a cyclic basis, which could mean operating for only 20 to 25 minutes every 75 minute cycle. This situation results in development of low grade heat exhibiting a temperature less than 43 C(110F) being available for recovery from the heat transfer fluid. Several previous designs have considered the employment of rejection heat from the refrigeration system in ice rinks and heat pumps to heat swimming pools in recreational complexes. This involves a heat requirement near an application that requires cooling. Heat pumps simply provide heat or chilling by extracting heat from, or ejecting heat to, an outside source. Considering heat pumps, the outside source of heating or cooling is the underground, where there is a greater heat density than in air, where air exchange systems are employed. In addition, underground sources tend to be of a moderate and relatively constant temperature year round.

A combined freezing and heating system has been employed in Halden, Norway, utilizing waste heat from an ice rink and geothermal heat (rock/ground) to meet the heat demand for the Gimlie School and a nearby indoor ice rink. Waste heat provides over 73% of the annual heat demand of 1,100 MWh, the remainder comes from the electricity grid and 5% from fuel oil. The average coefficient of performance (COP) was found to be 3.80. NRCAN-CANMET Technology Center has described employing a geoexchange system to freeze an ice surface, while using waste heat from the ice making heat pump equipment for space and water heating or sending heat for storage in a ground-loop system. The Port Hawkesbury Civic Center in Nova Scotia has been designed with over 75,000 linear feet of geothermal loop laid six feet below the ground to serve as the core of a heat pump and geoexchange system. Waste heat is captured from the refrigeration plant and used to heat the bleachers and floors of the arena and sidewalks outside the complex are lined with a loop system to carry the heat transfer agent ethanol to melt snow. The geoexchange system, along with natural sunlight and insulation glazing produces considerable energy savings by avoiding use of a large boiler and replacing the use of other energy sources. The Plume Coulee utility company of Manitoba Hydro in 2001 installed a geoexchange system with heat pumps to assist ice making operations at the Plume Coulee Hockey Arena. Waste heat from the refrigeration system is employed for heating the arena and excess heat is stored in 96 boreholes drilled to 85 feet each in the ground as a heat sink. The Richmond Olympic Oval speed skating track in Vancouver was designed to employ over 90% of the waste heat from the ice plant to provide a large percentage of the needs of the sports complex.

Ground-source heat pumps (GSHP) move or transport heat like air-source heat pumps, but exchange heat with the earth rather than the atmosphere. These GeoExchange systems are efficient, environmentally sensitive, comfortable and economical. The key feature is that these systems use electricity to move heat energy, not to generate it by burning fuel or using electric resistance elements.
GeoExchange systems are generally 2.5 to 4 times more efficient than resistance heating and water heating alone, and produce no combustion or indoor air pollutants. In addition, there is no weather-related maintenance. By employing geoexchange, the average home in North America could reduce green house gas (GHG) emissions by 2.5 to 5 tonnes annually.

The main function of a heat exchanger is to transfer thermal energy between two fluids. The two fluids are usually hot or cold water pumped in to the exchanger and cold or hot water pumped out of the exchanger.
To obtain a reasonable energy exchange between the fluids inside and outside of the exchanger pipe, it is necessary to design the surface of heat exchanger to be as extensive as possible. The pipe is usually constituted by a tube centered in a borehole, positioned in the casing of the borehole. A major consideration in achieving maximum efficiency in employing these borehole heat exchangers is to provide as large a surface area as possible for potential heat transfer. Past researchers have determined that when using heat pumps in the heating and cooling of buildings, the efficiency of an air-to-air heat pump is high only when the outside ambient temperature is moderate. For instance, at ambient temperature extremes, the coefficient of performance of a heat pump falls drastically. At an ambient temperature of 0 C o, its operation continues only at an energy loss because the evaporator must be defrosted. At an ambient temperature of 40C o, the heat pump would have to work extremely hard to produce cool air.
Considering these factors, alternate heat sources, which will remain essentially constant despite fluctuating ambient air temperatures were developed. This lead to groundwater-to-air heat pumps, which operate at a higher coefficient of performance (ratio of energy out to energy in) year-round. Sources of water were originally, well-water or city water, which would quickly become exhausted if used as a heat source/sink as well as competing with other uses of the water. These drawbacks were then overcome with the advent of a closed water loop in which the earth itself serves as a major heat sink for air-conditioning in the summer and as a heat source in the winter.

Closed-loop systems have unfortunately proven to work at lesser than desired efficiency levels because only minor amounts of the available heat in the earths crust could be abstracted with then existing heat exchangers. These heat exchangers typically comprised long sections of copper coil, with no enclosures surrounding the coils and no use of phase change materials. Copper has also become a rather expensive working material. Due to the low thermal conductivity and heat capacity of the earth, energy in close proximity to these earth coils was rapidly dissipated, when the instantaneous heating demand of a heat pump system was engaged. Consequently, the temperature of the heat transfer fluid would continue to fall, and in a short time period, a second coil would have to be substituted for the exhausted coil. This would ultimately lead to malfunction and a required shut-down of the heat pump system. The coils displayed other drawbacks such as costly installation, a large area requirement, a need for custom-designed components and destruction of laws and they are only reliable for small receiving unit usage.
It was noted that when employing aquifers act as heat sources or sinks, these sources could be quickly exhausted if frequently or widely used. This lead to the development of a closed-loop system (Leon et al, US Patent No. 4,327,560), issued in 1982, in which heat was pumped from the earth to a conditioned space, wherein the heat transfer fluid was circulated in a substantially closed loop through an improved earth coil. A phase change material was in thermal contact with both the primary heat transfer fluid (mixture of water and antifreeze) and the surrounding soil. This approach employed the earth itself as a giant heat sink for air conditioning in the summer and as a heat source, from which large amounts of heat, warmer than the ambient air could be extracted in the winter. The next step would be to employ earth materials and bedrock as an energy source and for energy storage to increase the potential energy available from a given point source.

Energy storage is an enabling technology for use in a variety of energy systems, from residential to commercial and from industrial to agricultural. By contributing to large-scale energy efficiencies; energy storage significantly reduces environmental impacts from energy activities, increases the potential uptake of some renewable energy technologies, increases the potential for sustainable energy development and subsequently contributes to enhanced energy security. Energy storage technologies overcome the temporal mismatch between energy supply and demand, and are especially useful for renewable energy technologies. IEA Experts indicate that in terms of Thermal Energy Storage (TES) (IEA Annex 14, 2004), cooling has been given a first priority, followed by combined cooling and heating, and lastly heating. Thus, building cooling for human occupancy and process cooling of industrial or commercial products or processes are the main areas of interest in alternative energy production. The potential for recycling heat from many sectors of municipal infrastructure, including industrial complexes and employing intermittent heat storage also presents great opportunities.

Borehole Thermal Energy Storage (BTES) is one type of Underground Thermal Energy Storage (UTES).
Over the last 15 years Borehole Thermal Energy Storage (BTES) energy type systems have been used primarily for seasonal heat storage with heat pump technology. Cost effective geo-heat transfer is considerably more difficult at low temperatures (below 40 C) for air conditioning. Generally, the larger the storage application is, the more cost effective the storage becomes. To double the capacity of the store only a small, incremental increase in the borehole is required.

To store cold only for direct cooling, using borehole thermal energy storage technology requires more efficient Borehole Heat Exchangers (BHE) than the single or double U-pipes that are normally applied in these types of storage systems. Traditional borehole designs have used either a grouted or water-filled hole with a U-tube. A more cost effective (low thermal resistance) coaxial (concentric) borehole heat exchanger suitable for cooling without chiller machines has been tested in Halifax, Nova Scotia, Canada with a patent pending by the authors of the current invention. Cruickshanks et al (2006) conducted field tests to determine whether a boreholes wall could be sealed with bentonite to make it water tight and suitable for a coaxial type borehole heat exchanger (i.e. no groundwater flux).

The temperature drop between the wall of the drill hole and the heating medium is comprised of three energy factors. The first factor is caused by the thermal resistance of the water between the wall of the drill hole and the exterior of the pipe. Negligible convection has been found in the water given the pipe and borehole dimensions and operating temperatures currently used. Thus, the heat transfer occurs strictly through conduction. It must be noted that water is a poor thermal conductor whose thermal conductance may be improved if heat recovery is continued until the water freezes in the hole. This factor remains prevalent if heat is supplied to surrounding rock.

The second factor regarding temperature drop is caused by the thermal resistance posed by the pipe wall.
Formulae are available to calculate these values, which decrease with increasing pipe diameter and decreasing wall thickness. The third factor involves the heat transfer resistance between the inside of the pipe wall and the heat transporting medium. This factor mainly depends upon whether laminar or turbulent flow prevails within the heating medium, although pipe dimensions and surface structure are also notable influences. Also noteworthy, is that low heat transfer resistance could be achieved by increasing the flow rate.

Employing short heat-conducting periods of the drill hole water, while using a thin-walled, large diameter pipe, should produce a small temperature drop between the wall of the drill hole and the heat transfer fluid. Previous designs required that clearance between pipe and drill-hole wall should be as large as possible to enable conventional heat collectors to be fitted and the pipe walls made sufficiently thick, so as to provide security against rupture.

A single conventional U-pipe in a grouted borehole will typically have a thermal resistance that corresponds to a 5-6C o temperature difference between the rock and the heat carrier fluid in the U-pipe.
A double U-pipe will reduce this loss of temperature quality to 3-4Co. As a major advancement, a coaxial pipe or tube will have an optimal thermal efficiency and cut the difference to 1-2 Co, since it allows the fluid to have direct contact with the entire borehole wall. Efficiency difference determinations by Hellstrom et al. (1988) proved that the coaxial single tube borehole energy system was noticeably superior to;
polyethylene U-tube, copper U-tube, polyethylene double U-tube, and multiple co-axial tube energy systems.

The requirement for small ?Ts in cooling applications for UTES (underground thermal energy storage) systems is a prerequisite for direct cooling without heat pumps or chillers, and this is what made cooling with borehole storage uneconomical in the past. The coaxial (concentric) borehole is a much more thermally efficient borehole heat exchanger than a conventional U-tube borehole. The coaxial (concentric) borehole system has the ability to operate at small temperature differences (?T), which is directly related to borehole thermal resistance (Rb). Heat exchanger efficiency is a function of contact area and the turbulent flow in the system. The larger the contact area and the more turbulent the flow, the more readily the approach temperature for the heat exchanger is achievable and the smaller the ?T required, to meet the delivered temperature.
It is important to note that each time a new BTES configuration is evaluated, other important parameters must also be considered as well. These include, but may not be limited to, the available land space, the thermal load to be stored and storage temperatures, the timing of cold availability, existing temperatures in the subsurface, building operating temperatures, and of course the thermal efficiency of the BHE. All are taken together in optimizing the final energy storage configuration. In addition, one should consider the availability of drilling rigs and operators who will be available and capable of drilling to the depth required, as this will improve the competitive nature of the tendering process and help ensure the success of the project. Thus, even though the thermal conductivity of the bedrock or soil is the single most important parameter required in dimensioning a BTES system, it is but one of a number of parameters to consider in the overall BTES design process.
The boundary conditions for Borehole Thermal Energy Storage are few, with the major condition being the temperature requirements. The system can be employed anywhere including in unconsolidated (loose) rock formations or soils (overburden) through the use of a stiff liner to stabilize the wall of the concentric borehole. The coaxial BTES is the only system than can take advantage of the low temperature difference values (0.5C to 8C degrees). For coaxial heat exchangers with an unlined borehole, soft sedimentary rocks are excluded. Crystalline rocks are the most desirable geological materials. Therefore, geologically suitable locations for coaxial boreholes include much of the eastern and western coasts of Canada and the United States. The interior plains or large sedimentary basins in Canada and the United States are generally excluded from development of the coaxial borehole designs. Similar crystalline geologic regimes around the globe are also suitable for deployment of the coaxial borehole technology.

DESCRIPTION OF PRIOR ART
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CA 2,523423 April 2007 Lenko CA 2,567,566 April 2008 Jackson et al.
CA 2,273,760 March 2003 Jorgenson, CA 2,523,423 April 2007 Lenko CA 2,523,423 April 2007 Lenko CA 2,567,566 April 2008 Akkerman et al Applicable USA and Overseas Patents -US 3,658,123 April 1972 Root US 3,965,694 June 1976 Vignal et al US 3,976,123 August 1976 Davies US 4,258,780 March 1981 Suo US 4,327,560 May 1982 Leon US 4,448,238 May 1984 Singleton Jr. et al US 4,495,781 January 1985 Gatling US 4,633,676 January 1987 Dittell US 4,637,219 January 1987 Grose US 4,867,229 September 1989 Mogensen US 4,940,079 July 1990 Best et al US 5,081,848 January 1992 Rawlings et al US 5,152,153 October 1992 Hsiao US 5,467,812 November 1995 Dean et al.
US 5,651,265 July 1997 Grenier US 5,678,626 October 1997 Gilles US 5,680,898 October 1997 Rafalovich et al US 5,738,164 April 1998 Hildebrand US 5,778,683 July 1998 Drees et al US 6,158,499 December 2000 Rhodes et al US 6,393,861 May 2002 Levenduski et al US 6,450,247 September 2002 Raff US 6,082,125 July 2000 Savtchenko US 6,170,278 January 2001 Jorgensen US 6,601,398 August 2003 Sing et al US 6.935,131 August 2005 Backman US 7,032,398 April 2006 Dilk et al US 7,231,775 June 2007 Dilk et al GB1326458 September 1973 Aladiev GB2058334 April 1981 Feist JP56053388 May 1981 Sebasuchiyan BE893570 November 1982 Bouckaert JP60162141 August 1985 Matsuo SE8601086 September 1986 Soron JP5039986 February 1993 Hamada CN1074018 July 1993 Xing DE4423702 January 1996 Wetzel-Horst JP10300266 November 1998 Yamamoto JP10274444 October 1998 Kuroiwa JP11142076 May1999 Inada JP11182943 July 1999 Uchikawa CN2432495 May 2001 Li CN1292478 April 2001 Zhang JP2002013828 January 2002 Sakai JP2003130471 May 2003 Morita et. al JP2003130494 May 2003 Aiga JP2003240358 August 2003 Matsumoto JP2003262430 September 2003 Ikeuchi JP2003302108 October 2003 Suzawa JP2003301434 October 2003 Suzawa JP2003307352 October 2003 Suzawa JP2003307353 November 2003 Suzawa CN1542357 November 2004 Ma JP2005233527 September 2005 Endo JP2005003272 January 2005 Sasaki JP2005048972 February 2005 Saeki SE8601086 September 2006 Soron JP2006071258 March 2006 Morita JP2006084097 March 2006 Hamahiro CN1546926 November 2006 Gao EP1934535 June 2008 Mueller ADDITIONAL REFERENCES

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US patent # 6,393,861 by Levenduski et al (2002) describes storing waste heat in a thermal storage unit during a hot part of the day and venting it during a cooler period to avoid having to provide a costly refrigeration cycle to cool the storage medium.
In the present invention, the objective is to store heat energy anytime it is available for future use to achieve an economical advantage. The heat in storage does not require cooling and is only rejected from the system to a heat sink as a last alternative.

In US patent # 5,152,153, Hsiao (1992) has described a water recovery pipe system and recovery tank designed to convey cool water from an underground coil to an air-conditioning/refrigeration system. The system by Hsiao is designed for smaller applications.
The current invention is designed to operate with an ice rink refrigeration system providing heat storage underground for future use, which is more economical and efficient than simply dissipating all excess heat. The heat and cold energy storage systems of the present invention employ concentric boreholes, which are more efficient and less costly than the system described by Hsiao.

In US patent # 5,081,848 by Rawlings et al (1992), the authors describe an air-conditioning system designed to transfer heat in a heat transfer fluid to an underground heat exchanger or a water reservoir to be sent to a location to perform a de-icing activity. In addition, the system may include a heat pump to create heat or cold for the inside of a structure. The current invention includes a refrigeration system instead of an air conditioning system and the heat exchanger is the borehole/s in the ground. The heat pump in the current invention simply converts heat and cold energy for use by demand points in the overall system. In addition, the heat pump is C02 and Freon based to be environmentally friendly.
Canadian patent #CA2,567,566 or US patent # 2008087034(A1) by Akkerman et al describes a thermal energy recovery system for an ice making apparatus that generates by product low-grade heat, which is picked-up by a heat transfer fluid and sent to a storage tank in a building HVAC system. A heat pump is used to convert low-grade to high grade heat. This system is designed for smaller applications since large tanks would be prohibitively expensive.

In the current invention, low grade heat rejected from the refrigeration system of an ice rink is stored underground in an advanced concentric borehole storage system, which is considerably more efficient than storage in a tank and can accept much larger volumes of heat energy without increased costs for use at many more demand points. The prior art approach uses multiple heat pumps, which are expensive to operate.

In US patent #7,032,398 by Dilk et al (2006) and #7,231,775 by Dilk et al (2007) the authors describe an energy management system for an ice rink where waste heat collected from the refrigeration system may be used to meet demand loads in an attached building. In addition, they employ a thermal storage cold sink reservoir and a load management control system to direct heat and from the refrigeration plant to a load or cold to a cold storage reservoir. The system also employs the potentially environmental detrimental and costly refrigerant and ammonia.
The present invention uses environmentally and less expensive glycol. Rejected heat from the refrigeration system is first stored in an advanced concentric borehole system, which is considerably more efficient than the system by Dilk et al and the current system permits much larger volumes of heat and cold to be stored for lengthy periods to meet large demand loads in a timely an economically opportune fashion. In addition, the present invention employs an advanced predictive modeling software system that is considerably more efficient and less costly than former binary-based control systems. The current invention provides a refrigeration system outside the rink, which avoids potential operations and safety problems.

Several prior art devices have utilized the earth as a source of heat and as a heat sink. One example is the geothermal heat pump having the working fluid from the pump flow through tubes that are buried several feet below the ground. The heat pump can act as either a heater or an air conditioner, thus the fluid flowing through the pipes uses the surrounding earth as both a heat source and heat sink.

US Pat. No. 5,738,164 (Hildebrand), issued in 1998, discloses a system for energy exchange between the earth and an energy exchanger. The device effects energy exchange between earth soil and an energy exchanger. The device is comprised of a soil exchanger and supply and return flow conduits for connecting the soil exchanger with the energy exchanger. The soil heat exchanger includes a thermo-insulated supply pipe arranged in a bore well drilled in the ground, with a pump provided at the end of the flow duct, and a shroud pipe surrounding the flow duct and the pump. The system also includes lateral inlet openings and a return flow pipe. A section of the shroud functions as a thermo-pipe and the system can reach a depth of 800 meters. A thermopile is designated as a thermal insulated section formed with a correspondingly greater wall thickness.

This prior art does not disclose a system for using the ground as a heat sink without a compressor. The abovementioned disclosures are functional, but noticeably more complex, often more expensive and less efficient than the new single coaxial borehole system. They emphasize extracting heat from underground water sources, which is less efficient that extraction of energy from bedrock and there is no provision for energy storage.

The next area of development has involved various approaches for storing heat underground and circulating heated water from underground earth, rock, gravel or other sources through boreholes to the surface, often through a below or above ground heat exchanger and/or heat pump, for use in heating and cooling applications.

Patent No. CN1074018 (Xing), issued in 1993, describes heating water to 40-60C
using solar energy or a heat exchanger, then pumping the water to an underground stratum using a reversible submersible pump.
The heated water may be pumped-up for industrial heating applications. Cold water may be pumped-up in summer as a resource for air-conditioning.

Patent JP10274444 (Kuroiwa), issued in 1998, describes a method of storing a large amount of intermittent, natural energy for long-term usage. The energy is supplied continuously as a heat source for hot water supplies and in air-conditioning applications and for refrigeration/cold storage. The system employs an underground heat exchanger, a high temperature heat source heat accumulating body and a low-temperature heat source heat reservoir, and a heat medium circulation line for connecting the underground heat exchanger and the heat source heat reservoirs with an improved heat conductive material around the underground heat exchanger. The heat reservoir continuously exchanges heat with the ground and intermittently exchanges heat with the heat exchanger, thus forming high temperature thermal storage from Spring to Autumn and low temperature thermal storage from Autumn to Spring.
Patent JP2003262430 (Ikeuchi), issued in 2003, describes a heat pump having inlet and outlet pipes, provided to take out underground heat at high efficiency of heat exchange, by improving upon an underground U-tube type heat exchanger. The heat pump is thermally coupled to the heat exchanger of a heat using facility above ground. Underground heat is transferred through the heat exchanger of the ground facility, while being held at medium temperatures, without being affected by the high or low temperature heat carrier flowing down the inlet pipes, which results in a greatly increased efficiency of heat exchange.

Patent No. JP2005048972 (Saeki), issued in 2005, describes an underground heat utilizing air-conditioning system, which can recover the heat collecting and heat releasing capabilities of an underground heat exchanger. The method couples an underground heat exchanger and a heat pump with the space to be air-conditioned and reverses the operation to cooling/heating by coupling the heat pump and heat exchanger with the atmosphere.

The proceeding energy exchange systems disclosures require use of heat pumps, separate heat exchangers inside or outside the borehole and employment of U-tubes. All these approaches are less efficient and more costly than the borehole heat exchanger employed by the invention.

The following disclosures relate to coaxial collectors mostly comprised of two pipes in a borehole for the purpose of withdrawing heat and passing it through a heat exchanger and in some cases a heat pump, for various surface applications.

Patent JP1 1182943 (Uchikawa), issued in 1999, describes a heat transfer pipe for ground heat exchange with a heat medium. The heat medium passes from ground surface through two adjoining pipes and returns via two other adjoining pipes. The pipes are enclosed by a borehole.

Patent US6,450,247 (Raff), issued in 2002, describes a well drilled deep into the ground and encased and sealed at the bottom to prevent water loss and to provide heat storage. Heat conduction occurs through the casing in contact with the surrounding earth. A pipe attached to a pump at its end is placed in the well to draw cold water from the well into a heat exchanger, where it absorbs heat and cools the air to cool a domicile. Exchanged water is returned to the well. Heat accumulated during summer cooling months is dissipated through heat pipes in winter.

Patent JP2002013828 (Sakai), issued in 2002, describes using an underground heat exchanger designed to improve thermal conductivity compared to conventional coaxial systems. It consists of an inner cylinder and outer cylinder for support and provision of a casing function. The finned outer cylinder is installed in a hole excavated in the ground. A heating medium is caused to pass through a space between the outer and inner cylinders downwards and then through the inner cylinder upwards.
Heat exchange occurs between the heat medium and the ground, while the lower end of the outer cylinder is closed.

Patent JP2003307353 (Suzawa), issued in 2003, discloses a device for storing underground heat and utilizing heat on the earths surface. It consists of an inner cylinder that is coaxially inserted and fitted inside an outer cylinder. The lower end of the outer cylinder is closed to form a heat exchanger with passage between the two tubes. An outside borehole is drilled into deep rock and the heat exchanger is inserted into the vertical hole. Silica sand is placed between the vertical hole and the heat exchanger. The upper end of the inner cylinder is connected to an inlet or outlet of the heat application.

These approaches are useful, but require antifreeze and an above or below ground heat exchanger to provide cold energy for cooling applications and their efficiencies are lower than the invention. The invention provides easier and less expensive installation than these approaches since by using the borehole as a heat exchange surface it does not require a separate heat exchanger and only requires one additional pipe, to efficiently move fluid in and out of the borehole. In addition, since the invention often moves cold fluid, heat pumps are not always required.

Patent No. JP11142076 (Inada), issued in 1999, discloses simultaneous storage of cold heat and heat in one underground heat storage region by forming a cavity surrounded by a wall face in underground base rock and partitioning the cavity into two sections by a heat shielding partition wall. A heat shielding cover prevents thermal diffusion from the cavity to the longitudinal hole. This disclosure is not particularly reliable at prohibiting energy losses and it would be difficult to maintain cold at the consistent levels achieved by the new coaxial borehole design.

Patent No. US6450247 (Raff), issued in 2002, describes an air conditioning system utilizing earth cooling employing a well drilled deep into the ground and filled with water. The well is cased and sealed to prevent loss of water. A pipe placed in the well draws cold water from within the well into a heat exchanger, where it cools the air, which in turn cools a domicile. Water that has released cold is returned to the well. Heat that is accumulated during summer months is dissipated during winter months.
Heat pipes extending outwards from the top of the well contain a substance to absorb heat that evaporates at the end in the well and condenses to release heat at the opposite end. This device requires heat pipes, a heat exchanger above ground and a heat absorbing substance to provide cold water, which greatly increases the expense and complexity of the system as compared to the new invention.

Patent No. JP2005003272 (Sasaki), issued in 2005, describes a rock underground storage space, such as an underground quarry site, linked to the surface by digging a horizontal or vertical well in the peripheral rock. Heat transfer U-shaped pipes are connected in series or parallel in the well to accumulated cold heat in the rock. A heat pump and heat exchanger are maintained in the storage space.
The spatial temperature of the underground storage space is controlled by the rock and heat pump. This device exhibits higher installation and operational costs by employing a heat pump, and U-shaped tubes, which are also less efficient than a coaxial borehole system, and this approach does not take advantage of storage duration to provide cold energy at peak demand times.

Patent JP2006084097 (Hamahiro), issued in 2006, discloses a device composed of a U-tube type storage pipe and air circulating pipe installed in the water storage pipe buried in the ground to at least 5 meters.
This device uses a less efficient U-tube system and due to the minimal depth of exposure is less efficient than deeply placed borehole energy exchangers. Patent CN1546926 (Gao), issued in 2006, describes a method for using one underground heat exchanger system to produce alternate heating and cooling. The heat exchanger is comprised of an outer pipe and a spiral core pipe in the outer pipe. The heat exchange media enters the underground from the outer pipe and flows out from the inner pipe during cooling. Heat exchange efficiency is upgraded. This disclosure exhibits the extra cost of two pipes as a heat exchanger in a borehole compared to the new coaxial borehole design and there is no element of storage to better meet the cooling demand of peak periods. The invention is less costly to install and operate and is more efficient than this approach due to employing the borehole as the heat exchange medium.

None of the prior inventions mentioned have explained their consideration of energy transfer surfaces and the influence on thermal efficiencies, which is the basis of cost-effective cold energy storage and the basis for higher efficiencies in the borehole heat exchange system employed by the invention.

SUMMARY OF THE INVENTION

There is provided an energy management system for an ice rink including a cold refrigerant (i.e. glycol) that is pumped from an energy distribution center (EDC) via a cold supply pipe to an ice arena for ice making operations. Warm air from the arena during daytime is assimilated by a phase change slurry and pumped back to the EDC via a warm return pipe. Heat is normally recovered from the arena for 16 to 18 hours per day. The warm air recovered from the arena is either pumped red via a hot pipe within a phase change slurry from the EDC to underground concentric boreholes for storage, or is pumped via a hot pipe to a heat pump housed in a green thermal utility (GTU). Then the heat pump either pumps the heat energy via an energy grid hot pipe to meet demands for heat within the district energy system (DES) or converts the heat energy to cold energy and pumps it via a cold pipe to meet air-conditioning demands within the said district energy system. Heat energy would normally be stored in the underground concentric borehole heat exchanger units for 2 to 6 months. At night time, heat energy is available from the heated storage boreholes to meet the demand from the arena or municipal infrastructure in the DES. In addition, an alternative action would be to pump cold energy directly from the cold storage concentric boreholes via cold piping to the EDC and then via cold piping to the arena or any demand point in the municipal infrastructure via the cold piping. Finally, excess heat may be pumped via a hot pipe to a dissipation unit comprised of a heat sink or fan coil and the carrying water pumped back to said EDC via an inlet pipe.
BRIEF DESCRIPTION OF THE DRAWINGS

Fig.1 is an overview of the waste heat recovery, transfer, storage and conversion system. The diagram indicates that waste heat recovered from a ice arena flows to a hot concentric borehole heat exchanger for intermittent storage, after which it is pumped to an EDC (1), then to a heat pump unit for potential energy conversion and finally to a demand application within a district energy system (12). In addition, Fig.1 indicates that cold energy is stored and taken from a cold borehole exchanger system and other parts of the energy management system and distributed to demand points.
Finally, Fig.1 indicates that excess heat may be dissipated to heat sink apparatus to maintain thermal equilibrium between the hot and cold borehole storage system.

The major improvements attributable to the invention are; (a) establishing the refrigeration plant outside the arena avoids potential operational and safety problems and permits the ice-making operation to be controlled by an efficient, sophisticated microprocessor unit (b) employing concentric boreholes as in-ground heat exchangers provides an infinite heat or cold storage capability at a low cost and high level of efficiency (c) constructing the borehole heat exchangers as a cluster formation establishes a low exergy UTES system, which exhibits a narrower temperature approach between fluid and borehole than with the conventional U-tube system (d) the EMS through use of a microprocessor behaves as a smart system such that it can query various parts of the EMS to ascertain the optimal course of action to meet energy demands within the EMS and the district energy system (e) the heat dissipation cycle employed with a concentric borehole heat exchanger energy storage system ensures maintenance of a thermal balance and prevention of potential thermal breakthrough in the storage system (f) the invention employs 60% less boreholes to achieve the same level of efficiency as conventional systems (g) the concentric borehole is the only design proven to demonstrate the ability to efficiently store cold energy (h) the efficiency factor for transferring cold energy directly to a demand point is 40:1, compared to transferring cold energy directly from a refrigeration plant at an efficiency of 5:1 (i) no individual heat exchanger nor heat pump is required above ground with affixed pipes to manage the energy storage aspect of the EMS and (j) general increased efficiency of hot and cold energy transfer and storage, savings in materials, construction and operational costs, and optimization of the energy transfer process for borehole energy exchange.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As required, detailed embodiments of the present invention are disclosed herein, however, it is understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting.

With reference to Fig.1, the energy management system consisting of a microprocessor-based control system, heat recovery system, hot and cold borehole heat exchangers, heat pump system, heat dissipation unit, connecting pipes and connecting valves (e.g. singular and butterfly) comprises; an energy distribution center (1) with an inlet pipe (2) to an ice rink (3) and outlet pipe (4) from the rink back to the said EDC (1) an outlet pipe (5) from the said EDC (1) to a heated concentric borehole storage unit (6) an outlet pipe (7) from the said heated storage unit (6) to the said EDC (1) an outlet pipe (8) from the said EDC (1) to a heat pump (9) housed in a green thermal utility (GTU)(1 0) an outlet pipe (11) from the said green thermal utility (10) to a district energy system (12) an outlet pipe (13) from the said district energy system (12) to the said heat pump (9) housed in said green thermal utility (10) an outlet pipe (14) from the said EDC (1) to a cold concentric borehole storage unit (15) an outlet pipe (16) from the said cold storage unit (15) to the said EDC (1), an outlet pipe (17) from the said EDC (1) to the said heat pump (9) housed in the said green thermal utility (10) an outlet pipe (18) from the said EDC
(1) to a heat sink (19) or fan coil (20) an inlet pipe (21) from the said heat sink (19) or said fan coil (20) to the said EDC (1).

A number of units comprise the overall energy management system (EMS) and are described by the following statements.
1) Energy distribution system The Energy distribution system (EDC) is comprised of;
(a) A refrigeration system that makes ice for the ice rink (3). The said refrigeration system consists of a modular refrigeration plant employing a conventional refrigeration compressor package.
(b) An energy transfer system consisting of; three plate exchangers and six centrifugal pumps connected so as to provide heat or cold energy to the ice rink (3) and the heat pump (9) at the thermal utility (10).
(c) A microprocessor (F-16-20) with a DS-1 8-20 microchip, which controls variability of flow in the energy management system (EMS). The said microprocessor provides communication between the EDC (1), the green thermal utility (10) and the overall energy system to ensure optimal performance between demand and supply. The said microprocessor provides demand side management for the said energy system. The said green thermal utility (10) will provide the support and the said EDC (1) will compensate for the demand. The purpose of the microprocessor in the EDC is to control the supply of heat and cold energy to the storage areas and various demand points in the overall EMS and district energy system (DES)(12).

2) Concentric borehole energy storage system There can be from two to a multitude of storage boreholes in a cluster formation for the hot or cold storage units (6) and (15) depending upon the size of the demand from the rink (3) or other demand centers in the said (DES)(1 2).. The number of storage boreholes in the hot or cold storage units depends upon the volume of hot or cold energy available and the anticipated demand for energy from the demand points.
The energy storage process is based upon a predictive modeling software package, which is controlled by the said microprocessor housed in the said EDC (1).

3) Green thermal utility (GTU) -The green thermal utility or GTU (10) consists of a high efficiency CO2 refrigerant based heat pump (9) used in a modular phase for capacity control of the said GTU (10). The purpose of said heat pump (9) is to convert waste heat energy into cold energy and to convert cold energy into heat energy as required.

4) Heat dissipation unit (HDU) The heat dissipation (HDU) unit is comprised of; a heat sink (e.g. water fountain, hot tube, bath house, swimming pool, snow and ice melting unit, desalination plant, agricultural and fisheries applications) or a fan coil (evaporation unit). The purpose of the heat sink is to reject heat from the energy management system, while the purpose of the fan coil is to act as an evaporation unit when said microprocessor detects a temperature difference between ambient and saturated ground temperature in the borehole-based energy storage system (6) and (15). The advantage of the system is to permit dissipation of heat when required to maintain equilibrium temperatures in the thermal borehole system, thus avoiding a thermal breakthrough.

Referring to Fig.1 and said parts (1),(2),(3) and (4), the 4 to 40 inch (102 to 1016mm) cold inlet pipe (2) connects the refrigeration plant in the EDC (1) to the refrigeration system of the rink (3) using an appropriate fitting. The 4 to 40 inch (102 to 1016mm) hot pipe (4) connects the rink (3) to the EDC (1) using appropriate valve fittings. The purpose of these connections and parts is to permit the flow of a refrigerant (glycol) from the EDC (1) through the refrigeration system of the rink (3), thus providing cold energy from the inflow pipe (2) and returning waste heat via the outflow pipe (4) to the EDC (1).

Referring to Fig. 1 and said parts (1), (5), (6) and (7), the 3.54 inch (90mm) hot inlet pipe (5) connects the EDC (1) to the hot concentric borehole heat exchanger (6) using an appropriate valve fitting, while the 1.97 inch (50mm) hot outlet pipe (7) connects the hot concentric borehole (6) to the EDC (1), using an appropriate valve fitting. The purpose of these connections and parts are to permit water originally heated by waste heat from the rink (3) to be returned from the hot borehole storage (6) via the hot outlet pipe (7) within the refrigerant (glycol) to flow to the EDC (1), where it is available for pumping to storage and use elsewhere. The advantage of this procedure is to store produced heat energy from the ice rink in an advanced borehole storage unit until called by the EMS to be transferred or to meet demand at points in the district energy system. This system can minimize large demands on the utility system or offset large peak loads created by the demand points. Considering the EDC, one can use phase change materials to increase heat extraction efficiency by 300% over conventional water or glycol systems.

Referring to Fig.1 and said parts (1), (8), (9), (10), (11), (12) and (13) the 4 to 40 inch (102 to 101 6mm) hot inlet pipe (8) from the EDC (1) connects to a heat pump (9) housed in a green thermal utility (GTU)(10), using appropriate valve fittings. The 4 to 40 inch (102 to 1016mm) hot outlet pipe (11) connects the heat pump (9) in the green thermal utility (10) to a demand point in the district energy system (DES)(12), using appropriate fittings. The 10 to 400 inch (254 to 10,160mm) cold pipe (13) connects the DES (12) to the heat pump (9) in the GTU (10), using the appropriate valve fittings. The purpose of these connections and parts are to pump heat energy from storage in the concentric borehole heat exchanger unit (6) to the EDC (1) and then to a heat pump (9) in the thermal utility (10), then to pump the heat energy to a demand point in the DES (12) to be used as heat energy. The cold outlet connection pipe (13) returns the cold water that has provided heat to the DES (12) back to the heat pump (9) in the thermal utility (10) using appropriate fittings. The advantage of this system is that the EDC and the GTU can act together to possibly scavenge heat or cold energy from the rink or other parts of the EMS
to meet demand, at an efficiency ratio (COP) of 15:1 as compared to drawing heat or cold using a conventional system at an efficiency of less than 5:1.

Referring to Fig 1 and said parts (14), (15), (16) and (1), the 4 to 40 inch (102 to 1016mm) cold inlet pipe (14), with appropriate valve fittings, transfers phase change material (PCM) from the EDC (1) to the cold concentric borehole heat exchanger (15). The PCM assimilates cold energy from the cold concentric borehole (15) and transports it via the 4 to 40 inch (102 to 1016mm) cold pipe (16), with appropriate valve fittings, back to the EDC (1). The purpose of these parts and connections is to transfer a PCM with cold energy from the cold concentric borehole heat exchanger (15) to the EDC (1) for pumping to demand points such as the rink (3) or DES (12). The advantage of this system is using the concentric borehole cluster technology and PCM to produce more narrow approaches in temperature between fluid and borehole than with the conventional U-tube approach. This permits such features as the heat dissipation cycle, hence allowing a water fountain or other heat sink or a fan coil to operate during night time hours to sub-cool the underground cold energy boreholes.

Referring to Fig.1 and said parts (1), (17), (9), (10), (13), (12) and (11), the 4 to 40 inch (102 to 1016mm) cold pipe (17), with appropriate valve fittings, connects the EDC (1) to the heat pump (9) in the thermal utility (10). The 10 to 400 inch (254 to 10,160mm) cold pipe (13), with appropriate valve fittings, transfers cold energy to the DES (12) , while the said hot return pipe (11), with appropriate valve fittings, transfers heat energy back to the heat pump (9) in the thermal utility (10), then to the EDC (1). The purpose of these connections and parts is to transfer cold energy from the EDC (1) to the heat pump (9) in the thermal utility (10) to be available as cold energy in the DES (12). The PCM
held heat energy is returned from the DES (12) via pipe (11) to the heat pump (9) in the GTU (1) and then to the EDC (1) for another cycle. The advantage of this system is that glycol is not used for cooling the rock mass and it eliminates the need for a heat exchanger on the surface as a result of a 2 C approach in temperature for the invention as opposed to a 12 C approach in temperature with conventional technology.

Referring to Fig.1 and said parts (1), (18), (19), (20) and (21), the 4 to 40 inch (102 to 1016mm) (18), with appropriate valve connections, transfers excess hot water from the EDC (1) to a water fountain (19) or similar heat sinks and/or a fan coil (20). The purpose of these connections and parts is to transfer excess heart energy from the hot borehole (6) and EDC (1) to a heat sink to dissipate the heat and maintain equilibrium in the borehole heat exchanger storage system. The advantage of this system is that heat can be dissipated at a preferred rate and at optimal times to maintain the thermal equilibrium in the borehole storage system to ensure that the differential temperature is less than 0.5C.

Referring to Fig.1 and said parts (15), (16), (1), (17), (9) and (10), an alternative mode of operation of the energy management system involves pumping cold energy from the cold borehole storage (15) via the pipe (16) to the EDC (1) and via pipe (17) to the heat pump (9) in the GTU
(10). The purpose of these parts and connections is to transfer stored energy to the heat pump (9), where it can selectively be transferred to the DES (15) or wholly or in part be converted to heat energy for use in the DES (15). The advantage of employing cold energy from storage is that using this direct energy store is less expensive and more efficient than converting energy for such demands as air-conditioning. Conversion of cold energy to heat energy is still advantageous if limited heat energy is available from other sectors of the EMS.

Referring to Fig.1 and said parts (12), (13), (9), (10), (17), (1), (3), (6), (15), an alternative mode of operation involves pumping of medium temperature water from the demand point in the DES (12) via outlet pipe (13) to the heat pump (9) in the GTU (10) then via outlet pipe (17) to the EDC (1) where it will scavenge any available additional cold or hot energy. The energy management system then examines two alternative courses of action; (a) it determines whether additional ice making or heating is required in the ice rink (3), or (b) it determines whether cold or heat energy should be pumped to the borehole storage units (6) and (15) or pumped to the GTU (10). This process is based upon a predictive modeling software package controlled by the said microprocessor housed in the EDC (1). The purpose of these connections and parts is to assimilated potentially useful energy from the DES (12) and bring this energy into the EMS
to supplement existing stored energy or add to scavenged energy, which may be sent to demand points in the EMS. The advantage of this system is the ability to access and utilize any excess heat or cold energy available in the district energy system for use in the rink and/or for storage in heat or cold borehole storage units so as to maximize system efficiency.

It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiment without departing from the spirit and scope defined in the Claims.

In warm climates, it is foreseeable that excess heat beyond demand of the local municipal infrastructure may be produced. When stored in a borehole heat exchange system, excess heat relates to a greater amount of heat than is required to maintain a thermal balance between the hot and cold concentric borehole heat exchanger energy storage system. This potential excess heat could create a thermal breakthrough between the hot and cold energy storage units, whereby hot and cold energy would mix and produce a temperature averaging effect, which would greatly lessen the thermal efficiency advantage established by the dual storage system.

The current technology underlying the invention is an application of seasonal Underground Thermal Energy Storage (UTES) technology, for storing renewable heat energy from waste heat and cold energy from bedrock, surficial materials and soil, surface water, lake, river or ocean water, or cooling tower water for air conditioning. The coaxial energy storage system utilizes a new coaxial borehole heat exchanger design that dramatically reduces the required size of the borehole field and enables cold storage for direct cooling, (i.e. without the use of heat pumps or chillers). Drilling costs of the borehole portion of energy storage systems may be reduced by 2/3rds with the use of the coaxial energy storage and cold transfer system.
The borehole design is a breakthrough in cooling applications. This new coaxial borehole system offers three significant advantages as it (1) reduces the borehole thermal resistance, (2) increases the effective thermal transfer surface area, resulting in increased thermal flow rates over current designs, and (3) produces higher volumetric flow rates, resulting in higher thermal transfer rates with minimum transfer losses. Collectively, the overall design increases borehole efficiency by 300 %.
Effective heat transfer is considerably more difficult at low temperatures (below 40 C), and direct cooling is not practical with current U-tube borehole designs. This is due to the high frictional heat gains by the working fluid during cold charging and cold discharging. This new coaxial energy storage design allows for direct charging and discharging of cold energy for air conditioning with low frictional heat gains and without the use of supplemental heat pumps or chillers.

Other advantages of this new coaxial energy storage approach are: (a) with this new heat exchanger design being 300% more efficient than current designs, the surface area required for the storage is significantly reduced, therefore, energy storage systems can fit in a confined space and are more adaptable in serving existing buildings, (b) water without antifreeze can be used as the heat carrier, such that the systems capacity is increased and the pumping costs decreased, (c) smaller diameter boreholes can be drilled to greater depths, which will reduce drilling costs and (d) the boreholes can be sealed with bentonite grout to make them water tight and suitable for coaxial type BHEs (i.e. eliminates groundwater flux to move cold water of site). In addition, the adoption of this technology will directly reduce greenhouse gas emissions from energy use and air polluting emissions from refrigerants.
The technologys primary focus is reducing energy consumption and its associated greenhouse gas emissions. The improved system could also be considered an enabling technology for application of other renewable energy sources such as cold harvested from lakes and ambient air.

Conventional U-tube drilling uses a 152 mm (6 inch) diameter borehole, whereas this new coaxial energy storage borehole system uses a 115 mm (4.5 inch diameter) to 152mm borehole.
In drilling a 115 mm diameter borehole as compared to a 152 mm diameter borehole there is a 25%
savings in fuel due to less drilling resistance. It takes about 2,000 litres of diesel fuel to drill a 152 mm diameter borehole to a depth of 150 m, by using a 115 mm borehole fuel savings of 500 litres per borehole (or 25 %) can be achieved.
In addition, there would be 42 % less drilling consumables (water and foam for example) used and 42 %
less drill cuttings by volume produced. The exact amount of fuel savings and consumables used depends on the locai conditions.

The coaxial borehole approach is a much more thermally efficient borehole heat exchanger than a conventional U-tube borehole. Therefore, further savings with respect to drilling costs are achieved by the simple fact that fewer boreholes are required. More specifically, the cost savings for BTES cooling is based upon the ability of the system to operate at small temperature differences (?T), which is directly related to borehole thermal resistance (Rb). The coaxial borehole can store cold energy and operate at temperatures ranging from approximately 0.5C to 8 C (?T of 7.5 C), which is an ideal range for'direct' (i.e.
no heat pump) cooling. A conventional U-tube system would have to store and operate at temperature ranges below freezing to accomplish the same task, due to higher borehole thermal resistances (Rb).
Therefore, to provide the same level of cooling, conventional U-tube type BTES
designs require heat pumps and antifreeze protected ground loops, whereas the new BTES approach eliminates the need for heat pumps and antifreeze.
Moreover, the issue of operating temperature differences (?T) in direct BTES
heating and cooling applications, and how this relates to drilling lengths, requires further explanation. An inefficient BHE gives up at least 5 to 6 C in the process of transferring energy to and from the borehole store. A heat gain of 5 to 6 C in a storage system operating with a ?T of 7.5 C would eliminate the direct cooling potential of the BTES system. In the case of high ?Ts, as in a high temperature BTES heat store (e.g. the Drake Landing thermal solar project in Okotoks, AB, Canada) the typical operating range is from 40 C to about 80 C.
This gives rise to a ?T of about 40 C in 'direct' heating mode. Adding 5 to 6 C to a ?T of about 40 C would not adversely affect the operational functioning of the thermal store as adjustments can easily be made at these temperature levels. Therefore, the thermal resistance of a borehole heat exchanger is less critical in heating applications with large ?T's, and conversely is far more critical in cooling applications with small ?T's. Based on field measurements, the coaxial systems Rb (<0.005 K/ (W/m) (Cruickshanks et al., 2006) is much lower than the U-tube Rb (0.2 K/ (W/m) (Helistrm et al., 1988) allowing it to handle even peak cooling loads.
Again, regarding drilling length, another issue with U-tube heat exchangers, especially in cooling applications, is the very small heat transfer contact area on the borehole wall. Essentially, the heat transfer fluid circulating in the U-tube has only a tangential contact area with the borehole wall at best, if properly installed. However, the coaxial/concentric BHE provides full contact of the heat transfer fluid with the borehole wall in the annular space between the centre tube and the outside borehole wall, thereby reducing the borehole thermal resistance (Rb) of the borehole compared to the conventional U-tube configuration. This greatly increases the thermal energy transfer to and from the rock store, subsequently reducing the total drilling length required.
The Earth Energy Designer (EED) modeling software, an industry standard, employed for illustrative purposes to conduct sensitivity analyses, has shown that thermal efficiency can decrease or increase the amount of drilling required. EED accepts measured Rb values or it can calculate Rb values based on standard installation practices. The calculated Rb values of 0.2 K/(W/m) for the U-tube system and 0.02 K/(W/m) for the concentric system were used. Since the in-situ (measured) Rb value of 0.005 K/(W/m) is an order of magnitude less than the calculated value, EED tends to penalize the concentric system in terms of drilling length required. Even with this factor considered, the new BTES cooling system would require significantly less total drilling length as compared to a U-tube type system.
The analysis showed that a U-tube BTES system comprising 162 BH x 150 m deep x 8 m spacing would take at least 10 years to achieve suitable cooling temperatures, whereas a concentric BTES system of the same depth and BH spacing achieves the same cooling temperatures in less than 3 years. Note that these timeframes are strictly illustrative examples. There would also be a need for many more boreholes, with the U-tube approach, as merely drilling deeper would actually cause cooling capacity to deteriorate due to the effect of the geothermal gradient (i.e. 15 C/km or 1.5 C/100 m).
There should be no significant energy losses from the cold store, only moderate anticipated energy losses. A
preliminary calculation indicates that the losses will be in the order of 14 % for a cold storage with a depth of 150 m x 64 m2 square. It is standard procedure to apply an insulating cap to reduce thermal losses. Since this is a renewable energy application with the cold source coming from the natural environment, make-up cold is readily available.
The radiogenic heat flow in Meguma bedrock is very low (1.6 W/m3) and will not adversely add to heat gain in the cold store. In terms of the geothermal gradient, the high value of 15C/km is used in calculations for the cold store, instead of the lower value of 13 C/km. In addition, all of the information provided here is predicated on the use of conservative data and assumptions, from average storage temperature availability, using the depth of the cold source from prior research, and even including the thermal performance of the boreholes.
It is to be understood that the foregoing description and specific embodiments are merely illustrative of the best mode of the invention and the principles thereof, and that various modifications and additions may be made to the apparatus by those skilled in the art, without departure from the spirit and scope of this invention.
In this patent document, the word comprising is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.
A reference to an element by the indefinite articles a or an does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the element.

EXAMPLE OF USAGE OF THE INVENTION

An example of employing the invention is to recycle waste heat energy from a local ice arena to supplement the heating and air-conditioning demands of a local hospital. This system could be equally applied to other commercial, industrial and institution elements of municipal infrastructure such as chemical plants, petrochemical plants, nuclear power plants, carbon fuelled power plants, refineries, metal and metallurgical processing facilities, sports domes, universities, resort complexes and military bases.

Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS
CLAIMED ARE AS FOLLOWS:

What is claimed is:

1. An energy management system comprising:
(a) an energy distribution center (EDC) for providing refrigeration, energy transfer and process control within the EMS
(b) a refrigeration system for preparation of ice within the ice rink or cold for HVAC systems (c) an energy transfer system to retrieve and transfer energy between storage and demand points (d) a microprocessor to control the functions of the EMS
(e) a hot borehole energy storage unit to store heat energy retrieved from other parts of the EMS
(f) a cold borehole energy storage unit to store cold energy retrieved from other parts of the EMS
(g) a green thermal utility to house a heat pump for energy conversion (h) a heat dissipation unit for rejection of excess heat from the EMS

2. The EMS according to claim 1, wherein there is provided a microprocessor to provide process control between all parts said functional parts of the EMS

3. The energy management system according to claims (1) and (2), wherein there is provided a modular refrigeration plant, which employs a conventional refrigeration compressor package for ice preparation.

4. The EMS according to claims (1) and (2), wherein there is provided an energy transfer system for transferring energy between retrieval, storage and demand points within the EMS and district energy system (DES).

5. The EMS according to claims (1) (2) and (4), wherein there is provided at least six centrifugal pumps for the distribution of system fluids.

6. The EMS according to claims (1) and (2), wherein there is provided an underground concentric borehole heat exchanger unit or cluster of boreholes for storage of heat energy

7. The EMS according to claims (1) and (2), wherein there is provided an underground concentric borehole heat exchanger unit or cluster of boreholes for storage of cold energy

8. The EMS according to claims (1) and (2), wherein there is provided a green thermal utility for effecting energy conversion using a standard heat pump

9. The EMS according to claims (1), (2), (7) and (8) wherein the borehole cluster method creates a low exergy UTES system with narrow temperature approaches

10. The EMS according to claims (1), (2) and (8), wherein there is provided a refrigerant-based heat pump to convert heat energy to cold energy and cold energy to heat energy

11. The EMS according to claims (1) and (2), wherein there is provided a heat dissipation/convection unit for rejecting excess heat from the EMS

12. The EMS according to claims (1), (2) and (10), wherein there is a fan coil to reject heat to the atmosphere.

13. In a method for sub-cooling water in the said EMS, the steps of;
(a) pumping cold energy from the said cold borehole energy storage to the said EDC and said GTU
(b) pumping return mid-range temperature water from said point load back to the said EDC and then to the said cold borehole storage for sub-cooling (c) pumping said sub-cooled water back to said EDC to scavenge any additional cold energy, and (d) employing the said microprocessor control unit, using a predictive modeling software, to analyze whether said sub-cooled water and said additional cold energy should be employed for ice making or pumped to the said GTU for use at demand points in the said DES

14. An energy management system according to claims (1), (2), (4), (5), (6), (7), (8), (9), (10), (11) and (12), which is applicable to other energy waste energy producing entities and utilities such as factories, refineries, institutions, military establishments, service establishments, sports arenas, desalination plants, mineral processing plants and convention and nuclear power facilities.