DISTRICT COOLING SYSTEM AND THERMAL ENERGY STORAGE TANK SYSTEM TECHNICAL FIELD [0001] The present invention relates generally to district heating or cooling systems and components utilized in such systems. BACKGROUND ART [0002] In commercial buildings today, air-conditioning systems can be broadly categorised into two technologies based on the refrigerant or working fluid adopted. The two technologies are known as Direct Expansion (DX) and Chilled Water (CHW). [0003] DX systems employ the use of the gas refrigerant which is compressed to a liquid within a condensing unit and gives off waste heat in the process. This liquid is allowed to re expand back into a gas at a controlled rate within a cooling coil and thus absorbs heat or creates a cooling effect as it does so. Within a fan coil unit, the air that is to be cooled is blown over the cooling coils and then passed into the desired room. While DX systems are widely used in commercial applications, they have a number of disadvantages including limitations on maximum pipe runs between the condenser and fan coil units, the space required to accommodate multiple outdoor condensing units, limitations in systems capacity and reduced operating efficiency at partial load conditions. [0004] In contrast, chilled water systems adopt a single central chiller plant which uses water heat transfer fluid in the buildings of which the temperature is typically lowered to approximately 6'C and supplies water at this temperature to all theme coil units. The flow of water is regulated through the various cooling coils using modulating valves to maintain precise control over the cooling coil and therefore the supply airstream temperature. The systems typically allow much more accurate control over temperature and humidity than DX systems. [0005] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country. SUMMARY OF INVENTION [0006] The present invention is directed to a district cooling system and thermal energy storage tank system, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.
[00071 With the foregoing in view, the present invention in one form, resides broadly in a district cooling system and thermal energy storage element system for providing suitable temperature fluid to a field, the system including A thermal energy storage element containing a fluid for heat transfer with a chiller unit operating a chiller cycle and for direct delivery to a field fluid distribution and return network in higher than average demand periods; A plant room including At least one chiller unit associated with the thermal energy storage element for cooling a fluid for delivery to the thermal energy storage element; at least one pump to move the fluid through the thermal energy storage element, at least one chiller unit and at least partially into the field fluid distribution and return network; attendant pipework to allow the fluid to be moved between the thermal energy storage element, at least one chiller unit and at least partially into the field fluid distribution and return network wherein the thermal energy storage element is located on one lateral side of the plant room with the field on an opposite side to allow at least one pipeheader of the attendant pipework to be mounted on at least one wall of the plant room for a more efficient layout. [0008] In an alternative form, the invention resides in a method of utilising a thermal energy storage tank together with a distributed cooling system to utilise off peak electrical power supply tariffs, the district cooling system including A thermal energy storage element containing a fluid for heat transfer with a chiller unit operating a chiller cycle and for direct delivery to a field fluid distribution and return network in higher than average demand periods; A plant room including At least one chiller unit associated with the thermal energy storage element for cooling a fluid for delivery to the thermal energy storage tank; at least one pump to move the fluid through the thermal energy storage element, at least one chiller unit and at least partially into the field fluid distribution and return network; attendant pipework to allow the fluid to be moved between the thermal energy storage element, at least one chiller unit and at least partially into the field fluid distribution and return network wherein the thermal energy storage element is located on one lateral side of the plant room with the field on an opposite side to allow at least one pipeheader of the attendant pipework to be mounted on at least one wall of the plant room for a more efficient layout and the method including the steps of delivery of at least a portion of the fluid in the thermal energy storage element directly to the field fluid distribution and return network during higher than average demand periods and charging the chilled fluid stored in the thermal energy storage element during lower than average demand periods. [0009] Preferably, the central energy plant is the centralised plant for the district cooling. It typically contains the chillers, cooling towers, pumps and thermal energy (chilled water) storage tank. It offers the benefits of high-efficiency, central plant, reduced maintenance, ease of expansion and technological upgrades as technology advances. On large centralised plants, redundancy or backup systems are typically included within the system architecture which allows for continuous supply in the event of a component failure. [0010] Thermal Energy Storage (TES) preferably makes use of periods of day or night when the site demand from the field for cooling is less than the average demand, by running the central chilled water plant during these times to chill returned water (from approximately 14'C) back to chilled water (at approximately 6C). During times when the site demand exceeds the average demand (typically in the afternoon), the chilled water is drawn from the storage tank. The pre cooled water is then reticulated through the field and delivered to fan coil units within each building. The installation of air-conditioning systems within the buildings themselves remains essentially the same as any conventional chilled water system except that the chiller plant takes the form of one efficient centralised plant rather than numerous different cooling plants. The central energy plant can be up to 2.5 times more efficient and aged smaller chiller plants. [0011] The district cooling system of the present invention comprises a central energy plant, large-scale stratified chilled water storage (TES) and associated piping reticulation to serve the selected customer group in the field. The central energy plant produces the chilled water for air conditioning or process plant use. [0012] Thermal energy storage by means of a stratified chilled water storage (TES) tank is _r preferably incorporated into the system in order to enable timeshifting of peak electrical loads and utilisation of cheap off-peak tariffs to generate chilled water for use during the day. This approach effectively reduces pressure on existing power generation and distribution systems and also defers infrastructure upgrade costs. [0013] The "field" is typically an air-conditioning network associated with the central energy plant and to which the chilled water years distributed to a number of fan coil units in order to cool buildings or rooms. Normally, the field includes one or more buildings or structures. [0014] There may be one or more tertiary chilled water pumps in order to assist with the distribution of the chilled water from the central energy plant to the field and to return the return water from the field. [0015] The field can be connected to the TES tank and/or to one or more chiller units in order to utilise chilled water from either (or both). Preferably however the field is connected to the TES tank in order to decouple the chiller units from the load which is applied by the field. [00161 The principal elements of a central energy plant of the present invention typically include: (a) a high-efficiency liquid chiller unit housed in a plant building to generate cooling energy; (b) a cooling tower system to remove heat rejected from the chiller cycle; (c) a thermal energy storage element designed to store large quantities of cooling energy in the form of chilled water and decouple chiller operation from the field load; and (d) a variable flow reticulation network to transport cooling energy in the form of chilled water from the central energy plant to the field load. [00171 The system may include at least one heat exchanger to exchange heat between the working fluid of the chiller cycle and a fluid distributed to and returned from the field. [00181 Appropriate pipework is provided to connect the inlet/outlets to the pipe headers provided in the central energy plant room. [0019] There are preferably at least three pumping groups provided in the system of the present invention, including one or more pumps per group, namely: 1. Primary Chilled water from chiller unit to tank; 2. Secondary Chilled water from tank to field; and 3. Condenser water about condenser cycle to cooling tower and back to condenser side of chiller unit. [0020] A bypass system may be provided to allow that tank chilled water supply temperature to the field to be elevated to maximise effectiveness of the thermal energy storage element. [0021] Water is a convenient heat storage medium for use according to the present invention, because it has a high specific heat capacity. Compared with other substances it can store more heat per unit of weight (and volume). Water is also non-toxic and low in cost. [0022] Typically, each chiller unit is a unit which includes a vapour-compression cycle with appropriate process equipment and which is linked to one or more cooling towers and which chills water for distribution to the field and receives return chilled water from the field for chilling and re-distribution in a continuous manner. [0023] The vapour-compression cycle uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the field chilled water and subsequently rejects that heat through the cooling towers. [0024] All such systems typically have four components: a compressor, a condenser, a thermal expansion valve (also called a throttle valve or TX Valve), and an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapour and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapour is then in the thermodynamic state known as a superheated vapour and it is at a temperature and pressure at which it can be condensed with typically available cooling water or cooling air in the cooling towers. That hot vapour is routed through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool air from the cooling towers flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the water or the air (whichever may be the case). [0025] The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapour refrigerant mixture to where it is colder than the temperature of the chiller water returning from the field.
[00261 The cold mixture is then routed through the coil or tubes in the evaporator where a portion of the heat from the chilled water return is transferred to the cold mixture. That heat transfer evaporates the liquid part of the cold refrigerant mixture. At the same time, the chilled water is cooled to the desired temperature. The evaporator is where the circulating refrigerant absorbs and removes heat from the chiller water used as the working fluid for the district cooling system, with the heat subsequently rejected in the condenser. [00271 To complete the refrigeration cycle, the refrigerant vapour from the evaporator is again a saturated vapour and is routed back into the compressor. [00281 There will therefore preferably be at least two working fluids in the vapour compression cycle, one being the refrigerant used in the chiller unit/cycle and the second with the chiller water used to distribute to the field. [0029] Preferably, one or more cooling towers are used in the chiller unit/cycle of the present invention to remove heat from the refrigerant in the chiller unit/cycle. Normally the at least one cooling tower has a cooling water cycle with the condenser. This cycle may include one or more pumps in order to circulate the cooling water from the condenser to the at least one cooling tower and back again, preferably in a closed loop. [00301 Typically, the thermal energy storage element is a tank or similar vessel having at least one warm water inlet/outlet and at least one chilled water inlet/outlet. [00311 In this configuration, an inlet/outlet is typically provided at a lower portion of the vessel (chilled water) and inlet/outlet is provided at an upper portion of the vessel (warm water). Each inlet/outlet is identified as such, as the vessel will normally be connected to related process apparatus in such a way that fluid can flow through the thermal energy storage tank in either direction and therefore, each inlet/outlet can be an inlet or an outlet depending upon the direction of fluid flow through the tank. [0032] The thermal energy storage (TES) tank is preferably a stratified thermal storage tank. Almost any temperature difference can be present in the tank however the storage volume required is minimized with larger difference in temperature between the top of the tank and the bottom of the tank. Preferably, a temperature difference of >8'C is present. Thermal diffusion between the hot and cold fluid is preferably confined to the interface region between the hotter and colder fluid called the thermocline. An important consideration to leveraging this phenomenon for thermal storage is creating stratified layers and keeping the stratification intact. Therefore, the flow into the tank should be as laminar as possible to prevent or minimise disruption of the thermoclines in the tank. [00331 One or more, typically a pair of diffuser assemblies are provided in the TES tank. These diffusers are designed to eliminate turbulence and provide a stable, sharply defined transition layer, or "thermocline", thus allowing for the natural stratification of warm water at the top of the tank and chilled water at the bottom. Preferably, a warm water diffuser is provided in an upper portion of the TES tank and a cold water diffuser is provided in a lower portion of the TES tank. [0034] The principal consideration for a thermal energy storage system is the amount of cooling load shifted to off-peak periods and the proposed mode of operation. A full storage system is sized and operated to disable the chiller during peak demand periods. By contrast, a partial storage system uses both the cool storage system and the chiller to meet the cooling load during peak periods, resulting in a lower peak period demand reduction. [0035] All thermal energy storage systems incorporate a storage vessel, which will be subject to thermal energy losses of about one to five percent per day. Therefore, thermal performance of a cool storage system varies depending on the inventory of ton-hours stored and the rate of discharge. The total capacity of the storage system depends on the cooling load profile imposed upon it. [0036] Generally there will be one large TES tank to allow effective stratification but more than one TES tank may be utilised depending upon site load and/or other design considerations. [00371 Where the vessel is provided in a cylindrical embodiment, the vessel may be oriented with the main longitudinal axis of the vessel substantially horizontally or substantially vertically. Where provided with the main longitudinal axis of the vessel substantially vertically, the vessel will normally be provided with a substantially planar or flat basewall and a substantially cylindrical sidewall. Normally, a partially spherical top wall is provided to close the vessel. The partially spherical top wall can be hemispherical or torispherical. [0038] In this configuration, the fluid flow through the separate chambers will normally be in a radial direction which is described more fully below. [0039] The tank of the present invention may include a plurality of internal dividing walls to divide the vessel volume into a number of separate chambers. Each separate chamber is formed to provide a separate fluid column and the provision of many walls allows one vessel volume to be divided into a number of separate fluid columns. This allows stratified hot water storage to 0 occur which is also known by other names including stratified thermal storage, thermocline tank and water stratified tank storage, in each of the separate chambers. [0040] The chambers may be provided radially (such as in the cylindrical embodiment with the main longitudinal axis substantially vertically) or longitudinally. The configuration which is used is typically dependent upon the shape of the vessel and/or the orientation of the vessel. [0041] Each of the internal dividing walls is typically a bulkhead wall which is designed to prevent fluid flow from one chamber to another chamber except as allowed through the respective connection conduit. [0042] Typically, the dividing walls will be planar but this does not need to be the case. Normally, each internal dividing wall will extend from one wall of the vessel to another wall of the vessel and from the base wall to the top of the vessel. However, depending upon the configuration chosen, an internal dividing wall may meet another internal dividing wall at a central or other location within the vessel in order to form separate chambers. [00431 Any material of construction can be used as outlined above with the materials of construction chosen dependent upon the use of the vessel. For example, a non-pressurised vessel can be formed from a nonmetallic material such as plastic. Further, a nonpressurised vessel does not have to be rigid but will preferably be rigid. [0044] The internal dividing walls will typically be shaped to seal the internal volume of the vessel into a number of internal chambers. Any number of chambers can be formed within the vessel which means that any number of internal dividing walls can be provided. Typically, the number and size of the separate chambers is designed for the efficient and effective thermal energy storage given the fluid used for the energy storage. [0045] The tank of the present invention will include a connection conduit between adjacent separate chambers to allow fluid to flow between adjacent chambers. Typically, each connection conduit will extend from a lower region in one chamber to an upper region in and adjacent chamber. Typically, each connection conduit will be tubular but may be of any shape. [00461 As mentioned above, it is preferred that the connection conduit be as large as possible in order to reduce fluid velocity through the conduits to as low as possible in order to maintain the temperature stratification within each chamber. [00471 Normally, a single connection conduit is provided in each bulkhead wall. All of the connection conduits are preferably oriented in the same direction. Further, all of the connection conduits are normally provided towards one lateral side of the vessel and all are preferably positioned on the same lateral side of the vessel. [00481 Each connection conduit is typically substantially L-shaped when viewed from the side. Each connection conduit preferably includes a horizontal foot portion in a substantially upright leg portion. Normally, an arcuate transition will be used between the foot portion and the leg portion, again, typically to reduce fluid velocity. [0049] Preferably, the substantially upright leg portion of each connection conduit will terminate spaced from the top wall of the vessel in each chamber. [0050] Each connection conduit will normally have an inlet/outlet at either end thereof. The upper inlet/outlet from each connection conduit maybe a divergent inlet/outlet. [0051] The lower inlet/outlet of each connection conduit may be flush with the surface of the bulkhead wall through which it extends or alternatively, may stand slightly proud of the surface. [0052] More than one thermal energy storage tank may be provided and connected to one another in series. For example, an inlet/outlet of one vessel is typically connected to an inlet/outlet of another vessel from upper to lower in series allowing the use of multiple vessels to function as a single thermal energy storage tank. [00531 The central energy plant is preferably laid out in a number of different, and separate areas. Typically, the central energy plant includes a plant room which is the location of the chiller units, the pumps, the pipe headers leading to the field and to and from the process equipment, a control room and electric power switches and transformers. Preferably, a hard stand with the cooling towers provided thereupon is provided adjacent the plant room and the TES tank is provided adjacent to both the plant room and the hard stand and tower bank. [0054] The plant room is typically divided further into a number of separate areas with the chiller units being located on one lateral side of the plant room with the pump groups opposite the chiller units and the control room and electrical power distribution equipment provided at one end opposite the TES tank. [0055] This particular layout allows the pipe headers to be provided along one of the side walls of the plant room. Typically, the pipe headers are provided on the wall adjacent the pumps IV with the pumps extending substantially perpendicular to the pipe headers. [0056] Further, it is preferred that the entry and exit from the pipe headers to the respective process equipment is angled, typically at approximately 450 in order to minimise the friction losses in the fluids flowing through the pipe headers. [00571 The pipework connecting the chiller groups with the pumping groups and/or the piping headers will typically extend from the chiller units on one side of the plant room substantially vertically over the top of a central access area and back to the pumps or pipe header as required. [0058] By orienting the chiller units substantially perpendicularly to the pipe header and the pumps substantially perpendicularly to the pipe headers, this increases accessibility to both the chillers and pumps for maintenance or any other reason. It also provides the piping headers on a single wall in order to centralise all of the piping headers in one location. [0059] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention. [0060] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge. BRIEF DESCRIPTION OF DRAWINGS [0061] Various embodiments of the invention will be described with reference to the following drawings, in which: [0062] Figure 1A is a schematic view of the typical daytime operation of a distributed cooling system with thermal energy storage. [0063] Figure 1B is a schematic view of the typical night time operation of a distributed cooling system with thermal energy storage. [0064] Figure 2 is a plan view of a system layout of a distributed cooling system with thermal energy storage according to a preferred embodiment of the present invention. [0065] Figure 3 is a plan view of a plant room for a distributed cooling system with thermal energy storage according to a preferred embodiment of the present invention.
1[ 1 [00661 Figure 4 is a sectional side view of the plant room illustrated in Figure 3 along line B. [00671 Figure 5 is an enlarged view of the portion of the plant room illustrated in Figure 4 and identified by reference numeral 80. [0068] Figure 6A is a detailed side view of the chilled water return piping header included in the plant room illustrated in Figure 4. [0069] Figure 6B is a detailed side view of the chilled water supply to field piping header included in the plant room illustrated in Figure 4. [00701 Figure 6C is a detailed side view of the chilled water discharge piping header included in the plant room illustrated in Figure 4. [00711 Figure 6D is a detailed side view of the chilled water supply to tank piping header included in the plant room illustrated in Figure 4. [0072] Figure 6E is a detailed side view of the chilled water suction piping header included in the plant room illustrated in Figure 4. [0073] Figure 7 is an enlarged view of the portion of the plant room and cooling towers illustrated in Figure 4 and identified by reference numeral 81. [0074] Figure 8 is a schematic view of chilled water flow through the system illustrated in Figure 2. [00751 Figure 9 is a schematic view of condensate water flow through the system illustrated in Figure 2. [0076] Figure 10 is a schematic illustration of a chilled water district cooling system with one in-room air conditioner or AHU. DESCRIPTION OF EMBODIMENTS [00771 According to a particularly preferred embodiment of the present invention, a district cooling or heating system with an associated thermal energy storage tank is provided. [0078] A preferred form of the district cooling system and thermal energy storage element system for providing suitable temperature fluid to a field is illustrated schematically in Figures 1A and 1B with Figure 1A illustrating the typical daytime operation of a distributed cooling system with thermal energy storage and Figure 1B illustrating the typical night time operation of a distributed cooling system with thermal energy storage. [00791 The preferred form of the present invention is illustrated in Figure 2 and includes a thermal energy storage (TES) tank containing a fluid for heat transfer with a chiller unit operating a chiller cycle and for direct delivery to a field fluid distribution and return network in higher than average demand periods and a central energy plant room including a number of chiller units 11 each associated with the thermal energy storage tank 10 for cooling a fluid for delivery to the thermal energy storage tank 10. [0080] A number of pumping groups each including at least one pump are also provided in the central energy plant room 12 to move the fluid through the thermal energy storage tank 10, chiller units 11 and at least partially to and from the field. [0081] Attendant pipework is provided to allow the fluid to be moved between the thermal energy storage tank 10, chiller units 11 and at least partially to and from the field. Importantly as illustrated in Figure 2, the thermal energy storage tank 10 is located on one lateral side of the plant room 12 with the field located on an opposite side to allow the pipe headers (illustrated in detail ion Figure 4) of the attendant pipework to be mounted on a side wall of the plant room 12 for a more efficient layout. [0082] In operation, the Thermal Energy Storage (TES) tank 10 makes use of periods of day or night when the site demand from the field for cooling is less than the average demand, by running the central chilled water plant during these times to chill return water from the field (from approximately 14C) back to chilled water (at approximately 6'C). During times when the site demand exceeds the average demand (typically in the afternoon), the chilled water is drawn from the storage tank. The pre-cooled water is then reticulated through the field and delivered to fan coil units within each building. The installation of air-conditioning systems within the buildings themselves remains essentially the same as any conventional chilled water system except that the chiller plant takes the form of one efficient centralised planned rather than numerous different cooling plants. The central energy plant can be up to 2.5 times more efficient and aged smaller chiller plants. [0083] The "field" is typically an air-conditioning network associated with the central energy plant and to which the chilled water is distributed to a number of fan coil units in order to cool buildings or rooms. Normally, the field includes one or more buildings or structures.
[00841 There may be one or more tertiary chilled water pumps in order to assist with the distribution of the chilled water from the central energy plant to the field and to return the return water from the field. [00851 The field can be connected to the TES tank 10 and/or to one or more chiller units 11 in order to utilise chilled water from either (or both). Preferably however the field is connected to the TES tank 10 in order to decouple the chiller units 11 from the load which is applied by the field. [00861 Water is a convenient heat storage medium for use according to the present invention, because it has a high specific heat capacity. Compared with other substances it can store more heat per unit of weight (and volume). Water is also non-toxic and low in cost. [00871 The central energy plant illustrated in Figure 2 is laid out in a number of different, and separate areas which may not be readily apparent at first view. The central energy plant includes a plant room 12 which is the location of the chiller units 11, the pumps 13, the pipe headers 14 leading to and from the field and to and from the process equipment, a control room 15, electric power switch room 16 and transformer room 17 for electrical power supply. Preferably, a hard stand with the cooling towers provided thereupon is provided adjacent the plant room and the TES tank is provided adjacent to both the plant room and the hard stand and tower bank. [00881 The plant room 12 is typically divided further into a number of separate areas as illustrated in Figure 3 with the chiller units 11 being located on one lateral side of the plant room 12 with the pump groups 13 opposite the chiller units 11 and the control room 15 and electrical power distribution equipment 16, 17 provided at one end of the plant room 12 opposite the TES tank 10. [00891 This particular layout allows the pipe headers 14 to be provided along one of the side walls of the plant room 12. As illustrated in Figure 3, the pipe headers 14 are provided on the wall adjacent the pumps 13 with the pumps 13 extending substantially perpendicularly to the pipe headers 14. [0090] Further, it is preferred that the entry and exit from the pipe headers to the respective process equipment is angled, typically at approximately 450 in order to minimise the friction losses in the fluids flowing through the pipe headers. [0091] As illustrated in more detail in Figure 4, the pipework 18 connecting the chiller units i -r 11 with the pumping groups 13 and/or the piping headers 14 extends from the chiller units 11 on one side of the plant room substantially vertically over the top of a central access area of the chiller hall 19 and back to the pumps 12 or pipe header 14 as required. Also illustrated in Figure 4 is the hard stand 20 and cooling towers 21 for use with the cooling water cycle for the condenser of the chiller units 11. [0092] By orienting the chiller units substantially perpendicularly to the pipe header and the pumps substantially perpendicularly to the pipe headers, this increases accessibility to both of the chillers and pumps for maintenance or any other reason. It also provides the piping headers on a single wall in order to centralise all of the piping headers in one location. [0093] There are at least three pumping groups provided in the plant room illustrated in Figure 3 including one or more pumps per group, namely: 4. Primary Chilled water from chiller unit to tank; 5. Secondary Chilled water from tank to field; and 6. Condenser water about condenser cycle to cooling tower and back to condenser side of chiller unit. [0094] Each chiller unit is unit 11 includes a vapour-compression cycle with appropriate process equipment and is linked to one or more cooling towers 21. The chiller units 11 chill water for distribution to the field and receives return chilled water from the field for chilling and re-distribution in a continuous manner. [0100] A more detailed view of the plant room of the preferred embodiment is illustrated in Figure 5. The important portion of Figure 5 is the location and positioning of the pipe headers on the wall of the plant room adjacent the pumps 13. [0101] There are five pipe headers illustrated in Figure 5 and from uppermost to lowermost the pipe headers are a chilled water return header, chilled water supply header to the field, condenser water discharge header leading to the cooling towers, chilled water supply header to the TES tank and a condenser water suction header leading from the cooling towers back to the pumps 13. [0102] As illustrated, the five pipe heaters are located on the same wall and run generally parallel to one another. A detailed view of each of the pipe headers ears given in Figures 6A to 6E showing the various connections of peripheral piping with each pipe header.
[01031 A preferred form of the hard stand 20 and cooling towers 21 is illustrated in Figure 7. A discharge pipe 22 from the condenser water discharge header of figure 5 provides condenser water to the cooling tower to be cooled and a suction pipe 23 provides the cooled condenser water back to the pump 12 to provide the cooled condenser water to the chiller units 11. The hard stand 20 with the cooling towers 21 is typically located adjacent the wall of the plant room 12 upon which the pipe headers 14 are located internally. [0104] The condenser water cycle between the chiller units 11 and the cooling towers 21 is illustrated schematically in Figure 9. [0105] The preferred thermal energy storage tank 10 and associated chilled water piping network between the TES tank 10, the field and the chillers of 11 is illustrated in Figure 8. The preferred TES tank 10 has at least one warm water inlet/outlet and at least one chilled water inlet/outlet. [0106] In this configuration, an inlet/outlet is typically provided at a lower portion of the vessel (chilled water) and inlet/outlet is provided at an upper portion of the vessel (warm water). Each inlet/outlet is identified as such, as the vessel will normally be connected to related process apparatus in such a way that fluid can flow through the thermal energy storage tank in either direction and therefore, each inlet/outlet can be an inlet or an outlet depending upon the direction of fluid flow through the tank. [01071 The thermal energy storage (TES) tank is preferably a stratified thermal storage tank. Almost any temperature difference can be present in the tank however the storage volume required is minimized with larger difference in temperature between the top of the tank and the bottom of the tank. Thermal diffusion between the hot and cold fluid is preferably confined to the interface region between the hotter and colder fluid called the thermocline. An important consideration to leveraging this phenomenon for thermal storage is creating stratified layers and keeping the stratification intact. Therefore, the flow into the tank should be as laminar as possible to prevent or minimise disruption of the thermoclines in the tank. [0108] As illustrated in Figure 8, each chiller receives return chiller water from the field at approximately 14'C. This water is then chilled to approximately 5 to 6'C and is provided to the TES tank via the lower inlet/outlet. A secondary chilled water pump associated the TES tank 10 provides the chilled water to the field. In Figure 8, the nomenclature is such that PCHWP refers to the primary chilled water pump and SCHWP relates to the secondary chilled water pump. [0109] According to the preferred embodiment, there will be one large TES tank 10 to allow effective stratification. [0110] A schematic illustration of the vapour-compression cycle chiller units 11 preferred is included in Figure 15. This cycle uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the field chilled water and subsequently rejects that heat through the cooling towers. [0111] All such systems typically have four components: a compressor 25, a condenser 26, a thermal expansion valve 27 (also called a throttle valve or TX Valve), and an evaporator 28. The chilled water is typically cooled in the evaporator 28 which is basically a heat exchanger. [0112] Circulating refrigerant enters the compressor 25 in the thermodynamic state known as a saturated vapour and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapour is then in the thermodynamic state known as a superheated vapour and it is at a temperature and pressure at which it can be condensed with typically available cooling water or cooling air in the cooling towers 21. A separate condenser water cycle with a pump 29 is provided, a preferred form of which is illustrated in Figure 9. [0113] That hot vapour is routed through a condenser 26 where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool air from the cooling towers 21 flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the condenser cooling water. [0114] The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve 27 where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapour refrigerant mixture to where it is colder than the temperature of the chiller water returning from the field. [0115] The cold mixture is then routed through the coil or tubes in the evaporator 28 where a portion of the heat from the chilled water return is transferred to the cold mixture. That heat transfer evaporates the liquid part of the cold refrigerant mixture. At the same time, the chilled water is cooled to the desired temperature. The evaporator 28 is where the circulating refrigerant absorbs and removes heat from the chilled water used as the working fluid for the district cooling system, with the heat subsequently rejected in the condenser 26. [01161 To complete the refrigeration cycle, the refrigerant vapour from the evaporator 28 is I / again a saturated vapour and is routed back into the compressor 25. [01171 There will therefore preferably be three working fluids, one being the refrigerant used in the chiller unit/cycle, the second with the chiller water used to distribute to the field and the third being the condenser cooling water. All three of these cycles are illustrated schematically in Figure 15. [01181 In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers. [0119] Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations. [0120] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.