The invention relates to an energy system for a data centre. More specifically, the invention relates to an energy system for a data centre including a water circuit for cooling and/or condensing a cooling medium, the cooling medium provided in closed loop in the data centre for cooling of data processing equipment, the water circuit extending between the data centre a commercial building.

Data centres are an energy-demanding industry that accounts for about 2% of the world's electricity demand. The electricity used to run the data equipment transforms into heat which is cooled off and exhausted as air or hot water. Today, most data centre-generated excess heat is just released into air or sea as waste.

Certain attempts have been made to use the excess heat from data centres to heat commercial buildings with high energy-requirements, such as public swimming pools. Suggestions have also been made to use hot air from data centres to heat greenhouses.

Common for these suggested solutions is that they have a relatively low transfer efficiency of re-usable thermal energy.

The invention has for its object to remedy or to reduce at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.

The object is achieved through features, which are specified in the description below and in the claims that follow.

The energy system according to the present invention aims at utilizing as much excessive heat from a data centre as possible and to use this heat to warm a nearby commercial building. The commercial building may be a greenhouse, a public swimming pool, a hospital, a shopping mall, an airport etc. In particular, a water-cooling circuit is provided that is made to exchange heat with a cooling medium in the data centre, while at the same time also the remaining thermal energy in the air of the data centre is utilised.

In a first aspect, the invention relates to an energy system for a data centre, the energy system including:

- a water circuit for cooling and/or condensing a cooling medium, the cooling medium provided in a closed loop in the data centre for cooling of data processing equipment, the water circuit extending from the data centre to a commercial building, wherein the energy system further comprises a heat exchanger for exchanging thermal energy between air in the data centre and air in the commercial building.

The fact that excess heat, after primary cooling of the data processing equipment, is utilized in an air-based heat exchanger with a nearby commercial budling will contribute to further increase the efficiency of heat transfer from the data centre to the commercial building.

In one embodiment, the cooling medium may be a two-phase, dielectric evaporating liquid. Liquid cooling with two-phase "on CPU" evaporators has been shown to be up to approximately 80% efficient. The remaining approximate 20% will then be released to air in the data centre. According to the invention, this hot air from the data centre, typically from the so-called "hot aisles", is allowed to exchange heat / thermal energy with the air in the commercial building through an air heat exchanger. The heat exchanger may in certain embodiment be a large-area cross-flow exchanger. The data centre may be placed adjacent the commercial building, such as in the order of 100 metres or less from the commercial building. In certain embodiments, the data centre may also share a common wall with the commercial building. In other embodiment, the air heat exchanger and appurtenant equipment may be place in a separate housing between the data centre and the commercial building. The separate housing may be a container, which will also be referred to as a HVAC (Heating, Ventilation and Air-Conditioning) unit herein, as will be explained below with reference to the figures. For new constructional projects, the data centre may advantageously be placed below the commercial building for maximum exploitation of the hot air through a chimney effect. As such, the heat exchanger may be included in / integrated into the floor of the commercial building. In certain embodiments, several layers of cross-flow heat exchanger may be integrated into the floor of the commercial building.

In one embodiment the commercial building may be a greenhouse. Greenhouses, in particularly in colder areas of the world where a lot of energy is required to maintain a stable temperature and controlled environment throughout the year, require a significant amount of energy supply. These cold areas, where greenhouses are most energydemanding, are also areas where natural cooling, such as from air and sea, is generally easily accessible. Hence, building a data centre adjacent or below a greenhouse may have a high degree of synergy in such areas.

In one embodiment, where the heat exchanger is integrated into the floor of the greenhouse or other commercial building, the heat exchanger may extend substantially over the full area of the floor in the greenhouse. By "substantially over the full area of the floor" is meant above 80% of the floor area in the greenhouse which is used for storing, growing or cultivating plants. In alternative embodiment, the heat exchanger may be integrated in 20% or more of the floor area, preferably 50% or more, or even more preferably substantially over the full area of the floor, i.e. 80% or more. Having a heat exchanger cover a large fraction of the floor of the greenhouse will allow high efficiency heat transfer with slowly circulating air. Preferably, the streams of air are separated from each other, which may be beneficial for keeping control of both the air in the data centre and in the greenhouse. In one embodiment, the heat exchanger may be a cross-flow exchanger in which air from the greenhouse flows, in one or more layers, perpendicularly to air from the data centre also flowing in one or more layers between the layers of air circulating through the greenhouse. After heat exchange, the now cooled air on the data centre side is circulated back into the data centre, typically to the so-called cold "aisles". In certain embodiments, additional cooling may be desirable before circulating the air back into the data centre / cold aisle and/or to the greenhouse. I such situations, the heat exchanger may also include one or more openings/intakes for additional, external air cooling as will be explained below. In a second aspect the invention relates to a data centre and commercial building sharing an energy system according to the first aspect of the invention.

In a third aspect the invention relates to a greenhouse and data centre sharing an energy system according to the first aspect of the invention, the greenhouse being positioned on top of the data centre.

In the following is described examples of preferred embodiments illustrated in the accompanying drawings, wherein:

Fig. 1 shows a schematic illustration of an energy system according to a first embodiment of the invention;

Fig. 2 shows a first embodiment of an arrangement of a data centre and a commercial building;

Fig. 3 shows a second embodiment of an arrangement of a data centre and a commercial building, and

Fig. 4 shows a schematic illustration of an energy system according to a second embodiment of the invention; and

Fig. 5 shows a schematic, exemplary flow diagram of various modes of operation for the energy system from Fig. 4.

Fig. 6 shows, in more detail, a flow diagram for operation of the water circuit heating the commercial building;

Fig. 7 shows, in more detail, a flow diagram for operation of the air circuit heating the commercial building; and

Fig. 8 shows, in more detail, a flow diagram for the commercial building.

In the following, reference numeral 1 will be used to denote an energy system according to the first aspect of the invention, whereas reference numerals 10 and 100 will used to denote a data centre and a commercial building, respectively. The figures are shown schematically and simplified, and various features therein are not necessarily drawn to scale. Any positional indications refer to the position shown in the figures.

In the figures, identical or corresponding elements are indicated by same reference numerals. For clarity reasons, some elements may in some of the figures be with-out reference numerals.

Fig. 1 shows a schematic illustration of an exemplary energy system 1 according to the invention. The energy system 1 is shared between the data centre 10 and the commercial building 100, here in the form of a greenhouse. The energy system is generally used to cool the data centre 10 and to heat the greenhouse 100. The data centre 10 is shown highly schematically with only one server rack 4 for illustrative purposes. In a real-life example the data centre 10 will typically include a plurality of such server racks arranged in multiple rows defining so-called hot and cold aisles, as will be understood by a person skilled in the art. A water circuit 2 extends between the data centre 10 and the greenhouse 100 and is generally used to cool, by heat exchange in the data centre, a cooling medium used in the data centre 10. The thermal energy absorbed by the water in the water circuit 2 during heat exchange in the data centre 10 is later released as heat in the greenhouse 100 through a hot water heating system. The hot water heating system in the greenhouse 100 may e.g. include a pipe grid 28 integrated into a floor 7 of the greenhouse 100 or a pipe grid 28 provided at an elevated height above floor 7, such as in between the plants. The water circuit 2 and the corresponding cooling and heating processes will be discussed in further detail below. Excess hot air in the data centre 10 will be allowed to heat exchange with air from the greenhouse 100 through an air heat exchanger 6, exemplary details of which will also be discussed below.

Hot air from one or more (not shown) hot aisles in the data centre 10 flows through an air circuit 3 on the data centre side into the air heat exchanger 6, which in the shown embodiment is integrated as a part of what may be referred to as a HVAC (Heating, Ventilation and Air-conditioning) unit 8. Cold(er) air from the greenhouse flows in an air circuit 5 on the greenhouse 100 side through the air heat exchanger 6 to be heated by the hot air from the data centre 10. The heated air is then circulated back and released into the greenhouse 100.

On an overall level the energy system 1 according to the invention thus includes at least two heat exchangers, the air heat exchanger 6 for exploiting the excess energy from heated air in the data centre 10 and a heat exchanger 12 for cooling the cooling medium in the data centre 10. Herein the heat exchanger 12 in the data centre will also be referred to as a "water heat exchanger", though it should be understood that in certain embodiments, water will only be used on the greenhouse side of the heat exchanger 12. The cooling medium used in the data centre 10 in one embodiment is a two-phase, dielectric evaporating liquid, such as the liquid commercially available from the company Zutacore™. The two-phase dielectric liquid is provided in a closed loop cooling circuit 13 in the data centre 10, i.e. on the data centre side of the water heat exchanger 12. Designated, not shown evaporators enable on-chip-cooling where the liquid evaporates generating an, at least partially, self-propelling cooling circuit. Heat from the computer chips is transferred as latent energy to the two-phase liquid, driving the evaporation and thus the propelling process. Through heat exchange with the water circuit 2, the two-phase, evaporated liquid is cooled/condensed back to liquid form. Through careful tuning of the boiling temperature of the two-phase liquid, it will be possible to optimise heat transfer in the energy system 1, e.g. depending on the type and power of computer chips and the desired operating temperature in the greenhouse. A pump 14 is provided to aid circulation of water in the water circuit 2 on the greenhouse side. Downstream of the pump 14 an expansion tank 16 is provided to account for thermal expansion of water in the water circuit 2. To remove any gas or air bubbles in the water a bubble trap 18 is provided downstream of the expansion tank 16. A filling valve 20 is operable to add water to the circuit. The filling valve 20 is, in the shown embodiment, placed downstream of the bubble trap 18, but could in principle be placed anywhere in the water circuit 2. A temperature-controlled single inlet three-way valve 22 regulates the amount of heated water in the water circuit 2 that flows into the greenhouse 100. When a desired temperature is reached in the greenhouse 100, excess heated water may be directed to a water cooler 24 instead of into the greenhouse 100. The three-way valve 22 is regulated in closed loop by a not shown control unit based measured temperature in the greenhouse 100 by temperature sensor 26. The single inlet three-way valve 22 makes it possible route the heated water solely into the greenhouse 100, solely into the water cooler 24, or any fractional split between the two. In the greenhouse 100, the water flows through pipe grid 28. The pipe grid 28 may be integrated into the floor 7 of the greenhouse 100, or alternatively be provided at an elevated height above the floor 7, preferably in between plants growing in the greenhouse 100. In the latter case, plants may be heated by radiant heat from the warm water in the pipe grid 28, potentially significantly increasing the energy transfer, and thus improving growth conditions for the plants.

From the server rack 4 hot air flows through the air circuit 3 and into the HVAC unit 8. In the HVAC unit 8, incoming, hot air is first filtered through air filter 30. A differential pressure switch 32 is provided in a bypass loop 33 around the air filter 30, allowing air to bypass the filter 30 in case of clogged or otherwise non-functioning filter. A not shown alarm system may be integrated with the differential pressure switch 32 to notify a user about the status of the filter 30 and to signal time for replacement of the filter 30. Motor- operated fans 34 drive the air through the air circuit 3, including through air heat exchanger 6. In the air heat exchanger 6 the heated air from the data centre 10 transfers thermal energy with cold(er) air flowing out from the greenhouse 100. Motor-operated fans 36 on the air circuit 5 on the greenhouse side circulate air from between the greenhouse 100 and the air heat exchanger 6. An air dryer 38 is provided on the air circuit 5 on the greenhouse side downstream of the air heat exchanger 6. It may be beneficial to keep a high CO? content in the air in the greenhouse 100 for optimised growth conditions. Therefore, to maintain a closed and COz-rich air circuit 5, an air dryer 38 may be provided to remove humidity from the air. An air filter 40 with pressure differential switch 42 in bypass loop 44 is also provided upstream of the air heat exchanger 6 in the air circuit 5 on the greenhouse side. Similarly to what was described above, a not shown alarm system may be integrated with the differential pressure switch 32 to notify a user about the status of the filter 40 and to signal time for replacement of the filter 40. The HVAC unit 8 is also provided with a first additional air inlet 46 for cold outdoor air on the data centre side into the air circuit 3. Air is sucked into the first inlet 46 by means of a fan 48 driven by a not shown motor and may be useful if additional cooling is need before circulating air back to the data centre 10. Intake of cold air through first additional air inlet 46 is regulated by means of a not shown control unit operating based on sensed temperature in the data centre 10. Similarly, a first exhaust outlet 50 is provided downstream of the air heat exchanger 6 in the air circuit 3 on the data centre side to release excess air from the circuit 3. A second air inlet 52 is provided in the air circuit 5 on the greenhouse side in case the air circulated back to the greenhouse is too warm. Air is sucked into the second air inlet 52 by means of a fan 54 driven by not shown motor. The intake of air through the second air inlet 52 is regulated by means of a not shown control unit operating based on sensed temperature in the greenhouse 100. A second exhaust air outlet 56 is similarly provided on the air circuit 5 on the greenhouse side to release excess air from the circuit 5. The whole HVAC unit 8 as such, including intake of cold air through the inlets 46, 52 is regulated by means of the not shown control unit(s) operating based on parameters from not shown sensors. The sensors will include one or more temperature sensors and optionally other sensors such as flow sensor(s), humidity sensor(s), pressure sensor(s) etc in the energy system 1, both in data centre 10, in the greenhouse 100 and in the HVAC unit 8.

Fig. 2 shows a possible configuration where the data centre 10 is placed under the greenhouse 100, typically in a basement of the greenhouse 100. This may be useful to fully utilise the chimney effect of the hot air from the hot aisles of the data centre 10. The air heat exchanger 6 may as such be integrated into the floor between the data centre 10 and the greenhouse 100. In one embodiment, the heat exchanger may be large-area cross-flow heat exchanger where the air circuits 3 on the data centre side and greenhouse side 5 are guided into two or more alternate cross-flow layers, such as corrugated layers or honeycomb layers, in the floor.

Fig. 3 shows an alternative embodiment, in which the data centre 10 is placed adjacent the greenhouse 100, and where the HVAC unit 8 is place in a separate housing, such as a container, between the two.

Fig. 4 shows an alternative embodiment of an energy system 1 according to the invention. The energy system 1 resembles the one shown in Fig. 1, but comprises an additional heat storage unit 200, here in the form of a geothermal well operating as a "thermos" in parallel with the greenhouse 100. Instead of routing excess hot water, if the greenhouse 100 is not in need of more heat, to the water cooler 24, the hot water additionally or instead may be routed to and stored in the geothermal well 200. This may e.g. be useful in warm periods, such as during summer, where the need for additional heating to the greenhouse 100 may be limited. Instead of using additional energy to cool off excess heat, the energy may instead be stored and used later when more heat is needed, such as during winter, and/or when electricity prices are higher. To regulate the flow of hot water to the geothermal well 200 and the greenhouse 100, a first regulation valve 80 and a second regulation valve 81 are provided. The first regulation valve 80 regulates the flow of hot water into the greenhouse 100 while the second regulation valve 81 regulates the flow of hot water into the geothermal well 200. The first regulation valve 80 is provided downstream of the three-way valve 22 regulating the flow of water between the water cooler 24 and the greenhouse 100 as explained above. It should also be noted that the water cooler 24 is to be regarded as optional also in this embodiment. The second regulation valve 81 is provided upstream of the geothermal well and regulates the amount of hot water flowing into the geothermal well 200. The two regulation valves 80, 81 make it possible to route all the hot water into three-way valve 22, all the hot water into the geothermal well 200 or any fractional split therebetween. In addition to the water cooler / heat pump 24, one or more additional not shown sources of heat may be provided as further back-up to be used if sufficient heating cannot otherwise be provided and/or if electricity prices are very high. One such additional or alternative, external heat source be gas boiler (see Fig. 8). It will also be understood that the logics involved in controlling the heating and cooling of the energy system may be enabled by one or more not shown control units operating i.a. based on sensed temperature from a plurality of temperature sensor and other sensors, of which only the temperature sensors 26 in the greenhouse is shown in the figure. Such other sensors may include flow sensor(s), humidity sensor(s), pressure sensor(s) etc.

Fig. 5 represents, on an overall level, different modes of operation of the energy system 1 as shown in Fig. 4. The legend shows that a single, thin line circle indicates the start of an event. Double, concentric circles indicate an intermediate event, while a bold line circle indicates the end of an event. This denotation is used throughout Figs. 5-8.

High temperature is produced in the data centre 10, representing "Mode 1" as start event. As long as the data centre 10 is operating normally, "Mode 1" will always be operational. As a result of this, the temperature in the data centre 10 is reduced by heat exchange with the water circuit 2. In "Mode 2" remaining heat in the data centre 10 is reduced by heat exchange with the air circuit 3. "Mode 3" represents heating of the commercial/public building 100, here exemplified by a greenhouse. The heat produced in the data centre 10 (Mode 1) is supplied to the greenhouse 100 from the water circuit (Mode 1) and the air circuit 3 (Mode 2).

The "+" signs in the flow diagrams of Figs. 7 and 8 generally define an "or" construction indicating the air temperature has been regulated by operation of the various fans (Fig. 7) or by choosing from different heat sources (Fig. 8) as will be explained below.

Fig. 6 shows an exemplary flow/logic diagram with focus on "Mode 1", i.e. the water circuit 2 of the data centre 10. As was also explained above, hot water is produced by heat exchange with the closed-loop cooling circuit 13 through the water heat exchanger 12. In normal operation, heat will always be produced from the data centre 10 and warm water will be pumped, by means of the pump 14, from the data centre 10. By means of the temperature sensor 26, the temperature in the greenhouse 100 may be monitored continuously (or at regular intervals). Depending on whether a desired temperature has already been reached ("Is heating needed?") in the greenhouse 100, the heat may be circulated to the greenhouse 100 (Yes) or to the geothermal well 200 (No). If the geothermal well 200 is already storing maximum capacity, excess heat may instead be supplied to the dry/water cooler / heat pump 24. In the exemplary embodiment of Fig. 6, "1-50" indicates that the geothermal well 200 includes 50 layers of storage, as an underground "onion". If each of the layers is heated to capacity, excess heat may instead have to be fed to the water cooler 24 to ensure sufficient cooling of the water before it returns to the data centre 10. In the exemplary flow diagram, a temperature difference (A) has been set to 2 °C as set-point, but this may of course vary between different set-ups. This means that if, in this example, there is more than 2 °C difference between the water circulated into the geothermal well 200 and the water flowing out from the geothermal well 200, then supply of hot water for storage may continue. If the difference is less than 2 °C and the greenhouse 100 is not in need of heat (see Fig. 8), then the water cooler 24 is activated to cool return water to the data centre 10 to safeguard sufficient cooling of the servers therein.

Fig. 7 shows an exemplary flow/logic diagram for the air circuit 3, HVAC unit 8 and greenhouse 100, corresponding to "Mode 2" from Fig. 5. It should be noted that the temperatures used as reference points in the data centre 10 hot aisle(s) (50 °C) and greenhouse 100 (27°C) are merely examples and may of course vary between different set-ups. In the greenhouse 100, the temperature of the air flowing from the greenhouse 100 into the air circuit 5 is measured continuously (or at regular intervals). If the air is colder than a certain set-point, in the exemplary embodiment 27 °C, circulation rate in the air circuit 5 in the HVAC unit 8 on the greenhouse side 100 may be increased by starting (or increasing the circulation rate of) the motor-operated fan 36 so as to increase the amount of heat exchange. In the same sequence, the motor-operated fan 54 may be stopped (or its circulation reduced) to avoid or reduce the amount of cool air drawn in from the outside into the system through inlet 52. In the exemplary embodiment, the air in the greenhouse 100 is set to have a temperature of 27 °C. If the temperature falls below this set-point, the motor-operated fan 36 is started, while the motor-operated fan 54 is stopped (or its circulation reduced).

At the same time, temperature is also sensed in the hot aisle(s) of the data centre 10. If the air temperature exceeds a defined set-point, here exemplified by 50 °C, the motor- operated fan 34 in the HAVC unit 8 on the data centre 10 side is started (or its circulation speed increased), which will increase cooling of the hot aisle(s) through increase heat exchange in the air heat exchanger 6. If the start of the motor-operated fan 34 on the data centre side is still not sufficient to bring the temperature below 50 °C, then the mo- tor-operated "outdoor" fan 48 may be started (or its circulation rate increased) to draw (more) cool air in from the outside through inlet 46. When desired temperatures have been obtained, the motor-operated fans, both on the data centre and greenhouse sides, may be stopped (or their circulation reduced). As can be seen when comparing the temperature regulation in greenhouse 100 and hot aisle(s), the air temperature in the greenhouse 100 is tuned towards an optimum temperature (here exemplified by 27 °C), while the air temperature in the hot aisle(s) is regulated if it exceeds a maximum temperature (here exemplified by 50 °C).

Fig. 8 is a flow/logic diagram focusing on heating of the greenhouse 100, i.e. "Mode 3", and its interaction with the geothermal well 200 and other heat sources. It should be noted that in this mode it has already been determined than the greenhouse 100 is in need of heat, which is in contrast to Fig. 7 / "Mode 2" where this logic is presented. In the shown embodiment, the greenhouse 100 initially receives heat from the data centre 10. The temperature difference (A) between the outgoing and incoming water to the heat exchanger 12 in data centre 10 is monitored continuously (or at regular intervals). As long as this difference (A T) is larger than 2 °C (in this exemplary embodiment), sufficient heating of the greenhouse 100 is obtained from the water circuit, and the data centre 10 continues to heat the greenhouse 100. If AT falls below the defined set-point, then heat needs to be supplied from alternative or additional sources. In this specific example, the greenhouse 100 has, in addition to the geothermal well 200, two alternative sources of heat. One is the water cooler 24, which in this mode operates as a heat pump with a yearly average coefficient of performance (COP) of 2.5. If AT of the geothermal well 200 (here referring to the difference in temperature between incoming and outgoing water to the geothermal well) is above 2 °C for one or more of the (here 50) layers in the geothermal well 200, then sufficient heating of the greenhouse 100 may be obtained from the geothermal well 200. If AT is less than 2 °C, which in practice means that the geothermal well (including its various layers) is not able to deliver the desired heat, the system / control unit instead assesses whether the water cooler 24 (now operating as a heat pump) is a suitable heat source. In the flow diagram, the exemplary logic test criterium is whether the COP is above 2.5. However, here it should be understood that also other factors, such as current prices, weather conditions etc, may also be relevant parameters and that "COP" just serves as a representation of such factors. If the "COP" is indeed above 2.5, then the heat pump 24 may be used to heat the greenhouse 100. If the "COP" is below 2.5, then instead yet another, alternative heat source may be used, here one or more gas boilers. It should also be emphasized that the heating temperature of the greenhouse floor 7 of 50 °C is also just an example.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The regulation of the HVAC unit 8 and the other not control units, including the logics of the flow diagrams shown in Fig. 5-8 may be implemented by means of hardware comprising several distinct elements, and by means of one or more a suitably programmed computers generally referred to as "control units" herein.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.