This invention relates to a cooling system. In particular, it relates to a cooling system for cooling data centres (ie environments where a plurality of IT equipment, eg data servers, is operated).

With increased heat output from IT (information technology) servers and other IT equipment there is a continuing requirement to close couple an IT cabinet (otherwise known as ITC) (housing the servers or other equipment) with a rack cooler, rear door cooler or a so-called active cabinet exhaust. Active cabinet exhausts are described in WO

2008/152416 and may comprise an active exhaust which is provided with temperature sensing and variable airflow means (such as a fan or fans) which can be adjusted to maintain a constant temperature differential. IT equipment is generally designed to operate in a free-field scenario which means that it has fans, heat sinks and thermodynamic management devices that are capable of maintaining required operating conditions assuming the correct quantity and condition of air is supplied to the inlet and that the pressures within the system are within an acceptable, manufacturer defined, range.

When these devices are close coupled, and assuming they are active devices, ie have fans that push/pull through the IT cabinet or which control airflow by other active means such as variable dampers, then they exert an influence in terms of a pressure differential between the air inlet and outlet of the IT equipment.

Such equipment can only operate over certain pressure ranges.

The most popular design of cooling system currently used in data centres uses CRAC (computer room air conditioning) units supplying cool air into a raised modular floor plenum effectively creating a higher pressure in the voids than in the IT space. This increased pressure forces cool air out of floor grilles that are generally located in what is termed a cold aisle. A cold aisle is an aisle between ICT equipment racks that has floor grilles across its width and length and has the front of two sets of racks facing one another. Cool air is drawn into the front of the equipment cabinet by the ICT equipment and discharged at the rear of the rack. The rear of the racks will generally face one another to form a 'hot aisle'. The 'hot aisle' will not have any floor tiles and may have some form of baffling to assist in returning hot air back to the CRAC units to cool and re-circulate once again. With the above system the only item that exerts influence on the ICT equipment differential pressure between inlet and outlet are the ICT equipment fans and it is based on such applications that ICT equipment is designed.

Another type of cooling uses rack coolers/active cabinet exhaust or rear door coolers.

All of these items exert an influence over the ICT equipment in terms of airflow because they control airflow on a rack-by-rack basis. For example: a server A may require 1501/s @ 2O ⁰ C inlet temperature to reject

4kW of heat - air discharge @ 42 ⁰ C, and a server B may require 2501/s @ 2O ⁰ C inlet temperature to reject 4kW of heat - air discharge @ 33.5 ⁰ C

Currently rack coolers, rear door coolers and active cabinet exhaust modulate airflow in accordance with temperature. This assumes that all ICT equipment has the same temperature differential Δt°K. If there is an imbalance ie ICT cabinet 1 is populated with server A and ICT equipment cabinet 2 is populated with server B there is the real possibility of trying to force/draw too much or too little air through the ICT equipment thus having an effect on the differential pressure across it.

The present invention arose in an attempt to provide an improved cooling system which maintains pressure levels within acceptable limits. According to the present invention there is provided a method for controlling the climate of a data centre, comprising providing cooling means adapted to cool equipment, monitoring a pressure differential across at least one item of equipment and controlling operation of the cooling means so that differential pressure remains within a predetermined range.

An algorithm or algorithms may be used for pressure differential and/or temperature control.

Pressure sensors may be mounted at positions relative to a unit of IT equipment, or an IT cabinet and the outputs of these used to determine pressure differential.

The pressure differential may be varied by varying fan speed and/or rate of change of temperature across the equipment or cabinet.

The control may be such as to ensure that pressures at the rear of equipment are not positive in order to ensure that discharge air which is warm relative to input air cannot recirculated to the front of the equipment or rack.

According to the present invention in a further aspect there is provided a system for controlling climate control equipment in a data centre, adapted to maintain predetermined pressure and temperature parameters. According to the present invention in a further aspect there is provided a system for cooling an environment housing a plurality of electronic equipment in one or more equipment racks, comprising; cooling means, pressure sensing means for determining a pressure differential across one or more racks and means for controlling the cooling means to maintain the pressure differential within predetermined limits whilst maintaining temperature also within predetermined limits. A cooling unit or units may be one or more, or a combination, of down flow CRAC units, rack coolers, active cabinet exhaust, rear door coolers or other coolers. Preferably, at least two pressure sensors are used across each cabinet to determine a pressure differential. They may be positioned in appropriate positions according to the type of cooling.

Advantageously, a normal operating range is defined and within this range pressure control is not used. For example, temperature control is given priority. A predetermined pressure differential below the normal range is defined and within this range temperature control is used by, for example, reducing a fan speed to control pressure. A predetermined range above the normal operating range is also determined and within this higher range temperature control is slowed as fan speed is increased to control pressure.

The present invention further provides a method of controlling ICT climate control equipment wherein the cabinet differential pressures are maintained within use of defined limits.

In a further aspect there is provided a control system adapted to ensure that positive pressure at the air outlet of an ICT cabinet is maintained, allowing air to recirculated to the inlet of the cabinet. Generally, but not necessarily, the outlet may be at the rear of the cabinet and inlet at the front.

There is further provided a control system adapted to maintain temperature and cabinet pressure within an IT cabinet within controlled limits. According to the present invention there is further provided a cooling system as described above incorporated into an air climate and/or conditioning unit for ICT equipment, for example into a unit such as rack cooler, rear door cooler, active cabinet exhaust or others. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a control philosophy; Figure 2 shows an ICT cabinet with a rear door cooler;

Figure 3 shows an ICT cabinet with an active cabinet exhaust; and

Figure 4 shows an ICT cabinet with close coupled rack cooler. Figure 1 shows generally one control philosophy. The figure is a plot or fan speed against differential pressure across an ICT rack or cabinet. In this example, a normal operating range is set as being a pressure differential between 0 and -30 Pa. Within this range, the speed of fans within a cooling equipment is maintained constant. Below this (ie the pressure differential or more than -30 Pa) the fan speed is reduced linearly as shown down to a minimum speed (marked as -100% on the figure) at -40 Pa. Temperature control can still take place but this slowed since the fan speed is reduced.

For a temperature differential or 10 Pa above the high set point differential, the fan speed is linearly increased with an increase in pressure differential as shown up to a maximum 100% of the fan.

Of course, the values given are nominal in this and other values and ranges might be appropriate for different situations and different environments. Pressure control may be exerted over the entire pressure range or over just upper and lower partial ranges as shown in the figure.

Figure 2 shows a schematic cross section through an ICT cabinet 1 provided with a rear door cooler 2. The rear door cooler is known in itself and includes a number of fans 3. Pressures sensors Pl and P2 are positioned at suitable locations so that pressure values measured by them can be used to obtain a pressure differential across the cabinet 1. Note that the control analytical parts of the pressure sensing circuit are not shown for clarity. The airflow direction in this case is from the front 4 of the cabinet to the back 5. Figure 3 shows a system in which an active cabinet exhaust (ACE) 6 is used for cooling instead of the rear door cooler. This ACE includes a fan or fans 7 and airflow controlling means (not shown) such as a vent or vents, operable flaps or other means. The ACE can control inlet temperature by modulating the performance (e.g. speed) of the fan or fans. Again, pressure sensors Pl and P2 are located at suitable positions to measure pressure differential across the cabinet. P2 is arranged and suitably positioned to measure pressure at the inlet to the ACE.

A pressure control feature operates by using a complex control algorithm to modulate the fan performance of the unit within a set pressure range to ensure the server fans, located inside the rack, are never operating outside of their flow and pressure envelope.

This pressure reactive control feature is achieved by measuring the pressure differential between the rear chamber of the rack (air off side of servers), and the pressure inlet on the ACE. The microprocessor modulates the ACE fan performance within a top and bottom limit, with the following control reaction:

Preferred, but not essential limits are:

Top Pressure Limit (Adjustable): +10Pa

Bottom Pressure Limit (Adjustable): - 40Pa

In the control mechanism:

If pressure differential is increasing and approaching +10Pa, the ACE fans increase in speed to reduce the pressure differential. PID control is utilised.

If pressure differential is decreasing and approaching -40Pa, the ACE fans decrease in speed to increase the pressure differential. PID control is utilised. Within the limits, temperature control is maintained as the priority. However, pressure control becomes the priority above OPa and below -30Pa. Against, these are limits from some embodiments and other embodiments may have other limits.

Figure 4 shows an example in which a closed coupled rack cooler 9 is mounted against an ICT cabinet 1. In this case, the direction of airflow from the fan 10, which is part of the rack cooler, is across the front of the track and thus pressure sensor Pl is mounted at or towards the front of the cabinet and P2 at or toward the rear. The sensors in one non-limiting embodiment are ones which can measure pressure between -50 and +50 Pa. The control strategy is typically as in Figure 1. A control algorithm is used to calculate the correlation between cooling demand and pressure and to adjust the fan speed accordingly. Whilst the pressures are within the defined limit 20 and 21 (Figure 1), then temperature control takes precedence. As described, only should the pressure set points 20 and 21 be exceeded (in a negative or positive direction) will both pressure and temperature be controlled in unison (as shown), ie typically by reducing or increasing fan speed as pressure reduces or rises.

In embodiments of the invention, algorithms are used to provide pressure/ temperature control by adjusting fan speed, for example. Fans can be sped up to reduce pressure or slowed down to increase it, for example. For example, if a low negative pressure or even positive pressure is experienced at the rear of a rack then the fan is caused to speed up. In doing this, it achieves any necessary increase in cooling more quickly but from a control perspective the influence of the temperature requirement lessens as the pressure increases. In effect, when a fan or fans speed up to reduce pressure, more heat is removed, as a by-product of pressure control, but control of temperature becomes less, in accordance with an algorithm.