HDRC Solutions

This is a cooling cabinet matching the height & depth of the server racks and installed between the server racks, spaced to approximately match the heat load. The in-row cooler includes a cooling coil and fans. Air is drawn over the coil and delivered it back into the room as cooled air.

In-row coolers are predominantly chilled water cooled but are also available with pumped refrigerant. In all cases either a mechanical chiller or a building chilled water heat exchanger are required to reject the heat from the in-row coolers absorb from the aisle space. In some cases in-row coolers can be spaced every 3 or 4 racks but in high density rack cooling applications they may be required on a one-for-one spacing.

These systems are most effective when used in conjunction with CRAC units and a hot/cold aisle containment system. When viewed as a complete system, the combination of in-row coolers, hot/cold aisle containment systems and CRAC units can often require more floor space than is available or reduce the future expansion possibilities. While this system can provide effective high density rack cooling it is unlikely to reduce energy consumption.

These are fan boxes mounted on top of the server racks, towards the rear with an EC (VFD) fan that increases air flow across the server rack, based on heat load. Top-hat fan boxes can be ducted back to the HVAC system above the racks (headroom permitting) with the same air flow separation characteristics provided by an aisle containment system described above.

These systems have achieved some success but are dependent on the existing (or new) air conditioning and air distribution system within the room since they do not include any cooling plant or equipment. Power savings are realized by fan power energy reduction in the data center air conditioning system, off-set by the added fan power installed in these systems. The energy limitation of this systems is that it must transfer the server heat to the air, which must then be cooled in a CRAC or air handler before the heat is finally rejected in a chiller.

Virtually all servers draw room air from the front and discharge it to the rear. Passive rear doors can remove heat at its source without taking up any additional floor space. A passive rear door cooler is comprised of a chilled water cooling coil installed in the rear door of the server rack. The existing server fans draw room air across the servers and discharge the hot air across the cooling coil in the rear door where the heat is transferred to the chilled water which is piped outside to the chiller or heat exchanger. This works well if the passive rear door cooler can handle the maximum heat output from the servers with the fixed airflow from the server fans.

Passive rear door coolers were originally developed for IBM servers, which have a design airflow at the high end of the industry scale. The current volume server producers generally have a lower airflow which reduces the effectiveness of passive rear door coolers. The current server design trend is to reduce the fan motor size in order to limit the server power consumption in a fiercely competitive industry. This is made possible by wider operating temperature limits now suggested by most server manufacturers.

The current limitation of a passive rear door cooler is about 20kW and is subject to specific chilled water temperature, optimum server fan air flow, room air temperature and initial temperature differential (ITD) between the entering air and the chilled water. In most cases passive rear door coolers are limited to low and medium rack cooling and not suitable for high density rack cooling.

Bolt-on Active Rear Door Coolers (Chilled Water): These occupy about ½ of the rear door surface area and include a chilled water coil and a row of fans to increase the airflow across the servers and the cooling coil. Because they are attached to the existing rear door of the server rack these coolers have a restricted coil area and limited fan capacity. These coolers are limited to about 8 kW server heat removal capacity and are therefore not suitable for high density rack cooling.

Active Rear Door Coolers (Pumped Refrigerant): These coolers include a pumped refrigerant coil and fans. The server heat is absorbed into the refrigerant which is then piped outside to a mechanical chiller to reject the heat. Alternatively the refrigerant can be piped to a heat exchanger so the heat can be rejected to the building chilled water supply. Pumped refrigerant rear door coolers are limited to a maximum of 30 kW cooling capacity.

Active Rear Door Coolers (Chilled Water): These effectively replace the rear door of the server rack with a full-size chilled water cooling coil and multiple EC (variable speed) fans. Motivair Chilled Door high density rack coolers are available up to 45 kW capacity per rack and therefore suitable for a wide range of racks and especially suitable for high density rack cooling.