Patent Application
20090260384
1. Field of the Invention
The present invention relates to cooling computer systems, and more particularly to the circulation of coolant to a rear door heat exchanger on a rack.
2. Description of the Related Art
Computer systems use electrical energy and produce heat as a byproduct of electrical resistance. Rack-based computer systems include many rack-mounted components in a high-density arrangement, which can produce a considerable amount of heat. Excess heat must be removed from the rack to control internal temperatures and to maintain system reliability, performance, and longevity. In a rack-based computer system, fans move cool air through the rack to remove the excess heat and cool the components. The heated exhaust air must then be transported to a computer-room air conditioner (“CRAC”) that cools the air before returning the cooled air to the computer room.
The racks in a computer room are commonly arranged in an organized hot-aisle/cold-aisle layout to minimize the likelihood of appreciable volumes of heated exhaust air from directly re-entering the racks. A hot-aisle/cold-aisle layout may include alternating hot aisles and cold aisles, with the front of each rack sharing a cold aisle with one adjacent rack and the rear of each rack sharing a hot aisle with another adjacent rack. The CRAC supplies the cooled air to the cold aisles. The air from the cool aisle is drawn into the front of each rack and the heated air is exhausted through the rear of the rack to the hot aisle. The heated exhaust air recirculates through the CRAC to be cooled and returned back to the cold aisles.
One embodiment provides a rack assembly with a rear-door heat exchanger for cooling a computer system. A rack provides support for one or more columns of heat-generating electronic devices. Device fans move air from an air inlet side of the rack through the devices and through an air outlet side of the rack. A unitary door has a support frame spanning the air outlet side of the rack. A hinge pivotally couples the door to a rear vertical edge of the rack. The unitary door includes an air-to-liquid heat exchanger panel spanning an air outlet passage inside the support frame so that substantially all of the air passing through the air outlet side of the rack must pass through the heat exchanger panel. A coolant circulation system includes a coolant distribution unit for chilling liquid coolant, a supply hose placing the coolant distribution unit in fluid communication with an inlet manifold of the air-to-liquid heat exchanger, and a return hose placing an outlet manifold of the air-to-liquid heat exchanger in fluid communication with the coolant distribution unit. The supply hose and return hose are routed outside the cross-sectional area of the air outlet passage.
One embodiment of the invention is a double-wide rack with an integrated liquid-coolant rear-door heat exchanger having a coolant circulation system that provides chilled coolant to the rear-door heat exchanger with minimal interference with airflow through the rear-door heat exchanger. The double-wide form factor of the rack gives the accompanying rear-door heat exchanger a larger surface area to achieve a cooling performance on the order of 100% heat removal. A plurality of modules is mounted in a chassis from the front of the double-wide rack. The modules are organized within two sets of high-power zones and adjacent low-power zones. The high-power zones contain primarily processor-intensive modules such as compute modules. Modules in the adjacent low-power zones are low-power devices such as network switches and power distribution units (PDUs) for supporting the modules in the high-power zones. The chassis include relatively large-diameter fans that drive airflow through the double-wide rack from the front to the rear. As a result, the capacity of the chassis fans is sufficient to drive airflow exhausted from the double-wide rack through the rear-door heat exchanger, without the use of external “booster” fans. A coolant supply hose and return hose are routed from a coolant distribution unit to respective inlet and outlet manifolds on the rear-door heat-exchanger in a manner that maximizes airflow through the rear-door heat exchanger and which maximizes the circulation of the coolant. The coolant supply hose and return hose may be routed underneath the base pan of the rack, perpendicular to a hinge axis of the rear-door heat exchanger. The coolant supply hose and return hose may be routed upward to the rack from a raised floor of the data center. Alternatively, the coolant supply hose and return hose may be routed downward to the rack from the ceiling, in which case the rack may be placed on a more economical slab floor. The inlet and outlet manifolds are spaced from the high-power zones, to avoid interfering with airflow through the rear-door heat exchanger from the high-power zones.
A plurality of fans inside the rack 10 generate airflow through the rack 10 to cool the various modules mounted in the rack 10. The fans drive the airflow through the rack 10 from the front of the rack 12 to the rear 14 of the rack 10 and through the rear-door heat exchanger 100. The double-wide rack configuration increases the area of the airflow through the matching rear-door heat exchanger 100 for greater cooling efficiency. A coolant distribution unit (“CDU”) 116 supplies the rear-door heat exchanger 100 with a chilled liquid coolant, such as water. The CDU 116 pumps the chilled coolant through a supply hose 102 to an inlet manifold 122, which distributes the chilled coolant throughout numerous serpentine tubes in the rear-door heat exchanger 100 to the outlet plenum 124. The numerous serpentine tubes are in direct thermal contact with internal heat exchange fins (further discussed in relation to
Each chassis has a number of openings (typically more than one) referred to as “module bays” for receiving a corresponding number of modules. The 2 U chassis 32 is shown independently receiving two 1 U compute modules 46. The 3 U chassis 34 is shown receiving a compute module 46 in a lower 1 U module bay and has already received twelve 3.5 inch disk drives 44 that are installed into drive bays that occupy the equivalent of 2 U space and which are a permanent part of the chassis 34. Additional chassis having additional modules bays may be mounted on the double-wide rack 10, such that the double-wide rack 10 supports numerous modules. The modules may be selectively interconnected with cable connections from the front 12 of the double-wide rack 10. Some of the modules, such as compute modules and hard drive modules disposed in the high-power bays 16, 18, may be interconnected within their common chassis.
A plurality of low-power module bays 50 are provided in the low-power zone 20 immediately adjacent to the high-power zone 16, and in the low-power zone 22 immediately adjacent to the high-power zone 18. The low-power module bays 50 suitably receive various low-power modules, such as network switches and PDUs. The close positioning of the low-power zones 20, 22 to the respective high-power zones 16, 18 facilitates cable connections between the low-power modules and the high-power modules they support. For example, a network switch may be positioned in one of the low-power module bays 50 in the low-power zone 20 and connected to a compute module 46 at the same vertical position in the high-power zone 16 to connect that compute module 46 to the network switch. The close positioning of the network switch to the compute module 46 minimizes the physical length of network connections made between the network switch and the compute module 46, and avoids interfering with other modules located elsewhere in the double-wide rack 10. Having these cables and connections in the front of the rack makes configuration easier and does not require access to the back of the rack. Still further, positioning the lower power module bays 20, 22 consistently to one side of the respective high-power zones 16, 18 make cabling even more convenient and manageable. Each chassis in the double-wide rack 10 may include a fan assembly for generating airflow through that chassis.
The top of the 2 U chassis 32 is partially cut-away to reveal an on-board fan assembly 60 having a set of four fans 58. The fan assembly 60 may be directly powered and controlled by the power supply for the chassis 32 according to thermal sensor data passed to it from the compute module 46. Although the number of fans may vary, the 2 U chassis 32 can accommodate larger diameter fans than a 1 U chassis due to the 2 U height. An even larger chassis can support even larger fans. For example, the 3 U chassis 34 may include four fans (not shown) that may each be larger than the fans 58 in the 2 U chassis of
The rear-door heat exchanger 100 spans the entire width W and height H of the double-wide rack, to maximize the cross-sectional heat-exchange surface area (i.e., H×W) through which airflow exits the rack 10. The cross-sectional heat-exchange surface area is equal to or greater than the combined cross-sectional area of the high-power zones 16, 18. For example, the high power zones 16, 18 may each have a width of about 451.5 mm (a combined width of about 903 mm), while the width W of the rear-door heat exchanger 100 may be about 999 mm. Also, the width W may be more than twice the effective width of a heat exchanger on a “single wide” rack having a single vertical column of high-power modules. The double-wide rear-door heat exchanger 100 provides more than twice the width of a single-wide door, because the effective cooling area of the heat exchanger does not include the door frame, and the door frame occupies a comparatively smaller proportion of the door. This increased area contributes to improved cooling capacity as compared with conventional means of cooling racks. The coolant flow rate through the rear-door heat exchanger 100 may be increased accordingly (e.g. doubled) to account for the increased width of the rear-door heat exchanger 100. The rear-door heat exchanger 100 may remove up to 100% or more of the quantity of heat that was added to the airflow by the modules in the double-wide rack 10.
A coolant circulation system provides a continuous supply of chilled coolant from the CDU 116 to the rear-door heat exchanger 100 without interfering with airflow through the large heat exchange surface area provided by the rear-door heat exchanger 100. In particular, the hoses 102, 104 are routed horizontally under a lower edge of the rear-door heat exchanger 100. The horizontally-routed portion of the hose 102 is coupled to an inlet manifold 122 with a hose coupler 103 and the horizontally-routed portion of the hose 104 is coupled to an outlet manifold 124 with a hose coupler 104, such that a flow axis of each of the hose couplers 103, 105 is substantially horizontal and substantially perpendicular to the axis of the hinge 107. As a result, the hoses 102, 104 avoid interference with airflow through the rear-door heat exchanger 100, to prevent any airflow losses (e.g. airflow impedance or airflow leakage) that may otherwise result if the hoses 102, 104 were routed in front of some of the modules. Routing the hoses 102, 104 along the lower edge of the rear-door heat exchanger 100 also allows heat exchange fins to be positioned along the entire height of the rear-door heat exchanger 100 (from top to bottom) such that 100% of the airflow through the rack 10 passes over the heat exchange fins. By contrast, a conventional rack-mounted heat exchanger, having heat exchange fins that do not extend the entire height of the rack, would otherwise require a “bypass zone” for exhausting air from some of the modules so that airflow impedance is not too high.
The relatively narrow diameter of the hoses 102, 104 as compared with their length allows the hoses 102, 104 to be positioned out of the way of the airflow, between the lower edge of the rear-door heat exchanger 100 and the floor 125, with ample clearance under the rack 10 for routing. The hose couplers 103, 105 are optimally positioned in the “shadow” of the base pan of the rack 10 so they do not interfere with forktruck access below, or interfere with air flow above in the rack 10. Also, positioning hoses 102, 104 low is desirable in the contingency that a leak occurs during use or if coolant spills while connecting or disconnecting the hoses 102, 104. By contrast, if the quick-connect couplers 103, 105 were vertically oriented, the quick-connect couplers 103, 105 would have to be positioned significantly higher, such as eight inches or more above the floor 125, to provide access for personnel to connect the hoses 102, 104. Such an elevated positioning of the quick-connect couplers 103, 105 would interfere with airflow through the rear-door heat exchanger 100 by shortening the effective height of the heat-exchange fins, by occupying horizontal space that may otherwise have been provided for the heat exchange fins, or by increasing the required depth of the rear-door heat exchanger 100. Thus, the horizontal routing of the hoses 102, 104 to avoid airflow losses contributes to maximizing the cooling efficiency of the rear-door heat exchanger 100.
The inlet manifold 122 and outlet manifold 124 are positioned at the free end 112 of the rear-door heat exchanger 100, opposite the hinged end 110. This location of the inlet manifold 122 and outlet manifold 124 places the manifolds 122, 124 next to the low-power zone 22, and spaced from any of the high-power zones 16, 18. Less heat is generated adjacent to the low-power zone 22 than at the high-power zones 18, 20. Thus, the inlet manifold 122 and outlet manifold 124 or additional structure (e.g. mounting brackets) used to support the inlet manifold 122 and outlet manifold 124 on the rear-door heat exchanger 100 could protrude slightly into the airflow through the rear-door heat exchanger 100 without interfering with the airflow directly in front of either of the two high-power zones 18, 20. By avoiding interference with the airflow in front of the high-power zones 18, 20, any incidental protrusion of the inlet manifold 122, outlet manifold 124, or supporting structure thereof into the airflow exiting the rear-door heat exchanger 100 is unlikely to significantly affect the cooling performance of the rear-door heat exchanger 100, or to substantially increase airflow impedance to the high power zones 16, 18.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components and/or groups, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.
The corresponding structures, materials, acts, and equivalents of all means or steps plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but it not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
