# The building is a machine for moving air > A data hall drawn in section shows arrows of cold air in and hot air out. The computers are almost incidental to the actual engineering in the room. August 19, 2026 · https://justog.club/stories/server-farm-cooling-plan A section drawing, cream and one pale blue, flat on a chart table. Two rows of racks face each other across an aisle. Arrows draw air in low at the front of every rack. Other arrows push it out high at the back, curving up and over to complete the loop. Nothing on the sheet identifies a single machine inside the racks — every line on it is about air. Take the computers out of this drawing and the building still has a full-time job: moving a huge volume of air from cold to hot and back again, forever. ## What is a server farm cooling plan? A section through a data hall, drawn to show where air enters, where it leaves, and the path it takes between the two. The racks are the least interesting objects on the sheet — they're boxes that happen to sit in the airflow. What the drawing actually documents is a loop: cold air pulled in at floor level on one face of the aisle, drawn through the equipment, and expelled hot at the top, where a return path carries it back around to be cooled again. It's an HVAC diagram that happens to have computers in it, not the other way round. ## Why does cold air enter low and hot air leave high? Because hot air rises on its own, and a good layout lets physics do part of the work instead of fighting it. Feed cold air in at the base of a rack and it has nowhere to go but up, through the equipment, and out — the same convection that empties a chimney. Fighting that by pushing cold air in from above would mean forcing it downward against its own buoyancy, which is more fan power for the same result. The low-in, high-out loop isn't a stylistic choice on the drawing. It's the cheapest route between two states of the same air. ## What makes this diagram genuinely technical rather than decorative? Arrows that describe a closed loop, not a scattering of ornamental ones. A convincing section shows air completing a circuit — in, through, out, back around — rather than simply pointing outward from the racks the way a decorative sunburst would. It sits in the same family as [a cutaway through a tower that shows every floor's actual load rather than just its silhouette](/stories/corporate-arcology-cutaway): the interest is entirely in what the section reveals that the outside of the building never would. Outlines only, no shading, keeps the airflow arrows as the one thing the eye follows. ## Is a cooling layout like this anyone's intellectual property? No specific building's floor plan is being copied, so there's nothing here that needs licensing. A hot-aisle, cold-aisle arrangement is standard practice across the industry, described in textbooks and trade literature rather than owned by any one operator — closer to [a fuse box's wiring convention than to a patented product](/stories/fuse-box-diagram): the layout is a shared engineering answer to a shared physical problem, and drawing your own version of it isn't reproducing anyone's proprietary work. ## Does the same idea work for a room that isn't full of servers? Any space where equipment produces more heat than the room can absorb on its own uses the same logic, whether or not the equipment is a computer. A commercial kitchen's extraction run, a plant room, a lighting rig on a stage that throws off more heat than the venue expects — [a plan of symbols meant for people running the room, not looking at it](/stories/lighting-plan-symbols), does comparable work for a different kind of load. The section through a server hall is one example of a much older drawing: whatever generates heat, something has to move the air around it. ## Isn't heat the boring part of a data centre, next to the computing itself? It's most of the actual engineering, which is the opposite of boring once you look at where the budget goes. A rack full of processors is, from a thermal standpoint, a very expensive way to make heat — the computation is almost a side effect of running current through silicon, and the byproduct is what the building spends the bulk of its design effort managing. The compute happens in software, invisible on any drawing. The heat is the one output with a physical shape, and the shape is what this section is actually documenting. ## Does it print well? Yes, provided the arrows stay confident and the racks stay flat. Two colours carry the whole idea: cream for the structural outlines, one pale blue for every arrow, so the airflow reads as a single continuous system rather than a set of separate marks. Keep the arrowheads simple and consistent in size — a mix of thin and thick arrows starts to read as different kinds of information, when here they're all the same thing. Slate or charcoal ground suits a technical drawing better than anything busier. ## How do I get one made? Describe the room at [JustOG](/) — how many rows, where the aisle sits, how the return path curves. Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to order and shipped. Designs other people have published are in the [shop](/shop). A loop of air with a rack of silicon sitting in the middle of it, mostly beside the point.