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<\/figure>\n\n\n\n<\/p>\n\n\n\n
Ninety percent comes back as heat<\/h2>\n\n\n\n
Compressed air is an expensive way to move energy around, and the loss is the point. Nearly all the electrical input leaves the package as heat. Some leaves with the compressed air. Some with the condensate. Not much. Ninety percent of input is the planning number, and it will not leave you short.<\/p>\n\n\n\n
Input power. Not the number stamped on the motor plate. They are not the same number. A 37 kW machine draws about 40 at full load. Roughly 36 of that ends up in the room. Size from the 37 and the error rides along quietly until a hot afternoon.<\/p>\n\n\n\n
Now walk the room. Count everything else in there. A refrigerated dryer adds 1 to 3 kW, all of it into the same air. A second compressor doubles the load. A receiver just holds heat and occupies floor. Cardboard stacked by the machine blocks the air path. It also burns. Different problem, same address.<\/p>\n\n\n\n
Add the input power of everything in there. Take 90 percent. That is the heat load.<\/p>\n\n\n\n
Part load does not save you either. A machine with a variable speed drive will drop its heat output as it unloads, but the cooling fan is usually sized for full speed running, and the room is sized once. Design for the worst hour of the year, not the average Tuesday.<\/p>\n\n\n\n
Kilowatts to cubic metres<\/h2>\n\n\n\n
Take 36. Divide by 1.15, the density of air in kg per cubic metre at around 40 degrees. Divide by 1.005, the specific heat. Divide by the rise you are willing to live with, in kelvin.<\/p>\n\n\n\n
Ten kelvin gives 3.1 cubic metres per second. Multiply by 3,600 and it is a bit over eleven thousand an hour, which is the unit a fan catalogue speaks.<\/p>\n\n\n\n
The ten is the decision. The arithmetic is not. Ten kelvin means air leaves the room ten degrees warmer than it arrived. Choose five and the fan doubles, along with the duct and the hole in the wall. Choose fifteen and the fan shrinks, but the room runs hotter than the machine was built for.<\/p>\n\n\n\n
In a hot climate this stops being a comfort question. Thirty eight outside plus ten is forty eight. The compressor now cools itself with air past its own rating, and it will do that every afternoon for years without complaint, right up until it stops.<\/p>\n\n\n\n
Which is why the honest answer in Guangzhou in August is often not more airflow. It is to stop diluting and start ducting.<\/p>\n\n\n\n <\/p>\n\n\n\n Dilution: hot air into the room, wall fan to clear it. Fine for a small room, a modest load, and genuinely cool outside air. Cheap, and most sites already have it.<\/p>\n\n\n\n Ducting collects the hot air at the cooling outlet and puts it outdoors, so the room stays close to ambient. In a hot climate, or where the compressor shares space with anything else that gets warm, this is the only version that survives a summer.<\/p>\n\n\n\n Ducting brings its own tax. Every bend eats static pressure. Flexible duct costs more per metre than smooth spiral, more than people budget, and one 90 degree bend plus three metres of flex will swallow whatever margin the axial unit was picked with. Past six metres of run, or past two bends, go up a size or add a booster.<\/p>\n\n\n\n Short straight run, axial is normal. Our axial fan range<\/a> covers the diameters these rooms ask for.<\/p>\n\n\n\n Air goes out. It has to come back in.<\/p>\n\n\n\n The hole it returns through is part of the fan’s problem, and it is the part everybody skips.<\/p>\n\n\n\n At three metres per second, that 3.1 needs about 1.03 square metres of open area. Open is the word. A louvre is not a hole. A weather louvre with a bird screen and a damper passes 60 to 70 percent of what you cut, so the requirement becomes 1.6.<\/p>\n\n\n\n Cut a 1.0 and the motor still turns. Fewer amps, same speed, less air, and an ammeter reading that looks perfectly healthy while the room cooks.<\/p>\n\n\n\n Placement settles the argument. Opposite walls, as far apart as the building allows.<\/p>\n\n\n\n What gets built instead: louvre on the left, extractor three metres along the same wall. Hot air leaves, wraps the corner, comes back in. The extractor works all day. Nothing cools. On paper the airflow number was right, which is why nobody finds it.<\/p>\n\n\n\n No opposite wall? Go vertical, low in and high out. Still beats a metre of separation on one wall.<\/p>\n\n\n\n Then check what else is pulling from that space. A spray booth or a dust collector on the far side of a partition can drag the room negative and turn the inlet into an outlet. The fan curve says fine. The thermometer disagrees.<\/p>\n\n\n\n Most industrial compressors cap ambient between 40 and 45 degrees. That number lives in the manual and rarely makes the sales page, since it is not a selling point.<\/p>\n\n\n\n Past it, things happen quietly. Oil runs hotter and the separator ages faster. The motor loses cooling, because the air cooling it is already hot. Insulation degrades at a rate that roughly doubles for every 10 K above rating. Nothing trips. The machine dies in year four instead of year ten, and the compressor gets the blame.<\/p>\n\n\n\n Motors are usually built to IEC 60034-1 at a 40 degree reference ambient. Reference, not permission.<\/p>\n\n\n\n Altitude stacks on top. Thin air carries less mass and less heat, so above about 1,000 metres the free air delivery drops while cooling gets worse, both pushing the same direction. Site on a plateau? Say so before ordering. Derating is arithmetic. A second machine is not.<\/p>\n\n\n\n Cold climate, compressor room, winter. The heat is free and it is leaving through the wall.<\/p>\n\n\n\n Run it into an adjacent workshop and you recover something real, and you give somebody a reason to maintain the duct, which fixes the ventilation as a side effect.<\/p>\n\n\n\n Paint booth, clean room, anywhere oil mist would ruin the batch. Keep it out. That air has been through the machine. Backdraft damper, or August pours straight back in. Leave a bypass in case a damper sticks. And accept that every metre of duct is a maintenance item, and a seized damper is a high temperature trip waiting for the first hot week of July.<\/p>\n\n\n\n Where the saving is small and the run is complicated, exhaust outdoors and stop. Simple systems get maintained. Clever ones get bypassed with a bit of cardboard and forgotten.<\/p>\n\n\n\n Four numbers and you are done.<\/p>\n\n\n\n Input power of everything in the room. Times 0.9. Divide by 1.15, then 1.005, then the rise you will accept. That gives cubic metres per second. Times 3,600 for m\u00b3\/h.<\/p>\n\n\n\n Size the inlet from the same airflow at 3 m\/s, then divide by the free area ratio of the grille somebody will actually install, not the one in the drawing. Inlet and outlet as far apart as the walls allow. Site ambient against the machine rating. Altitude.<\/p>\n\n\n\n If the answer looks absurdly large for the size of the room, that is not an error. It is the room telling you to duct the heat out instead of trying to dilute it.<\/p>\n\n\n\n Send us the model and the site ambient and we will run it. Input power sits on the specification sheet for every machine in the screw air compressor range<\/a>, the page de contact<\/a> reaches the engineers who do this every week, and the about page<\/a> shows where the machines are built. The fans come out of the same factory, so the advice and the hardware are not two separate conversations.<\/p>\n\n\n\n <\/p>","protected":false},"excerpt":{"rendered":" Size compressor room ventilation by heat load, not by room size. Airflow formula, ducting traps, ambient limits, and when heat recovery actually pays.<\/p>","protected":false},"author":1,"featured_media":4365,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_joinchat":[],"footnotes":""},"categories":[3,32],"tags":[],"class_list":["post-4933","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-resources","category-blog"],"blocksy_meta":[],"_links":{"self":[{"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/posts\/4933","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/comments?post=4933"}],"version-history":[{"count":4,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/posts\/4933\/revisions"}],"predecessor-version":[{"id":4948,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/posts\/4933\/revisions\/4948"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/media\/4365"}],"wp:attachment":[{"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/media?parent=4933"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/categories?post=4933"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/sayiair.com\/fr\/wp-json\/wp\/v2\/tags?post=4933"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"SAYI](\"https:\/\/sayiair.com\/wp-content\/uploads\/2026\/10\/23acdf3c7dd36d21a64ceafaff235d5c.png\" "\\"\\"")
<\/figure>\n\n\n\nDuct it or dilute it<\/h2>\n\n\n\n
The inlet is half the job<\/h2>\n\n\n\n
The rating in the manual<\/h2>\n\n\n\n
Heat recovery, when the duct earns it<\/h2>\n\n\n\n
![\"High](\"https:\/\/sayiair.com\/wp-content\/uploads\/2026\/10\/0d1da9ecfaf6515bb88705ea7c37e663.jpg\" "\\"\\"")
<\/figure>\n\n\n\nDo the arithmetic before the builder arrives<\/h2>\n\n\n\n