cooling - Page 1
Forum section: electronics / projects

author: pete g
author_rank: Regular Contributor
timestamp: April 26, 2023, 10:29:19 pm
content: hi, i want to cool an enclosure. is it better to blow air into or out of the enclosure?

author: Benta
author_rank: Super Contributor
timestamp: April 26, 2023, 10:36:45 pm
content: hi, depends.

author: Someone
author_rank: Super Contributor
timestamp: April 26, 2023, 11:43:48 pm
content: As above, depends. Luckily those choices are easy to test:https://sound-au.com/heatsinks.htm#s18

author: pete g
author_rank: Regular Contributor
timestamp: April 27, 2023, 12:24:58 am
content: i meant blow air into or suck air out of the enclosure. thanks someone for your response. i read the article you proposed. blow in, is the choice.

author: james_s
author_rank: Super Contributor
timestamp: April 27, 2023, 01:06:54 am
content: In theory it doesn't matter, any air you blow out has to come in from somewhere and any air you blow in has to go out somewhere. In practice how effective either is depends on the layout of what's in the enclosure and where the heat is being produced. Sometimes blowing air in allows you to blow cooler air directly at some heat producing parts. It's possible to design an enclosure to work well with either arrangement though.

author: srb1954
author_rank: Super Contributor
timestamp: April 27, 2023, 02:19:07 am
content: It is often better to blow air into the enclosure so, with the appropriate placement of the fan, you can direct the highest velocity air flow to a hot spot for best cooling. Another advantage of blowing air into the enclosure is that you can fit a filter to the fan and reduce the amount of dust drawn into the equipment.Sucking air out of the enclosure draws dust in at any and all entry points. It used to be a problem with early PCs where they would draw dust-laden air in through the floppy disc drive door slots and that dust would get then deposited over the internals of the floppy disc drive.

author: pete g
author_rank: Regular Contributor
timestamp: April 27, 2023, 04:39:00 pm
content: thanks to all who responded. pete g

author: macboy
author_rank: Super Contributor
timestamp: April 29, 2023, 02:17:11 pm
content: Consider that pulling air out will also rarefy (thin) the air in the enclosure. Pushing air into it has the opposite effect, making the air inside even denser. Denser air will cool better.

author: james_s
author_rank: Super Contributor
timestamp: May 18, 2023, 09:10:06 pm
content: Quote from: macboy on April 29, 2023, 02:17:11 pmI wonder if that has a measurable effect. The static pressure produced by a typical cooling fan is pretty low, I don't think it is capable of compressing the air to any meaningful degree but perhaps it does have some small impact.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 18, 2023, 10:15:41 pm
content: Quote from: james_s on May 18, 2023, 09:10:06 pmThe pressure differential is minimal –– we're talking about less than 4 mmH2O, i.e. less than 40 Pa, or 0.04% of the nominal atmospheric pressure of 1 bar, with typical quiet 120mm or larger fans.At the upper part of the range, it is just enough to reduce the amount of dust collecting inside the enclosure a bit.I've built a few PC enclosures myself, and the difference is just big enough so that you want to have more forced airflow (fans) blowing in than out. If you arrange for turbulent airflow inside the enclosure using baffles, you can actually keep surfaces clean of dust. For example, 140x140x25mm Noctua NF-A14 PWM can generate about 2mmH2O pressure, i.e. 20 Pa over ambient, moving 80 CFM or 140 m³/h, while generating less than 25 dBA measured at 1 meter distance. Bloody expensive, but among the best 140mm 12V fans at of May 2023.Anything higher, and we're talking about fans that necessarily generate 40 dBA or more noise at 1m distance.

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: May 19, 2023, 02:59:38 am
content: blow out of enclosure is probably a better choice. It will prevent water droplets from being sucked in during rain or water leak, especially if fan is powerful. Another thing I was taught in 90s for is that blowing in will increase of dust/dirt build up inside enclosure, e.g. insects. Blowing in will lower temperature by some amount, but if we reverse power supply fan we may end up with cooler power board, but hotter air inside the enclosure, because air will be warmed up by power board components first.

author: eTobey
author_rank: Super Contributor
timestamp: May 19, 2023, 10:07:54 am
content: If you would use (need) a filter, then you should blow in, with a filter on the fan. This way there will never be dirt in it.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 19, 2023, 10:13:31 am
content: A fan with zero pressure on the sucking side would do nothing. The lower the pressure on the sucking side, the worst. Therefore, it would be preferred to position the fan such that it will pump the air into the enclosure, not out of it.

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 19, 2023, 01:14:02 pm
content: Quote from: Georgy.Moshkin on May 19, 2023, 02:59:38 amPractical experimentation has shown the opposite.

author: PeteH
author_rank: Unknown
timestamp: May 19, 2023, 01:24:33 pm
content: Other thing to consider is the fan itself would be running at higher temperatures if it was pushing the heat out, vs being at the external air temperature.

author: Miyuki
author_rank: Frequent Contributor
timestamp: May 20, 2023, 02:06:12 pm
content: Some 1U and 2U rack enclosures have fans in the middleSo they suck and blow at the same time

author: Nominal Animal
author_rank: Super Contributor
timestamp: May 20, 2023, 02:43:00 pm
content: Quote from: Miyuki on May 20, 2023, 02:06:12 pmSure, all my PC enclosures do that too; consider the fans on the heatsinks inside the enclosure. I also tend to have both intake and exhaust fans.It's just that ensuring there is a little bit of overpressure, i.e. more intake than exhaust, and turbulent airflow over surfaces, seems to work best overall.