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I have a home-made home-automation system that includes a CCTV unit, circuit boards for controlling PIRs and outside lights, a UPS and power supplies. In the summer the loft gets hot (>40C) and the CCTV gets even hotter and is operating outside of limits.

The air is full of dust, fragments of loft insulation and bugs, so I want to re-circulate the air inside the cabinet - pull air from the top of the cabinet, cool it, and blow it back through the bottom of the cabinet?

How can I cool the recirculating air?

If I use Peltier chips, the power supply for them will be inside the cabinet. It will be like leaving the fridge door open to cool a room.

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  • \$\begingroup\$ Slightly off-topic word of warning: never operate a UPS in an enclosed space that isn't ventilated to the outside world. Charging of the battery releases hydrogen gas, which is very explosive in the right mix with air. \$\endgroup\$
    – Mels
    Commented May 23, 2017 at 8:41
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    \$\begingroup\$ The only proper solution I see is either to re-locate the equipment to a cooler / better ventilated location or to draw air from outdoors, filter it and use it to cool the equipment. Keeping a closed system (equipment case or the loft itself) will not decrease temperatures. \$\endgroup\$ Commented May 23, 2017 at 8:45
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    \$\begingroup\$ Do you have any (rough) figures on the amount of power that's being dissipated in the cabinet? \$\endgroup\$
    – Mels
    Commented May 23, 2017 at 8:46
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    \$\begingroup\$ "If I use Peltier chips, the power supply for them will be inside the cabinet." That is asking for the thermal equivalent of a perpetual motion machine. Why can't you put the power supply outside the enclosure? \$\endgroup\$ Commented May 23, 2017 at 13:17

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Really, the usual way to deal with this is a good air filter and forced air exchange (a fan) as well as components rated to work at an industrial-grade temperature range (that is, typically, up to 85°C). For a battery-based UPS, those temperature ranges might be impossible to achieve. An easy solution would be to run cables from the UPS to your unit, and store the UPS underground.

This only works as long as air outside the enclosure is cooler than the thermal limits of your components. When that breaks down, yes, you'll need some form of heat pump (a fridge/Air Conditioning system, an or a Peltier element). Peltiers that are capable enough of getting 10s of watts out there are ... special, so you almost certainly would go for the usual e.g. server-cooling mechanism of electromechanical (read: like a fridge, compressing/decompressing a coolant cycle) heat pumping to a large cooler.

Sealed enclosures aren't all that easy – not only do you need something to get the heat from inside out, you also get condensation issues that are hard to manage.

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  • \$\begingroup\$ Is there a limit to how cool something can get by blowing 40C air over it? \$\endgroup\$ Commented May 23, 2017 at 14:13
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    \$\begingroup\$ yes. 40°C, exactly. Simply blowing air over a surface only speeds up the process of exchanging heat from the hotter to the colder medium. Once both sides have the same temperature, there's nothing to be won anymore. \$\endgroup\$ Commented May 23, 2017 at 15:05
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For the heat critical components you could try and actual minifridge (Peltier) as sold on eBay

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  • \$\begingroup\$ Not realistically, no: en.wikipedia.org/wiki/Thermoelectric_cooling#Performance So, to cool a UPS that let's say produces 10W of heat, you'd need to draw 100W from that same UPS, in turn increasing the heat production by more than 10% – a vicious cycle. At the inefficiencies of Peltier elements, you can't cool a self-sustained energy system. \$\endgroup\$ Commented May 23, 2017 at 10:02
  • \$\begingroup\$ Well, don't put the UPS in the fridge. Locate that elsewhere, somewhere cooler and run cables. \$\endgroup\$ Commented May 23, 2017 at 10:11
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    \$\begingroup\$ "put it somewhere cooler" is basically the solution to this problem, isn't it? \$\endgroup\$ Commented May 23, 2017 at 10:31
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    \$\begingroup\$ @DirkBruere This is better served as a comment, it doesn't answer all of the OP's questions. \$\endgroup\$
    – Voltage Spike
    Commented May 23, 2017 at 15:14
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I live off grid in australia and realized that the loft was making the whole house hot during summer. there's an easy fix (if youve done house renovations). i have an exhaust fan mounted to the side of the building blowing air thru a vent. the fan runs directly from a solar panel. you will need some hole in the ceiling OR a vent on the opposite side of the house so it can draw fresh air thru the loft. this will make the house rooms stay cooler as well (which was why I done it).

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    \$\begingroup\$ This site isn't really for discussion, please try to answer the question. The OP wants to know how to cool a cabinet so that question needs to be answered directly. \$\endgroup\$
    – Voltage Spike
    Commented Sep 29, 2017 at 22:35

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