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I have a strange question/theory that I'd like some advice on.

I currently have a garden shed that is being used as a home office. On sunny days, the inside of the shed gets very hot - too hot for me to be comfortable - about 30C. Outside temperature would be around 22-23C during these times.

My understanding is that the inside of the shed is getting heated by radiation - both from the small perspex window as well as the wooden walls/roof (the walls and roof are insulated with thin PIR insulation and plasterboard. This only has limited insulation capability as the frame of the shed is only 20mm thick so I couldn't fit any thicker celotex.)

Now, I have installed a single-hose portable air conditioning unit inside the shed, with its hose fed outside through a hole that's been drilled. This unit does work, but at 30C inside (with the unit set to 25C), it does struggle to bring the temp down.

Due to the single hose nature of the unit, this creates a negative pressure differential causing outside air to come inside. Normally, this is why single-hose units are deemed "bad" and inefficient. However in my case, as the outside air is significantly cooler than inside the shed, and I'm only setting the unit to 25C, does opening the door actually help with efficiency in my case? From a very brief and quick non-scientific experiment, the shed does seem to cool down faster....

Am I on to something here? I'm running the unit on solar power to efficiency does matter.

If the answer is "yes", then my next question is: Is is more efficient than a simple fan extractor installed at the opposite end of the door (instead of the air conditioning unit)?

Thanks for your help

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    $\begingroup$ Is there a reason you don’t just use a fan? $\endgroup$
    – Eric S
    Sep 5, 2023 at 13:43
  • $\begingroup$ If you're asking about a simple desk fan pointed to my face, I do indeed use this as well. But it's not enough to keep comfortable when it gets close to 30C. $\endgroup$
    – user42931
    Sep 5, 2023 at 14:16
  • $\begingroup$ no, a box fan in a window $\endgroup$
    – Tiger Guy
    Sep 5, 2023 at 14:32
  • $\begingroup$ @user42931 are you asking if bringing in 22-23C air from the outside cools off the shed? $\endgroup$
    – jsotola
    Sep 5, 2023 at 15:32
  • $\begingroup$ An attic fan would help a lot. $\endgroup$
    – Eric S
    Sep 5, 2023 at 16:06

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Based on what you're telling us, venting the space is likely a better option than this one-tube air conditioner. It will use much less power and make the space cooler. ACs do have an advantage in that they also dehumidify the air, which can increase the comfort level dramatically.

Why not cut a box shaped hole in the side and install a window AC? That should cool the space adequately. It doesn't draw in outside air the one-tube AC.

You may also be able to reduce the radiant heating of the exterior by shading it, perhaps with a tarp or other covering stood off by a meter or so.

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    $\begingroup$ In addition to a fan blowing in, you need to consider how the hot air exits. Roof vents would be an option. Otherwise an attic fan and inlet ducts. $\endgroup$
    – Eric S
    Sep 5, 2023 at 16:07
  • $\begingroup$ In my context with the outside air being only 22-23C, how will a window AC (or a dual host portable AC) unit be any beneficial compared to my single hose unit? $\endgroup$
    – user42931
    Sep 6, 2023 at 14:04

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