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I am building in equatorial Indonesia. My building is roughly 10x4.5 metres in footprint, and it will be a two storey (3.5 metres each) concrete structure. The building backs directly onto a limestone rock, which is massive, being around 20 metres wide, six metres high.

For a variety of reasons, air conditioning is undesirable, so I would like to minimise ground-floor afternoon temperatures. Daily temperatures can go up to about 34C, but sometimes only up to 31C, and at night maybe 25C as a low. Humidity is very high.

What can I do in terms of window/ventilation design to keep things cool inside? Normally here they tend to use simple ventilation blocks (hollow concrete or wooden block with wire mesh installed), but I am not particularly keen from the perspective of appearance. Also it's worth noting that the tropical rains can be very heavy and necessitate closing windows/doors - you can be sitting three metres from an open window in heavy rain and still get wet.

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    Interesting. Is the limestone rock on your property? Which direction is the rock from your house? How much room do you have around the 10x4.5 footprint? Can you afford to excavate tunnels or deep ditches? You may have the potential for some very novel approaches to passive cooling, with that massive rock so close. – A. I. Breveleri May 9 '16 at 1:14
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As others have mentioned, you could use that large rock to your advantage, but for less money, you can simply design your house to take advantage of passive cooling methods. Quickly, I'll preface that I get most of these ideas from the visitor center in Zion National Park. It gets exceptionally hot and humid in the summer there, but they maintain near-zero usage of AC due to the building design.

Window Angle

You can position your windows with overhangs or sunshades that passively block sunlight (and potentially some of that rain you mentioned) during the summer months. Indonesia, being so close to the equator (as you said), would likely have less variation in sun angle year round, so it's possible these sunshades would work continuously to prevent heat ingress.

Check out these examples: Zion, Sunshades, Google Images

On a similar note, using Low-E glass can help reduce any stray IR radiation from entering, further helping cool your house.

Passive Cooling Tower

You are making a two-storey building, so you can take advantage of a vertical passive cooling system. I have been next to the one in Zion, and it's amazing how well it works. Check out this diagram.

It works on the principle of evaporative cooling. You have wet fabrics exposed to the air at the top of the tower. Warm air rises from your house through a chimney (of sorts). When it reaches the fabric, the warm air causes some water to evaporate, causing the air to cool as it transfers heat into the water. The cool air then returns down the chimney and into your house.

It's even possible to do this without needing the wet fabrics (though those help significantly due to the latent heat of vaporization of water). Skylights can accomplish the same task, and many have automatic controllers to close when they sense rain.

Ultimately, by having ventilation both high and low, you get passive (or natural) convection cooling. This is also where that large limestone rock can help. If you can get ventilation through that rock, you can take advantage of geothermal buffering, which helps maintain a constant, cooler temperature. Effectively, you are tying the thermal capacitance of your house to the rock, making it harder to heat up easily.

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What an interesting set of challenges.

I would spend some time studying passive cooling and attempt to incorporate the best possible concepts that you can find that would apply to your locale.

I was always fascinated by a solar chimney that uses the heat of the sun to create a draft effect drawing air into the house as the hot air exits the chimney. This concept is more applicable in very sunny hot climates.

Another idea is to use an earth tube to cool air as it passes through the earth before it enters the house.

I am sure you could find some passive cooling ideas that would apply to your locale.

Good luck!

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Location and placement are the top concerns for windows if they are to be used as your primary source of cooling. There's probably computer software for flow diagnostics now; architects used to have to build mock-ups and run colored water through them.

You might want vertical casement windows and/or awnings to deal with the rain. Additionally, I recommend a 'whole house fan'. Unless the house is hermetically sealed, it will pull in outside air, regardless if the windows are open.

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