Air Conditioning Metal Buildings in Tropical Climate
Tropical Mountain Air Conditioning?
The setting: latitude 10 degrees, altitude 1300m (4500′), daily temperature range: 12-24C (55-75F) more or less year round. Humidity: high in the short “dry” season to dripping in the wet season.
The structures: a closely spaced collection of 6-7 uninsulated but reasonably airtight metal buildings 4m x 6m (~260 square feet) each on concrete slabs. The buildings surround a large central courtyard with an (again) uninsulated metal roof, and not so airtight.
The goals: keep building interior humidity low enough to prevent condensation, keep interior temperatures “comfortable”. Bonus points for improving the climate in the ~380 square meter (4100sf) 3m-4m (10′-14′) high ceiling enclosed courtyard.
The perceived challenges: Nights are on the cool side, humidity is often 100% and condensing on metal as air temps rise in the mornings.
The proposed air conditioning system: water-to-water heat pump, such as: https://www.miamihp.com/online-store/5-0-ton-water-to-water-geothermal-heat-pump fed electricity by solar panels both chilling, and heating, water in insulated non pressurized buffer tanks, such as: https://www.sunmaxxsolar.com/product/400-gallon-non-pressurized-buffer-tank-copy-2/ – hot water tank can feed in-slab hydronic heating coils to keep indoor night time temperatures moderate (and the floors dry and toasty), while cold water can be circulated to de-humidifiers at times when the room-air could also stand a little chilling. The 5 ton heat pump would seem to be sufficient for ~1600 square feet of conditioned space, any excess capacity provided from the solar could be used to warm the floor and maybe a little dehumidification of the central courtyard.
Concerns: how toasty are the uninsulated metal roofs likely to get in the sun – re-radiating into the rooms? Is white paint like: https://www.energy.gov/energysaver/cool-roofs#:~:text=White%20roofing%20products%20stay%20coolest,preferentially%20reflect%20this%20invisible%20light. enough, or is it still going to be re-radiating more heat than the cold water to air is likely to make comfortable?
I haven’t seen a whole lot of selection for the chiller/dehumidifier units, there’s this: https://nlsolarheating.solartubs.com/ultra-thin-hydronic-fan-coil-heating-cooling-water-radiator-100v-p-357.html#productDescription but are there more like that, possibly smaller for the smallish rooms they will be serving?
Is 400 gallons of “hot” going to be enough to get through the night? If it starts around 60C (140F), is that likely to make “hotspots”, or are there (reasonably available) controllers that can “pulse” the hot water in so the heat is evenly distributed, but not continuously running making the floor burning hot, and then intelligently extend the pulse duty cycle as the hot water gets cooler?
Anything else I’m missing, or should consider instead? Would like to stay away from traditional air to air conditioner units both for the noise and for the lack of “free” power during the night.
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Replies
You don't need air conditioning. If you feel hot, use a fan. If you don't like high humidity, buy a dehumidifier.
What are these buildings used for?
Bedrooms - family mountain getaway. Hang out outside, or in the courtyard when it's raining, sleep in the bug and other creature proof rooms. Main concern is the sweating walls / ceiling when a couple of sleepers are pumping up the humidity to stay at 100% while the walls are chilling down below dew point.
I grew up in that environment without AC, but homes were open, porches all around and ventilated tile roof systems. Fans were common, but nowadays, some folks are using minisplits.
Metal buildings are different and difficult to insulate in the tropics (Central America, SE Asia or Central Africa). If fans are not good enough for your purpose, I would recommend you insulate them.
https://www.greenbuildingadvisor.com/article/insulating-a-metal-building
https://www.cdmg.com/building-faqs/tips-to-prevent-condensation#:~:text=Use%20Proper%20Insulation,-Insulation%20that%20regulates&text=It%20also%20prevents%20warm%2C%20moisture,and%20seep%20into%20the%20insulation.
Yeah, insulation is the
moderncontemporary answer for all climate control, but... not only does it complicate and increase construction cost, it also makes habitat for "things" to live in. Single wall construction like in old Hawaii has a lot of appeal that way - simple, easily inspectable, no questions like "did these termites just blow in, or is there a nest inside the wall?"