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Ventilation in Thailand is usually either traditional roof gap airflow (hot air rises), or air conditioning in the rooms and un-airconditioned hallways and bathrooms. Some buildings will have some ventillation of bathrooms, but that is usually an open window. Because of the high heat (even in the face of high humidity) bathrooms are generally left to ventilate themselves, which yields a significant amount of mold and mildew. This is only during the rainy season, about five months of the year. In addition, about four months of the year there is significant air pollution (PM2.5), which makes open air ventillation unacceptable for health reasons.
Anyone building, remodeling, or simply living in Thailand during the burning and rainy seasons needs to take measures to combat these two problems. Usually, the use of portable air purifiers and air conditioners is seen as the only method (and only in buildings without open air ventillation). Besides open air ventillation and ductless air conditioners + portable air purifiers, there are other options. In sum:
- Open air ventilation
- Ductless (wall-mounted) air conditioners
- Ducted air conditioning (usually only in larger or commercial buildings)
Thailand with its varied (and high) humidity and heat calls for ERV (Energy Recovery Ventilation) rather than HRV (Heat Recovery Ventillation. In all cases, ventillation is needed, as well as air purification during the burning season. In order to avoid or reduce air conditioning requirements, ERV recovers both a certain amount of humidity moderation (averaging 50-55% in some cases), as well as the energy used in cooling (including passive cooling).
- Whole house mechanical ventillation
- ERV with HEPA filtration option
- Smallest ERV unit vs. RecoupAerator
Note that if a ducted system is to be used, it should be in the rafters, and the attic super-insulated. There are other options such as vented passive, and other designs. Look closer, especially for hot/humid climates. It would be useful to have HEPA and dehumidification as well in a single unit, but possibly impractical in terms of what is available. Might be best for two or three systems to combine. MERV 16 is basically 95% filtering of 0.3-1.0 micron wheras HEPA is 99.7%. MERV 12 is a high standard for residential ventillation, which filters 80-9-% of 1 micron and larger particles but is not rated for 0.3-1.0 micron particles (e.g., P.M. 2.5). Note: a research study showed no effective difference between MERV 16 and HEPA in some tested mining equipment.