The typical active design approach when considering A/C buildings is the most compact and massive type, with minimum opening and sealed to avoid excessive convective gains. The typical passive design approach when considering houses in tropical regions is a building with many openings on the North and South walls for natural ventilation, lightweight and completely shaded to avoid solar heat gains. This houses designed for full cross ventilation was quite successful in achieving relative comfort as long as the residential densities were low. With the growth of suburban densities, the air velocity is reduced to such an extent that it no longer produces the desired relief. Furthermore, this type of construction does not seem to cope with noise problems, privacy necessities and thermal comfort for different activities.

From traditional knowledge, low mass materials such as wood construction are considered appropriate for free running operation in hot humid climates as their indoor temperature drops rapidly in the evening, when the winds usually subside. High-mass buildings cool down more slowly during the night, which causes discomfort during sleep.

The dual mode project has demonstrated that ventilated high mass buildings can have lower indoor maximum temperature than low-mass buildings. High mass buildings on a 24- hour period can have more discomfort in cumulative degree hours of discomfort but on a daytime basis only have far more advantages. And also, if at night time there is ventilation (natural or ceiling fans), the indoor night temperature in high mass buildings is very close to those in low mass buildings. The conclusion is that for free running operation, if there is assisted ventilation at night, high mass buildings can be more comfortable during most of the time than low mass ones.

For a conditioned operation, a high mass building can be more energy efficient during a 24 hour period. If insulated, a low mass building can also have high performance. During daytime as well, high mass is far more efficient. However, for nighttime use only, the accumulated heat of the high mass structure almost triples the energy requirements for high mass buildings. This could be reduced by an "economy-cycle” — (night air flush) operation of the A/C system.

In summary, compared to the base case, an optimized all free running house will improve up to 19% the levels of thermal comfort. However, it will be unsuitable for air conditioning operation. An optimized fully conditioned house will improve up to 35%, but will have high levels of thermal discomfort if a free running operation is used. All the dual mode cases (1­

5) had superior performance for both conditioned and free running operation modes. If a dual mode operation (5 use patterns) is being used, the following savings are possible, compared to the base case:

1) TOC o "1-5" h z 51% improvement in thermal comfort and 87% reduction in cooling loads

2) 17% improvement thermal comfort and 78% reduction in cooling loads

3) 38% improvement in thermal comfort and 66% reduction in cooling loads

4) 31% improvement in thermal comfort and 98% reduction in cooling loads

5) 40% improvement in thermal comfort and 89% reduction in cooling loads