Comfort Ventilation

From Swikipedia

Introduction

In new houses with good insulation against outside noise there is hardly any natural ventilation. This can lead to high humidity and low oxygen levels. To eliminate the possibility of harmful effects developing, it is essential to introduce fresh air. This is termed as Comfort Ventilation. It is a direct physiological effect created for example by opening the windows to let the wind in and thus providing a higher indoor air speed which makes the people inside the building feel cooler.

Therefore, Comfort ventilation is providing ventilation to produce immediate human comfort, mainly during the day. Baruch Givoni, the doyen of passive design, presents threshold for the operation of different types of passive cooling systems. The threshold value of the maximum ambient temperature for the variability of comfort ventilation he gives as 28-32 degrees a indoor air speeds of 1.5-2.0 m/s, depending on the comfort requirements. This is based on the observation that the indoor air temperature approaches the outdoor air temperature as the ventilation air increases.

Brief Description

The simplest strategy for improving comfort when the indoor temperature, under still air conditions, is felt as too warm is to open the window and to enhance comfort by ventilation: providing comfort through higher indoor air speeds. Introducing outdoor air with a given speed into a building may provide a direct physiological cooling effect even when the indoor air temperature is actually elevated. This is particularly the case when the humidity is high, as the higher speed increases the rate of sweat evaporation from the skin, thus minimizing the discomfort people feel when their skin is wet.

Such comfort ventilation may be desirable, from the physiological viewpoint, even when the outdoor air temperature is higher than the indoor air temperature, because the upper temperature limit of comfort is shifted upward with a higher air speed. Therefore, even if the indoor air temperature is actually elevated by ventilation with a warmer outdoor air, the effect on the comfort of the occupants, up to a given temperature limit, might be beneficial. This is specially the case in hot, humid regions.

References:

Baruch Givoni(1994). “Passive and low energy cooling of buildings” Ventilative Cooling. pp 38.

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