The conclusions expressed are those of the authors.
Article originally published in edition July/August 2024 Buildings and energy.
The health and quality of indoor ambient air is fundamental and critical to ensuring quality of life, comfort and preventing health problems. When a space is not adequately ventilated and sterilized and does not have appropriate sanitary conditions, there is an increased risk of contamination with pathogens, such as bacteria, viruses and fungi. In addition, this situation can contribute to problems with cognitive development.
Controlling the emission of non-human pollutants should be the first strategy. The selection of healthy building materials, surface preparation, maintenance and furniture in general have an impact on the emission of non-human pollutants into the interior spaces of buildings, so they must be chosen carefully and wisely so as not to cause the release of volatile organic compounds (present in various components, such as building materials and furniture). Next, we have vital needs.
To ensure good indoor air quality, Portuguese regulations define methodologies, criteria and standards depending on the type of building.
The selection of healthy building materials, surface preparation, maintenance, and furniture in general have an impact on the emission of non-human pollutants into the interior spaces of buildings, so they must be chosen carefully and wisely.
Non-residential buildings
In non-residential buildings, air flows are allocated depending on the type of activity, occupancy periods and air distribution profiles in the environment. The minimum new airflow to which spaces in commercial and service buildings are subjected corresponds to the maximum value obtained by comparing standards, which is calculated according to the methodology set forth in the Guide to the Building Energy Certification System, or SCE Guide, in accordance with paragraph 4 of Art. 4 of Decree-Law No. 101-D/2020, dated December 7, and Decree No. 138-I/2021.
- Occupancy standards are determined using one of the following methods:
The guideline, in which the minimum new airflow values for reducing pollutant load due to occupants is based on fixed values per person that can vary from 16 m3/(h for occupants) for environments with low activity (sleeping, for example), such as bedrooms or dormitories, up to 98 m3/(occupied space) for weight rooms or gymnasiums in gyms.
An analytical method, whereby the minimum new airflow rates necessary to meet a protection threshold for CO2 and VOCs during an occupancy period are determined based on the profile and physical characteristics of the occupants.
Minimum new air flow values depending on the interior space to reduce the pollutant load generated by the building itself and depending on the type of materials used in construction, surface coverings and furniture for different situations in the building.
HVAC engineers have adequately solved this control problem for many years, based on the use of highly energy efficient air handling units equipped with an exchange system to recover the energy of the exhaust air, as well as the use of air at low thermal conditions beneficial for Helping to overcome the internal loads of commercial and service spaces, which are always high, taking into account high occupancy rates (Free cooling).
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Residential buildings
In the case of residential buildings, the legislation establishes as the basis for the design methodology approximately half of the housing renovation per hour by volume. Before July 1, this indicator was at 0.40 renewals per hour. The goal is to bring air into bedrooms and living rooms and extract it outside into service spaces, such as sanitary facilities and kitchens. The various legislation applicable to construction imposes the need for ventilation 24 hours a day.
Regarding ventilation in residential buildings, there is still a long way to go as there are great obstacles and difficulties regarding the use of air intake networks directly from the outside in bedrooms and living rooms, although good technical rules always favor flow networks which must be controllable. Self.
Ventilation and air renewal in residential buildings can be carried out with three possible systems, which are as follows:
- Natural ventilation system, which consists of introducing outside air by natural means through grilles on the facade or in air and exhaust ducts in sanitary facilities and the kitchen. It allows, on average, to ensure the renewal of air that is promoted exclusively by the effects of temperature differences and wind movement, without any mechanical system.
- Mechanical ventilation system, which relies on the use of systems and equipment that promote the renewal of indoor air by extracting and/or blowing air with electrically powered mechanical ventilation devices. These systems can and should be equipped with an exchange battery to recover energy from the exhaust air.
- Finally, mixed ventilation systems are a combination of natural and mechanical ventilation systems, controlled by users or automatic, with mechanical equipment, namely hoods and individual bathroom hoods, intended to intensify ventilation in service compartments, when necessary.
More innovative ideas can be thought of in terms of natural ventilation and mixed ventilation, but we need to think at the project team level to implement innovative solutions that achieve the goal and regulatory compliance that are most suitable for citizens.
Currently, we choose operating systems, such as the fan, on the kitchen stove, which is activated for a very short period of time daily, and air intake systems in sanitary facilities, with air intake guaranteed, either by differences in negative pressure generated by mechanical extraction, or by regulation networks Self-adhesive in fascias, blind boxes and/or frames.
The regulations specify several levels of water resistance of tires which are evaluated in relation to the degree of air permeability to evaluate natural leaks, classified from 0 to 4, through flow rates determined in pressure test benches according to the EN ISO 9972 standard.
We often feel resistance from both architectural technicians and citizens in particular when we are faced with the idea of having grilles on the facades of bedrooms and living rooms, which should be open 24 hours a day throughout the year. There is a particular aversion to the more aggressive seasons in terms of temperature and air speed, although the grilles can be equipped with self-regulating devices.
Mixed solution can occur in two ways. The first method may be the introduction of outside air by natural means through grilles on the facade or ducts in bedrooms and living rooms and exhaust by mechanical means in sanitary facilities and the kitchen. Another method, based on infiltrations through negative pressure differences generated by mechanical exhaust systems in service compartments, might be to use low-level waterproof tires with permanent mechanical exhaust in order to ensure regulatory renewals.
More innovative ideas can be thought of in terms of natural ventilation and mixed ventilation, but we need to think at the project team level to implement innovative solutions that achieve the goal and regulatory compliance that are most suitable for citizens.
We recommend conducting a market study of the latest constructions carried out by government agencies to consolidate some of the solutions that have been used.
Finally, we must add that the definition of ventilation systems is closely related to the calculation of the energy class and can constitute a serious obstacle to the realization of almost zero-energy buildings, whose compensatory measures usually include increasing the thickness of the thermal insulation.
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