Study and improvement of indoor air quality in office building

We spend many hours in the workplace. When the quality of the air in offices is inadequate, work performance suffers. It is a determining factor in the comfort, well-being and, therefore, productivity of workers and users.

This case study covers the monitoring of indoor air quality in an office building during four weeks in winter. The aim of the project was to propose improvements, mainly in relation to low relative humidity.

A progressive drop in indoor relative humidity has been detected, which is a direct cause of discomfort due to its contribution to irritation and dryness of the respiratory and ocular mucous membranes and to a greater proliferation of suspended dust.

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Measurement and analysis

Based on the data obtained from the monitoring, the evolution of a typical week in each of the parameters is analysed. In addition, taking into account only the periods of occupation of the space, the percentage of time in which the workers and users of the building were in comfort ranges is calculated.

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From these results, we draw the following conclusions:

• There is an excess of temperature indoor for 67% of the occupancy time.
• We found a relative humidity below 40% for 97.7% of the occupancy time , with average values around 30% and minimum values down to 25% relative humidity.
• The company housed in this office building has opted for formaldehyde-free furniture , verified by monitoring continuous values of less than 40 µg/m3. formaldehydeFormaldehyde emissions, verified by continuous monitoring of values below 40 µg/m3.

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Actions for improvement

High temperature and low relative humidity are clear symptoms of inadequate regulation of the air-conditioning system, which requires clear and immediate action:

• Reducing the control temperature in the interior spaces to the ranges set out in the RITE regulations:
• Operating temperature in winter: 21 - 23ºC
• Operating temperature in summer: 23 - 25ºC.
• Bringing humidity to indoor air

La baja humedad relativa (<40%) en espacios interiores favorece el polvo en suspensión, con la consecuente afección para la salud y confort de quien trabaja en estos espacios. A partir de calcular la humedad específica se prescribe la integración de humidificadores evaporativos portátiles con alta capacidad evaporativa (1,4 – 2 l/h), filtro de polvo y control de humedad relativa máxima.

At the same time, phytoremediation is used as a secondary action to improve the indoor environment. Indoor plants have the ability to regulate the ambient humidity through the effect of evaporation, reducing the physiological effects of low relative humidity. Plants use about 5 % of light for photosynthesis. About 60 % of the light reaching the plant is converted into heat and must be evacuated. This is mostly done through the process of evaporation.

Plants that can withstand well indoors with low relative humidity such as sanseviera trifasciata, beaucarnea, aspidistras, clivias, phoenix, potos, crassulas, or cacti are recommended , depending on exposure and available natural light.

Finally, the recommendations on the cleaning protocol are adjusted to avoid a greater impact of airborne dust:

• Only use hoovers with a high efficiency HEPA filter.
• Increase the cleaning and maintenance of air supply and exhaust filters and grilles.
• Reduce synthetic surfaces as much as possible.
• Favour the cleaning of dust on surfaces by means of wet wipes, without the addition or spraying of other by-products to avoid secondary contamination of indoor air with unnecessary volatile compounds.

Thanks to monitoring over a continuous period of time, we have been able to detect the causes of the low relative humidity in the environment and to carry out the appropriate sizing of the solutions to be implemented. These will significantly improve the performance and well-being of the workers.

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