The indoor environment is where more and more people spend 90% of their time and because of this the World Health Organisation states that the human right to a healthy indoor environment includes the right to breathe clean air, the right to thermal comfort and the right to visual health and visual comfort.

And as people start to take notice, indoor air quality (IAQ) has become an important occupational health and safety issue. People working indoors can often experience headaches, shortness of breath, coughing or other symptoms but not all people are affected in the same way. Those who are more sensitive or more exposed will often experience symptoms earlier than others, but, without an appropriate assessment of indoor air quality it is difficult to prove that these symptoms are as a result of a particular indoor air contaminant.

IAQ problems

IAQ problems are a result of interactions between building materials and furnishing, activities within the building, outdoor environment, and building occupants. Contaminants can originate within the building or be drawn in from outdoors and IAQ problems can arise when contaminant concentration is excessive, even if the HVAC system is properly functioning.

Feelings of discomfort and illness can also come in many forms and may be related to many different causes including noise levels, thermal comfort (inadequate control of temperature and humidity, inappropriate air movement), lighting, chemicals, dusts, moulds, bacteria, vapours and odours. There is also some evidence that there is an inverse relationship between fresh air ventilation rates and sick leave rates.

But whatever the reasons for the discomfort, the fact remains that the Health and Safety at Work Regulations states that the workplace should be maintained in an efficient state with suitable services to support the business operation. The main problem here is that maintaining a healthy and comfortable indoor environment in any building requires integrating many components of a complex system.

What we have to remember is that while IAQ problems are preventable and solvable, the complex potential causes of IAQ problems in buildings, means that those responsible for building services specification, design and maintenance will need to call on specialist assistance either as a positive policy or a positive response to genuine complaints.

Site investigations

BSRIA has 25 years of experience in site monitoring and the following case studies are examples of the site monitoring carried out in two office blocks, both built in the 1960s/1970s. One was monitored in March 2004 and the other in July 2004. Both projects were instigated by FM managers responding to concerns raised by the occupants of the building stating that they were not happy with the IAQ of their work environment.

Field trials in commercial buildings

Office block building A BSRIA monitored this building on three of the eleven floors over three days. The area chosen by the client provided a good representation of all the floors. The following parameters were monitored under ‘as found conditions’:

External

• Temperature • Relative Humidity • Wind speed • Wind direction Internal • Temperature • Relative Humidity • Dust levels • Volatile Organic Chemical (VOC) levels • Carbon dioxide (CO2) levels • Carbon monoxide (CO) levels

The internal temperatures on the three floors were above the CIBSE recommended range of 21 to 23°C for internal office conditions in the winter. The internal Relative Humidity was 10 points below the 40% minimum level recommended by CIBSE.

BSRIA recommended that if the internal temperature was lowered, the Relative Humidity (RH) would increase towards a more satisfactory level given that there was no RH control. The levels of all the other internal parameters monitored were satisfactory.

Office block building B

The occupants of this open plan office had previously been transferred to this building from a modern air-conditioned office in another building. This had happened less than a year before the monitoring period took place.

On the day of the monitoring, the external daytime temperature was approximately 23°C. Because of the way the air handling unit worked, without provision of cooling, the external temperature had a big influence on the internal temperature. If the external daytime temperature had been 30°C then the internal temperature would also been have nearer 30°C. This would have been very uncomfortable.

Only one open plan area of one floor was examined in this building. The following parameters were monitored under ‘as found conditions’:

External

• Carbon dioxide (CO2) • Carbon monoxide (CO) • Dust Internal • Temperature • Relative Humidity • Dust levels • Volatile Organic Chemical (VOC) levels • Carbon dioxide (CO2) levels • Carbon monoxide (CO) levels • Thermal • Bacteria and fungi o Swabs o Settle plates

The levels of all the internal and external parameters monitored were satisfactory at the time of survey. Ideally BSRIA could have been able to monitor the conditions at different times of the year but due to client financial restrictions and urgency of the work, BSRIA could only test at a particular time that was mutually convenient.

This snapshot approach provides an appropriate response to IAQ issues in the workplace.

Field trials in a domestic building

The previous two examples involve commercial buildings but people are becoming increasingly aware of the air quality of the domestic environment that they live in. Another parameter that can affect the health of occupants in a building is the fresh air ventilation rate. To this end, BSRIA has been involved in a major project carrying out field trials of slot ventilators in a domestic dwelling funded by the Office of the Deputy Prime Minister in partnership with a university.

A two-bedroom house was rented for six months and three types of active ventilators were installed for five-week periods, back to back. The first set of ventilators were Relative Humidity controlled, the next two sets were pressure controlled. A system of releasing moisture and heat into the rooms controlled by daily timers was installed in the house to represent occupancy. The following parameters were monitored:

External

• Temperature • Relative Humidity • Wind speed • Wind direction Internal • Room temperatures • Temperatures either side of the ventilators • Room Relative Humidity • Relative Humidity either side of the ventilators • Thermal comfort • Carbon dioxide (CO2) levels • Carbon monoxide (CO) levels • Static pressures at various points • Differential pressures across the ventilators • Movement of the control flap on one ventilator

The data from 87 sensors was logged every five minutes. The data-logging computer in the house automatically saved the data to a text file at midnight every 24 hours. The university partner working with BSRIA in the project created a computer model to simulate the different types of ventilators installed in the house. The three sets of five-week raw data were used to seed the computer model and produce annual simulations of the conditions inside the dwelling for each of the types of ventilators.

This project shows the complexity of work that can be undertaken and how large amounts of data can be analysed relatively easily.

Examining indoor thermal comfort using computer modelling

Measuring and assessing indoor air quality is not only limited to site investigations. The constant increase in computer processing power stimulates a growing role for computer modelling techniques. Computational Fluid Dynamics (CFD) can be used to inform building designers about airflow and contaminant transport. For example the locating of discharge flues from combustion appliances and fume cupboards can be assessed for a number of wind conditions. Results of the computer calculations can then provide the information needed to locate the flues wisely and limit the impact on the building air intakes. Similarly the selection of intake location can be explored.

CFD has been successfully used to examine indoor thermal comfort for many years and constant increases in the capability of the technology has been realised. By calculating the patterns of air movement and the distributions of temperature within the room, CFD can pinpoint a host of potential thermal comfort problems. Examples include cold downdrafts and excessive head to ankle temperature differences. In addition to thermal comfort issues CFD analysis of indoor airflow can highlight problems of short-circuiting of fresh air supply and the contamination this can generate.

Summary

The importance of taking notice of genuine complaints about IAQ in the workplace cannot be over emphasized. It is important to investigate complaints and understand how you can obtain an understanding of the operating characteristics of the indoor environment.

Colin Judd is Senior Research Engineer at the BSRIA MicroClimate Centre, Telephone 01344 465600, E-mail: microclimate@bsria.co.uk

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