Indoor and Built Environment

Ventilation provides a key defence for the protection of the indoor environ ment from the adverse effects of poor air quality. However, it can also contrib ute substantially to building energy use. Furthermore, the need to install large ventilation capacity is expensive both in terms of capital cost, maintenance needs and floor space. Hence there is considerable interest in the development of efficient ventilation systems and in minimizing the emission of pollutants within buildings. The International Energy Agency's (IEA) Air Infiltration and Ventilation Centre (AIVC) has a responsibility for providing a focal point for assessing the energy and air quality implications of ventilation. This paper is aimed at introducing the AIVC's strategy on ventilation research and at outlining the work and results of related IEA annexes. Conclusions stress the need for providing practitioners and policy makers with precise guidance on the energy implications and the role of ventilation in controlling indoor air quality.

Indoor air quality (IAQ) is of prime importance to human health because we spend >80% of our time indoors. Occupants of indoor environments may be exposed to a variety of pollutants originating from human activities or pres ence in the home, combustion for heating and cooking, consumer products, furnishings, building materials and outdoor air. Because of the potentially adverse effects to human health resulting from exposure to pollutants in the home, the 'Exposure Guidelines for Residential Indoor Air Quality' were developed. Exposure limits were prepared for the following compounds or groups of compounds: aldehydes, carbon dioxide, carbon monoxide, formal dehyde, nitrogen dioxide, ozone, particulate matter, sulphur dioxide, water vapour and radon. In addition, the guidelines suggest recommendations for controlling exposure to some contaminants for which the formulation of acceptable exposure ranges was deemed inappropriate or was not feasible. This group includes: biological agents, chlorinated hydrocarbons, fibrous materials, lead, pest control products, polycyclic aromatic hydrocarbons, product aerosols and tobacco smoke. A review of five substances (xylenes, toluene, 1,4-dichlorobenzene, benzene and tetrachloroethylene) to determine potential health risks has revealed the primary route of exposure to be through indoor air. They will be considered for guideline development and possible inclusion in the existing Exposure Guidelines for Residential Indoor Air Qual ity. Health Canada has an active research programme including a variety of projects: a survey of the occurrence of selected volatile organic compounds in Canadian residences representing a range of energy efficiencies; development and evaluation of analytical methods for measurement of human exposure to airborne organics; a study to measure home dampness and moulds to validate the observed association between respiratory health and indicators of home dampness; and participation in projects related to energy conservation and air quality as part of the research programme of the Panel on Energy Research and Development.

Sick leave records of sample populations of workers in seven office buildings were examined for evidence of correlation between average absence rates and rates of supply of outdoor air for ventilation: no such significant relationship exists in the samples studied. Other relationships were noted, suggesting that the incidence of minor illness depends on complex factors, which may be relat ed to the workplace or to external circumstances or both.

A simple systematic guide for architectural practice is proposed in the form of an IAQ-based design aid that can be utilized when decisions regarding the selection of envelope materials and energy systems are made. It is intended to be the first step towards the effective bridging of the existing gap between IAQ information and the architectural profession. The proposed guide is in a writ ten form as well as a simple computer hyper-text and is intended to be a quick reference for obtaining direct information on types of pollutants associated with each finish material, health risks, and possible alternative materials with less polluting impact on indoor air.

The American Conference of Governmental Industrial Hygienists (ACGIH) has issued a number of recommendations aimed at preventing abnormally high levels of bioaerosols. These include the elimination of stagnant water, microbial substrates, and microbial growth centres in ventilation systems, and the implementation of effective maintenance programmes. Disinfection tech niques (e.g., HEPA vacuuming, hypochlorite disinfection, and steam cleaning) are capable of eliminating microbial substrates and growth centres from ducts and other contaminated surfaces, but there is no information in the scientific literature on the optimum frequency of these operations. This study evaluated a number of corrective measures aimed at reducing aeromicrobial flora (bacte ria and saprophytic moulds). Samples of inside and outside air were taken at a laundry serving 30 hospitals. The outside air and that from 3 ventilation sys tems was sampled using a Burkard (Jet Spore) sampler, while an Andersen N-6 sampler was used to gather air samples at 6 workstations. Four 1-day sampling surveys were performed; in each case, samples were taken at least twice a day. In the first survey, carried out in June 1988, the contamination of outside air was found to differ significantly (p ≤ 0.05) from that of the air at some of the workstations, both qualitatively and quantitatively. The same workstations were re-evaluated in December 1988, 2 months after the ventilation system had been disinfected with hypochlorites and the operating conditions modi fied. No significant differences, either qualitative or quantitative, were observed between inside and outside air. The third sampling survey was undertaken in September 1989, 2 weeks after a specialized firm had per formed a complete disinfection of the system and ducts (HEPA vacuuming, steam cleaning, and disinfection with dilute hypochlorites). Visual inspection of the workplace and the ventilation system, now operating under normal con ditions, was also performed, in keeping with ACGIH recommendations. No significant difference was observed between inside and outside air. A 4th sur vey was conducted 8 months later, in May 1990, to verify the frequency of maintenance operations. Again, no significant differences were observed between inside and outside air. Ventilation systems should be disinfected before use, i.e., in the spring and autumn for air-conditioning units and heat ing units, respectively. The frequency of maintenance operations should be established on the basis of visual inspection.

A computer simulation model was used to study condensation and the air quality index in typical French homes (temperate climate). The correlation between condensation and overall air quality was low. The main risk of con densation occurs in kitchens and bathrooms. Hygro-adjustable ventilation, especially when combined with accelerated ventilation flow, reduced conden sation with little additional energy cost. It is concluded that ventilation sys tems should be designed that are capable of operating with three levels of activity: a reduced level for periods of non-occupancy, a low level for low occu pancy and a forced operating state, which can be governed by ambient humid ity and/or CO ₂ levels.

A double-blind trial was conducted to evaluate the effect of an ultraviolet air sterilizer in reducing the incidence of upper respiratory infections in children and the concentration of micro-organisms in 3 day-care centres located in Montreal. A population of 122 children (12-36 months of age) was under daily surveillance for respiratory illness during an average period of 12 weeks. Four ultraviolet and four control units were placed in the children's rooms. Indoor parameters were measured in four rooms, before and after installation of the devices. Even when a reduction in concentration of indoor micro-organisms was observed, the effect of the devices on the respiratory illness was negligible. The results suggest that the other routes of infection transmission are predom inant in the day-care centre.

Traditional Japanese concepts for comfortable living in the summer include the use of the thermal convection ventilation by exhausting warm air at the ceiling level. Generally outdoor temperatures during the summer months in some regions, including Hokkaido, can reach 30 ° C in the daytime, but those at night can be very cool. The convection rates of the exhausted warm air and the inflow of cool outdoor air through open windows located in the upper levels of a test house were measured throughout the day by using CO₂ as a tracer gas supplied to the bottom zone of the space. The gas concentration in each of 5 zones was simultaneously measured, and the airflow rate between each zone and the others was calculated. It was confirmed that the technique is useful for measuring convective airflow rates and processes through upward openings, such as open windows, and that the vertical ventilation exhausts the stored heat of 1 kW. It was concluded that, for the purpose of energy conserva tion, architects and engineers should consider the utilization of passive venti lation by thermal convection in the summer in highly insulated houses located in cold regions.

This paper presents an analysis of the impact of an increase of the air ventila tion rate on the energy cost in a large existing office building in Montréal, based on a computer simulation using the MICRO-DOE2 program. An increase of 3.2% or CAN$ 37,000 in the total annual energy cost could be expected if the ventilation of outside air is increased from the present rate (7.6 1/s/person) to a higher one (10.0 1/s/person), which corresponds to ASHRAE recommendations. By extrapolating this result to the case where the ventila tion rate is increased from 2.4 to 10.01/s/person, the expected increase in the total annual energy cost would be about 10% or CAN$ 117,300. This increase is higher than those previously estimated by other workers.

More than 50 papers on thermal comfort are presented in various meetings and symposia every year in Japan. Topics covered by these papers include comfort zone, the effect of fluctuating air movement and asymmetric thermal radiation on human responses, the dynamic analysis of human responses, psy chological and behavioral aspects of thermal comfort, and the development of environmental indices, to name a few. This paper briefly reviews these investi gations.

Spatial distributions of air velocity, turbulent kinetic energy and temperature were measured in a full-scale office room (7.32 X 4.72 X 2.44 m) under non- isothermal conditions. Numerical simulation was also conducted with the computational fluid dynamics code `EXACT3'. The numerical simulation results agreed with the measurements qualitatively but were quantitatively different. Possible reasons for these differences and future research needs are discussed in this paper.

The carbon dioxide concentration patterns in a large, high-rise, office building in Ottawa were examined experimentally using an automated data acquisition system. Daily CO₂ concentration profiles throughout the building and air change rates, using SF₆ as a tracer gas, were measured at minimum outdoor air supply rates during much of a heating season. Of particular interest was how well mixed the indoor air was and how well the CO₂ concentrations that were measured in the central ventilation system's return air plenum represented the average CO₂ concentration behaviour in the building as a whole. CO ₂ concen tration profiles were also measured on individual floor spaces in the building to determine the range of variability in the concentration behaviour. The mea surement results are presented and discussed in the context of demand-con trolled ventilation.

The energy savings associated with the air-tightening of new houses equipped with exhaust-only ventilation systems are evaluated in this paper. Potential savings are identified that would result from reducing the leakage area of the envelopes of houses. For most regions of Canada, the air leakage through the envelopes is currently about the same order of magnitude as that needed for air quality. Further tightening would increase the need for supplementary ven tilation in most houses. The increased cost of ventilation using exhaust-only fans would offset potential savings due to reduced air leakage with tighter envelopes. It is recommended that this analysis be repeated to evaluate the role of the tighter envelope as a complement to heat recovery ventilation and demand-control ventilation systems.

The effect of airflow through an opening (or a crack) on the natural convection in a stairwell model is presented. The flow is driven by energy input from an electric panel heater located in the lower floor of the stairwell. The work con centrates on the effect of the size of inlet opening by varying it while keeping the area of the outlet constant. New data are presented for the measured tem peratures and velocities at various cross-sections of the stairwell. The results also include gross parameters of the flow, such as the mass flow rates of the throughflow and recirculating flow, heat losses from the lower and upper floors and also from the stairway. The results show that the size of the opening has a significant effect on the flows of mass and energy within, and through, the stairwell.

A numerical study has been carried out to predict the indoor air quality and thermal comfort in a classroom with a low ventilation rate. Four different air supply methods were used: displacement ventilation, well-mixed ventilation, and two types of low-wall-diffuser ventilation. The airflow pattern, predicted percentage of dissatisfied occupants, percentage of dissatisfied people due to draught, CO₂ concentration, and percentage of dissatisfied people due to indoor air quality were determined using a program based on a k-ε turbulence model. It was found that the secondary flow generated by the buoyancy effect produced by the pupils in the room is much stronger than the primary flow supplied from the diffusers. As a result, the overall ventilation effectiveness and thermal comfort are similar under the four air supply methods, except in the region near the diffusers. Supplying fresh air at a lower level (near the floor) may cause draughts. For an acceptable perceived indoor air quality, the ventilation rate should be increased to meet the requirement stated by ASHRAE Standard 62-1989.

Unlike conventional ventilation systems, the displacement ventilation system supplies air in the low region of a room, while the exhaust opening is usually placed near the ceiling. When partitions are used in the occupied zone, the diffusion of supply air may be obstructed; thus, the existence of the partition may present important effects on air diffusion, retarding the removal of a con taminant. The present study considers the effects of office partition layout on air diffusion and indoor contaminant control in a large partitioned office equipped with a displacement ventilation system. The investigation was con ducted by computer simulation for three-dimensional turbulent flow with a k-ε two-equation model of turbulene. The average contaminant concentra tions and age of air in each chamber were indicators in the evaluation of the air exchange efficiency and ventilation effectiveness under five different partition layouts. The displacement ventilation system provides fresher air to all cham bers than a conventional ventilation system, and a proper arrangement of office partition can reduce the overall level by about 37%. With partitions in the office, the advantage of displacement ventilation may not be pronounced.

This paper reviews a selected number of tracer gas techniques which are suit able for use in ventilation studies and indoor air quality investigations in mul ti-storey office and residential buildings. Emphasis is placed on those tech niques which have been successfully used by IRC researchers for such applica tions. Examples of using these techniques in field measurements are dis cussed.

One floor of a large office building in the Ottawa area was monitored during a month-long recarpeting project in which nylon carpet and latex adhesive were used. Total volatile organic compound (TVOC) samples were collected in sev eral locations at various times after recarpeting. The TVOC concentration due to the recarpeting process showed the expected exponential decrease with time. Emission rates calculated from TVOC concentrations and measured air change rates agreed well with values determined in laboratory studies, and were much greater than the emission rate of the carpet alone. Information was collected that provided a link between symptoms of occupant discomfort and exposure to the recarpeting process.