Potential effects of permeable and hygroscopic lightweight structures on thermal comfort and perceived IAQ in a cold climate.

UNLABELLED: In this study, we simulated and measured the effect of permeable and hygroscopic lightweight structures on indoor air quality (IAQ) and thermal comfort in a cold climate. The potential effect of hygroscopic mass was assessed with the simulation of extreme cases, where permeable and hygroscopic lightweight structures with unfinished surfaces were compared with impermeable and non-hygroscopic ones. Measurements were conducted in 78 rooms of 46 newly built detached timber-framed houses and analyzed according to hygroscopic surface materials and envelope permeability. From the simulations, it was shown that permeable and hygroscopic structures considerably improved perceived air quality in summer, when a ventilation rate of 6 l/s pers. in the non-hygroscopic case corresponded roughly to 4 l/s pers. in the hygroscopic case. However, window airing and furnishing will reduce this difference in practice. Both simulated and measured results showed that permeable and hygroscopic structures significantly reduced peak indoor relative humidity levels and daily changes in relative humidity, but had no long-term effects. Measured results also indicated that completely non-hygroscopic houses did not exist in reality. PRACTICAL IMPLICATIONS: Limited knowledge is available about building envelope and ventilation system interactions with consequent effects on indoor climate. To take such effects adequately into account in design and construction of buildings, solid scientific data explaining the significance of the phenomena studied are needed. We have demonstrated that moisture exchange has evidently enough importance to be taken into account in future building simulation tools.

Reduction potential of urban PM2.5 mortality risk using modern ventilation systems in buildings.

UNLABELLED: Urban PM2.5 (particulate matter with aerodynamic diameter smaller than 2.5 microm) is associated with excess mortality and other health effects. Stationary sources are regulated and considerable effort is being put into developing low-pollution vehicles and environment-friendly transportation systems. While waiting for technological breakthroughs in emission controls, the current work assesses the exposure reductions achievable by a complementary means: efficient filtration of supply air in buildings. For this purpose infiltration factors for buildings of different ages are quantified using Exposures of Adult Urban Populations in Europe Study (EXPOLIS) measurements of indoor and outdoor concentrations in a population-based probability sample of residential and occupational buildings in Helsinki, Finland. These are entered as inputs into an evaluated simulation model to compare exposures in the current scenario with an alternative scenario, where the distribution of ambient PM2.5 infiltration factors in all residential and occupational buildings are assumed to be similar to the subset of existing occupational buildings using supply air filters. In the alternative scenario exposures to ambient PM2.5 were reduced by 27%. Compared with source controls, a significant additional benefit is that infiltration affects particles from all outdoor sources. The large fraction of time spent indoors makes the reduction larger than what probably can be achieved by local transport policies or other emission controls in the near future. PRACTICAL IMPLICATIONS: It has been suggested that indoor concentrations of ambient particles and the associated health risks can be reduced by using mechanical ventilation systems with supply air filtering in buildings. The current work quantifies the effects of these concentration reductions on population exposures using population-based data from Helsinki and an exposure model. The estimated exposure reductions suggest that correctly defined building codes may reduce annual premature mortality by hundreds in Finland and by tens of thousands in the developed world altogether.

Performance and costs of particle air filtration technologies.

This paper predicts the reductions in the indoor mass concentrations of particles attainable from use of filters in building supply airstreams and also from use of stand-alone fan-filter units. Filters with a wide efficiency range are considered. Predicted concentration reductions are provided for indoor-generated particles containing dust-mite and cat allergen, for environmental tobacco smoke (ETS) particles, and for outdoor air fine-mode particles. Additionally, this paper uses a simple model and available data to estimate the energy and total costs of the filtration options. Predicted reductions in cat and dust-mite allergen concentrations range from 20 to 80%. To obtain substantial, e.g. 50%, reductions in indoor concentrations of these allergens, the rate of airflow through the filter must be at least a few indoor volumes per hour. Increasing filter efficiencies above approximately ASHRAE Dust Spot 65% does not significantly reduce predicted indoor concentrations of these allergens. For ETS particles and outdoor fine-mode particles, calculations indicate that relatively large, e.g. 80%, decreases in indoor concentrations are attainable with practical filter efficiencies and flow rates. Increasing the filter efficiency above ASHRAE 85% results in only modest predicted incremental decreases in indoor concentration. Energy costs and total costs can be similar for filtration using filters with a wide range of efficiency ratings. Total estimated filtration costs of approximately $0.70 to $1.80 per person per month are insignificant relative to salaries, rent, or health insurance costs.