Contaminant transport

Attached garages can pose a threat to a home’s indoor air quality because the garage air, which often contains some contaminants such as particulate matter, carbon monoxide, and volatile organic compounds, can migrate into living spaces. In this paper, a model is developed to characterize the transport of contaminants from a garage to a living space based on a measurement of single tracer gas decays without limiting the numbers of zones in the building.

Building simulations are used to investigate building performance and design the building systems optimally. In particular, the air exchange between zonesand with the environment has a pivotal role inmodernventilation system design. Nevertheless, the model of the airflow becomes difficult for the modeler, motivated by the complexity of the grid that has to be modeled. IDEAS, a Modelica library, includes components for thermal multi-zone models of buildings as well as models for heating, ventilation, air conditioning and other elements that interact in the same model.

The well-mixing assumptions, uniform distributions of air temperatures and contaminant concentrations and neglect of air momentum effects in a zone, used in multizone airflow network models could cause errors in some cases. Through dimensional analysis of the published data from the literature, this study has found correlation between the errors and mixing levels. Our study concluded that the assumption of uniform air temperatures is not appropriate if the  vertical non-dimensional temperature gradient is higher than 0.03.

A number of interzonal models have been developed to calculate air flows and pollutant transport mechanisms in both single and multizone buildings. A recent development in multizone air-flow modeling, the COMIS model, has a number of capabilities that go beyond previous models, much as COMIS can be used as either a stand-alone air-flow model with input and output features or as an infiltration module for thermal building simulation programs.

We describe a novel modeling technique, based on Duhamel's theorem, to study the effects of time-varying winds on radon transport in soil near buildings. The technique, implemented in the model RapidSTART, reduces computational times for transient, three-dimensional, wind-induced soil-gas and radon transport by three to four orders of magnitude compared with conventional finite-dierence models.