Rethinking ventilation: A benefit-cost analysis of carbon-offset increased outdoor air provision

Abstract

The indoor built environment critically impacts occupant health, and improvements to indoor air quality have been demonstrated to significantly reduce illness while improving cognitive function. While the link between increased outdoor air ventilation and improved occupant heath and productivity are established; many energy codes and sustainability rating systems penalize building designers for ventilating above code minimums. This paper argues that this approach is short-sighted and proposes instead that carbon emissions associated with any increased ventilation rates be offset and all limitations removed. A benefit-cost analysis considered energy costs and carbon emission offsets to achieve net-zero carbon operation for large office buildings across international climate zones with ventilation rates ranging from 125% to 1000% ASHRAE 62.1 minimums. Key findings: (1) the productivity benefit was substantially larger than the incremental energy costs; (2) carbon offset costs were relatively low compared with energy costs and had a negligible effect on results; (3) increasing outdoor air resulted in consistently increasing net benefits on an area basis; and (4) the benefit-cost ratio was inversely proportional to the severity of the climate, with the most moderate climates actually showing a net energy decrease with elevated outdoor air. This paper frames the question of ventilation rates in sustainable buildings not as an energy issue, but as a health and productivity issue and provides an alternative framework for this evaluation within a carbon-neutral context. This paper presents a quantitative analysis across climate zones and achievable ventilation flow rates to provide financial justification within the contemporary building design context.