Exceedance Degree-Hours: A new method for assessing long-term thermal conditions.

Several "discomfort indices" have been proposed and codified into building standards, with several needs usually reported for such indices. They should: express the severity of discomfort in time steps while incorporating all environmental and personal factors; be usable with any comfort model (and thus, a variety of interests, for example, traditional thermal comfort, sleep comfort), among other requirements. The existing indices, however, fall short of meeting all these goals, limiting their usefulness in many situations, such as assessing conditions in mixed-mode buildings, especially when used for building performance simulation and design optimization purposes. Here, a new discomfort index called "Exceedance Degree-Hours" is developed, which accounts for all six main environmental and personal factors. By using an equivalent temperature index, "Exceedance Degree-Hours" can capture variations in discomfort severity between different thermal conditions that other indices cannot. In contrast with other indices, "Exceedance Degree-Hours" can be paired with various comfort definitions from literature, and, importantly, it can be used to assess thermal comfort in mixed-mode buildings, providing a single value as a result. Here, the results of the proposed method are compared to those of existing discomfort indices suggested in standards, and the advantages and limitations of the proposed approach are discussed.

Housing as a critical determinant of heat vulnerability and health.

Municipalities use Heat Vulnerability Indices (HVIs) to quantify and map relative distribution of risks to human health in the event of a heatwave. These maps ostensibly allow public agencies to identify the highest-risk neighborhoods, and to concentrate emergency planning efforts and resources accordingly (e.g., to establish the locations of cooling centers). The method of constructing an HVI varies by municipality, but common inputs include demographic variables such as age and income - and to some extent, metrics such as land cover. However, taking demographic data as a proxy for heat vulnerability may provide an incomplete or inaccurate assessment of risk. A critical limitation in HVIs may be a lack of focus on housing characteristics and how they mediate indoor heat exposure. To provide an objective assessment of this limitation, we first reviewed HVIs in the literature and those published or commissioned by municipalities. We subsequently verified that most of these HVIs excluded housing factors. Next, to scope the potential consequences, we used physics-based simulations of housing prototypes (46,000 housing permutations per city) to estimate the variation in indoor heat exposure within high-vulnerability neighborhoods in Boston and Phoenix. The results show that by excluding building-level determinants of exposure, HVIs fail to capture important components of heat vulnerability. Moreover, we demonstrate how these maps currently overlook important nuances regarding the impact of building age and air conditioning functionality. Finally, we discuss the challenges of implementing housing stock characteristics in HVIs and propose methods for overcoming these challenges.

Integrated design workflow and a new tool for urban rainwater management.

Low Impact Development (LID) practices provide more sustainable solutions than traditional piping and storm ponds in stormwater management. However, architects are not equipped with the knowledge to perform runoff calculations at early design stage. In response to this dilemma, we have developed an open-source stormwater runoff evaluation and management tool, Rainwater+. It is seamlessly integrated into computer-aided design (CAD) software to receive instant estimate on the stormwater runoff volume of architecture and landscape designs. Designers can thereby develop appropriate rainwater management strategies based on local precipitation data, specific standards, site conditions and economic considerations. We employed Rainwater+ to conduct two case studies illustrating the importance of considering stormwater runoff in the early design stage. The first case study showed that integrating rainwater management into design modeling is critical for determining LID practice at any specific site. The second case study demonstrated the need of visualizing runoff flow direction in assisting the placement of LID practices at proper locations when the terrain is of great complexity.