HVAC System Design in Healthcare Facilities and Control of Aerosol Contaminants: Issues, Tools, and Experiments

Healthcare buildings (HCBs) like conventional buildings need some forms of indoor climate control, in terms of temperature, humidity, and air quality. Heating, ventilating, and air-conditioning (HVAC) systems in buildings are leading to indoor environment quality and exert a key role in occupant’s comfort and health. In the HCB context, indoor air quality requires by far the greatest attention: to ensure a healthful indoor air quality (IAQ) is widely recognized as a mandatory goal in HCBs to protect the patients and healthcare workers against hospital-acquired infections (HAI) and occupational diseases. It is worth noting that not the thermal comfort issues but IAQ, the ventilation needs, and the interactions between air movements and dispersion of contaminants are becoming the key factors within the context of HCB services design and operation. IAQ is really a determinant of building design and has impacts on the societal values such as people’s health and energy use. However, the problems with measuring and defining what is “good IAQ” are multimodal and unprecedented and require a multidisciplinary approach in order to find new and adequate solutions. Let us stress that we are at a turning point in IAQ. Until now, we have relied on prescriptive codes dictating quite simple but indirect physical quantities such as target air flows (per person or per floor area), air changes per hour (ACH), or pressure differences and specifying some features of equipment (e.g., air filter efficiency) and of the building (e.g., air tightness of the envelope, and low-polluting materials). There is at the moment a quite limited use of air quality sensors, and therefore, HVAC design and operation are based on inadequate knowledge of contaminant presence and of their spatial and temporal concentrations. Technical advancement and cost reduction of IAQ sensors (notably low-cost optical particle counter, OPC, for particle concentration) and of computerized simulation tools (CFD) and the wide adoption of Internet of Things (IOT) technologies will allow the shift to performance-based concepts for ventilation and to customized/personal solutions that acknowledge the primacy of healthy indoor air measurements. Ventilation for hospitals is a very broad and complicated field: ventilation has to serve a large number of different spaces and processes, many with special requirements that cannot be met without special considerations. There are many different approaches and recurrent options as follows: (1) natural ventilation versus mechanical and hybrid ventilation; (2) outdoor air only (no recirculation) versus secondary/recirculation air systems; (3) ventilation rate per person (or per emission source) versus air changes per hour (ACH); and (4) concentration limits for particles (particles/m3) and/or for microbiological contaminants (CFU/m3). Moreover, HCB ventilation is ruled by binding national laws and regulations, but is technically driven by a multiplicity of standards and guidelines that are voluntary and an expression of the state of art, pertaining to different geographical areas [e.g., local, national, European, and international (FGI 2014; CDC 2003; WHO 2009;ASHRAE 2014)]. In order to rightly address the goals of IAQ future issues in HCBs, we should bear in mind the rising concerns for antibiotic resistance and therefore the increasing need to use ventilation as an effective way to control infection in hospitals. But, at the same time we cannot ignore the HCB massive energy consumption and the strong push to save energy and reduce hospital’s carbon footprint. Aiming to contribute to the mentioned goals, this paper describes current technologies and encourages using novel approaches and not very often employed tools (i.e., particle measurement, and CFD simulation).