When infectious epidemics occur, they can be perpetuated within health care settings, potentially resulting in severe health care workforce absenteeism, morbidity, mortality, and economic losses. The ventilation system configuration of an airborne infection isolation room is one factor that can play a role in protecting health care workers from infectious patient bioaerosols. Though commonly associated with airborne infectious diseases, the airborne infection isolation room design can also impact other transmission routes such as short-range airborne as well as fomite and contact transmission routes that are impacted by contagion concentration and recirculation. This article presents a computational fluid dynamics study on the influence of the ventilation configuration on the possible flow path of bioaerosol dispersal behavior in a mock airborne infection isolation room. At first, a mock airborne infection isolation room was modeled that has the room geometry and layout, ventilation parameters, and pressurization corresponding to that of a traditional ceiling-mounted ventilation arrangement observed in existing hospitals. An alternate ventilation configuration was then modeled to retain the linear supply diffuser in the original mock airborne infection isolation room but interchanging the square supply and exhaust locations to place the exhaust closer to the patient source and allow clean air from supply vents to flow in clean-to-dirty flow paths, originating in uncontaminated parts of the room prior to entering the contaminated patient's air space. The modeled alternate airborne infection isolation room ventilation rate was 12 air changes per hour. Two human breathing models were used to simulate a source patient and a receiving health care worker. A patient cough cycle was introduced into the simulation, and the airborne infection dispersal was tracked in time using a multi-phase flow simulation approach. The results from the alternate configuration revealed that the cough aerosols were pulled by the exhaust vent without encountering the health care worker by 0.93 s after patient coughs and the particles were controlled as the aerosols' flow path was uninterrupted by an air particle streamline from patient to the ceiling exhaust venting out cough aerosols. However, not all the aerosols were vented out of the room. The remaining cough aerosols entered the health care worker's breathing zone by 0.98 s. This resulted in one of the critical stages in terms of the health care worker's exposure to airborne virus and presented the opportunity for the health care worker to suffer adverse health effects from the inhalation of cough aerosols. Within 2 s, the cough aerosols reentered and recirculated within the patient and health care worker's surroundings resulting in pockets of old contaminated air. By this time, coalescence losses decreased as the aerosol were no longer in very close proximity and their movement was primarily influenced by the airborne infection isolation room airflow patterns. In the patient and health care worker's area away from the supply, the fresh air supply failed to reach this part of the room to quickly dilute the cough aerosol concentration. The exhaust was also found to have minimal effect upon cough aerosol removal, except for those areas with high exhaust velocities, very close to the exhaust grill. Within 5-20 s after a patient's cough, the aerosols tended to break up to form smaller sized aerosols of less than one micron diameter. They remained airborne and entrained back into the supply air stream, spreading into the entire room. The suspended aerosols resulted in the floating time of more than 21 s in the room due to one cough cycle. The duration of airborne contagion in the room and its prolonged exposure to the health care worker is likely to happen due to successive coughing cycles. Hence, the evaluated alternate airborne infection isolation room is not effective in removing at least 38% particles exposed to health care worker within the first second of a patient's cough.

The National Institute of Standards and Technology constructed the Net-Zero Energy (NZE) Residential Test Facility to support the development and adoption of cost-effective NZE designs and technologies. In support of indoor air quality goals, contaminant source control approaches were implemented that minimized the use of products containing urea-formaldehyde resin and utilized products with relatively low volatile organic compound emissions. Indoor and outdoor concentrations of formaldehyde and acetaldehyde were measured approximately monthly for 15 months. Independent emission measurements of formaldehyde were made in a small chamber system to determine the emission rates from samples of the wood flooring, plywood, and wood cabinetry taken from the house. Blower door tests were performed to determine the leakage area of the exterior envelope, the interior floors, and transfer grilles between floors. Real-time formaldehyde concentration and energy measurements were used to verify the indoor concentrations and energy predictions of a coupled CONTAM-EnergyPlus model of the house. The verified model was then used to evaluate the impacts of different outdoor air ventilation rates on indoor concentrations and energy. This work demonstrates the need for consideration of source control options during product selection and the provision of mechanical ventilation, especially in homes with relatively airtight envelopes.

This article presents local convective boiling measurements in a micro-fin tube for three low global warming potential refrigerants: R448A, R449A, and R452B. An existing correlation was modified to predict multi-component mixtures, which predicted 98% of the measurements to within ±20%. The new correlation was used to compare the heat transfer coefficient of the three test fluids at the same heat flux, saturated refrigerant temperature, and refrigerant mass flux. The resulting comparison showed that refrigerant R452B exhibited the highest heat transfer, in large part due to its approximately 28% larger liquid thermal conductivity and smaller temperature glide as compared to the tested low-global warming potential refrigerants. For the example case, the heat transfer coefficient for R449A was approximately 8% larger than that for R448A, while the heat transfer coefficient for R452B was more than 59% larger than either R448A or R449A. The heat transfer coefficients for R448A and R449A were roughly between 26 and 48% less than that of R404A for the example case. In contrast, the model predicts that the R452B heat transfer coefficient was approximately 13% larger than that of R404A for the same conditions.

The NIST Net-Zero Energy Residential Test Facility (NZERTF) is a highly instrumented, highly configurable, single-family, net-zero energy house occupied by a virtual family of four. A detailed transient model of the NZERTF and the accompanying mechanical equipment was created using information available before construction; the model incorporated building geometric details and construction material properties, as well as manufacturers' specifications for HVAC, water heating, solar PV and other equipment. This model represents the typical design paradigm, where actual building performance and detailed equipment operation are not known. This original model underpredicted the measured annual energy consumption by 13.8 %. The measured data were used to understand and correct the sources of error at the component level; modifications to the HVAC system, interior thermal capacitance, and domestic hot water system improved the energy consumption prediction to within 1.6 % of measured data. The differences between the original and modified models are useful for understanding the sources, magnitudes, and possible corrections to errors in energy models for high-efficiency residences. The modified model will be used in future studies of alternative energy system configurations and control strategies, contributing to cost-effective and optimum design of net-zero energy houses in America.