![]() Expanding the number and size of pressurised areas in any building means paying more attention to resulting issues like high humidity levels, sticky entryways, mold growth, and increased energy costs. While pressurised rooms are helpful for health care workers, patients and staff, they also present challenges to HVAC techs and facility managers. The idea has extended beyond the hospital room to include waiting rooms, triage, bathrooms and other areas that could contain contaminants or susceptible people. The COVID-19 pandemic has extended the use of pressurised rooms to combat the disease. Inadequate or infrequent testing puts patients and others at risk. Still, accurate testing and consistent monitoring is the best way to maintain the effectiveness of a pressurised room. Electronic pressure monitors offer continuous, accurate monitoring, but they’re expensive to purchase and install. The smoke just needs to move in the right direction. ![]() If the smoke flows inside or outside, then a pressure differential exists. During a smoke test, technicians create puffs of smoke next to known intakes like registers or under doorways. They’re cheap and easy to administer, but aren’t continuous or highly accurate. Smoke tests are a common way to test the effectiveness of a pressurised room. ACH is a measure of how often air within a space is replaced every hour and is essential to combating contaminated, stale and unhealthy air. To aid air quality, HVAC technicians design HVAC systems to include specific numbers of air changes per hour (ACH) based on the size of the room. Air quality is particularly important for medical facilities, since suboptimal humidity levels can contribute to illness. Like any conditioned environment, pressurised rooms must also maintain humidity and air temperature to ensure comfort and safety. The more leakage, the more energy required to maintain a room’s negative or positive pressure. These entryways are also safe areas for removing PPE or as a failsafe against pressure loss. Designers often outfit NPRs with ante rooms to minimise leakage. Pressure room designers try to keep rooms as air tight as possible, but some leakage occurs through gaps in doors, windows and electrical outlets. Because PPRs form barriers to outside spaces, their HVAC systems must filter out any contaminants from the interior air while ensuring optimal pressure and safe air quality. PPR hospital rooms often house immunocompromised patients susceptible to infection or disease. PPRs exist within surgical theatres and in vitro clinics where contamination is possible. Air escapes the room without letting in outside contaminated air. Positive pressure rooms maintain a higher air pressure inside than the surrounding environment. Interior air then moves through a filtration system to remove contaminants before safely exiting the pressurised environment. When someone opens the door of an NPR, negative pressure draws passive air inside, forming a barrier against the escape of pathogens or dust. The purpose is to control the direction of passive airflow. That is, a negative quantity of air maintained. ![]() To create a NPR, HVAC professionals must move air out at a faster rate than it comes in. If done correctly, the result is a stable environment with lower or higher air pressure than the surrounding area. The natural movement of air without the aid of mechanical equipment like a fan is called “passive” air flow, and techs use passive air flow to keep debris and contaminants from entering or exiting a room. Building managers use HVAC equipment, fans and ventilation systems to control this natural propensity of air to escape-to keep the “balloon” knotted as it were. The bigger the pressure differential, the faster the balloon will fly around the room. Pressure DifferentialĪnyone who’s ever let go of an un-knotted balloon has witnessed the propensity of air to move from a higher pressure area to a lower one. The difference between positive vs negative pressure rooms is mostly one of pressure differential and air flow. Both approaches use air pressure differentials to control ventilation and contamination. Hospitals and clinics employ negative pressure rooms (NPR) to contain the spread of infectious diseases. ![]() For example, semiconductor makers use positive pressure rooms (PPR) to ensure their integrated chips are free of contaminants in the air. Many industries use pressurised rooms to stop cross-contamination between one area of a building and another. ![]()
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