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AIRFLOW AND ACH The ASHRAE Standard-170 contains an extensive list of recommended ACH per application type to introduce fresh air into the space as well as the recommended air-recirculation per application ( or no air re-circulation ). It must be considered that in medical facilities the HVAC system will likely be operating continuously , for 24-hours a day .
“ Reception areas are often a place where HVAC gets neglected , but is one of the places that can hold the most risk with as-yet undiagnosed patients coming in and being admitted .”
Introducing fresh air into a space and exhausting air out of a space also needs careful consideration . In medical facilities , more so than other buildings , the exhaust air must be kept well away from the fresh air intake . In some cases , as it has been alluded to already such as with tuberculosis ( TB ) facilities , air may not be expelled without the necessary filtration . Location of the hospital also plays a major role when it comes to fresh air as the outdoor air quality is not as consistent as one thinks .
Controlling of air movement is critical from a design aspect from space to space . Correct applied air movement control allows the facility to avoid contamination , and this has been a particular element of focus through the Covid pandemic . This includes the strategy around the facility ’ s ventilation . As an added challenge , medical facilities have continuously changing occupancy , and would not necessarily be designed to handle a sudden mass of patients , however , adapted designs today allows for different operating modes with the intention of supporting crisis situations .
“ One of the bigger challenges within a hospital environment that is seldom considered are lint , fluff and dust from things like hospital linen and gowns . These fine particles , over time , fill up filters and the equipment within the areas . This proves a challenge especially in a theatre for example , where the return air ducts are most commonly installed in the corners of these rooms . Because the inlets are at low levels with unidirectional flows the return air lines pick up everything that lands on the ground . This can affect the air flow rates and require regular maintenance ( that often also requires stringent health and safety protocols and the use of hazmat suits ),” says Bester .
In theatres , the airflow comprises what is essentially a constant air wash through the laminar flow design principle . “ The concept of this design is that you have this constant wash to direct the flow of any bacteria or contaminants into the ducting and take the stale / compromised air away . Some surgeries are naturally more intense than others , where infection can result in the worst outcomes ,” adds Schaefer .
Ensuring the correct airflow and recirculation in theatre rooms is another element that can cause challenges for doctors and nurses when considering leakage of anaesthetic gases . On long operating procedures that can be up to 10 or more hours , poor air circulation can result in the concentration of anaesthetic gases , which has been found to affect the teams working in the space . Another property of some anaesthetic gas is their flammability , and hence explosion-risk in confined spaces , however , with modern anaesthetics , this risk has been mitigated .
HUMIDITY CONTROL HVAC systems used in these facilities will always make use of either a humidification process or de-humidification process as no location is the same , so outside air properties as the source of air needs to be managed as well as internal conditions based on particular room effects . Accurate humidity control also helps protect electronic equipment used against possible electrostatic discharges in very low humidity conditions .
www . hvacronline . co . za RACA Journal I May 2021 21