Lower Relative Humidity in the Hospital Setting: What the Doctor Ordered
The comfort level and air quality in an indoor environment is directly tied to the relative humidity level of the space. In a hospital setting, relative humidity is generally well controlled to provide for the safety and comfort of patients. Lower relative humidity in a hospital environment, however, also can have benefits for surgeons and medical practitioners.
In operating rooms, for example, surgeons typically wear several layers of clothing, surgical masks and latex gloves. This protective gear helps keep both surgeon and patient safe from contamination and infection. However, the extra clothing can cause surgeons to experience excess perspiration. In an environment with a high relative humidity, this sweating can be even more severe. The discomfort and interference caused by sweating can impair the surgeon’s concentration and performance, causing unnecessary risks to both patient and doctor. By maintaining a lower relative humidity in a hospital environment, surgeon comfort can improve, which results in better outcomes for patients and physicians. Operating rooms generally require drier air than other areas of a hospital. Air in a waiting room or other public location may have a relative humidity of 50 percent at a temperature of 75 degrees, resulting in a dew point of 55 degrees. Operating rooms should generally be maintained at temperatures and humidity levels resulting in a much lower dew point, such as 60 degrees at 50 percent relative humidity, which creates a dew point just above 40 degrees.
Preconditioning of Outside Air
Air brought into the hospital’s indoor environment through ventilation systems is a common source of moisture. The wetter and more humid the air in your section of the country, the more likely you will have to practice some form of preconditioning for the air used to provide ventilation.
You may need to:
- Dehumidify all incoming makeup air to the necessary dew point.
- Take into account internal sources of moisture, such as open water, infiltration and moisture produced by humans.
- Reheat incoming air as necessary to prevent overcooling, Consult with your trusted local HVAC contractor for expert advice on ventilation and how to maintain proper humidity levels and dew points based on your local climate.
Dehumidification methods to lower relative humidity in a hospital environment.
There are two main dehumidification methods that are common in hospitals: using a low-temperature chiller or using dessicants, materials designed to absorb moisture.
- Low-temperature chiller method: This method uses a chilled-water system to bring the mixture of incoming ventilation air and return air to the correct temperature, usually about 40 degrees. Depending on the type of equipment you have, it may be a one-step or two-step process. The two-step process cools air using standard chilled water in the first stage and a cooler water/brine mixture in the second stage. A one-stage chilling process may be accomplished using a larger chilling coil and a water/brine mixture at 35 degrees.
- Dessicant method: Dessicant dehumidification is accomplished using specialized dehumidifiers containing a dessicant wheel that absorbs and releases moisture. These wheels require two air streams, one for supply air and the other for reactivation air. After absorbing moisture from the supply stream, the dessicant wheel rotates into the reactivation air stream, where moisture is transferred to heated air and removed through an exhaust system. Reactivation air in dessicant humidifier applications can often approach 300 degrees; the drier indoor air, the hotter the reactivation air must be. In general, dessicant humidifiers are the least expensive of the two dehumidification options, often as much as 40 percent cheaper than using a low-temperature chiller.
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