Healthcare facilities have prescribed interior climatic conditions to maintain occupant health and safety. While local health departments may offer specific requirements, this writing will reference guidance related to RH, temperature, and ventilation conditions offered by Facilities Guidelines Institute (FGI) as the basis for discussion. Forty-two states have adopted some edition of FGI, and three states allow its use as an alternate path. FGI also incorporates the American National Standards Institute (ANSI)/ASHRAE/American Society for Healthcare Engineering (ASHE) 170, Ventilation of Health Care Facilities, which includes Table 7.1, “Design Parameters – Hospital Spaces.” The parameters for many of the spaces listed in the table are designed and operated for temperature ranges between 21 and 24 C (70 and 75 F) with an RH between 20 and 60 percent. Air changes per hour (ACH), which is a measure of air volume added to or removed from a space divided by the volume of space, as well as pressure relationships, can also vary greatly according to the function of the space.
It is also important to note the higher end of the RH range often occurs during summer months based on seasonal exterior climate changes. In fact, facilities in climate zones with colder wintertime temperatures are often operated with seasonal setbacks that lower the interior RH during the coldest times of a year. Many of the spaces listed in Figure 1 include a lower RH that would fall below the recent guidelines that are outlined in the ASHRAE PD.
Specialized building types, such as laboratories, museums, natatoriums, may more closely align with healthcare facilities due to their likelihood to operate at comparatively higher interior RH than offices or commercial spaces. Other building types, including offices, residential, commercial, schools, etc., reference different standards, such as ASHRAE 62.1-2019, Ventilation for Acceptable Indoor Air Quality, which now expresses humidity control as dewpoint and not an RH. However, in prior editions, the lower boundary of the recommended RH range was set at 25 percent (ASHRAE 62-2001), which at 20 C (69 F), can equate to a dewpoint of 32 degrees.
It is also important to note the reference standards discussed above outline design parameters but may not represent what the actual wintertime RH is during operation. Further, the enclosures for many of these types of buildings were not designed with the intent to have active interior, humidification provided during colder, winter months, and it is the authors’ experiences that many existing buildings operate below 20 percent RH for periods of time during heating months.
Many existing buildings are also fully or partially naturally ventilated. This may be accomplished via operable windows or intended/unintended openings in the building enclosure. In these instances, airflow may be variable or unpredictable, which creates difficulty for maintaining a stable environment via a mechanical strategy. This also highlights the need for air control between the interior and exterior, as well as among interior areas that may operate differently.
Given the issues previously indicated, an evaluation is recommended to gain an understanding of capabilities and limitations of the existing building enclosure prior to modification. To illustrate these issues, the authors will review some common details associated with existing building enclosure, their limitations related to condensation resistance and air infiltration/exfiltration/intrusion, and some techniques that can be utilized to evaluate anticipated performance.
A great article. There should be more articles like this.