Hello Modeling Community,

I am working on a small building (<2300 m2) project that incorporates Heat Pump systems for cooling and heating. I noticed in the OpenStudio output that a significant number of hours of the year had a relative humidity <30%. I tried controlling the humidity with a humidification and dehumidification setpoint schedule but noticed no effect.

I realized that the packaged terminal heat pump does not incorporate any systems that can implicitly control humidity. I could add an air loop with a humidifier and control but began to wonder what ASHRAE Standards recommended.

I looked into ASHRAE 90.2 6.10.3, ASHRAE 90.1 6.5.2.3 and 6.5.2.4, and ASHRAE 62 5.9.1. Each of these sections discuss a relative humidity range of 30%-65% with an ideal value of 50%. However, the wording is a bit confusing regarding whether it's required. Much of the wording in these sections outline humidity control if a system is precent that controls humidity.

For example, ASHRAE 90.2 Section 6.10.3 Humidity Control states:

"If additional energy-consuming equipment is provided for adding moisture to maintain specific selected relative humidities in spaces or zones, a humidistat shall be provided. This device shall be capable of being set to prevent energy from being used to produce relative humidity within the space above 30%".

So my question is: For a system that does not implicitly incorporate humdification or dehumidification, is it required to incorporate them as an additional system into the model?

Thank you,

Justin