Figure 1: Water droplets form on the surface of piping of a water coil
Figure 2: Condensate on panel with temperature differential (Mumma, 2002)
Figure 3: Condensate Sensor
- Ventilation load: Generally the largest moisture load, particularly in a humid climate.
- Infiltration load: Moisture that crosses the building shell through windows, cracks, and other penetrations. Non-operable windows and pressurization of the building are ways to minimize this moisture source.
- Occupant load: As people breathe and perspire, moisture is released into the space.
- Other loads: Fountains, doors and windows left open, wet clothing, etc.
- Monitor the local dew point temperature. This is often accomplished by using zone relative humidity sensors, which can be located on the surface of the chilled product, on an interior wall surface, or in the return air duct. For more information, please see the Price Engineering Handbook, Chapter 18.
- Monitor condensate on the chilled water supply (CHWS) piping. I like this approach as the piping is often located in the ceiling cavity or other space where the air is stagnant. Moisture content may be higher in these places due to ducted air return systems and infiltration across the building envelope.
- Reset the CHWS temperature based on outdoor conditions. Consider this approach when the building envelope does not have good control of infiltration, such as historical buildings that do not have a vapor barrier. This method is not directly connected to building performance and should not be the only mode of control.
Often, a combination of these control strategies is used. Other considerations are the type of fresh air systems (DOAS), system response time, building start up, night setback and recovery after high humidity levels in the interior space.
For more information on this and other topics, please see the Price Engineer’s HVAC Handbook or email firstname.lastname@example.org with specific beam related questions.