1 – Total Energy Wheel 2 – Cooling Coil 3 – Desiccant DH Wheel 4 – Room SHR = 0.7 5 – Sensible-Only Wheel 95DB/78WB 1 2 74DB/67WB 58DP 4 4 74DB/52%RH/55DP 74DB/40%RH/48DP 5 55DB/54WB 3 66DB/46%RH/44DP Figure 2: Psychrometric evaluation of a desiccant dehumidification wheel vs. a sensible-only wheel. wheel and cooling coil provide saturated 55°F (12.8°C) supply air off the coil. When a sensible wheel is used for reheat, the moisture content of the air remains the same across the wheel to provide a 68°F (20°C) discharge at 61% RH. Using a 0.7 sensible heat ratio (sensible heat load divided by total heat load) and a lab space temperature setpoint of 74°F (23.3°C), the space conditions will be 52% RH and a dew point of 55°F (12.8°C). When a desiccant dehumidification wheel is used for both reheat and dehumidification, the moisture content of the air will be absorbed as it passes through the wheel. Supply air is then provided at 66°F (18.8°C) and 46% RH. Using the same 0.7 sensible heat ratio and lab space temperature setpoint of 74°F (23.3°C), the space conditions will result in a space humidity of 40% RH and a dew point of 48°F (8.9°C). This is an important analysis to complete because the desiccant dehumidification wheel has a 10% cost premium over the sensible-only wheel. The sensible wheel provides a space dew point of 55°F (12.8°C), and the desiccant dehumidification wheel provides a space dew point of 48°F (8.9°C). When supplying chilled water to the chilled beams at 56°F to 58°F 48 ASHRAE Journal The northwest corner of the building 75% complete, July 2011. (13.3°C to 14.4°C), it is impossible to guarantee that the beams would not condense with only a 1°F (0.5°C) safety factor. If the space dew point exceeds the chilled beam chilled water ashrae.org September 2012