Adequate levels of ventilation reduce the likelihood of sick building syndrome. (See BIO...

Adequate levels of ventilation reduce the likelihood of sick building syndrome. (See BIOCONNECTIONS on p. 753.) The outdoor air used for ventilation must be conditioned, and this requires energy. Consider the air-handling system for the commercial building illustrated in Fig. P12.13D, consisting of ducting, two dampers labeled A and B, a vapor-compression dehumidifier, and a heater. The system supplies 25 m³/s of conditioned air at 20°C and a relative humidity of 55% to maintain the interior space at 25°C and a relative humidity of 50%. The recirculated air has the same conditions as the air in the interior space. A minimum of 5 m³/s of outdoor air is required to provide adequate ventilation. Dampers A and B can be set to provide alternative operating modes to maintain required ventilation rates. On a given summer day when the outside air dry-bulb temperature and relative humidity are 25°C and 60%, respectively, which of the following three operating modes is best from the standpoint of minimizing the total heat transfer of energy from the conditioned air to the cooling coil and to the conditioned air from the heating coil?

1. Dampers A and B closed.

2. Damper A open and damper B closed with outside air contributing one-quarter of the total supply air.

3. Dampers A and B open. One-quarter of the conditioned air comes from outside air and one-third of the recirculated air bypasses the dehumidifier via open damper B; the rest flows through damper A.

Present your recommendation together with your reasoning in a PowerPoint presentation suitable for your class. Additionally, in an accompanying memorandum, provide well-documented sample calculations in support of your recommendation.