This CIR is in reference to the ventilation design for a two tower high-rise office building. The project in question uses several Air Handling Units (AHUs) which all use 100% Outdoor Air (OA). Those AHUs are equipped with heat recover units (run-around-coils) but don\'t have any economizers or air dampers. Unlike to a similar posted CIR, our systems utilize Variable Frequency Drives (VFD) to deliver a variable amount of the 100% OA to the space. The total volume flow between its minimum and maximum for each unit is dependent on the occupancy in the rooms and areas being served. The minimum requirements for fresh air according to ASHRAE 62.1-2004 are always met. Since we have only 100% OA systems, we intend using the frequency readout from the VFD as a measurement for the OA being delivered to the space. The VFD and its frequency readout will be calibrated to achieve an accuracy of plus or minus 15%. We would use the frequency of the VFD equal to the minimum air, which must be delivered to the space, as set-point for the minimum outdoor airflow rate as required by LEED for New Construction Version 2.2 EQc1. In case conditions vary by 10% or more from the set-point the building operator will be alarmed via the building automation system. Would this measurement method qualify for earning this credit? For the same system as described above we are planning to install CO2 sensors for densely occupied spaces to obtain the credit. The installation location of those sensors will be in the return duct of every densely occupied room and not in the breathing zone between 3 ft and 6 ft. This installation location makes sure no averaging of measurements from several rooms takes place. According to ASHRAE 62.1-2004 User\'s Manual page 6-27, 3rd column, this would be appropriate. Is the designed installation location in conjunction with the EQc1 requirements to qualify for this credit?
The project is requesting guidance to determine if the project\'s Air Handling Units (AHUs) Variable Frequency Drives (VFDs) are a valid alternative to meeting the credit requirements (in lieu of installing a direct outdoor air measurement device), and if the installation of CO2 sensors in the return ducts also meets the credit requirements. Based on the description of the systems, fan speed can be calibrated to airflow and used to meet the EQc1 requirement for a "direct outdoor airflow measurement device." In this case, using the VFDs to determine the outdoor air intake flow in 100% outdoor air supply systems is a reasonable outdoor air delivery monitoring strategy. As for CO2 monitoring, the credit requires CO2 sensors to be installed in the breathable zone (3 to 6 feet above the floor) in densely occupied spaces. Even though ASHRAE 62.1-2004 may allow return duct CO2 sensors, the CO2 monitoring requirements for this credit are not specifically associated with ASHRAE 62.1-2004. Therefore, CO2 sensors are required in the breathable zone. Applicable Internationally.