In almost all settings, ventilation with outdoor air is critical to ensure proper indoor air quality. Research has shown that occupant health, cognition, and productivity all benefit from the introduction of fresh air and the exhaust of polluted indoor air. Determining the proper outdoor air ventilation rate is the primary topic of ASHRAE Guideline 62. ASHRAE 62.2 should be used for residential buildings; ASHRAE 62.1 should be used for all others. Below, the most recent version is referred to simply as ASHRAE 62.
In the early design stage, work with the owner to identify the expected occupancy and activity type in all areas of the building, and use these or ASHRAE design occupancy levels to begin ventilation rate calculations. Determine the appropriate ASHRAE procedure for calculating these, either 1) the Ventilation Rate Procedure (VRP), 2) the Indoor Air Quality Procedure (IAQP), or 3) the Natural Ventilation Procedure (NVP). If using the standard VRP, it is recommended to adopt an air distribution configuration such as displacement ventilation that improves the zone air distribution effectiveness and reduces the total zone outdoor airflow. This may also result in reduced energy consumption and help meet SB 2030 energy targets.
Early in the design phase, determine a strategy for controlling emissions from printers, copiers, and MFDs. If these devices will use dry toner, emissions to the air must be contained within an enclosed room and exhausted directly to the outdoors. Alternatives to this approach include using inkjet printers rather than laser printers, or requiring laser printers to meet the emission certification of Blue Angel RAL-UZ 171. Such printers could be dispersed in an open-office setting, for example.
Throughout mechanical design, the mechanical design team should coordinate with the energy analysis team so that ventilation rates are consistent in both processes. Update the design ventilation rate as any changes are made to the occupancy levels planned for the building. Communicate these changes to the parties evaluating energy performance so that ventilation rates compliant with these guidelines can be taken into account in energy calculations. The SB 2030 program considers ventilation rates in the creation of the SB 2030 Energy Standard; ensuring that these rates are noted allows an appropriate standard to be created.
The mechanical design team should consider using strategies that provide the opportunity to reduce energy use associated with ventilation. The list of recommendations includes but is not limited to:
- Use of CO2 sensors or other types of occupancy sensors to reduce ventilation in spaces when they are unoccupied.
- Use of ventilation strategies that increase ventilation efficiency such as displacement ventilation.
- Use of economizer cycles where possible.
- Use of heat recovery strategies in the ventilation design chosen.
For many building types, use of these strategies can significantly reduce total energy consumption and help the building achieve challenging SB 2030 energy targets.
For ventilation systems serving over 5000 sq. ft., determine how outdoor airflow will be monitored. Yearly spot checks are allowed, but if continuous monitoring is desired, ensure that air flow can be measured for all large spaces that are high occupancy and that these values are reported to the Building Automation System (BAS) or other tracking and recording device. These systems should be shown on the HVAC plans.
All new buildings, regardless of type or location, must protect against hazardous soil gases, including radon, using at least the passive measures found in the ANSI CC-1000 standard. Radon is a soil gas, and typically enters buildings through air leaks at or below grade. Therefore, passive measures such as the creation of a robust air barrier between the building’s at/below grade space and the ground is critical and effective. Further control is offered by passively venting the ground below the building’s floor slab. This is typically done with a sub-slab layer of crushed stone and perforated drain tile, which can collect soil gases migrating through the stone layer. These gases are safely routed through a vertical ventilation stack and released above the roof of the building. The ANSI CC-1000 Standards guide engineers on the design, layout, and venting requirements of the sub-slab collection plenum and vent system. Be aware that each vertical ventilation stack can vent only a limited area, and may require space for a powered fan.
Following construction, testing radon levels is also required for all buildings, regardless of type or location. Testing should be performed per CC-1000 Annex D, and be performed for radon and any other hazardous soil gas identified as a risk for the building. If radon levels are found above 2 piC/L, the passive stack ventilation system must be retrofitted with fans to provide a powered ventilation assist. These fans will require extra space for installation and access in case of replacement or maintenance. They will also require a source of electrical power since they must run continuously. Take these issues into consideration at the design stage to minimize expenses if radon testing shows fans are required.