Air Quality and Ventilation
Keeping an eye on air quality and ventilation is a significant part of maintaining a comfortable and energy-efficient facility, and it can often benefit from performing an airflow audit. Audits may be useful in larger faculties (air load is over 150 horsepower) to examine air supply and demand, inspect compressed air system, and provide a report with findings and recommendations.
Airflow audits can result in energy savings up to 30 percent and a reduction of up to 50 percent in operating costs. They can also help you improve system reliability, increase productivity, and reduce unscheduled downtime.
Before scheduling an audit, be sure to perform an initial inspection of your equipment and repair clogged filters, major leaks, damaged filter/regulator/lubricators and inoperable drains as well as restoring any unauthorized modifications that have been performed.
There are a number of areas where you can positively impact your facility air quailty:
Use air doors, airlocks and air curtains
Air doors usually pay for themselves in as little as two years by preventing the negative impacts of door openings and cooling loads. They prevent the flow of air into neighboring spaces, while providing an open passageway, thereby saving energy.
Before installing an air door consider:
- Door location and size
- Space requirements
- Air stream coverage and strength
- Entrance and exit rates
Make sure to review appropriate standards (ANSI/AMCA 220 Laboratory Methods of Testing Air Curtains for Aerodynamic Performance Ratings and NSF/ANSI 37: Air Curtains for Entranceways in Food and Food Service Establishments).
Consider air-to-air heat exchangers
Use air-to-air heat exchangers to recover energy from the building's exhaust air. Make sure to consider installation space, exchange rate, and desired efficiency when choosing a system. Types of heat exchangers include
- Cross-flow and counter-flow HRVs
- Plate heat exchanges: these are the most maintenance-free system and are used for dusty applications.
- Rotary heat exchangers made of corrugated aluminum media
- Heat pipe heat exchangers: these recover heat using a continuous counter-flow configuration.
Exchangers can recover 60-80 percent of potential energy loss and reduce costs throughout the year.
Use demand-controlled ventilation systems
Demand control ventilation systems utilize carbon dioxide sensors and economizers to reduce energy usage and improve indoor air quality, while providing a healthy, safe, and productive environment. Carbon dioxide sensors measure CO2 concentrations and provide a signal to the HVAC system controls. This estimates intake rates and adjusts based on space population.
These systems work best in high-density environments. ASHRAE recommends no more 700-ppm carbon dioxide (CO2) above outdoor air levels, which are between 300-500 ppm.
Adhering to ASHRAE voluntary standards can improve indoor air quality. These requirements may be mandatory and required by state or locality:
ASHRAE defines acceptable indoor air quality as "air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which a substantial majority (80 percent or more) of the people exposed do not express dissatisfaction." The suggested minimum outdoor airflow is 30 cfm/guestroom and 35 cfm/bathroom (ASHRAE 62.1-2004).
ASHRAE uses 62.1-2007 Ventilation for Acceptable Indoor Air Quality (IAQ), and offers the following options:
- VRP (Ventilation Rate Procedure) measures ventilation rates per square foot and per person.
- IAQP (Indoor Air Quality Procedure) reduces ventilation rates by analysis of contaminant sources, contaminant concentration targets, and perceived acceptability targets.
- Control point source pollutants or use ventilation, depending on which is practical
- Adhere to local building codes.
- Review and monitor rooftop building configurations, including parapets, roof, screens, and
equipment. This will ensure negative air pockets are not created and bad air is not circulated
back into the building.
- Adhere to code clearance ventilation requirements. This involves the distance of air intake
from adjacent buildings' operable windows, building edges, exhaust air streams, and sanitary
waste vents. Observing these requirements helps prevent short-circuiting of foul air into the
ventilation system or adjacent building systems.
- Keep cooling vents closed in unoccupied areas to prevent unnecessary cooling.
- Upgrade insulation levels in the ceilings and walls and for chillers. You can use a payback
tool to determine return on investment with the Insulation Payback Calculator.
- Replace windows, window coverings, and window film to minimize solar heat gain, reduce
energy use and ensure building comfort.
- Air balance your building, which ensures positive building pressure and prevents
- Change your system's air filters regularly.
- Use desiccant systems to improve indoor air quality by lowering humidity levels to prevent
mold and mildew damage. Desiccant systems run on natural gas—which saves energy—and
do not emit ozone-depleting chemicals. They also reduce the required space for central air
ducts and equipment.
- Monitor/consider air distribution, airflow, vent placement, and periods of operation. DO NOT
block vents. DO NOT place vents near sources of pollution (exhaust vents, heavy traffic