Combat poor indoor air quality
June 3, 2008
EPA estimates as many as one in three commercial buildings in the U.S. have poor indoor air quality (IAQ). Causes can include contaminated ductwork; improper filtration; airborne particulates; mold-producing water leaks; off-gassing of chemicals from carpets, vegetation and other bio-sources; and carbon dioxide (CO2) from human exhalation, to list but a few. Advances in instrumentation and technology help remedy these types of indoor air problems.
CO2 gained increased attention after research linked CO2 buildup in buildings to decreased worker productivity and occupant discomfort, fatigue and asthmatic symptoms. Combined with poorly operating ventilation systems, this produces Sick Building Syndrome.
CO2 monitors use infrared sensing optics and can be hardwired to standard junction boxes or other 4-20mA power sources for on-demand activation of the ventilation system. Sensors are housed in small plastic enclosures that blend with other building security system devices. Other models can be duct-mounted with powerful pumps to monitor incoming and returned airflow. These units enhance building comfort in a measurable way.
A “fixed” prescription
Fixed-install gas detectors capitalize on the latest developments in sensing technologies and interoperability with building management systems (BMS). New capabilities provide real-time information about gas concentration levels and other relevant data through PLCs (programmable logic controllers) in the control room or to a wireless mobile communications device. In critical life safety situations, the process can be totally automated.
Another option is to use gas sensors that provide an output suitable for direct interface to the BMS. In this case, the BMS can cut the gas supply, switch off any potential ignition sources and vent gas as needed.
Increasingly, new fixed-mount gas detector systems are being integrated into an indoor environmental quality (IEQ) system that also monitors heat, smoke, temperature, humidity, particulate filtration and other atmospheric variables. If any combination of these (within a zone) exceeds a pre-determined level, communication to the DDC (direct digital control) is instantaneous and the relays are triggered.
Hand-held portable gas leak detectors with infrared and electrochemical sensors provide diagnostic and troubleshooting features to supplement fixed instrumentation systems. A portable instrument with a PID (photoionization) sensor detects a broad range of volatile organic compounds (VOCs). Characteristically, VOCs evaporate at room temperature and may or may not be discernible to one’s sense of smell. Some VOCs may pose a combustible threat, and all can degrade IAQ.
Hand-held portable IAQ monitors are specifically designed to test IAQ conditions including temperature and humidity as well as the most common gas hazards found in buildings, usually carbon dioxide, carbon monoxide and natural gas.
1 Boiler rooms: Natural gas is one of the most widely used fuels for heating commercial and industrial property. An undetected leak can present an explosive risk.
Predominantly methane, natural gas is approximately half the weight of air and will rise toward the ceiling or roof space of a boiler room. Sensors should be located over potential leak areas, such as the gas burner assembly, gas train assembly, pressure boosters (if so fitted), gas shut-off valve, combustion air intake and gas meter. On a small gas boiler installation, a number of these points may be closer together, requiring a single point of detection.
Because most boiler rooms are visited infrequently, a leak may go undetected if gas sensors are not properly positioned. When positioning a sensor, consider mechanical ventilation and its likely effect on the path of leaking gas. Strategically placing gas detectors should be a collaborative effort involving an experienced gas detection system installer or engineer, facility manager and HVAC technician.
The prime objective for boiler room ventilation is to ensure an adequate supply of combustion air. For this reason, gas detection systems are widely used.
The process can help reduce the buildup of a flammable gas concentration; however, this cannot be guaranteed. Potential sources of ignition are many, and include any uncertified electrical equipment such as lighting, switches and control panels.
2 Mechanical equipment rooms with refrigerants: Leaks from CFC, HCFC and HFC refrigerants such as R-11, R-12, R-22, R-123 or R-134a can be expensive and potentially dangerous. Mechanical equipment rooms that use these refrigerants now require stationary sensors for permanent, continuous monitoring. Refrigerant leaks can come from mechanical wear of system components, vibration, bad soldering, corrosion, operational problems and more. To spot test leaks, the technician should use portable hand-held equipment with a wand attachment.
When boilers and chillers are located in the same room, a refrigerant detector is employed to automatically shut down the combustion process. Shutting down the refrigeration system at high concentration of refrigerant in the mechanical system is a good way to minimize refrigerant loss. But this can have a major impact on the HVAC system of the building. Analysis of the effects of such actions on the facility is a critical undertaking.
3 Confined spaces: More than half of all confined spaces are located below the surface level of a building. Electrical vaults, sewer channels and tanks are some examples of confined spaces. In these environments, common gases include methane, carbon monoxide and hydrogen sulfide. Oxygen deficiency can also pose a threat. A multi-gas portable monitor is advisable, with a PID sensor for detecting a range of VOCs.
4 Parking garages, offices and other areas: Vehicular exhaust products contain carbon monoxide and nitrogen dioxide. In parking garages, these can form gas clouds that migrate through HVAC ductwork to contaminate air inside the building envelope. Gas transmitters that use powerful internal pumps can be installed in ductwork to monitor air.
New technology uses mesh wireless communications to relay gas readings to a central controller connected to the DDC. Wireless systems require little conduit or electrical wiring, making it easy to retrofit a building or augment an existing hard-wire system. These wireless detectors are good at sniffing for toxic CO and NO2 in hard-to-reach areas. Wireless systems may become the preferred sensing network as battery life is extended; the industry is moving toward a 10-year “fit and forget” operating life.
Today’s tight building envelopes require fast, reliable sensors to detect toxic and combustible gas hazards and other airborne contaminants. A good IAQ strategy begins with the right tools of detection, followed by a well-executed plan of protection.