Recently, there has been an increase in the societal awareness of the impacts of degraded indoor environmental quality factors, including but not limited to internal air quality and consumable water quality. Smog clouds and pollution that affect quality of life and endanger health have prompted increased governmental regulation on emitters of pollution such as power plants. International agreement has been reached that particulates and gaseous emissions pose a serious threat to humans. At a local and individual level, some large cities have implemented restrictions on driving and burning during periods in which particulate matter or smog reach dangerous levels. In many cities where particulate matter reaches particularly high levels, the use of personal disposable respirators is common.
Water quality likewise can be affected by polluters including but not limited to industry, farming, residential wastewater, and storm drain runoff. The effects of polluted water and air can include higher risk of premature death among the elderly, birth complications, increases in respiratory disorders or onset of asthma attacks, and other diseases or adverse health effects.
Against this backdrop, many homes, offices, and other buildings seek to improve the quality of their internal environmental factors such as air and water. Even in areas that do not suffer from high pollution levels, indoor air quality can be improved by removing irritants such as pollen or pet dander. The primary mechanism for removing these irritants is the use of ducted, recirculating Heating Ventilation and Air Conditioning (HVAC) systems.
HVAC is the technology of indoor and vehicular environmental comfort. Its historic goal is to provide thermal comfort and acceptable indoor air quality. HVAC is an important part of residential structures such as single-family homes, apartment buildings, hotels and senior living facilities, medium to large industrial and office buildings such as skyscrapers and hospitals, on ships and submarines, and in automotive and marine environments, where safe and healthy air conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.
Ventilating or ventilation (the V in HVAC) is the process of conditioning, exchanging or replacing air in a space to provide high indoor air quality. Ventilation facilitates temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases and particulates. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air. Ventilation includes both the exchange of air to the outside as well as circulation and conditioning of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings.
HVAC systems typically include a ducted plenum for providing air that has been treated to a premises. The HVAC system also includes a return air flow, which can be a second ducted plenum that receives air from the premises. The air received via the return plenum is often heated or cooled after passing through a filter. Conventional filters for HVAC systems (herein “furnace filters”) are sized to fit within the duct corresponding to the return air plenum. Such filters collect particulates and are typically replaced periodically during operation of the HVAC system.
While limited attempts have been made to monitor specific aspects of air quality within an HVAC system (e.g., humidity monitoring, etc.) various technical, economic, and societal factors have historically provided obstacles to expansion of such monitoring to include other air quality factors. Systems developed to date have typically taken the form of hand-held air quality instruments, which are used by HVAC professionals to point-check (i.e., instantaneous, rather than continuous, monitoring) for a specific air quality factors (e.g., carbon monoxide). Other conventional systems include stand-alone air quality monitors, which can be placed in one location of a multi-room structure. An example of a stand-alone device is a smoke detector.
The systems described above are limited in that they take measurements at a precise location within the structure. Therefore, for critical detection (such as smoke alarms and carbon monoxide detection) multiple sensors are used throughout a premises. Furthermore, the systems described above are not designed for continuous, extended operation without power, either by direct wiring or frequent replacement of batteries. The systems described above are difficult to effectively implement throughout a complete multi-room structure and often require redundant sensors or expensive modifications to the HVAC system.
Another type of conventional device is an add-on to an HVAC system, which typically requires some mechanical modification of the system. For example, a humidity subsystem can be attached to operate in conjunction with an HVAC system. These systems are typically wired separately for power and sensing. In the example of a humidity subsystem, a humidifier and a set of sensors can be attached to the ducting of an existing HVAC system. The sensors can include, for example, a humidity sensor and a pressure sensor or airflow sensor. In operation, the sensors detect operation of the HVAC system and the need for additional moisture, and are powered to add humidity to the airstream as needed.