Environmental sensing unit

#The present invention relates to environmental sensors for detecting characteristics of a fluid in a duct and, more particularly, to a duct mounted environmental sensing unit for detecting a plurality of parameters of a fluid in a duct of a heating, cooling and ventilation system.

#Temperature and humidity are primary factors in the comfort and quality of an indoor environment. While temperature is important to comfort, the humidity is a substantial factor in determining whether a specific temperature is comfortable. Temperature is commonly regulated as a function of the relative humidity in a space and humidifiers, to control the relative humidity, are often a part of the heating, cooling and ventilation systems of office buildings and industrial plants.

#Carbon dioxide (CO2) is a product of human respiration and, while high levels of carbon dioxide are toxic to humans, the concentration of carbon dioxide in an indoor environment is commonly used as a surrogate to indicate the presence of other indoor pollutants that may cause occupants to grow drowsy, have headaches, or function at a lower activity level. Since human respiration is a primary source of carbon dioxide in indoor environments, building codes typically specify the amount of outdoor air to be added to an interior space by the ventilation system on the basis of the occupancy of the space. In the past, ventilation systems commonly maintained a ventilation rate, at all times, that was sufficient for full occupancy of the space. However, heating, cooling, humidifying and moving this volume of air at times when the occupancy is low is wasteful of energy and expensive. Demand controlled ventilation seeks to vary the amount of outside air added to a space to optimize the comfort and well being of occupants and reduce energy consumption under conditions of variable and intermittent occupancy. Carbon dioxide concentration is used as an indicator of the occupancy and as a control parameter for demand controlled ventilation.

#FIG. 1 is a perspective view of a portion of a duct and a duct mounted sensing unit.

#FIG. 2 is a top view of an environmental sensing unit.

#FIG. 3 is an elevation view of the environmental sensing unit of FIG. 2.

#Building codes commonly specify ventilation requirements for indoor spaces on a per-person basis. In the past, sufficient ventilation was provided at all times to satisfy the per person requirements of a fully occupied space. However, building occupancy varies throughout a day and often varies from day-to-day and considerable energy is required to heat, cool, humidify and move the replacement air. Providing full occupancy ventilation, even on a periodically varying basis, can be very energy inefficient and expensive. Demand controlled ventilation seeks to optimize occupant comfort and well being and energy consumption under conditions of variable and intermittent occupancy by varying the amount of outside air added to the space in response to changes in the occupancy. The level of carbon dioxide (CO2) in the environment is an indicator of the presence of other pollutants that effect human performance and, since carbon dioxide is a product of human respiration, its concentration in the indoor environment is used by CO2 demand controlled ventilation systems as an indicator of the occupancy in establishing ventilation rates necessary to satisfy the per person ventilation requirements for a space with variable occupancy.

#In addition to supplying outside air to interior spaces, the air handling system typically heats, cools and modifies the humidity of the air circulating in a structure. Since comfort is a function of humidity as well as temperature, air handling systems commonly include sensors for both temperature and humidity.

#In some applications, the CO2 concentration, the humidity and the temperature are sensed with one or more sensing units mounted on the wall of the individual space(s) to be monitored. However, wall mounted sensing units are only exposed to the local conditions so at least one sensor for each parameter must be installed in each space to be monitored. The sensors are not inexpensive. In some applications, particularly where several spaces have the same or similar occupancy, or where the space is periodically remodeled and walls are moved, the cost of the ventilation system can be reduced by locating a sensing unit in the duct that carries the return air from the space(s). The present inventors realized that combining sensors for each of a plurality of environmental parameters, such as temperature, humidity and carbon dioxide concentration, in a single environmental sensing unit that could be installed at a single insertion point in a duct would substantially reduce the cost of installing and maintaining sensors for an air handling system.