Duct-mountable sensing unit

#The present invention relates to a sensing unit mountable on a wall of a duct for detecting a plurality of parameters of a fluid in the duct.

#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.

#Relative humidity may be sensed by a sensor that comprises a polymer that is typically mounted on a porous ceramic plate and has a resistivity that changes as a function of the humidity. This type sensor is usually not sufficiently accurate for use with a ventilation system and is subject to deterioration in harsh environments.

#FIG. 1A is a perspective view of a portion of a duct and a duct mounted sensing unit arranged to sense a pressure of a fluid in the duct.

#FIG. 1B is a perspective view of a portion of a duct and a duct mounted sensing unit arranged to sense a pressure differential between two points in a duct.

#FIG. 2 is a top view of a duct-mountable sensing unit.

#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 commonly 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 a space. Since carbon dioxide (CO2) is a product of human respiration and its presence in an indoor space is often relatable to the presence of other pollutants that effect human performance, CO2 concentration is commonly used by demand-controlled ventilation systems as an indicator of the occupancy in establishing the amount of outside air that is required to satisfy the per-person ventilation requirements of building codes.

#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, the sensors are not inexpensive and, since wall mounted sensing units are only exposed to the local conditions, at least one sensor for each parameter must be installed in each space to be monitored. 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).