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The role of sensors in stable HVAC systems: Heavy duty pressure transducers

Mon, 07/15/2013 - 9:05am
Ketan Mehta, Honeywell

The right sensors help create more stable HVAC systems

Whether it’s a high-rise office tower or a manufacturing floor, Heating, Ventilation and Air Conditioning (HVAC) systems are designed for building occupants’ comfort. When systems operate at optimum levels, they’re energy efficient and go unnoticed. When they’re not, efficiency drops and complaints rise.

Each component system (heating, ventilation and air conditioning) comprising the overall HVAC system uses pressure sensors: board mount pressure sensors in air-handling systems, high pressure air flow sensors in Variable Air-Flow Volume Systems (VAV), and heavy-duty pressure transducers in the compressors, coolers, furnaces and boilers. It’s important to look more closely at each of these sensors and their role within HVAC systems as each have different differs functions from one another.

When specifying sensors, consider quality, accuracy, consistency, ease of installation and replacement, and interoperability. High performing sensors help reduce the design costs, development and testing cycle time. They’ll also require less frequent calibration and replacement.

A sensor’s quality is indicated by the Total Error Band (TEB) – one number that quantifies all possible errors, from the offset, to the full scale span, and pressure and thermal factors. The lower the TEB, the more accurate the sensor and the less testing and calibration it needs. If sensors are also made to Six Sigma and ISO9001 standards, they will provide the highest level of product quality, performance and consistency.

Because each type of sensor performs distinct functions in an HVAC system, we’ll look at each individually, starting with heavy duty pressure transducers used in the heating and cooling source units. In a follow-up article, we’ll look more closely at the role of board mount pressure sensors and high pressure air flow sensors.

Heavy duty pressure transducers
Higher pressure applications within HVAC systems – rooftop cooling towers, boilers, pumps and chillers – require pressure transducers that are durable, CE compliant, designed for IP69K sealing protection, and able to withstand wide temperature ranges and contact with harsh media (e.g., refrigerants, driving rains, hydraulic fluids and compressed air up to 1000 psi). With stainless steel housing and ports, these transducers can minimize moisture infiltration and shorts at the sensor location, and in turn, downtime and replacement costs.

Heavy duty pressure transducers provide two measurements:
1. The amount of pressurized air being delivered to the application
2. The presence of air pressure leaks
These measurements come from continuously monitoring the pressure of the compressor outlet, chiller outlet, evaporator coil outlet and the cooling tower supply, ultimately providing data to regulate the flow of heating/cooling media during partial load conditions.

Because these transducers are used in a variety of applications, choosing parts configurable to your specifications is important. Honeywell’s PX2 Series, for example, has connectors, ports, pressure types/ranges and output options totaling more than 5,000 different configurations. This helps accommodate custom-designed applications while containing design and implementation costs. The PX2 Series has a TEB of ±2% and, like all Honeywell sensors, controls and thermostats, is designed to Six Sigma and ISO9001 standards.

From the source units, the cooled or heated air or water is dispersed through the ventilation system, where additional sensors are used. The role of board mount pressure sensors and high pressure air flow sensors will be examined in a subsequent article.

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