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In HVAC control systems, actuators that control dampers and valves may be fail-safe, for example, to prevent coils from freezing or rooms from overheating. Older pneumatic actuators were inherently fail-safe because if the air pressure against the internal diaphragm failed, the built-in spring would push the actuator to its home position – of ...
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality .
An FMEDA can predict failure rates per defined failure modes. For Functional Safety applications the IEC 61508 failure modes (safe, dangerous, annunciation, and no effect) are used. These failure rate numbers can be converted into the alternative failure modes from the automotive functional safety standard, ISO 26262.
Failure Modes, effects, and Criticality Analysis is an excellent hazard analysis and risk assessment tool, but it suffers from other limitations. This alternative does not consider combined failures or typically include software and human interaction considerations. It also usually provides an optimistic estimate of reliability.
A fault tree diagram. Fault tree analysis (FTA) is a type of failure analysis in which an undesired state of a system is examined. This analysis method is mainly used in safety engineering and reliability engineering to understand how systems can fail, to identify the best ways to reduce risk and to determine (or get a feeling for) event rates of a safety accident or a particular system level ...
Analog outputs control the speed or position of a device, such as a variable frequency drive, an I-P (current to pneumatics) transducer, or a valve or damper actuator. An example is a hot water valve opening up 25% to maintain a setpoint. Another example is a variable frequency drive ramping up a motor slowly to avoid a hard start.
The U.S. Department of Housing and Urban Development halted its health and safety inspections of public housing for about two weeks because of a technical failure. U.S. halted safety inspections ...
HVAC (Heating, Ventilation and Air Conditioning) equipment needs a control system to regulate the operation of a heating and/or air conditioning system. [1] Usually a sensing device is used to compare the actual state (e.g. temperature) with a target state. Then the control system draws a conclusion what action has to be taken (e.g. start the ...