Control Voltage Sensing for HVAC Compressor Brownout Shutdown
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Solution Overview
Problem
HVAC compressors are vulnerable to stalling and thermal damage during brownouts, leading to prolonged protection device activation times and potential power outages due to reduced line voltage, which can cause widespread power issues when multiple compressors restart simultaneously.
Innovation Solution
A system and method that include a controller monitoring control voltage derived from line voltage, initiating a time delay if the voltage drops below a threshold, and deactivating the compressor if the voltage does not recover within a predetermined duration, with the option to impose a random time delay before reactivation to manage power demand and prevent simultaneous restarts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection device is used to deactivate the compressor during brownouts, then the compressor is protected from thermal damage, but the protection device takes three to five times longer to trip the compressor at reduced line voltages, making it unable to prevent thermal damage
Solution Approach 1:
The patent introduces an intermediary control system that monitors line voltage and compressor current, and actively controls the contactor to disconnect power. This intermediary system bridges the gap between the slow-responding thermal protection device and the need for rapid response, enabling timely compressor shutdown during brownouts before thermal damage occurs.
Solution Approach 2:
The system continuously monitors line voltage and compressor current, using this feedback to dynamically control the contactor. When voltage drops below a threshold or current exceeds a threshold for a predetermined time, the feedback mechanism triggers immediate contactor disconnection, overriding the slow thermal protection response and enabling rapid compressor shutdown.
2Productivity
If multiple compressors return online simultaneously after brownouts or blackouts, then the compressors restore cooling capacity, but they draw substantial current that reduces line voltage and causes widespread power outages
Solution Approach 1:
The patent implements periodic action by introducing random time delays for contactor reclosure after brownouts or blackouts. Instead of all compressors restarting simultaneously, each compressor waits for a randomized period before attempting to reconnect to power. This spreads out the inrush current demand over time, preventing the substantial current draw that would otherwise cause line voltage reduction and widespread power outages.
3Ease of operation
If the contactor is controlled to disconnect power during brownouts, then compressor operation is prevented, but the system requires monitoring control voltage derived from line voltage to detect brownout conditions
Solution Approach 1:
The patent applies universality by using the control voltage transformer and control circuitry that already exist for normal compressor operation to also detect brownout conditions. The same transformer that provides control voltage for the contactor and other control devices serves dual purposes: it powers the control system during normal operation and enables brownout detection when its output voltage drops. This eliminates the need for separate monitoring hardware.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively protects HVAC compressors from thermal overload during brownouts, reduces the risk of power outages by managing compressor restarts, and stabilizes line voltage, thereby preventing widespread power failures.
Implementation Method 1
a transformer that is operable to convert line voltage to control voltage used to selectively energize at least one switching element
Data Source
AI summary
A method is provided for controlling operation of an air conditioning unit. The method comprises supplying line voltage to activate a motor configured to operate the air conditioning unit, and monitoring a supply of control voltage in order to control operation of the air conditioning unit, the supply of control voltage being derived from line voltage. In response to detecting a control voltage below a predetermined threshold and/or by a predetermined percentage, a time delay is initiated. The method further comprises deactivating the motor if a predetermined increase in control voltage is not detected before the time delay expires.