Chiller suction flow limiting with input power or motor current control

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Solution Overview

Problem

In refrigeration systems, the carryover of liquid droplets from the evaporator to the compressor due to increased suction flow rate can decrease efficiency and damage mechanical components, particularly when the compressor operates under conditions that lower the differential pressure, making it essential to manage compressor operation to prevent liquid droplet flow.

Innovation Solution

Implementing a chiller suction flow limiting system with input power or motor current control, using a controller that predicts energy levels and modifies power or current to the compressor prime mover to prevent liquid droplet flow by comparing predicted and actual energy levels, thus ensuring operation within design velocity limits.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the compressor operates under conditions that lower the differential pressure, then the compressor capacity and suction flow rate increase, but liquid droplets are carried over from the evaporator to the compressor

Engineering Contradiction:
Improvecompressor capacityVSAvoidliquid droplet carryover
Core Design Contradiction:
ProductivityVSObject-affected harmful factors

Solution Approach 1:

The controller predicts the energy level of operation before liquid droplet carryover occurs by monitoring evaporator and condenser pressures. When the predicted energy level indicates conditions that would cause carryover, the controller proactively limits the input power or current to the compressor prime mover, preventing the harmful effect before it occurs.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The system continuously monitors the actual energy level of the compressor by measuring evaporator and condenser pressures, compares it to the predicted energy level, and uses this feedback to dynamically adjust and limit the input power or current to the prime mover, maintaining operation within safe parameters.

Inventive Principle:
Principle #23Feedback

2Productivity

If the suction flow rate is increased, then the compressor capacity improves, but the velocity in the evaporator increases causing liquid droplets to be pulled into the compressor

Engineering Contradiction:
Improvecompressor capacityVSAvoidevaporator gas velocity
Core Design Contradiction:
ProductivityVSSpeed

Solution Approach 1:

The controller changes the operating parameters of the compressor by limiting the input power or current to the prime mover when the predicted energy level indicates that evaporator gas velocity would exceed the design limit, thereby preventing liquid droplet carryover while allowing maximum safe capacity operation.

Inventive Principle:
Principle #35Parameter changes

3Productivity

If the compressor operates at higher capacity, then productivity increases, but chiller efficiency decreases due to liquid droplet flow

Engineering Contradiction:
Improvecompressor capacityVSAvoidchiller efficiency
Core Design Contradiction:
ProductivityVSLoss of energy

Solution Approach 1:

By predicting the energy level and proactively limiting compressor operation before liquid droplet carryover occurs, the system prevents efficiency losses while maintaining maximum safe capacity, thereby avoiding the trade-off between productivity and energy efficiency.

Inventive Principle:
Principle #10Preliminary action

4Productivity

If the differential pressure across the compressor is lowered, then compressor capacity increases, but mechanical components are damaged due to liquid droplet flow

Engineering Contradiction:
Improvecompressor capacityVSAvoidcompressor component integrity
Core Design Contradiction:
ProductivityVSReliability

Solution Approach 1:

The controller predicts and prevents liquid droplet carryover conditions before they occur by limiting the input power or current to the prime mover, thereby protecting mechanical components from damage while allowing the compressor to operate at maximum safe capacity.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The system prepares for potential liquid droplet carryover by continuously monitoring predicted energy levels and preemptively limiting compressor operation to prevent harmful effects, cushioning against potential damage before it occurs.

Inventive Principle:
Principle #11Beforehand cushioning (Prior cushioning)

Data Source

PatentEP3803234B1Chiller suction flow limiting with input power or motor current control
Publication Date: 2023.08.23 JOHNSON CONTROLS TYCO IP HLDG LLP

AI summary

A chiller (22) includes an evaporator (46), a compressor (48) including a prime mover (84), a first pressure sensor (86) that detects a first pressure in the evaporator (46), a second pressure sensor (88) that detects a second pressure in a condenser (50), and a controller (100). The controller (100) determines a predicted energy level of the compressor (48) based on the first pressure and the second pressure, the predicted energy level associated with liquid droplet flow into the compressor (48), compares the predicted energy level to an operating energy level, and modifies the at least one of the input power and the input current to the prime mover (84) based on the comparison satisfying a modification condition.