Centrifugal Chiller Compressor Control for Extended Free Cooling

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Solution Overview

Problem

Chilled liquid systems using centrifugal compressors often fail to operate efficiently due to limited environmental conditions that allow for energy savings, as they typically shut down the compressor during free cooling conditions, resulting in reduced cooling capacity and energy inefficiencies.

Innovation Solution

A method of continuously operating the compressor in various temperature ranges by comparing the temperature of the liquid entering the condenser with the temperature of the liquid exiting the evaporator, using a variable speed drive to control the compressor's rotational speed, and maintaining a refrigerant loop with magnetic bearings, allowing the compressor to operate across a broader range of temperatures and pressures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the compressor is shut down during free cooling conditions, then energy savings are achieved, but the range of environmental conditions is limited

Engineering Contradiction:

Improveenergy savingsVSAvoidrange of environmental conditions

Core Design Contradiction:

Loss of energyVSAdaptability or versatility

Solution Approach 1:

The system dynamically adjusts compressor operation based on real-time comparison of condenser water temperature and evaporator water temperature. The control method continuously monitors temperature differentials and adjusts compressor status accordingly, enabling the system to adapt to varying environmental conditions and expand the range of free cooling opportunities beyond traditional static operating thresholds.

Inventive Principle:

Principle #15Dynamics

2Productivity

If the compressor is continuously operated, then chiller load capacity is increased, but energy consumption increases

Engineering Contradiction:

Improvechiller load capacityVSAvoidcompressor energy consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The invention changes the operational parameters by continuously comparing condenser water temperature with evaporator water temperature and adjusting compressor operation based on the temperature differential. This parameter-based control allows the system to maintain higher load capacity while consuming less energy by operating the compressor only when thermodynamic conditions are favorable, rather than using fixed shutdown thresholds.

Inventive Principle:

Principle #35Parameter changes

3Loss of energy

If the compressor is shut down to achieve energy savings, then cooling capacity is reduced, but system simplicity is maintained

Engineering Contradiction:

Improveenergy savingsVSAvoidcooling capacity

Core Design Contradiction:

Loss of energyVSPower

Solution Approach 1:

The control method implements a feedback mechanism that continuously monitors both condenser water temperature and evaporator water temperature, comparing these parameters to determine optimal compressor operation. This feedback loop ensures that the compressor is operated only when the temperature differential indicates favorable free cooling conditions, thereby maintaining cooling capacity while achieving energy savings without requiring complex additional hardware.

Inventive Principle:

Principle #23Feedback

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 approach significantly increases the range of environmental conditions for energy savings, enhances chiller load capacity, and minimizes energy costs by maintaining efficient operation across different temperature conditions, providing nearly twice the design cooling capacity compared to conventional systems during free cooling conditions.

Implementation Method 1

Low-temperature condenser water condenses refrigerant

Methodology Applied

Scientific EffectCondensation: Condensation

Implementation Method 2

condenser for thermal communication with refrigerant in the condenser

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 3

Higher-temperature chilled water causes the refrigerant to evaporate

Methodology Applied

Scientific EffectEvaporation: Evaporation

Implementation Method 4

evaporator for thermal communication with refrigerant in the evaporator

Methodology Applied

Scientific EffectHeat transfer: Conduction (thermal)

Implementation Method 5

compressor utilizing magnetic bearings

Methodology Applied

Scientific EffectMagnetic levitation: Maglev

Data Source

PatentUS11441828B2Method for operating a chiller

Publication Date: 2022.09.13 JOHNSON CONTROLS TYCO IP HLDG LLP

AI summary

A method of operating a chiller having a closed refrigerant loop including a compressor, a condenser and an evaporator. The refrigerant used in the loop defining a pressure-enthalpy curve representative of different phases (vapor, liquid and vapor, and liquid) of the refrigerant at different combinations of pressure and enthalpy. The loop defining a process cycle (compression, condensation, expansion, and evaporation) of the refrigerant during operation of the loop relative to the pressure-enthalpy curve of the refrigerant. The method including continuously operating the compressor when a segment of the process cycle corresponds to the refrigerant being in the liquid phase.