Evaporator Fan Speed Control for Container Pull-Down Cooling

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Solution Overview

Problem

Traditional refrigeration systems in cargo containers consume excessive energy during the pull-down phase to rapidly lower the temperature of sensitive cargo, leading to inefficiencies and increased energy dissipation as heat within the container.

Innovation Solution

Operating the evaporator fan at a reduced speed initially and increasing its speed when the supply air temperature approaches the set-point temperature, while maintaining constant compressor power, to optimize air flow and reduce energy consumption while maintaining the desired temperature.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If the evaporator fan is operated at high speed to circulate refrigerated supply air rapidly, then the pull-down period is shortened, but energy consumption increases significantly

Engineering Contradiction:

Improvepull-down periodVSAvoidenergy consumption

Core Design Contradiction:

Loss of timeVSUse of energy by moving object

Solution Approach 1:

The evaporator fan operates in periodic cycles, alternating between high-speed operation during initial pull-down and low-speed or idle operation during maintenance phases. This periodic action allows the system to achieve rapid temperature reduction when needed while conserving energy during stable operation periods.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The evaporator fan speed is dynamically adjusted based on real-time temperature conditions. The system transitions from static high-speed operation to dynamic control, increasing fan speed when temperature deviation occurs and reducing it when the set-point is maintained, thereby optimizing the balance between pull-down speed and energy consumption.

Inventive Principle:

Principle #15Dynamics

2Productivity

If the evaporator fan operates at high speed to maximize refrigeration effect, then the cargo temperature reaches set-point faster, but energy dissipated as heat in the container increases

Engineering Contradiction:

Improverefrigeration effectVSAvoidenergy dissipated as heat

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The evaporator fan operates at high speed only partially during the pull-down process, specifically during the initial phase when rapid temperature reduction is critical. Once the set-point temperature is approached, the fan speed is reduced, avoiding excessive energy dissipation while maintaining sufficient refrigeration effect to complete the cooling process.

Inventive Principle:

Principle #16Partial or excessive action

3Use of energy by moving object

If the evaporator fan speed is reduced to save energy, then energy consumption decreases, but the pull-down period extends

Engineering Contradiction:

Improveenergy consumptionVSAvoidpull-down period

Core Design Contradiction:

Use of energy by moving objectVSLoss of time

Solution Approach 1:

The evaporator fan operates at high speed in the preliminary phase of pull-down to rapidly reduce cargo temperature toward the set-point. This preliminary high-speed action establishes a temperature trajectory that allows subsequent transition to low-speed operation, thereby achieving both rapid initial cooling and energy conservation during the maintenance phase.

Inventive Principle:

Principle #10Preliminary action

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 reduces energy consumption, shortens the pull-down period, and maintains the cargo temperature at the set-point, thereby enhancing the refrigeration system's efficiency without degrading its performance.

Implementation Method 1

The extracted return air is blown past the evaporator to refrigerate the air, and the refrigerated supply air is blown as into the container where it circulates and exchanges heat with the cargo and/or with the walls of the container

Methodology Applied

Scientific EffectForced Convection: Forced Convection

Implementation Method 2

The extracted return air is blown past the evaporator to refrigerate the air

Methodology Applied

Scientific EffectHeat Exchanger: Heat Exchanger

Implementation Method 3

One commonly used refrigeration technique is the vapor-compression cycle. The vapor-compression cycle is used in most household refrigerators as well as in many large commercial and industrial refrigeration systems.

Methodology Applied

Scientific EffectVapor-compression cycle:

Data Source

PatentUS8538585B2Control of pull-down in refrigeration systems

Publication Date: 2013.09.17 JOHNSON CONTROLS TYCO IP HLDG LLP

AI summary

A method for operating a refrigeration system for a container to pull down the temperature of cargo from ambient to a predetermined set-point temperature, and a system employing the method. The method includes operating a compressor at a first power to compress a refrigerant and direct the refrigerant through a condenser and an evaporator of the refrigeration system, initially operating an evaporator fan at a first speed to supply refrigerated supply air from the evaporator to the cargo within the container, sensing the temperature of the supply air, comparing the temperature of the supply air with a predetermined set-point temperature, and increasing the speed of the evaporator fan to a second speed faster than the first when the temperature of the supply air is lower than the predetermined set-point temperature to maintain the temperature of the supply air at the predetermined set-point temperature.