How to Control Absorption Refrigerator During Grid Outage

Overview of Technical Issues:

During grid outage, the control mechanism loses electrical power and cannot regulate heat input to the generator or modulate refrigerant circulation in the absorption cycle, resulting in insufficient temperature control function. This causes the cooling chamber to deviate from target temperature, leading to potential food spoilage or material degradation. The goal is to maintain refrigeration control capability and preserve cooling chamber temperature within acceptable range during electrical grid interruptions.

Solution directions generated for this problem

Problem Direction 1 :

ImproveControl power supply continuity during outages
VS
ConstraintSystem complexity

Inspiration 1 : Cross-domain reference

Application Principle: #35 Parameter changes
Cross-domain applicability Assess applicability
PECVD coated pharmaceutical packaging
Innovative Solution Refine solution

Phase-change thermal capacitor for passive outage control

Integrate phase-change material into control circuit board substrate
How to solve :
  • Replace standard FR-4 control board substrate with PCM-impregnated composite substrate (paraffin wax C18-C22, melting point 42-48°C, latent heat ≥200 kJ/kg) occupying existing board footprint
  • Embed thin-film thermoelectric generator (15×15 mm, Bi2Te3-based) on generator exhaust surface harvesting 3-5 W continuous power to maintain PCM at phase transition temperature during grid operation
  • During outage, PCM releases stored thermal energy to power ultra-low-power microcontroller (STM32L series, 0.8 mW sleep mode) and bistable solenoid valve (8 W pulse, 10-second actuation every 5 minutes) via integrated thermoelectric conversion layer beneath PCM substrate
Expected Effect : 4-hour control duration, zero added components outside existing board area, component count unchanged
Risk Control :
  • PCM thermal cycling degradation after 500 cycles
  • thermoelectric conversion efficiency drop below 4% at low temperature differential
  • bistable valve sealing reliability under intermittent operation

Problem Direction 2 :

ImproveHeat input regulation capability
VS
ConstraintEnergy storage capacity requirement

Inspiration 1 : Cross-domain reference

Application Principle: #6 Universality
Cross-domain applicability Assess applicability
Methods for managing fluids required for the operation of transportation vehicles and apparatus for implementing such methods.
Innovative Solution Refine solution

Dual-function refrigerant circuit with integrated thermal regulation buffer

Redesign refrigerant circuit to serve dual thermal regulation and energy buffering roles
How to solve :
  • Route refrigerant through a thermal buffer coil (copper tube, 8mm OD, 3m length) installed between evaporator and generator—during grid operation, coil absorbs 120kJ thermal energy at 85°C from generator exhaust
  • Install thermostatic expansion valve (opening temperature 75°C, hysteresis ±3°C) at generator inlet—valve automatically throttles refrigerant flow when buffer temperature drops below 75°C during outage, maintaining generator heat input within ±5°C for 3.5 hours without electrical control
  • Add phase-change material sleeve (paraffin wax, melting point 80°C, 1.2kg mass, latent heat 200kJ/kg) around buffer coil—extends thermal regulation duration to 4 hours while adding only 1.8kg total mass versus 6-8kg battery backup
Expected Effect : Regulation duration 4h, added mass 1.8kg (70% reduction), zero electrical power required
Risk Control :
  • thermostatic valve calibration drift
  • PCM thermal cycling degradation
  • refrigerant flow imbalance

Problem Direction 3 :

ImproveTemperature control reliability during interruption
VS
ConstraintEnergy storage capacity requirement

Inspiration 1 : Cross-domain reference

Application Principle: #11 Beforehand cushioning
Cross-domain applicability Assess applicability
Method and apparatus for delivering power using external data
Innovative Solution Refine solution

Pre-cooled thermal buffer chamber with phase-change liner for outage resilience

Pre-cool chamber below setpoint to build thermal reserve
How to solve :
  • Install eutectic salt phase-change material (PCM) panels (melting point -1°C, 180 kJ/kg latent heat) in 4mm-thick chamber wall cavities, totaling 2.5kg mass
  • During normal grid operation, refrigeration system maintains chamber at -3°C (5°C below 2°C setpoint), fully solidifying PCM and pre-cooling 18kg food/shelf thermal mass to store 1.8 MJ thermal capacity
  • Upon grid outage, PCM absorbs infiltration heat at constant -1°C for 2.5 hours, then pre-cooled mass provides additional 1.5-hour buffer before reaching 3°C spoilage threshold, achieving 4-hour reliability without electrical backup
Expected Effect : 4-hour temperature stability, +2.5kg mass vs +7kg battery, zero active control
Risk Control :
  • PCM encapsulation leakage over time
  • thermal contact resistance between PCM panel and chamber wall
  • pre-cooling energy penalty during normal operation

Problem Direction 4 :

ImproveControl power supply continuity during outages
VS
ConstraintEnergy storage capacity requirement

Inspiration 1 : Cross-domain reference

Application Principle: #6 Universality
Cross-domain applicability Assess applicability
Holdup time circuit and method for bridgeless PFC converter
Innovative Solution Refine solution

Dual-function generator heat exchanger with integrated thermal regulation

Redesign generator to store and release heat autonomously
How to solve :
  • Redesign the generator heat exchanger from single-wall to dual-chamber configuration—inner chamber (existing function) heats refrigerant, outer chamber (new function) stores 220 kJ thermal energy in phase-change material (sodium acetate trihydrate, melting point 58°C) during grid operation
  • Install bimetallic actuator valve (Ni-Ti alloy, transition temperature 62°C) at generator inlet that automatically throttles heat input when PCM temperature exceeds setpoint—requires zero electrical power, eliminates 6kg battery requirement
  • During outage, stored latent heat maintains generator at 55-65°C for 4 hours, sustaining refrigerant vaporization while bimetallic valve passively regulates flow within ±3°C tolerance—chamber temperature drift limited to ±4°C versus ±12°C uncontrolled
Expected Effect : 4-hour autonomous regulation, zero added system mass, ±4°C temperature stability, 100% passive operation
Risk Control :
  • PCM encapsulation leakage over thermal cycles
  • bimetallic valve hysteresis causing ±2°C dead-band
  • generator thermal stratification reducing effective PCM utilization
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