Hybrid Refrigerator Using Outdoor Air

Capstone concept: exploit Canadian winter for “free cooling”, and reject heat outdoors in summer to avoid heating the home.

The condenser–compressor is isolated in a sealed compartment and selectively vented outdoors, improving heat rejection in winter and preventing indoor heat gain in summer.

Scope Thermo modeling , HVAC ducting, Controls concept, CAD integration • Context Capstone project (uOttawa) • Year 2025
Hybrid refrigerator concept — outdoor air integration
Cabinet overview and dimensions
Vapor-compression refrigeration cycle (compressor, condenser, expansion, evaporator)
Air ducting system — intake/exhaust, motorized damper, hood vent
Insulated condenser box and airflow path
Control module concept (LCD, sensor, PCB)

1/7 — Outdoor-air hybrid concept

/ Challenge

Reduce the fridge’s energy consumption while preventing indoor heat gain and keep the system autonomous, safe, and easy to install/remove.

/ Solution

Create an insulated condenser compartment connected to outdoors by two short insulated ducts (intake/exhaust), use a motorized damper + temperature/humidity logic to switch between winter “free cooling” and summer operation, and model the full loads + vapor-compression cycle with R600a.

/ Results

Quantified a full cooling load model (Q̇load ≈ 335 W) and demonstrated a dramatic winter-side performance lift (modeled COPwinter ≈ 229 vs COPsummer ≈ 4.08) driven by improved condenser heat rejection using outdoor air.

> Workflow: model-driven concept + practical install constraints

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  1. Mandate
    Reduce energy + indoor heat
  2. Requirements
    ≤ 4°C • safe • removable
  3. Loads
    Walls • infiltration • product
  4. Cycle
    R600a • COP • ṁ
  5. Air system
    Ducts • dampers • fan
  6. Controls
    Sensors • mode switching
  7. Integration
    Service access • robustness

Cooling load model

Q̇wall = U·A·ΔTInfiltration (ASHRAE method)Hot product load scenarioWorst-case summer assumptions

Vapor-compression cycle

R600a selection (low GWP)ηis compressor = 85%ṁ from Q̇L and enthalpiesCOP = Q̇L / Ẇcomp

Air + ducting system

Short insulated ducts (intake/exhaust)Motorized louvered damperBackdraft protection + hood ventSingle fan, controlled pressure

Autonomous operation

Outdoor temperature sensingHumidity / frost-prevention logicMode switching (winter vs summer)Service access + reliability
MANDATE
Use outdoor conditions to reduce compressor workload (winter) and reject heat outdoors (summer) to avoid heating the home.
REQUIREMENTS
Maintain ≤ 4°C • cost-effective • durable/corrosion-resistant • easy install/remove • reliable user-independent control.
REFERENCE FRIDGE
French-door scale: W ≈ 0.91 m · D ≈ 0.86 m · H ≈ 1.78 m
COOLING LOAD
Q̇load ≈ 335 W (walls + infiltration + product load)
REFRIGERANT
R600a (low-GWP), domestic-scale compatible
MODELED COP
COPsummer ≈ 4.084 · COPwinter ≈ 229 (free-cooling effect)
COMPRESSOR WORK
Ẇcomp,summer ≈ 82.1 W · Ẇcomp,winter ≈ 1.5 W
AIR SYSTEM
Insulated condenser box + two short insulated ducts (intake/exhaust), motorized dampers, hood vent + backdraft protection.