Heat rejection equals removed heat plus work, and COP depends on the useful transfer.
Figures 4.6–4.7 and equations 4.3–4.4 support the energy ledger.
OpenStax · Refrigerators and heat pumpsCooling has a warm side.: sources & model
Look through a cold room and follow its refrigerant loop. Count the heat removed and the work added, then try putting both sides in the same room.
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refrigeration-1 · content 1 · setup format 1What supports the explanation?
Cold rooms use a refrigerant circuit linking evaporator and condensing equipment.
Manufacturer system architecture reference, not a universal household-fridge diagram.
Danfoss · Cold-room systemsA thermostatic expansion valve regulates evaporator superheat through a sensing mechanism.
Manufacturer dry-expansion explanation. No quantitative valve model is claimed.
Danfoss · Expansion valvesWhat this model assumes
- One qualitative commercial cold-room vapor-compression architecture. It does not claim that every household fridge uses this valve or layout.
- COP is an imposed accounting assumption. No refrigerant properties, operating pressures, temperature solver, refrigerant mass flow, defrost or controller simulation.
- Changing the useful-output viewpoint changes accounting only. It does not reverse the physical circuit or simulate a reversing valve.
- Count energy across a boundary: For one accounting batch, Q_hot=Q_cold+W. The default removes 200 J, adds 100 J of work and delivers 300 J to the warm side. These are chosen example transfers, not a measured appliance cycle.
- COP is not a percentage efficiency: Cooling coefficient of performance is Q_cold/W. Heating COP is Q_hot/W, so it is one greater for the same budget. A COP above one is possible because heat is moved as well as work supplied.
- An open fridge is no room cooler: If both heat exchangers interact with the same isolated room, the removed heat returns to that room along with work input. The net gain is W. A real controller changes its behavior with the door open; this accounting comparison predicts no time or temperature curve.
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About the cover illustration
The topic card uses an AI-generated editorial illustration. It introduces the subject; it is not a validated anatomical reference or a measured landscape. The experiment’s diagrams, readouts and assumptions explain the model separately.
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