Introduction
Overview of heat pumps and their working mechanism.
Differences between heat pumps and general air conditioning or heating systems.
Basic Functioning
Heat pump = Reverse cycle air conditioning/refrigeration.
In air conditioning mode: Discharge gas from the compressor goes to the outdoor coil (condenser), then to the indoor coil (evaporator).
Heating Mode
Introduction of the four-way reversing valve.
Discharge gas routed to the indoor coil (now functions as a condenser).
Air Conditioning System Basics
Outdoor coil as a condenser.
Indoor coil as an evaporator.
Reversing valve changes gas routing for heating mode.
Reversing Valve Details
Four connections: discharge line, permanent discharge port, and two ports that change function.
O terminal or B terminal on the thermostat controls the reversing valve.
Modes Explained
Cooling Mode: Discharge gas to the outdoor coil.
Heating Mode: Discharge gas to the indoor coil.
Different geographical locations affect valve fail-safes (heat mode vs. cooling mode).
Metering Devices
Fixed bore metering devices (piston system).
Movable piston acts as a check valve.
Heating and cooling mode operations.
Thermostatic Expansion Valve (TXV)
Modulates flow based on load.
Requires check valves for bypassing refrigerant.
New TXVs have internal check valves.
Outdoor Unit Components
Four-way reversing valve, biflow filter dryer, and suction line accumulator.
Importance of biflow filter dryer in heat pump systems.
Defrost Cycle
Defrost needed for air-to-air heat pumps.
Switches refrigerant flow back to cooling mode temporarily.
Electric heaters run during defrost to avoid cooling the house.
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