How Does a Heat Pump Dryer Work: 11 Step-By-Step Guide

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A dryer with a heat pump works thanks to a refrigeration system that recovers and reuses thermal energy. It consists of a compressor, condenser, evaporator, and expansion valve. 1) The warm air passes through the clothes and absorbs moisture; 2) the damp air passes over the cold evaporator coil where moisture condenses; 3) the refrigerant captures this heat, is compressed (which raises its temperature), then passes through the condenser it releases heat into the air; 4) this hot and dry air is redistributed on your laundry. It consumes less than half of the energy used by conventional dryers.

Fundamental: Closed Circuit Heat Pump System

Closed Circuit Heat Pump System

A heat pump dryer has a closed circuit that allows it to dry evenly at low temperatures. These are their main parts:

Evaporator

Cools down the air in your dryer so it can turn water from your clothes into drops.

Compressor

Pushes gas molecules together which makes them hotter.

Condenser

Turns hot vapor back into liquid and releases all its thermal energy.

Expansion Valve

Regulates how much pressure gets released before entering the evaporator again.

These four parts rotate through a loop, each time heating up colder surfaces so they remain dry while taking out humidity from your clothes to save power.

Step-by-Step Process

Heat Pump Dryer Working Steps
How Does a Heat Pump Dryer Work

Here’s what happens inside a washer-dryer combo when you press start:

1. Hot wet air taken from wet clothes goes inside an evaporator coil made of copper tubes with liquid coolant running through them.

2. The dryer spins the tub around as warm wet air goes past the tubes cooling off coolant until it turns into a gas state removing moisture too.

3. Cold dry air continues traveling toward another copper tube assembly called a condenser coil. This time filled with hot coolant gas and under high pressure.

4. In contact with tubes, cold air starts warming up again but energy from heat makes liquid coolant gas return to a normal state releasing even more heat.

5. The dryer sends the warmed-up dry air back inside the drum and it absorbs moisture from the clothes.

6. Water extracted is carried to evaporator coils by airflow where it forms droplets that are then drained.

7. To make coolant gas reach tubes again, the compressor intensifies its pressure forcing it to warm up even further using electrical energy and mechanical work.

8. Afterwards high-temperature vapor goes to condenser coils which release enough heat into the incoming air stream to start cooling down turning gas back into a liquid.

9. High pressures make liquid go through an expansion valve where most of this excess gets taken away so it can enter the evaporator safely at low pressures.

10. Finally, the low-pressure liquid coolant returns home to your wet clothes’ molecular party cooling them off while generating heat for evaporation in future cycles.

This way you get warm clothes while protecting them from damage caused by higher temperatures needed in traditional models.

Key Components of Heat Pump Dryer

The main parts of a heat pump system that allow it to save so much energy are:

The evaporator is a heat exchanger. Its job is to remove heat from the air inside the drum and convert water from a vapor phase to a liquid phase. In layman’s terms, it makes hot air cold and wet air dry. Here’s how:

  1. As you fill your dryer with wet clothes, it pumps in warm, humid air that passes over the evaporator coil, which rapidly lowers its temperature.
  2. This causes water vapor in the air to condense into water droplets.
  3. After this process finishes, cool dry air returns to the drum for another round of drying clothes.
How Does a Heat Pump Dryer Work

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Technical details

  • Copper tubing bent into coils 
  • Aluminum fins increase surface area 
  • Refrigerant flows through coils absorbing heat from the surrounding air 
  • Fins provide up to 10 square meters of additional surface area
  • Airflow across tubing and fins facilitated by a rotating drum with holes and baffles
  • Air-cooled by up to 13°C as it passes through the evaporator

Compressor 

What’s its role?

The compressor pressurizes refrigerant gas. It then pumps refrigerant through the sealed system so that it can do its cooling magic elsewhere.

The technical stuff  

  • Hermetically sealed pump driven by voltage supplied by an induction motor
  • Most models use high-efficiency brushless DC rotary compressor
  • Oil lubrication is required for moving parts 
  • Compresses refrigerant from 0.15 – 0.31 MPa to 1.72 – 2.1 MPa
  • Displacement ranges from 6 – 8 cm3 per revolution depending on the load

Condenser

What’s its role?  

This part removes heat from pressurized gas refrigerant coming from the compressor and condenses it into a liquid so that we can repeat this cool cycle later.

The technical stuff  

  • Coil shape with extended copper tubes and aluminum fins 
  • Provides 15 – 25 square meters of heat transfer surface area
  • Refrigerant enters as a hot gas between 60°C – 90°C
  • Ambient air cools gas to liquid between 40°C – 50°C 
  • Overall heat transfer rate between 750 and 1,200 watts

Expansion Valve

What’s its role?  

It rapidly reduces refrigerant pressure. This allows rapid evaporation in the evaporator (that I mentioned earlier) and begins absorbing heat that will continue its cooling cycle.

The technical stuff 

  • Fixed orifice metering device
  • The most common is the thermostatic expansion type
  • Reduces pressure from approx 2MPa liquid to 0.15MPa mix 
  • Creates a pressure differential that begins refrigerant evaporation 
  • Located away from the evaporator to ensure a liquid state

Heat pump dryers benefits:

Heat pump dryers provide substantial efficiency and cost benefits over conventional dryers:

  • 50-60% reduction in electricity consumption compared to conventional electric resistance heating, translating to 100-200kWh in annual savings for the average household
  • Drying times are shortened by 20-50% through precise control of the drying chamber temperature and airflow rate optimization. Temperatures are maintained between 30-60°C via a variable speed compressor and electronic expansion valve.
  • Lower drying temperatures between 30-60°C (vs 90°C+ for conventional dryers) enabled by the heat pump cycle are gentler on fabrics and reduce wrinkling and shrinkage.
  • Estimated $250+ in lifetime energy cost savings given current electricity prices and a 10-year operating lifespan. Savings could be greater if the lifespan exceeds 10 years.

Additionally, heat pump dryers have a longer lifespan of up to 20 years thanks to less wear on components from lower operating temperatures.

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