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Heat Recovery Ventilator (HRV) — Operating Principle

A recuperator (heat recovery unit) transfers heat from exhaust air to incoming fresh air without mixing the two streams.

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How It Works

Two airflows:

Exhaust air (warm, from indoors)

Supply air (cold, from outside)

They pass through a heat exchanger:

separated by plates or channels

no direct mixing

heat transfers through the material (conduction)

Result: → supply air is preheated
→ exhaust air is cooled
→ overall heat loss is reduced

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Types of Recuperators

1. Plate Heat Exchanger

aluminum or plastic plates

efficiency: ~60–90%

no moving parts

2. Rotary (Wheel) Heat Exchanger

rotating drum

transfers heat and some moisture

efficiency: up to ~85–90%

3. Counterflow Heat Exchanger

air streams move in opposite directions

highest efficiency: up to ~95%

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What Is Transferred

heat (primary)

sometimes moisture (in enthalpy units)

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Efficiency Example

outside: 0°C

indoor: +22°C

after recovery: ~16–20°C

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Advantages

reduced heating energy demand

continuous ventilation without major heat loss

improved indoor air quality

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Limitations

frost formation in winter (needs bypass or preheater)

filter maintenance required

upfront cost

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Core Idea

A recuperator doesn’t generate heat — it recovers and reuses it.