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What is the heat exchanger for the air handling unit?

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The heat exchanger inside an air handling unit (AHU) is a component that transfers heat between two airflows — typically between the incoming fresh air and the outgoing exhaust air — without mixing them directly.

Its main purposes are:

  • Energy recovery: save heating or cooling energy by preheating or precooling incoming fresh air.

  • Improve efficiency: reduce the load on the building’s heating or cooling system.

  • Enhance indoor air quality: by maintaining ventilation without wasting energy.

There are different types of heat exchangers used in AHUs:

  • Plate heat exchanger (fixed plate): Air flows across thin metal plates, transferring heat through the plate without mixing.

  • Rotary heat exchanger (thermal wheel): A rotating wheel picks up heat from one air stream and transfers it to the other.

  • Run-around coil: Uses a liquid (usually glycol water) circulating between two finned-tube coils to transfer heat between separate airstreams.

  • Heat pipe: A sealed pipe with refrigerant inside moves heat from the warm side to the cool side passively.

air to air heat pump how does it work

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An air-to-air heat pump works by transferring heat between the outside air and the inside air to either heat or cool a building. Here's a simple breakdown:

  1. Heating Mode (winter):

    • Even when it's cold outside, there is still some heat energy in the air.

    • The heat pump extracts that heat using a refrigerant that evaporates at low temperatures.

    • The refrigerant absorbs heat from the outside air, becomes a gas, and is compressed, which raises its temperature even more.

    • This hot refrigerant gas moves inside and releases its heat into the indoor air through a heat exchanger (basically like a radiator).

    • After releasing the heat, the refrigerant cools down, turns back into a liquid, and the cycle repeats.

  2. Cooling Mode (summer):

    • The cycle is reversed.

    • The heat pump extracts heat from inside the building and releases it to the outside.

    • This cools down the indoor air, working like an air conditioner.

Main parts of an air-to-air heat pump:

  • Outdoor unit: captures or dumps heat to the outside air.

  • Indoor unit: releases or captures heat inside the house.

  • Compressor: increases the pressure and temperature of the refrigerant.

  • Expansion valve: lowers the pressure of the refrigerant so it can absorb heat again.