Abstract
Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.
Abstract
Efficient energy recovery from used air with the goal of reducing energy use is important for realizing low energy houses. Rotary heat exchangers are very energy efficient, but have the drawback of transferring odours from exhaust air to fresh supply air. To avoid this, flat plate heat exchangers are commonly used where odour transfer might cause problems. Nevertheless, these may not properly handle water condensation and frost formation at low outdoor temperatures. The so-called membrane-based energy exchangers are an alternative to the flat plate heat exchanger. In a membrane-based exchanger, moisture is transferred from the humid exhaust air to the dry supply air avoiding condensation at the exhaust airside. In this work, a membrane energy exchanger was compared to a thin non-vapour permeable plastic foil heat exchanger. The study focused on verifying condensation and freezing problems and evaluating the performance of the membrane energy exchanger. The experiments showed that non-permeable heat exchangers have problems with condensation and freezing under test conditions. Under the same conditions, the membrane-based exchanger did not experience the same problems. However, additional problems with swelling of the membrane in high humidity conditions showed that the tested membrane type had drawbacks and needs further development to become commercially applicable.