Knowledge · Guide

Cross-flow or enthalpy: which design fits?

Cross-flow transfers heat, enthalpy transfers moisture as well. The comparison shows the strengths, limits and selection criteria of both designs.

Both designs sit in the same housing principle - a plate stack with two separate flow paths. The difference lies in the plate itself: solid in the cross-flow unit, vapour-permeable in the enthalpy exchanger. Different fields of use follow from that.

What does the cross-flow plate heat exchanger do?

The cross-flow exchanger transfers sensible heat only. Its strengths:

• Strict separation: nothing from the exhaust air reaches the supply air - a precondition for loaded, odorous or process-related extract air.
• Free choice of material: aluminium, coated, stainless steel or plastic - the plate may be anything that is tight. That also covers hot or corrosive extract air.
• Cleanability: smooth metal plates can be cleaned; for process exhaust air carrying dust or grease this is the decisive point.

Its price: in winter a good deal of condensate occurs, and the recovered air is dry - indoor humidity falls.

What does the enthalpy exchanger do differently?

Its membrane lets water vapour through while keeping the air streams apart. It therefore transfers sensible AND latent heat:

• Humidity recovery: the supply air arrives less dry in winter - relevant for offices and homes, museums, anything with a comfort or humidity requirement.
• Less condensate and freezing risk: what passes into the supply air as vapour cannot freeze on the plate.
• Summer operation: in cooled buildings the membrane keeps part of the outdoor humidity outside and relieves the cooling plant.

Its limits: the membrane does not tolerate aggressive or greasy extract air, cannot be cleaned abrasively and is limited in temperature. For process exhaust air, cross-flow remains the choice.

Side by side

Criterion	Cross-flow	Enthalpy
Transfer	heat only	heat + moisture
Separation	complete	air separated, water vapour diffuses
Materials	4 materials up to stainless/plastic	membrane (fixed design)
Loaded process air	suitable (material selectable)	not suitable
Condensate in winter	plenty, drain required	considerably less
Freezing risk	present, strategy required	reduced by design
Typical use	industry, process, halls	offices, housing, comfort ventilation

How to decide?

Two questions usually suffice: may moisture pass into the supply air - and what does the exhaust air carry? Comfort ventilation without loaded extract air speaks for enthalpy; process, kitchen or hot exhaust air for cross-flow with a suitable material. In the configurator you do not have to commit in advance: without a restriction the sizing calculates both designs and shows what each achieves under your requirements.