Many heat recovery ventilators use either aluminum or polypropylene cores.
They work with opposing airflows to achieve efficiency. If both airflows were going in the same direction (in parallel), once the temperatures reached equilibrium, no more energy could be transferred. Opposing airflows means that there is a diffence in temperature along every inch of the core. The more core surface area you have, the more energy that can be transferred.
Some dual core systems are achieving 96 percent efficiency @ very low outdoor temperatures. A core defrost cycle is usually part of the hrv design.
The unit either goes into recirculation or exhaust only to accomplish this.
A forum community dedicated to professional HVAC contractors. Come join the discussion about The industry, safety, ducting, finishing, tools, machinery, projects, styles, scales, reviews, accessories, classifieds, and more!