In response to a question about building an efficient heat exchanger, the author provides some options for DIY heat recovery ventilators (HRV). They mention that most HRVs use a cross-flow cell with a 90-degree angle and have an efficiency of 60-70%. However, there are also experiments with a 180-degree cross-flow that showed an increase in efficiency. The author mentions a wheel type HRV that claims efficiency up to 90% and provides a link for more information. They also mention the difference between HRVs and energy recovery ventilators (ERV), with the latter using a water permeable membrane to re-humidify incoming air. The author shares a hack for a de-humidifier that can extract heat from outgoing air and return it to incoming air. The author expresses enthusiasm for this hack and suggests that it is worth trying. Overall, the post provides information and options for building efficient heat exchangers.
https://ecorenovator.org/forum/showthread.php?s=41c17447383e29b03903f4e0136e55be&p=5792