Down the AHRI Wormhole: Evaluating Air-to-air Energy Recovery Technologies
As an HVAC specialist, I confess I’m also a bit of an air-to-air energy recovery junkie. Over the years, I’ve seen technical advancements that provide exceptional energy conservation opportunities. That being said, adoption is slow and I still see specifications using old technologies that deliver only marginal benefits. These often come with a higher price tag due to the limited number of manufacturers still offering these systems.
I thought it would be an interesting exercise to mine data from the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) via their handy online search directory. This data is third-party tested and verified, thus garnering acceptance from the engineering community at large. There also happens to be a very large amount of available information. In fact, there was so much that I had to narrow the exercise down to include only active “Commercial Air-to-Air Energy Recovery” devices with airflows from 2,800-3,200 standard cubic feet per minute (scfm).
There are many product tests undertaken throughout the AHRI certification process, as outlined in AHRI standard 1060. (Available for free download at www.ahrinet.org) For my purposes, I narrowed it down to looking at pressure drop and thermal effectiveness with zero pressure differential between outdoor and exhaust air streams. (Note: I disregarded OACF and EATR because while also very important, they were not relevant to the scope of the task.)
I further drilled down the data collected from 285 products into average performances for each of the four major heat recovery technologies: Wheel, Plate-Latent, Plate and Heat Pipe. These are the only technologies currently certified by AHRI. While there are other counter-flow technologies not currently AHRI-certified, my understanding is that tests for these have not yet been developed by AHRI.
Here are some noteworthy findings:
- As expected, they had the best effectiveness across the board. (Sensible, Latent & Total)
- They have the highest airside pressure drop, so there would be greater motor power required.
- I was pleasantly surprised by the performance of LATENT plates. Although less than wheels, their reduced airside pressure drop would close the gap.
- Great sensible effectiveness out of a static device with minimal maintenance.
- If I included EATR & OACF in the review, plates get even more appealing
- Heat Pipes
- As expected, heat pipes deliver the worst performance. This is why they are widely considered a dying technology with minimal application today.
Within Southern Ontario, I still see a lot of heat pipes being specified. So I did take time to further dig into the AHRI data to see if there was a compelling reason. I made the same chart looking at every heat pipe with AHRI certification.
Some interesting observations from the raw data:
- There are only two manufacturers with AHRI certified heat pipes: Heat Pipe Technologies & Thermogain. Neither certified a packaged unit; all certifications are for the component only.
- Latent effectiveness was zero in all 180 certified heat pipes.
- Low pressure drop does not redress overall poor performance.
In general, these data mining results were consistent with what I would’ve assumed with respect to performance. Namely, wheels are the best solution for the majority of applications. However, in critical applications where cross-contamination is a concern, applying a plate heat exchanger is a better fit. Performance and reduced maintenance requirements of latent plates make then an attractive alternative to wheels. Within high humidity environments, like pools & change rooms, sensible only plates are best. Finally, heat pipes have limited applications today, restricted to contaminated air applications such as kitchens and oily industrial environments.
I’d love to hear your feedback and comments.