Accubloc: Efficient Energy Recovery in Cold Climates

In this Coffee Break, we discuss how Innovent has reinvented the (enthalpy) wheel

Since enthalpy wheels were invented in the 1970s, they’ve become a standard energy recovery device in many HVAC systems. But for all their success, enthalpy wheels present problems as well. They require regular maintenance, are prone to lost capacity from frost control, and feature multiple moving parts and air seals.

In this Coffee Break, Dave Milligan and Jake Saewart from Innovent, a Minneapolis manufacturer of custom HVAC equipment, introduce us to Accubloc, an ultra-efficient heat exchange technology meant to improve on the deficiencies of enthalpy wheels.

How is Accubloc heat recovery technology different from an enthalpy wheel?

Accubloc utilizes two banks of vertical heat exchange media. These are tightly packed aluminum sheets, up to 24” deep, available with or without a desiccant coating.

It looks like an enthalpy wheel but with a few key differences. The most evident is that the heat exchange media in Accubloc is fixed in place. A set of industrial-grade, fast-acting aluminum dampers control the airflow in and out of the device.

How does Accubloc transfer energy?

The heat exchange media is split in half with no airflow exchanged between the two sides. The outdoor air gains heat as it travels through the media, while the return air relinquishes its heat energy on the other side of the media before exiting as exhaust air.

After a 20-second charging interval, the dampers flip positions. Now, the outdoor airstream gains energy from the side of the heat exchange media that was charged by the return airstream during the previous interval.

Is there any cross-contamination of the two airstreams?

Innovent has verified that it is roughly the same as with an enthalpy wheel. The 2-3% of cross-contamination happens when the dampers are flipped, and the small amount of return air inside the exchange media is forced back into the supply airstream.

Accubloc is designed for applications that could utilize an enthalpy wheel for heat exchange. It is not intended for applications that require a flat-plate heat exchanger that guarantees no mixing of airstreams.

How does Accubloc perform?

Accubloc achieves 90-95% effectiveness in winter and 75-80% in summer with a desiccant coating. It can accomplish these efficiencies because of the physics of heat transfer. The device features a large surface area for heat transfer — 20” or 24” deep — and it’s given a comparatively long interval during which to transfer that energy.

The other significant advantage of Accubloc is that it can be run in cold climates with no preheating required. By continually reversing the airflows through the heat exchanger, there’s no chance for frost to build up on the media. The only time it becomes a problem is when ambient temperatures creep below -50 °F, frost can potentially start to build up on that side of the unit.

A secondary benefit of Accubloc is that it’s highly efficient at retaining moisture in a space. The relative humidity maintains itself. Any moisture from the return air will build up during the 20-second interval and be immediately introduced back into the supply airstream when the dampers reverse.