Manufacturers of heat-recovery ventilators (HRVs) and energy-recovery ventilators (ERVs) know that HRV or ERV cores can get clogged with ice in cold temperatures. During the winter, this type of appliance brings cold outdoor air in close proximity to a stream of humid indoor air. If the outgoing air is humid enough, and the incoming air is cold enough, the moisture in the exhaust air stream can turn to ice.
How cold does it have to be for these problems to occur? The answer depends on indoor moisture levels and the design of the HRV or ERV core. In general, HRV cores can ice up when outdoor temperatures drop to the low 20s, while ERV cores may not develop icing problems until outdoor temperatures drop to the low teens. That means that people who live in the warmer parts of Texas, Georgia, and Florida probably don’t have to worry about HRV defrost strategies.
Fortunately, the ice-up problem is easy to solve, and almost all HRV and ERV manufacturers offer solutions to this problem. There are five basic strategies:
Some HRV manufacturers bristle as the term “defrost.” Instead, they talk about “frost prevention” strategies.
Ultimately, it doesn’t really matter whether a few ice crystals have begun to form, or whether the first ice crystal has yet to form, when the frost-prevention cycle is initiated. All the owner cares about is that the warming cycle prevents damage to the core. For the purposes of this article, I’m going to talk about defrost cycles. You can mentally substitute the words “frost prevention cycles” if you prefer.
Your car has an automatic choke. Why? To make it easier to start the engine when it’s cold outside.
Engineers invented the choke to solve a problem. Once the choke was invented, it became…