When Heat Pumps Become Killing Machines

Heat pumps have been a boon for efficient residential heating and cooling, at least in those regions of the country where winter temperatures do not consistently hover in the frigid range. In the southern United States, whole house heat pumps are arguably the most efficient way to heat and cool a house. Outside temperatures rarely fall below twenty degrees Fahrenheit, and even at 20°F, there is plenty of ambient heat available to heat a well-insulated home.

Owners of heat pumps have probably noticed that in the summer, heat removed from the home is released into the outside air. Heat coming off the outdoor unit, the actual heat pump, is hot. On the other hand, they may not have ventured out on a winter night to see how cold the exhaust from a heat pump is when it is in “heat” mode. But cold it has to be. Compared to a temperature of absolute zero, winter air is hot as hades. A heat pumps works by extracting some of that heat and sending it into the house to warm the house occupants.

But you can’t get something for nothing. Once the pump extracts a portion of the heat from cold outside air, that outside air must become colder.

Into this thermodynamic saga enters a non-native lizard called the Cuban or Brown Anole. The lizards are invasive, which means they are decimating the native Green Anoles which have long existed in the South Eastern United States. The Cubans are larger, more aggressive than the Greens, and reportedly feed on young Green Anoles. 

Cuban Brown Anole [Anolis sagrei]

However, they have a weakness. As you might expect for any species originating in Cuba and the Bahamas, they don’t like the cold. Whereas Green anoles range as far north as the Carolinas, the Browns do not. In fact, after a cold night in the Florida Panhandle I found a Brown Anole hard frozen on my doorstep. Perhaps he sensed warmth seeping from under the front door, and was trying to get in the house. Well, he didn’t make it.

The Greens, on the other hand, apparently shelter on or underground in leafy areas to survive the occasional cold dip.

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Green Anole (Anolis carolinensis)

As the outside temperature begins to drop in the late fall and winter, heat-seeking tropical lizards can be found warming themselves on top of the outdoor heat exchanger of our AC unit. When the proverbial nip is in the air, owners of well-insulated Florida homes plagued with high humidity, continue to run their air conditioning until late in the season.

For the Anoles, that is both a boon and a risk; it can prove to be a dangerous warming strategy. If frightened by the sudden appearance of a homeowner, Anoles run. When in their panic they fall into the running fan, the attempted evasion does not end well.

But the greatest insult is a thermodynamic one, which comes when the outside temperature drops even lower. Naturally, that chill makes the warmth from the heat exchanger even more attractive to the lizards. That is, until one of the human occupants decides it’s time to turn on the heat.

Thermodynamics being what it is, that switch almost instantaneously turns a warming source of air from the AC unit into a frigid blast of air.

Which explains why one morning after turning on the heat, I discovered the freeze-dried carcass of a Brown Anole clutching tightly to the grill of the AC unit. Apparently, the already chilled tropical lizard had what little strength it had left suddenly sapped by the high velocity blast of cold air. It died in place. (I have spared you the photo I took at the time.)

There is a moral to this story I believe.

As we grow cozy with new technology we don’t understand, while basking in the warmth and seduction of advanced engineering with its seemingly miraculous capabilities, perhaps we should remember this little lizard. It had acquainted itself with the bright side of thermodynamics, without realizing there was a dark side. Likewise, with the throwing of a switch, seemingly magical technology could be our undoing.

A serving of Artificial Intelligence, anyone?