Pool covers save more energy than all other efforts put together!

Where do pool-blanket energy savings really come from? This question is the most significant yet least understood consideration when pool owners consider the use of pool-blanket systems. In the simplest terms, swimming pool blankets stop evaporation. It's only incidental that they insulate to a small degree. Insulation, the property usually attributed to blankets, contributes from one or two percent of the energy savings for pools (a little more when used on outdoor spas). Evaporation retardation is overwhelmingly the larger contributor, up to 50% savings on energy usage!

Without delving into the physics too deeply, a brief "scientific" explanation helps our pool operator to understand the significance of evaporation: Water, that master-standard chemical, requires just one “calorie” (an energy unit) per milliliter (cubic centimeter) to raise its temperature exactly one degree Centigrade. Conversely, it loses one calorie as the temperature drops one degree. However, vastly increased amounts of energy are either given off or required to be "taken in" for changes of state − that's the transition between the vapor, liquid and solid states of water. For the shift from liquid to vapor, the energy required is called the "heat of vaporization" − 540 calories. It takes five hundred forty times as much energy to vaporize any quantity of water than it does simply to raise that same quantity of water one degree Centigrade! That's a killer of a statement. Read it again...

Here is an example: We have an outdoor spa at a ski resort with snow on the ground. Water temperature is 42 degrees Centigrade (103 degrees F) and the air temperature is freezing − zero degrees C (32 degrees F).

The zero-Centigrade air that is in contact with the warm water, (42 degrees C,) naturally takes energy form the water. Ultimately, 42 calories are lost for each milliliter of water if it cools to the temperature of the air (or this much energy must be replaced by the heater to avoid that temperature drop). At the same time, each tiny milliliter of water that evaporates absorbs fully 540 calories from surrounding water... or twelve times the energy-replacement requirement as the conduction energy exchange. A spa cover was essential in this true-life example in order that the skiers could shush up and take a warm, relaxing soak.

Wind and humidity as well as radiant energy and ground conduction affect this ratio, but not enough to invalidate the example. The point is this: an impervious membrane stretched across the surface can halt evaporation entirely, thus saving a huge portion of heat energy which otherwise would be lost! And that membrane can be anything; it could even be Visqueen or Saran Wrap! Something more substantial, removable and reusable might be a better idea, of course.

Cover those pools! It’ll pay your salary!