Pool covers?
Why do people use pool covers?
Pools lose energy in a variety of ways, but evaporation is by far the largest source of energy loss for swimming pools. When compared to evaporation, all other losses are small.
Since evaporation is the major source of heat loss for all swimming pools, to minimize evaporation one must cover the pool. Covering the water with a pool cover when it is not in use is the single most effective means of reducing heating costs. Savings of 50-70% are possible.
Types of pool covers
Technically, all you really need is a large sheet of plastic. Plastic meets the requirement of being a vapor barrier. But a large sheet of plastic that you get from the lumber store is probably not your best choice. It will be very difficult to handle and store, it tears easily, and sunlight will deteriorate it rapidly. You can use it, but it will be very inconvenient and will only last 1 to 2 seasons max.
There are a number of manufacturers that produce covers designed specifically for swimming pools (see Pool Gear Plus's solar covers page for information about ordering a pool cover online). They can be made of different materials, such as UV stabilized polyethylene, polypropylene, or vinyl. They can be transparent or opaque. They can be light colored or dark colored.
One of the lowest cost pool covers made specifically for swimming pools is the bubble cover (some call them solar covers). They are similar to bubble packing material except that they use a thicker grade of plastic and have UV inhibitors, etc.
Vinyl covers are a heavier material and have a longer life expectancy. You can also get insulated vinyl covers with a thin layer of flexible insulation sandwiched between two layers of vinyl.
Outdoor pools gain heat from the sun, absorbing 75-85% of the solar energy striking the water's surface. This is an important contribution to its heating needs.
So when considering a pool cover, note that a cover will also decrease the solar gain contribution to some extent, depending on the type of pool cover used. A transparent bubble cover may reduce solar energy absorption by 5-15%, and a completely opaque cover by 20-40%.
Methods of using pool covers
There are several ways of covering your pool. The simplest and lowest first cost method is to manually pull the cover on and off, fold it, and place it somewhere out of the way. If you are paying someone to do this, you need to consider that cost in your economic evaluation. You can also purchase a pool cover reel that can be used to manually roll the pool cover up. The reel, usually on wheels, can then be rolled out of the way.
Semi-automatic covers use a motor driven reel system. They use electrical power to roll and unroll the cover, but usually require someone to pull on the cover when unrolling, or guide the cover onto the reel when rolling the cover up. They can be built into the deck surrounding the pool, or can use reels on carts.
Automatic covers have permanently mounted reels that automatically cover and uncover the pool at the push of a button. They are also the most expensive first cost option. But you have to weigh the cost of labor for the manual and semi-automatic covers to determine which route is best for your particular situation.
Some pool covers are fitted into tracks along the sides of the pool. This prevents anything or anybody from getting into the water. They even support the weight of several people. If liability is a concern, these are a good option to explore. They can be run manually, semi-automatically, or automatically.
When to use pool covers
For pools which are open all day, a cover should be placed over the water as soon as it closes, and taken off just before it opens for the day.
For pools which are not in use during daylight hours, the effectiveness of a pool cover will depend on whether the evaporation and other losses prevented by the cover exceed the solar gain reduction caused by the cover. This balance is affected by the type of cover and the climate. In dry and/or windy conditions the evaporation rate increases, and it is generally beneficial to have a transparent or bubble cover on during daylight hours. In warm, humid conditions the evaporation rate decreases, and it may be more beneficial to leave the cover off during the daytime.
Other benefits of pool covers
Pool covers also provide many other benefits beside the tremendous energy savings. They conserve water by reducing the amount of make-up water needed by 30-50%. They can reduce chemical consumption by 35-60%. They also cut cleaning time by keeping dirt and other debris out of the water.
It is highly recommended that the first step to cutting energy loss be the evaluation of the economics of using a swimming pool cover. (To clarify, we are not talking about pool covers that you use to cover the pool in the off season or mesh safety covers. Those do not save energy. We are talking about plastic or vinyl pool covers that you use during the swimming season when it is not in use.)
See Pool Gear Plus's solar covers page for information about ordering a pool cover online.
This information on pool covers was edited by Chris Whitten based on source material
from the U.S. Department of Energy RSPEC (Reduce Swimming Pool Energy Costs) Program.
