Page 251 - Alternative Energy Systems in Building Design

PASSIVE SOLAR WATER HEATING 227

it into the waterways. The advantages of metal panels include their rigidity and their
durability of construction. Like rubber mats, glazed versions of these panels are also
available for application in windy areas and cold climates. A significant disadvantage
of this type of technology is that these panels require significantly more surface area,
have low efficiency, and have no manufacturer’s warranty.

Plastic pipe systems In this technology, plastic pipes are connected in parallel or
are configured in a circular pattern. The main advantages of this system are that instal-
lation can be done inexpensively and the system easily can be used as an overhead
“trellis” for above-deck installations. The main disadvantage of this type of installation
is that it requires a significantly larger surface area than other systems, and like metal
panels, it does not carry a manufacturer’s warranty.

PANEL SELECTION

One of the most important considerations when selecting a pool-heating system is
the amount of panel surface area that is required to heat the pool. The relationship
of the solar collector area to swimming pool surface area must be adequate to ensure
that your pool achieves the temperatures you expect, generally between 75 and 85°F,
during the swimming season. The ratio of solar panel surface area to pool surface
area varies with geographic location and is affected by factors such as local micro-
climates, solar collector orientation, pool shading, and desired heating season.
It is very important to keep in mind that solar energy is a very dilute energy source.
Only a limited amount of useful heat falls on each square foot of panel. Consequently,
whatever type of solar system is used, a large panel area is needed to collect adequate
amounts of energy.
In southern California, Texas, and Arizona, where there is abundant sunshine and
warm temperatures, the swimming season stretches from April or May to September
or October. To heat a pool during this period, it is necessary to install enough solar col-
lectors to equal a minimum of 70 percent of the surface area of the swimming pool
(when the solar panels are facing south).
Generally, it is desirable to mount the panels on a southerly exposure. However, an
orientation within 45 degrees of south will not decrease performance significantly as
long as shading is avoided. A due-west exposure will work well if the square footage
of the solar collector is increased to compensate. However, a due-east exposure gen-
erally should be avoided unless significantly more solar collectors are used. Figure 6.6
diagrams a roof-mounted solar power pool-heating system.
As the orientation moves away from the ideal, sizing should increase to 80–100 percent
(or more for west or southeast orientations). If climatic conditions are less favorable,
such as near the ocean, even more coverage may be required. In general, it is always
recommended to exceed the minimum to offset changing weather patterns. However,
there is a point of diminishing return, where more panels will not add significantly to
the pool’s heating function. Table 6.1 shows the economics for a typical pool-heating
installation.