Systems for outdoor swimming pools using the relatively inexpensive unglazed collectors can be particularly cost effective.
For DIY or new build system installations, costs can be reduced - particularly in the case of large scale new building projects.
SOLAR WATER HEATING
Solar Water Heating Technical Bulletin, Volume 3
Flat Plate Collectors v. Evacuated Tubes – A Brief
Overview
The 1 st Rule of Solar – Use the Right Collector for the Job
There is no single collector that can be labeled
‘the most efficient,’ as the efficiency of collectors
depends on what they are hooked up to. For seasonal swimming pool
heating, an unglazed collector will beat out
a flat plate collector at a fraction of the cost. An unglazed collector
can pull off this feat because it is heating a pool at 80 °F when
it is right about 80 °F outside. Under those conditions, the collector
is running at ambient temperature and has no heat loss, therefore
it does not need to be insulated.
When we start moving up in temperature it becomes more important to
insulate the collector against losses.
Whereas collectors on seasonal pools operate within 10-20 °F of
ambient, domestic hot water (DHW) collectors are designed to run through
the colder winters and at higher temperatures in a wide range of 25-125
°F above ambient, depending on location and season.
The last application of thermal is in high-end process
heat such as steam production or powering absorption chillers in the
range of 150 °F above ambient. Efficiency plots of the various
collector styles against collector inlet fluid temperature above ambient
are shown in the figure below.
As discussed above, unglazed pool collectors dominate in low temperature
applications 0-25 °F, flat plates hold sway in the mid range of
25-125 °F, and evacuated tubes come into their own at the upper
end at 125+ °F. This is the reason why no particular collector
has dominated the entire thermal market, each collector has its own
place.
As you move from unglazed to glazed and on to evacuated tubes you
move up and up in price. Evacuated tubes could be used to heat swimming
pools, but it would not make economical sense to do so given that
an unglazed collector is 1/10 th the cost and 30% more efficient.
A well designed system using any good quality collector (i.e. evacuated tube, selective surface flat plate or non-selective surface flat plate) can provide a significant contribution to a householder's hot water requirement.