Perth College, located in Mt Lawley, is the oldest independent girls’ school in Western Australia. It has a large outdoor pool which is heated by a gas heater. The 50 meter eight-lane swimming pool is utilized by the school as well as the Perth City Swimming Club and by the Perth Swim Academy, to promote education, instruction and development of swimming sports.
Motivated by the desire to lower its gas bills to heat the water and reduce CO2 emissions, the school decided to install an evacuated tube (EVT) solar pool heating system. This is an excellent example of the utilization of a commercial solar pool heating system. Such a system can produce twice the heat per unit area as a traditional flat plate panel system, and because of its high efficiency it can maintain warm pool temperatures in the colder months.
The solar pool heating system was installed by Supreme Heating WA and includes a 72-panel EVT system. Supreme Heating WA was able to complete the project in approximately five weeks. The system is designed to generate very high water temperatures needed copper fittings to handle the temperatures. The Viega Propress system was utilized and Viega assured them that their fittings would sustain temperatures up to 200°C.
Evacuated tube (EVT) collectors were developed more recently than flat plate collectors. Introduced to the market in the 1970’s, there are several varieties of evacuated tubes. The most commonly used type utilizes a heat pipe surrounded by a glass tube under a vacuum.
- The glass tube consists of two walls of glass.
- In between the two walls, all the air is removed, resulting in a vacuum.
- The vacuum is ideal for insulation and has much better heat retention than air space.
- The heat pipe is also pressurized, allowing the liquid (usually water) to boil very rapidly, at a very low temperature (usually between 75F and 80F).
- As the water boils, it carries the collected heat to the top of the collector, where the heat is then absorbed by water or heat transfer liquid that flows.
Cost is typically the primary consideration. Collector for collector, evacuated tubes can cost around 20% to 40% more to buy than flat panel collectors. However when comparing price one should consider cost per BTU capacity, and consider year round performance. In cool climates, evacuated tube collectors will have a lower cost per BTU.