Bethel Business and Community Development Centre (BBCDC) updates us on some solar innovations that they have recently undertaken relating to a new collector manifold for an aging solar water heating system and, a heat exchanger design.
New 20 heat-pipe collector manifold
An average solar radiation of 6kWh per square meter per year provides enough solar thermal energy for Leotho's BBCDC to rely on solar water heating for its hostel’s hot water requirements. Having been early adopters, some of the installed infrastructure is already 15 years old and recently needed some maintenance. At the same time, Lesotho’s very cold winters present challenges due to freezing, resulting in the rupturing of pipes within the aging infrastructure.One of the girl’s hostels had a 200 litre galvanized tank and 4 square meter flat plate collector made out of galvanized pipes installed.
This year, the BBCDC decided to replace the galvanized pipe collector with a 20 heat-pipe collector manifold. Since the new heat pipes are freeze resistant up to -32°C, freezing should no longer be an issue. The heat pipes also have a higher efficiency than the galvanized pipe collector, meaning that more hot water will be produced.
The new collector was installed by second year Solar Technology students at BBCDC.
Heat exchanger
The BBCDC is also experimenting with its own heat exchanger to deal with sub-zero temperatures and the damage caused by freezing. It is made out of copper pipes and copper sheeting which is soldered together. The collector is filled with freeze-resistant heat exchange fluid which in turn heats water in the storage tank. The heat exchanger is highly insulated so that all the heat in it is transferred to the water to be heated. The dimensions of the heat exchanger are 50cm x 7cm.
On the day it was tested, the loop from the collector with the heat exchange fluid reached 65°C, while the loop going to the tank reached 56°C. On the test day, the solar radiation averaged at 800 watts/m2, and in 4 hours the heat exchanger managed to heat 20 l of water from 20 to 50°C.
A 2m2 copper pipe flat-plate semi-closed collector was used in the testing. More tests on the heat exchanger will be conducted.
