|
The system works with a small circulation pump,
controlled by a temperature differential controller,
which circulates the heat transfer fluid from the
collectors to the heat exchanger in the solar geyser.
Collectors are mounted outside on the roof, with the
solar geyser installed in a space provided.
Pumped systems can be more expensive than natural
convection systems due to the added technology,
particularly if antifreeze measures are required.
However, they can be the right solution if your roof
structure and support beams (trusses) cannot support the
weight of the solar water tank. If the pumps performance
is maximised then your systems operation and savings
will be maximised.
A temperature differential controller is used to control
the pump:
- This differential controller switches on the pump
when the correct temperature is detected at the hot
water outlet (the controller will only allow water to
be released once the water in the collector is higher
than that stored in the storage vessel/water tank at
any given time).
- The differential controller therefore also
switches the pump off when the fluid in the collectors
is within 5 C of the return temperature's cold probe
from the solar geyser.
The pumps in forced circulation systems have low
power requirements. Direct current (DC) pumps powered by
small photovoltaic (PV) panels which convert sunlight
into DC electricity are sometimes used. Although, care
needs to be taken here as photovoltaic technology works
on light received and not heat.
Should a photovoltaic pump be used, emphasis should be
made not to control the pump using panel voltage. A
differential temperature controller must be included.
This will ensure the system is not cooled in the late
afternoon when there is sufficient light to run the pump
but insufficient solar radiation to heat the water.
Advantage: if you are concerned about aesthetics,
you will not need to place the system on your roof.
Disadvantage: unless you use photovoltaic
technology to power the pump, if there is no electricity
you will not have hot water.
All geysers taking part in this programme with
electrical backup will use timers in order to maximise
savings. The use of a timer has being proven to be the
most efficient way to use a solar water heater in South
Africa.
|