SA Affordable Housing January - February 2020 // ISSUE: 80 | Page 18

FEATURE
explains that many of the boasts of heat pumps to save 60% to
80% of the heating bill is achieved under laboratory conditions,
‘all things being perfect’, when the reality is that the coefficient
of performance is entirely dependent on the ambient
temperature out in the real world. From his experience the
actual savings are in the order of 40% to 50%. “The higher the
temperature in the area, the better heat pumps work. In contrast,
the solar resources of this country are of such an order that solar
heating can be installed anywhere and use no electricity.
Another consultant suggests the main reason there are a lot
of negative reports on solar water heaters to the effect that
they are saving only 20-30% of electrical usage is because the
resistance heating back-up is uncontrolled, and because hot
water storage volumes are insufficient in relation to daily usage.
wool insulation or blankets. In addition, all hot water pipework
is required to be insulated to a minimum of class R1 ('R' stands
for thermal resistance. The R value depends on the type of
material, its density and thickness). In a ceiling, if you have the
insulation resting on the ceiling boards, there is a cold void
created at night in the roof space. In all areas, particularly in
winter, where thin copper piping has been installed without
insulation, there will be significant heat losses, and as a result it
takes some time to get hot water if some time has elapsed since
the previous hot water usage. If insulation is applied to the
piping there is almost no noticeable drop in temperature,
thereby saving electricity.” He says this can be done not only in
new developments, but can be retrofitted to existing homes.
HOW TO REDUCE ENERGY CONSUMPTION
ON AN ESTATE
In this respect, says Bredenkamp, we are seeing a focus among
affordable housing developments on a ‘thermal passive’ design
which builds in insulation and orientation – in South Africa that
would mean being north-facing to maximise light and heat in
winter, something which was not a concern for such
developments as recently as ten years ago, he explains.
“Architects are designing and building according to window
building specifications which prescribes how much window
area there must be in relation to the total square footprint (or
net floor area) meterage. This is to allow more natural light and
reduced heat losses and reduces the need for energy-using
mechanical lighting and heating.
“In summer, we advise people to practise the low-cost option
of keeping the curtains closed from midday to limit the need for
artificial cooling.”
While many savings on estates are based on economies of
scale due to the number of units, Bredenkamp makes the point
that many technologies relating to energy saving have fallen in
price to such a degree in recent years – and the cost of energy
in turn increased to such a degree - that they are affordable for
smaller developments, and even individual homes on a ‘retrofit’
basis. “The pay-back period on such technologies as LED lights
is one to three years and they have lifespans of five to ten years.
For instance, even a few years ago the payback period for solar
heating was over 20 years, and today it is five to seven years
and continues to fall on virtually a monthly basis.
“When it comes to building an energy efficient house, the first
consideration is the best way to achieve cooling and heating,
without ‘money’ evaporating into the air,” says Bredenkamp. He
lists the most economical savings as the orientation of the home
and insulation at the time of construction, followed by use of LED
lighting. If retrofitting a home, he suggests residents at least
insulate the ceiling and the first two meters out of the geyser and
last two metres into the geyser, convert their geysers to solar
water heating and install a geyser blanket.
Heating water typically amounts to 30-40% of the electricity
bill. The time to do these interventions is at the beginning of
the design work, so that the best use of energy saving
technology is built into the cost of the house.
Many developers have preferences for heat pumps over solar or
vice versa, and Bredenkamp is a proponent of solar heating,
though he says there’s a place for both technologies. He
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JANUARY - FEBRUARY 2020
SAAffordHousing
SOLAR HEATING VS HEAT PUMPS
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SA Affordable Housing
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