ENVIRONMENT AND ENERGY
When designing an underfloor system, it is important to
get the most out of your heat source. Heat pumps do
not like stop-starting and would rather run for longer
periods, less frequently. As such, Pioneer designs
these systems with a buffer tank rather, because
generally, every time you have a circuit calling for hot
water, the heat pump engages for one or two minutes
and then switches off, stressing the compressor.
You would rather have it come on once or twice an
hour and run for 10 minutes and get the buffer tank
up to temperature again and then switch off again.
“It reduces the number of start-ups on the machine
by 50–60%, which has a direct impact on the life
expectancy of the machine,” says Schröder.
EcoSmart also used to link their systems to heat pumps
as the heat source but now prefer using pellet boilers as
they consider these more efficient. “The problem with
heat pumps is that they still use energy, even when not
on,” says Wolfgang Stöhr of EcoSmart.
When a client had a concern that the system was still
using a lot of energy, Stöhr put a meter on the heat
pump to track its energy usage. They found that the heat
pump used 0.483kW just because it was on — not even
when it was heating the water. It used almost 12kWh
a day just by being on, which is not usually taken into
account when calculating the efficiency of a heat pump.
“The COPs are done under perfect conditions; it doesn’t
take all other factors into account,” explains Stöhr.
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Schröder calculated that for a 200m 2 underfloor system,
you have to store 128kW of power to run that system
during the night. “It’s not impossible, but it will be
expensive. Prolonged bad weather will affect the system
too and you will need a backup anyway. So, you might as
well just put in a heat pump.”
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Boiler pellets are made from waste wood from
processing. EcoSmart buys pellets from Pietermaritzburg
and ships them to Cape Town to supply their clients. Last
year, they supplied 1 000 tonnes of pellets. “It costs the
client 60c per 1kWh produced energy wise if they use
pellets,” said Stöhr. “That is much cheaper, at least half,
than if they were using a heat pump.”
The more things you heat with the pellet boiler, the quicker
your return on investment. According to Stöhr, around 30kW
is the dividing point — at 30kW the pellet boiler and heat
pump capital outlay are pretty much on par. “Anything bigger
than that and the pellet boiler starts becoming cheaper.” It
is a good investment for large installations like apartment
blocks, or housing developments. They are currently doing
an apartment block where they can reduce the electrical
connection by 50% because they went for pellet burners
instead of heat pumps in the end.
1.
2.
Make sure to leave the
work to the professionals
for a tidy, effective
installation.
Underfloor heating is
finally taking off in South
Africa, but hydronic
heating in particular
must be installed by a
professional.
“What a heat pump uses in three days in winter, our
pellet systems would use in a year, electricity wise,” says
Stöhr. With 1kg of pellets, you can generate 5.4kWh of
energy. A tonne, which takes up roughly 1.2m 3 of space,
gives you 5 400kWh.
Note: Every single supplier I spoke to, provided their
own calculations to prove in rand for watt value which
system is more efficient. Some preferred heat pumps,
some pellet boilers. Heat pumps seem to be the most
cost-effective for smaller systems, with pellet boilers
becoming more feasible the bigger the system becomes.
In the end, it will depend on the application. So, do your
research for what you would need!
NOT ALL PIPES ARE EQUAL
In terms of piping, you get what you pay for, says
Schröder. But it is worth investing in imported piping
Continued on page 27 >>
February 2019 Volume 24 I Number 12