ENVIRONMENT AND ENERGY
27
<< Continued from page 25
with a 50-year guarantee. “The piping is built in under
the slab; you want it to last at least 50 years.” Pioneer
mainly uses cross-polymer PEX pipe out of Europe. It is
a multilayer cross-link pipe with three layers: two cross-
linked layers of PEX and an oxygen EVOH barrier.
One of the most important things to consider when
designing an underfloor heating system, is the
temperature of the water that goes to the floor, explains
Stöhr. The higher the temperatures used, the faster the
deterioration of the water underfloor heating pipes. High
water temperatures will heat the floor and thereby the
room much faster; however, it will also be more difficult
to control the set temperature of the room.
These systems are all closed-loop systems and they
get filled once. A water treatment takes place, which
displaces the oxygen out of the water so you don’t have
bacterial growth in the piping structure. If you do not use
an oxygen-barrier pipe, you will have limited amounts of
oxygen seepage through the actual wall of the pipe over
prolonged periods. After a year or two, this will render
your water treatment system useless, explains Schröder.
Heat pumps are a good heat source for hydronic underfloor
heating systems, in particular systems under 30kW.
The pipes deteriorate due to the changes in temperature
when heating and allowing the pipes to cool down,
before heating again. “If you do it right, your pipes will
last a minimum of 50 years, maybe even 100 years.”
You have to calculate the water temperature according
to the requirement and application, but it is generally
37–42°C —you shouldn’t be going higher than that,
Stöhr advises. Though, there are exceptions.
DOS AND DON’TS — TIPS
The various experts interviewed have learnt a lot over the
many years spent manufacturing, supplying, designing,
and installing underfloor heating systems in this country.
This is their advice for getting the most efficient, most
effective systems.
Step one, as mentioned, is ensuring your pipe runs are
not too long. Schröder advises that depending on the
amount of bends, he is willing to go up to a 110m pipe
run in one circuit. “Anything longer and the pressure
drop becomes too high and the change in temperature
too drastic. We aim to have a fixed-degree delta T
temperature drop of 10°C over the circuit.”
Step two is making sure it is designed for the right capacity,
Britz explains. If the system is designed under capacity in
terms of the heat source, the area will never quite heat
up enough and it will shorten the life expectancy of the
equipment. Or if the wrong circuit breaker is installed, it will
not be able to handle the heat source and it will keep tripping.
www.plumbingafrica.co.za
Another issue is not including the underfloor heating as
part of the initial design. As it will affect the rest of the
building, this has to be considered in the building plans
from day one.
There are various systems
of laying out a piping circuit,
but it is important not to
damage the piping and to
get an even spread of heat.
It is important to leave the installation of hydronic
underfloor heating systems to the professionals, says
Schröder. One of the biggest problems is incorrect
circuit layouts: It is common to just loop a system and
then loop the cold water return around, causing an
uneven spread of temperature. Instead, you should
loop the hot water and do a cold central return in-
between the loops. That means an average spread of
temperature between high and low. No matter where
you are on the floor circuit, there will be an average
spread of temperature.
Michael Carter of The Tech Butler, who does radiant
heating and cooling installations locally, suggests
rendering an energy model of the underfloor heating
system before starting your design. This should be done
after the heat load calculations.
Continued on page 29 >>
February 2019 Volume 24 I Number 12