22
DESIGN: DEAR MR PLUMBER
Hot water generation
and reticulation systems
By Vollie Brink, Pr Eng
Hot water generation and reticulation, as well as the
requirements and some new changes to a number of SANS
documents, have a number of issues and affect the design of
such systems negatively, making it more expensive.
Vollie Brink
Vollie Brink is one of the
industry’s longest serving
wet service engineers.
He continues to serve on
SABS committees and has
been involved in the
Green Building Council Star
rating system.
Brink continues to consult
for various organisations
while enjoying a well-
earned retirement.
Health and safety is of paramount importance
and forms the basis of both the SABS standards
and the regulatory requirements of the National
Regulator for Compulsory Specifications. However,
cost-effectiveness and affordability are essential
elements of the National Building Regulations, too,
which cannot be ignored. The reasons for these temperatures do not consider
other elements such as the chlorination of the water
and a number of other elements, including the cold
water quality and condition. Millions of water tanks
are situated on roofs and in the bare sun and the
requirement is that the temperature in these tanks shall
not be more than 20°C.
It seems that the technocrats sometimes ignore these
elements when they sit around the table to formulate
standards and make it compulsory. It is often a case
of people who have researched and then blindly follow
other countries’ practices. In terms of SANS10400-XA, all new buildings shall
comply with the requirement that 50% of the annual
hot water generated shall not be by electrical elements
and, therefore, the remainder shall be by solar, heat
pump, or gas.
I have also found that some of these technocrats are
people who have never done a design, have never
worked in the field, but have a lot to say. Heat pumps have become the most preferred for many
reasons, but the problem with it is that if you use a heat
pump that delivers 60°C directly, then the cost of such a
heat pump is substantially more than a heat pump that
delivers only 55°C. If you want to use one of these heat
pumps, then you must also add electrical elements to
raise the water temperature to 60°C.
One technical committee I know of has a chairperson
without a qualification that relates to the work of the
technical committee — this I find amazing.
There is supposed to be some liaison between the
various technical committees on matters of common
interest, but I find there is no real feedback from the
liaison representative to the other committees. Some of
the issues are critical to be discussed and decided on
before it is published.
One of the critical issues is the water temperature (hot
and cold) in relation to legionella. We have to fit the
legionella temperatures within a number of present
parameters, such as the following:
• The maximum pressure allowed in a building
system, which is 600kPa.
• The maximum and minimum temperatures of hot
water in a hot water generation system, which is
60°C.
• The minimum temperature of hot water discharged at
any water fixture in a building, which must be 55°C.
July 2017 Volume 23 I Number 5
SANS 10252-1 and SANS 10400-XA require that a
water discharge fixture shall not discharge more than
four litres of cold water before it is at temperature,
which has now been decided to be at least 55°C. This
margin of 5°C between the maximum of 60°C and
the minimum of 55°C in a hot water generation and
reticulation system is workable for a house but not in a
large building, such as a hospital or a hotel where the
pipe runs are very long.
In these buildings, the hot water generation temperature
of 60°C is not a problem, but the return temperature of
55°C is just not achievable unless the return water is
reheated midway back to 60°C, which is an expensive
exercise and a constant operational cost.
It was decided to change the four-litre requirement,
as it is complex to test, and instead have a table with
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