Geysers in parallel

The following is a summary of an IOPSA/PIRB Tech Talk by Adriaan Myburgh, edited by Eamonn Ryan, relating to pitfalls and potential mistakes in installing geysers in parallel.

Multiple water heater installations are predominantly used in commercial or industrial applications where a high volume of heated water may be required during peak hours, or where insufficient planning was done to supply hot water to a new build in order to comply with XA 2.

There are two main methods of interconnecting these hot water cylinders:

  • Series connections
  • Parallel connections

This Technical article will deal with Parallel connections.

In a series connection, cold water is fed through each tank – one after the other – with the hot water outlet from the first tank becoming the cold supply to the next tank. The installations of geysers are governed by a single regulation, SANS 10254:2017: The installation, maintenance, replacement and repair of fixed electrical storage water heating systems. This document covers the safe installation of new and replacement fixed electric storage water heaters, complete with all the relevant and applicable safety and hydraulic control units. However, this standard does not cover the sizing or hydraulic design of the storage water heating system or the design and installation of industrial hot water systems.

In other words, it is for simple off-the-shelf units installed onto a client’s premises. Section of 10254 states, “Where some of the provisions of this standard cannot be applied, the installation shall comply with the details given in a rational design developed by a professional engineer on acceptable installation drawings, and such rational design shall not compromise the safety and performance principles incorporated in this standard.”

Myburgh described the reason for the Tech Talk as being the following sub-section “On completion of the installation, a certificate of compliance from the professional body for plumbers registered in terms of the relevant national legislation [in this instance the PIRB], shall be issued to the owner of the installation or to the body requiring such a certificate.”

parallel 1As a plumber, the maximum size geyser that he can install is 450 litres, under the scope of his qualification. This means if a plumber is installing geysers in a series that is in aggregate more than 450 litres, at some point another professional competent person has to sign it off based on an approved design. This not only applies if they are interconnected, but when they are stand-alone geysers as well. Even where it is signed off by a competent person as to the design, a CoC must still be issued by the plumber as to the materials and workmanship.

The regulation ‘5.6 Mains shut off’ applies to a geyser installation in parallel: “5.6.1 For ease of maintenance, the inlet pipe to a pressure control valve and to a float valve (water storage tank cistern-type or cistern-fed heater) shall be furnished with an isolating valve.

“5.7 Vacuum control valves: In closed systems and in valve-operated vented systems, vacuum control valves shall be installed on both hot and cold water pipes to and from the heater to ensure that both lines and the water heater are vented and that siphonage is prevented.

“5.8 Expansion control valve on cold water supply: When an expansion control valve is installed on the cold water side of the water heater, it shall be installed downstream of any isolating valve, gate valve, non-return valve or any other flow-control device.

Myburgh emphasised that when doing multiple geysers in parallel (or in series) the above regulations apply to each unit – not just the first one but leaving the rest.

This means if a plumber gets a job falling outside the scope of this standard, he/she needs to ensure the job is based on drawings, even if just the manufacturer’s layout of how the system is to be connected, and that the plumber is satisfied with the drawing. The following being an indication of what an installation could look like, but it is not a design.
He highlights potential problem areas: “In the position of the shut-off valves each cylinder needs to be isolated on its own in that system. Failure to do so would negate the purpose of the entire job of giving a client a greater volume of hot water at one time.
“When looking at shutting off cylinders individually in parallel or in series you will require additional expansion relief. In addition, the pipe work has to be exactly measured – otherwise the water will take the shortest route and there will not be an even distribution of water. Regarding power supply, in a normal geyser replacement you will have 2.5mm wire, with an isolator. When you start adding more 250 litre geysers together there will be considerably increased current drawn through it, so a qualified electrician will be required to potentially upsize it.”

parallel 2

parallel 3

The above is how the system is supposed to look. Each cylinder has a shut-off valve and expansion relief on either side downstream from the shut-off valve.

Points to consider when installing cylinders in parallel:

  • The system operates equally well at both low and peak demand
  • A bypass pipeline is not required as was the case with geysers in series
  • All geysers that are to be part of this parallel connection are to be of exactly the same rating, same size and same model
  • Pipe sizing is not limited by the inlets and outlets of the cylinders – the size of the headers can be increased
  • SANS 10142 isolator per geyser: this may lead to increased wire thickness, possibly additional breakers at the DB, and must be installed by a qualified electrician
  • Being a rational design, the safety requirements are that all valves are to be labelled, special operating instructions are to be provided and relevant warning signs are to be posted
  • Most new electrical-only geyser installations will not comply with XA2 of the National Building Regulations, so you have to make sure that somewhere in the system there is energy efficiency

In terms of geyser installations – be careful when signing off on these types of installation that may or may not be compliant – by making sure they are compliant. Parallel connections of hot water cylinders are not covered by SANS 10254:2017. Each installation will be unique, with different layouts, different flow rates, space for working, demand from building occupants, and more. There is no one-size-fits-all or generic design.

Myburgh notes that if a PIRB plumber is called in to replace one of a series of geysers, a CoC has to be issued for that single geyser, and the plumber is also required to note on the CoC – and bring it to the attention of the owner – any non-compliant issues relating to the remainder of the geysers.

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