Regulation Water services
> the hot water distribution system includes a central
thermostatic mixing valve wherever any primary heat
Key documents
There is no
source is capable of raising the domestic hot water CIBSE Commissioning Code M: Commissioning
longer any
temperature to above 80C during normal operation. Management – this is the approved methodology
mention of
This would principally apply to domestic hot water for management of the commissioning process for
competent
vessels that are heated by some types of solar systems fixed building services.
or solid-fuel systems.
installers in the
CIBSE Domestic Building Services Panel: Solar
regulatory text
Unvented hot water systems: competency Heating Design and Installation Guide – covers
The new Part G has ‘softened’ the references to predominant types of systems and notes their
competent installers. There is no longer any mention advantages and disadvantages. The broad range of
of competent installers within the regulatory text, systems covered will assist those engaged in repair
although the guidance advises that installers should and maintenance work to understand the principles
be competent. The requirement to inform building of operation of existing equipment, as well as guide
control of the identity of the installer when notifying the design and installation of new systems.
them of an unvented hot water installation has been
revoked.
Some installers may be certified as competent in
unvented hot water system (UVHWS) work, but may
not be registered with a competent persons scheme
(CPS). It should be noted that, in order for an installer
to be exempt from giving notice to building control
or providing full plans in respect of an unvented
installation, he/she must be competent AND belong
to an approved CPS. There is a list of CPSs on the
CLG website.
Connecting unvented systems to
sanitary discharge stacks
The new Approved Document acknowledges Plastic discharge pipes for unvented systems
that discharge pipes from unvented systems may The new ADG accepts that suitable plastics may
connect to a sanitary discharge stack. This has proved be used for ‘D2’ pipes, and recommends the use of
extremely successful since about 2004, especially polybutylene or PE-X to BS 7291 – a flexible piping in
when designers are dealing with multi-storey which the water flows under pressure. It is difficult to
apartments and commercial buildings, where the understand how this piping could be considered to be
installation hitherto has been based on BRE guidance, ‘best practice’ for conveying emergency discharge by
Self-sealing Waste Valves for Domestic Use (2007), for gravity flow because:
the HepVo self-sealing waste valve. • The flexibility of the piping increases dramatically at
Although the new ADG has sensibly avoided high temperatures, therefore maintaining a continuous
naming a commercial product, it has simply stated gradient whilst discharging boiling water would require
that a device with a ‘mechanical seal’ should be used. very careful installation
But this could open the door for inferior gadgets – • Bends take the form of 90 degree ‘knuckle’ elbows,
it would have been more prudent to state that the whereas the normal convention for a pipe operating as
device should be a self-sealing waste valve that has a gravity drain is for any bends to have a swept radius
been independently certified for the application. The at an 87.5 degree angle to facilitate correct gradients
list of provisos included in the associated text also and minimal flow resistance.
fails to mention some key requirements for a reliable The new text advises that plastics pipes ‘may’ have a
installation, including: different bore to copper pipes, and that the maximum
• The self-sealing waste valve must be installed in the discharge lengths given for D2 pipes should be
vertical position; adjusted accordingly. The bore of a 22mm plastics pipe
• A PVC-U sanitary discharge stack should have a is about 18mm and will produce a significant reduction
traditional open vent (for example, it should not in gravity flow compared to a copper pipe. Although
be fitted with an air admittance valve or be a stub reference is made to BS 6700, there is no guidance
stack); on how this reduction can be calculated and installers
Contacts
• The tundish should not be located in a position that (and building control) will not know how to assess this
www.communities.gov.uk
is unlikely to be seen by the user on a regular basis; point with confidence. l
www.nhbc.co.uk and Also see Legal column, Journal, September, page 22
www.bre.co.uk
• The tundish should not be located lower than the
spill level of the lowest sanitary appliance connected
Brian Whorlow is a consultant and CIBSE Mid-Career
www.trustcorgi.com
College presenter
to the stack.
32 CIBSE Journal November 2009 www.cibsejournal.com
CIBSEnov09 pp30-32 PartG.indd 32 22/10/09 16:52:46
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