Page 380 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

‘Quick recovery’ hot water storage cylinders
The quick recovery cylinder has a multi-coil heat exchanger that is made up
of several smaller bore coils rather than one large one. This encourages a
rapid recovery of the hot water because the coil has a greater surface area
of heat presented to the water in the cylinder. They work in a similar way
to instantaneous hot water cylinders and are replenishing the hot water
even as it is being used. This reduces the amount of storage required and
can save up to 40 per cent on fuel bills when compared to the standard
cylinder type. When cheap-rate electricity is used for heating the water,
it is most economical to heat the entire contents of the cylinder overnight.
This reduces the need to use the immersion heater during the day when
electricity is more expensive. Key points are:
● rapid heated water recovery; generally, recovery times are 15 minutes for
45 litres and 45 minutes for 210 litres (assuming a boiler output of 9 kW);
4 minutes for 45 litres and 19 minutes for 210 litres (assuming a boiler
output of 30 kW)
● multi-coil heat exchanger
● smaller storage cylinder means more space in the airing cupboard
● reduces boiler cycling
● saves on fuel bills
● can be used with conventional fully pumped systems.

Quick recovery cylinders work at their most efficient when installed
alongside condensing boilers running at maximum temperature. This will
ensure that recovery times are at their absolute minimum and the lower
p Figure 6.13 Quick recovery return temperature of the condensing boiler will maximise the time the boiler
(Superduty) cylinder
spends in condensing mode.

 Table 6.7 Advantages and disadvantages of Superduty cylinder systems
Advantages Disadvantages
Quick turnaround of hot water Initial cost of the cylinder
Only small storage capacity needed
Very energy efficient
Fully compliant with Doc. L of the Building Regulations

 Table 6.8 Criteria of choice for quick recovery cylinder systems
Property size Storage capacity Fuel type Installation cost Fuel efficiency
All domestic Usually 80 litres. Can be used with Initial cost of the cylinder is Extremely energy efficient when
properties. Economy 7 electricity expensive, but is installed as used with condensing boilers due
and fully pumped a double feed indirect cylinder to fast heating of the water. Can
heating systems. with comparable costs. cut fuel costs by up to 40%.

Storage cylinder insulation
Cylinders are insulated with polyurethane foam, which is sprayed on to a
predetermined thickness. The thickness of the insulation is covered by Building
Regulations Document L: Conservation of heat and power, which was updated
in October 2010. The insulation thicknesses have been modified to deliver

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