Reasons To Use Hot Water Storage In Heat Networks

The Hot Water Association reinforced McDonald Water Storage’s campaign to use hot water storage within heat network schemes, whether central plant or district heating.

With their 29 page publication of the Design Guide for Stored Hot Water Solutions in Heat Networks, the document provides design guidance and advice for engineers who are looking to specify stored hot water solutions working within a heat network.

We have been championing the benefits of hot water storage for many years, but the document also lists no fewer than 22 advantages of using stored hot water over instantaneous systems. Using stored hot water solutions within heat networks has many advantages over systems that generate hot water instantaneously. These include:

  • It requires very little power to keep the whole system topped up as it works on the Fly-Wheel Principle.
  • It makes diversity at the taps irrelevant to the heat network. ie separates out supply from demand.
  • The rate of supply against rate of demand can be manipulated to suit each installation.
  • The timing of recovery allows further load levelling by staging recovery of the DHW cylinders connected to the network.
  • It reduces the size of the central plant.
  • Smaller networks are easier, quicker, and cheaper to install.
  • Lower capital costs of the network counter the additional cost associated with the cylinder.
  • Lower primary flow rates required, so smaller pumps can be specified.
  • Smaller pipe sizes are required.
  • A smaller network requires smaller expansion vessels and less inhibitor.
  • Heat losses in primary circuit are lower.
  • Lower operational cost mean payback is quicker and price per unit of energy is lower.
  • Reduces the designers risk relating to consumer usage pattern being different to diversity curve assumptions.
  • Offers electrical input as standby for increased consumer security and / or last stage heat-up to allow use of low primary temperatures and renewable heat sources.
  • Being able to input electrical energy from renewable sources close to point of use (ie within the dwelling) reduces primary pumping costs.
  • It can provide somewhere for low grade intermittent heat sources such as PV, solar thermal, wind, etc to store energy.
  • Flexibility of design, set-back regime, delta T control, phased charging can all help reduce peak demands and lower heat losses.
  • Ability to purge heat from individual heat network branches using a phased recovery approach.
  • Ability to switch off central plant which will increase the life expectancy of the central plant as it doesn’t run all the time.
  • No need for primary bypasses for keep warm purposes.
  • Controllability of hot water temperature throughout the flow rate range. Valve authority during low demands can be problematic with larger HIUs.
  • Reaction time to changes in demand are less critical.


With many technical challenges surrounding boiler sizing, diversity requirements and pipework infrastructure, the significant benefits which localised water storage can provide should be considered. Having localised storage means that the boiler size and therefore pipework infrastructure can be dramatically reduced in size, saving money and building the efficiency of the system by smoothing out the running load of the boiler.

McDonald Water Storage product and marketing manager, Wayne Hyde, commented, “We have worked with a number of consultants and social landlords across the UK providing hot water solutions for use with heat networks, which include vented, unvented and thermal stores.”

In full transparency, the HWA did advise that the negatives for traditional cylinders in a heat network setting are:

  • Greater space required to site the cylinder. This can be countered by fitting the store on a frame so that a washing machine can be fitted underneath a cylinder.
  • Cost of the cylinder including controls.
  • Heat Loss from cylinder. Smart cylinders and no need to keep primary pipes hot counters this argument.
  • Potential to run out of water when the store and its recovery rate does not match the application.
  • The need to heat the stored water to 60 degrees centigrade for 1 hour per day to meet legionella regulations.
  • Cost of cylinder maintenance.


However, with our thermal store solutions you would overcome all the points other than the cost of the cylinder and controls, as they don’t apply to thermal stores.

Wayne Hyde also commented, “Our thermal store range provides a perfect solution as they can achieve significant savings on running costs as well as avoiding costly and problematic issues surrounding G3 and discharge pipework and provide the resident with built in scald protection and no risk of legionella.”

CUBEflow“The CUBEflow rectangular thermal store comes into its own, bespoke manufactured to fit where space is a premium, meaning we can manufacture virtually any variety to optimise the central plant operation. This ability to manufacture custom sized units and match connection layouts, means we can minimise installation times and associated costs.”

Contact us today to discuss your project.

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