Why Use Hot Water Storage In Heat Networks?

Plant 1

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.
  • Controlability 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.

For further information on the benefits of hot water storage within heat networks and how thermal storage can provide the perfect solution, click here.


Wayne Hyde

Product and Marketing Manager

Having been in the cylinder industry for nearly 20 years, in both product and marketing roles, I have extensive knowledge of all aspects of hot water storage, from domestic through to commercial applications, including vented, unvented and thermal store solutions.

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