Hot water cylinder insulation drives energy efficiency in the home

Kingspan Environmental explain the benefits of cylinder insulation and how it can help your housing stock be more energy efficient

Based on an initial survey that revealed homes with higher SAP values were not necessarily reducing residents’ energy costs, Sustainable Homes has followed up with a second investigation of over 500 homes from 13 Housing Associations that brings into focus specific reasons why, including the way people use hot water. If nothing else, the National Energy Study highlights that stored hot water is perhaps the preferred option for households that require frequent hot water supply, and indeed, a high flow performance from taps and showers. Even for smaller homes, the survey challenges conventional assumptions on efficiency.

While important for a world in general that is increasingly concerned with energy saving and the carbon footprint, it is perhaps an even more compelling argument for landlords, private and social, who take responsibility for helping tenants better control their energy consumption and avoid falling into fuel poverty. The main gist is that the way we use hot water, the way we manage draughts and our fear of thermostats and timers, determines how energy efficient we actually are. For example, the survey reveals that those who admit the least understanding of their heating system tend to be the highest energy users, concerned more about comfort than cost.

SAP methodology is not an exact science and the assessment is based on standardised assumptions for occupancy and behaviour, not necessarily what happens in the real world. An Energy Performance Certificate may give an estimate of the building’s typical annual spend of energy but ultimately is no guarantee of an efficient home. Sustainable Homes claims that the patterns of actual energy usage reveal a very different picture from a purely ‘technical performance’ standpoint.

Despite scepticism from the boiler manufacturer’s lobby, evidence from this study goes on to suggest that homes with combi boilers actually use 13 per cent more energy than homes using system boilers fitted with a hot water cylinder, even those with low occupancy. One of the key reasons for this is that heat loss performance of unvented hot water cylinders has been vastly improved, with the best insulation thickness now measuring over 60mm. Also boiler efficiency is significantly reduced by being turned off and on, known as ‘cycling’, as happens with instantaneous hot water applications

Why is this important? Because, replacing the central heating system in a home is a significant expense for landlords and, while continued investment in energy efficiency is needed, SAP should not be the only guideline. Realistic energy usage patterns should also be taken into account by landlords genuinely concerned about fuel poverty and lowering residents’ energy bills.

 

As far as the hot water system is concerned, it’s about underlining the importance of calculating demand patterns, in terms of quantity and frequency, when specifying a new or replacement plumbing system. Hot water storage continues to be an integral part of modern day hot water system design, reinforced by a developing renewable energy market which requires stored hot water to harvest the energy and bank it for later use. A system boiler and indirect unvented hot water cylinder has significant ‘green’ credentials. The stored hot water can also be kept hot if necessary by an immersion heater, a secondary direct power source, in the vent of a boiler breakdown. It is, of course, not difficult to see the attraction of combi boilers when it comes to space and ease of installation but for family households with regular hot water demand, specifications should look at unvented hot water cylinders to provide the required hot water volumes and flow rates, often more economically.

With heat loss performance such a critical factor these days, the insulation features of hot water cylinders become an increasingly important differentiator. The highest grade insulation materials and insulation thickness, can dramatically reduce heat loss over a 24 hour period, as does insulating the top of the cylinder where the hottest water is stored. Side positioning of the hot water outlet allows this and better design integration of the immersion heater and wiring centre will further improve energy efficiency at points which traditionally lose heat. Extensive pipework is also a potential inefficiency so easy plumbing connections will make a considerable difference, not least for access and servicing. An internal air gap device not only improves thermal efficiency and reduces heat loss but also does away with the need to fit a separate, space hungry expansion vessel.

As the energy efficiency of homes in the UK continues to improve, cylinder insulation ranks as one of the most important developments in the reduction in energy use. Design and material innovation from cylinder manufacturers may well contribute to better SAP scores, which is a good thing, but user education on energy wastage from heating water will also go a long way to improve comfort and reduce bills.