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August 28 2018

Let’s stop binning heat


Paul Sands of Stokvis Energy Systems examines the potential for making more use of waste heat to tackle our energy needs.

A quick glance along almost any residential street in the UK when the rubbish collection is due reveals the extent to which recycling has become a part of our lives; with the once ubiquitous metal bins replaced by a varied set of brightly coloured containers to take plastics, paper, glass and other recoverable materials.

It is a key element to an internationally-driven agenda which is aimed at making our use of finite resources more sustainable. Yet reducing energy usage and thereby carbon emissions is arguably an even more important goal. Which raises the question; why are we so bad at recycling heat?

There have been some significant steps forward over recent years with high-efficiency or condensing boilers, which feature larger heat exchangers recovering more energy from the flue gases, now dominant. But technologies such as mechanical ventilation with heat recovery (MVHR) are rarely seen in domestic situations as, although recognised within SAP calculations, they are only mandatory for dwellings built to PassivHaus, or the Canadian Super-E specifications.

The latter two standards have been responsible for shaping some of the UK’s best performing properties but our own aspirations for having all new dwellings designed to the Code for Sustainable Homes Level 6 were shelved. Cost has also constrained the targets for improving the millions of existing properties which often score a ‘D’, or lower under an EPC. This means our homes are frequently cited as being responsible for more carbon emissions than transport or industry combined.

However, looking across our infrastructure, manufacturing and even power generation, it is all too easy to see where heat energy is going to waste. It is not just huge cooling towers spewing out steam, but our supposedly low carbon nuclear power plants sucking in millions of gallons of seawater to cool the reactors, or factories ‘dumping’ process heat in rivers.

The idea of capturing waste heat and using it to warm our homes is certainly not new, but compared to many of our European neighbours, the UK’s uptake of so called district heating schemes – or Heat Networks – has been negligible.   

One of the key aims of the Government’s Round 6 HNDU funding is to move consumers away from employing individual boilers, and onto communal schemes including centralised plant, CHP and solar. More adventurously, however, district heating schemes being fed by incinerators are growing in number while, in the capital, plans are in place to draw excess heat from the London Underground network.

All these initiatives offer huge energy saving potential, but one of the reasons district heating has failed to gain the traction it deserves has been the collective memory of early failures involving problems from leaking distribution mains to armies of Pharaoh ants marching around the ductwork of social housing schemes.

Improved jointing and integral insulation have addressed these issues but poor controllability and an inability to charge customers for what energy they actually use continued to stifle the successful of otherwise high quality installations. Which is why the modern Heat Interface Unit, or HIU, has the potential to finally deliver scale to district heating.

For anyone not familiar with HIUs, they create the interface between the primary circuit and the consumer, using high efficiency plate heat exchangers (PHEs) to extract heat for the dwelling’s own requirements. They can incorporate a heat meter to provide accurate billing information and supply both domestic hot water and space heating, depending on their design. Importantly, though, they should be specified to match each system’s characteristics, including temperature, flow and demand load. They can also be customised to suit special needs such as space limitations in retrofit situations.

With wind farms proving not only unpopular, but costly and unreliable, and other renewable technologies such as wave power still in their infancy, the short to medium term viability of UK energy policy remains dependant on making best use of existing, mainly fossil fuel based generation. Modern Heat Networks using HIUs to meet consumers’ precise needs offer a ready solution.

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