Letters to the editor: volume 16, issue 5

How will hot water storage fit in?

It’s good to see wider public debate of the challenges and benefits of decarbonising domestic heating. On 4 April, the Daily Telegraph reported that, “Radiators would have to run 10 degrees cooler under changes to homes needed for Britain to hit net zero, the public has been warned”. It’s not clear whether the impact of this would be obvious to all the paper’s readers – reducing the primary flow temperature by 10ºC doesn’t mean the heated space will be 10ºC cooler, but it will have an effect, especially in colder weather.

With a few exceptions, heat pumps can’t heat water to the same high temperatures as a gas- or oil-fired boiler. To maintain the heated space at the same temperature with cooler primary water, some combination of more and/or larger radiators, installation of underfloor heating or better thermal insulation will be required.

There’s another large pachyderm lurking in the corner – domestic hot water. Let’s take a modest requirement: 40ºC temperature rise (10ºC in, 50ºC out) at 10 litres per minute. An instantaneous electric heater to produce this would be rated at 28kW, well beyond the capacity of the typical 100A single-phase domestic supply in the UK. I’m not aware of any heat pumps that offer instantaneous hot water production (although some larger indoor designs do have a buffer storage tank), so future electric domestic hot-water production is going to rely on some form of storage.

The hydraulics of unvented storage cylinders allow them to be sited anywhere in a property but does every home have a suitable location to house one and support its 200kg+ mass? To minimise energy and water loss from ‘dead legs’ in piping, the storage vessel should be sited as close as possible to the outlet taps. Phase-change hot-water storage may reduce the space required but mass remains significant. In many homes, installation of a ‘combi’ gas boiler has led to the airing cupboard being re-purposed. So, where does the hot-water storage go?

Jonathan Barker CEng MIET

Tunbridge Wells

Renewables need infrastructure revolution

Steve Proud makes a strong point regarding inertia and synchronous generation, and its importance in maintaining a safe and secure supply of electricity through the National Grid transmission system (Letters, April 2021). The current infrastructure was not designed for an influx of non-synchronous renewable energy generators.

Wind turbines, for example, are inverter-connected, using electrical decouplers that disconnect electrically the generator’s motion from the grid frequency and as such do not have the same inertial response as a conventional generator. During peak times of wind generation the system operator currently has to find the right balance between adding this energy into the mix while maintaining a stable change of frequency. Tools such as demand response are used to achieve this. However, millions are still being paid out through constraint payments – ultimately paid for by the public – where wind-farm operators are asked to switch off their output during peak wind conditions for fear of destabilising the grid.

Changes to the infrastructure will be required if we are to achieve a much higher penetration of wind and other renewables into the energy mix. This could be through a much smarter way of electricity consumption, requiring behavioural changes from the public in the way we consume energy, or through physical costly upgrades to the electricity transmission system to adapt to the characteristics of intermittent energy.

Chris Martinez MIET

By email

We must face grid change head-on

The concept of a national grid was developed in the first half of the 20th century, to connect the various distribution networks. One major aim of the grid was to deliver power from coal fields to large industrial users and the British public. The abundance of coal was a major driver.

We no longer have significant coal fields, and coal is now largely absent from power generation. Furthermore, we have lost much of the large demand, in the form of massive steel works, alumina smelters and the like. Also ‘base load’ – nuclear or otherwise – is now so low as to be practically irrelevant: today, gas power is the major balancing mechanism on the grid.

The reality for the future is that we will have large and small wind farms, solar installations and, hopefully, tidal barrage systems on the distribution networks and perhaps on the national grid. One similarity to the coal fields is that these renewable energy systems are also in remote locations, away from the major demands of the cities.

We should not be addressing a “threat to grid stability”, as this is a clear case of the tail wagging the dog. We should, instead, face the new reality head-on. There are many ways this can be done, for example large plants to generate hydrogen, methanol or ammonia, pumped storage and all the other storage technologies that are coming to the fore. To ensure these things happen, the government and the National Grid company itself need to make clear commitments to promote the market conditions that will allow these projects to proceed.

Declan Pritchard MIET

Anglesey

Waiting for hydrogen makes sense

Are the UK plans to ban sales of new internal combustion engine cars after 2030 a sensible policy? Battery-powered electric vehicles emit so much more carbon during manufacture that even with ‘green’ electrical charging their carbon footprint doesn’t reduce to that of a diesel car until maybe more than 50,000 miles. Worse is that they emit more tyre particulates because of their average 30 per cent greater weight.

Going all-battery will permanently increase global emissions and urban particulates. And they cost nearly 40 per cent more to manufacture, so are expensive to buy. Would not the logical course be to allow lighter, less-polluting diesels until ‘green’ hydrogen is readily available, then go for hydrogen-fuelled internal combustion-engined or fuel-cell cars that aren’t so heavy or expensive? We hear that by 2030 proton-exchange membrane hydrogen generation will be able to produce it on-site at filling stations. And that electrolysis may be 80 per cent efficient by the same date.

BMW and Mercedes produced hydrogen-powered demonstrators as long ago as the 1970s. They emit virtually no NOx below nearly full power and are no heavier than current IC engines. Hydrogen storage would be a challenge, but the same will apply to fuel-cell vehicles.

The second advantage of awaiting ‘green’ hydrogen is that it could power heavy trucks and buses, which are the worst urban polluters, and be used for house heating, which at present emits more than the cars they own.

Dr EurIng Colin Mynott

Northants

Cross-Channel delays

Graham Collins regrets loss of the free movement of goods to France that he experienced immediately after Britain’s EU entry (Letters, April 2021). While we share names, our experiences differ markedly. Travelling for business to France in the 1980s I found les douanes taking a considerable interest in demonstration equipment or even demountable hard disks carrying computer programs. At times of international trade fairs held in France, much delay would be experienced in bringing non-French equipment to the shows.

Perhaps the improvements he experienced were the result of his company using an effective export agent to prepare documents and carnets, rather than any EU-driven seismic change in French processes?

Phil Collins MBE

By email

Rings, plugs and fuses

As described in the ‘From the IET Archives’ column in the April 2021 issue of E&T, Dame Caroline Haslett was undoubtedly a potent force in the development of UK domestic electrical installations, initially pressing for installations in inter-war houses, then for sockets and for an adequate number. On the post-war reconstruction Electrical Installations committee (managed by the IEE but not an IEE committee), she demanded a universal socket and plenty of them. Her main contribution was the development of the fitted kitchen, with lots of sockets.

The ring circuit and the 13A plug both have their defects: the ring circuit because it needs complicated testing and it is possible for a section to be overloaded, the 13A plug because of the heat generated by the fuse and the additional connections that the presence of the fuse requires.

The ring circuit lies very much at the door of Forbes Jackson, at the time chief electrical engineer of the London County Council, who had long advocated the all-electric house and took the opportunity to bring it to fruition. One of his bêtes noires was the profusion of meters, fuse switches, splitters and fuse boards at the intake. He wanted a single tariff and the smallest possible fuse board.

Eric Jacobi, director of a firm of contractors who did a lot of work for the LCC, calculated that a 900-square-foot house could be heated with 30A if the hall and landing were ignored. The contractors said that it could not be a single radial because 7/.036 cable was too stiff; Forbes Jackson would not budge so it was a 30A ring (the primary guidance is now is two 20A radials). If Jackson had accepted two radials it is arguable that a fuse in the plug would not have been necessary.

What about the plug? Manufacturers did not want a new-gauge plug and proposed to update the 5A plug to 10A, eventually being forced to 13A, a new gauge and a fuse. But what about the fuse to protect the flex, the universal use of 30A flex being unacceptable? The only one they knew was the 15A BS88 fuse, which was far too big (even to put in the socket). Up came Beswick, who pointed out that a fuse which broke 80kA was not necessary and produced the fuse we know.

So, we have the 30A ring circuit and the fused 13A plug. No-one has followed us, but Dame Caroline got her universal plug.

David Latimer CEng FIET

Former Vice-Chairman, Wiring Regulations Committee

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