Category Archives: Bogus claims

Network operator promoting voltage reduction

Regular readers of my newsletter will know that I take a pretty dim view of people who try to sell voltage reduction — or what they often misleadingly call “optimisation” –as an energy-saving technique (see footnote for more details)

One of my readers was therefore surprised to read an Observer article on the Guardian web site in which a network operator, Electricity North West (ENWL), was touting the benefits of voltage reduction as a way to cut customers’ bills. The article correctly stated that customers’ kettles would take longer to boil because of reduced power output, but suggested wrongly that their consumption would go down as a result. In fact, it will slightly increase because the longer heat-up time increases the duration of heat loss from the kettle, and that extra heat loss needs to be made up from extra electrical energy input (the amount of heat put into the water is the same, so no effect on consumption there). This same perverse result – higher consumption at lower voltage – will apply to all thermal appliances operated on intermittent cycles.

I looked at some research that ENWL had commissioned on parts of their network, which had shown that a 1% drop in substation voltage had resulted in a 1.3% drop in power to connected customers. That is plausible but not the whole story. It’s true that for some unregulated appliances like incandescent lamps and toilet extract fans, reduced power will have resulted in reduced output (which nobody noticed) and hence lower energy consumption. But for thermostatically-controlled appliances like space heaters, ovens and immersion heaters, lower power will be compensated for by increased run times and there will be no saving. ENWL’s public-relations people have confused power (kW) with energy (kWh).

In reality ENWL probably have a different agenda and I think that the research behind their conclusions is part of a lobbying effort to get the legal limits on voltage relaxed, which will make it life easier for them in a world of distributed generation. When customers’ solar panels are generating at their peak, they tend to push the voltage up on the low-voltage network; and conversely being able to drop the voltage maximises how much solar power can be absorbed. Pretending that lowered voltage saves money is part of their pitch.

Footnote: 

Different types of electrical equipment will respond in different ways to reduced supply voltages. In short:

1. If the equipment is regulated in any manner, either in terms of its output or internally to maintain set voltages for electronics, don’t expect voltage reduction to save energy.

2. If it is unregulated and you don’t mind reduced output, voltage reduction will save energy.

3. If it is a thermal application used on an intermittent cycle, voltage reduction will have a perverse effect, increasing energy consumption.

Phase-change thermal storage materials

Ice storage is sometimes used in central air conditioning systems as a way of smoothing demand for chilling, thereby reducing the installed chiller capacity or allowing demand to be time-shifted. It’s attractive because the latent heat absorbed or released as the water changes phase between liquid and solid is an order of magnitude more than can be stored and recovered just by heating or cooling liquid water.

With phase-change storage established as a legitimate and effective element of central air conditioning and heating plant, it should come as no surprise that we now see vendors offering phase-change materials (PCM) to be embedded in the fabric of buildings as a way of stabilising internal temperatures and thus (according to their claims) saving energy. Are such claims likely to have any merit?

The concept of a PCM such as ice is that as any substance melts (or solidifies), it absorbs (or releases) heat without a change in temperature. PCMs for use in building elements such as walls or ceilings are usually either salts or waxes that change phase at the building’s internal set-point temperature. The argument goes that when daily outside-air temperatures swing above and below the internal set-point, heat stored during the hot part of the day is released during the cold part, avoiding the need for artificial cooling or heating. However, such circumstances are rare. What would happen in a more realistic scenario where, say, the weather is cold and the space needs heating? Firstly, if the space needs heating continuously, the PCM will never change phase and will thus be redundant. It will either be permanently solid or permanently liquid, depending on which side of its melting point the space is being held.

Now suppose the space is heated intermittently. If the internal set-point were below the PCM’s melting point, it would never melt, so it would have no effect. But if the heating set-point were above the PCM’s melting point then it would absorb heat during the warm-up part of the heating cycle. The problem with this is that it would retard the rise in space temperature and delay the achievement of set-point. This would call for a longer pre-heat period — which  incurs an energy penalty. At the end of occupation the heating would go off and any heat stored in the PCM would dissipate to no effect, first to the outside and then — once the internal temperature was sufficiently low — back into the unoccupied space.

Similar considerations apply to cooling. If the PCM is effective it will retard the effect of the room air-conditioning system. This could result in complaints, for example in settings such as hotels where this technology is being actively promoted.

The ‘demonstration’ rig used by one vendor in an online video. In each of two sealed cells a lamp heats the floor, which has insulation beneath it. The right-hand cell has PCM immediately beneath the floor. Temperatures were measured at the top of the insulation, so the right-hand cell indicates the temperature of the PCM, which naturally levels off at its melting point. What neither thermometer showed was the important thing: the temperature inside the cell.

Skeptical of the online video purporting to demonstrate the effect (see diagram), I set up a simple mathematical simulation of the warm-up cycle of a heated room with PCM embedded behind plasterboard in its outer wall. The outcome was even worse than the description I gave earlier. At 5C outside the PCM did not start to store heat until the room temperature went nearly two degrees above the PCM melting point This is because the intervening plasterboard acts as a thermal insulator, keeping the PCM below the room temperature even though it I had 100mm of insulation on its cold side.

On a positive note, PCM layers may have a role to play in moderating overheating from solar gain to roofs in particular, for example in attic rooms. I have measured external roof-tile surface temperatures of 50C in the UK, which even with insulation behind it results in uncomfortable internal temperatures on the sloping ceiling behind it. 25mm of PCM under the roofing felt would absorb, by my calculations, the first 2.5 kWh per square metre of solar gain. Keeping the internal surface cooler would help alleviate discomfort and with internal insulation the stored heat would dissipate preferentially to the night sky.


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Ultra-rapid charging

StoreDot and BP present world-first full charge of an electric vehicle in five minutes” runs the headline on this news item from BP which actually talks about an electric scooter. The Storedot website is a bit more gung-ho about their new battery technology, which they think would enable a 5-minute full recharge of an electric car with 300 mile range. Really?

Quick sense check: for a 300 mile range you’d be talking probably about a 100-kWh battery for which a 5-minute full recharge would demand 1.2 megawatts of charging capacity. That’s going to be some meaty charger. Moreover, even upping the charger voltage to 1,000 volts you’ll be drawing 1,200 amps, so I reckon the charger cables are going to need a pair of conductors of (say) 4 square centimetres cross section. And cars would need to be engineered with DC charging circuits to match …

I put these points to StoreDot and they pointed me to Chargepoint’s website which talks about “up to 500 kW” Express Plus charging using the CCS Type 2 connector, although as far as I know CCS2 goes nowhere near that rating and when those kinds of powers are achieved they are going to need thousand-volt water-cooled charging cables with thermal sensing on the plug because of the risk of overheated contacts.

Our next course on transport energy and carbon is on 17 October: click here for details

Back to the scooter that BP had seen recharged in 5 minutes. The  model in question has two 48V 31.9 Ah batteries (so about 3.1 kWh) which to recharge in 5 minutes would require a 37 kW charger – plausible in a non-domestic setting. I imagine the demonstration to BP involved removing the batteries to recharge them because obviously the scooter’s onboard electrics would not be designed to handle a charging current of 800 amps.

My colleague Daniel did some digging and unearthed this priceless video from StoreDot in 2014, purporting to show a smartphone being completely recharged in 30 seconds using battery technology that would be released in 2016 (I’m still waiting…). The sceptical comments are worth reading — especially the ones about fake phone screens, and indeed the ones about exploding phones — but you can’t help but notice in the video itself they are actually “charging” a huge battery glued to the back of the phone. So a big dose of scepticism is in order, I think, and if the link to the video no longer works you can guess why.

More credible is the news this April about battery developments using vanadium disulfide cathodes stabilised with a microscopic layer of titanium disulphide: this promises faster charging but they are careful not to say how much faster.

Product awards: handle with care

This article may upset some of my friends in at energy publications and associations, but we have a problem which people need to be aware of. It is that we can no longer trust awards for energy-saving products as indicators of merit.

I get asked for advice about dubious products by my newsletter readers and often they’ll say “I smell a rat but it has an award from [insert name of prestigious body]“. How can something bogus get an award that it does not deserve? To  answer that you have to understand how award schemes work. In particular you need to appreciate that their promoters are driven by profit. The commercial imperative is simple: get as many bums on expensive seats as possible at a gala-dinner awards ceremony. To do that, they need to have a lot of short-listed candidates, because those are the people who will pay on the off-chance that they get to pose as a winner with the celebrity host. Having a big shortlist means putting an awful lot of entries in front of the judging panel (44 for one  panel I sat on). But these judges are unpaid, and as volunteers they simply cannot spare enough time to scrutinise entries thoroughly, even though some do take it seriously and try to be diligent. They aren’t helped by the fact that candidates often submit little more than rehashed sales blurbs full of unsubstantiated claims — a short-cut which promoters condone in the interests of maximising the number of bums on seats.

Some judges, moreover, will have been selected more for their celebrity than their knowledge (celebrity judges equals more bums on seats), and will lack the ability to spot snake-oil propositions or even to understand counter-arguments from more knowledgeable fellow-judges. The majority of any panel will be easily swayed by the plausible nonsense in the entries, will not question the credibility of testimonials, and will naively assume that no competition entrant could possibly have criminal intent.

It is asymmetric warfare. The snake-oil peddler just needs to keep plugging away with award entries because the spurious credibility that they get from their first award is too valuable to forego. Once they have landed one award, they are effectively immunised against rejection by judges for other awards and probably even have their chances boosted.

I don’t want to tar all awards with the same brush: in an honest world they would all work to everyone’s benefit, and no promoter is knowingly complicit in the occasional fraud that slips through the net. But sadly a few bad apples have devalued energy awards and my advice would be this. If you have doubts about a product,  seeing the phrase ‘award-winning’ should put you on alert.

Project sketch: vetting product offers

My client in this case is an international hotel brand. Individual hotels get approached by people selling questionable energy-saving products and rarely if ever have enough knowledge to defend themselves against bogus and exaggerated offers.

The company has established a core group of engineers and sustainability staff to carry out centralised vetting. My job is to provide technical advice during the initial filtering phase and to join a twice-yearly meeting to interview suppliers who are being taken further.

Pants on Fire Award

And the winner of the Pants on Fire Award is… DB2 Management OÜ who sell a product called ‘Ecovolt’. This device, which plugs into a standard 13A wall socket, is claimed to cut 30-50% off your electricity consumption. What makes it a stand-out candidate for the Pants on Fire Award is the advertisers’ invocation of conspiracy theory::Their web site includes a short video purporting to prove the device’s energy-saving effect. It shows a pair of electric hair clippers on an extension adaptor drawing 0.28 A. When the Ecovolt device is plugged into a neighbouring socket, the current falls to 0.08 A. Electrical engineers will recognise this as an example of power-factor correction and nothing to do with reducing the real power drawn by the appliance; like the EPS Energy Saver which I reported on a couple of years ago (pictured below), the Ecovolt probably contains a big capacitor and not much else.

The visitor to the web site sees continual pop-up notices saying that Tatiana, Sara, or Phillip and so on have just ordered Ecovolt. Keep your eye on those alerts for more than 70 seconds and Tatiana, Sara and Phillip appear again followed by six other repeated names. That’s the kind of loyal customer we all want.

The firm operates out of a Post Office Box in Tallinn, Estonia, and sells a diverse product range including night driving glasses, dash cams, and non-stick frying pans. I ought also to mention that Ecovolt is someone else’s trade mark.

 

Door air curtains

In situations where it is necessary to keep a building’s outer doors open, you will sometimes find “air curtains”, fans which blow a sheet of air down across the width of the doorway. These are an effective way of preventing dust and insects getting in through the door: they are entrained in the outer layer of airflow, and where the jet hits the floor it splits, with the outer layer discharging the contaminants back outside.

Convective circulation in open doorway

Some suppliers of air curtains claim that they conserve energy as well. The basis of this claim lies in what would naturally happen in an open doorway in still conditions, namely convective circulation in which warm air at high level flows out to be balanced by cold air flowing inwards at low level (right). This effect will be especially marked with high doorways. The claim for air curtains is that they disrupt the flow of escaping warm air, forcing it down to floor level where the jet splits, with the warm inner layer returning inside.

However, even in still conditions there is a problem here, because the fan is drawing air from high level inside and at floor level only half of it returns inside. 50% of the internal air drawn into the fan is diverted outside when the jet splits at floor level (left).

A further problem with pedestrian doorways particularly is that the air curtain usually needs heating to prevent the perception of cold that the air’s velocity would create. If the building actually doesn’t need that heat, it is all a waste of money. Even if it does need the heat, half of what is put in goes straight outside.

In windy conditions the argument for air curtains as heat barriers really breaks down. A moving sheet of air is simply not as effective as a door. If there is any differential pressure whatever, that sheet of air will be displaced, and the problem is exacerbated if there are open doors or windows on the far side of space – or extract fans. In one instance I visited a restaurant that operated an open-door policy. Their air curtain had a 20kW heater that ran continuously, but the downjet did not reach the floor: about 60cm above the floor it turned inwards along with a layer of cold air at floor level, thanks to the kitchen extract depressurising the space.

Condensing boilers (not)

The exhaust from a natural gas appliance contains about 0.15 litres of water per kWh of gas input, and about a tenth of the thermal output is lost because that water is emitted as vapour. Condensing boilers are a good idea in theory because they can condense the vapour and recover latent heat from the products of combustion, boosting output by around a tenth.

In practice, too few condensing boilers achieve their potential because they cannot cool the flue gas below its dew point (around 59C ). Result: plumes of vapour outside. This one resembles what you’d see boiling a 2-3 kW kettle in the open air, and that’s a measure of how much energy is being wasted.

The truth is that so-called condensing boilers need to be installed in heating systems with low return water temperatures. Underfloor heating, or systems with oversized radiators for example. Only then will they get sufficiently-low temperatures in their heat exchangers to get the exhaust vapour to condense.

 

Nice try, but…

A recent issue of the CIBSE Journal, which one would have thought ought to have high editorial standards, recently published an article which was basically a puff piece for a certain boiler water additive. It contained some fairly odd assertions, such as that the water in the system would heat up faster but somehow cool down more slowly. Leaving aside the fact that large systems in fact operate at steady water temperatures, this would be magic indeed. The author suggested that the additive reduced the insulating effect of  steam bubbles on the heat-exchanger surface, and thus improved heat transfer. He may have been taking the word ‘boiler’ too literally because of course steam bubbles don’t normally occur in a low or medium-temperature hot water boiler, and if they did, I defy him to explain how they would interfere with heat transfer in the heat emitters.

But for me the best bit was a chart relating to an evaluation of the product in situ. A scatter diagram compared the before-and-after relationships between fuel consumption and degree days (a proxy for heating load). This is good: it is the sort of analysis one might expect to see,

The chart looked like this, and I can’t argue that performance is better after than before. The problem is that this chart does not tell quite the story they wanted. The claim for the additive is that it improves heat transfer; the reduction in fuel consumption should therefore be proportional to load, and the ‘after’ line ought really to have a shallower gradient as well as a lower intercept. If the intercept reduces but the gradient stays the same, as happened here, it is because some fixed load (such as boiler standing losses) has disappeared. One cannot help wondering whether they had idle boilers in circuit before the system was dosed, but not afterwards.

The analysis illustrated here is among the useful techniques people learn on my energy monitoring and targeting courses.