# Additives in chillers: limits of plausibility

Most people who understand the physics of heating systems will understand why the claims for energy-saving boiler-water additives ring hollow. But similar products (possibly the same ones with different labels) are now being touted for central chiller systems and it is evident that some users have fallen for them. Time to look at these new claims.

First, as a quick potted revision of the context, I’ll describe an air-cooled chiller with ordinary basic control:

1. Heat is abstracted from the building by means of a closed loop of chilled water leaving the chiller at a set temperature and returning at a higher, and variable, temperature.
2. The water boils refrigerant in a heat exchanger called the ‘evaporator’ which operates at a temperature just below the chilled-water set point (the difference, called the approach temperature, is typically 2°C or less).
3. After compression the refrigerant (now at elevated temperature) passes through an air-cooled heat exchanger called the ‘condenser’ which runs maybe 10-15°C hotter than ambient. Here latent heat is lost from the refrigerant, which condenses back to liquid.

Thermodynamically the key thing is the temperature ‘lift’ in the refrigerant between the evaporator and condenser. As users we are interested in the coefficient of performance (CoP) of the machine, which represents the ratio of cooling power out to electrical power in. The theoretical CoP is given by the formula:

Tc/(Th-Tc)

Where Tc and Th are the absolute refrigerant temperatures in the evaporator (cold) and condenser (hot). Let’s put some numbers on this as an example:

1. Chilled water set point: say 6°C. This is self-evidently fixed.
2. Evaporator approach temperature: let’s say 2°C. This is the thing which we might be able to influence by improving heat transfer.
3. From (1) and (2) above we have an evaporator temperature (Tc) of 6-2=4°C or 277K
4. Ambient air temperature: let’s go for 35°C
5. Condenser approach temperature: let’s say 12°C
6. From (4) and (5) we would have a condenser temperature (Th) of 35+12=47°C or 320K

So our theoretical CoP is

Tc/(Th-Tc) = 277/(320-277) = 6.44

(actual CoPs are always lower but that won’t matter if all we want is a comparison)

Now let’s repeat the calculation with an evaporator approach temperature of 1°C instead of 2°C. This means Tc will go up from 277 to 278K and our new CoP will be:

Tc/(Th-Tc) = 278/(320-278) = 6.62

This is slightly less than a 3% improvement,  but even that could well be an exaggeration because it assumes (a) that there was scope to reduce the approach temperature in the first place and (b) that poor heat transfer from the chilled water was the cause. Actually if the chilled water system is clean and properly treated it’s unlikely to be the problem: it’s a closed loop so contaminants won’t be getting in. In fact if the evaporator approach temperature is too high the reason is far more likely to be loss of refrigerant, or unbalanced distribution in the chiller, or oil in the circuit, none of which is affected by water treatment. It follows that if you suspect that your evaporator approach temperature is higher than it should be, look to ordinary maintenance steps first before anything else.

Vendors of additives will point to possible heat-transfer improvements within air-handling units or room air conditioning units. This is a red herring. These don’t affect the cooling load presented by the building, which is entirely and solely dictated by its heat gains and control settings.

Finally if anyone shows you a case study demonstrating an improvement, be skeptical. It’s far more likely they made the gains by cleaning the condenser coils, enabling evaporative cooling, servicing the chillers, or raising the chilled-water set point. These proven solutions are all things which perhaps are opportunities for you to exploit today.

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# “Pants on Fire” award goes to Voltex

See Why Power Companies Are Scared Over This Breakthrough Device That Cuts Your Power Bill By Up To 90%“. Yeah, right. Open up a ‘Voltex’ unit and this what you’ll find: a capacitor. You can ignore the printed-circuit board, whose purpose seems to be solely to power the LED indicator.

Several of my newsletter readers have reported this device to me. Apart from the product being obviously bogus and its claims ludicrous, Voltex’s online marketing is so poor that it’s worth a visit just for a laugh.

• It includes video clips that actually show different products: (a) the Power Perfect Box (probably also a capacitor, but bigger) which is shown needing holes drilled in a wall and a connection into a distribution board; and (b) “Greenwave”, which at least is a plug-in device like Voltex but is promoted on the basis of removing dirty electricity and improving your sleep. I kid you not.
• Look at the photos of Voltex units and you’ll see that they have retouched the wall sockets to look like UK 3-pin ones but of a pattern nobody has ever seen.
• The testimonials from UK customers quote suspiciously-precise savings, but they have forgotten that we don’t use dollars here.

The technology is also supposedly patented – always a warning sign. I asked them for the patent number and their reply was: “the patent is a very complex thing, so in order to be able to sell in multiple places, it’s been decided to risk for the expansion“. What? When I pointed out that this made no sense they elaborated as follows: “For security reasons, we cannot disclose some information related to the product. One of which is the patent number”. So, particularly bearing in mind that they cannot have patented the capacitor, I conclude that there is no patent. They are liars and cheats and it gives me great pleasure to award Voltex the coveted Pants on Fire Award.

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# Generic refutations of bogus products

I have prepared some product category briefings are intended to assist readers who want to reject suspicious product offerings in circumstances where other people in their organisation need to be convinced that the products are worthless.

Supplementary air removal for heating systems (i.e. other than the conventional devices already fitted)

Burner anticycling controls

Magnetic fuel treatment

Super-thin insulation

Voltage reduction (or “optimisation”)

If readers have other product categories which they would like me to add, or specific suspect offerings, please get in touch.

# Energy recovery in lifts

Reader Chris B. had seen someone promoting a product  that could be retrofitted to passenger lifts to recover kinetic energy rather than dissipating it in friction brakes. He wrote to ask if it was a plausible offering.

Certainly there are lift systems that use regenerative braking, that is, motors which turn into generators when switched into reverse to decelerate the descending car. It is a legitimate idea, but usually a feature designed into the installation at the outset. As such it offers other advantages such as reduced heat dissipation in machine rooms. But it’s hard to believe that it would be viable to retrofit an existing installation because the available energy is not as much as you might think, as you can see from this rough calculation making some very optimistic assumptions.

Suppose a lift drops 36 m vertically carrying an excess mass equivalent to ten 80-kg passengers. As gravitational field strength is about 9.8 N/kg its change in potential energy would be 36 x 10 x 80 x 9.8 = 282,240 joule. That’s 282,240 / (3,600 x 1,000) = 0.0784 kWh. If you could harvest all that energy it would be worth approximately one penny. Factor in some more conservative assumptions and realistic conversion efficiency, and the value of the recovered energy is totally negligible.

Why are worthless bolt-on products like this promoted? In the case of products supposedly under development, it is usually to lure naive investors. For readily-available and easily-deployed products like bogus boiler additives and fuel-line magnets, it is to lure naive franchisees.

Learn about energy-saving techniques that actually work at this tutorial: “Energy efficiency A to Z” on 26-27 May

# Microwave weirdness

IN MARCH AND APRIL this year several national newspapers, including the normally sober Economist, carried articles promoting the concept of a microwave central heating boiler which could be fitted in place of a gas-fired one. The same story appeared in H&V News, a trade journal.

The originators’ objective is to promote the idea of decarbonising your heating by substituting (renewable) electricity for gas. The articles compare two options: electrifying your existing central heating system versus installing a heat pump. The latter, quite reasonably, they consider costly and not always feasible. But somewhat disingenuously they fail to mention another electrification option which I’ll come back to at the end.

Now suppose for some reason you did want your radiators fed by an electric central boiler. Why opt for the complexity of a microwave one rather than one based on simple resistive immersion heaters? It makes no sense because either way you can only get as much heat out as you put electrical energy in. Microwave sources confer no thermodynamic advantages. The promoters justify the more complex technology because (according to the account published in the Economist) immersion heaters “…must run continuously to deliver water at a suitable temperature. That often warms water which is never used.” Well, er, no. Immersion heaters would be thermostatically controlled, and wouldn’t consume energy that is never delivered as output heat.

Event alert: “Decarbonising heat: practical realities” on 8 July. Details at https://vesma.com/z200

In the version of the story on the Guardian web site, the company claims that the electrical load “will be about the same as an electric oven”. This also makes no sense. A built-in electric oven might be rated at 3 kW while a central heating boiler could quite typically have an output of around 30 kW and an electric version would need input power to match. Indeed according to the piece in H&V News  these microwave boilers can be up to 60 kW in capacity. And therein lies a problem. Even a 30 kW appliance would need a 120-amp mains supply at 250V, and that’s on the assumption that it is a simple resistive load. To put that in context, our whole house is fed through a 100-amp supply. Microwave units, however, have notoriously poor power factor so will inevitably draw much more than 120A for the same 30kW duty, all of which makes claims of quick and easy installation ring somewhat hollow.

The coverage in H&V News is rich in whizzy-sounding technology and buzzwords. For example it says that the heart of the system is termed a “technology stack”, which they say is a “solid-state, robust RF framework that uses configurable and controllable high performance amplifiers to generate energy”. Elevating the merely meaningless to Olympian heights of drivel.  The version of their story in the Economist includes the bizarre assertion that “the pipes that carry the water are also made of microwave-sensitive materials, as is the insulation that lags them”. Microwave-sensitive? Wait… like lasagne? And if the pipes heat up under microwave radiation what’s the benefit of the insulation doing likewise?

The article in H&V News quotes a director of the company claiming that their electric boiler “would cost the same to run as a gas boiler”. At least the Guardian had the wit to expunge that remark from the on-line version of the article. The truth is, if you want to use electricity for heating and a heat pump is not an option, individual room heaters would be the obvious way to go. Apart from being cheaper to fit than a new electric boiler, they would enjoy the advantage of room-by-room controllability.

# 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 back into the unoccupied space, keeping it at an artifically elevated temperature and losing heat to outside at an unnecessarily-high rate until the PCM had resolidified.

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.

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.

For training on energy management topics see http://vesma.com/training

# 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[1] at the time of writing was a bit more gung-ho about their new battery technology, which they claimed would enable a 5-minute full recharge of an electric car with 300 mile range[2]. 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.

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 (update January 2023: 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 from April 2019 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.

Postscript 13 January, 2023: Storedot hasn’t as far as we know actually released a product yet, but they have opened an ‘Innovation Hub’ in the U.S. Hooray!

[1] The web page that this article originally referred to has been moved

[2] This was in 2019: by 2022 StoreDot’s ambitions were more muted, manifested in a roadmap that would “see the delivery of mass produced battery cells capable of 100 miles of range in five minutes of charge by 2024, 100 miles in three minutes by 2028 and 100 miles in two minutes by 2032”.

# 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.