The power of mesh

Two recent manufacturers’ announcements indicate that shortly the Apple HomekIt smart home ecosystem could be getting even more robust. The announcements concern threading which creates a mesh between smart home devices. Apple have announced that the HomePod mini smart speaker will be their first device with threading capability, while Eve have announced that an imminent software update will add this capability to both Eve Door and Window and Eve Energy devices (of which we have six in total now).

The way the ecosystem currently works is that the hubs (of which we have two, both Apple TVs) communicate to each other via WiFi (or potentially wired Ethernet, both in orange) while my many smart home devices typically communicate with the nearest hub by Bluetooth (in dark green). This arrangement works well while both hubs are online, but if occasionally a hub is having issues then some devices are out-of-reach until the functionality of the hub is restored as Bluetooth struggles with the range.

However the new threading capability allows some Bluetooth devices to form a mesh (in cyan) where messages can can be passed by multiple routes from one thread-enabled smart home device to another and not just directly to and from hubs. Non-threading Bluetooth devices can then communicate to a nearby thread-enabled device (rather than a comparatively distant hub) and their messages have multiple alternative paths via the thread-enabled devices to eventually reach a hub.

BLE devices communicating to HomePod Mini hub via thread-enabled devices.

I had previously considered the Eve Extend as device capable of extending coverage to distant Bluetooth devices, but I see threading as much more attractive for me as follows:

  1. Eve Extend is configured to relay signals from a predefined set of devices (which threading does not require pre-definition),
  2. Eve Extend only covers some devices and in particular not my first-generation Eve Thermos (while threading supports any device, although only a limited range of devices form part of the mesh), and
  3. Eve Extend device allocation is fixed (so if the Extend goes down the connection goes down) but threading is dynamic, so if a threaded device goes offline (such as due to a flat battery) then an alternative path may be found via other devices in the mesh.

Eve Extend does however work differently in that it sits between BLE devices and WiFi and could thus extended coverage over a greater distance since WiFi carries further than BLE.

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No fuss fuse

As we look to install a second electric vehicle charger that becomes a challenge for the electrical supply to our home which is limited to 60 Amps. I recently saw a page online by which our DNO (District Network Operator) – UKPN – could be requested to install an uprated fuse.

(Some readers may be curious regarding the irregular size of the hole around the cutout and meter. When we looked around the house I recall reflecting upon the fact that I didn’t know where the meters and consumer unit were. The mystery was explained when we moved in and these items were found to be behind a false wall in what is now my study having previously been concealed by pictures. We continued the practice by buying pictures to conceal three holes in the wall (now four) covering: electricity meter, gas meter and consumer unit (adding generation meter and isolator for solar panels).)

I’m delighted to report how smoothly the change went. I was advised that it might be the case that the work could not proceed on a first visit, and that it might be necessary for my electricity supplier to update meter and/or cables from meter to consumer unit; but the installation proceeded on the first visit with not only the cutout changed from 60 to 100 Amps but also the cables between the cutout and the meter renewed. All of this at a price of precisely nothing.

I had been reasonably confident in the meter as that had been renewed almost exactly two years ago when we moved from Economy 7 to a smart tariff, but I was less clear about the cables between the meter and the consumer unit. In the event all was fine.

The extra 40 Amps should now mean that I have no issues adding a 7.4 kW car charger which draws 32 Amps. I have previously posted about the new car charger. My task of writing the software for it is now considerably simplified as I shouldn’t need to worry about managing the after diversity maximum demand of the house to not exceed 60 Amps, and can concentrate on the other smart controls – tracking my solar surplus and responding to the smart tariff.

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Eve Thermo Versions 1 and 2 compared

We currently have eight Eve Thermo electronic thermostatic radiator valves (eTRVs) in service. These valves allow us to set heating schedules and target temperatures for rooms individually, for example don’t heat the lounge of weekdays before the evening or don’t heat the playroom after the children’s bedtime. All the existing valves are the original version.

However I’ve just bought two more valves with a view to expanding control to the bathroom and ensuite. I want to add these rooms as they tend to be rooms where the windows are left open (allowing heat to escape) and the ensuite in particular is often too hot and difficult to it’s difficult to regulate the temperature as it’s immediately above the boiler. These new valves are the second generation. So what are the differences between versions?

The two versions are very similar if not the same size. The most obvious difference is that the new version has a small display and buttons allowing the temperature to be adjusted. A setup item allows the orientation of the display to be adjusted so that the temperature display is the preferred way up. The display illuminates briefly when the buttons are used to adjust the temperature.

However there are other small differences:

  1. Vacation mode. The older version has a vacation mode for winter vacations when the schedule is disabled, but heating will be enabled below the lower temperature set point. The newer version doesn’t seem to have this mode, so my existing vacation scene sets these individually: mode = on, schedule = off, temperature = 10 Celsius to achieve the same result.
  2. Lower temperature set point. In the older version the minimum possible scheduled temperature stored in a valve was 10 degrees, but a scene could set a lower temperature down to 5 degrees. I use this facility overnight to stop a rarely-used room pulling on the heating overnight in winter while still providing frost protection. However the newer version seems to have a common minimum temperature of 10 degrees. I have thus modified and renamed a scene that previously explicitly set 5 degrees to set minimum temperature, that is either 5 or 10 degrees according to valve generation.

I plan to install my two new valves in the lounge which has two radiators, and use the displaced older valves in the bathroom and ensuite.

After installation we’re now up to 10 eTRVs divided between 8 rooms (bathroom, cloakroom, daughter’s bedroom, ensuite, lounge x2, master bedroom x 2, playroom and wife’s study). Most of these rooms have individual schedules; while bathroom, cloakroom and ensuite heating is on when any other room heating is on. The latter also have window sensors and are disabled while the window is open, while the lounge also has a movement sensor which curtails heating in the evening if no movement is detected (which otherwise provides heating for my wife’s late film viewing).

Valve position for the ensuite eTRV.

The image above shows the operation of the eTRV in the ensuite which was previously the room with the greatest difficulty in maintaining an appropriate temperature – often being too hot as almost directly above the boiler. Here we can see brief morning openings and much longer evening openings on weekdays, and heating all day on Saturday. In all cases the valve initially opens wide (60-80%) to warm the room up, and then gradually closes over time until the temperature is maintained with a relatively small opening (~10%).

The system has several modes:

  1. Summer – which provides temperature monitoring, but no control.
  2. Vacation – which provides minimum temperature control, but no schedules.
  3. Winter – which provides temperature scheduling with two schedules available – one for working days and one for non-working days (not necessarily weekdays and weekends) selected from a standard Apple calendar.
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Automations in HomeKit

Last night I was refining some of my HomeKit automations (rules) and it occurred to me that it might be an idea to capture some tips from the last few years.

HomeKit versus HEMS functions

I currently have around 30 automations delivering:

  • Space heating – 8 eTRVs / smart valves linked to a smart plug for boiler control and both movement and window sensors.
  • Window management – 4 window sensors and a movement sensor indicating via colours smart bulb when windows are left open (typically checked prior to leaving the house)
  • Lighting control – dusk-to-dawn lighting with colour-override by window management.
  • Watchdog – robustness aid.
  • Wet goods – control and dishwasher and washing machine in conjunction with HEMS.

In total I currently have:

  • 8 smart radiator valves (eTRVs)
  • 6 smart plugs
  • 4 door / window sensors
  • 3 smart bulbs (two coloured + 1 on/off)
  • 2 movement sensors
  • 1 environment sensor (temperature, humidity, air quality)

So, what are my tips:

It Is much more intuitive to write rules in the Eve app.

  • The free Eve app can pretty much do everything that Apple’s own Home app can do for HomeKit devices (not just Eve’s own devices). The construction of rules in the form: IF {any of one of more triggers} AND {all of none or more conditions} THEN {set one of more scenes} is very intuitive in the Eve app.
  • Eve also allows rules to be names, whereas Apple’s own Home app sets names to a trigger condition, so if you have many rules as I do with common triggers then you end up with a confusing list of rules with duplicates names which need to be opened to tell one from another.
A rule in the Eve app.

Comparison with conventional logic. Simple IF rules are very straightforward: IF {any of one or more triggers} THEN {set one or more rules}, however AND rules take a bit more thought: IF {list of AND conditions} AND {same list of AND conditions} THEN {set one or more scenes}.

A watchdog makes execution more robust. HomeKit rules are triggered by changes of state such as going from open to closed or from movement to no movement, but if some some reason a trigger is missed you may have the wrong scene set for hours. My watchdog rechecks rules every 5 minutes as described here.

AND rules. AND rules may be converted to use the watchdog principle by simply adding an additional trigger to reference the change of state of the smart plug used for the watchdog: IF {original list of AND conditions + new smart plug trigger} AND {original list of AND conditions} THEN {set one or more scenes}.

Simple IF rules. IF rules with single triggers are easily converted. The same principle applies to AND rules: If {original single trigger + new smart plug trigger} AND {original single trigger} THEN {set one or more scenes}.

Complex IF rules. IF rules with multiple triggers are more involved to convert to the watchdog principle. If you just add the smart plug to the trigger list as per the earlier AND paragraph then the rule triggers every time the smart plug cycles. If you were to add the other triggers to the conditions list then the rule would become an AND not an OR. Instead to convert an IF with multiple triggers then it needs to be converted to multiple rules – one for each original trigger condition – all driving the same scene. Each of the new rules is an IF with a single trigger as per the earlier paragraph. The existence of multiple rules setting the same scene(s) creates a multiple-trigger IF.

Multiple hubs. Having multiple hubs (in my case two Apple TV’s) can make the system more robust both during occasional software updates (it’s improbable that both will update simultaneously) but also by extending Bluetooth robustness (hubs commonly communicate to devices by Bluetooth but between each other by WiFi). Obviously the hubs need to be placed in different parts of the home. (Eve Extend can also be used to reach out-of-range Bluetooth devices over wifi, but isn’t compatible with my older 2015 Eve Thermo eTRVs.)

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Contrasts in Smart Lighting

We recently enjoyed a week’s holiday at Pevensey Bay. The home that we rented, like our own, includes many smart features but there are some similarities and differences in approach. One area of difference in smart lighting.

The Studio, Pevensey Bay

Both our own home and The Studio have smart lighting but differ in approach. Our own smart lighting concentrates on smart bulbs, while The Studio (with the exception of the kitchen) concentrates on smart switches. So why choose one approach over the other?

At our home we have a handful of smart bulbs, with standard dumb switches. The bulbs incorporate functions like dusk-to-dawn lighting and colour change for status indication (open windows, movement in garage etc). At The Studio there are a large number of smart switches controlling an even larger number of standard dumb bulbs.

So let’s think about choices:

Cost.

If you are going to control multiple bulbs together on one circuit then it’s generally cheaper to have one smart switch than multiple smart bulbs.

4 gang Lightwave switch

Coloured smart bulb

Colour.

Smart switches can either control on/off or act as dimmers, but they don’t vary colour. Some smart bulbs can vary colour. If you want to control colour then you’re going to need some sort of remote control (like The Studio in the kitchen) or access via smart device like a phone or tablet.

Wiring.

Most smart light switches require a neutral wire. However many UK homes do NOT provide a neutral wire at the switch. A typical UK light switch has a live, switched live and earth only (I.e. no neutral) although there may be confusion as the switched live is commonly blue (or black in older homes) like a neutral would be.

Adding a neutral can be relatively costly as it requires a new cable between the ceiling rose and the switch. If having a re-wire it’s worth adding neutrals to the specification just in case.

Typical ceiling rose wiring UK.
Example automation

Automation.

Both switches or bulbs can be automated via a smart hub for on/off or brightness to respond to time-of-day, movement, door or window opening etc; so that’s not really grounds to chose between smart switches or smart bulbs.

What about combining smart switches and bulbs on the same circuit?

In short I don’t really know why you’d want to. Even if it worked properly you’d have incurred extra cost for the second smart device for limited benefit as you’ve duplicated the smart functions, but it’s likely not to work properly. Even with simple on/off functions the smart bulb will be missed by the hub when the power is off at the switch (although some ecosystems allow this error to be masked), but with dimmers it will probably be worse as the bulb may not function correctly when the dimmer is set to less than 100% brightness.

You might consider using the smart switch as an smart button without using the switched output, and feed the smart bulb from a permanent live, but that’s not combining them on the same circuit. This could be achieved physically by something as simple as moving the switched live output to the live input on a switch. However the two smart devices, switch and bulb, would then need to be linked entirely programmatically through the hub. That would be at least two automations in HomeKIt – an ‘on’ automation and an ‘off’ automation.

Conclusion

There isn’t a right answer whether smart switches or smart bulbs are best. The best choice will depend on your situation.

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Inducted into the hall of fame

One of the features of our home is the all-electric kitchen. We do have gas for space heating and as a back-up on the hot water for days that are both dull and have relatively high cost electricity, but the kitchen is all-electric. I have to say that this was not our choice, rather the kitchen came that way when we bought the house five years ago. We have replaced the oven in the meantime, but until today the hob was that bought with the house.

Unfortunately the hob suffered a failure of the two of the rings and today we’ve replaced it like-for-like with a new inductive unit. Inductive is attractive as it’s relatively efficient, but I was struck by the fact that the one hob required a 32 Amp supply, but the new one manages with a 13 Amp plug.

Bosch PUE611BF1B inductive hob.

So, by what magic does the new hob use less than half the power of its predecessor?

itemold hobNew hob
Smallest ring1,200 Watts1,400 Watts
Second smallest 1,400 Watts1,800 Watts
Second largest1,800 Watts1,800 Watts
Largest ring2,200 Watts2,200 Watts
Total *6,600 Watts3,000 Watts
Tabulated of maximum non-Boost power per ring with manufacturer’s total

The first thing to observe is that the sum of the ring powers does not equal the manufacturer’s total for the new hob, although it does for the old hob. The second would be that the sum of the new ring powers at 7,200 Watts is more than the sum of the old ring powers even though the required total is less!

The answer is that the new hob features power management capability. In any hob the rings will spend much of their time cycling on and off to maintain the required heat. In the old hob all the rings might on at one time drawing maximum power, but a few moments later they might all be off. However the power management in the new hob the total power would be levelled out so that the average over time might be the same, but the peaks smaller and the troughs shallower.

For most people this levelling out of the power demand would pass unnoticed, but for us it could be quite useful.

We do most of our cooking in the evenings for which, particularly in winter, power is taken from our Powervault storage battery with any excess from the grid as illustrated by the series of evening spikes in the image to the right. The Powervault has a relatively limited maximum power (hence the spikes) but as the new hob has power management then any spiking beyond battery maximum power capability should be reduced thus avoiding what, for us, could be peak rate electricity at 35 p/kWh on our dynamic smart tariff which is a direct cost save.

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Charger two – updating the hardware

Well, it had to happen. After thirteen-and-a-half years of ownership of a plug-in vehicle we’re about to have two. I have had two briefly before during a vehicle changeover having bought a new one and then sold the old one privately, but now we’re replacing the hybrid that my wife generally drives with a plug-in hybrid. Not only will that give us two plug-in vehicles, but in the six years that I’ve owned the Ampera the standard inlet connector has changed from 5 pins to 7 pins so I can’t charge the new car on my existing smart charger either.

Stepped Mode 3 EVSE in consumer unit case

Most people of course will be content with an off-the-shelf charger, but I had some family uniquely requirements. One of the requirements that influenced my original charger was solar self-consumption (the charger automatically turns on when the home is in sufficient solar surplus) but this is now available commercially. My existing charger also adjusts its charge times around the Agile electricity tariff but this too is now available commercially with Ohme. However I still want to be able to coordinate it all centrally via my HEMS so that I can prioritise loads when constrained, or enable interactions like stopping the fixed battery discharging into the car at night and that’s not available commercially.

My solution is similar, but different, to my old charger. Both are modified from existing production chargers as a relatively affordable source of parts, but the new one will retain the production case (because it needs to be waterproof for outdoor use) and be better protected electrically than the old one. It needs to be better protected as electrical standards have moved on and, being outdoors, it needs to be more sophisticated to make up for the UK’s somewhat unusual earthing system (at least by international standards). It will also be smarter, but that will be described in later posts.

The most common earthing system in the UK involves a cable between the home and the substation called a Protective Earth Neutral (PEN) conductor which, as its name implies, provides both the neutral and earth on a single core. Remember PEN as it will come up later..

My new charger will also be higher power than the old one. The old one is designed for 10 Amps continuous grid load (16 Amps peak from solar) based on the limitations of my garage supply, but the new one is designed for 32 Amps continuous load in anticipation of a future fully-electric vehicle. I have owned a fully electric vehicle previously, but for the moment both our vehicles will be plug-in hybrids. Some would argue the case for one being an Extended-Range Electric Vehicle (E-REV) or Range-EXtended Battery Electric Vehicle (REX BEV).

The two internal pictures above show a similar production charger alongside my updated charger. The differences are (from top to bottom):

  • RCBO (combines over-current and residual current detection) – is actually carried over donor, but my charger came with a later model than the similar charger illustrated.
  • Earth terminal – I relocated from centre middle row to right top row to make space.
  • Residual Current Monitor (RCM) – The RCM (a small black box which encircles the live and neutral) sits behind the RCBO and triggers shutdown in the event of a D.C. fault.
  • PEN Loss Current Transformer – between the top and middle rails a small black ring sits around the earth cable. This is similar in principle to the RCM but rather than detect a D.C. fault on the supply, its role is to detect a fault current to earth. That’s not enough alone to provide PEN-loss detection alone but provides additional detection to that in the Protocol Controller (which we’ll get to soon).
  • Power contactor. The second rail starts on the left with a power contactor which disconnects the live and the neutral from the car when not charging. Mine is similar to the Rolec original, but smaller,
  • Switched Protective Earth (SPE) contactor. In the centre of the unit sits a second similar contactor, only this one switches the earth. Switching an earth is unusual but is required to protect against a failure of the PEN conductor between home and substation. The power contactor will not close and the car will not charge if the SPE is open with the result that the car is completely isolated from the mains supply during this failure mode.
  • Protocol controller. To the right of the centre rail is the protocol controller. This replaces the the original protocol controller which was in a similar position. The fundamental need to change was driven by the requirement to vary the charge current dynamically, but the new protocol controller also monitors not only the two current transformers (RCM and PEN-loss) but also the supply voltage in order to decide when to open the SPE contactor.
  • Raspberry Pi. At the bottom is an empty Raspberry Pi case to illustrate the sufficient space is available. The actual Raspberry Pi will be smaller. The role of the Pi is to tell the protocol controller how much current should be drawn. The Pi will tell the protocol controller via an analogue voltage, and the protocol controller will tell the car via a Pulse Width Modulated (PWM) signal – that is the width of a stream of voltage pulse indicates the current that the car should draw. The replaces the Programmable Logic Controller (PLC) and RF Solutions radio link in my older smart charger.
  • LED leads. At the very bottom 4 leads with red connectors leave the picture on the left which go to an external multicolour LED for charger status. I haven’t yet decided how to reproduce this. The donor LED is unsuitable as it only has three colours (Red, Green and Blue) but the protocol controller assumes that two further colours (white and purple) are also available,
ItemMy original smart chargerNew donorMy New smart charger
SwitchDouble pole+ RCBOc/o from donor
RCM CTNoNoNew
PEN-loss CTNoNoNew
Power contactorYesYesYes
SPE contactorNoNoYes
Protocol controllerViridian v1.0
(variable current)
Rolec
(fixed current)
Viridian v2.0
(variable current with extra safety content)
Smart controllerProgrammable Logic Controller (PLC)NoRaspberry Pi
External communications Radio (RF Solutions)NoWi-Fi (Part of Pi)
Status LEDLED on protocol controller visible through clear cover.External LED.
No LED on protocol controller.
External TBD.
LED on protocol controller (not visible).
Comparison. between my existing smart charger, new donor, and new smart charger.

The new hardware will thus shutdown in the event of the following faults:

  • Over-current
  • Residual current (live – neutral)
  • DC current *
  • Earth leakage current *
  • Over-voltage *
  • Under-voltage *
  • Inferred PEN loss *
  • Lack of earth continuity between vehicle and wallbox

* These are additional protections in my new hardware that weren’t present in the old one.

At this point I should have a working dumb charger with 32 Amp capability, albeit that it’s untested as yet through lack of a compatible vehicle with a Type 2 vehicle inlet.

There are two items for which I’m awaiting delivery. Firstly I’ll be using a Raspberry Pi Zero to generate the current demand signal which will replace the empty black case in the picture and secondly I have a small 5V power supply on order to power that Pi.

Future posts will look at adding the smart controls.

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Assault and battery

Like many households we actively embrace recycling, sorting our routine household waste into (i) garden and kitchen waste (i.e. uneaten food), (ii) glass (jars, bottles etc), (iii) other recyclables (paper, card, tins, some plastics) and (iv) non-recyclables. Other sorts of waste can be returned to the recycling centre including (I) electrical and electronic (WEEE), (ii) batteries, (iii) used oil and (iv) wood. This post concerns batteries.

The 3Rs: Reuse, Reduce and Recycle

Like many households with small children we have many batteries in use in toys as well as in items like TV remote controls, burglar alarm sensors, and the doorbell. However we also have dozens in smart home devices like radiator valves and sensors including window, movement and environmental. Of the 3Rs of Reuse, Reduce and Recycle we are clearly far from Reduce.

Recycle is clearly possible with many supermarkets adding bins to collect used alkaline batteries which at least prevents that material going to landfill, but does involve energy and other inputs for recycling.

The alternative that I’ve been exploring for some time is Reuse. The closure of the Maplin chain in early 2018 prompted me to acquire some discount Nickel Metal Hydride (NiMH) batteries in both AA and AAA sizes and a suitable charger from my local store’s clearance sale. These batteries are the same size as the mostly commonly used alkaline batteries but have a slightly lower voltage being 1.2 Volts rather than 1.5 Volts.

Different battery sizes compared

I’ve been running these NiMH cells of AA size in Eve smart home devices for two and a half years gradually replacing alkaline batteries as they became exhausted. My only issue has been that the low battery warnings on the Eve devices are almost always set since the batteries have a lower voltage even when full, even though the batteries have plenty of power to run the device. One thus cannot rely on the low battery warning to flag the need to change the batteries, and so I have adopted a pattern of swapping freshly recharged batteries for part-discharged batteries on a quarterly basis. Over the first weekend of the first quarter I work my way around the house room by room swapping and recharging batteries.

After two and a half years I’ve acquired multiple types of rechargeable NiMH batteries from different brands or of different capacities. I make a habit of charging and using only like cells together.

So far I’ve had no failures of rechargeable batteries.

The latest change is that I managed to locate a rechargeable replacement for the 1/2AA non-rechargeable lithium batteries used in the door/window sensors. These 1/2AA batteries are half the length of a regular AA battery, but are 3.7 Volts rather than the 1.5 Volts of an alkaline cell. The voltage of these rechargeable cells is the same as the standard non-rechargeable equivalents so hopefully the near-continuous low voltage warnings can be avoided.

1/2AA batteries with Lithium-based chemistries are commonly described as being of size 14250 – that is a diameter of approximately 14 mm and a height of 250 1/10ths of a millimetre (I.e. 25 mm).

Next time a door or window sensor battery requires changing I’ll be able to put these to the test.

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Tapping the Admiral

I was recently amused to see a smart home feature in a television advertisement for Admiral Insurance. In that advertisement George the householder meets The Admiral outside the local bistro and, as the day is set to be warm, decides to turn down his smart heating from his smart phone.

George and The Admiral

Unfortunately George manages to hit the wrong button on his smartphone and instead of turning off the heating manages to open the garage door.

An unfortunate chain of events

The opening garage door hits George’s red car, which hits the yellow car, and pushes down the boundary wall onto the road. George witnesses all this as it turns out that the bistro is on the opposite side of the road to his home, so has a go with another button.

Sprinklers on

George’s second attempt at adjusting the heating is no more successful as he manages to turn the fire sprinklers on which floods the house. Hopefully George has more than just multi-car Insurance.

So, besides amusement, what else might we gain from George’s issues?

  1. Firstly, I’ll observe that in my home you can put the whole heating system into summer which disables heating completely (such as in the summer), or vacation which disables the schedules but which continues to heat as necessary to maintain a minimum temperature (such as winter frost protection), or turn off the radiators in individual rooms, or turn down the temperature until such time as the schedule turns them back up.
  2. You don’t always get many characters to label a device or scene, but it does need to be clear what function will be achieved by pushing the button. (I find rules particularly frustrating in the Apple Home app as you can’t name rules and it becomes hard to distinguish between them, although Eve’s app which edits the same rules does allow naming and is much clearer for programming rules generally. The WIFIPLUG app also allows the button to be customised with a photograph of the appliance which is quite neat.)
  3. Devices like garage door openers can be linked to safety interlocks. I don’t have one myself but you can have a light beam, for example, across the doorway so you can’t close the door when obstructed by a car. I haven’t come across an interlock which ensures that the car is far enough from the door to allow opening, although in reality I think that a domestic car door opener would likely stop when it touched the car, detect an over torque / current condition, and then automatically reverse.
  4. Finally I think that smart home systems would benefit from a configurable ‘Are you sure?’ question to double-check that the user really wanted to perform some potentially damaging action such as open or unlock a door.
Click to play the advertisement

(Tapping the Admiral is a nautical expression referring to being prepared to drink anything alcoholic rather than be without a drink, notably including drinking the contents of the barrel in which the body of a recently deceased and pickled admiral was being carried.)

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Leading the charge

Regular readers will know that my Energy Smart home includes a storage battery. That battery is either charged from my solar panels (effectively free electricity), or low cost electricity bought from the grid, or some combination of the two depending on the solar forecast for the day ahead.

The logic of how much battery charging is required has until now been driven by a set value for the number of charging hours required. The number of hours of solar charging predicted is deducted from the the number of charging hours required to calculate the number of bought charging hours required outside the solar production window.

Bought charging hours required :=

Total hours required – Solar hours predicted

However with experience this appears to be a sub-optimal arrangement. At one extreme on a very sunny day the battery will fully charge and then be allowed to discharge continuously through all other hours, there is no middle ground in which the battery is not permitted to discharge through the night. However at the other extreme if the battery is replenished entirely from the grid then there will be hours when discharge is not permitted since, after accounting for cycle efficiency, the value of the electricity in the battery is higher than the cost of that from the grid and thus it’s better value to use grid electricity than stored electricity. As there are fewer discharging hours then fewer hours of charging will be required to refill. Thus the depth of discharge is greater when charged from solar than from the grid requiring more charging hours to refill. Leaving the longer charge time for a full charge in use then creates a risk of charging the battery when the grid price is higher than necessary leaving the battery possibly full by the time the lowest cost grid energy is available. Having a more accurate target for the charge time would enable the lowest cost charging periods to be selected more precisely.

Schedule with some solar

The new refinement is to automatically adjust the bought charging hours between two existing user-defined values: the existing target hours and the maximum charging hours currently used just to cap charging hours during plunge pricing events (i.e those with negative cost events). The new algorithm can adjust to any value between the two limits in half hour intervals. As currently configured that’s anything between five and seven hours. The new algorithm is:

Total hours required := minimum (Maximum hours from plunge,
maximum (Target hours, Solar hours predicted + 1))

max hours (A)Target hours (B)Solar hours (C)C + 1Max (B, c+1)Min (A, Max(B, C+1))
7.05.0>= 6.5>= 7.5>= 7.57.0
7.05.06.07.07.07.0
7.05.05.56.56.56.5
7.05.05.06.06.06.0
7.05.04.55.55.55.5
7.05.04.05.05.05.0
7.05.0<= 3.5<= 4.55.05.0
Output of new algorithm,
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