Elegant solution to supply overload problem, Electric boiler.

MeldrewsMate

MeldrewsMate

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A friend has a flat in Andorra. That's in Abroadland, and he's going to upgrade his supply to 10kW maximum.
Here is a list of the main electrical items:
Electric water heater (1.5kW)
Hob (2 x 500W, soon to be 4 x 500W) Assume 50% diversity, so 1kW.
Kettle (2.2kW)
Washing machine (2kW)
Microwave oven (3kW)
Lighting, TV, other entertainment stuff, computer, etc. Assume 500W.
Portable blower heater 2 x 1kW.

He wants to install an electric flow boiler, maximum demand for this is 6kW.
Clearly a combination of the heating being on, plus the kettle, washing machine, and the other paraphenalia of modern life will exceed his maximum load and, especially at breakfast time, he can predict frequent nuisance trips.
He wants to be able to turn off the heating automatically when the non-boiler loads exceed 4kW, and turn it back on when, say, the kettle has boiled and the load due to other causes drops below 4kW.
He proposes to feed the 10kW supply tails to a new fuseboard, with the electric boiler and water heater as loads (7.5kW max), then take a pair of tails from there to a second 'board with all the other loads connected. A current sensitive relay (current transformer feeding the controls of a relay) will be mounted between the first 'board and the second, set to operate at about 4kW and above (>18A), and the volt free contacts of this relay will interrupt the room thermostat's 'call for heat' signal, thus turning the heating off until the loads fall below 4kW.
He also wants a timing function to delay the switching on of the heating for a few minutes to prevent short term switching due to use of the kettle or hairdryer.

I can see that careful management of the appliances in use would mostly prevent going into an overload condition, i.e timing the water to heat before the heating switches on, delaying use of the washing machine until he goes out, etc., but occasionally the gf comes to stay. She will want the heating on, plus the telly, the hob, and the microwave, plus kettle and toaster, even an extra blower heater! If she trips the supply she'll phone him at work in a mini panic, worse still he's reluctant to show her how to reset the trip because a) it's 3 floors below in a switchroom common to the other 8 flats in the block, and b) he doesn't want to get her into the habit of regularly tripping the supply and resetting it.

Does anyone here know of an elegant way to provide the functionality he wants, without building a custom rig using RaspPi or Arduino? It would be even better if the solution includes a web based interface, so he can see how much load the gf puts on the system while he's out at work!

MM
 
I think you'll struggle for a solution that solves all the problems without going for a Raspberry or whatever poor mans' PLC.
You could set up some interlock type arrangement (where, for instance, if the thermostat controlling the 6kw thing is calling for heat then all other power circuits are disconnected until the thing is satisfied) then have a temporary interrupt (one of those old push button light switches rentals used to have in the communal areas would do- can usually set them from 5 seconds to an hour- via a relay so if she/he wants a brew or whatever then prod the button, supply to thing is dropped, other power circuits re-energised for your preset period). It would be a bit brute force and possibly quite annoying but relatively cheap and easy. Cycling an electric element doesn't have the same inefficiencies as cycling a combustion device so that isn't a big worry
 
oldbutnotdead said:
I think you'll struggle for a solution that solves all the problems without going for a Raspberry or whatever poor mans' PLC.
Click to expand...

I think you're right.

I've decided on going down the Arduino (micro-controller) route. It'll be a bit of a steep learning curve for an old duffer, but that route gives the best flexibility.
The input current will be sensed with a current transformer (CT) on the 'not the boiler' consumer unit, i.e all other loads except the boiler.
Interface the CT with the Arduino, using its ADC (analog to digital converter) to give a signal of 0 to 1000 corresponding to 0 - 40 Ampere.
Create a software trigger point cooresponding to 'maximum allowed load minus 6kW', when this is exceeded energise a relay R1 whose volt free contacts will open the room thermostat connection, thus tricking the boiler into believing the room temperature has been achieved (boiler heater elements turned OFF).
Add an amount to this ADC value equivalent to 1kW to prevent rapid switching of the relay.
When the (ADC value + hysteresis) value drops below the trigger level, de-energise the relay and remove the hysteresis.

That's the barebones logic, or functional design spec. Now all I need is the skills to write the Arduino software, and enough time to faff around with it to tune out the inevitable bugs....then see if I can modify the boiler control to modulate the 6kW heater to allow it to run at reduced power and keep the total load just below the 10kW maximum.

Can anyone here tell me how the Sadia Amptec boiler elements are arranged? Is it a single 6kW, two 3kW elements, three 2kW elements, or something else?
Stay tuned....

MM
 
There is an elegant, but not cheap, solution to this which I used when I lived in France. It's called a délesteur, which translates as 'shedder'. It's role is simply to monitor the total load, in amps, and to shed a non-priority circuit when the total load approaches the limit. Searching amazon.fr gives a fair choice, but you need to understand quite a lot of electrical French to get the best out of the various choices. (By all means try automatic translation in Chrome if you have a good electrical background but not much French.)

Whether this would be suitable in Andorra is another matter. I have some experience of apartments there and many have a 3-phase supply, and quite a lot have no Consumer Unit/Fuse box! (The authorities are trying to rectify the latter over time.) If it is 3-phase, unless he has a 3-phase flow boiler, it would never work anyway, as 10 Kw works out at 3.33 Kw per phase max.
 
I've gone down the Arduino route and successfully built a piece of kit to interrupt the room thermostat when those 'other' loads exceed 4kW (16A)
It's a single phase 40A supply - the maximum he's allowed due to the size of the flat (so many kW per m2 of floor area).
The kit works as it should, the complication being that the Heatrae Sadia control has anti-cycling and soft-start controls built into it, so even a short operation of the interrupt relay means no heating for about 5 minutes - significant if a second and third interruption occur within the following 10 minutes.

Mark II is now being designed, it'll do away with the Heatrae control and use triacs to directly drive each of the two 3kW heating elements, thus a continuously variable output of 0 - 6kW can be controlled. If 'other' loads add up to 6kW the output to the heating will be 4kW, etc.
The safety controls will continue to be used, an overheat 'stat and a flow temperature sensing thermistor., plus a 'desired flow temperature' setting pot.
Mark II will also have a 4 line LCD display, plus thermistors to directly sense room and outside temperature. The present internet connected roomstat will serve as a timeclock/thermostatas it does now.
it's still in the development stage.

Mark III will have a wifi connection so the user can read the actual room temperature, flow temperature, and power output, etc., but the biggest change will be that I would like to extend the control to modulate the hot water heating, which is via a 1.6kW immersion heater. The strategy here is that I would want the hot water to take priority over the heating in the morning; that is until it gets the HW up to 40C or above (just hot enough for a reasonable shower). Once 40C has been achieved I want to look at the room temperature and, based on the rate at which the flat warms up, decide whether to forego increased HW temperature in favour of more power to the heating, and vice versa. Later in the day the priorities will change, as will the relative importance of hot water as occupancy increases!
I'll need to improve my coding skills before that happens...
 
Thats all sounding good, the fun bit will be rendering the multiple inputs/outputs down to if x y z then a...
Does the jobbie control the phase angle on the triacs directly or are you running via some dimmer circuitry (or have you not worked that bit out yet)? If you needed some high power modules you could have a look at 2nd hand theatre dimmers...good work, ta for the update
 
There are devices designed for narrow boats that can combine a grid tie inverter battery and mains supply to reduce maximum load, I think Tesla also do one, but I have found travelling the world where there is a problem they also sell some thing to get round the problem with, so better looking local, as all locals will have same problem so there is likely a local product to get around it with.
 
oldbutnotdead said:
Does the jobbie control the phase angle on the triacs directly or are you running via some dimmer circuitry (or have you not worked that bit out yet)? If you needed some high power modules you could have a look at 2nd hand theatre dimmers...good work, ta for the update
Click to expand...

Further update Oct 2020:
Owner decided to buy a 9kW Amptec boiler, which has three 3kW heaters. I can't pursuade him that 6kW is enough for his flat! What he didn't realise when on test last year (with the old supply) is `11\that the volt drop across the 20 metres of 2.5mm2 supply cable gave us only 190vac at the heating elements, and only about 4kW of heating - and it still got the flow temperature up to 50 Celcius.

The code is written, and barring some minor bugs, will fully proportionally control the 0 - 9 kW heaters (0-8kW with 220vac).
The modulation is by burst fire over a two second period, that's 100 cycles at 50Hz so a 1% control resolution is possible, and an overload for up to 2 seconds is very unlikely to trip the 40A thermal breaker.
The strategy uses two 20A relays, plus a solid state switch for modulation, such that a load of 5kW would be 1 relay (3kW) + SSR @ 2/3 of 2s = 1.33s = 2kW average. The beauty of the SSR is that it has a zero volt crossing switch circuit built-in, and this will reduce RF noise and other interference. The relays will be timed to switch on and off using some zero crossing software detection (what I wrote). The reason for not using 3 SSRs is that they generate more heat in use than a relay...and relays can be manually held on in the case of control system failure!

The LCD display option will have to wait until Mk3; at present the tested prototype is being mounted on some spare uPVC facia cladding before being made electrically safe with a tupperware cover; cutting edge stuff.

MM
 
I'd like to return to the 'wonders' of the Andorran (& Spanish) electricity supply. Are you certain that the supply is monophase? Perhaps it's a more modern apartment than mine, but my apartment in Andorra is 3-phase, 5Kw max (shared over the 3 phases), so tripping occurs when any phase goes over 1.66Kw! My main property is in Spain, where I do have 10Kw but again shared over 3 phases, so power showers are a big no-no (unless I could find a 3-phase one, I guess.)
 
There is also the question of the suitability of the Amptec Boiler for the shower, as it's designed for use with water-based central heating systems, not for showers. The recommended temperature increase across the Amptec unit is 5°C to 10°C with a maximum of 14°C. See https://mediacdn.heatraesadia.com/-...nstallation-manual.pdf?v=1&d=20200521T094429Z
The boilers contain a very small amount of water, and so require a sufficient flow rate of water to ensure proper operation. Insufficient flow of water through the boiler may cause nuisance trip outs. The maximum temperature differential between input and output of the boiler must not exceed 14°C. If the temperature across the boiler exceeds this then the flow rate is too low and will potentially damage the boiler. Set the flow rate to give 5°C - 10°C across the boiler on full heat.

An alternative possibility is the Heatrae Sadia 8.5kW Sapphire Electric Shower
 
satprof said:
There is also the question of the suitability of the Amptec Boiler for the shower, as it's designed for use with water-based central heating systems, not for showers. The recommended temperature increase across the Amptec unit is 5°C to 10°C with a maximum of 14°C....

An alternative possibility is the Heatrae Sadia 8.5kW Sapphire Electric Shower
Click to expand...

You may have missed the list of main items in the first post. He has a seperate hot water cylinder (the French type hung on the wall) with a 1.5 kW electric immersion element, so the shower argument is redundant. Plus he'd have to shower with all the lights off if it were 8.5kW!:ROFLMAO:
The Amptec is simply heating the radiators.

The supply is most definitely single phase, that is two conductors with 230vac between them, and a protective earth.
 
It sounds as if you've finished the work on the main job, but, looking for the 'elegant solution', I'd always go for the French délesteur. I had one when I lived in France and, of course, one could readily be obtained for Andorra. Some French companies will send by post to Andorra as it's treated as part of France for many postal purposes. Alternatively, you can normally get something sent to a relais which is a shop or post office within France where you have a week or so to pick it up. There's quite a good selection on Ebay.fr, where you can pay from about €100 to €600 for new pieces.
 
satprof said:
It sounds as if you've finished the work on the main job, but, looking for the 'elegant solution', I'd always go for the French délesteur....
Click to expand...
Thanks, but that's a decision for himself. My job is to prevent the heating from tripping the supply, and that aparatus is scheduled for a December installation. If he wants to délesteur other stuff down the line he's quite welcome to do so while I'm out skiing at his expense! In actual fact a couple of extra relays controlled by the Arduino could well do a good job of copying the actions that a délesteur would do.

Do they do a délesteur that attaches to the gf's mouth?:censored:(y):ROFLMAO:
 
There are possibly two products along the lines you suggest that would have a worldwide demand: gf's (& wife's) mouth cut-out on overload & gf (or wife) shedder (plain & simple). It must be borne in mind, however, that there would also be massive sales for the masculine equivalents.
 
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