TerryE

or stick some instrumentation on the SunAmp that is still working to work out its operating characteristics Taking the element out of the SA is going to be a total PITA.

@joth, This struck a cord for me and something that I leant through my slab modelling. I described in this in my blog post Plumbing Design – Part II, and which incidentally has been supported by 2 years of actual data on slab performance. If we want to limit the output temperature of the inline heating element to say 75°C, then from "cold" the PCM cells will be in solid phase and may 30+°C colder than the circulation input. The phase transition alone from melting the salt will absorb the full 2.8kW output of the element. The cells will reach thermal equilibrium at the melt point of around 58°C (is that correct @Nickfromwales) with the absorbed heat melting the salt and changing the % liquid. At some point the % of solid salt and the melt rate will be such that for the flow rate of the pump, the cells will be incapable of 2.8 kW without the return water temperature rising to the point for the flow rate where the output from the element will rise above the 75°C maximum target temperature for circulation. At this point we have a number of heating strategies: Stop heating and accept that the cells are only charged to say 80-90% of thermal capacity. Modulate the heat output of the element down and in practice this means some form of PWM modulation. OK, the modulation epochs used to control something like a stepper motor aren't needed, but we do need to keep the temperature ripple on the circulating water within some form of tramline, say <5°C. I need to do the sums but the on-off cycle is probably in the 10s of seconds rather than sub-second or super-minute. Case 2 makes using a relay a no-no, IMO, and pretty much mandates the use of a zero-crossing SSD. The pump relay is only switching a few times a day and is carrying maybe 2-300 mA so a relay would work OK here. @JSHarris would you agree with this?

@Gooman, I tend to buy my Wemos modules in batches of 10. This is my favourite as well but I am a bit biased since I am on of the lead developers for the NodeMCU Lua firmware for the ESP8266 and ESP32 modules.

Nick, have a look at the video tear-down that linked to above. The control side of the SSR is opto-isolated from the power side. You just need to drive the SSR with TTL level signals, can use something like an MSP23008A 8 port multiplex and drive this using I2C from an RPi. Darlingtons are really used to protect / drive larger currents, e.g. DC input contactors typically use 12V or 24V DC. For <16A you might prefer to use SonOff devices discussed above. You can reflash the propitiatory onboard firmware wit Tasmota (various how-to YouTube videos available). If you have low power stuff then you can buy opto-isolated 12,4 and 8 relay boards that you can drive direct from your RPi GPIOs. For an extra £5-10 you can get the equivalent with a USB interface.

Maybe in some future we might have all devices publicly addressable everywhere, but I am a bit more paranoid. Only my HA system can talk to my devices, and if I want to talk to them or allow them to talk to me then this all goes through the HA system.

@MikeSharp01, This is really the subject of a separate boffin's topic but I really dislike the whole concept of allowing any global access to or from IoT devices. The vulnerabilities are just too great IMO when you aren't using a proper locked-down OS. I far prefer the concept of all my IoT devices being on a private dedicated control LAN and the only device which bridges to the general LAN is some locked down trusted device such as the HA system. I feel that HTTPS is just the wrong protocol because whole issue of certificate negotiation / validation is difficult to implement within a private LAN and the whole mbedTLS stack is just far too bloated in terms of RAM requirements for the current generation IoT devices. In terms of isolation all current (respectable) SSRs and most relay modules include opto isolation. I also socket my MSP23008A's making them trivially on-site replaceable. I've also played around with ULN2803a's which are a nice packed Darlington implementation. Have you though about any preferred relay module alternative to SSRs?

My topic, SunAmp PV spares and maintenance issue, has triggered a couple of classic "Boffin's corner" discussions for me. and the first is "What is the best way to switch power circuits using Arduino-class modules? If we assume a 240V/16A resistive load as the target of control, then this is well above the power rating for the range of low price I2C / USB / TTL relay boards that are typically rated as around 1A operating current at 240V AC. My personal preference is to have a clear separation between the control side which is typically at 5V or less -- but anyway at a max current and voltage rating where there isn't an electrical safety issue -- and the 240V side which needs to conform to BRegs for electrical safety. I can see two separate approaches here: The first is to use CE-approved off-the-shelf products to do the power switching. An example here (though possibly not the best) is the Sonoff TH16 series IoT relays. The advantage of this device is that proprietary control software can be easily replaced with Tasmota or your own control software and typically implementing a MQTT control protocol. This also means that the device can also be directly controlled by your HA system. The second is to use a quality CE-compliant module that is TTL controlled. I've use DIN rail-mounted Crydom SSRs for my current control system and I am considering switching to their panel mounted equivalents. Devices which accept TTL signalling levesl make interfacing these to an IoT processor straightforward. Even though many ESP and Atmel devices can't provide 5V 50mA outputs, my approach here is to use a MSP23008A I2C to 8 TTL port chip which can be controlled by a <10mA 3.3V I2C input and this can output at the TTL levels needed to operate the SSRs. For those interest BigClive give a teardown of an SSR on YouTube (this is flawed cheapie, but this videos still explains how they work). SSRs have a lot of advantages for power switching but the big downside is the need for thermal management. They give off roughly 1W / A switched or ~12W when running a 3kW resistive load, but if you are radiating this from a 300×600mm panel then this panel needs to be roughly a Δt of 10°C above ambient to dump this heat radiantly. You can get 16A rated relays and contactors and switching resistive loads is a lot more benign than inductive ones, but you still need some spark suppression circuitry around the relay and most relays need a reasonable power to operate, but you can get 16A relay modules such as this one which contains the extra protection circuitry on module , though I don't know how good they are. So what are views of other boffins in this area: @JSHarris, @Ed Davies, @ProDave, @PeterW, @MikeSharp01 for example?

If you've got the space and don't mind the extra heat losses then a TS is probably the simplest and most robust solution at the moment. Given that you are only using the water as a thermal capacitor, I can't understand why they have to make them cylindrical, and they don't need to be pressurised. Why not a cube something like this that you bury in the garden lagged with 150 mm of slab PUR? Do the sums and it's daily heat loss would be less than 1 kWh -- that's a lot better than most TSs and you could always stick a greenhouse on top of it With a small rocket stove in the greenhouse. Back to reality ...

Thanks Jeremy. We've got to catch up anyway.

It's the latter Ed. Rather than connecting to some help agent who might give you the bum's rush, I thought that Nick or Jeremy might have the direct current contact. I haven't spoken to anyone in SunAmp since Jan 2017. The current system is based on an RPi + SSD with two USB serial connected ESP8266s doing the sensor collection and relay control, so it is independent of the IP network. However, after a couple of years running, I've decided that in terms of timeliness Internet access is more critical to the house occupants than control of the SunAmps. (It took us days for us to realise that one of them had failed. Ditto for the slab which we heat overnight. I posted separately about once where I had a failure in the Wills heating and the slab heating was off for a day in November IIRC; the house cooled down by about ½°C during this outage.) The way that I demand any heat (whether SunAmp or Willis) is that the maximum on-time request is 35 mins and the so the HA system reissues the on commands every 30 mins as needed. This gives a reasonable fail safe: if the HA fails then the ESPs will shut down after 30 mins or so. Minute-by-minute control at the HA level isn't needed. The biggest source of outages since we've lived in the house has been power cuts. (We bought AEG ovens for our kitchen, and the small Microwave / grill /oven was a piece of junk that kept tripping the power, so we've since replaced it with a Bosch.) The RPi was OK, but everything else would die because the kitchen and utility are on the same RCB in our power distro box. My current thinking is to keep all of these control devices on a private control WifiLAN: the HA RPi is gigabit-connected to the house switch, and I'd use static IP allocation for the control LAN on a private SSID with the RPi running hostapd. I don't need to set up routing tables in the RPi, since by design my control ESPs only communicate with the HA mothership. I've got a spare RPi, and ESPs so everything is cold-swap repairable. The control system will keep running if the rest of the house or BT OpenReach network infrastructure fails. This will be no less reliable than the current setup.

Nick, they were installed an 17 Jan 2017, but apart from sharing my good experiences on the forum, I've not had anything to do with the company itself, so perhaps you might have a bit more leverage so thanks very much for your kind offer of doing the contacting. Having a replacement / spare controller would avoid me doing one of the options below The cell is themselves as a simple as can be: about the size of a 20 ltr Jerrycan, with water in & out at the top and a safety vent on the other side. The heater and mechanicals should have a 10-year life at least. The weakness is the control board and especially those these budget mechanical relays. Other than the relays, the main design weakness on the boards are the couple of chunky electrolytic caps on board which (depending on quality) tend blow or leak in that 10-year time frame. I've been brooding about this, ILS and reliability. Sorry ILS - Integrated Logistics Systems and probably JSH is the only other sad fart on the forum that I could had this conversation with. The military were into this stuff 40 years ago and probably still are: how you repair and maintain kit in the field; when you repair in place, when you junk and replace, when you sap out and send back to central maintenance for repair, etc. The current wave of consumer devices don't even think about such stuff any more: if its broken then get junk it and get the latest model. But for me as an end-user, I don't want to be out of water or heating for weeks just because some manufacturer has declare a model end-of-life. Parallel failure modes are good; they give you a step improvement in MTBFs. Serial failure modes just make things worst: example a single engine plane and the engine fails -- you are going to come out of the sky and you might get out of with you life. A twin rotor Chinook is far worse - either rotor fails and you are going to die, but with a twin engine plane when one engine fails -- you will need to land at a nearby airfield (though the latest twin jets such as the 777 have can an ETOPS rating of over 300 which means that "nearest" can be 5 hours flying away.) So having twin SunAmps means that I can risk taking a month or so working out the best approach. (I also have one working system to instrument and to work out the operating characteristics.) By way of another example with our UFH: having an ASHP + Willis means that neither system is critical. Back to the SunAmp, my preference would be switch the 240V AC with a couple of panel mounted Crydom SSRs which can be driven by a 50mA 5V TTL input. Field replaceable on failure. These and everything else could be driven by my favourite ESP8266 or ESP32 and could configured as MQTT clients driven directly by my HA system, and this would also simplify my central panel as these would now be always-on devices from a power distribution PoV with no active control functionality.

I am not really comfortable poking around a PCB blind when it has 240V tracks on it

which why I prefer socketed or Din-mounted contactors. Line replaceable parts. As far as BITE goes, I see that the board has a couple of UART jacks as well as the SMS interface, so something should be possible, though I am not sure how it could self diagnose a relay failure. . Even having a test point to allow you to probe the relay demand inputs would be nice.

Yup I thought about that which is why I measured the resistance across the switch and the heater -- which gave 18Ω rather than open circuit, which would have been the case if the switch had tripped.

The low hanging fruit here is your air leakage. I you are going for Willis backup then it makes sense to use 2 in parallel; if your are using E7 then you can shift the bulk of your heating to overnight window. But 10 kW should be fine, IMO.

The back story here is that I was one of the SunAmp early adopter buying and self-installing 2×SunAmp PVs rigged in parallel and heated by mains E7 electricity. I have been very happy with the product and I did not see the need to change to the UniQ range as I expected at least a 10-year operating life. A couple of day ago, Jan noticed that the HW isn't running too hot at the mo. Checking through my HA data logs, one of the SunAmps failed about 10 days ago, and cooled down over a couple of days. So we were mixing roughly 50:50 60°C:20°C into our HW manifold -- which is at about the temp we shower at in our warm climate, hence our not noticing. So I opened up the unit and did some diagnostics. The line through the inline heater and thermal cut out is reading 18Ω which is nominal for 240V 3 kW heater, so this isn't a heater failure. The two thermistors register the same resistance; I don't know what the part no is but since they are within 1% of each other, I suspect that they are fine. Power is arriving correctly to the control board, but and it seems to be sequencing the pump fine. It just that the 12A 240V heater O/P isn't turning on. So I suspect that the power relay has died and since this a soldered-on component then it is time for a controller board change, IMO. So Q for @Nickfromwales, @JeremyR etc. do you have a SunAmp contact that I can discuss getting a now controller board from. Overall I am impressed by the internals of the unit apart from a few quibbles and one more serious concern. The quibbles are about the layout of the pipe runs in the head -- for example replacing the inline heating element would be a pig to do -- but this is the sort of issue that could be expected from early iterations of the product. My greater concern is the controller board design. There seems to be what I would regard as inadequate isolation between the 240V and low voltage areas on the board. Not good. They've also seemed to have use the same budget relay for switching the pump and the heater. Even though many of these units are nominally rated to switch up to 12A at 240V, this is at the limit of their operating range. Switching AC at the power is really hard on the relay contacts and so these tend not to have a good operating life. Whilst this might be acceptable in a low cost easily replaceable unit, it is not in the critical control board of an expensive piece of kit. Jeremy and I have discussed off-the-self vs. self-built trade-offs but my concerns here are: What is the realistic life of such a board? How long will they be obtainable given that the product is past end-of-life? Will SA require some price prohibitive replacement cost / installation cost? I am loath to go to the hassle of replacing what seems to be excellent units because of design flaws in a controller board. My fallback would be to swap out the controller entirely and do my own control implementation but using a CE certified unit for the 240V switching, and that way I can get my local electrician to check over the 240V installation. Not my preferred route, but easily doable.

@Conor, as @ragg987 says, the heating costs do mount up. We have a reasonably large 3-storey 4-bedroom (5 really because we have one room in the loft which is a general store room / drying room / dressing room for my son.) and as @PeterW says we heat this with a single Wills heater which runs in the E7 slot, though I do top this up with a little 1kW oil rad in my office on the first floor running in an E7 slot for the coldest month or so. This means that all of our heating is at E7 cheap rate. We will be getting an ASHP some time (we've got all the piping in place) but probably next summer, but this will be a self install as I can't make the payback numbers work if I pay someone to do it. I just don't see the point of MCS myself. The upfront markup you pay to for an MCS certificated installer is difficult to recover, IMO. One last thing: Don't bother with the woodstove. They make it a pig to seal the house and unbalance the MVHR and a passive compliant one costs a fortune. You'll never use it. Ask you wife when you last lit a fire between June-Aug, because if you've designed your house right that's how your house feels all the year round. We have enough problems with 6 people sitting socialising in one room as these warm bodies are enough for the temperature to start to rise, and we couldn't have the 1kW heater on with the room door closed for the same reason. The minimum that a ticking over woodstove will emit is 2 kW and some go up to 6kW! There have been a couple of topics on ethanol burners which give the aesthetic effect of a real woodstove without cooking the occupants.

Yup, especially as there is a complete section of the submission for invoices where the VAT isn't separately itemised! It seemed a bit capricious to reject what is clearly a valid order confirmation and payment from a major retailer because net amounts and VAT were not separately itemised. Perhaps this would be reasonable if there were multiple VAT rates, but in this case everything is at 20% anyway. I suspect that the processing admin needed to "add value" or be seen to do her job by finding at least one error, and this was the one she chose. However, I feel it totally counter-productive to let any irritation or sarcasm show in your responses when dealing with this sort of process administration, whether it is Planning, BControl, or as in this case VAT Reclaim. The person that you are dealing with is usually having to do a pretty shitty job on a pretty low salary, so being a smart-arse is quite unfair, IMO. I just try to bite my tongue, and write a friendly but direct response to any issues raised. I also leave it for 12+ hours before both Jan and I reread the response, in case I've left some signs of irritation in. Get rid of it.

I spoke too soon. One of the salesman has just emailed us a VAT invoice. It just took some shaking of the tree Let's hope that HMRC accept this one.

The good news is that HMRC have settled our claim on all items bar one. The bad news was that this was our single largest item: our fitted kitchen which we bought from Wickes. The claimed total was correct in that we excluded the non-claimable items. The refusal reason wording was "Not a VAT invoice -- Pro--Formas / Quotations / Sales Orders / Order Confirmations / Illegible Invoices / Photocopies / Invoices without company VAT registration numbers are not acceptable invoices". The Issue seems to be that Wickes Document does not have the word "Invoice" on it. It does include everything else: Customer details Seller details Order reference VAT number Order itemisation Pricing details based on Wickes list prices plus discounts, and itemisation of installation services (£0). Confirmation of Payment details. What it doesn't do is to separately itemise VAT and excl VAT subtotals. We've chased the Wickes salesman a couple of time and we getting the run -around. "That's what we issue customers; we don't give any other document". They got no interest in this as this was an order completed a couple of years ago. I've tried the customer service -- no response. And time is ticking towards or 30 day appeal limit. Very frustrating as this is worth £2K to us. We will see what happens, but the main lesson learnt is that you should make sure you get a valid VAT receipt for big ticket items at the time of purchase.

As Ed says, definitely not true in our case. No BGas installation fees; no daily standing charge, no boiler maintenance charge, and that's before we do any other side-by-side comparisons. (The annual maintenance on my last BGas boiler was over £300). Because my house is very energy efficient, the Willis does the job fine; it's tiny and doesn't need an area of external wall for its install. We have about a 6-year payback if I self-install and self-maintain an ASHP, and if I reckon on a 10 year working life then this is just about viable -- but there's no cost-benefit case for a professional install. One nice side-effect of having the Willis as a fallback is that the ASHP isn't "mission critical". If it were to break down in peak mid-winter and I needed to order a part or even replace it, then the only real impact would be that my electricity bill would go up by maybe £10 or so per week for the outage.

Martin as Nick says, limescaling is a slow killer for plumbing systems. It knackers everything over time. See https://youtu.be/yF_dLlQ6RIo as an example of what I mean. This is what is happening inside your SunAmp if you don't use a softener.

@K78 You need to be careful with sources. The Institute for Energy Research is an NFP funded largely by Charles Koch and oil industry money. A quote from the WP article: "IER was among the most prominent organizations questioning the existence and extent of anthropogenic climate change". I wonder why they conclude that diesel cars are greener than EVs? Humm. The large majority of studies which have also cranked the numbers come with the opposite conclusion.

As Jeremy says, I can only make the payback work if I do the install myself (around 5-6 years). If I use a typical provide and install quote then this would go up to nearer 15 than 10 years, and with the expected life of an ASHP being around 10 years, this makes no sense at all. Of course this equation and payback would all change if I had a lower-spec energy efficient house.

Yup, we've still got 2×SunAmp PVs and we've had no problems so far except that the total actual thermal capacity seems to be a bit less than stated. Perhaps as a bit of kit, this is over engineered. Given that I love my little Willis (which heats our UFH) and the probs that many of the UniQ users have had, I think that if I did have to replace the PVs then I'd go for something like a UniQ HW 9 with an external Willis and pump to top it up -- that way I can do the heating control integrated into my overall heating strategy. One Q for Martin: do you use a water softener on the HW supply-side? IIRC, when I talked to the SunAmps guys, they though one pretty essential, so we use a Harvey and no complaints here.