TerryE

I have just been searching the forum for posts on oil-filled rads, because my "big old clunky" has finally given up the ghost after 20 years, and TBH the most informative posts are my own. 🤣 I've been through a number of supplier sites and Amazon and the postings continue to be misleading quoting the electrical heating element power rather than the actual typical thermal output. I note that the CPC technical datasheets on the site that @ProDave linked to do quote an actual thermal power O/P so 👍 for CPC. I also note that many now include some form of embedded micro control with timer and remote options. I want a dumb heater where I can (statically) switch select the heater power that I want, and then control the timing and actual energy use through a Tasmota smartplug and my HA system. CPC lists some nice simple models. Simple is good as far as I am concerned.

If the ext walls, floor, roof do genuinely have a U-value of 0.1 then that is pretty much an order of magnitude better then interior wall so treating floors as a single zone and ignoring interior walls is a good simplification. Don't forget airtightness and go for 0.5 ACH + MVHR. so no weep vents. I circulate my UFH loops for 15 min every 3 hours so I can use the manifold return temp to take the average slab temp and this also spreads any solar gain across the whole slab.

We've lived in a 3 storey new build with a comparable spec for 7 years now. Our ACH is around 0.5. We have an MBC WarmSlab that's 100 mm reinforced concrete on ring-beams encased in (mostly) 300 mm structural EPS and UFH embedded in the concrete raft, so ground floor only. The UFH is run as a single zone and heated by a single 3kW inline resistive heater. We keep the whole ground floor 24 × 7 within a ~ 1°C tramline of 22½°C, the 1st floor is typical 1-2°C cooler in peak midwinder, though I do use an 1kW oil-filled rad (controlled by my CH system) on the 1st floor for the peak midwinter period. My son's bedsit in the warm loft is mostly heated by his Games PC and huge TV screens. 🤣 The house was built as ASHP ready, but we put the inline heater as a stopgap until we had confirmed the heating characteristics and loses of the house. However in practice, the heating costs are relatively small, and we have never made a payback case to install, maintain and depreciate an ASHP. We have never missed upper floor CH. I also use the Green Octopus Agile Tariff so my CH system schedules the CH and HW on-times to buy and use the cheapest half-hourly price slots. I am not necessarily suggesting you do the same, but what I am saying is that for this class of house running the whole GFL as a single zone is entirely workable, and we use less than 30 kWh heat daily even in cold Dec-Feb, so a ~ 5kW ASHP should be fine for this class of house. With a ~ 10m³ slab acting as a thermal store, it is even questionable whether you need a separate buffer tank for the UFH. I suspect that most ASHP installers have no idea how to design and right-size an ASHP for a (near) passive-class house.

So is ~£100 plugin rad in the hall. Yes, it costs more to run, but no installation costs. How many years before you break even, if ever?

IMO, if you have a reasonably low energy build with UFH then you need to think very carefully about the pros and cons of multiple zones, upper floor heating, etc.. There's a lot to be said for KISS (Keep It Simple Stupid) IMO, as this saves in installation costs, complexity and through life maintenance. E.g. upper floor heating is a PITA. You can run UFH at ~30°C so you can run your ASHP at a low temp and have a significant boost in CoP in doing so. Low temp rads take up lots of wall space and are expensive to install. We have no heating on our 1st and 2nd floors, but use a cheap oil-fill electric rad for a few hours on cheap rate electricity during the really cold months just to top-up upstairs.

@JohnBishop, you need to be careful switching 240 VAC stuff especially at high current draw especially if you don't have a grasp of current Building and IEEE regs. If you do this without Certified Electrician sign-off and have a fire then you could find that your insurance company rejects the claim. This is my set up. The CU to right was installed by my sparky. I added the left-hand extension myself because he couldn't find the time when I needed it installed, but I did this in a way that he'd be happy to sign off. He's comfortable with the 24VDC / 240VAC spilt as there isn't really a safety issue with the 24VDC side. Node-RED is a Javascript based environment that is well suited to IoT control and comes as a Home Assistant add-on as well as being able to run standalone. There are lots of YouTube videos on this.

This depends on what you are controlling and what inputs it needs. You can't make a general choice, as it depends on context. A lot of this was discussed in my topic with this post summarising my final setup and we are pretty happy with it. In short I have a bunch of contractors in a CU extension next to the main Consumer Unit and these switch power to the HW immersion, slab heater and pump. These are in turn driven with 24 VDC control signals by an off-the-shelf ESP32 relay board running Tasmota. The Tasmota firmware is switched by my NodeRED app. I do have a lot of Zigbee sensors but I prefer to use TCP layered stacks such as Tasmota for any switched devices relating to Central and HW Heating.

@WisteriaMews, sorry I am in Greece ATM, and so not checking the forum daily. The OSO UVC has an double skin: inner steel pressure vessel and our plastic or powder coated aluminium with vacuum panel insulation between. The two immersions are installed in small access panels with the wiring terminals, thermostatic switches etc. There is an internal duct channel for the 3kW flex cabling running from the bottom to up the two access panels. I used a couple of waterproof ds18b20 digital thermostats to measure temperatures. Look them up on eBay etc. The "waterproof" bit isn't important, but they are encapsulated in a ~8mm dia aluminum can that can be thermal-taped directly to the steel cylinder with a bit of foil+mineral wool insulation on top; you can get a get a range of lead lengths but 1½ or 2m is enough to take it down to the bottom channel of the cylinder, and thin enough to be run alongside the flex in the internal cabling duct. These thermometers are wired into a small IoT board, a Wemos D1 Mini which in a small ABS box about 25×40×50mm IIRC and powered using a USB lead; This ESP8266-based module uses ESPhome firmware to talk back to my home automation system over local Wifi. I use the Node-RED javascript code to track temperatures, do the heating calcs, and send the MQTT commands to power on and off the power to the two immersions. Here is a screen grab from my Home Automation system for the last 24 hours. You can see that my son had a bath or long shower at 5PM, and it scheduled top up at 00:30, 04:30 and 09:30 to bring the UNC to target 50°C because of the cheap spply pricing in those slots. (The price actually went negative in two of these slots so I actually got paid to heat the water.) The ~ 4°C cooling / day is the parasitic heat loss from the UVC which is very small compared to conventional cylinders or thermal stores.

@ProDave, in a nutshell, our decision to replace the SunAmps was because of the poor reliability of their engineering implementation: the circuit boards broke basic layout design guidelines, e.g. lack of 240V isolation and inadequate track sizing for 3kW power routing, so they had an MTBF of maybe 2 years; all of the pump and control plumbing was hidden inside a pretty steel case, which looks sexy but makes maintenance and repair a total dog. Yes, the concept of a PCM thermal store for DHW has great potential, but not this model and company. @Duncan62, Jan is our procurement specialist; she found a supplier online, which had the model we wanted in stock and could deliver it in a week. Seek and ye shall find. @WisteriaMews, We have an electric-only passive-class house. All of our white goods use timer-controllable cold-fill in-device heated water, so our HW use is pretty low: primarily showers for three adults and occasional shared baths for the 2 OAPs (mostly in the winter). Our OSO model is double immersion heated only, which makes sense for our use. I need to do I full blog post on this, but my CH control system uses 4×Finder contactors driving the 2 OSO UVC Immersions, my UFH pump and a 3kW heater that heats the UFH. I use Home Assistant to do the user interface and graphics for my Home Automation, but in terms of CH and HW control I have a custom NodeRED application (about 900 lines of Javascript that I wrote) to control a 4-relay Tasmota module via MQTT, and this in turn outputs 24V control signals to drive the contactors. I buy my electricity using an Octopus Agile Tariff. This has an API which published its day-ahead half-hourly prices at around 5PM starting midnight C.E.T. In essence, at 11PM each night, this app schedules the daily CH and HW heating for the next 24 hrs to use the cheapest half-hour slots. In terms of HW and heating the OSO, I have installed top and bottom digital thermometers to monitor the tank temp. The app uses these 2 tank temps to estimate the total kWh needed to bring the tank up to 50°C and it uses the day-ahead prices to schedules the cheapest time slots to heat the tank. (If the top temp falls below a preset, it also stuffs in a ½hr top-up regardless of price, but this happens so rarely that this isn't a significant cost premium for always having HW.) The OSO has a parasitic loss of just over 1 kWh / day, plus replenishing used water, which varies but is typically equates to another 2-3 kWh at most except during the winter bath season. The kWh price for this last couple of weeks has been negative on 4 days , small pence on another 4 and only peaking at 14½p on the stiller overcast days, so the cost of of our water use runs at under 50p / day on average. We tend to have our big bath days when Octopus will pay us to do this or it only costs pence. I've been coding for over 50 years so the Javascript bit is easy for me, but I understand that those who aren't so IT literate will have a lot fewer options. I believe the like of Octopus and OVO are exploring some Smart Control options, but these aren't yet prime time.

I call our build passive-class or low energy rather than passiveHaus complaint. For me, IanR hit the spot with his above comment. BTW, we use resistive heating only, and on current Octopus Agile tariff pricing our monthly energy bill varies from about £75 or so in the warm season to maybe £200 for the coldest months. It's hard to put a precise value for the bill as we take all of the price variation risk on the Agile tariff. However, looking at the potential monthly savings in going from a CoP of 1 to an ASHP-based 4, say, for the heating element of these costs; These savings are significantly less than amortised cost for the installation, maintenance and depreciation costs of adding an ASHP, so unless something changes radically in our case we won't be installing an ASHP.

I am 182 cm tall, and a couple of our internal doors were about 181 !! I'd just duck slightly automatically, but about twice a year (especially is some spoke to me from behind) I'd forget and clip my bonce. Ouch. 🤣

In our previous ~2-300 year old Cotswold stone farmhouse we put it a silicon DPC back in the mid 80s and completely repointed over the next 10-20 years the infill showly turned from damp loam to bone dry dust and grain husk. The effective U-value slowly improved down to around 1½ W/m2K. The main problem was that the house leaked air terribly and the floor slab was uninsulated. Our current house has a U-value for exterior walls, roof, floor in the range 0.12-0.15 W/m2K and an an ACH of around 0.4, plus MVHR. Just no comparison in terms of winter comfort. When the kids were young, they ran around naked in doors in the winter but then again gas was dirt cheap in the 90s so the boiler was going flat out when we were in the house.

Actually the code and graph were mine; the context was a passive house twinwall (high insulation with decent thermal capacity) with an outer stone skin. This is a world away from the thermal characteristics of you stone cottage (which is of similar construction to my previous house). The U-values you get from a solid stone wall are terrible as stone is an awful insulator compared to a passive profile (the U-values are typically 10-20× greater). Yes there is little temperature variation inside as the walls are just always cold in the winter. You can really only mitigate this by adding something like an inner aerogel backed plasterboard liner to the exterior walls. As heat just wicks away through every external surface, you just need to input a lot of heat to get a comfortable room temperature.

That being said, I believe most ASHPs can be programmed to have a few time slots each day when the ASHP outputs at the higher temperature setting and a Y-plan valve switches between the UCV and the manifold loop, so the CoP is 4, say, when doing the heating, but 2½ say when heating the water. This assumes of course that you using that you are using low temp rads or UFH. But this all adds complexity. @JohnMo or @ProDave will tell us if I am talking rubbish. 🙂

The LCoE for new solar and wind is about £30 / MWh, that's 3× less. The revenue starts to come into on about a year after the mean investment point, that 10-15× less. It is just really hard to make new nuclear numbers economically competitive, even SMR technology. We can get up to ~90% renewable with investment in grid-scale battery and maybe pumped hydro, whilst running our existing gas peaker stock until EoL. By then other options will be available.

Octopus are quite transparent about how they set their Agile price: 2W+P where W is the half-hourly EU wholesale price which is fixed for the day-ahead each Midnight CET. The 2 is a markup of 100%; P is another uplift of 14p/kWh from 4-7pm GMT -- a time limited markup to discourage peak use. The two markups combine to cover their distribution and service costs. This 2+ markup may seem a bit steep but it is less than the others charge. This total price also capped to 100p / kWh inc VAT as per current UK legislation, but other than this, consumers on the Agile tariff don't have to pay a premium for buying future prices, so whilst they take the pricing risk, the expected price is less overall. If I we doing this, I'd have had the markup 2 for W>0 and 1 otherwise, but I am not going to make this suggestion. 🤣

Yes. there's an excess of energy being generated -- such is the variable nature of renewables.

The 20A Power Relay and the 25A Contactor are pretty much identical in form factor. The contact is far more robust and only about 20% more expensive. I'll just buy 10 1N4007s and make up my own flyback straps.

Mike, it's nice to give back on this one. ESPhome does now support the Pico W. See ESPhome - Raspberry Pico W. The ESPhome environment is layered over RTOS, so I assumes this is just a port of their RTOS build. The standard ESPHome dev environment typically runs in a docker container -- either via the Home Assistant add-on or a standard docker container from the Docker Library running under Docker. This is just a builder WebUI using a load of Python scripts to wrap around the make environment. I find it easy to use. I like it. You configure the particular device using a YAML file which can include C encoded actions using the "lamba" nodes. It's all pretty straightforward once you are past the initial learning curve. Update is normally via OTA, so if you need to tweak a config, then you just edit the YAML file and hit deploy. The build and update takes less than a minute. If you want to discuss further then why not spin off a specific ESPhome (on Pico) topic? PS. The Pi Hut 8-relay board that you linked to has a similar form factor to the ESP one that I suggested, but you would need to mod the case slightly to take the external Wifi antenna. Pi Hut also sells a 4 relay version. It's a pity that I can't find a proper 24VDC relay driver board / hat for the Pico or ESP32. I see that some designs use PWM relay drivers with RC smoothing and flyback protection. The idea here is that you set the op to 100% for 50 mSec for force contact close then drop the PWM to 50% dropping the smoothed voltage to ~ 12V which is enough to keep the contactor closed but only a ¼ of the power loss in the relay and if you don't need sharp one, then drop the PWM ratio to 0 over 100 mSec, say, which pretty much dissipates the coil energy before open. Anyone know of / recommend such a off-the-shelf board? PPS. ESPhome can be configured to act as I/O subsystem for HA or work independent of HA using MQTT as its command interface.

Precisely. And the answer is no, not at the moment 😱 but I should have a freewheeling diode across the control contacts of each. Do the math and Finder relay coil stores about 0.6mJ of energy when closed and as soon as the Sonder relay opens this coil field collapses creating a flyback voltage in the kV range at its contacts which will rapidly degrade the relay. Probably don't need an RC snubber with a freewheeling diode (something like the 1N4007 which are orderable in 5 off quantities from Farnell etc. for pence). What I hate about this was that I really wanted to avoid customise tweaks. I really wanted a compute off-the -shelf module. I have found a for ~£200 from an AliExpress supplier I've used before but it has 32 channels and is really overkill. No the 22.20s are power relays really designed for straight AC1 resistive loads like the immersion heaters. The 22.32s have sensible AC7a rating but the profile is slightly different so I need to check that they fit in my enclosure. If anyone have setter advice then I am more than willing to listen.

A quick update. The system has been working well (subject to the caveats below) for over 3 months now. I've stripped out and refined the Node-RED application, and am reasonably happy with it, but a few lessons learnt: I have now retired all of my custom ESP code. I use ESPhome for my Wemos D1 mini based temperature loggers using One-Wire DS18B20s controlled by the ESP8266 chip. ESPhome just proved the easiest way to configure these and the pre-built environment is available as a Home Assistant add-in. The relay controller uses Tasmota, though I am considering switching to ESPHome, but am not sure whether this is worth the hassle. The UVC heating algorithm works really well: once a day I use the average cylinder temperature (from the top and bottom DS18B20s) to heat it to target. The CH system then schedules this top-up at the cheapest time slots. The relays are powered off early if the top/bottom is at target temperature. For example, today's top-up was 1.3 kWh at a price of~ (-3p) credit. The Finder coils are about 0.5H inductance, so the relay contact opens are particularly hard on the little Songle relays on the ESP32 relay board. Even though they have a nominal electrical life of 100K cycles, the one controlling the circulation pump failed the other day. I think that I really need to add RC snubbers across the finder coil contacts to get a decent operating life. Doing the math, the capacitor needs to be ~ 0.3μF and the resistor 1.3 kΩ. Most pre-made snubbers seem to be designed for 230VAC rather than 24DC. I killed one finder relay myself as a typo on a small change I was testing. I accidentally set the relay in blink mode (where it was cycling every second). Unfortunately, Jan interrupted this with a demand that we leave to go out for the day and I didn't get back and discover this cock-up some 10 hours later. In the meantime the relay was buzzing like a chainsaw, and by the time I realised I'd worn the poor thing out. Scratch one power relay. The Finder 22 Series relays do not handle AC7b loads well even a 30W. I am currently cycling my pump 48 times a day or ~1.5K times a month. 5K cycles at this load has already knackered the power relay controlling it. I really need to move to a contactor which might increase the snubbing requirement or back to an SSR for controlling this pump.

We've got an MBC twinwall with a blow cellulose filler. We were impressed with the choice and its implementation. I found the thermal characteristics great: a good balance of low conductivity and good specific heat which gives a very stable environment with low decrement delays through the walls. It is pretty solid with no voids. It is essentially a product made from recycled newspapers, etc. with some added fire retardants and insect repellants. I liked the idea of using a recycled product with low environmental impact. It is a plant-based rather than mineral product, so it does need additives, but this isn't a potential health issue for the occupants -- so long as your build includes a proper vapour barrier inside the fill. The fill process is a bit disgusting for those doing it. TBH I felt that our MBC crews were a little sloppy IMO when it came to things like personal HSE, and only used them when necessary rather than on a precautionary basis. However, the blowing process was notable in that they were fully kitted in masks, respirators and dust suits for this. Definitely not something to do DIY, IMO. So they have their pros and cons, with cellulose winning on eco credentials and slightly on thermal performance, but less suitable for DIY installation.

This being said, my control system does cycle the UFH loops for 6 min every 30 min for two reasons: (i) to spread any solar heating from windows across the entire slab, and (ii) so that I can use the return flow temp as a proxy for the slab temp. My Grundfos pump has just failed. 🙃

I suppose you are right: we have been living in "cloud cuckoo land" for 7 years now. And very comfortable it is. 😱 🤣🤣 Models are tools with limits and uses. What you seem to forget in this polemic is that many of us live in builds that were the designed were tuned using such tools, and they worked for us.

Nah, the biggest fubar was that they decided to build a reservoir on the island sized to sustain a 7-year drought. To save maybe 5% of the budget they decided the geology meant that they didn't need to line half. It leaks badly so is never more than about 5% full (Google Earth, here). The German construction company declared bankruptcy after screwing up more than a dozen water schemes across the Greek Islands.