sharpener

Fortunately my cylinder has the outlet pipe running downwards from it, after about 3/4 m its surface temp under the lagging is approx 30C. Airing cupboard is only faintly warm and all within thermal envelope anyway. I agree a heat trap might be esp useful with a vented cyl where the vent pipe typically runs straight upwards but I have never seen it done in any house I have had. BTW I note you use what look like Tectite fittings, what is yr experience of them? (I have only ever used the one but it is at mains pressure and has been fine.) However to judge from their pix of completed HP installations the professionals seem now to use crimped fittings instead and I have wondered why that is, it might be price but then the crimping tools themselves cost £00s.

How is it supposed to work? Doesn't prevent conduction. Might prevent parasitic convection currents. Also we would not allow a shut-off valve between tank and expansion vessel!

Yes, I was really only commenting on the order of magnitude involved vs usage. I imagine the standard methodology allows you to compare one make with another but not necessarily to have much relation to the real world, like EV range. My observations are probably not directly comparable, and are for when the house is unoccupied. They do not seem to vary noticreably from summer to winter which is odd.

Well, not a lot. By chance I was looking at Megaflo earlier today, their current 300l is quoted as 1.77 kWh. But is has got better, my OSO from 1996 takes about 2kWh after the battery is full and another 0.5 or so two hours later when some mixing/diffusion has taken place and the temp has fallen back by the thermostat hysteresis.

Well my plan for when the 12kW Vaillant gets installed is to charge my 210 l tank off E7 to 50C from 0500 to 0600, and again in the afternoons to capture any free surplus PV. This will allow 0600 to 0700 for the HP to recharge the thermal store and pre-heat the UFH. This mirrors our current usage on an oil boiler. We usually have 2x showers when we get up, but sometimes more if we have guests, and sometimes in the evenings as well or instead if we have been gardening. So 210 l is enough storage for us allowing for dilution to a comfortable temperature and I am a bit surprised by the amount you say you want though I suppose 3 kids baths might use 240l. What, hotter than 50C (see above)? A modern 300l tank has losses under 2kWh/day so it will not make a great deal of difference if it is left hot overnight or not. But I see no particular point in re-heating it earlier than you need to and I think the advice that it is less efficient is plain wrong. OTOH there is every chance even with a complicated schedule you will not achieve perfection, having it on just during the (entire) day may be the answer as you say.

Glad you got it sorted. I am still on my original FIT tariff with GE as have been told there is no reception for a smart meter. I don''t know what will happen when the BBC finally turn off the radio teleswitch service which controls my E7 meter.

(Sorry am a bit late to this thread.) It's the FIT export database. You have to de-register your FIT scheme before they will give you SEG payments otherwise there would be double counting. Ovo seem to have done this correctly. Your quarterly Good Energy payment notifications will like mine originally have shown the deemed export payments separately from the FIT and now they no longer do, I would have thought that Octopus (a) would accept this "before and after" documentation and (b) will anyway have access to the deemed export register so they can verify that Ovo have removed it.

Both Gledhill and Newark have a vast range and will also do custom cylinders with your own choice of aspect ratio, coil, tappings and immersion bosses.

As it happens I have this week received a revised quote qualified by the following wording Subject to a 2ndTechnical survey visit with Vaillant Technical to confirm existing cylinder is compatible as a replacement has not been quoted so maybe I am beginning to wear them down...

It's all relative. The OP is talking about an unusually small cylinder with a disproportionately large coil (15kW, presumably rated for a boiler though) and a small heat pump which can probably turn down to 3kW or less.

All that is true as per @JamesPa 's spreadsheet model. But a lot of this thinking is out of date; now that we can get higher flow temps with R290 refrigerant it is much less important than it used to be.

I took it that @Beelbeebub has no cylinder ATM i.e. a combi boiler but is planning to squeeze one in somewhere. I have had this experience in spades with three different installers. Am currently awaiting final confirmation from Vaillant that they will accept my existing 210l cyl on a 12kW Arotherm Plus (R290) so long as I fit a secondary circulating pump to stir the contents. (I sent a detailed perfomance model thanks to @JamesPa's spreadsheet). But with a 6 kW HP and the same coil area much less of a problem. You will probably find yr chosen HP mfr has a compatibility table. One installer came up with a "need" to increase my cyl to 300 l (for a 4-bed house) but I think this was only from some mfr's data sheet not any standard. 90l for a 1 bed flat sounds reasonable to me. Edit: see under. IIRC the MCS rules require that the HP provides the HW (though immersion top-up is allowed), so you will not get the BUS grant if it doesn't, someone will be quick to correct me if I am wrong. Octopus Cosy would be good for yr situation as there is also a 3 hr afternoon boost, so long as you can avoid the evening peak 1600 - 1900 i.e. don't cook your supper by electricity.

Don't forget to let us know how you get on!

But this is what you said in yr original post, is the HP output just sufficient or not? Perhaps we can reconcile the two statements if you don't consider 20C warm enough, in which case I would endorse the suggeston to put on another jumper. A former colleague of mine heated his house so he could wear shirt sleeves in the depths of winter. He now lives on the isle of Skye(!?!). I wonder what his fuel bills are like.

From what you say you are lucky enough to have an HP that is exactly the right size for your property. So you will benefit from the best possible turndown ratio, the least cycling, the highest efficiency and the lowest capital cost!

Sounds like it! If the house is warm enough in the coldest weather though I would not worry. If it bothers you maybe you can shift the zone timings so that everything is not calling for heat simultaneously? You could try changing it back but you will have to wait until it is really cold to see the result.

Do I infer that you have actually got one ot these things then?

Modern or what? DEC PDP-15 needed booting from paper tape!

AFAICS if you have an EV you can combine these two tariffs Octopus Intelligent (which is a better bet than their HP tariff Cosy if you don't need the afternoon boost) with their export rate Octopus Outgoiing which pays 15p/unit for exports and will even allow you to arbitrage between the two using your battery. Check the actual rates for your particular postcode though.

I don't recall there being any options for setting this. You could explore the simulator I linked to earlier.

I imagine so. Noise reduction was a claimed advantage of the top exit on the original RED HP. But it's probably goodbye to the patented RED hw tank. I was curious as to why Jason Cassells was simultaneously a director of Harlequin Plastics but this would explain it. Lots of other interesting profiles of their people on the Ocotpus web site too. So it's a bit strange I can't find any mention or pics of the new HP! Even more strange that the entire RED web site is still up more than a year after the Octopus takeover.

Not so much of a problem with a 6kW unit (bigger sizes are said to be in the works).

... will be available from December and is claimed will be installed for free (after BUS) if you do not need new rads or a cylinder upgrade. Presumably since it is made in NI it is a spinout of the RED acquisition. Their own web site has not been updated yet but there is this and more or less identical coverage in many other publications.

Not as such. I plan on having a 200 litre thermal store so that the bedroom rads will run on off-peak heat. All the returns will go back to the HP via its bottom tappings, to give more engaged volume for defrosting. Installer seems happy with this and is considering my other suggestion of having a perforated baffle above that layer to improve stratification when the store is not in active use. We are currently awaiting Vaillant's final say on the schematics. They will do one-offs for individual systems but are not very responsive, I would say first try and find an installer who believes in your ideas. V. will give you a few suggestions if you use their find-an-installer scheme.

Yes I worry but after installing the Evohome BRD91 in parallel with the original thermostat on the landing I have kept it as a frost stat set to 5C. The system is programmed to come on 0200 - 0500 if this calls for heat. And I can control the system remotely as well. In other houses I have left the system running on deep setback just like you @JohnMo. Vaillant recommend using glycol rather than antifreeze valves, this gives total peace of mind and you will not come home to find all the coolant on your driveway. Unlike e.g. Daikin they do not waste a lot of electricity keeping the compressor warm either.