JohnMo

Think the bend radius for getting pipes through is way to small, firstly. Why run pipes through floor at all. Take them from outside direct in to house.

Need some help My next job is a hot tub, will be a round wooden one, heated by a heat pump. Looking to build an insulated base for it to sit on. Weight approx 2.4Te, diameter approx 1700mm. My initial thoughts were, dig down, DPM, PIR insulation 100-150mm thick covered in slabs (have loads to use up). But base will be square, hot tub round, heat will just move sideways out of the base and make the insulation useless. So not sure that works. Anyone any ideas?

Think you have the task of going the manual and the actual settings. There should be something that is flagged to do DHW as a priority after a power cut. It's not a normal ASHP behaviour. Normally resumes the last mode active.

In Scotland air tightness better than 3.0, balance inlet outlet ventilation mandatory, so MVHR. 3 to 5 MEV or dMEV (with trickle vents), after that whatever fancy passive vent intermittent fans etc, all with trickle vents.

There effectively a piece of string, but the string expands and contracts with changes in humidity - it senses room humidity it changes length as the humidity increases to open the vent more. You to have them coupled with MEV or dMEV fans in wet rooms. If these boost automatically, you get a system that self compensates for changes in room habitation etc. So example everyone in lounge in evening, vents in lounge window open, but rest of house vents go to min position, fans draw air through house taking most air from lounge. Everyone goes to bed, lounge vents close and bedroom vents start to open etc

Be careful using nameplate rating - you need a heat pump that does just under 6kW at -3 as you are England. Your defrost derate and DHW allowance takes it to just under 6kW. Most important bit is modulation at 7 to 10 degs, that where the heat pump operates most the time - long steady running at there temps makes the difference between SCoP of 4 or 5. They will come in thousands above grant, so why are you wasting your time. Your not going to get any change from the grant especially with SteibelEltron, as will cost as much as the grant just buying the unit.

You have what you have, you seem to want run an on off system and have loads of modulation immediately. It isn't going to happen, the boiler has plenty of work to do playing catch up. Then you switch it off again. Thick stuff - 25mm wall thickness, cover in aluminium tape to stop mice eating it.

As I said, you have made a simple system very complex. I think you are trying to reinvent the wheel. For systems that have already been designed tested and approved, overlaying a 24v system, just seems OTT.

So based on the flow rates, it's around 400m² property - that's a big retirement pad. If it isn't that big you are going to massively over ventilate and maybe suffer a very dry indoor environment in winter to get 6kW.

Gee you were either wrapped off, massive house and or tiny centres. I have 600m in the floor (192m²), so about £350 today. That must be a massive house? If it's passive? I would definitely not do heat and ventilation as individual items. One dead both dead, when combined. Also look at the hot water generation time with your combined unit. How are you getting that much energy out of a micro HP? Any links to the product?

Plus you need to take into account the deletion of the standing charge, if the boiler is deleted which is currently £127 per year.

Think this all getting a little confused. A2W, cooling via a fan coil at low flow temps, below condensation temperature, needs pipe insulation and it needs a condensate drain. A2A needs exactly the same. A2W can use a fan coil, operated above condensation temp, which doesn't need insulation or condensate drains. A2A cannot work in this mode. A2A generally doesn't do DHW (some can, but an expensive option). A2W does do DHW out the box. Both A2A and A2W do heat and cool, but I'm not a fan of blown heating systems, don't find them comfortable. UFH can heat and cool, cooling isn't the same as a fan coil. But takes the edge of the house nicely. Fan coils are just like radiators need to be sized for the performance needed, at the flow temperature you specify.

Been plenty of discussion on here, "we have a passivhaus so we don't need much or any heating". Even to passivhaus spec you have a heat load of 10W/m², which isn't much, but is still some. Heating element in mvhr can supply that (passivhaus heating spec, is designed around it). But if it's a heating element on direct electric, costs can soon stack up. So 200m² house at 10W, is 48kWh a day on your coldest day, or £13 in money terms. A well sized heat pump should be doing better than a CoP 3 on the coldest day, so now you are down to £4. Plus air heating you are going to need additional heat in bathrooms, I would think? Do UFH on 200 to 300mm centres, and a small good modulation ASHP. Looking at about £4k in materials, plus the cylinder. Plus the ASHP can do your water heating and it costs a third it would, via direct heating. DHW heating could be costing £600 a year on direct electric, or £200 via a heat pump. I would rather spend an amount up front, get a proper heating system that's cheap to run for ever more.

I suppose you get to the question of why with r290 heat pump do you need the immersion connection at all. The heat pump itself can do a legionella cycle, if you have risk assessed and deem required. If you haven't switched the output off as mentioned by @ProDaveyour immersion can take over, because the heat pump control thinks it's taking too long to do a DHW cycle.You may decide to use immersion exclusively in winter, does the heat pump control allow that?

You sound like you are making it difficult. If you are using a 3rd party cylinder, the immersion will already have can in built safety cutout as part of its thermostat. If you want a diverter as well, I would simply move all the immersion stuff away from the heat pump controller, and do it all stand alone. Then use a standard immersion controller and diverter in parallel. So either diverter or normal timer override can power the immersion. Take power direct from consumer unit.

About the same. ASHP shouldn't last as long as good fridge. But technically a heat pump produced today will be over taken efficiency wise every few years. A poor boiler or heat pump install, is unlikely to last a a good one. So many variables.

But an R290 with 55 Deg flow at -2 outside will still deliver a CoP of 2.75, then at 7 degs flowing 40 to 45 it's COP increases to about 4. As most gas boiler installs are based on limited run time get house hot quick, there maybe less radiator changes really needed. Couple an open system, well sized decent heat pump, and a time of use tariff, even flowing high temps on a cold day, would perform pretty well. Add hydraulic separation, zones etc, you may as well stay on gas.

But without that, an ASHP is already cheaper than gas. Even in the north of Scotland where temps over winter are much cooler than England.

Don't get hung up, on yours compared to mine, it's meaningless. I would keep things simple first. Keep your on-off heating, bring down the CH flow temp first and extend your heating windows, so you slow the whole thing down. Plus don't switch off during the nighttime etc, just cut the target temp a couple of degrees. Trim 5 degs of flow temp every couple of days and see how it responds. Once house gets a little to cool, add a couple of degrees flow temp back on. But before you start, make sure any radiator valves or thermostats, are set to the same time periods, so everything works together. The above will get the boiler running very efficiently, it's simple and costs nothing and then gives to good starting place to understand how you house responds to different flow temperatures.

First you need to really understand your heating load at design temperature, so for -3 degs. Your heat load at 7 degs will be half that and at 10 under half. So say it's a 6kW design load, you want to choose a heat pump that does close to or a little over (allow for DHW heating and defrosting) at -3 at your design flow flow temperature. Manufacturer nameplate rating are pretty meaningless. So you need to find the technical data. A few snippets from a 6kW Hiaer R290. So -2 full load it puts out 6.4kW at 30 Deg flow temp and at 45 it's 5.66kW, so if you have radiators it's too small but ok for UFH. It's min output at 25 flow and 12 degs outside, it's min modulation is 1.7kW. pretty much would tick away all day every day. ScoP should be about 5.0 if UFH and an open system on WC, so heat pump doesn't cycle.

Or big enough for a cosy tariff and charge 3x

Could also be old fuel. Unless new dump the fuel and our in new

May have a winter summer switch, to change the carb settings. In winter it could be running really lean.

3 phase (still no idea why anyone needs it in a domestic house) allows 16A per phase export on G98. So about 3.6kW X3. G98 you tell DNO after you start generating. But how you manage the phases, to make best use of the solar is something I have looked into. As most the house will only make use of a single phase.

Sounds about right, plus you delete a standing charge, so win win.