sharpener

There was a recent thread which is highly relevant to all this, maybe @JamesPa can provide a link as it was his IIRC.

Also consider access for servicing. A way to address both points is to set the unit back from the walls of the garage and then have a removable housing to cover the gap. I am thinking of 3/4 in chip board lined with 50mm fibreglass insulation which IME will absorb noise quite effectively. And having this inside the garage simplifies the task of keeping it dry.

Depressing comment on the Heating Design FB group "I’ve given up fitting weather comp to my customers boilers, causes too many problems, people just cannot get their head round a simple thing of moving a dial to set it." Not sure which dial he means, my WC curve is set by a preset pot behind a dummy knob, not exactly a user adjustment! And several others saying e.g. ppl don't like it because the rads don't get hot and they cannot dry their smalls on them. WC never enabled on new build housing bc there are too many callbacks (I thought it was now mandatory). So not a specific problem with heat pumps, however WC clearly needs some kind of Auto-tune sw before it will achieve much greater market penetration.

Methinks time for a visit to some of these reference sites and talk to the owners...

Old joke. Two engineers in France: "It works just fine in practice" "Yes but will it work in theory?"

Not unique to heat pumps. I had to fit a relay to my Vokera boiler to inhibit the weather compensation when there is a call for the HW. A side benefit is that this gives fast warmup for the CH first thing in the morning. I might change the timings though as this takes it out of condensing mode which is not ideal. Really good explanation of the various 3 port valve wiring etc with animated diagrams here.

Presumably UKPN have put in two cables, supply heads and meters. In which case there is no way you can have any equipment which is connected to both supplies at once. So you are a bit stuck as to what you can do. Maybe have the HPs on one supply and the PV/batteries/EV on the other, then you could have different tariffs which are optimised for each use pattern.

Am surprised there is no night setback possible. Or a low-noise setting which would limit the heating available during night-time hours. Maybe you could make use of this to simulate two zones with different temp/time settings? You might need to use both outputs but connect them to the same actuator. With or without two relays.

The OP is charging the floor slab with the UFH during cheap rate and then switching to the rads to heat the bedrooms. There seems to be little point in having the water un-necessarily hot for the UFH (and then tempering it with a mixing valve!) when the rads are anyway not going to be on at the time in question. I think so, Vaillant Arotherm + certainly, don't know about the OP's Daikin. Presumably when zones are on together the one demanding the highest temp has priority, hence the need for the mechanical mixing valve. Or you can control zones separately with electronic mixing valves but AIUI the HP will still have the leaving temp of the highest circuit, and so involve an increase in entropy for the others hence less than ideal CoP. So turning off the UFH for an hour while you heat the bedrooms would give you a small improvement and you probably wouldn't notice the gap.

Assuming the flow temp is high enough for the rads you could maybe set the temp back during the UFH phase, to avoid the mixing valve having to temper it down again which will be costing you in terms of CoP. If the controls will allow it when using WC.

Is that the OAT reading? Have you got a proper OAT sensor fitted and is it working? You could check it with e.g. gentle application of a hair dryer. WC curve looks vaguely plausible but I would expect no heating at 16C not 35.

Might also be a hangover from the age of non-inverter drives where the high electrical and mechanical stress of frequent direct-on-line motor starts will shorten the life of motor and compressor. Wouldn't think this a problem now. The above report's main conclusions (in 2012) were Both ASHPs and GSHPs should be designed for a minimum run time of circa six minutes, which will avoid the worst excesses of detrimental performance caused by short cycling...run times of ~ 8 minutes for the ASHP gave COP values close to catalogue steady state values. which is significantly shorter than the 15 mins often quoted. So perhaps this problem is less severe than many people seem to think?

Did you ever explore the possibility of splitting the rads from the UFH? I would have thought this could give a worthwhile improvement. You could then preheat the slab at night rate until say 0600 then switch to heating the rads to get the bedrooms warm. Maybe changing every 10 mins as @Beelbeebub suggests is a bit too frequent though, there will be a lot of water still at the higher temp pushed into the UFH at the changeovers which will reduce the savings. And it would maybe require an external controller.

Sorry, my mistake, I meant the demand inputs S6, S7, S8, can you confirm if these are contacts closed for heat or the opposite, it's not entirely clear from the wording The text for S6 says "DEM1 External heating switch-off for heating circuit 1" and the footnote says "Closing the "DEM" contact ends the heating demand for the relevant heating circuit" which is the opposite way round for the usual (S-plan) boiler controls. In my case S6 will be the radiator circuit, I will anyway have to add a relay to get a voltage-free contact, so that can be either way round. S7 will be the UFH, the signal from the manifold location will be the OR function of all the four thermostat call contacts which at present calls the boiler so I would need to invert the sense of that with another relay. S8 will be the call for the thermal store, that is an external timeswitch with changeover contacts so can be either at no penalty.

Sorry, my mistake, I meant the demand inputs S6, S7, S8, it's not entirely clear from the text if these are contacts and circuit closed for heat or the opposite.

Sorry, my mistake, I meant the demand inputs S6, S7, S8, it's not entirely clear from the text if these are contacts and circuit closed for heat or the opposite.

Sorry, my mistake, I meant the demand inputs S6, S7, S8, it's not entirely clear from the text if these are contacts and circuit closed for heat or the opposite.

For anyone else looking this is the best I have been able to find, in a 700/2 controller manual online. VR71 pinout.pdf Seems to have suffered a bit in translation, @Lofty718can you confirm that the demand inputs R6, R7, R8 are for external contacts that need to be closed for heat demand (as it would be for a conventional boiler)?

Have you found any decent documentation for the VR71 @Lofty718? By which I mean a description of what all the inputs and outputs are intended for and what the voltage levels are? Seems to be lacking, though I have reverse-engineered a version by looking at numerous schematics and Vaillant tell me my interpretation is correct as far as it goes. The SensoComfort simulator on the web is quite good. It is designed to be hierarchical in the following way (and commissioned in this order): So at the bottom level is the HP and its native controls, this should work to give DHW, and plain WC heating if the frost stat on landing is turned up so as to create the demand. Zones and thermal store do nothing in this mode. I will get the installer to achieve just this level of functionality to begin with. The thermal store comes next, the re-purposed external timer will control when it charges (e.g. 0500 - 0600 on Economy 7, and 1300 - 1600 from surplus PV or Octopus Cosy) and when it discharges (to feed bedroom radiators 0700 - 0830 and 2200 - 2330). Then we have the Honeywell zone control system. If any zone is calling for heat it will turn on the Honeywell boiler relay wired in parallel with the frost stat so calling the HP on its two-wire voltage free heating input. Other than that it is electrically separate. Lastly is the internet control box. By judicious use of the 4 normally closed and 4 normally open relays it will default to allowing all of the above to operate normally if it is powered down, is reset by a power outage, or fails. Two of its timers also do the night setback for the MVHR fan speed.

Yes, 100% I have spent quite a few hours working out if/how to integrate my proposed Vaillant Arotherm Plus with my existing controls. Fortunately its standard interface box has a voltage-free call for hot water and defaults to heating. With the extension box (VR71) it will accept v/f contacts for three further zones e.g. (i) radiator circuit (ii) underfloor heating (iii) thermal store. So the electrical interface is fairly straightforward, the wrinkle is optimising whether this box is placed near the existing controls, or near the pumps and valves which will be on the other side of the room. Fortunately there are 6 control cores to the hw tank location and another 6 to the remote underfloor manifold which should be sufficient, though both will need to be re-purposed somewhat. I have previously traced and documented all this when installing a wireless Honeywell Evohome zoning system, which I want to retain because of the usage patterns and shape of the house. So it is all basically do-able. Also I plan to re-use the current dual channel timeswitch to control the charging and discharging of the thermal store. On top of it all I have an 8-channel internet timer box which enables me to control the existing setup remotely. Still debating whether to keep this, it is long in the tooth but the installer has no experience of the Vaillant internet add-on beyond one webinar, and the app has not got a very good press on this Arotherm fb group. Maybe the answer is to keep it in service until the Vaillant product has bedded down and then add it to the system as a DIY enhancement. If all this were simply left to a good heating electrician I imagine the result would be ditching everything that exists, pulling lots of multicore through the house, and making do with what the native Vaillant control system is capable of. So far I have concentrated on getting an agreed pipework schematic, I sense there are further challenges to come!

That sounds like the equivalent of the Honeywell BRD91. Shame, you might have been able to benefit from incorporating it.

Well yes, there are still lots of machines on the market that use R32. But R290 gives you higher flow temperatures and higher CoP for any given temperature so it is the way to go. As the amounts of refrigerant are tiny (and you are allowed to have bottled or piped propane in the house for cooking) I think the dangers are exaggerated, but I can see that no-one would want to install in a non-compliant fashion. I think the caution stems from the fact that many German houses have cellars/basements where it could accumulate to dangerous levels.

Thanks for following that up! Performance looks useful too. Surprising there is no effective representation in the UK though. But after all the aggravation I think I will stick with Vaillant now they have agreed with my proposed scheme.

Wouldn't have thought so. But did the Tado provide a "call for heat" signal to the boiler, and if so can you connect it to the HP so when all the rooms are up to temp it cuts out? I plan a similar set up with an existing Honeywell Evohome TRV network (with the necessary output) and Vaillant HP (with the necessary input) so I think it could be made to work. The TRVs will be set as overtemp limits as in practice I expect the WC will do the heavy lifting controlwise.

This is the actual spec: