MikeSharp01

Hopefully! Yes the balance / trade off between flow rate and delta temp I have done calcs based on 3, 5 & 8 K against our limiting UFH (pressure drop wise) loop. Our pump can deal with 7m head and at 3K it will be running at 6.3m head drop.

Technically you are correct the flooring company say 27 but I set the max at 24 in my calculations to see if we could get the output, I think we can, and have a good safety margin - the floor is second only to the windows package cost wise.

Feels way to high for our floor. Got to get my head around this WC thing we need to keep our slab interface to the wooden floor maxed at 24oC so a max water temp of 26 perhaps. What was your floor surface temperature?

So your heat demand should be 10W/m2 or there abouts. Unless you have a huge house or live in the Arctic circle you probably need less than 3kW.

I cannot imagine that the heat pump can overheat the cylinder so I have discounted that issue. My motivation for wiring as it is was just protection for the immersion but also so I could add the PV control later. I looked at the details of your system and thought I might give it a try at some point. There are several other probes in the tank pockets - one for the heat meter, one for the heat pump and one for the BMS monitoring. There are so many safety systems in this system my failure mode analysis (FMA) figured all would be OK. Here are the bare facts: The immersion has a stat of its own that limits the water temperature it can achieve. The immersion has a over temperature cutout should it get that far. The tank has a temperature and pressure safety device. The BMS probe has an upper limit setting that can raise an alarm at a chosen set point (85oC variable) The 24V system has the over temp cutout and the temperature control cutout I could put them in line with the immersion - one or both, but doing so would limit the ability to use all the PV up to 80oC when you wanted only 50oC from the standard cycle. I did consider taking a feed from the immersion live connection, at the immersion and using the BMS logic to tell me if it is powered up when it should be off but have discounted the need for this as the protections above mean it is not really needed. I did figure the Heat Pump would do the whole job but having an immersion as a standby makes sense to me.

I am finalising the wiring for the Heat Pump install and have got to the immersion. When I originally drew up the wiring I had a 24V contactor in the circuit and all the safety / interlocking done on the 24V side to give the BMS full control. Now I am wondering if: a. Am I allowed to have the immersion controlled by a contactor with all the thermal cutout and setpoint control stats in the 24V circuits managing the contactor. (See Image below) b. Should I consider a solid state contactor - if so which? c. What provision should I make for a possible PV diverter, ie terminals below the contactor or what!

Surely the thing about MVHR is that it is controlled ventilation, complimented by heat recovery, and so when combined with great airtightness, which has other benefits in addition, you are in control of the ventilation and the more of the heat that is recovered. You are brining air in and taking it out again in such a way, at such flow rates and in such places that draughts are not a thing, are not subject to the vagaries of the external wind direction / strength. Because it's all warmed so is less obtrusive because it is already mixed and not arriving through very effect venturis that increase its velocity and create discomfort. So it seems to me that, in such a scenario, draughts don't flow freely they flow in a highly controlled manor - it's not pure external air rushing past you to get into the place but air at room temperature flowing slowly past you in from the supply vents and out of the extract vents. It is also, however, clear that the recommendations around the Air Change (AC) volumes is a bit OTT as most people here seem to get by with a fraction of the recommended levels. I started out wondering if MVHR was for us but I have been convinced it is the best way forward and so just allowing air in and out in an uncontrolled fashion is not for us although it would be a lot cheaper at the outset without doubt.

Yes it feels right just to replace all of it. I won't be draining the system down, they will need to wait and get the plumber back for that. I will just run a couple more checks with the heating off later to see if I can hold the water back from cold.

Yes I forced it closed with a spanner and wedged it, left it for a period of 30 minutes no change in temperature.

The valve moves freely and you do feel a certain squishiness when you close it with a spanner. I have not managed to power up the head because I didn't want to disturb the settings, the hot water is set off. I can play a bit now as the heating has warmed up their house. There does not seem to be any other way for the water to flow so the valve must be letting by. I did notice that with the head on that the the manual lever di not seem to engage until almost the end of its travel but the head does drop onto the valve in the correct position.

Friends of ours are having problems with their hot water over a period and they have had a plumber look at the problem, who said it was an issue for an electrician, they don't want to call a plumber today for obvious reasons, and so I said I would pop round and have a look at it. Its not a particularly odd one, basically the hot water tank is getting flow through the heating coil despite the call for hot water being off. So I looked at the S-PLAN valves and and noticed that that their electrician, under instruction from the plumber, had already fitted a new head to the hot water valve (A Honeywell 272848 normally closed valve) but they left the new valve body on the floor! Cutting a long story short I took the motorised head off the valve and forced the valve shut with a spanner and it looks like it still lets by so my question is: Do these valves let by when they are forcibly closed - I thought they were rubber balls so pushing past the end stop of the motor, without the motor attached, should close it but it does not appear to. So my diagnosis is that the valve body will need to be replaced but I wanted confirmation that forcing the valve shut can still result in flow getting through - has the ball fallen apart for instance?

Don't listen to him, nobody uses bulldozers any more! Welcome to THE forum for people like us.

Welcome @markg123 to THE forum for people like us.

I heard that one can now build a granny annex in ones garden without issues - well that if you get turned down for planning permission (PP) you can expect to win on appeal.

Far too small - 4mm is minimum and 6mm prob better for run lengths.

We have two Tundishes (Only one un-trapped version in the picture but two new trapped versions have arrived today and will be fitted tomorrow). I have roughly plumbed them to arrive at what I think of as a good layout, see pic. (The plastic is just to get the dimensions right it will all be copper.) I have / would like to join the control group overpressure relief flow and that for the heating circuit overpressure together to one Tundish. It will be easy to workout which is flowing as they are on different circuits and the relief pressures differ significantly. The other Tundish will be exclusive to the Pressure / Temperature relief on the tank. Both then drop in 22mm to 28mm copper and then be routed to the drain in 28mm JG Speedfit plastic pipe. The runs to both Tundishes are less than 600mm the copper and JG pipe are both proof against the max output temperatures. I still need to figure out how to get from 28mm - to something I can connect to the soil pipe. so any thoughts on that gratefully accepted.

No room! I have 60l and a massive slab, no radiators, so although the heat transfer from the slab back into the water is not as good as on the tank the temperature drop is still only fractions of a degree for a 0.8kWh defrost 0.06 deg C if my calcs are correct.

I was thinking about this on Thursday when I realised that our system volume is only enough when the Underfloor Heating (UFH) is in the loop when its just running through the domestic hot Water (DHW) tank the volume is a lot less. However I also feel that as far as the DHW tank is concerned the heat transfer is roughly reversable, I guess entropy and a few other factors will have a part to play, so the hot water in the tank will give its heat up to the circulating HP circuit and so all will be well. I dimly recall working out that we might need ~0.8kWh for a defrost, if all that comes from the Tank - because the other volume in the system during a DHW cycle is only around 31l (Including the tank coil) we would see a drop in water temperature of a few degrees which may or may not be a worry depending. (To use that side the heat pump will be in DHW mode so a set point is engaged somewhere and defrosts could result in it getting in loop trying to reach set point while being knocked back by defrost cycles). When the slab is in the loop and based on the same assumptions as for the tank defrost the temperature drop is a fraction of a degree across the slab, the systems volume then is around 60l, the slab is 60T of concrete and there is no close in setpoint to worry about.

Depends which end of the telescope you are looking down so either a great way to while away a decade and spend loads and loads of cash or a tiny thing not remotely likely to be a problem and still a very long way off.

The wisdom of crowds - used in ensemble method AI models (random forests) so yet another example of an old idea (Aristotle understood it) getting a new lease of life as part of AI, along with Bayes Theorem (1761) and the Neural Network itself really stemming from the 1950s development of the perceptron.

Yep - you get today's prize. The drawing is crap, makes you wonder how good this stuff is. Your right I will be running mine at 1.5 bar - enough to meet the spec of the heat meter but no so much as to blow the socks off.

The heat pump install proceeds at pace, well two steps forward and one back mostly. Todays one back is this filling loop I got from the plumbers merchant. Allegedly it is automatic, you dial up the pressure you want, open the valves and once it has done its business you close the valves. See if you can see anything wrong with the instructions and the parts as supplied.

Yes that makes sense. So "b. be a separate branch pipe with no sanitary appliances connected to it;" means (not implies) the D2 pipe is a branch pipe itself? Hope that helps @Nickfromwales

I guess I will look into that but I suspect it will be simpler just to put a stat on the manifold in the ASHP enable line to shut it down if the water temp at the manifold gets too high.

How so?