John Carroll

The available volume for any accumulator is (1-((prechargepressure+1)/(chargingpressure+1)) X accumulator volume) For example, in a nonpumped accumulator, if 1.0bar is sufficient for your needs then a 200L accumulator will be precharged to 1.0bar, and assuming a fully charged accumulator from mains at 3.0bar, then the available volume on mains failure is 1-(1+1)/(3+1) X 200, equals 0.5*200, 100L A pumped accumulator like yours, assuming you require a minimum pressure of say 2.0bar would be precharged to 2.0bar and assuming the pumped charging pressure is 4.0bar, then the available volume is, 1-(2+1)/(4+1) X 200, equals 0.4*200, 80L. but remember then, because the diaphragm will now have bottomed out that you you won't get a single drop of any extra water even if 0.5bar is enough in a emergency.

I thought I replied to this, anyway, That pump setting of proportional pressure PP1 is not suitable, apart from being far too low, for UFH, suggest setting to constant pressure CP2, (LED on far right, no4), this is a constant pressure of 3.0M, then set your flowmwters to 2 to 2.5 LPM and see how it goes.

Yes John, The fixed speed is settable, 50% to 100%, and a few tests showed a (vaillant) flowrate of (converted from LPH) 24.3LPM at 100%,and 11.53LPM at 50% which makes good sense, since flow is directly proportional to speed. The dT tests did nothing, there is also a constant pressure option, settable between 100mbar and 400mbar but the tests were inconclusive as 400mbar gave ~ 23LPM but 150mbar didn't produce a much lower flowrate whereas it should theoretically, have been, 23*sqroot (150/400), 14.1LPM.

The rads flow/return are 60C/50C, mean of 55C, so a, (55-20), T35 Rad, which will emit (35/50)^1.3, 63% of a T50 rating, irrespective of what is going on elsewhere, you then have ( UFH), 3.84LPM@32C mixing with (rads), 5.73LPM@50C to give 9.57LPM@42.8C goint to LLH secondary but because the boiler circ pump is circulating 21LPM then the primary side recirculation of 11.43LPM@60C is mixing with that returning 9.57LPM@42.8C, you end up with a boiler return of 21LPM@52.2C. As you allude to, a LLH can becomes a DLH, (Dead Loss Header?) unless the primary and secondary flows are equal., hence the desire to get that dT control working, I have read of other conventional installations (no LLH) where that boiler doesn't achieve this either.

This is what someone is trying to do (if Vaillant can sort out this dT control problem). There is a rad(s) demand of 4kw and a UFH demand of 7.5kw, a boiler flow temp of 60C is required to give the required rad output, this means the boiler return is 52.2C, 7.8dT, not too bad, but just about condensing, this is with a boiler circ pump flowrate of 21LPM, if the boiler dT was increased to 16.5C, then the boiler return temp should be ~ 43.5C with quite considerable condensing, this is with a boiler circ pump flowrate of 11.5LPM, if my calcs, attached, are correct. LLH + Rads and UFH Rev0.xlsx

Don't know if new cylinder is installed but just for interest, OSO technical inform that its cylinders do not have a baffle so removing the dip tube and installing a EV to give that ~ extra 20/25% extra capacity does not leave something to bang about inside.

What is the ufh demand in kw, how many loops?. Coil rating is often based on a flow temperature of 80C and maybe 30/35 LPM flowrates so ensure both coils are suitably rated.

Looking at the OAP's pump it seems to have just 3 speeds so should be just a case of pressing the setting button (arrow) and try speed I, first check and see if its running at setting III.

That makes sense, I think those settings are 4M,5M,6M&7M, so try the 4 or 5m curve.

It states above, "Without PWM signal, the pump runs at maximum speed" so if there isn't another cable plugged into the pump PWM socket and it looks like there isnt, then that pump will be running at a 7M head so can't be set to one of its other heads down to 4 or 5M?. These UPM type pumps seem popular with UFH systems, wonder why, as all the normal type can run in all the different modes/settings. most don't have this PWM socket but its very rarely needed.

Unless this pump has a external (PWM) signal then it will only run at the highest speed, a 7M head. This will more than likely cause noisy operation IMO especially when coupled with Evohome control which continually throttles the motorized rad valves, don't know what the cure for this is.

UFH by its very nature has to run with relatively low temperatures to avoid damage to floor surfaces, so is sized accordingly, Rads are sized on a T50 basis so a required room temperature of 20C would require temps, flow/return/dT, of 75C/65C/10C at whatever the lowest OAT they were sized to. Most of my own would just about deal with a OAT of -10C, consequently I would need to oversize by a factor of at least 2 even with at a OAT of 5C or so and by a factor of 2.5 at a OAT of 0C to enable running with lowish ASHP temps, see attached. ASHP WC Extract.xlsx

Came across this sometime/somewhere where some one was (ASHP) running their rads on WC of 43C@-10C & 35C@15C, must have had mighty big rads, if I ever installed a ASHP I reckon if I installed a extra rad in 3 downstairs rooms the I could probably run reasonably comfortably with a more aggressive WC slope. ASHP WC.xlsx

Can you identify which pump is serving the CH (rads only) by just requesing rads only on and then take a photo of the front of the pump showing its LEDs, which should show what head the pump is producing.

In another thread you also had a Grant ASHP 17 KW, did you have noise while this was installed or is it at another location?

Can the same temperature compensation models be used for the above, ie a house with Radiator heating only and another house with UFH heating only. In the attached Vaillant WC Curves, one might use Curve 1.8 with radiator heating where a rad temperature of 70C might be required at -5C but use say Curve 0.6 with UFH heating where a UFH flow temperature of 42C might be required at -5C. Can some one post their UFH WC curves please. Vaillant Weather Curve.docx

Well, any flowrate up to ~ 5 LPM with both rad valves fully open, should not be problematic, IMO. Assuming a flowtemp of 42C then the rad output will be 33.4% of a T50 with a dT of 0.95C, if it is running with a dT of 5C then its output is 29.4% of a T50 with a flowrate of 0.84LPM. If it is running with noisy operation at say 7.0LPM then its output is 33.7% of a T50 with a dT of only 0.68C. These numbers are all based on a 1.0kw, T50 rad.

Have you smart radiator valves controlled by Evohome or such? Check circ pump settings and post its make/model/mode/settings and flowrate if it displays it. Check UFH manifold meter settings (throttled etc) and flowrates. Does one circ pump serve the rads and the UFH? Where is the expansion vessel located?.

https://www.wolseley.co.uk/product/neomitis-2-port-zone-valve-22mm/?srsltid=AfmBOoqv_ENIV53nUqWT0o_kPleTlp7Vrj29abrEn4EMV9R9BhMx7LT7

This might be of interest as it shows the effect of the cold feed teed in both before and after the pump, I just calculated the pressures at 4 or 5 points in a system with a loop of pipe, but doesn't matter, the differential pressure through any system is still the pump head. Point of No Pressure Change M Rev0.xlsx

That's the valve, below, operates like any 2 port valve, you can see the lever in the Auto position, on the end to the left, when you pull on this you should feel a fairly stiff resistance while pulling it across to the right, when its almost fully over, just push the lever up and let it move back towards the left, the lever will then latch in (up) and keep the valve open, but, as stated above, will not operate the micro switch as its only latched open when draining or refilling the system and you don't want your boiler, that you forgot to switch off!, firing up with no water in it. When energised open the valve will move fully across and engage the micro switch to fire the boiler. If the lever feels loose and floppy without any resistance when pulling across when NOT energised then the actuator is kaput and needs renewing. Another feature of these valves is that if you have it manually latched open say when refilling the system and its then energised, when its deenergised again the valve will close automatically as the lever will have fallen down, out of its latch, when motorised fully across.

A boiler flowrate of 0.6m3/hr, 10LPM, with a dT of 10C gives a output of, 10*60*10/860, 6.98kw, with rad(s) outputs of ~ 21% (flow/return, 40C/30C) of their T50 rating. I really can't see any reason for the system to be pulling in air, the distance from the F&E cistern level to the pump is 3.7M and because the vent & cold feed are teed in before the pump suction then the pump discharge pressure will be 6.7M (@3.0M pump head) and irrespective of the pump head, the lowest pressure in any part of that system has to be 3.7M or greater. Try and do that glass test before you go on holiday (and enjoy), IF the vent is pulling in air continuously then very very strange, the obvious one is wrong pump orientation but we know that the pump is pumping upwards. Apart from that, air ingress, over time, can occur through pump gaskets or non barrier "plastic" pipework etc.

Thats a nice circ pump, I've installed a few of them in my relations systems. They also show the flowrate in m3/hr, you might post this while running in CC2 (Fixed speed2) @ 3.0M on CH, you might expect to see ~ 0.7/0.8m3/hr, the pump also displays the power in watts (W), please post this as well, How many rads??, Not sure what you mean by the pipe calcs, for every meter change in level in a 22mm copper pipe, 0.32L of water has either to be added to it or removed from it?, IMO. Do you leave the shut off caps on the two (automatic?) vents open allways and do you see or hear any air venting from them?, if you don't leave them open, why not?.

Can you post a photo of the pump&pipework as is now? How far is the boiler (elevation wise) below the pump? You might do that glass test again but in a slightly different way which should prove whether the vent is continually drawing in air or not. With the pump running at ~ 3M, only then immerse the vent end in the glass of water and see does the level remain the same. 22mm of copper pipe has a ID of 20.2mm so should have a capacity of 0.32L/M, a " 1 pint" glass say 0.5L, if all the water was sucked out of it on pump start up then the level in the vent must have dropped by 1.6M, or 0.8MM if a 1/2 pint glass, I've read that the level in a normal system falls by ~ 10mm in both the vent&cold feed with a running pump.

The photo shows either a mid position valve or a diverter valve (with the adjustable spanner), why/how is the F&E cistern only feeding the CH circuit, its teed into the pump inlet?, and whats the other pipe for?