UFH manifold problem

[dpmiller]

where is the NRV?

[joe90]

3 minutes ago, dpmiller said:

where is the NRV?

It’s in the connection between the lower rail and the bottom of the pump. It acts like a bypass in case the TRV shuts so the pump can still move water and also allow cool water to blend with the hot into the pump. @ProDave was right that the NRV was opening as it gave less resistance than the pipework back to the buffer tank 10m away. It would be good if I could adjust the spring in there so it would only open if the TRV shut.?

Edited January 1, 2022 by joe90

[dpmiller]

gotcha. can you remove the NRV and preload the spring with a spacer or give it a stretch out?

[joe90]

13 minutes ago, dpmiller said:

gotcha. can you remove the NRV and preload the spring with a spacer or give it a stretch out?

It appears to be pressed into the casting and I can’t get to the back of it to give it a clout! ?‍♂️

[joe90]

Ha! this noise must have been air, ran it for a bit, let it rest then bled it again and it’s gone quiet ?

[Nickfromwales]

So, the “NRV” is a bypass valve and not an NRV in this instance?

Removing this or allowing flow through it can only take away from the pump energy pushing water around the loops, so a bit lost as to how this will promote flow ( even if it has ! ). Most bypass valves are user-adjustable so they can be ‘slackened off’ to allow them to operate at a lower resistance. Was this one not adjustable?

[joe90]

17 minutes ago, Nickfromwales said:

Was this one not adjustable?

No mate, it’s inside the lower connection and only visible by removing the casting from the rails. It’s not that I want to remove it, it’s just that it lets water through it too easily so when the pump is running it’s easier for the water to bypass the pipework from the buffer tank, it just circulates water round the UFH loops. My blocking it off works well as long as the TRV is removed otherwise the pump could burn out pumping against a full blockage. I am relying on the buffer stat to regulate water temp and will monitor it regularly. The heating (manifold pump) is controlled by a room stat.

 

 

Edited January 2, 2022 by joe90

[joe90]

17 minutes ago, Nickfromwales said:

and not an NRV

It is a non return valve in that it only allows water to flow in one direction.

[joe90]

Right, the blocking of the one way valve and removing the TRV has allowed hotter water to reach the  UFH loops, the next problem I am having is the ASHP does not appear to be heating the buffer to a set 35’, it’s run all day and still the temp has not reached the stat temp yet the DHW tank fairly quickly gets up to 48’ after a bath/shower etc. ?‍♂️ Any idea what’s causing this?

[dpmiller]

got a schematic for your system? Are DHW and buffer on zone valves?

[joe90]

26 minutes ago, dpmiller said:

got a schematic for your system? Are DHW and buffer on zone valves?

I will do a CAD (crayon assisted drawing) later, only a diverter valve from heating to DHW.

Edited January 6, 2022 by joe90

[dpmiller]

and that's where I'd start looking. Diverter or mid-positio? Make sure it's going the whole way over and back.

[joe90]

26 minutes ago, dpmiller said:

and that's where I'd start looking. Diverter or mid-positio? Make sure it's going the whole way over and back.

Diverter, yes a good place to start ?.

[joe90]

Right, been monitoring this fir a while, when the DHW tank calls for heat it’s topped up fairly quickly (fir an ASHP) with a flow temp of 50.5’ and the diverter valve fully open. When the buffer calls for heat (tank stat) the flow temp is about 40’ and the buffer never gets to the stat temp of 35’ despite running fir hours. When the room stat calls for heat which energises the manifold pump the temp at the manifold rises to 30’ but falls within the hour as tho the ASHP/buffer cannot keep up with the demand. I have tried slowing the manifold pump down but this makes little difference. 
 

I cannot understand why the DHW tank is heated fairly quickly to the required temp but it fails to heat the buffer fully and keep up with demand. Luckily the house rarely needs heat due to good insulation. Any ideas chaps?

 

(I have checked/bled for air etc)

Edited January 7, 2022 by joe90

[ProDave]

Could it be that the UFH is simply extracting heat from the buffer at a faster rate than the input coil to the buffer can keep up with?

 

Try shutting down some of the loops so it is only running say half the UFH and see if that gets up to temperature?

[saveasteading]

2 hours ago, joe90 said:

been monitoring this fir a while,

Your sketch is brilliant at explaining the principles. The manufacturers don't do this as well as you.  If you waive copyright I will print it for training the family and questioning prospective installers.

I didn't know the system sent the right temperature in different directions at different times. Perhaps not all do.

 

A basic question if you don't mind. When a tank calls for water does a valve switch to that tank only, and is the ASHP switched to provide the higher/lower temperatures?

[Adam2]

Shouldn't the bottom of each coil be indicated as an output?

 

You could test having UFH off and see how long the buffer takes to reach temp, possibly setting same ASHP temp as for DHW and see if it seems comparable given the volume differences

[dpmiller]

Monitor the temp of the pipe from the diverter valve to the DHW tank when the buffer is heating. It should drop to ambient. If not, the diverter *isn't*...

[joe90]

2 hours ago, saveasteading said:

Your sketch is brilliant at explaining the principles

Thanks 

 

2 hours ago, saveasteading said:

didn't know the system sent the right temperature in different directions at different times. Perhaps not all do.

No, mine does not (but others do). I set the water temp from the ASHP to 50’, I Set the stat on the DHW tank to 48’, I set the sat on the buffer to 35’ (to give a better COP hopefully!!!).

 

2 hours ago, saveasteading said:

A basic question if you don't mind. When a tank calls for water does a valve switch to that tank only, and is the ASHP switched to provide the higher/lower temperatures?

When the DHW calls for heat it energises the diverter valve to send the hot water there, if the heating calls for water the diverter valve (in its “normal” position) sends water to the buffer (or directly to the UFH if no buffer exists).

 

2 hours ago, Adam2 said:

Shouldn't the bottom of each coil be indicated as an output?

Yes it should, go to the top of the class.

 

2 hours ago, Adam2 said:

You could test having UFH off and see how long the buffer takes to reach temp,

I have, it never gets up to temp, was running for hours yesterday and only got to 30’ which is what I don’t understand because the DHW gets to a higher temp ?

 

2 hours ago, dpmiller said:

Monitor the temp of the pipe from the diverter valve to the DHW tank when the buffer is heating. It should drop to ambient. If not, the diverter *isn't*...

I have, (by hand) and apart from heat within the copper coming from the diverter it cools a lot. I have checked that the diverter operates correctly (without taking it apart)

 

right I am off to cut some more kindling for the wood stove, but to be fair even with no heating (I have left it off) the house never gets below 20’.

Edited January 7, 2022 by joe90

[joe90]

Right, just done a test, from cold, ASHP feeding the buffer tank at 48’, buffer got to 35 and stat turned off, room stat turned on to call for heat, manifold pump started and quickly got to 35’ but over 20 minutes this dropped to 27’. Back at the buffer the stat had turned back on so the ASHP feeding the tank again. After 20 minutes it all settled down to a steady 40’ from the ASHP into the tank but a constant 27’ leaving and the same temp at the manifold.

 

conclusion,   The buffer don’t work,    
 

note, the manifold and ASHP pumps matched fir speed.

[PeterW]

Turn the ASHP pump up slightly - sounds like the UFH is drawing heat too fast 

[ProDave]

36 minutes ago, joe90 said:

conclusion,   The buffer don’t work,    

My suspicion is the input coil cannot handle the power level that the UFH is sucking out.  Do you have any data on the buffer tank?

 

Try slowing the manifold pump to reduce the rate heat is taken out and see if the equilibrium temperature rises?

 

EDIT: Peters idea is tackling the same issue in the opposite way. Try both.

[joe90]

1 hour ago, PeterW said:

Turn the ASHP pump up slightly - sounds like the UFH is drawing heat too fast 

Tried that, no difference , I wonder if too fast a pump speed would overwhelm a small ASHP?

Edited January 7, 2022 by joe90

[joe90]

1 hour ago, ProDave said:

Do you have any data on the buffer tank?

I will look it up, yes you may  be right which is why I said earlier it might be better if I remove the buffer altogether, I don’t know why but I thought a charged buffer tank would last a while heating the floor, turns out to be the opposite ?

[joe90]

It’s a tempest indirect, 90 litre, heat up time from cold 26min (not from an ASHP EH!!!). I would have thought it should be a Tempest indirect high gain, heat up time 13minutes (so the coil must be different?). This was all specced by @Nickfromwales as he got a few of us a good deal, any comment mate ?.