Heat pump plumbing thumps on change over from heating water to heating the UFH.

[MikeSharp01]

Been running the new heat pump today testing and commissioning the EMON heat meter. The heat meter is working well and telling me I get about 4.2 COP on heating the slab - with a cold slab at about 12^oC.

 

When I switch to heating the hot water the changeover happens smoothly and the heat meter starts reporting HW correctly BUT when I switch back at the end of the valve close we get an awful thump, I guess water hammer? Is this common and what might the / a cure be?

[JohnMo]

How are you controlling the 3 port valve and pump - is all via the heat pump controller or something else?

 

What valve are you using?

[MikeSharp01]

Its controlled by the heat pump and its the valve that came with the heat pump - this one I think: 

The ZVM28

[Nickfromwales]

You may need a differential bypass valve, across flow and return before the valve.

 

Are you 100% sure that the flow and return are the correct way around, as the thump is often associated with the valve 'paddle' being slammed shut in the flow.

[MikeSharp01]

1 hour ago, Nickfromwales said:

as the thump is often associated with the valve 'paddle' being slammed shut in the flow

Interesting thought and entirely plausible. Here is the basic circuit I used from the install manual - except that the Underfloor Heating (UFH) is where the buffer tank is as we have no buffer tank. This circuit makes sense this way round although I guess you could put the valve in the return junction. The valve is normally open to the UFH and the Heat Pump sends a signal to the valve to change over when Hot Water heating is called for. So the flow comes up the middle of the valve and goes out either to the UFH circuit or the Tank circuit. Hence as the valve closes, on the spring, to the tank circuit it will have the flow helping it close.  If that is the cause of the thump then it's a control problem. Perhaps the Heat Pumps circulating pump should be shut down while the valve changes over although that would be a firmware issue in the controller? 

 

 

[JohnMo]

40 minutes ago, MikeSharp01 said:

Perhaps the Heat Pumps circulating pump should be shut down while the valve changes over

Had a look at mine, and pump doesn't shutdown, it may slow down but doesn't stop. As the paddle moves it doesn't cut flow off, flow basically transitions from one port to the other, with both ports open until the DHW port closed.

 

Assuming the UFH manifold is fully open it shouldn't see an issue.

 

Do you have the piping all clamped up as it should be?

 

No air in the system?

 

If it's water hammer, the pressure wave need something to hit, and bounce back. A photo of the valve and the piping to UFH may help.

 

Assume you don't get any fault codes?

[MikeSharp01]

7 hours ago, JohnMo said:

Assume you don't get any fault codes?

No fault codes.

 

7 hours ago, JohnMo said:

Do you have the piping all clamped up as it should be?

I think so it is all 28mm, one clip at least every 500mm, more often usually inside, although not on the risers to the tank entry points albeit they are fixed at the top of course - can look at that and see if there is any flexing. Outside runs are clipped outside the insulation to cable trays with a flexi at the end to the heat pump.

 

As to air I cannot be sure but there is a trap at the highest points of both the tank and UFH loops (see pic for UFH) and I bled the stubs that will be running to the fan coil units upstairs. (Although I could check those again now its been running for a bit.)

 

Here is a pic of the valve and the UFH pipe work

 

[JohnMo]

Plumbing wise nothing looks obvious.  UFH manifold flow meters, do you have those fully open? Fully open allows the heat pump to vary the circulation pump flow to better manage modulation. Your circulation pump doing DHW is most likely running full speed, so 20+L/min. If you have the flow meters screwed down to 1.4L/min  you flow will be hitting a brick wall with a small hole in it. This could be the reason for the thump on change over also.

[MikeSharp01]

1 hour ago, JohnMo said:

UFH manifold flow meters, do you have those fully open? Fully open allows the heat pump to vary the circulation pump flow to better manage modulation. Your circulation pump doing DHW is most likely running full speed, so 20+L/min. If you have the flow meters screwed down to 1.4L/min  you flow will be hitting a brick wall with a small hole in it. This could be the reason for the thump on change over also.

I did have them almost wide open, little red floaty things as close the bottom of the dial as possible but I backed off the outer two in an attempt to balance the flows a bit as the middle loop is twice as long as the other two happy to leave it all wide open. Will experiment tomorrow.

[Nickfromwales]

18 hours ago, MikeSharp01 said:

ZVM28

Ah!

 

I think you have the wrong valve. 
 

Google says this is a mid-position valve, and you should have a diverter valve.

 

Can you confirm you have a mid vs diverter plz?

[JohnMo]

6 minutes ago, Nickfromwales said:

Ah!

 

I think you have the wrong valve. 
 

Google says this is a mid-position valve, and you should have a diverter valve.

 

Can you confirm you have a mid vs diverter plz?

That's a good spot - even Cool Energy say it's a mid point valve

 

[Nickfromwales]

Yup. Defo the culprit if it’s not a diverter!!

[MikeSharp01]

2 hours ago, Nickfromwales said:

I think you have the wrong valve. 
 

Google says this is a mid-position valve, and you should have a diverter valve.

 

Can you confirm you have a mid vs diverter plz?

Its a diverter not a mid position, this is what is on the invoice: "CE-ZVD28PW - 28mm 3 Port Diverter Valve" sorry for the misdirection.

 

 

 

 

[Nickfromwales]

1 minute ago, MikeSharp01 said:

Its a diverter not a mid position, this is what is on the invoice: "CE-ZVD28PW - 28mm 3 Port Diverter Valve" sorry for the misdirection.

 

 

 

 

:reaches for drinks cabinet: 

 

🙃🤣. 

[MikeSharp01]

5 minutes ago, Nickfromwales said:

:reaches for drinks cabinet: 

Yes, sorry, tomorrow I will make a short video of what's going on, I wonder if the thump is happening out at the machine so I will check that as well.

 

[Nickfromwales]

9 minutes ago, MikeSharp01 said:

Yes, sorry, tomorrow I will make a short video of what's going on, I wonder if the thump is happening out at the machine so I will check that as well.

 

You don’t have to keep saying sorry lol.

 

Water hammer noises are difficult to locate / fault find, but as said the diverter (ahem) valve does a smooth transition, so would not be the usual suspect.