Correct temp of buffer tank

[Wingover]

LG Therma V monoblock set up for DHW and UFH. The DHW is set at 50c and seems to be accurate on the mechanical gauge on the tank itself vs the temp prob of the LG.  The buffer tank is 100L and the LWT on the LG is set to 40c but the tank gauge shows +/- 31c.  Is the buffer tank temp of the mechanical gauge the average between the 40c coming in and the 32c coming back from the manifolds?  Or do I have a problem?  I thought that setting up the LG to 40c would be 40c inside the buffer tank.

[JohnMo]

How is buffer plumbed in 2 ports or 4 ports? And where are you measuring temperature on the buffer?

 

Really you set it for weather compensation, to get the best economy out the heat pump. A set flow temp could be cost you money on anything the coldest day.

[Wingover]

Thank you for your answer.  The buffer tank has 4 pipes in it and in the center of the tank there is a round temp gauge.

[JohnMo]

So the way the buffer is supposed to work.

 

Hot water from ASHP goes in to top port, and out the other side pumped by a pump, return water from heating system go in to the bottom port, the heat pump pulls the water from other other bottom port. In a ideal world the flow either side of the buffer is equal and supply and return water never mix.

 

The temperature in the centre of the buffer should see the mean temperature of the flow and return.

 

Some mixing of the flow and return will move the reading temp up or down.

 

The more unbalanced the flows either side of the buffer the more mixing that occurs, this requires a higher flow temperature from the heat pump than is delivered to the heating system to compensate. Resulting in a drop in CoP.

[Wingover]

Much appreciated, Is there a way to "fix" the mixing and have a better equal temp as you explained?

[IanR]

5 hours ago, Wingover said:

The buffer tank is 100L and the LWT on the LG is set to 40c but the tank gauge shows +/- 31c. 
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I thought that setting up the LG to 40c would be 40c inside the buffer tank.

From the info you've provided, it's difficult to tell. Even if working correctly, the buffer temp at its centre will be cycling between flow and return temp, and there may be some lag in the Temp the sensor is reading as it's likely to be placed in a pocket on the buffer and not within the water itself.

What's your distance between ASHP and Buffer? Is much of that distance outside? and how well insulated are the pipes?

I'm trying to gauge what your losses may be.

Since the HP is set to switch off at an LWT of 40°C, a well designed 4P Buffer would be almost fully charged at the point the LWT temp hits 40°, so the centre of the tank should show close to 40°C (ie. 40°C - losses in flow pipe), once the pocket and sensor have stabilised and as long as the heating circuit isn't circulating at that point. If the heating circuit is circulating the buffer will discharge and the temp will drop. 

At what point were you measuring the 31°C temp? and was it stable at that temp for say 10 mins?

Your DHW is controlled differently, ie, by a temp sensor in the tank, or perhaps the return temp, so the HP LWT will exceed the UVC set point until it's temp requirement is met (potentially masking any losses in the flow/return pipes). The temp of the water in the UVC is also likely to be less transient than the buffer temp, so the gauge is more likely giving stable/accurate readings.

Edited December 15, 2023 by IanR

[Wingover]

The temp sensor is as you said a mechanical one that sits in a pocket and not like the DHW tank that has a real sensor that feeds the heat pump controller.

The ASHP sits about 2m from the outside wall and the buffer is about 3.5m from that wall so in total about 5.5m.  The pipe is insulated.

 

I was looking at the temp while the UFH was running for about 5 hours and the LG controller was showing 40c out 31c back. The incoming temp into the two manifolds was about 34c.

[Marvin]

14 minutes ago, Wingover said:

The temp sensor is as you said a mechanical one that sits in a pocket and not like the DHW tank that has a real sensor that feeds the heat pump controller.

The ASHP sits about 2m from the outside wall and the buffer is about 3.5m from that wall so in total about 5.5m.  The pipe is insulated.

 

I was looking at the temp while the UFH was running for about 5 hours and the LG controller was showing 40c out 31c back. The incoming temp into the two manifolds was about 34c.

Your figures suggest that more heat is lost from the water travelling from the ASHP to the manifolds (unless they blend the flow and return) than from the UFH and returning to the ASHP.

 

I insulated our ASHP flow and return pipes, which are outside the building thermal envelope, to within an inch of their lives and I would recommend everyone do the same. I also insulated the same pipes heavily all the way to the tanks and would recommend do that as well.

[Wingover]

Mine are insulated all the way to the manifolds.  I'm going to take a few pictures and post the setup.

[JohnMo]

Sounds like a typical 4 port buffer, with a decent mismatch in flow rates, so plenty of mixing going on.

[Marvin]

Inside 25mm walled Climaflex pipe insulation for 28mm pipes. View looking up to the ceiling:

 

 

 

 

 

Outside the same wrapped in supersoft insulation and sealed with EDPM

 

 

 

 

[Wingover]

5 minutes ago, JohnMo said:

Sounds like a typical 4 port buffer, with a decent mismatch in flow rates, so plenty of mixing going on.

I adjusted each loop's flow based on length and it seems that all rooms heat up evenly.  What else can I look at?  Here are two pictures of the setup.  What is the flow control valve?  should it be adjusted?

Edited December 15, 2023 by Wingover

[Marvin]

Bypass valve set to about 6 foot head. 30 foot *0.2 = 6foot or 2 meter head. When the pressure to go through the UFH reaches over the 0.2 bar the valve will open and the water will circulate through the bypass valve.

 

Edited December 15, 2023 by Marvin
clarification

[Marvin]

No internal pipe insulation??

[Wingover]

1 minute ago, Marvin said:

No internal pipe insulation??

From the ceiling and up yes. I haven't insulated the pipes from the tank to the ceiling.  I will.  Is the valve set correctly?  The upstairs manifold is 3.8 meter above the orange pump in the picture.

[JohnMo]

3.8m.is .38bar, plus piping pressure losses, so it's likely the pump is just pushing the bypass open.

 

You should be able to here it passing. Get everything up and running and slowly increase the setting until you cannot hear it passing. You should also adjust pump speed, reduce setting until flow rates at the UFH drop a little.

[Wingover]

16 minutes ago, JohnMo said:

3.8m.is .38bar, plus piping pressure losses, so it's likely the pump is just pushing the bypass open.

 

You should be able to here it passing. Get everything up and running and slowly increase the setting until you cannot hear it passing. You should also adjust pump speed, reduce setting until flow rates at the UFH drop a little.

I can hear the water slowly flowing past the bypass valve right now. If I increase (turn towards the 0.50) a little I can hear it flowing much more.  I should not hear any flow??

 

I adjusted the pump to the mid flow setting.  Less and the head pressure is at 2.7 meter and flow is way too low.

[JohnMo]

5 minutes ago, Wingover said:

I can hear the water slowly flowing past the bypass valve right now. If I increase (turn towards the 0.50) a little I can hear it flowing much more.  I should not hear any flow??

 

I adjusted the pump to the mid flow setting.  Less and the head pressure is at 2.7 meter and flow is way too low.

In normal operation you shouldn't hear bypassing water, as the UFH starts to close down, it should start to open. The valve volume increases as the valve is just about closed, then goes silent once completely closed.

 

Sounds like your pump setting was ok.

[Wingover]

Okay, so if I am hearing water flowing past the valve while all zones are open, there is an issue with that valve?

[Marvin]

9 minutes ago, Wingover said:

Okay, so if I am hearing water flowing past the valve while all zones are open, there is an issue with that valve?

Only in as much as it might need turning to 0.3 or further. ( change the valve a bit and wait a while to see the result, by turning the black top clockwise when viewed from above). If you still hear water passing then perhaps turn a little more, doing this when ALL zones are open.

Edited December 15, 2023 by Marvin
further thoughts

[Wingover]

8 minutes ago, Marvin said:

Only in as much as it might need turning to 0.3 or further. ( change the valve a bit and wait a while to see the result, by turning the black top clockwise when viewed from above). If you still hear water passing then perhaps turn a little more, doing this when ALL zones are open.

Okay, all zones are open and I turned it to the 0.3 and now I don't hear a flow.  Could that have been my buffer tank mixing issue?

Edited December 15, 2023 by Wingover

[JohnMo]

4 minutes ago, Wingover said:

Could that have been my buffer tank mixing issue?

Maybe check the temperatures in a hour or soto see if things change.

[Marvin]

2 minutes ago, Wingover said:

Okay, all zones are open and I turned it to the 0.3 and now I don't hear a flow.  Could that have been my buffer tank mixing issue?

Er... When the bypass valve is closed, the water from the pump goes more forcefully to all the zone valves. If any zone valves are open the water will flow through the zone. If they are all closed the pumping will cause the pressure to rise and the pumped water will go through the BYPASS valve as a way out (assuming its not tightened down too much)

 

Some pumps show what pressure they run at, and that pressure has to be taken into consideration when setting the bypass. HOWEVER @JohnMo is right - wait and see what the result is.

[Wingover]

31 minutes ago, JohnMo said:

Maybe check the temperatures in a hour or soto see if things change.

It seems that the temp in the buffer is creeping up slowly so it looks like on the right track.  Thanks for the help!

29 minutes ago, Marvin said:

Some pumps show what pressure they run at, and that pressure has to be taken into consideration when setting the bypass. HOWEVER @JohnMo is right - wait and see what the result is.

So my pump shows:

Head pressure 4.7m

Liter per Minute 39

W (I assume watts??) 63

 

With that info can you figure out the bypass valve setting?

[Marvin]

13 minutes ago, Wingover said:

It seems that the temp in the buffer is creeping up slowly so it looks like on the right track.  Thanks for the help!

So my pump shows:

Head pressure 4.7m

Liter per Minute 39

W (I assume watts??) 63

 

With that info can you figure out the bypass valve setting?

No. The Bypass is dependant on the resistance on the water caused by the length of the UFH zone pipes. However your well below the 0.47 Bar (4.7meter head pressure) that the pump is producing. Basically you want it to be set high enough that when all the zone valves are open no water passes through the Bypass valve but low enough that the pump doesn't try too hard to send the water through the Bypass valve when all zones are closed. I guess where you are is about right if you have only turned it a little. Where does the marker say you are at?