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ASHP failing to reach delta T


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4 hours ago, J1mbo said:

Higher pump speed = higher average temperature = greater energy transfer.

 

Assuming higher pump speed implies higher flow rate,  then there is more energy in flow to UFH, yes  BUT a higher flow rate also means less time for energy to transfer to the slab and a higher return temperature.  Energy transfer to the slab is a function of delta-t  (between flow and return) and flow rate, not the temperature in itself.

 

A high return temperature and low delta-t can be indicative of a flow rate that is too high, preventing sufficient energy transfer to the slab.  This is where the Salus actuators various people on the forum use come in handy, as well as acommodating runs of different lengths without requiring manual balancing.

 

Our recent install had this issue as the installer did the bulk of the work before Christmas, but didn't install the Salus actuators and left all UFH ciruiits fully open and 2 pumps on maximum so eveything was working like crazy, but slab wouldn't heat up.  Playing around with things over the new year, I reduced pumps to minumum and manually adjusted the UFH loops down to 1L/min each and now works great with approx 7C delta-t.

 

Edited by Dan F
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3 hours ago, Dan F said:

 

Assuming higher pump speed implies higher flow rate,  then there is more energy in flow to UFH, yes  BUT a higher flow rate also means less time for energy to transfer to the slab and a higher return temperature.  Energy transfer to the slab is a function of delta-t  (between flow and return) and flow rate, not the temperature in itself.

 

A high return temperature and low delta-t can be indicative of a flow rate that is too high, preventing sufficient energy transfer to the slab.  This is where the Salus actuators various people on the forum use come in handy, as well as acommodating runs of different lengths without requiring manual balancing.

 

Our recent install had this issue as the installer did the bulk of the work before Christmas, but didn't install the Salus actuators and left all UFH ciruiits fully open and 2 pumps on maximum so eveything was working like crazy, but slab wouldn't heat up.  Playing around with things over the new year, I reduced pumps to minumum and manually adjusted the UFH loops down to 1L/min each and now works great with approx 7C delta-t.

 

Interesting… Can I replace thermostat activated actuators with those? What’s happens when the thermostat calls for heat? Are they just constantly on instead?

 

Also, what does the actuator actually do? I thought it just opened/closed the flow of water and the glass gauge controlled the actual flow to that pipe

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4 hours ago, Dan F said:

Energy transfer to the slab is a function of delta-t  (between flow and return) and flow rate, not the temperature in itself


The energy transferred from the pipes to the slab depends only on the temperature difference and thermal conductivity between them. Water speed within the pipe cannot alter the thermal loss across that boundary. If there is a higher average water temperature in the loop, more energy will be transferred (per unit time) all else being equal.

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35 minutes ago, J1mbo said:

The energy transferred from the pipes to the slab depends only on the temperature difference and thermal conductivity between them. Water speed within the pipe cannot alter the thermal loss across that boundary. If there is a higher average water temperature in the loop, more energy will be transferred (per unit time) all else being equal.

 

You are correct, and it's also true that the energy transferred to UFH (as a system) is a function of delta-t and flow rate, not the temperature in itself.  What I said that was erronous was regarding "less time for energy to transfer to the slab".  That said, high flow rates do impact the energy transfer to the slab, but this isn't due to time, but rather due to reduced temperature difference between water in pipe and the slab (assuming constant ASHP output).

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1 hour ago, rhymecheat said:

Interesting… Can I replace thermostat activated actuators with those?

 

Yes.  You could use them constantly on if you aren't using zones (we aren't), or they can be used instead of standard zone actuators and will balance when on.

 

Quote

Also, what does the actuator actually do? I thought it just opened/closed the flow of water and the glass gauge controlled the actual flow to that pipe

 

"The actuator has two remote sensors which are clipped onto the flow and return floor heating pipes from the manifold (16mm pipe only). These sensors are constantly monitored and the actuator will adjust the flow rate to maintain a Delta T of 7°C for the UFH circuit."

 

https://salus-controls.com/uk/product/thb23030/

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/controls-quickshop/actuator-auto-balancing/#

 

Edited by Dan F
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12 minutes ago, Dan F said:

 

Yes.  You could use them constantly on if you aren't using zones (we aren't), or they can be used instead of standard zone actuators and will balance when on.

 

 

"The actuator has two remote sensors which are clipped onto the flow and return floor heating pipes from the manifold (16mm pipe only). These sensors are constantly monitored and the actuator will adjust the flow rate to maintain a Delta T of 7°C for the UFH circuit."

 

https://salus-controls.com/uk/product/thb23030/

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/controls-quickshop/actuator-auto-balancing/#

 

If the actuator controls the flow, what does the actual flow gauge do? I’m referring to those glass things with the indicator that you can adjust by rotating it

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3 minutes ago, rhymecheat said:

If the actuator controls the flow, what does the actual flow gauge do? I’m referring to those glass things with the indicator that you can adjust by rotating it

 

You don't need to use it (unless you want to know what flow-rate is for some reason).  These are typically used for manual balancing, but this isn't required with these.

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2 minutes ago, Dan F said:

 

You don't need to use it (unless you want to know what flow-rate is for some reason).  These are typically used for manual balancing, but this isn't required with these.

Oh I see! Thanks, I’ll look into them

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14 hours ago, Dan F said:

 

Yes.  You could use them constantly on if you aren't using zones (we aren't), or they can be used instead of standard zone actuators and will balance when on.

 

 

"The actuator has two remote sensors which are clipped onto the flow and return floor heating pipes from the manifold (16mm pipe only). These sensors are constantly monitored and the actuator will adjust the flow rate to maintain a Delta T of 7°C for the UFH circuit."

 

https://salus-controls.com/uk/product/thb23030/

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/controls-quickshop/actuator-auto-balancing/#

 

I have these, brilliant bit of kit. Highly recommend them.

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On 12/01/2022 at 14:10, rhymecheat said:

Yes, there is a buffer tank, it’s a Cordivari 29W 26L

Just something which I think was not referred by anyone. Is your buffer tank connected "in series" with the heating circuit, or is your ASHP heating the buffer tank and then another water circuit goes to the UFH/rads (with another circulating pump)?

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38 minutes ago, Bruno said:

Just something which I think was not referred by anyone. Is your buffer tank connected "in series" with the heating circuit, or is your ASHP heating the buffer tank and then another water circuit goes to the UFH/rads (with another circulating pump)?

The second one. Outdoor unit connects to the indoor one which connects to the buffer tank. Then a Grundfos pump (set at speed 3) pumps from that tank to the UFH/rads

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14 minutes ago, rhymecheat said:

The second one. Outdoor unit connects to the indoor one which connects to the buffer tank. Then a Grundfos pump (set at speed 3) pumps from that tank to the UFH/rads

Oh, that might be your problem. The buffer tank is probably too small IMO.

Your ASHP's output goes to the buffer tank and returns. As the water mass is too small it can't transfer enough heat to the "secondary" circuit so there is no temperature drop.

 

edit: why is the consumption so high, that I don't know...

Edited by Bruno
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34 minutes ago, rhymecheat said:

The second one. Outdoor unit connects to the indoor one which connects to the buffer tank. Then a Grundfos pump (set at speed 3) pumps from that tank to the UFH/rads

Have you been reading my thread “UFH manifold problem”? My problem was not getting warm enough water to the manifold and it appears using an indirect buffer was the problem (the ASHP connected to the coil was not transferring enough heat to the buffer). I am still trying to get mine to work properly with thanks to @PeterWand @Nickfromwales and @ProDave.

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1 hour ago, joe90 said:

Have you been reading my thread “UFH manifold problem”? My problem was not getting warm enough water to the manifold and it appears using an indirect buffer was the problem (the ASHP connected to the coil was not transferring enough heat to the buffer). I am still trying to get mine to work properly with thanks to @PeterWand @Nickfromwales and @ProDave.

Ah, however the manifold gauge shows the same temperature I set on the heatpump. And it’s showing a return of about 7C below that so I think it’s looking good in there. 

 

38 minutes ago, J1mbo said:

@rhymecheat have you been able to read the flow and return with the infrared for the heat pump and also for the backup heater as yet?

Behold… temperatures in there are as expected with a nice delta between leaving and return temperature. Now I’m thinking what I see in that inlet sensor is coming from the buffer tank instead. 
 

So today things took a bit of a turn. I turned everything to the max yesterday before bed and let it rip: pump at 55C, unrestricted speed, UFH manifold mixing valve at 55C too and opened all the flow gauges. Temperature downstairs in the morning was 19C which is a tremendous improvement. What surprises me the most though was the consumption: 2/3kwh every hour. The smart meter notes about 10min of pump off followed by about 12min of pump on at about 1kwh (which I’m guessing is topping up the buffer tank). 
 

The UFH manifold then showed a delta of less than 3 which indicated to me that I had the flow too fast so I adjusted the zones little by little throughout the day until I got a consistent 7C delta. Ultimately I think I’ll order those self balancing actuators for this. 
 

Usage seems stable and the downstairs has been at at constant 19.5C the whole day. 
 

good results but I’m still not sure what’s happened. I wonder if I had to do the work of heating the house first. 

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