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ASHP failing to reach delta T


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Hello there,

 

Ive recently installed a Daikin Altherma 3 H HT and have noticed that it never seems to reach the configured delta T.

 

The heat pump main zone is configured for UFH which the manual claims should follow a delta T of between 3-10C. Leaving water temperature is set to 35C and it seems to be able to heat the property to about 19C when outside is 8C.  
 

However, from the sensor readings it seems that inlet temperature is often the same (occasionally, even higher) as the leaving temperature. This tells me the heatpump is working for nothing as no heat is leaving the loop. 

 

Because of this the heat pump seems to runs almost continuously costing energy in the the lower 30s kWh/day which is costing me a fortune…

 

The UFH manifold shows a delta of about 8C (35C in, 28C out). Why do I not see this same drop on the heat pump?

 

By the way, the second zone is comprised of large radiators and it’s configured for 40C (there’s a mixing valve on the UFH preventing it getting too high temp water). 

 

Any help with debugging this issue would be much appreciated. 

Edited by rhymecheat
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So if both zones or just the radiators are demanding heat then the output water temperature will be 40 C but if only the UFH zone is demanding heat then the output water temperature will be 35 C?  And the heat pump is consuming a lot of energy but appearing not to do so because the return water temperature is almost the same as the leaving water temperature?  Could the pump speed be too high?  Reducing the pump speed ought to increase the delta T.

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3 hours ago, ReedRichards said:

So if both zones or just the radiators are demanding heat then the output water temperature will be 40 C but if only the UFH zone is demanding heat then the output water temperature will be 35 C? 

Correct!

 

3 hours ago, ReedRichards said:

And the heat pump is consuming a lot of energy but appearing not to do so because the return water temperature is almost the same as the leaving water temperature?

Indeed.

 

3 hours ago, ReedRichards said:

Could the pump speed be too high?  Reducing the pump speed ought to increase the delta T.

Manual states that any pump limitation will compromise the ability to achieve delta T so I’m not sure but I still have it a shot. 
 

It also states a minimum of 25l/min is required at all times but when I checked, it was at about 30l/min. Now, there are 3 pumps in the system: the heatpump one, a pump to send water to the system, and a pump for the UFH manifold pump. 
 

When I reduce the heatpump speed (have options for 90, 80, 70 or 60% limitation) I can get it down to almost 20l/min. Still, the return temp is as high as leaving. 
 

However, I don’t fully understand what reducing the other pumps would do to the system. Currently, these other 2 pumps are  Grundfos set at speed 3 (the UFH manifold pump can also do constant pressure instead). I don’t know if reducing these other pumps would reduce the heatpump speed or just fail to move all the water the heatpump is dishing.

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10 hours ago, rhymecheat said:

From the sensor readings it seems that inlet temperature is often the same (occasionally, even higher) as the leaving temperature. This tells me the heatpump is working for nothing as no heat is leaving the loop.


This doesn’t seem to make much sense from the point of view that the ASHP (when running) simply must be increasing the temperature of the water running through it otherwise it would not be 35* in the first place - and the property is warm.

 

Does it ever achieve 40*?

 

Are you able to compare the predicted heat loss at 8* outside temperature with the electrical consumption?

Edited by J1mbo
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What heat pump do you have that has a fixation about delta t?

 

My own (LG) heat pump just sets "Leaving Water Temperature" i,e, the temperature of the flow leaving the heat pump. It does not care about the return temperature, it just adjusts it's power output to keep the leaving temperature at the set point.  When only 1 UFH zone is active the return temperature can be very close to flow temperature and the heat pump will run at very low power.

 

Exactly how are you measuring that the heat pump is consuming a lot of power when delta t is very low?  that does not make sense.

 

 

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Are the sensors fixed in the correct locations and wired to the correct terminals on the control panel? Not unheard of for installers to mix these up. 

 

Also could it be that inlet temperature is a sensor further down the line from the ASHP. Ie. just before it enters the UFH manifold?

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1 hour ago, J1mbo said:

Does it ever achieve 40*?

 

Are you able to compare the predicted heat loss at 8* outside temperature with the electrical consumption?

Yes. When the rads come on, it has no issue achieving 40C. It has no issue achieving 55 if needed either. What I find weird is that it never seems to maintain a temperature for longer than a minute before dropping drastically. This is why I think it’s consuming so much power in the first place. How do I go about comparing the heat loss?

 

29 minutes ago, ProDave said:

What heat pump do you have that has a fixation about delta t?

 

My own (LG) heat pump just sets "Leaving Water Temperature" i,e, the temperature of the flow leaving the heat pump. It does not care about the return temperature, it just adjusts it's power output to keep the leaving temperature at the set point.  When only 1 UFH zone is active the return temperature can be very close to flow temperature and the heat pump will run at very low power.

 

Exactly how are you measuring that the heat pump is consuming a lot of power when delta t is very low?  that does not make sense.

 

 

I’m just looking at the warnings in the manual regarding the delta T. I can’t really correlate the high power with the low delta T, I’m just noticing that the power usage is abnormally high and that return and flow temperature are always close together which I didn’t think they should be. 

 

32 minutes ago, Luke1 said:

Are the sensors fixed in the correct locations and wired to the correct terminals on the control panel? Not unheard of for installers to mix these up. 

 

Also could it be that inlet temperature is a sensor further down the line from the ASHP. Ie. just before it enters the UFH manifold?

That I don’t really know but I can try and confirm.

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4 minutes ago, rhymecheat said:

Im just looking at the warnings in the manual regarding the delta T. I can’t really correlate the high power with the low delta T, I’m just noticing that the power usage is abnormally high and that return and flow temperature are always close together which I didn’t think they should be. 

So you are just guessing.

 

Make and model of ASHP?

 

Type size and age of house? insulation levels etc?

 

Has this just been fitted? what if anything was there before?

 

Was any SAP or other analysis done predicting heat load requirements?

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How is your flow and return measured?  My ASHP's flow and return sensors were poorly installed; zip tied to plastic pipes.  Luckily they both read low so delta is about right.  Might be worth checking how and where they are installed.   

Edited by Kevm
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11 minutes ago, ProDave said:

So you are just guessing.

 

Make and model of ASHP?

 

Type size and age of house? insulation levels etc?

 

Has this just been fitted? what if anything was there before?

 

Was any SAP or other analysis done predicting heat load requirements?

I’m hypothesising. I’m asking here to be corrected or validated. If I see two things that are strange I can’t help but think they’re related to the same issue. More probable then there being two separate issues. 
 

The unit is a Daikin Altherma 3 H HT. indoor unit is the etbx16ef6v (the wall mounted one). 
 

House just got fully renovated and properly insulated. Used a FLIR camera to look for week spots and couldn’t find any obvious ones. 
 

the heatpump is new and is replacing a 35 year old boiler that couldn’t even heat the house to 16C in the winter. All the pipes have been replaced, all the rads replaced for bigger low temperature ones. Downstairs is UFH and it seems to be the only area that never reaches desired temperature (max I can get with 35C is about 19.3C over a period of about 6/7 hours). I could increase the leaving temperature but then the costs become even higher. 
 

yes, analysis was done but I have no access to it unfortunately. 

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11 minutes ago, Kevm said:

How is your flow and return measured?  My ASHP's flow and return sensors were poorly installed; zip tied to plastic pipes.  Luckily they both read low.  Might be worth checking how and where they are installed.   


I believe the indoor unit for the heatpump measures this from pipe in/pipe out

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12 minutes ago, rhymecheat said:

House just got fully renovated and properly insulated.

 Downstairs is UFH and it seems to be the only area that never reaches desired temperature (max I can get with 35C is about 19.3C over a period of about 6/7 hours)

What is the floor finish downstairs? Do you know the thickness of floor insulation? Perimeter insulation (not 5mm lagging only) present?

30kWh of heat (or x COP, as you were quoting leccy use I believe) is dissipated somewhere each day, so the question is to find where.

12 minutes ago, rhymecheat said:

Used a FLIR camera

Can you use it to confirm flow and return temperatures, in case ASHP have sensor/wiring/mapping fault?

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11 minutes ago, Olf said:

What is the floor finish downstairs? Do you know the thickness of floor insulation? Perimeter insulation (not 5mm lagging only) present?

30kWh of heat (or x COP, as you were quoting leccy use I believe) is dissipated somewhere each day, so the question is to find where.

Can you use it to confirm flow and return temperatures, in case ASHP have sensor/wiring/mapping fault?

Floor is amtico on a 40mm insulation I believe. Not sure about perimeter insulation. 
 

I’ve used the FLIR on the pipes. Right now leaving temperature is at 35C. Inlet at 36C

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37 minutes ago, rhymecheat said:

I’m hypothesising. I’m asking here to be corrected or validated. If I see two things that are strange I can’t help but think they’re related to the same issue. More probable then there being two separate issues. 
 

The unit is a Daikin Altherma 3 H HT. indoor unit is the etbx16ef6v (the wall mounted one). 
 

House just got fully renovated and properly insulated. Used a FLIR camera to look for week spots and couldn’t find any obvious ones. 
 

the heatpump is new and is replacing a 35 year old boiler that couldn’t even heat the house to 16C in the winter. All the pipes have been replaced, all the rads replaced for bigger low temperature ones. Downstairs is UFH and it seems to be the only area that never reaches desired temperature (max I can get with 35C is about 19.3C over a period of about 6/7 hours). I could increase the leaving temperature but then the costs become even higher. 
 

yes, analysis was done but I have no access to it unfortunately. 

 

Could it also be that the system is compensating for a big change in your desired room temperature? 

Are you running the system in Weather Compensation mode and are you generally keeping the house at a steady temperature, minimising the use of any setback temperatures?

UFH and especially ASHP benefit from longer run time and not in short bursts, but I'm sure you're already aware of this? 

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5 minutes ago, Luke1 said:

 

Could it also be that the system is compensating for a big change in your desired room temperature? 

Are you running the system in Weather Compensation mode and are you generally keeping the house at a steady temperature, minimising the use of any setback temperatures?

UFH and especially ASHP benefit from longer run time and not in short bursts, but I'm sure you're already aware of this? 

Yes good point. I’m running it at a constant 35C but setting the thermostats to go down during the night. During the night the thermostat is set to go from 20 to 18. At this stage the leaving temp from the heatpump can go too as low as 25C (but not lower). But, in the morning when I come down it read 17.3 and in the evening when I go up it’s never above 19.3. 

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1 hour ago, rhymecheat said:

I’m hypothesising. I’m asking here to be corrected or validated. If I see two things that are strange I can’t help but think they’re related to the same issue. More probable then there being two separate issues. 
 

The unit is a Daikin Altherma 3 H HT. indoor unit is the etbx16ef6v (the wall mounted one). 
 

 

 

Why did you need a High Temperature model of heat pump?  Why do you think over 30 kWh per day is wrong?  I have 12 kW ASHP.  For the last couple of days it has been quite mild for the time of year and the daily consumption was about 26 kWh.  There have been a couple of cold days when consumption was over 40 kWh in a day.  But my average for the entirety of last year was 19 kWh per day.       

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so this is about 11kW, depending on configuration. The brochure is sparse on details of efficiency vs temp, is it possible that being an HT unit it'll perform better at a slightly higher LWT?

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I don't see any particular problem with R32 here. But anyway, understanding what the property heat loss is supposed to be, seems key. Does the controller give any metrics indicating the total thermal output, or the environmental yield?

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2 minutes ago, dpmiller said:

so this is about 11kW, depending on configuration. The brochure is sparse on details of efficiency vs temp, is it possible that being an HT unit it'll perform better at a slightly higher LWT?

Brochure claims a COP of 4.86 at 7C outside and 35C leaving.

And 3.70 at 7C outside and 45C leaving. 
 

so setting it at 35C should be better than 45. When I set it to 45 however, the cost goes up considerably. 

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3 minutes ago, J1mbo said:

I don't see any particular problem with R32 here. But anyway, understanding what the property heat loss is supposed to be, seems key. Does the controller give any metrics indicating the total thermal output, or the environmental yield?

Sadly no as the thermal output is only displayed when glycol is not in the system, which it is.

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24 minutes ago, ReedRichards said:

 

Why did you need a High Temperature model of heat pump?  Why do you think over 30 kWh per day is wrong?  I have 12 kW ASHP.  For the last couple of days it has been quite mild for the time of year and the daily consumption was about 26 kWh.  There have been a couple of cold days when consumption was over 40 kWh in a day.  But my average for the entirety of last year was 19 kWh per day.       

I didn’t but it was the only one with a design my wife approved (insert massive eye roll). I think over 30kwh/day is wrong as with a COP of over 3 at 45C and 8C outdoor, that would seem like a massive amount of heat. But then the return temperature always stays high which tells me the heat is not leaving the loop or too much heat is being produced 

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You need to understand the building heat loss to draw any conclusions here.

 

My advise (FWIW) would be to contact the installer and get that. Then set the system to run 24x7 for a week and start making measurements after that, as currently the consumption is feeding thermal loss and increasing the stored thermal energy of the structure each day (which is then dissipated outside of the heating period). Coupled with monitoring the outside temperature (e.g. degree days for the location), the energy supplied can then be compared to the calculated thermal loss of the structure and some conclusions drawn from that.

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So you had an oil boiler that struggled to keep the house warm.  You have replaced it with a heat pump that is probably lower power than the previous boiler (I have failed to find what output power this heat pump is, Daikin don't make it easy to find out) and still have the problem that downstairs does not heat up enough.

 

You are relying on the improvements to insulation to even make the new lower powered heat source work for your house, but don't seem to know much about the insulation fitted.  You talk of 40mm floor insulation, if that is all you have it is WAY too little for under floor heating.

 

Did you pay for all the upgrades to insulation and the heat pump install as a package to one company?  If so I would be getting them back to sort it out.

 

If you are struggling with an outside temperature of 8 degrees, you are really going to struggle when it gets properly cold.

 

To give us some idea of expectations, how much oil did you burn in a year with the previous boiler?  That will give an idea of the heat losses of the house prior to any improvements.

 

Unless they fitted a dedicated electricity meter for the heat pump, or your has it's own metering built in, it is hard to actually measure how much it is using. In our house the heating is only about a quarter of all electricity usage.

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4 minutes ago, ProDave said:

So you had an oil boiler that struggled to keep the house warm.  You have replaced it with a heat pump that is probably lower power than the previous boiler (I have failed to find what output power this heat pump is, Daikin don't make it easy to find out) and still have the problem that downstairs does not heat up enough.

 

You are relying on the improvements to insulation to even make the new lower powered heat source work for your house, but don't seem to know much about the insulation fitted.  You talk of 40mm floor insulation, if that is all you have it is WAY too little for under floor heating.

 

Did you pay for all the upgrades to insulation and the heat pump install as a package to one company?  If so I would be getting them back to sort it out.

 

If you are struggling with an outside temperature of 8 degrees, you are really going to struggle when it gets properly cold.

 

To give us some idea of expectations, how much oil did you burn in a year with the previous boiler?  That will give an idea of the heat losses of the house prior to any improvements.


it’s the EPRA14DV3 on this brochure: https://www.daikin.co.uk/content/dam/dauk/document-library/Brochures/Heating/Heating Installer brochures/Daikin Altherma 3 H HT_767.pdf

 

Heatpump installation was done by one company and house upgrade by another. The property was massively extended so all both companies had to work with was the drawings regarding calculations. Both plumber responsible for the build and the heatpump engineer were in contacting regarding what the UFH should look like but ultimately plumber installed it. Heatpump engineer however, was fully in charge of the rads. 

With the old boiler, total consumption for last year was 14890kwh if that helps. 

 

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So it's a 10kW heat pump then.  Probably half the power of the previous oil boiler (that struggled to heat the original house) so lets hope the now enlarged house really has some better insulation.  you NEED to pester the builder to find what calculations they did about the expected heat loss of the enlarged and hopefully improved house now, AND find out exactly what insulation has been placed under the UFH pipes.

 

Assuming the enlarged, but better insulated house still needs the same amount of heat, then 14890kWh of heat delivered by a heat pump at a COP of 3 and a present electricity price of 20p per kWh will cost £992 pa

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