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High air source heat pump running costs – Vaillant AroTherm Plus

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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  

Hi everyone, I'm looking for some advice please and have seen that there are some very knowledgable people using this forum.  One month ago we moved into a new build house which has underfloor heating throughout the ground floor and radiators upstairs. The property has a large number of floor to ceiling glazed windows, but a high B rated EPC. The primary heat source is a air source heat pump, and the running cost for the first month appears to be very high - especially since it has been so mild. I will try to include all the details here in the hope that someone can provide an insight into our setup and what might be done to optimise it.

EPC details

  • 276 square meters
  • B rated (86 score)
  • All scores "very good", except:
    • Hot water "good" from main system
    • Airtightness "average" - air permiability 9.9m3/h.m2 as tested (the three and two should be superscript)
    • Primary energy use for propert is 58 kilowatt hours per square meter (kwh/m2)
    • Estimated yearly energy cost for the property = £1001 (presumably this is based on gas?)
    • Space heating 14994 kWh per year
    • Water heating 2425 KWh per year

Current electricity usage (last month)

  • Day rate = 1761.1 kwh
  • Night rate = 579.7 kwh
  • Total = 2340.8 kwh
  • Average daily usage during December = 70.93 kwh per day (today's usage is 112kwh!)

Installation details

  • Airsource Heat Pump Model - Vaillant ecoTherm Plus VWL 105/6 or 125/6 (not sure which)
  • uniSTOR HP
  • Buffer cylinder VPS R 100/1 M (I think)
  • Controller multiMATIC VRC 700/4
  • Heat Pump control interface module VWZ AI
  • Weather compensated system control VRC 700/6 - I am not sure whether this is optimally setup because the rep indicated it could have been done differently, with a full Vaillant system rather than the themostat setup used. It looks to have just one zone configured and DHW. The temp is set to 26.0 degrees and set back to 26.0 degrees. See image of the big number on the panel the temp is normally around 16 degrees whenever I've looked - is this the flow heat? The DWH is set to 50 degrees. The water always seems to be hot enough. Is it correct for the weather compensated system control to be in the insulated area of the garage?
  • VWZ MWT 150
  • Six heating zones, five downstairs and one for the whole of upstairs. They are controlled using Heatmiser Neo2 Thermostats.
  • Thermostats have been set to 20-22 during the day and around 17 at night depending on the room. The upstairs stat rarely seems to reach temperature (note large glazed windows on all sides and high ceilings)
  • There are manifolds for the zone heating in the garage (boxed in) and the understairs cupboard.
  • The system is installed in a store room section at the rear of the garage which I assume is reletively well insulated for this purpose, but definately not as well insulated as the house itself.
  • My neighbour has a very similar setup (two similar new build properties are sited next to each other) in a slightly different house design and has experienced similar high levels of consumption.

Other information:

  • I noticed water pooling on the plaform built for the unit (after raining) - I will flag this to the installer, might this impact performance?
  • I have noticed some draughts in the house that need addressing, but can't believe this is the root cause.

If anyone can offer any advice about how to maximise efficiency of our system I would be extremely grateful because this is currently costing well over £400 per month which is significantly higher than expected, and we're still on a fixed tariff and it's not been that cold yet! We are in contact with Vaillant and any information that might help inform discussions will help a lot.

Happy to provide further information as required. Many thanks in advance.

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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  

Sorry, it's not an ecoTherm Plus, it's an aroTherm Plus.


   
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(@kev-m)
Famed Member Moderator
5561 kWhs
Joined: 3 years ago
Posts: 1299
 

@webcmg 

I'm sure @derek-m will help you with the technical details. However, although my house is smaller than yours at 160m2, its heat requirements are similar because it's older.  My average in December is 25.5kWh/day to heat the whole house to 21C for 19 hours/day.   As long as the design of the system is sound you should be able to improve on 70kWh/day.  

If the EPC is correct, your heating requirements are c. 15000kWh/year.  You should normally need 15% of that in December, say 2300kWh.  Even at a COP of 2.3, that's 1000kWh/month consumed; a lot less than you're using. 

A question; how much hot water do you use?

   


   
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(@derek-m)
Illustrious Member Moderator
13722 kWhs
Veteran Expert
Joined: 3 years ago
Posts: 4165
 

Hi @webcmg 

I have been searching for a manual that details how to check and set the weather compensation curve, but have not been able to locate one.

Unless you have a manual that shows this information, then I would suggest that you ask your installer to demonstrate how the weather compensation has been set on your system, and how it can be adjusted if necessary.


   
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(@spdtdl)
New Member Member
0 kWhs
Joined: 2 years ago
Posts: 1
 

I have a 5KW aroTHERM plus.

Manual:

My settings (desired temp 20.5 / setback 20.5) System on 24/7

Adaptive heating curve: OFF
Heating Curve 0.6 (Temp Mod)
Min Flow Temp 20 / Max Flow Temp 45

Domestic hot water 48C
Cylinder boost offset 8K

3 bedroom detached new build, my unit also pools water below it.

HTH

This post was modified 2 years ago by SPDTDL

   
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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  
Posted by: @kev-m

@webcmg 

I'm sure @derek-m will help you with the technical details. However, although my house is smaller than yours at 160m2, its heat requirements are similar because it's older.  My average in December is 25.5kWh/day to heat the whole house to 21C for 19 hours/day.   As long as the design of the system is sound you should be able to improve on 70kWh/day.  

If the EPC is correct, your heating requirements are c. 15000kWh/year.  You should normally need 15% of that in December, say 2300kWh.  Even at a COP of 2.3, that's 1000kWh/month consumed; a lot less than you're using. 

A question; how much hot water do you use?

   

Thanks for replying Kev. This is very reassuring.  We don't use a great deal of hot water. There are two of us in the house and we normally have a reasonable length shower each day.


   
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(@derek-m)
Illustrious Member Moderator
13722 kWhs
Veteran Expert
Joined: 3 years ago
Posts: 4165
 

Hi @webcmg 

Look at pages 15 and 16 in the manual kindly provided by SPDTDL. Try setting the weather compensation curve at 0.6 or 0.8.

 

 


   
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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  
Posted by: @spdtdl

I have a 5KW aroTHERM plus.

Manual:

My settings (desired temp 20.5 / setback 20.5) System on 24/7

Adaptive heating curve: OFF
Heating Curve 0.6 (Temp Mod)
Min Flow Temp 20 / Max Flow Temp 45

Domestic hot water 48C
Cylinder boost offset 8K

3 bedroom detached new build, my unit also pools water below it.

HTH

Thanks, what is the function of the set back temp and cylinder boost offset?


   
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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  
Posted by: @spdtdl

I have a 5KW aroTHERM plus.

Manual:

My settings (desired temp 20.5 / setback 20.5) System on 24/7

Adaptive heating curve: OFF
Heating Curve 0.6 (Temp Mod)
Min Flow Temp 20 / Max Flow Temp 45

Domestic hot water 48C
Cylinder boost offset 8K

3 bedroom detached new build, my unit also pools water below it.

HTH

Also what's your target flow temp set to please? Also by 24/7 should I update this in the Time Programmes menu? Currently set to 06.00-22.00.

My heat curve was set to 1.1, now changed to 0.6

This post was modified 2 years ago 2 times by webcmg

   
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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  
Posted by: @derek-m

Hi @webcmg 

Look at pages 15 and 16 in the manual kindly provided by SPDTDL. Try setting the weather compensation curve at 0.6 or 0.8.

 

 

Done, assume this is the same as heat curve? Changed to 0.6 for now.  


   
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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  

Just quick message of thanks to everyone for their help so far. Cheers, it's appreciated.


   
Derek M, Morgan, Derek M and 1 people reacted
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(@webcmg)
Estimable Member Member
515 kWhs
Joined: 2 years ago
Posts: 105
Topic starter  

@spdtdl just learnt how to tag! Sorry, meant to do so in reply with questions above. 


   
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