@webcmg Silly question, but this happened to my system. Are you sure the ASHP is not trying to heat the water and the house at the same time? During the cold spell last year I was pushing 95kWh per day. Having fixed that problem (not the only one we have) the usage during the current sub-zero temperatures is now around 55kWh per day.

I don't know if it is true of all installations but ASHP's are often specified with a capacity to do one or the other but not both. If you call for both space and hot water heating at the same time they just demand ever more power in a fruitless effort to meet the demand.

If that is the issue then it's one of the easier ones to address.

Mike

Hi @webcmg 

I have a 5KW arotherm plus unit installed as a part of a hybrid system in my old and fairly leaky property (163m2, D rated semi detached sandstone house ~ 1900). No upsized rads etc. The way my system is setup, it currently defaults to running off Gas almost 100% of the time as this is the most cost effective fuel source, however, being nosey and wanting to see how the system would manage on only the ASHP over the Christmas period, I decided to deactivate the gas boiler and have it run solely from the ASHP for a couple of days. Granted, outside temperature was mild for this time of year, but to heat the house to 21°C for the 2 days, using what would likely be considered an undersized pump for the house used 22kwh one day and 28kwh the following, so substantially less than your usage. I must admit I was very pleasantly surprise how well it performed, the house was a lovely temperature! 🙂

Obviously this is a different setup than yours, and I don't have the controller settings to hand (it is the Vaillant sensocomfort we are using), but if they would be useful, I will dig them out tonight and post. In a new build like yours I would have thought you would be able to achieve better than you are getting for sure.

Edit: Just saw Mike Patricks reply, I should have added my system relies on the gas for DHW, so that will also be reflected in my lower elec usage. not sure by how much though!

Posted by: @webcmg

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.  

Have you noticed any difference in energy consumption? Are you certain that your system is set for weather compensation control and not fixed water flow temperature?

You ask: 

“Is it correct for the weather compensated system control to be in the insulated area of the garage?”

the answer is, it depends (!). 

in Germany since 1985 the requirement on a boiler is that it has an out door sensor. This is relevant because heat genrtator controls have become sophisticated around this. (There are other reasons why this is the case, but that’s a bit if a rabbit hole)

in this case this controller will work well with no indoor reference,  just on the outside temperature.

so if it’s commissioned correctly it will be fine…

Posted by: @mike-patrick

@webcmg Silly question, but this happened to my system. Are you sure the ASHP is not trying to heat the water and the house at the same time? During the cold spell last year I was pushing 95kWh per day. Having fixed that problem (not the only one we have) the usage during the current sub-zero temperatures is now around 55kWh per day.

I don't know if it is true of all installations but ASHP's are often specified with a capacity to do one or the other but not both. If you call for both space and hot water heating at the same time they just demand ever more power in a fruitless effort to meet the demand.

If that is the issue then it's one of the easier ones to address.

 

Mike

@mike-patrick thanks for the message - how might I check if this is the case?

Posted by: @derek-m

Posted by: @webcmg

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.  

Have you noticed any difference in energy consumption? Are you certain that your system is set for weather compensation control and not fixed water flow temperature?

Hi @derek-m, I made the school boy error of not noting down the Kwh usage before changing the settings. I took an energy consumption reading earlier today so will check tomorrow. We've also had work people in the house so had windows open due to covid so hopefully we can get back up to temperature and monitor properly now having turned off the zones they were working in.  One thing that doesn't make sense to me is the use of UFH downstairs and radiators upstairs.  My target flow temp is around 32 degrees, which maintains a 20c temp downstairs, but this doesn't seem sufficient to provide enough heat for the radiators upstairs.  Is the combined use of UFH and Radiators common? If so, how is this differential heat requirement efficiently overcome?

@webcmg in the first best world you would have an electronic mixer controlled by a vaillant wiring centre for the floor and two heat curves..

@webcmg I was afraid you would ask that! 

The way this is achieved varies from one make to another. I have a time switch like you find on conventional heating systems that controls the times when the hot water is on and separately the space heating. You just set those times so that the space heating is off when the water heating is on.

But I know others on this site, who are much more technically informed than me, will offer other suggestions.

I'll be interested to learn what you find.

Mike

@mike-patrick it might seem to you there are choices of approach, but for for optimum performance of the heat pump and vrc700 you really should select and install the components as they indicate in vaillants schematics.

I don’t know why installers and specifiers think they know better that vaillant design engineers!

Posted by: @alec-morrow

@webcmg in the first best world you would have an electronic mixer controlled by a vaillant wiring centre for the floor and two heat 

@alex-morrow our UFH zones have a manually set mixer (currently set to 50c - so largely redundant), if these were set to 22c or somewhere in that region would that help? Based on the suggested settings today's target flow temp is 33c, so assume the efficiency would be lost due to having to significantly increase flow temp. I assume this is why an electronic mixer and two heat curves would be best so it can fluctuate the heat flow as required? Does anyone run a similar setup with upstairs radiators and UFH downstairs without the electronic mixer?

I spoke to the plumber who setup the pipework today, he didn't really know anything about about ashp- but just said the 33c flow temp won't be enough to heat the upstairs radiators. I worry that the design of the ufh and radiators is not optimal for a heat pump.

Hi @webcmg 

Check to see if any of the valves are partially closed on any of the radiators.

Check that your water pump is producing adequate pressure and flow to get the water up to the radiators. Try measuring the temperature of your radiators and then shutdown your UFH so that all the flow is going to the radiators. If the temperature of the radiators starts to increase then you have a pressure or flow problem. Try increasing the pump speed.

Posted by: @webcmg

Posted by: @alec-morrow

@webcmg in the first best world you would have an electronic mixer controlled by a vaillant wiring centre for the floor and two heat 

@alex-morrow our UFH zones have a manually set mixer (currently set to 50c - so largely redundant), if these were set to 22c or somewhere in that region would that help? Based on the suggested settings today's target flow temp is 33c, so assume the efficiency would be lost due to having to significantly increase flow temp. I assume this is why an electronic mixer and two heat curves would be best so it can fluctuate the heat flow as required? Does anyone run a similar setup with upstairs radiators and UFH downstairs without the electronic mixer?

I spoke to the plumber who setup the pipework today, he didn't really know anything about about ashp- but just said the 33c flow temp won't be enough to heat the upstairs radiators. I worry that the design of the ufh and radiators is not optimal for a heat pump.

Hi,

If after checking the pump operation you still cannot get the correct temperatures upstairs, then change the weather compensation curve from 0.6 to 0.8.