Discussion ... ASHP(Air/Air) with Solar pv ....

ForestBluebells

thank you all for taking the time to reply. I am just trying to determine which units to go for now. I am 100% sold on the idea. Ideally i want a COP of over 5 so its just trying to determine which ones have that and also have a low input so can run at low usage to tick along. I have mitsubishi heavy industries down as having a high COP so far although from what i can tell the min input is 900watts, i may be wrong. essentially its better for the environment than my current electric heating as it will be using about 1/4 of the electricity to operate.  Although they do cooling, i actually only really have interest in heating and it will replace my existing heaters. there may be 2-3 days a year i consider using the cooling.

zeupater

ForestBluebells said:

thank you all for taking the time to reply. I am just trying to determine which units to go for now. I am 100% sold on the idea. Ideally i want a COP of over 5 so its just trying to determine which ones have that and also have a low input so can run at low usage to tick along. I have mitsubishi heavy industries down as having a high COP so far although from what i can tell the min input is 900watts, i may be wrong. essentially its better for the environment than my current electric heating as it will be using about 1/4 of the electricity to operate.  Although they do cooling, i actually only really have interest in heating and it will replace my existing heaters. there may be 2-3 days a year i consider using the cooling.

Hi

If you can, get hold of a .pdf copy of the manufacturer's data book for whichever unit you are interested in as it should provide considerably more performance detail than whatever marketing information would ...

Regarding the min input of 900W ... that seems extremely high and would likely be addressed in an EDB in the form of electrical draw (W) vs thermal output (W.t) at various external temperatures and percentage of unit load capacity .... it may mean you'll need to divide one number by another but you'll also be able to work out the COP expected for particular operating conditions.

Earlier in the thread I provided some basic details of how our unit actually ramped performance through a couple of heating cycles which you might find useful ... for comparison (vs 900W), in running our system earlier today it was typically drawing somewhere in a range of around 150W - 250W, being switched off when the PV was no longer generating house base load + heat ... it's ~6hours since switching the unit off and currently 20.5C where I'm sitting and 14C outside, but I can't emphasise enough that priority must be focussed on keeping the provided heat in over providing the heat and that's why we use so little energy whatever the source ..

HTH - Z

shinytop

Have a look at this.  

https://www.linkedin.com/pulse/scop-who-goodies-baddies-graham-hendra/?fbclid=IwAR0wK1Y66Mi0GmV-qi9firNsCvOvxDYVgvHWnZuUpzwKU7JX8UeD0ol_llU

 @zeupater is talking about this sort of thing.

https://library.mitsubishielectric.co.uk/pdf/book/ATW_Databook_R32_2020#page-30-31

A small Ecodan will be able to run continuously at a lot less than 900W.  My large 14kW one can do that.  They can modulate down to about 40% of their badged output.

zeupater

shinytop said:

Have a look at this.  

[ ...]

 @zeupater is talking about this sort of thing.

https://library.mitsubishielectric.co.uk/pdf/book/ATW_Databook_R32_2020#page-30-31

A small Ecodan will be able to run continuously at a lot less than 900W.  My large 14kW one can do that.  They can modulate down to about 40% of their badged output.

Hi

Yes, that's exactly the kind of information that describes performance in the detail that really makes sense if you're looking to balance heat to power input.

Page A-56 onwards tabulates heating capacity (kW.t) and the associated COP at various ambient temperatures and flow temperatures. The format of the data is a little different to that provided for our unit (which is based on kW input & kW.t output at 10 loading (based on min/max) bands (10%, 20% .. etc)  for a range of ambient temperatures whereas the Ecodan provides 4 (min, mid, nominal & max) , but what you can deduce from it is essentially the same. For the Ecodan unit simply taking the appropriate capacity (kWh.t) and dividing by the associated COP should accurately reflect the power being drawn by the unit for those conditions/settings .. eg if the unit of interest was the first on page A-56, the outside temperature was 12C, the flow temperature was set to 45C and the unit had been running for a while & was simply maintaining heat by ticking along at somewhere near it's minimum output, then you could expect 1.8kW.t of heat at a COP of 4.67, therefore the power being drawn should be 385W ((1.8x1000)/4.67) .. once you've got used to the concept you can pick & memorise some relevant data points & start to estimate heat provision just by looking at the house power consumption ..

HTH - Z

shinytop

zeupater said:

shinytop said:

Have a look at this.  

[ ...]

 @zeupater is talking about this sort of thing.

https://library.mitsubishielectric.co.uk/pdf/book/ATW_Databook_R32_2020#page-30-31

A small Ecodan will be able to run continuously at a lot less than 900W.  My large 14kW one can do that.  They can modulate down to about 40% of their badged output.

Hi

Yes, that's exactly the kind of information that describes performance in the detail that really makes sense if you're looking to balance heat to power input.

Page A-56 onwards tabulates heating capacity (kW.t) and the associated COP at various ambient temperatures and flow temperatures. The format of the data is a little different to that provided for our unit (which is based on kW input & kW.t output at 10 loading (based on min/max) bands (10%, 20% .. etc)  for a range of ambient temperatures whereas the Ecodan provides 4 (min, mid, nominal & max) , but what you can deduce from it is essentially the same. For the Ecodan unit simply taking the appropriate capacity (kWh.t) and dividing by the associated COP should accurately reflect the power being drawn by the unit for those conditions/settings .. eg if the unit of interest was the first on page A-56, the outside temperature was 12C, the flow temperature was set to 45C and the unit had been running for a while & was simply maintaining heat by ticking along at somewhere near it's minimum output, then you could expect 1.8kW.t of heat at a COP of 4.67, therefore the power being drawn should be 385W ((1.8x1000)/4.67) .. once you've got used to the concept you can pick & memorise some relevant data points & start to estimate heat provision just by looking at the house power consumption ..

HTH - Z

If you like a spreadsheet, have a look at this.  It uses the 14kW Ecodan data to do some modelling. You can easily replace with data from other Ecodan models.  It's based on the data in the data book.   

https://renewableheatinghub.co.uk/wp-content/uploads/wpforo/attachments/6/418-Ecodan-14kW-ASHP-Data.xlsx

  

ForestBluebells

That’s great thank you. I think the ecodan is air to be water and I’m looking air to air but I’ll keep digging. Just so overwhelming trying to decide. It’s now trying to decide if the most energy efficient models are worth paying an extra £600 per unit for 

ispookie666

ForestBluebells said:

That’s great thank you. I think the ecodan is air to be water and I’m looking air to air but I’ll keep digging. Just so overwhelming trying to decide. It’s now trying to decide if the most energy efficient models are worth paying an extra £600 per unit for 

Mitsubishi would be the go to for me followed by Daikin. They usually come with 5 year warranty and preferably R32. You could look into multisplit VRF if £ is not limiting.  

orbit500

ispookie666 said:

ForestBluebells said:

That’s great thank you. I think the ecodan is air to be water and I’m looking air to air but I’ll keep digging. Just so overwhelming trying to decide. It’s now trying to decide if the most energy efficient models are worth paying an extra £600 per unit for 

Mitsubishi would be the go to for me followed by Daikin. They usually come with 5 year warranty and preferably R32. You could look into multisplit VRF if £ is not limiting.  

I’d be very wary of multi split VRF following my experience. Pairing a large outdoor unit with multiple indoors often means the modulation floor is too high for a single unit to achieve a reasonable efficiency.
I have a 14kW outdoor Toshiba VRF and 4 indoors, 2x2.5 and 2x3.5. Running a single indoor in heat gives a measured COP of 1.7 which is dreadful. Running the whole system gets 3.1 which is just acceptable but way worse than the best 1:1 splits and I don’t want to heat the bedrooms at the same time.
Added to which the installer wasn’t aware that VRFs need indoor power to each unit rather than a feed from the outdoor.
The units are noisier than regular splits as they run oil recovery cycles regularly.
Last straw was it losing all its gas with no cause identified.
I’ve thrown the towel in and demanding he replace them with 1:1 splits. He specifically recommended the VRF for single unit efficiency. 
My cheap 1:1 in my old house ran at COP 4 for 11 years without fault and cost under half per unit.

Coastalwatch

Hi Orbit, I'm interested to learn of your unfortunate experience as, prior to installing our first unit,I believe it was Mart who placed a post suggesting that installing multiple single splits was a more cost effective means of heating than precisely the setup you describe.

I had no knowledge of this until Marts post and do not know how or where the information came from. But as usual it would appear his views are well founded!

ForestBluebells

I’m looking at single splits too as I think it’s most efficient