Input energy to grant 10kw

[andyj007]

Evening all. 

looking at the specification for my grant aerona 10kw heat pump it states an input max of 2.10 kw air 7 flow 35 degrees,, ..  

is that the max the system pulls energy  at?  im trying to calculate what battery capacity and or  solar panel  would be required need to run this in spring and autimn .. 

could someone look over and see what im missing pls 

https://www.grantuk.com/media/4759/aerona3-r32-data-sheet_feb-2022.pdf

 

Edited March 12, 2023 by andyj007

[sharpener]

Yes but you also need to take account of the declared max running current, the 17.5A represents some 4.2 kW which I presume is the max at startup, your ESS needs to be able to handle this. Victron systems can IIRC supply 200% rated power for 10s, don't know about others.

 

Am considering this Grant 10kW for my own system but plan to connect to grid side of the ESS as it would eat through the 10.65kWh battery pretty quickly. I think the capital cost of thermal storage would be much lower/kWh.

 

Also the 7/35C conditions may not be worst case. I have asked Grant for performance curves covering Ta down to -10 and Tw up to 55C but have had no response.

[JamesPa]

 

2 hours ago, andyj007 said:

im trying to calculate what battery capacity and or  solar panel  would be required need to run this in spring and autimn

The easiest way to estimate this is mostly to ignore the Grant spec and just work out how much energy you need to store to heat your house assuming a COP of say 4-5 or whatever seems reasonable at the ambient temp you want it to work at.  So if your house needs say 3kW input at say 12C and the cop is 4 at that temp, you need a total of 3*24/4=18kWh.  Storage requirement is perhaps 30-40% less because you don't need to store when the solar panels are generating.  Also (possibly do this first!) use pvgis to work out how much solar capacity is required to harvest the total energy requirement (in my example 18kWh) at the relevant time of year.  Once you have got approx sizing use pvgis again to work out how much actually needs to be stored and how much you will use in real time.

 

Unless your 10kW hp is well oversized for your house or you are prepared to cover a large garden with solar panels I think you may conclude it's not possible to cover anything more than a  fraction of the demand with solar, and that only modest storage is needed to shift the daytime peak to the daytime shoulder.

 

This simple calculation is the way to go to scope what's achievable, then you can refine as appropriate.

Edited March 12, 2023 by JamesPa

[JamesPa]

38 minutes ago, JamesPa said:

Also (possibly do this first!) use pvgis to work out how much solar capacity is required to harvest the total energy requirement (in my example 18kWh) at the relevant time of year. 

Eg in mar pvgis says that a south facing 1kWp array at 35deg to horizontal generates about 80kWh per month, an average of 2.6kWh per day.  Of course this is an average so some days will be quite a bit more and some days quite a bit less.  So if you have space for a typical 4kWp array you will generate 10kWh average, perhaps twice that on good days (???), enough for the example calculation (better than I had guessed when writing the above to be honest).  If you were to download the hourly figures you could work out exactly how much is generated on good days and thus how much storage is worth having.

 

I'd work it out this way first, assuming you are constrained in practice by solar capacity.  Obviously if you have plenty excess solar capacity then only the hp demand needs to be considered.

Edited March 12, 2023 by JamesPa

[JoeBano]

On my grant aerona3 10kw, the grant control panel tells me the power consumption is 3200w when doing a hot water cycle. That’s the highest I’ve seen it at. 

[sharpener]

 

14 hours ago, JoeBano said:

On my grant aerona3 10kw, the grant control panel tells me the power consumption is 3200w when doing a hot water cycle. That’s the highest I’ve seen it at.

 

@JoeBano what flow temp do you achieve for the hot water and are you otherwise happy with the Grant 10kW? Do you use their controller, or external/third party controls and what would you recommend in the light of your experience?

 

TIA for your help.

 

Edited March 13, 2023 by sharpener

[HughF]

23 minutes ago, sharpener said:

 

 

@JoeBano what flow temp do you achieve for the hot water and are you otherwise happy with the Grant 10kW? Do you use their controller, or external/third party controls and what would you recommend in the light of your experience?

 

TIA for your help.

 

The Grant unit is made by Chofu, and is very capable. The controller is also a capable unit, but Grant configure/supply them to work as a drop in boiler replacement, and thus they often run with a terrible COP.

My neighbour bought their place 2 years ago with a 18 month old Pico/MTEC 12kW already installed, a great unit by a superb Austrian manufacturer. Their plumber wanted to make some changed to the DHW strategy and for some reason the 12kW MTEC was replaced with a 6kW Grant..... 

 

I see that this has now been removed and the neighbour has gone back to gas, probably because of the poor performance of the Grant unit when installed badly.

[JoeBano]

Flow temperature on the hot water is 55c, it will heat my megaflo cylinder from cold to 50c in around 40 mins. I don’t use any of the grant heating controls they are in the dark age. I use the Chofu system control do my hot water. It has a two storage temperatures, one for peak (50c) and off peak work (40c) just hot enough for washing up and a shower. On my heating side I use a 2 nest controllers one downstairs (UFH) and one upstairs (RADS). My weather compensation is -2 45c and 20c 35c 

I had to up the minimum because my radiators wasn’t warm enough when it was mild outside. I fitted the my heat pump in July and it was second hand unit. It’s r410 gas not r32, my scop so far has been around 3 I’m still playing with at the moment. I did get the cooling mode working last summer which worked great for the Ufh. I would buy again! 

[JoeBano]

Have a look at the Chofu manual

https://www.centralheating.co.nz/assets/resources/Chofu-Operating-Installation-Manual.pdf

same heat pump before grant put there name on it. So much more features. 

[DanDee]

I really wonder what makes the COP increase of the Chofu heat pump when they land in UK, is it the tea or the humour?

[sharpener]

Thanks for that @JoeBano, looks very comprehensive and flexible. After reading that it would seem I could connect it up as follows:

 

60l buffer tank plumbed as volumiser in return line, or 3 port with secondary pump controlled as "except when DHW activated". Possibility to add 3kW heater as supplementary source in extreme cold conditions.

 

Heating zone 1 UFH on ground floor (four zones, existing room stats used as high limits only, might change living rm to smart starts as only used evenings)

Heating zone 2 Radiators on 1st floor. Call for heat from existing Evohome boiler relay. Individual room controls by existing Honeywell wireless TRVs.

 

DHW: exisiting 200l OSO cylinder. Call for heat from existing cyl stat (55C). Use low tariff setting to charge in small hours. Recovery time unimportant as mostly only two occupants, there is also an immersion with solar diverter to boost to 60C as necessary foc.

 

Programming: UFH 24/7 with night setback. Master bedroom first thing and late evening, guest rooms as required. DHW small hours and afternoon boost.

 

No it will never qualify for MCS but plumbing and wiring routes are long and difficult so with a few larger rads this would make the best of my existing infrastructure.

 

TIA for any thoughts on the above.

[JamesPa]

 

22 hours ago, andyj007 said:

Evening all. 

looking at the s,,pecification for my grant aerona 10kw heat pump it states an input max of 2.10 kw air 7 flow 35 degrees,, ..  

is that the max the system pulls energy  at?  im trying to calculate what battery capacity and or  solar panel  would be required need to run this in spring and autimn .. 

could someone look over and see what im missing pls 

https://www.grantuk.com/media/4759/aerona3-r32-data-sheet_feb-2022.pdf

This chart might be of interest and, given your heat demand (and other electricity use), will help you size your array (or, if your array sized is already fixed, work out how many 'free' days you will get). 

 

It shows the number of days per month in which the solar PV output exceeds a given %age of the average daily output.  Its plotted for south facing panels at 45% to the horizontal.  It uses data from PVGIS for 2018-2020.  The average daily output for a 1kWp array with these conditions is 2.96kWh (call it 3kWh)

 

So for example in March there is about 1 day when the output exceeds 6kWh (200%), 7 days when the output exceeds 4.2kWh (140%), 16 days when the output exceeds 2.4kWh (80%) etc. 

 

In my example calculations above, if your house demand is 3kW at 12C, and the CoP at this temp is, say 4, you need 18kWh to heat the house.  A typical house uses about 10kWh/day for purposes other than heating, for a total demand of 28kWh.  So if these figures applied to you, the temp were a constant 12C, and you were lucky enough to have a 11.7kWp array (28kWh=80% of average daily o/p), you would be able to cover all your electricity needs on about 16 days in March and 21 days in April.

 

Thats a big array and a big battery, so unless the figures are way out, you have lots of space, or your 10kW HP is well over-sized, you wont do this well.

 

Hope that helps.

 

 

 

 

 

 

Apologies, the chart below is identical to the one above except for the title, but I cant seem to delete it.  Please ignore the chart below

Edited March 13, 2023 by JamesPa

[HughF]

You don’t have a call for heat from a dhw cyl with a heat pump. The heat pump itself drives the three port then uses a thermistor to monitor cylinder temp.

 

most heat pumps work by being in dhw priority when they are turned on, then a call for heat drives them over into central heating mode.

[sharpener]

That's one of the constraints I'm working with. The previous owners who did the barn conversion built the cyl into a loft void above the airing cupboard in a way that makes it extremely difficult and costly to replace. However from p99 of the installation instructions kindly posted above it looks possible to command the Grant/Chofu HPs to produce DHW by an external contact closure with the thermistor input disabled (p. 97)

 

Can you see any reason why the existing thermostat (or the switch on the S-plan valve) could not do this? This control interface is for me one of the attractions of this particular HP, it is supposedly marketed as a replacement in S-plan boiler systems though I clearly want to optimise its performance as a HP.

 

The other bright spot is that the wiring for this valve is already in place down to the utility room. Although the 4 cores + E could be re-purposed I am not sure whether the tank has a suitable pocket for a thermistor.

 

No I don't know why they didn't just bring the 2 stat wires down and put the valve downstairs where you could get at it but there are a lot of things I would have done differently. Luckily I am ATM still able to get parts for the Kidd boiler even though they have gone out of business, but the former service manager who now holds the stocks is nearing retirement so it is very much on borrowed time.

[JoeBano]

You can have a call for hot water I used to have this via my nest hot water schedule but the reason I changed to a temperature probe and the using the Chofu controller my tank is too small for my household like so I can maintain two different temperature depending on the time.

[andyj007]

Hi All, firstly thank you for all the replies..   its interesting that as pointed above a 10kw Grant pulled 3kw when it reads max is less.. perhaps it pulled a bit on immersion?  

thought id try better to explain my thinking.. sorry if it doesnt make sense,  and i coud be very wide of the mark  

 

I have found over the years that it is very hard to apply and work with calculations based on predicited heat usage ..  kwh , kw ..  whilst  a piece of paper and  S.A.P software can throw about some interesting  figures .. there are too many varibles that can effect the outcome.. ..and in reality struggle to reflect anything accurate IMO.   

Its quite simple maths for me..  my 7.2kw W facing array at 5 deg   pumps out just approx 2kw at 9.am on a cloudy day ..  3kw  if its sunny  (early march 2023) .

I have a grant 10kw ASHP which calculations show I need 90% of this to heat my house -3 ..  its a fair size at just under 4000sq ft..  .  i did try this in early december 2022 cold spell and it worked a treat...  but then turned it off as its not been needed.   The house has been designed  to maximise solar gain, I installed a log burner with back boiler , which can heat my 300l of water to 60 degress in 50mins , then will divert to the buffer tank from whic feeds the  under flloor, within a couple  of hours the floor is charged (some zones not all 4000 sq ft of floor!) which keeps the house pretty nice until the next night. where if needed i can choose if i want to add a little heat and of what source to provide it ..  I fitted some  IR heaters to the en suites for instant extra warmth  comfort  when you juct get out the shower  ....  and have a log burner in an open plan lounge..   along with x 2 A2A units ( which i can run from the solar to heat the rooms withour cost)     I think if i my ASHP runs constant and pulls  2kw,  I  could dump heat energy  into my floor 3 hours in morning & 3 hours in afternoon and it not cost me a penny . and set this up automatic ..  say from march - april , october -november..  , based on my previous experiance I will not need any heating at all from mid april to end november unless we hit  a perticulary prolonged cold spell without sun...   what complicates matters is the ASHP  is diverter driven and ramps down (i think) so i cant just turn it on flat out and see what it costs ove a given period..

Perhaps i could pre heat my flow and return to 35 degrees , whack the thermostats up very high , limit teh ashop flow rate and run it for three hours when its about 5 deg and see what it pulls on the graph..  .. that was my thinking anyway .. .

     

 

 

Edited March 14, 2023 by andyj007

[JoeBano]

You can check the power consumption on the little white grant control unit. Hold the cog symbol to a 0000 comes up and using the up & down keys put in 0103 press the tick button. This is the power consumption at the time, it’s read only so you can’t change anything. 3200w was hot water cycle, heating cycle around 2700w then will drop down to depending how cold it is outside. 

[andyj007]

If anyones interested : some real life data 

today, I  heated my 300l DHw that was down to 22degres to 54.7deg  in 90 mins  , The energy delivered to the heat pump was 2.6kw . total , with peak draw hitting 2.5kw  twice during the 90min session.  . outside temp was 11-12 degrees ..  

currently I  have x2 3.5  batteries  and both were charged to 100% before I  switched on the HP..  it was bright  with cloudy / sun today, and the 7.2kw panels (west facing at 5 degee. off flat   covered the water heating costs... ..  leaving the batteries untouched..  we then exported another 5kw this afternoon, so a third battery would have easy been charged .. ..even still in March . 

 

 

 

Aj

 

Edited March 23, 2023 by andyj007

[ReedRichards]

1 hour ago, andyj007 said:

The energy delivered to the heat pump was 2.6kw . total , with peak draw hitting 2.5kw  twice during the 90min session.

 

 

Can I presume that the first figure should be 2.6 kWh (kWh being a unit used to measure energy)?  Whilst the second figure is a peak power of 2.5 kW?  

[andyj007]

1 hour ago, ReedRichards said:

 

Can I presume that the first figure should be 2.6 kWh (kWh being a unit used to measure energy)?  Whilst the second figure is a peak power of 2.5 kW?  

Yes your presumption is correct..  big fingers little keys ..  

thanks

 

[SteamyTea]

13 hours ago, andyj007 said:

.even still in March

Depending on your roof angles, March can be a good month because the 'direct solar beam' aligns nicely with the roof, creating a flat plain.

Yesterday Cornwall was getting, during the day, about a quarter of its electrical power from local solar.

[andyj007]

On 24/03/2023 at 08:32, SteamyTea said:

Depending on your roof angles, March can be a good month because the 'direct solar beam' aligns nicely with the roof, creating a flat plain.

Yesterday Cornwall was getting, during the day, about a quarter of its electrical power from local solar.

5 degrees West ..  appears to be more pruductive at this time of year than my south facing system at 37 degrres on my last house .