We have a grant pre-plumb cylinder with digital thermostat. Thermostat reading is all over the place, still giving us hot water at 45degC when the thermostat says 16degC. For general hot water, 50degC is fine, with a weekly Legionella boost up to 60degC. Standard tariff: generating hot water in the early afternoon is most energy efficient - best CoP from the ASHP. If you have a low rate night tariff that will be cheaper. Modern tanks are really well insulated, and you'll only lose a few degrees in 12hours. From generating at 1-2pm up to 50degC our hot water is plenty warm enough next morning at 7am for showering. We charge just once a day and a 250L tank will charge in 75 minutes even with a defrost thrown in mid-charge in the winter.

The energy consumed by the ASHP for space heating will shoot up in the winter. Make sure you are running it on weather compensation and fully open system circuit. No TEVs (set only to prevent overheating), no room thermostat, just let the ASHP run on weather compensation and it will be fine. If you have a digital on/off thermostat directly switching the ASHP on and off, set it to 30degC whenever you want space heating. Forget using the thermostat to switch the ASHP on and off, it will do this multiple times an hour and the ASHP never gets a chance to modulate down on inverter control. It's always playing catch up.

Thanks for the heads up Mr A Fish

I have 4x Nest Thermostats running a zone each. scrapped all the extra boards from grant and just run 2 independent relays. PDHW & CH. S-Plan is a bit old school (2wa diverter, better setup) however it's all working now...

Flow rates for the UFH needs serious attention, but I'll save that for long heatings run come Autumn/winter.

Not configured yet for a schedule - I take your open plan, long run information on board

What is your schedule for heating - 24/7? I'm all UFH which will impact my schedule - thermal mass and all - but cannot see it being the most frugal to run 24/7 regardless of efficiency improvements.

Say tomorrow, the house all be empty all day - but you still want it warm enough for a late evening homecoming. How would you schedule?

@ggw we have the heating running about 17hrs a day, on early morning around 4.30am, off abound 9.30pm. 1.25 hours in the middle of the day set of HW. We like it cooler overnight and there doesn't seem to be a set-back facility with Grant equipment to offset the leaving water temperature say, 2degC or something. For days away or short holidays we just leave the schedule as set as it's really efficient anyway.

We're a retrofit install with radiators, most were upgraded for lower design temperature. The system was designed for 50degC but we run it at 45degC and it's fine.

We found with TRVs that were closing down, or smart programmable electronic versions, we were losing too much system volume. That was causing slow recovery from defrost cycles in winter and sending the heating circuit flow temperatures. So we have flow through all emitters all of the time when heating, with some simple manual balancing. Lots of trial and error with the weather compensation settings, but Grant's default suggestion didn't turn out to be too far away from where it now is.

@allyfish 

17Hrs a day is a good ballpark to hit for a first winter

With my system being entirely underfloor - getting the flow rates right is the key, i feel.

Ran CH the other day (In july!) the "warm" up time for all of downstairs circuit was around 3Hrs - WC on - flow temp was between 28-32Deg when i was watching it. floor wasnt hot, but was just nice. More tweaking of the temperature curve ahead.

Do you measure your electrical usage for the HP? any suggestions?

I have WiFI now so can log.

@ggw True electrical usage requires power monitoring & logging of the ASHP monobloc and any additional circulating pumps, controls, etc. There is a user parameter 3 in the Grant Chofu controller which displays real time power consumption in watts. It's for the whole monobloc including compressor, evaporator fan and circulating pump. The value is rounded to the nearest 100W. Refer to P.50 of the installation manual. Add a further 50W for a second external circulating pump, eg: Grundfos UPS3 15-50/65

@allyfish 

I've been keeping a track of this parameter - circa 4000w when the DHW is running. to be honest, it bounces about a bit - like most of the number on the grant controller.

Not enough usage to judge CH yet.

I totally agree with yourself on the tank thermostat temp - it makes no sense! reads 27Deg and still water for a shower - it about 2/3's the way down my tank.

Any 3rd party CT's you'd recommend to log electrical usage - i'd be interested - to keep a track of costs, experminate and determine the validity of parameter changes. 

*Update

So the heating season has begin in earnest - which means £..

But besides that - been looking at the grant 10kW running - and the ad hoc data from the controller, well let's say it doesn't always make sense.

After a 6.5hr solid ON run - WC is setting the flow to 29Deg - return is 25Deg - the watts parameter is never below 2200w - is this the maximum turn down of the unit? I'd doubt it personally.

Understand that there is many variables to this.

Posted by: @ggw

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After a 6.5hr solid ON run - WC is setting the flow to 29Deg - return is 25Deg - the watts parameter is never below 2200w - is this the maximum turn down of the unit? I'd doubt it personally.

I don't have the full specs to hand (Grrant don't publish them AFAIK, but Chofu, the oem, might) however a 4:1 turn down for an a2w pump is a good figure, many claim much less than this.  So very likely this is the maximum turn down.  Does it cycle on/off or is the load actually 2.2kW?

@ggw Hi there. I'm in heating too with my 10kW Grant Aerona. I'll share some info and hope not to tread on any of this forum Stalwarts' toes....

Your indicated 2.2kW power consumption seem high. The Grant Aerona 10kW has a maximum input power of around 3.6kW, I've never seen mine indicate higher. It can modulate down to 25% or 0.9kW. I've seen mine run down to 20% or 0.7kW. Below that it cycles on and off.

Right now, I've been heating continuously for 4.5hrs, outside air 10degC, flow at 37degC, return at 34degC, power consumption 1.2kW. Flow about 22l/m indicated. Roughly that's (22/60)*4.2*(37-34) = 4.6kJ/s (kW). COP = 4.2/1.2 = 3.5. (Not an exact measure, very approximate!)

Compressor operating frequency [d1] equates roughly to consumed power, the higher the frequency, the more power. Evaporating suction and condensing discharge temperatures come into play as well. My compressor is running at 38Hz. It can get as high as 70Hz, I've never seen it above that on the controller display.

Do you know what flow in l/m your unit is showing? Your LWT and RWT seem about right: 29 & 25degC. The numbers are rounded on the controller display, so be mindful of that. Have you any other means of monitoring your ASHP power consumption? Perhaps a smart meter? If you know what average power your other appliances in the house draw, then you can simply subtract that from the real time power consumption. Is it really drawing 2200W?

If I recall you have underfloor heating, so the thermal mass it quite high. It may take quite a long time in first heat demand of the season for the floor fabric to initially absorb the heat being supplied by the ASHP and then to start transmitting that into the heated space. It will reach equilibrium, but may take several hours. Conventional wed rads have much lower thermal inertia as there's little material in them and steel or aluminium is a good heat conductor - they get up to the average temperature of your flow and return quite quickly. Underfloor heating is usually plastic piping and non-metallic materials, with lower thermal conductivity, so the thermal response is much slower.

Posted by: @ggw

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Understand that there is many variables to this.

 

If your flow rate is about 25l-30l/m then that would be a normal behavior given that you are reheating an empty UFH.

This 6kW ecodan was doing something similar to a UFH(putting all it can get out) after a long pause from heating

*SITREP

Thanks for the replies - I've been basically babying the unit for the last week trying to find the sweet spot for WC - and it was all over the place. Some mornings freezings - others roastings. I was scratching my head...

Then, I saw and seen some very awkward info - that my unit is not reading the outside temp correctly. This is playing havoc with the output flow temp - to the point that it is turning the unit on/off constantly. Very bad, I know for Cost. outside was close to 8Deg but unit reading 19+Deg

The temperature only reads wrong when the unit is running (possibly being contaminating from flow temp) - it is accurate when unit off - like all over the summer.

HW is unaffected and is working fine.

As a stop gap, I've WC set off and flow temp set to 29Deg. it's not ideal but the unit runs for hours now, and the Watts value is much lower. around 0.9 - 1.1kW when settled. and i get some heat into the property.

A clamp monitoring has arrived - I just need to fit to track energy. Grant has been contacted, but not much so far - The manual shows an option for external mounted temp sensor - but i'd rather not - would look bad

To be continued.