@batalto will reduce further tomorrow, just trying to work out what the mean temperature ( with the HP cycling on and off), is at the moment that is more or less maintaining desired room temp, and aim for that being the set value at current ambient ( 2C)

@bramshot what I mean is that you have a flow temperature from the weather compensation. Cycling means it's heating up and then turning off, or defrosting. If you turn down the flow temperatures (weather comp) you'll have less cycling and less defrosting as it'll run more consistently. The higher the temperature the more like a gas boiler it becomes. Also high temps mean you'll ice up much faster

@batalto I know and understand what you mean. I am trying to work out what temp I should set for the current ambient, based on what it is reaching on average during the present cycle. Looks like about 45. (As opposed to 54 at the moment).

@bramshot just put it down by two or three degrees. Leave it a couple of days to see how the house feels. If it's ok, then tweak a bit more. Organically you'll find the right "feel"

@batalto It will not make any difference unless it stops continuous defrosting, or at least significantly extends the interval between defrosts. I can tell that almost straight away, as I can see the power consumption of the HP as it cycles, on the power traces from my Solar / battery system.

@bramshot the defrost cycle is directly linked to the flow temperature your system is operating. The lower flow temperatures mean the pump will not get as cold, which in turn will reduce the number of times it ices up. Physics dictates that if you are taking heat you must be balancing it out by cooling.

What are your current weather compensation settings? How much power are you using as a background? Mines ticking along at under 2kw, no defrosting

@batalto Thank you, I am well aware of the physics , but you have to make enough heat to warm the house adequately. 
My present weather compensation is 50 @ -5 deg, 30 @ 15, so a degree per degree between those points. Changed to this yesterday from hotter following advice on here. The house is not warming adequately as standing about 1 degree below my temp setpoint, which are not excessively high

Interval between defrost cycles has approx doubled to about 2 hours, ambient currently 3 deg .

Power consumption rises to about 3.6 kW after defrost while reheating water cooled during defrost followed by a fall to about 2kW while maintaining it until the next defrost.

This house is about 400 sq m over two floors.

For reasons unknown to me the installers fitted hydraulic isolation between the heat pump and radiator circuits, also although they  use the same water the flow through the HP can be different to the flow rate through the rads. It is like having a permanently open bypass for the heat pump to be able to circulate around. There is one pump in the HP  which is variable flow under HP control and a second fixed speed pump circulating round the rads. The delta T seen by the HP is therefore going to be different to the delta T produced by the rads. 

I will continue to investigate but may have to boost the temperature a bit above where it is now set. At the moment the energy consumption looks lower overall , but a bit hard to tell when compared with the average cycle energy from before, though cycling cannot be very efficient.

One has to wonder what the point of a high temp heat pump is if you have to run it at low temp HP temperatures to avoid it frosting up though!

Now I have to investigate why my batteries are no longer charging fully during cheap overnight period!

@bramshot

What model is your heat pump? It is weird that it can't reach high temps if it is advertised as being able to do so.

Also, what's the ventilation around the heat pump like? Is it free from obstruction including any meshing or wood panelling you might have put around it to block it from view? 

@oswiu have you model before, External unit is EPRA18DAV3, supposedly a 18 kW High Temp Altherma unit.

If is installed as per instructions , no structure around it to shield.

Here is a photo off it frosting up nicely. I do not know why there seems to be one tube in the evaporator that is not frosted.

Hello,

I have the exact same system as you.  Daikin HT 18kw and the separation tank between the radiators and heat pump system.

Was curious if you resolved your icing up issues??

I also have the same defrost issues as you, when it's colder i.e. around 3 - 4c or lower the outside unit will ice up and spend most of it's time defrosting vs heating the house.

I have radiators, no UFH, ~260msq floor space, limited insulation.  (say none!)

this is my 2nd winter.  The APSH needs to be set at a high temp as i have an older house with radiators.  This High Temp heat pump (according to Daikin) is designed to replace a Gas boiler and provide high flow temps up to 70c.  So while it may operate at 30c, the house would be cold as my RAD's are designed to work a flow temps of 60c

Anyway, i faulted this to Daikin this year, they have been out and tell me the Booster heater isn't coming on.  Apparently this should some on when it's cold to help out the compressor unit.  I wasn't aware this HP (as explained above) is essentially a 12kw ASPH with a 6kw electric booster? 

I will see what happens once Daikin come back with a new booster heater and PCB.  

I have mine set at 55c fixed leaving water flow temp currently, i have played about with weather compensation, no real difference with icing.  I have set it to fixed just to get it in a steady state and monitor.  I effectively run my heating 24/7 now too, with the aim being to reduce / top large temp. fluctuations between in/out temp on the ASHP to try and keep it less stressed.

When it's "warm" outside i.e. above 5c it seems to work fine, no icing up.  I hope the new booster heater sorts the problem, i'm inclined to think though the HP is simply working too hard, combined with UK high humidity, results in freezing up???

I have just set up "Home assistant" monitoring on it and will see what that reports. 

 any one else have icing up issues with these Daikin units?

Thanks.

@haggistrap 

Having a 6kW booster heater operating may help reduce the load on the heat pump, and hence reduce the need for defrost cycles, but I suspect it will have a dramatic effect upon your bank balance.

Improved insulation and/or larger heat emitters would probably be a better use of the money.

@derek-m 

agree, am pondering some Radiator upgrades in the summer.  I can’t help but think these Daikin HT ASHP, sold and marketed as a retro fit for gas boiler to ASHP with no other work is at best not strictly true, worse complete fabrication!

like the OP who started this topic, I had this ASHP installed to replace an old Gas boiler.  There was no need to replace anything or add insulation, as this HT unit is retro fit!

I’ll update when my ASHP has an new booster unit.