Hi all

I did a lot of digging into this , there are 2 things I head to tweak which apparently are common settings to change on the Daikin Altherma:

Set delta to 4 - this increased the min flow rate from 6-7 L/min to 8-12 L/min and I now have sufficient flow on the UFH to keep is comfortable.

reduce the LED brightness of the light and the blue heating indicator in the madoka to the lowest setting. The heat of the LED adds up to 1c of variation and throws the modulation off as the led immediately heats up the sensor when heating is called for.

Yesterday I achieved a cop of 5 which I’m very pleased with. Now waiting for winter!

Posted by: @pie_eater

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Yesterday I achieved a cop of 5 which I’m very pleased with. Now waiting for winter!

Beware the OEM COP 'vanity data' - most if not all heat pump controllers give very flattering [for flattering read exaggerated] COP data. True measurement requires external energy monitoring equipment, some of which is open source and can be viewed here: https://heatpumpmonitor.org/ That data is a truer picture. A whole load of things don't get factored into many controller COP data readings, such as evaporator fan motor power, circulator pump power, controller power and inverter losses, thermal efficiency of primary to secondary plate heat exchanger, etc...

@allyfish ok that's good to know, little bit less smug now! I do have a grid consumption meter and can isolate the heatpump from everything else, it's showing a very stable 0.4-1 KWh per hour (slowly modulating up and down each hour) and the house is comfortable at 20-21c. Given it's an 8kw unit and outside is about 7-10 C, that to me does sound acceptable as the heating costs from home battery/night tariff is c 70p per day now, big saving compared to gas. But maybe I should indeed invest in that monitoring kit to get the full picture (the DIY version!). Not sure it's worth the time investment considering very low running costs (at least at current outdoor temperatures)

@pie_eater different manufacturers have differing accuracies of COP data, some are just considering the refrigeration compressor, some are total unit power consumption. They all seem rather flattering. If your unit displays flow rate and supply and return water temperatures reasonably accurately you can calculate the thermal output and, knowing the electrical power consumption, the instantaneous COP, by the flow rate in l/s x delta T temperature difference x the specific heat of the circulating fluid. Water is 4.2kJ/kgdegC:

Example: 10 litres/minute, 5degC delta T, pure water, power consumed 1kW

(10/60)x5x4.2 = 3.5kJ/s (kW)

So 3.5kW thermal energy generated / 1kW electrical energy consumed = COP 3.5

Glycol solutions reduce the specific heat capacity of the circulating fluid, you can Google the specific heat at the average of the ASHP flow and return temperature for varying % glycol concentrations by volume 🙂

Quick question. Octopus have contacted me to suggest installing a wireless 3rd party thermostat on the ground floor to replace the existing madoka . 

Any potential issues with that approach, for instance I read somewhere modulation may not be possible with a 3rd party thermostat ?

@pie_eater I don't know the Daikin Madoka product, but having had a quick look on-line, it seems it's a simple binary [digital on/off] thermostat compatible with Altherma and other Daikin products. If so, it has no modulation.

It would need to have analogue proportional control (0-10V, 4-20mA, etc.) to provide modulation control of any connected heating or cooling source. So it looks like every other so-called smart thermostat - just a glorified on/off timed switch.

Replacing it with another less expensive on/off timed switch, such as one that's wireless, wouldn't change anything. That said...

For best efficiency, weather compensation should be your principal means of indoor temperature control, this is usually linked to and external outdoor temperature sensor built into the ASHP, or separate and mounted nearby. Warmer outdoor temperature = lower heating flow temperature and vice versa. [I'm sure you know all this, forgive me.]

Load compensation is another method some ASHPs use, that's basically an indoor room temperature sensor modulating the flow temperature, i.e.: analogue proportional control as described above. It's rarely used on domestic ASHPs, and nearly all use external temperature.

So, ideally, thermostats that switch the ASHP on or off should not be used as a principal means of control. They usually have too narrow a control hysteresis, some as a low as 0.1degC, e.g.: HIVE, and cause short cycling, where the heat source is switching on and off many times an hour. If the source is an ASHP, it never gets a chance to run 'low and slow', as they are designed to. Aside from the undesirable reliability affect of frequently switching the ASHP on and off, or fired boiler for that matter, the ASHP power consumption can be excessive. When it switches on the circulating water is below set point, so it has to work hard to raise that, only to be abruptly switched off again 10 minutes later. It hasn't got a chance of establishing stable control.

Thermostats, TRVs and blending valves are best avoided, or if used, set solely to avoid overheating a space. The weather compensation should have control and hierarchy over all other on/off thermostat switches or flow restricting devices. If you have an imbalance with your heating, too much on one room or floor, too little on another, the way to solve that is with mass flow balancing, to proportion the flow rates and thereby the thermal energy to where it needs to go. The way not to solve it is using thermostats, TRVs, etc. Getting the heat mass flow balance right takes time & skill, fine tuning radiator or manifold settings, monitoring delta T over the emitters, adjusting, etc.. Banging a WiFi thermostat on the system takes an hour at most.

I would ask Octopus why they think a WiFi thermostat is a suitable control device if it is a one that will switch the ASHP on and off several times an hour. They are no substitute for proper commissioning by a competent engineer who can monitor and measure heat energy delivered from each emitter and set it up room by room per your heat loss report.

@allyfish thanks a lot for your comprehensive reply!

ok I think my system seems to be pretty ok then, basically the madoka is calling for heat all day but I got the weather curve in such a way it never quite gets there so it bobs along very gently just below target temp at a low kWh . 
I thought it was the madoka unit doing all the logic but I think you’re saying thats the result of WC+ delta T + flow rates working in a balanced way. 

the only switching the thermostat then does is the night time set back (I have a 1 degree set back for now). That will effectively switch it off 23-4am. While reducing cop I get the sense that a set back at night still works out more economically especially if the inefficient reheat is at low night rates , do you agree?