Welcome to the forums @hightower – I don't really know much about Nest and how it works. Is it a central thermostat that regulates and calls for heat for your entire property or do you have other smart thermostats scattered around the property? Have you been watching your ASHP and is it cycling? Ideally, you want it running non-stop except when it has to do defrost cycles.

You'd also be better off, based on the numerous conversations amongst Ecodan owners here, to enable your weather compensation and run the pump like that. You've asked about heat curves and I'm sure one of the Ecodan crowd will fill you in and what's best to do.

@hightower,

welcome to the forum. The most important thing is that your house is warm so that's a good start.  And without knowing any details about your house, your numbers look OK I (I assume you mean kWh not kW).

There are probably two things to start with.  First, is the system running on weather compensation?  If you have radiators it's probably going to be more efficient if it is. If your controller screen has a number around zero with up/down arrows it is.  If you're not sure post a picture/ask

The second thing is the thermostats. External thermostat can only tell the FTC to switch the ASHP on and off, nothing else.  Once it's on, the ASHP does its own thing.  This will work but it may not be the most efficient way to run it because it can make the ASHP switch on and off more than it needs to.  As you say it will work better if it's running steadily.  

A good start then would be to run the system on weather compensation and get that right while keeping using the thermostats. The next step would be to turn the thermostats up a couple of degrees more than you want and start adjusting the weather compensation curve to maintain the house temperature. 

I have thermostats but they are now set to 30 degrees and I just let the weather compensation vary the radiator temperature and this keeps the house at a constant 21C or so.   I find that uses 20-25% less energy than using the thermostats and a constant flow temperature. 

The Mitsubishi thermostats claim to be able to do something cleverer with room temperature but I haven't tried it (yet)

Please ask if you're not sure about anything.

Thanks both for the swift and welcoming replies - hoping to get up to speed with this all eventually!

Kev-M - yep it's on weather compensation. And certainly seems to operate in a pulsed manner from the thermostat rather than on all the time.

The idea of setting a high temp on the thermostat makes sense - albeit I'm used to the notion that it would keep the old boiler firing at max until achieved. 

I'm fairly tech savvy and can get into all the sub menus to change the weather compensation points and curve - but the understanding of what I'm doing isn't quite there!

I'd like to try your route of an 'always on' approach (thou it does render the fancy nest thermostat redundant! - was good for the oil boiler however so not a total waste!) 

Hows best to go about it settings wise? I can wrap my head around the temperature settings for the outflow from the pump, but the mythical 0 degrees number I can adjust on the display doesnt quite make sense to me yet!

Thanks again!

@hightower I have a Nest, however for my HP its just being dumb. I set it to 22 degrees and adjusted the room temp via weather comp and TRVs

Posted by: @hightower

Thanks both for the swift and welcoming replies - hoping to get up to speed with this all eventually!

Kev-M - yep it's on weather compensation. And certainly seems to operate in a pulsed manner from the thermostat rather than on all the time.

The idea of setting a high temp on the thermostat makes sense - albeit I'm used to the notion that it would keep the old boiler firing at max until achieved. 

I'm fairly tech savvy and can get into all the sub menus to change the weather compensation points and curve - but the understanding of what I'm doing isn't quite there!

I'd like to try your route of an 'always on' approach (thou it does render the fancy nest thermostat redundant! - was good for the oil boiler however so not a total waste!) 

Hows best to go about it settings wise? I can wrap my head around the temperature settings for the outflow from the pump, but the mythical 0 degrees number I can adjust on the display doesnt quite make sense to me yet!

Thanks again!

Hi Hightower,

Welcome to the forum.

The 0 (zero) is just an offset value, so if the present parameter settings for your weather compensation produce an indoor air temperature of 20C, but the desired temperature is 21C, then changing the offset from 0 to +1 should achieve the objective.

The required parameters for your weather compensation will mainly be dependent upon the heat loss of your home and the output capacity of your heat emitters. Probably a good starting point would be a 1C fall in outside air temperature would require a 1C increase in water flow temperature to maintain the indoor air temperature at the desired level. That would require parameters of water flow temperature of 20C at outdoor air temperature of 18C and water flow temperature of 48C and outdoor air temperature of -10C. If the heat loss from your home wasn't as great, and the water flow temperature only needed to increase by 0.8C for every 1C fall in outdoor air temperature, then the weather compensation settings would be more like 20C water flow temperature at outdoor air temperature of 18C and water flow temperature of 42.4C at an outdoor air temperature of -10C.

Any thermostats should be set at 1C or 2C above the desired temperature, to allow the FTC controller to use weather compensation to control the indoor air temperature. If your FTC controller is located in your main living area then you could consider using auto adaptation control, which would provide more accurate control of the indoor air temperature.

@hightower 

Good advice from Derek as always.  It's a bit of a leap of faith to turn the thermostats up and leave the heating on. It takes a bit of tinkering to get it right and I overshot to start with and was sweltering at about 25C.  But now it keeps the house very constant. If I do want it a bit warmer or cooler I just use the offset on the main FTC screen and I use TRVs to keep the bedroom a bit cooler.  I also turn the heating off 12-5am . That's more for comfort as it makes little different to kWh used because the saving in the 5 hours is partly cancelled out by a big spike as it kicks in at 5am.

If you (or anyone else is interested), this is what happens when a thermostat controls the ASHP; you can see it starting up after a period off in this graph.  The COP trace is what the FTC is reporting; ignore the actual number because it's a bit meaningless at the moment for various reasons but note the way it changes as the ASHP is doing different things.

Thanks again both.

So just to check as I embark on some tweaking:

I've adjusted the temp curve as per Derek M instructions

 And I've got the thermostat in the loung at 23C to aim for a house temp of 21C (small kids!).

So now I wait it out for a bit and see if house gets to temp? Then presume initially use the offset value to test small changes if too cold/hot, then reprogram the curve once happy and just leave it be? 

Is there a point as the weather warms where you only tend to run your pumps in the eve/nights? I wonder when the offset of 'cold' starts vs continual running hits an equalish point?

Hi @hightower

Heating systems, particular those with a heat pump, react very slowly, so it does become much of a waiting game. Make a small adjustment then wait for the system to stabilise, before making further changes. Where is your FTC controller located?

I think that Kev and others have found that the heat pump will start to cycle when the outdoor air temperature gets up to 7C or 8C. This is because the heat pump cannot turn down any further, it has reached its lowest operating speed, so will switch off for a period of time whilst the water flow temperature falls. This is normal operation as the weather gets milder.

@derek-m The FTC controller is in the utility room so one of the colder bits of the house tbh. 

Posted by: @hightower

@derek-m The FTC controller is in the utility room so one of the colder bits of the house tbh. 

Hi,

Provided that the air temperature within your utility room is being affected in a similar way to the other rooms in your home, then you could possibly use auto adaptation control, which should provide more accurate control of the indoor temperatures.

I've been looking in the manual but can't quite figure out if the ftc6 can do the auto adaptation on it's own, or if it needs a seperate room temp sensor - that I guess the mitsubishi one would be - and not sure if the nest does or not...