Posted by: @kev-m

Is there a sensitivity setting on your room thermostat will stop it reacting to small variations in room temperature

Morning,

@peacenes 

Mirnes, good progress. You now have a slightly more clever thermostat, which will switch the ASHP on and off less often, running at a constant flow temp.  The next step (I think) is to do the same at a weather compensated flow temp and see how that goes. 

What I, @batalto and others are trying, is to bypass the thermostats by turning them up high (so that they are always calling for heat) and let the weather compensation control the temperature of the house by varying the flow temp.  Currently, doing this, my house has stayed at 21-22C when it's been between 6C and 12C outside.  So far so good but I need some colder weather to test it more. 

Posted by: @kev-m

is to bypass the thermostats by turning them up high (so that they are always calling for heat)

I understand, but wouldn't that mean that the ASHP is always working, because weather compensation just lowers or raises the waterflow temperature, but doesn't actually turn the unit OFF? 

@peacenes 

Hi Mirnes,

Your ASHP will still start and stop when on weather compensation, but should operate more efficiently. There are two main factors which affect the efficiency of your ASHP, one is the outside air temperature, which as it gets colder means that your ASHP has to work harder to extract heat energy from the surrounding air, and the other factor is the water flow temperature. The higher the required water flow temperature, the longer and harder your ASHP has to work to achieve the required water temperature. When your ASHP is operating on weather compensation, the required water temperature is set dependent upon the outside air temperature, but in the same way as your thermostat stops your ASHP when the room is up to temperature, the weather compensation will stop your ASHP when the water is up to temperature. During milder weather conditions the required water flow temperature will be lowered, so your ASHP will not have to work so hard and will be more efficient.

Because you have to select a weather compensation curve from those available, it is unlikely that it will perfectly match the requirement for your home, so you will still need to operate your system with the thermostat controlling the indoor temperature. But by setting the water flow temperature automatically using weather compensation, should improve the overall efficiency of your system.

Do you have any reading of Coefficient of Performance (COP) on your controller?

Just like a car engine, your ASHP is designed to operate for many years, and prefers to operate for longer periods, rather than be starting and stopping.

To keep the room at a more constant temperature you could set the hysteresis on your thermostat to +/- 0.25C, which again could slightly improve the efficiency.  

@peacenes,

Mirnes,

Here are a couple of graphs that show my ASHP working your way and then my current way. The first is 24 hrs, the second is 6-7 hours.  Take care looking at the y-axes; the scales are different although the units are the same.

Here, the ASHP is responding to a thermostat with the flow temp controlled by weather compensation.  It's set to 21C morning and evening and 18C at other times.  From midnight, it's coming on periodically because the ambient temp is 5C or below - that's automatic.  I assume it's to stop watrer pipes freezing.  In the morning and evening the ASHP responds to the thermostat and comes on.  In between the house stays at 18C or above so no heat required. The peak midday is hot water. In the evening you can also see the thermostat stop calling for heat, making the ASHP turn off and then calling and starting up again. The energy peaks are high, although the ASHP is off a lot of the time.  

Below is with the thermostats turned up.  As @derek-m says, the ASHP isn't heating all the time if it doesn't have to.  Most of the time it runs for a bit then stops.  These cycles are every 30-40 mins.  When it gets a bit colder (look at the blue line), it can run at its minimum level constantly.  

As Derek also says, these units are built to last for years.  They are the same technology as your freezer and fridge and these don't break very often. My freezer compressor turns on and off all the time.

Which way is better?  Well currently my house is warm all the time, which is nice.  The ASHP is running more efficiently (better COP), which is good.  But, it's running for more time.  Is it cheaper?  I suspect it is, but I don't know yet.

Hope this helps.