How inefficient is this temperature pattern?

[tonymorris24]

We have a large kitchen/dining area and I've measured the temperature. It's an interesting pattern... up and down.. and up and down... even though the thermometer is set at a constant temp. No night time set backs or anything like that... just inertia.

We have a GSHP and ancient controls (see forum post here) but I'm wondering whether it's a very inefficient to have the floor warmed up and cooled down, or whether it's not a big deal. It's about 14 hours from peak to trough.

Any thoughts!?
Thanks!

 

[snowhead]

Is that measured from the thermostat?
Where is the thermostat, or probe used for the measurements, in relation to other heat sources in the Kitchen, including windows?

 

[tonymorris24]

Is that measured from the thermostat?
Where is the thermostat, or probe used for the measurements, in relation to other heat sources in the Kitchen, including windows?

It's measured from a separate thermostat (just one I bought online), and sited near the 'actual' thermostat that the control uses.

 

[Knappers]

It means very little on its own but its very normal for a traditional thermostat to control temp within a 2deg range. It could be that it takes 14h to get to temp or that it's effected by outside temp on 24h cycle (trough to trough).
Comparing to outside temps and times when heating is on would be much more telling.
Efficiency wise, would need to know output of system room sizes etc

 

[tonymorris24]

It means very little on its own but its very normal for a traditional thermostat to control temp within a 2deg range. It could be that it takes 14h to get to temp or that it's effected by outside temp on 24h cycle (trough to trough).
Comparing to outside temps and times when heating is on would be much more telling.
Efficiency wise, would need to know output of system room sizes etc

Thank you! Unfortunately I can't easily do 'heating on' graphs given my system is from the 2015s, but I'll see what I can create. I think outside is a little less relevant because the peak to trough seems to happen at all times of day/night.

 

[Chuck]

I'd want to replace the current (bi-metal?) thermostat with one that has a narrower hysteresis band or TPI. Ideally, one purpose-made for UFH with a floor sensor and setback programming. This will allow you to run the room at a lower average temperature without sacrificing comfort so, in this sense, your current system is 'inefficient'.

A tighter thermostat controlling the system should allow you to reduce the average temperature from 19°C to 18°C, which could save up to 11% of fuel (assuming average external temperature of 10°C. Using a setback period, e.g overnight will help further.

If the thermostat is reasonably new, you may be able to change it's mode / parameters by following instructions in the installation manual.

 

[tonymorris24]

I'd want to replace the current (bi-metal?) thermostat with one that has a narrower hysteresis band or TPI. Ideally, one purpose-made for UFH with a floor sensor and setback programming. This will allow you to run the room at a lower average temperature without sacrificing comfort so, in this sense, your current system is 'inefficient'.

A tighter thermostat controlling the system should allow you to reduce the average temperature from 19°C to 18°C, which could save up to 11% of fuel (assuming average external temperature of 10°C. Using a setback period, e.g overnight will help further.

Interesting.. thanks! No idea how I'd do that without it costing a fortune... any ideas on how to retrofit those controls?

The GSHP is simple - it just tops up the buffer tank when it gets cold, but the controls (linked to the WLM3 wiring centre) are a nightmare

 

[Chuck]

Interesting.. thanks! No idea how I'd do that without it costing a fortune... any ideas on how to retrofit those controls?

The GSHP is simple - it just tops up the buffer tank when it gets cold, but the controls (linked to the WLM3 wiring centre) are a nightmare

I doubt it's the problem, but check that the buffer tank is being maintained at a sufficiently high-temperature for the UFH before blaming the room thermostat.

It's a cost-benefit calculation. Will the cost of a new thermostat, or whatever is needed, be paid back by a 10% reduction in fuel over a period of, say five years? If not, it's probably not worth doing from a financial point of view.

Also, changes to controls don't always deliver all the expected cost saving in practice. You won't save a penny, for example, if the wife decides that the new stable 18°C room temperature is 'feels cold' and resets the thermostat to 19°C!

 

[PETE 123]

Old thermostats have about 1-3 degrees between on and off digital ones are about 0.5 degrees.