If only this WC Curve setback was available as a scheduled setting as a night time setback.
For what it is worth, the way the Vaillant heat pump control works in pure wc mode (where actual room temperature is not part of the control loop) is that, when you adjust 'desired room temperature' it shifts the wc curve. Since desired room temperature can be time programmed, this means it does exactly what you want.
I'm actually rather surprised that mitsubishi doesn't offer a similar function, as it's generally a pretty sophisticated controller so far as i have read. Are you certain that it doesn't in one of its modes?
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
There are other modes as you have queried within the Ecodan scope of operation. You may be aware of the Auto Adaptive setup. This does however use a target room temperature and a version of its own weather compensation. We have used this mode quite a lot in the past but have found it often overcompensates when recovering from a setback.
Following certain shutdowns and setbacks the recovery can be quite extreme and becomes fixed as a learned recovery process.
For us we just find AA a bit temperamental. We are currently preferring to use full weather compensation and use it’s more predictable behaviour.
My previous post outlined useful and efficient ways to use setbacks. But these efficiencies are only available in Weather Compensation Mode. These particular efficiencies are not available in Auto Adaptive Mode.
So, while it might be just a pipe dream, if ever a new operating system for Ecodan was to be considered then we would certainly find scheduled Flow Temperature adjustment a useful energy saving tool.
Following discussion on what is missing in the controls of heat pumps I've done a trial on a different kind of setback for overnight operation which might be more efficient than simply dropping the target room temperature.
On the Ecodan controls the only way to operate a scheduled setback is to program a temperature drop on the set temperature control. On the current system there is no way, in weather compensation of making a setback FLOW TEMPERATURE.
Im suggesting that there is already a theoretical advantage of making a setback using flow temperature drop of say 5c and based on the widely quoted benefit of a 3% energy saving for every 1c reduction in flow temperature. This would mean a potential 15% saving on just a room temperature setback of say 2c.
But there would appear to be a second big saving which only revealed itself during the test responses from the heat pump.
The first thing to notice in the reheat graph is the large ramp up when the room stat setback temperature is reached. This is because the HP is following the NORMAL WEATHER COMPENSATION CURVE. However this is night time. Do we need a heavy duty ramp up?
Another costly activity of the heat pump is the defrost cycle which only takes about 5 minutes to complete but induces another ramp up and the return flow temperature takes around 25 minutes to reach its pre-defrost temperature.
The Ecodan controller has an on screen flow temp adjustment option. This simply adjusts the weather compensation curve flow temperature up or down. So we have induced a low reaction setback by manually adjusting downwards the flow temperature to -5c.
The resulting lower flow resulted in a gentler start during the overnight setback. It was lowered in 2 stages from 40c down to 38c and then finally to 35c flow temp. The first graph shows the step change at 3.35am.
The last graph shows the flow temperature returned to the normal WC Curve setting. You might notice it goes straight into defrost mode when the flow temp is raised back to normal.
Here is the hidden result...
the outside ambient temperature was 2c so we were operating with hourly defrosts.
However, by reducing the Flow Temperature the system appeared to operate below the rapid output which induces the defrost cycle.
This low flow temp adjustment of 5c off the WC Curve appears to have saved 8 defrosts. In addition to have reduced the consumption by as much as 10 to 15%.
If only this WC Curve setback was available as a scheduled setting as a night time setback.
(resultant temp drop at 6am showed a room temp of 18.5c. This raised to 20c during normal operation by 9am)
Update: it looks like Daikin do exactly what I’m looking for in this post.
I’ve just seen this video done by Heat Geek… over 2 years ago. It’s at 8mins 46 seconds.
To recap what I was looking for was : *While operating our Ecodan in Weather Compensation, a scheduled setback which sets the flow temperature lower rather than the room temperature lower. Reason being a room temperature setback will result in the temperature dropping then reheating at ‘full’ weather curve output until the lower room temperature is passed again.
The Daikin system has the option of setting up a schedule for night time (or any time) where a cooler more comfortable night time is preferred. And by lowering the flow temperature say 5c this would also produce an improved energy saving over just lowering the room temperature. Even better- the room target could stay the same but by lowering the flow temperature the target room temperature will simply never be reached.
I guess you would need to play around with the flow temp drop so that the room temp only drops by 2c but it seems it can be done.
I wonder if there are any Daikin owners reading this post who use this setback feature who might shed some light on its effectiveness?
So now wondering if Mitsubishi have any plans on introducing such a control?
I've just recently started using pure weather compensation which is what you seen to be looking for.
It's building the same weather curve, but removes the thermostat and just works on leaving water temperature that can be offset in the daily/weekly planner or via the app.
I've near enough set up right for us, with a -2 Deg offset at 9pm and reverting back to 0 at 5am
I've just recently started using pure weather compensation which is what you seen to be looking for.
It's building the same weather curve, but removes the thermostat and just works on leaving water temperature that can be offset in the daily/weekly planner or via the app.
I've near enough set up right for us, with a -2 Deg offset at 9pm and reverting back to 0 at 5am
yes I’m already using weather compensation on our Mitsubishi but, as stated above, there isn’t a scheduled LWT setback option available. The trial I have done was by manually adjusting the flow temperature just to see how the system responded. And the graphs shown above were the results.
But I’m using an Ecodan system which doesn’t appear to have a programmable schedule for the flow temperature the schedule only appears to adjust the room set temperature.
Is your system a Daikin model or is it another make? How have you found the setback operates? Have you seen any benefits using the LWT setback? And just to clarify; when you state -2c setback that means your schedule takes 2c off the LEaving Water temperature during the setback period? Is that right?
Yes the -2 takes it off the LWT, and I have the Daikin 8kw
Using offset, obviously keeps the heat pump running as opposed to stop/start thermostat control, saving the 20 ish mins start up boost that Daikin do every time it restarts before settling back to set LWT.
I initially tried thermostat control overnight but that's not accurate enough with Daikin (0.5 to 1.5 deg variation that can't be adjusted)
im curious, If you’re putting a 2c drop on the flow temp what’s your room temperature drop at the end of the setback? (Of course this might vary from day to day)
I’ve been very impressed with the Daikin MMI controller. I’ve been helping a neighbour set up their WC curve and found it looks good and is easy to navigate.
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