Posted by: @richard24738

↑

James: Just noticed the timing of the drop: from 21 c at 16:05 to 10c at 16:45.

Useful.  When did it go into shade?  If not then, what else was happening at the same time?

@jamespa Sorry not exactly sure about when it went into shade but my feeling is at the same time as the temp drop.

Clutching at straws:

 - I did have a Tesco delivery at 16:05 so the front door to the house was open for a while but I can't see how that would influence the outdoor temp.

 - my heating timing has a room temp increase from 21c to 22c at 16:00

If it's sunny tomorrow, I'll keep an eye on the temp and if it spikes I'll try to add some shade.

@richard24738 if the sun's out, aren't you getting solar gain in the house?. We have the same thing, our HP is on the south side so get sun directly on it, but although it's only a couple of degrees outside we get warmed up a lot for free from the sun. The next day it may be cloudy and so not affect the HP. So it's not really an actual problem for us. Do you find the same? Or am I missing the point?

I think the point is that the sun can be out, but it can still be very cold, so you still need some heating.  @richard24738 seems to have a problem that, when the sun is out (?), his outdoor sensor which controls the weather compensation reads 20 degress plus, so the ASHP stops heating altogether.  It seems likely that its because its in the sun (it should be in the shade), but this is yet to be proved.

@boycey Heat pump is located at the back of the house and yes I agree, yesterday the sun was out and the rooms at the back of the house had some solar gain. 

Mitsubishi were concerned that the outdoor temperature reading would adversly affect the Auto Adapt calculations.

@jamespa Many thanks for comment.

I can't recollect any location instructions from Mitsubishi stating that the unit should be in the shade, only physical positioning. Maybe it's an unwritten rule.

I believe other heat pump manufacturers allow the relocation of the outdoor thermostat sensor.

Posted by: @richard24738

↑

I can't recollect any location instructions from Mitsubishi stating that the unit should be in the shade, only physical positioning. Maybe it's an unwritten rule.

 

Thats bizarre.  It definitely needs to be in the shade!  There is a reason small weather stations are inside Stephenson's screens!

@jamespa The mitsubishi outdoor thermostat is attached to the protection frame at the back of the heat pump and connects via a short red cable. There doesn't appear to be any flexibility in positioning.

When the original thermostat was replaced, the engineer positioned it in the same place..

It looks like today is going to be sunny again so will watch things more closely.

@richard24738 yes, the R32 its attached to the frame, on the new R290, then can be places away from the unit. This make the weather comp much worse on the R32 units

Posted by: @richard24738

↑

@jamespa The mitsubishi outdoor thermostat is attached to the protection frame at the back of the heat pump and connects via a short red cable. There doesn't appear to be any flexibility in positioning.

Thats a bit of a design flaw.  Maybe a strategically placed sunshade is required!

@richard24738 have you popped the cover of to see if there's any length tucked inside, if you (we) could position it nearer the bottom of HP I would think that could make a fair difference.  Mines on the top right rear corner, looking from the front.

Posted by: @boycey

↑

@richard24738 have you popped the cover of to see if there's any length tucked inside, if you (we) could position it nearer the bottom of HP I would think that could make a fair difference.  Mines on the top right rear corner, looking from the front.

Good idea.

If you can move it, try to avoid placing it somewhere it gets affected by whether the unit is on or off. 

Midea heat pumps (or at least the Midea heat pump owned by @cathoderay) have an air intake sensor which doubles as the outdoor temperature sensor.  This appears to be pretty much OK when the heat pump is running, because its constantly drawing fresh air over the sensor, but when its not running the sensor gets warmed by the residual heat in the unit, thus distorting the readings.  In practice this probably doesn't matter much unless you are trying to work out whether setback costs money or saves money, which is how the issue came to light.

Temperature sensors are often fairly high resistance thermistors and so can be extended with any ordinary two core cable.  My installer did that for my DHW tank sensor.  It probably invalidates the warranty though!