Is it spiking or is it gradually reaching the required FT following a defrost.  You can tell it is going into defrost mode (which is expected given current weather conditions) because FT<RT.

It doesn't say anything to do with defrost on the controller when it's spiking. Even if it was, would a defrost cycle really be that aggressive with flow temp? Energy usage spikes too for the times it spikes

Just realized the 2 of the screenshots above have set tank temp instead of actual tank temp. It looks like it is calling for heat sometimes when there is only a 1 or 2 degree drop in tank temp. Here is updated screenshot with actual tank temp. However I'm pretty sure the controller did not saying it was heating DHW during that(but I'm not 100% sure)

The peaks in your graph (which I presume are the 'spikes' you are referring to) appear to be at different FTs.  What is the set FT, what is the set FT for DHW and when is DHW heating scheduled for (or is it scheduled 'continuously' ie DHW priority).  Also whats the 'tank' - is it the DHW tank?  If so your most recent graph clearly shows the Tank temperature increasing when the spike occurs, which clearly indicates its heating DHW.  Is it possible that the system is set up to give priority to DHW with only a small hysteresis?

@jamespa thanks for your help. I think the problem was that the "DHW max operation time" was too low on the DHW settings. It was at 30 mins. I think during cold weather it was just taking too long so was having to try twice. This is why it only happened occasionally.

@eleusis The high flow temps are when it is heating your hot water, I set mine to run for 90 mins and I don't reheat during the day 210L tank is enough for 2 showers and a bath and general washing up.

Posted by: @eleusis

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Hi there. 

Currently I have my heat pump set to WC mode. Fairly low temps (under 30 degrees) because heavily insulated airtight house. 1 zone with no rads. .only underfloor heating.

Now and again for some reason the flow temp spikes massively. I'm hoping to understand why it is doing this. Can anyone tell me what's going on?. Any help appreciated. Thanks

 

hi @eleusis 

these graphs are all DHW cycles and nothing to do with WC mode.

and as @jamespa says you’re first graph with the split reheat shows signs of being in defrost during a DHW CYCLE.

A 30 minute DHW cycle is not a problem for an Ecodan. This has been stated by some people on this forum, as a problem and this is incorrect. it’s  just down to other settings like immersion intervention or at what temperature you set it to reheat. By that I mean if it reheats when the water is 40c it should reheat adequately to 50c in 30 minutes and that’s very efficient. See below. 

 This is also dependent on what type of cylinder you have fitted, eg performance between different manufacturers or technologies, ie a plate heat exchanger or a coil heat exchanger.

However if all else is equal if you operate a DHW reheat when at 30c it might take closer to 45 minutes to get to 50c.

However the key point in terms of efficiency and economy is - the longer your hp is operating at a flow temp of 55c or above the less efficient your hp will perform. And obviously the more frequent the DHW reheats are the less efficiently also.

I first proposed 30 minute reheats as a way of shortening the period that a HP is in high temperature mode and it works. But as we personally often let our DHW go down to 30c before a reheat we have now opted for a 43minute DHW reheat period with a touch screen actuation when we need it. IE it’s not scheduled. But that’s just our intermittent needs.

this last graph shows 30 minutes reheat when starting at 30c and it doesn’t quite reach 48c

Posted by: @sunandair

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i first proposed 30 minute reheats as a way of shortening the period that a HP is in high temperature mode and it works. But as we often let our DHW go down to 30c before a reheat we have now opted for a 43minute DHW reheat period with a touch screen actuation when we need it. IE it’s not scheduled. But that’s just our intermittent needs.

Presumably it stops heating when the DHW reaches temperature, so if it only needs 30 mins then it will only take 30mins and then return to space heating at WC temperatures.  At least thats how I would expect it to work...but you never can be certain.

@jamespa yes, I think you’re right but it might be worth checking.  it can also be seen that the target temp  usually over runs by a few degrees, presumably because the HW is rising in the cylinder and finding it’s level.

We have a 250 L cylinder and know that when the mid tank temp reads 50c the upper thermistor is reading 56c. This is read from a thermistor which is not part of the Ecodan setup but is part of our solar thermal system. So it’s handy information.

@jamespa 

so I put the DHW on while the existing hw temperature was elevated. (To see how the HP would react when it reached DHW target temperature early in the cycle)

Even though it has a pre-set (Max) duration of 43 minutes, it reached target temp in 32 minutes and switched itself into standby. ( the room temperature was 21c so it didn’t return to space heating) 

 So on the Ecodan system it would appear that the system reacts to the set duration as a maximum duration if the target cylinder temperature is reached early.

Posted by: @sunandair

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@jamespa 

so I put the DHW on while the existing hw temperature was elevated. (To see how the HP would react when it reached DHW target temperature early in the cycle)

Even though it has a pre-set (Max) duration of 43 minutes, it reached target temp in 32 minutes and switched itself into standby. ( the room temperature was 21c so it didn’t return to space heating) 

 So on the Ecodan system it would appear that the system reacts to the set duration as a maximum duration if the target cylinder temperature is reached early.

 

 

That's reassuring.  Hopefully it would have returned to space heating if there demand was there.