ASHP question

Spoonie_Turtle
Spoonie_Turtle Posts: 8,148
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edited 23 January at 2:33PM in Heat pumps
Our Ecodan is set so that between 11pm and 5am the heating does not come on, nor the hot water.  Yet almost every night something is humming away in the off hours in the vicinity of the water cylinder - anybody have any ideas what that could be?  It's been happening consistently since mid-September when I changed the settings, so it's not to do with being freezing outside.

The unit is a PUZ WM115VAA, one of the ones with the massive vampire load, if that helps, but it's definitely not the outside unit working away because I went out and checked.  At first we assumed it was next door's, but then realised it was from the water cylinder or something around there.
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  • matelodave
    matelodave Posts: 8,571
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    edited 8 December 2022 at 10:10PM
    If its a buzzing sound, it could be that a contactor (big relay) has been energised.

    Have you got a sterilizing function set, if so at what time and how often. It will try and heat the water above 50 using the immersion heater. I can hear the contactor in my Daikin when it turns on the immersion heater for sterilisation it clunks when its energised, hums when its energised and clunks again when its released.

    What temperature is your hot water set to and is it also timed. There's a possibilty that if your water temp has been set much above 50 degrees that the heatpump is trying to heat it using the immersion heater if you've got one. Heatpumps cant usually get above 50-55 degrees and so use the immersion heater if the water temperature is set higher.

    It's why a lot of people whinge about the energy consumption of their heatpump because the immersion heater or even backup/boost heater kicks in if the temp is set above 50ish.

    Lastly, what settings did you change?, what happens if you set it back to its previous configuration. Hopefully you noted what the old settings were and what effect the new settings made


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  • Hot water is set to 50℃, allowed on between 5.30am and 9 or 10am.  Legionella cycle is 3am Saturday morning as before when we were all ignorant to how to even find the settings, much less what they meant or how to change them.  I did change the cycle to in the daytime when the water would be warmer so the immersion would have less to do, but then realised the risk of scalding wasn't worth the energy saving and changed it back.  (None of us would remember and be mindful at the right time, it's hard enough to keep track of which day it is let alone remember something's happening.)

    It's not a buzzing but a humming thst sounds very much like a motor whirring, to the point I always thought it was the outside unit before.  The heating and hot water were allowed on at any time and I knew that from the installation, which is why I didn't query it or my assumption before.

    Prohibiting heat at night and hot water after the morning are the settings that are different now.
  • shinytop
    shinytop Posts: 2,088
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    edited 8 December 2022 at 10:53PM
    Our Ecodan is set so that between 11pm and 5am the heating does not come on, nor the hot water.  Yet almost every night something is humming away in the off hours in the vicinity of the water cylinder - anybody have any ideas what that could be?  It's been happening consistently since mid-September when I changed the settings, so it's not to do with being freezing outside.

    The unit is a PUZ WM115VAA, one of the ones with the massive vampire load, if that helps, but it's definitely not the outside unit working away because I went out and checked.  At first we assumed it was next door's, but then realised it was from the water cylinder or something around there.
    Freeze Stat?   I also have my heating off at night (with the timer, not properly off) and freeze stat runs a lot.  It doesn't use a lot of energy. It runs the pumps to circulate the flow and if it (the flow) gets too low it heats it up to 20 deg.  Some people disable it if glycol is used in the water. 




  • Spoonie_Turtle
    Spoonie_Turtle Posts: 8,148
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    edited 8 December 2022 at 10:56PM
    Frost protection did cross my mind but it's been doing it all year round in the past.  I don't think it dropped below 10℃ until sometime in October, and it was certainly doing it in September both before and after I changed the settings.  Not sure about August as we were away for half the month and I can't remember much before that. 
    [Although it did manage to use 50kWh in August for "heating" (0kWh output, obviously, we were in the midst of heatwaves).]
  • shinytop
    shinytop Posts: 2,088
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    Frost protection did cross my mind but it's been doing it all year round in the past.  I don't think it dropped below 10℃ until sometime in October, and it was certainly doing it in September both before and after I changed the settings.  Not sure about August as we were away for half the month and I can't remember much before that. 
    [Although it did manage to use 50kWh in August for "heating" (0kWh output, obviously, we were in the midst of heatwaves).]
    It can be set to work at up to 20 degrees.  Also, don't know where you are but it did dip below 10 deg occasionally in September here.  Do you know how to access the settings to check?
  • Mstty
    Mstty Posts: 4,209
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    edited 9 December 2022 at 10:39AM
    How's your daily usage Spoonie turning it off overnight, is there a big spike in the morning.

    Reason I ask as we are experimenting with it on 24/7 
  • shinytop said:
    Frost protection did cross my mind but it's been doing it all year round in the past.  I don't think it dropped below 10℃ until sometime in October, and it was certainly doing it in September both before and after I changed the settings.  Not sure about August as we were away for half the month and I can't remember much before that. 
    [Although it did manage to use 50kWh in August for "heating" (0kWh output, obviously, we were in the midst of heatwaves).]
    It can be set to work at up to 20 degrees.  Also, don't know where you are but it did dip below 10 deg occasionally in September here.  Do you know how to access the settings to check?
    No I have no idea how to check.  Would welcome the enlightenment please :smile:

    Mstty said:
    How's your daily usage Spoonie turning it off overnight, is there a big spike in the morning.

    Reason I ask as we are experimenting with it on 24/7 
    I don't know, we don't have a smart meter and now electricity prices are sitting at the EPG cap (we're on Tracker) I've not felt the need to take frequent readings.  Just resigned to it being an expensive month!  In terms of the heat pump consumption I was going to check at the end of the month, but when I can get in the cupboard sooner than that I'll let you know what it says.  We don't have the data from previous cold snaps to compare even basic data though.

    With this cold snap I completely see why people do a setback temp for overnight (especially if it's going to be using energy keeping itself defrosted anyway!).  I don't know if that's possible with this model and controller though, haven't been able to find anything yet.
  • Mstty said:
    How's your daily usage Spoonie turning it off overnight, is there a big spike in the morning.

    Reason I ask as we are experimenting with it on 24/7 
    I'm replying to this because there is a lot of similarity between our installations.  5 bed detached EPC 87B, 212 sq. m.  Ecodan PUZ-wm112VAA.  UFH on ground and first floor.  300L DHW.

    Our FTC6 number have averaged an implied COP of under 2 from commissioning in February until late November when the outside unit broke down, with a refrigerant leak from the 4-way valve.  The entire unit has now been replaced.  

    It works fine in the sense that the house is warm and the DHW is hot (set to 48C).  It's on 24/7 and the suppliers recommended that we leave it set that way.

    The implied COP has not improved. I can't make sense of the data in Melcloud so I will be talking to Mitsubishi for some help in understanding what is going on.

    November's heat pump electricity usage for the first 3 weeks until it broke down, averaged 12kWh per day.  This has leapt with the colder weather (and the change of unit) to 25kWh per day for the 3-7 December, after the unit was replaced, and the last couple of days which have seen mean outside temps around freezing have been about 36kWh per day.

    Downstairs stats are set at 22-23.  Unused rooms upstairs at 18, others at 21 or so.

    Have you looked at the flow temperature drop in Melcoud? (assuming you have an Ecodan).  Mitsubishi commented last April that ours looked a bit unusual with only about 2 degrees drop between flow and return, where they would expect 5 degrees.  That is still the case.  Given the unit is actually keeping the house warm, I am wondering whether the thermistors for flow and return are correctly fitted/located - if they weren't that might also affect the reported energy production (the usage reported by the FTC6 is about right, it's the estimated energy produced that looks too low).  It might well be the case that the system is working fine but the estimated energy produced is way off.

    Our November electricity bill was about £200.  December's looks as if it could be double that if outside temps stay low.  Our non-heat-pump use is however highish at around 15kWh per day.  I think that probably includes the heating pumps, we also have MVHR, and quite a lot of parasitic stuff, internet switch, alarm, CCTV, outside lights.

    My own forecast estimate is a total usage of 8200kWh per year.  I might be too optimistic.

    It would be interesting to have some comparison if you are prepared to share your experience.
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  • Mstty
    Mstty Posts: 4,209
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    @redbuzzard

    So we inherited a 6 year old Mitsubishi Ecodan 8.5kwh ASHP with the FTC4 controller and no Mel cloud. Also as this was installed as part of the house build it did not come with any seperate energy monitor as there were no payments due to the previous owners as the builder installed it as part of the design. 

    4/5 bedroom house in an L shape configuration.. Downstairs all under floor heating except the towel radiator in a downstairs en suite.

    So historically it's been a steep learning curve. Our first winter was 2021 and Mrs mstty suggested I move into the plant room as I spent so much time manually adjusting the temperature flow depending on weather as At that time I had not discovered the weather compensation curve.

    Our first year we had a nice all round temperature of 21oC in the house but I was always fettling and changing things and we were lucky we only used 7,211 kWh in our first year as we had left the backup electric heaters to kick in when needed.

    This winter I have setup the weather compensation curve, turned off all auxillary electric heaters and have so far left it to do it's own thing. 

    So far this our second year which starts July up until today December 9th 1824kwh (bright app screenshot below)

    Our non-heating and non-hot water usage averages out at 10kwh a day in winter due to the tumble dryer taking longer and being used more as well as the oven being used more.

    So focusing on November we had 300kwh non-heatpump usage and 300kwh heatpump heating and hot water usage.

    December is looking like coming out as 310kwh non heatpump usage (10kwh a day) and 620 heatpump usage (20kwh a day) but let's see how that pans out.

    If our estimates go as planned we could sneak in under 6000kwh for the year. That would be the dream.

    Currently the large open plan vaulted kitchen at 17oC. L shaped hall at 19.5oC and formal lounge at 20oC. Snug at 20oC and plant room, WC, utility, downstairs bedroom and ensuite and office at 18-19oC

    Upstairs always reads 20oc or over


  • Thanks Mstty, that's very helpful.  Seems we're quite close in terms of usage.
    "Things are never so bad they can't be made worse" - Humphrey Bogart
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