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  1. #1
    Join Date
    Dec 2021
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    Ireland
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    Daikin Altherma not reaching LWT and poor COP



    Hi, I'm new to this site, so apologies if this isn't the right forum!

    I have a Daikin Altherma LT split (indoor unit: EHVH08S26CB9W, outdoor unit: ERLQ006CAV3) and I've never been satisfied with its performance. The system is about 5 years old now and its COP is about 2 for the space heating function (a bit less for the DHW function). The listed COP is about 4.74. I've had it inspected a few times, and I've been in touch with Daikin who have admitted that the system isn't performing but I haven't been able to get them to actually do anything about it.

    The system is set to weather dependent with the LWT varying between 30 and 35 degrees. When it comes on it often gets the LWT up to (close to) the desired temperature but then, after an hour or so, the outdoor unit seems to go into a low power mode: I've monitored this using my house energy usage and it drops to using about 1kW. Once it goes into this low power mode it fails to maintain the LWT anywhere near the desired temperature. The "Quiet Mode" is set to "OFF". The function which allows it to limit its power consumption is enabled, but is never in use - I can check this on the menus. I've had the temperature of the refrigerant checked at the outdoor and indoor units and it seems lose very little temperature between the outdoor and indoor (maybe a degree).

    Has anyone had a similar experience, or had any insight into what might be going on? I've an engineer coming again this weekend and I'm keeping a daily record of the power consumed and power output. Any help/hints would be very greatly appreciated.

    Thanks,
    Turlough



  2. #2
    Join Date
    Nov 2006
    Location
    Guernsey
    Age
    65
    Posts
    241
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    Re: Daikin Altherma not reaching LWT and poor COP

    Without knowing the flow rate throught the heat exchanger, delta T across the water heat exchanger, ambient conditions, actual refrigerant pressures and discharge pipe temperature it is a bit difficult to make any judgement.

    You could try taking the system off of weather compensated control and set it to say 45°C fixed flow rate to see if it can reach this new setpoint.

    I have an 8.0kW system installed in my old draughty granite cottage and it works great, but at ambients of around 2°C there is no way it can reach flow temperatures above 47°C. That is fine for my design as we are using fan convectors that need a maximum temperature of 45°C to maintain the building temperature at our lowest ambient conditions.
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