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  1. #1

    Temperature fluctuation: What is safe

    Hi all.

    I am experimenting with a recent second hand heat pump purchase. I have a temperature controller recording temperature fluctuations and a smart plug monitoring power consumption.

    In order to be as efficient as possible, I've put a timer on the heat pump so it only runs during the day when the air temp is near its peak. I'm wondering what a reasonable swing in temperature is across a 24 hour period, 1 degree?

    My hp is powerful and probably bring the pond temp up by 1 degree in about 3-4 hours. Is this too fast?


    Last edited by willshill; 19-08-2019 at 02:56 PM.

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  3. #2
    Extreme Koi Member Rank = Supreme Champion john1's Avatar
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    I would think a one degree swing would be ok Will.
    John

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  5. #3
    Extreme Koi Member Rank = Nanasai Fishplanetkoi's Avatar
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    I feel that during the summer months, because the water is always around the 18c mark without heat, then the fish are always at a comfortable temp, fluctuation will never be a problem if raised or lowered a degree or two.

    Although you say the overall pond temp could be raised by 1 degree, but around where the inlet from the HP returns you will often see the fish hanging around in the warmer water, especially as the water cools nearing winter. Meaning the return water is far higher than the overall pond temp at that point. I have never checked but to increase a large pond by 1 degree, the return temp has to be far higher. So the fish are in maybe 4-5 degrees higher than the pond at that point, but as its higher they are quite safe and happy with it,

    You say that you are only heating the pond during the day, which for now ok, but when the cooler nights start, and you are not heating, that will probably give you a much bigger drop than you imagine. Which then can be an issue.

    Its ok thinking economy, but even now I would be heating through the night and not the day, It really means that all the good work that the HP is doing through the day, the pond is losing at night due to much larger temp drop with cooler air. This drop won't be anywhere as severe during the day. Mine is set on 24 hours, at 21 degrees and is hardly ever on during the day this time of year. It does however, run during the night quite often until the sun arrives.


    Come the winter you will find that you will need the HP on 24 hours, at minus temps and it will run most of the day to hold temps and even then your pond will have to be covered.
    You will find that many on here, have backup heating, including myself, via electric heater, as HPs can really struggle during prolonged very low temps. I think the secret is to always go bigger than you think you need with heat pumps, as if on the limit the pump will hardly keep up with set temps, even at 12 degrees, during very cold spells.

    Obviously this depends on the integrity of the heat retaining design of your pond and cover etc. but all pipework should be protected to get the best from the HP, and again every pond is different, so I cannot vouch for others, but now having run a heat pump for 5 years, that is just my experience with it.

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  7. #4
    Thanks for your reply! I think you are 100% right, I should just use it like its meant to be used and leave it active 24 hours Being new to ASHP's and interested in working out their efficiency at different temperatures, I was keen to see if I could maximize efficiency with this warm weather.

    I'm keeping the pond at 21 degrees now and they are eating like crazy! I have a backup electro heater already which was burning £60 per month last winter, even with a poly carb cover The heat pump only cost £100 and i'm not expecting it to work below 0 degrees however this is only 5% of the year so worth a punt at £100 and just see how it gets on this winter, knowing I have a backup ready to kick in if needed.

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  9. #5
    I will be entering my seventh year with a ASHP, strangely enough similar to what you suggested, I heat only during the day to use peak temperature, comes on about 9am and off about 5pm, all depends how well your insulated, covered in 25mm polycarbonate. Heated to 20 degrees till the end of October then let it drop to 18 then 16 by the end of November the lower you have the pond temperature the longer it will take to drop. Come New Years Day I set the ASHP to 8 or 9 degrees depending on the weather it can take 6 to seven weeks to get to 9 degrees, don’t like it sitting in aeronomous alley, I could set it the ASHP to cool but had no issues for the previous six years. Holding 16 I lose 1 degree with an overnight frost, don’t see the sense of running the ASHP all night to stand still. Been bitten by running Electro’s left one in the line the first year with the ASHP but never had to use it.

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  11. #6
    Interesting stuff. I have 60mm poly carb for the winter but at the moment I have it open fully and it drops by 1 degree overnight if I dont heat. But I am not sure if it's ok to let this happen and then return the heat back up 1 degree during the day. Is this too much fluctuation?

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  13. #7
    Quote Originally Posted by willshill View Post
    Hi all.

    I am experimenting with a recent second hand heat pump purchase. I have a temperature controller recording temperature fluctuations and a smart plug monitoring power consumption.

    In order to be as efficient as possible, I've put a timer on the heat pump so it only runs during the day when the air temp is near its peak. I'm wondering what a reasonable swing in temperature is across a 24 hour period, 1 degree?

    My hp is powerful and probably bring the pond temp up by 1 degree in about 3-4 hours. Is this too fast?

    There is no research that I'm aware of on the subject of diurnal temperature changes because fish have to change their metabolism to suit the water temperature and the ease with which they can adapt to a new temperature depends on many factors. Koi can do this easily for small temperature changes or the one-off temperature change when a fish in a bag is floated in its new pond to equalise the temperature. But larger changes, especially temperatures that regularly yo-yo up and down have the potential to cause stress.

    With that in mind, I recommend a common sense approach. If your pond only drops by 1C overnight and the heat pump takes three or four hours to bring it back to the set temperature then I wouldn't worry. An occasional change greater than this would be ok but, if much larger changes are happening daily, I would try to limit them.
    Last edited by Manky Sanke; 23-08-2019 at 05:01 PM.

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  15. #8
    Many thanks MS! Very good to hear this.

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