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  1. #1

    When less = more

    Just made very interesting experience I hope worth sharing with you here - in real life confirming, that there are optimal flows for everything - this time via desk heat exchanger and in my particular setup LESS flow gives actually MORE heat transfered into my pond.

    All this despite heat transfer power / flow chart showing for my desk heat exchanger maximum heat transfer of 70 kW at delta T 20 dC between primary (house heating water) and secondary side (pond water) with primary flow of 1.500L/h - at secondary flow of 4.000 L/h, actually by reducing it down to 3.000 L/h - rest equal, the heat transfer shown in the chart is only 60 kW so 10kW lower, but my pond temperature started to RISE noticeably - by 1 dC over last 24h - while outside temperature - if not the same - started to cool down a bit by about 1 dC.

    What happened:
    Original setup - I am picking up pond water for heating from 600L IBC Anoxic filter (prefiltered by RDF) and by 5.000L/h submerged pump in the AF run it via 1" pipe first through the lid up and than down to our house basement, where the desk heat exchanger is installed - pipe run approx. 3m one way - see picture bellow - pond water entering from right bottom - desk heat exchanger is the middle vertical black box - house heating water entering from left top - controlled by solenoid (blue) connected to pond thermostat - Wilo circulation pump in right upper corner on pipe exit back to pond:
    Attachment 22594

    The actual head is minimal - as the heat exchanger is about 1m lower than water level in the 600L IBC Anoxic filter housing, but as the second circulation pump on this heating circuit shown on the picture - Wilo Yonos Para 25/6 RKC (45W max) is not self priming, I thought I needed to push water to it by submerged pump at water pick up point - first up from the IBC tank through the top lid and than only down.

    As Wilo circulation pump has maximum flow of 3.600 L/h, I thought the second pump - Pontec Smart Line Eco 5.000 L/h (40W max.) - should boost the final flow to the max 4.000L/h flow thus maximizing heat transfer output as per the manufacturer's power / flow chart to reach max. 70kW.

    But I was wrong - as I learned - when I have removed the first pump - Pontec 5.000L/h from the heating circuit as I wanted to re-start my Denitrifying Trickle tower combo (more here - Building Denitrifying Trickle Tower Combo) I stopped almost one month ago, when I removed original Nexus 220 from where it was fed as Nitrates went up a bit from under 10 mg/L to just under 25 mg/L now.

    So I left only Wilo circulation pump with 3.600 L/h max. flow - real flow probably 3.000L/h - powering the pond heating circuit - and by reducing the flow via desk heat exchanger I gained higher heat transfer efficiency - visible in 1 dC pond water temperature increase over last 24h.

    Parameters - primary water (house heating) is at 32 dC, pond water was at the time 11,6 dC, air temp was around 5 dC - while today - 24h later - pond water reached 12.6 dC - and keeps growing - 29 hrs later it is already 12,8 dC - while air temp dropped down to 4 dC and stronger cold wind picked up on top of it.

    Lesson learned - while manufacturer's flow / power output charts are very good information, we should consider it as a starting point and always test different setups / flow rates - to find the sweet sport for best performance in our particular setup - in my case I learned this my lesson today by mere coincidence - when I needed one of the two pumps for another task - worrying if heat transfer efficiency would drop down - but actually surprised to find out the opposite.

    Happy ponding - and keep experimenting to find your own sweet spots!


    Last edited by milaz; 08-01-2018 at 12:40 AM. Reason: Arrached picture does not show up properly see next post please
    You get what you pay for - or better - what you make yourself.

  2. #2
    Picture upload still does not work....

    Last edited by milaz; 09-01-2018 at 01:50 AM.
    You get what you pay for - or better - what you make yourself.

  3. #3
    Trying for the third time to insert the picture - hope it will finally work - but seems something is wrong and need to get forum admin to look at it - sorry guys.
    Last edited by milaz; 09-01-2018 at 01:50 AM.
    You get what you pay for - or better - what you make yourself.

  4. #4
    Desk heat exchanger.jpg

    Finally was able to add the picture - sorry for takiing so long.
    You get what you pay for - or better - what you make yourself.



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