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Water heat exchanger for Aircon units

  1. Apr 3, 2009 #1
    I am leaving in the tropics and have 7 aircon units (about 12,000 BTU each). The heat released from each unit is collected by a water loop that runs through an air cooling tower.
    While the system runs ok, the air tower is exposed to weather and therefore requires continuous cleaning. Furthermore, the electrical consumption is rather high if only one AC unit is on as the cooling tower runs continuously. Finally, the air tower also generate noise…
    As I am leaving along a big river, I would like to remove the air tower and replace it with a heat exchanger that would be dipped in the river. This would reduce the electrical consumption and enable running clean water in a closed circuit thereby removing the continuous requirement of cleaning…
    My problem is how to guess the sizing of the heat exchanger. I know that this is more likely to be a ‘trial & error” project but some indication of initial size would be welcome.

    Existing installation data:
    • 7 Aicon units – max load 74,000 BTU if all running and cooling in the same time
    • Air cooling tower cooling capacity 78,000 KCAL/hour
    • Air cooling water flow 260 liters/min
    • Circulating pump rating 9,000 liters/hour or 150 liters/min
    • Dia of circulating water pipe 50mm
    • Temperature of the river varies from 30 to 34 degrees (near the bank)
    • Embankment length is not a problem – more than 40 meters
    Initial planned heat exchanger

    The circulating pipe would be extended till the river bank where a “rake” type connection would be installed to subdivide into 6 or 8 smaller copper (or galvanized) pipes of a 25mm dia. Those pipes would run straight in parallel for about 22 meters where a “rake” type collector would be installed for the water return.

    With this installation, I estimated that the water would be retained in the heat exchanger for about 26 seconds. The total heat exchanger surface of pipes is about 10 sqm.

    1. Are the above assumptions realistic and feasible?
    2. Is there a great difference between copper pipes and galvanized pipes (of which cost is much lower)
    3. Would it be better to reduce the dia of exchanger pipes and increase their number?
    4. Is be better to increase the length or the number of pipes to increase the time water has to release its heat?
    5. Would there be an advantage to reduce the circulating pump’s rating volume to increase the retention time in the exchanger?

    For your convenience, I have attached a sketch of the installation

    Any suggestions or comments would be much appreciated.

    Thanks in advance

    Attached Files:

  2. jcsd
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