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Thread: Side or bottom connect

  1. #1
    DIY Junior Member kukae's Avatar
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    Default Side or bottom connect

    I am installing an active open loop solar water heating system. The tank has a side connect to attach the return line from the collectors. But, the installer insists that connecting the return line to the drain at the bottom of the tank is better. My instinct says that he is wrong, because you are sending hot water that just came from the collector back to the collector (the connection to the collectors is only a few inches away) which isn't very efficient. Also, the only way for the hot water to reach the top of the tank is through a slow convective process, unless you use a lot of hot water, pulling the water up from the bottom. His claim is that with a side connect, the hot water doesn't reach the bottom and so you are only using half the tank. But, I think that is wrong, because the pump is forcing the hot water down. Does anyone know of any studies or evidence that a bottom connection is better? It seems that if it were, the manufacturer of the tank would have moved the "From Collector" connection.

  2. #2
    DIY Junior Member kukae's Avatar
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    I talked with a second installer and he agreed with my installer, that nearly every installer in Hawaii connects the return to the drain port. Many installers use a dip tube to create some separation between the return and the feed, my installer doesn't believe in them. While the installers agree that the system may run less efficiently, the rationale has to do with night time heat loss. The claim is that side connect return lines stayed hot at night and that even with check valves (that they claim to stop functioning in on a year or so), the heat traveled up the return line and radiated out the panels. Having the return at the bottom means that the line is cold at night (our backups are off during the night) and heat doesn't travel up the pipe. What do you guys think? Do you see much heat loss with side connects? Our tanks and panels are sized to heat water to well over 140 degrees on a sunny day and provide 100% of the hot water without the backup ever kicking in.

  3. #3
    DIY Junior Member frankflynn's Avatar
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    I'm not a professional but I do have a similar system. I use the side connector for the return as the manufacture instructs (Rheem - Solaraid in my case).

    I find it odd that a manufacture would recommend installing their product in an inefficient way. I can product 100% of my hot water even in the winter - 140 is achievable on sunny days; it the summer it will shut down after it gets to 160.

    But your issue was nighttime cooling because a check valve would fail. My though about that is use a better check valve; perhaps one specifically designed for this purpose.

    On the other hand if you have confidence these installers have produced working systems for others that can perform to your needs then go with their advice.

  4. #4
    Homeowner Thatguy's Avatar
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    In other debates that are hard to settle it seems that each side speaks some truth.
    The installer already knows the manuf. recommendations; ask the manuf. about the installer's recommendations. There may be cases where the installer's way is better, or there may be accessories you can buy so you get the best of both worlds.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    Most heaters which have "accessory side connections" have both a supply and return tapping. The supply is low and the return is high. I have never heard of any one making both connections at the same level.

  6. #6

    Default

    Quote Originally Posted by kukae View Post
    I talked with a second installer and he agreed with my installer, that nearly every installer in Hawaii connects the return to the drain port. Many installers use a dip tube to create some separation between the return and the feed, my installer doesn't believe in them. While the installers agree that the system may run less efficiently, the rationale has to do with night time heat loss. The claim is that side connect return lines stayed hot at night and that even with check valves (that they claim to stop functioning in on a year or so), the heat traveled up the return line and radiated out the panels. Having the return at the bottom means that the line is cold at night (our backups are off during the night) and heat doesn't travel up the pipe. What do you guys think? Do you see much heat loss with side connects? Our tanks and panels are sized to heat water to well over 140 degrees on a sunny day and provide 100% of the hot water without the backup ever kicking in.
    I'm wondering that if the line from the collectors is connected to the midpoint of the tank, what about installing a heat trap in that line? If my thinking is correct, a heat trap would prevent heated water from the tank migrating to the collectors at night and a check valve wouldn't be necessary.

    Anyone familiar with heat traps? I've just learned about them, not about stopping migration of hot water to solar collectors but minimizing heat loss up the top of the tank to the house. Why couldn't they be used in the line from the midpoint of the tank to the collectors?

    HRG

  7. #7
    Moderator & Master Plumber hj's Avatar
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    The "hot" water belongs at the top of the tank. The lower in the tank that the "hot" water from the collector is connected, the more "cool" water it has to pass through before it reaches the top of the tank, and therefore the cooler it will be. Tanks with the solar connections on top use a "dip" tube to extract the lower "cold" water to the collector and deposit the hot water right back at the top of the tank. It makes no sense to heat the water and then connect it back at the drain valve so that it loses its heat on its way to the top.

  8. #8

    Default

    Quote Originally Posted by hj View Post
    The "hot" water belongs at the top of the tank. The lower in the tank that the "hot" water from the collector is connected, the more "cool" water it has to pass through before it reaches the top of the tank, and therefore the cooler it will be. Tanks with the solar connections on top use a "dip" tube to extract the lower "cold" water to the collector and deposit the hot water right back at the top of the tank. It makes no sense to heat the water and then connect it back at the drain valve so that it loses its heat on its way to the top.
    I've been rethinking the heat trap idea. On our solar water heater installation, the return line from the collectors is connected to the drain port on the tank using a T fitting (similar to Kukae's configuration). Since the line already goes to the bottom of the tank, if I disconnect it from the T fitting and just extend it to the upper side port on the tank wouldn't that effectively become a heat trap? And prevent hot water in the tank from migrating to the collectors on the roof at night without needing a check valve?

    Thanks,
    HRG

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