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Thread: Solar water heater tank connections

  1. #1
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    Default Solar water heater tank connections

    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
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    Hi Kukae - Welcome to Solar Panel Talk!

    On my system the connections are as follow (from lowest on the tank upward):
    1)cold water entry (from the well)
    2) outlet to the recirc pump and the panels
    3) return from the panels - about the center of the tank
    4) hot water to consumers - at the tank top

    That is as per the notations on the tank as well as installed.
    The tank is a 325 liter tank with electric backup

    The tank top section is the hottest water in this way - I guess that rather than to have to heat the entire tank before getting benefit of the solar they have effectively divided the tank into two sections.

    The hot water in the tank rises - the tank is always stratified.

  3. #3
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    pic or sketch would be nice to see where cold inlet is, exit to heater panels.....

  4. #4
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    SunEarthInc SU120-1
    The coldwater and hotwater connections are on top.
    Look at the picture for side connect and you can see how close the drain and to collector connections are.
    http://sunearthinc.com/wp-content/up...EarthFlyer.pdf

  5. #5
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    The pdf you attached shows the same connections as my system uses.

    I would definitely go with the factory and not the installer.

    Russ

  6. #6
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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.

  7. #7
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    If the check valve fails to function you will be seeing the hot water from the tank circulating in reverse and you will lose temperature.

    With your open loop system I assume you mean the water being heated goes through the panels. No heat exchanger in the tank?

    If the water being heated goes through the panel (as compared to a closed loop where the water going to the consumers never comes in contact with the panel) there is every chance of getting crud in the check valve.

    What the installer should have told you that if this happens the remainder of the system including panels is seeing crud buildup as well.

  8. #8
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    I will only respond to the idea of recirculating the heated water back into the tank to be heated again. I tested my solar panels on 10/29 & came to the same conclusion to obtain my desired goal heat temperature. I want HOT water to pump thru baseboard/pex under the floor. If I add a recirculating line back in my water source/storage tank, the hotter the water going into the panel...the hotter it comes out.

    I intend to use this additional return line to get the desired temp I want. I will be pumping the hot water thru the baseboard/pex at the same time as returning it to the tank.
    Jeff


    Quote Originally Posted by kukae View Post
    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.

  9. #9

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    Kukae,

    Our solar water heater was installed like yours with pipes to/from the solar panels connected to the water heater at the bottom. The connection that's about 3 inches higher than the drain connection says "TO COLLECTORS" and it goes to the circulation pump then to the solar panels. The line from the panels connect to the drain port using a T fitting with the drain hose bib on the other side. --- There's a connection about 2/3 rds up the tank that says "FROM COLLECTORS" but it's capped off.

    I also question whether both connections at the bottom of the tank is technically efficient. Like you I think the "entire tank" has to be heated before the full effect of the solar water heating can be felt at the faucets. So we end up wasting electricity heating water in the mornings because it takes too long for the water in the tank to reach satisfactory temperature.

    Hope you get more responses. I'll be actively watching.
    HRG

  10. #10

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    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.

    Are you 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 collectors to the midpoint of the tank?

    As soon as our solar water heating system warranty expires I want to reconfigure the connections to our solar water heater using the midpoint connection and a heat trap.

    HRG

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