Why aren't there drainback systems with NO heat exchangers?

rollandelliott
rollandelliott Solar Expert Posts: 834 ✭✭
in Energy Use & Conservation #1
I've always been curious Why aren't there drainback systems with NO heat exchangers?
The below web site lists the various Solar hot water heating methods.
I'm guessing there might be mineral build up over time in the solar collector plates?

I called one company and they said that bacteria would build up, but I kind of find that hard to believe given the temperatures solar hot water heaters run at.

Any thoughts?

https://homepower.com/articles/how-use-solar-water-heating
Thermosyphon is the next simplest system. These entirely passive (meaning no pumps) systems rely on the collector being below the tank, so that natural convection moves the hot water out of the collector and to the tank for household use. These systems are also inappropriate for freezing climes.

Direct forced-circulation is similar to the thermosyphon system, but adds a pump and controller. The pump makes it possible to pick up more heat out of the collector. The controller measures when the collector is hotter than the tank and turns the pump on or off as appropriate. These systems also have no freeze protection.

Drainback systems add a tank and a heat exchanger. The drainback tank is sized so that all the water in the collector and lines can drain down into it, when the pump turns off. That way there is no water left in the collector at times when it could otherwise freeze. The water in the system is separate from the household water, so it needs a heat exchanger to transfer the heat from the collector water to the domestic water.[/code]
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #2
    Re: Why aren't there drainback systems with NO heat exchangers?

    I have an active pumped loop system with no heat exchanger, freezing is not an issue however. There is a 80 gallon tank and a pump with a thermal differential controller, when the temps in the panel are higher by X amount than the tank the pump starts. The 80 gallon tank is a "pre heater" for the 50 gallon gas unit and I turn that down for 10 months out of the year to about 105 F.
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  • rollandelliott
    rollandelliott Solar Expert Posts: 834 ✭✭
    #3
    Re: Why aren't there drainback systems with NO heat exchangers?

    "when the temps in the panel are higher by X amount than the tank the pump starts"

    Maybe this is a dumb question, but doesn't your water get too hot? Seems like that design the water temperture has the potential of reaching very hot temperatures? What prevents it from scalding you?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Why aren't there drainback systems with NO heat exchangers?
    rollandelliott wrote: »
    "when the temps in the panel are higher by X amount than the tank the pump starts"

    Maybe this is a dumb question, but doesn't your water get too hot? Seems like that design the water temperture has the potential of reaching very hot temperatures? What prevents it from scalding you?

    The classic method uses a tempering valve on the output of the tank. With arguments about whether it should go at the output of the holding tank or the main tank. (I join the latter camp.)
    SMA SB 3000, old BP panels.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #5
    Re: Why aren't there drainback systems with NO heat exchangers?
    inetdog wrote: »
    The classic method uses a tempering valve on the output of the tank. With arguments about whether it should go at the output of the holding tank or the main tank. (I join the latter camp.)

    Yes thereis a tempering valve, tank pump cutoff is in the 140 - 150F range. We do warn that the summer temps are pretty hot at the tap but well below that temp.
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  • LucMan
    LucMan Solar Expert Posts: 223 ✭✭✭
    #6
    Re: Why aren't there drainback systems with NO heat exchangers?
    rollandelliott wrote: »
    I've always been curious Why aren't there drainback systems with NO heat exchangers?
    The below web site lists the various Solar hot water heating methods.
    I'm guessing there might be mineral build up over time in the solar collector plates?

    I called one company and they said that bacteria would build up, but I kind of find that hard to believe given the temperatures solar hot water heaters run at.

    Any thoughts?

    https://homepower.com/articles/how-use-solar-water-heating

    Then it wouldn't be a drainback system.
    The drain back tank & HX separate the solar and the domestic water. When the solar collectors are inactive there is no water in them to freeze or overheat creating dangerous pressures because the water is stored in the drainback tank and the collectors are empty. The water pressure in the collector, drainback tank and HX loop is 0 the domestic side is 40-100 psi. Domestic water quality also has no effect on on the collectors so they should work at max efficiency for 25 + yrs.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,891 ✭✭✭✭✭✭
    #7
    Re: Why aren't there drainback systems with NO heat exchangers?

    There are drainback tanks without heat exchangers!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • CDN_VT
    CDN_VT Solar Expert Posts: 492 ✭✭✭
    #8
    Re: Why aren't there drainback systems with NO heat exchangers?

    Lots of info on Solar Water Pumping & it's own section , But Not much on Solar Collection for water heating .
    I just bought 2 units / panels / pressurized heat collectors , I will be doing a split system with exchanger's running Propylene Glycol.
    This system will integrate into the winter Airtight water heater.

    I don't see many threads on these systems.
    VT
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
    Re: Why aren't there drainback systems with NO heat exchangers?
    CDN_VT wrote: »
    Lots of info on Solar Water Pumping & it's own section , But Not much on Solar Collection for water heating .
    I just bought 2 units / panels / pressurized heat collectors , I will be doing a split system with exchanger's running Propylene Glycol.
    This system will integrate into the winter Airtight water heater.

    I don't see many threads on these systems.
    VT

    This is due to the nature of the forum. Mostly we are centered around the electrical power aspect of solar & wind and its application. Thus a section for using sun and/or wind to pump water, but nothing much on solar thermal collectors.

    If you are interested in that, I'd suggest you visit Build it Solar: http://www.builditsolar.com/
    There's no sense in our trying to duplicate the tons of good information there! :D
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  • CDN_VT
    CDN_VT Solar Expert Posts: 492 ✭✭✭
    #10
    Re: Why aren't there drainback systems with NO heat exchangers?

    Thanks Coot !!


    Another WIP (werk in progress)
    VT

    And since were all here to learn & help !

    I found this tid-bit for this thread.

    & more info .

    Naws Is my sparky store ;)
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