Suitable plumbing for vacuum tube solar installation?

SystemSystem Posts: 2,511 admin
I am just embarking on my first solar project: a vacuum tube system for my pool.

I have already bought (a bit impulsively!) two 18 tube racks and a stainless steel heat converter, but from the warnings in the (rather poor) documentation that came with the solar panels there is a potential for the water to be coming out *very* hot - 160 degrees celsius is mentioned.

I can't quite get my head around that so I'm throwing the questions out there:
  • What temperatures do you find at your installations?
  • What type of plumbing would you use?

I would dearly like to use the plastic pipes commonly used for domestic hot and cold water but would that cope???

Thanks in advance,

David

Comments

  • mike95490mike95490 Solar Expert Posts: 8,333 ✭✭✭✭✭
    Re: Suitable plumbing for vacuum tube solar installation?

    With vacuum water heating systems, you can quickly reach very hot temps, and should have a way to quickly cover the panels.

    If you keep your flow rate high, you won't get the high temps, but that eats into your electrical budget.

    How much pressure is in the system, plastic has specs for reduced pressure, at higher temps, but you may have to go to copper if you have a chance of no-flow happening.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
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  • mike95490mike95490 Solar Expert Posts: 8,333 ✭✭✭✭✭
    Re: Suitable plumbing for vacuum tube solar installation?
    DaveQ wrote: »
    water to be coming out *very* hot - 160 degrees celsius is mentioned.

    You may need a union steam fitter to weld up some live steam joints for you.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • russruss Solar Expert Posts: 593 ✭✭
    Re: Suitable plumbing for vacuum tube solar installation?

    Your real problem is if the system is stagnant - power failure situation with no flow.

    İ am not aware of plastic rated for the 160 Deg C temperature. Most solar systems use copper just for this reason.

    İ hope you have the heat tube type of collectors.

    You really don't want the pool water going through your solar system due to the crud in it - a heat exchanger would be better and protect you from the very hot water as well.
  • BB.BB. Super Moderators, Administrators Posts: 29,349 admin
    Re: Suitable plumbing for vacuum tube solar installation?

    Those types of solar thermal panels are intended for very hot water (probably over 160F)--Some vacuum tube units have a "thermal switch" inside that limits maximum temperatures.

    Anyway, what is it that you want to do with the hot water? If it is heating a domestic hot water heater--they will have a T&P valve set to vent before 150 PSI and 212F (or there about)...So, that can take care of two problems (assuming you simply use an AC powered or Solar power water circulation pump. You don't want the collector to boil--it will collect hardware deposits (and will do that with domestic water anyway).

    If you want to use the hot water tank for domestic hot water--you will need a tempering valve to mix hot and cold water down to 140F maximum (or what is required by code in your state) (I am not a plumber).

    This is a nice do it yourself site with lots of explanations and components to install your own hot water system (don't know if they really support the vacuum tube type systems):

    www.solarroofs.com

    Solar Guppy has used these guys before and was happy with their site.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Suitable plumbing for vacuum tube solar installation?

    DaveQ do you have a web site link for you system/instructions?
     
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  • pbartkopbartko Solar Expert Posts: 37 ✭✭
    Re: Suitable plumbing for vacuum tube solar installation?

    DaveQ,

    Why have you selected Vacuum tubes for a pool installation? They are expensive and not very efficient in a pool application. You are generally better off with an unglazed solar panel system. Unglazed panels are more efficient at lower temperatures like you get with a pool.

    Vacuum tubes are more efficient only if you need higher temperatures (e.g. DHW) in very cold weather (e.g. below 30 deg F). Glazed panels are most efficient at heating higher temperature water with outdoor temperatures in the range of 30-90 deg F.

    Unglazed panels are best for low water temperatures (e.g. a pool) and outdoor temperatures above 70 deg F.

    Pete B
  • System2System2 Posts: 6,290 admin
    Re: Suitable plumbing for vacuum tube solar installation?

    Guys,

    thanks for your responses. I think I will use 22mm copper pipe with compression fittings (I might solder away from the collector, where presumably the heat will have dropped a bit?)

    The risk of stagnant system is something I hadn't considered and is a bit worrying; we do get power cuts here every now and then. Whether I can get a solar or batter backed up water pump will be an interesting challenge. I live in rural France and getting hold of stuff isn't easy (that partially explains the choice of vacuum tubes btw - big diy chain started selling them).

    Thanks again,

    Dave
  • SlappySlappy Solar Expert Posts: 251 ✭✭✭✭✭✭
    Re: Suitable plumbing for vacuum tube solar installation?

    Here is an article about copper pipe and chlorine, if you are using an open loop system. http://www.wssc.dst.md.us/copperpipe/recent_phl_research.cfm

    and by the way dont know if it is true or not, but I heard when I was a kid, about copper pipes used in swimming pools, is that if you have blonde hair it will turn green, something about the chemical reaction. :D

    But other articles mention about the PH levels; if low can be corrosive to the pipe?
  • System2System2 Posts: 6,290 admin
    Re: Suitable plumbing for vacuum tube solar installation?

    Its OK - the solar heater will be on a separate pumped circuit, transferring the heat to the pool through a stainless steel heat exchanger.

    Dave
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Suitable plumbing for vacuum tube solar installation?
    DaveQ wrote: »
    Guys,

    The risk of stagnant system is something I hadn't considered and is a bit worrying; we do get power cuts here every now and then. Whether I can get a solar or batter backed up water pump will be an interesting challenge. I live in rural France and getting hold of stuff isn't easy (that partially explains the choice of vacuum tubes btw - big diy chain started selling them).

    navitron.org.uk sells DC pumps and PV panels for use in solar hot water systems. Their user forum is also very active and knowledge about evacuated tube systems. I remember seeing a user on their with a 5 x 30 tube setup for pool and central heating... just can't remember his name.

    [Edit] 3 x 20 ET installation in Portugal for pool heating: http://www.navitron.org.uk/forum/index.php/topic,6941.0.html
  • LucManLucMan Solar Expert Posts: 223 ✭✭✭
    Re: Suitable plumbing for vacuum tube solar installation?
    DaveQ wrote: »
    I am just embarking on my first solar project: a vacuum tube system for my pool.

    I have already bought (a bit impulsively!) two 18 tube racks and a stainless steel heat converter, but from the warnings in the (rather poor) documentation that came with the solar panels there is a potential for the water to be coming out *very* hot - 160 degrees celsius is mentioned.

    I can't quite get my head around that so I'm throwing the questions out there:
    • What temperatures do you find at your installations?
    • What type of plumbing would you use?

    I would dearly like to use the plastic pipes commonly used for domestic hot and cold water but would that cope???

    Thanks in advance,

    David

    Those temperatures are for the collector loop.
    For pool water heating you should never have a situation where your water would reach those high temps as long as you maintain flow through your heat exchanger. You should see a delta T of 1-4 degrees F over your entering pool water when using your pool pump.
    Your only problem is reaching stagnation temps if you lose power or a pump and that would only affect your collector loop. The collector loop should be protected with an expansion tank and properly sized relief valves to prevent damage to the system. Just pipe your blowoff as per code (6" from the floor).
    The solar pump won't help you unless you also have a solar pool filter pump because you would loose flow through the HX. You would have to have 2 solar pumps 1 for the solar loop and 1 for the pool loop.

    Use only copper or the flexible stainless steel line sets for your collector loop. You can use PVC for the pool loop to the HX.

    I recommend that you use a titanium heat exchanger as they last much longer than the stainless steel type, especially if you are using ozone & salt disinfection over chlorine.
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