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New Project

EddieG Member Posts: 150
Went out for an estimate on a Solar System last week. It is for a fish farm. Basically it is a huge metal type building with about 30 - 3500 gallon fish tanks. They raise fish there and sell them to a lot of restaurants in the Washington, DC area. They are only using 6 of tanks which are currently heated by individual electric spa / hot tub water heaters. The owner says it is costing him a fortune in electric bills, especially in the winter. The building is unconditioned and the fish tanks need to be kept between 71 to 75 degrees for the type fish he is raising.

There used to be a central boiler plant that heated all the tanks. But it has been ripped out. The previous owner apparently used to operate a lot more tanks. I am thinking of taking a couple of the un-used tanks and using them for storage tanks. I was going to submerse some copper coils into the tank(s) and then insulating and sealing the tanks off. So basically the solar would heat up that tank via a copper coil(s) and I would have another coil(s) to draw the heat from the storage tank to heat the actual fish tanks.

Also will be designing a boiler type system to supplement the solar. I am also going to give him some options to heat at least a portion of the building. So the fish tanks won't lose as much heat to the room.

I have a rep. coming out from Kingspan next week to take a look at the job. There is plenty of roof space for panels and it is not shaded at all. I have never designed a solar system for an application like this. Has anybody done a job like this before? Any advice or tips would be much appreciated. Thanks for any help in advance.  


  • ABSolar
    ABSolar Member Posts: 41
    Fish Tanks

    Hi EddieG,

    Sounds like a fun project.  You're on the right track by utilizing the spare tanks (don't forget to super insulate ALL sides of the solar storage tanks AND the fish tanks).  I think you can eliminate one set of heat exchange coils to increase efficiency - probably the solar loop side (assuming you can do a drainback system).  This limits the exposure to fish tank contamination to just the heat transfer fluid (fish tank water) circulating from the solar storage tank coils (probably stainless steel for sanitary/ and PH issues) to the fish tank. The solar storage tank water simply circulates to the collectors and stratifies independantly. 

    A drainback system will also self high limit automatically, with no collector stagnation issues and no glycol maintenance concerns, either.  I would be inclined to use evac. tubes for collectors because you're looking to get heat collection in the winter.  For back-up heating, it would probably be more cost efficient to install either 1) natural gas/ propane condensing boiler or 2) oil condensing boiler (electric resistance heating is TOO expensive!)

    I'm not sure if the collector manifolds on the Thermomax evac. tubes can properly allow for drainback configuration (the concern here is small pockets of heat transfer fluid being caught and remaining in the manifold after the pump shuts off, which could then freeze and rupture the system).  I have used Sunmaxx evac tubes (VHP30) in drainback format w/ positive results.  They are less expensive, also.  No need for the over temp spring device (added product cost) in each tube (Thermomax) for a drainback system.

    Good Luck to you on this project!
  • hot_rod
    hot_rod Member Posts: 19,260
    in Milwaukee

    we supplies and helped design the thermal system to het the tilapia tanks at Growing Power. www.growingpower.org/

    They are inside the greenhouses and use pool boilers to heat them, now the collectors cover a fraction of the load. The next upgrade we suggested is to replace the pool boilers with condensing boilers now that they have tanks with HX to seperate the pool water.

    We used the Caleffi solar tanks as the heat exchangers between the solar glycol loop and the two pools.

    They have been data logging the system to see how close the design simulation comes to the actual operating conditions.

    If you are in the Milwaukee area you can drop by for a tour, it's quite an operation.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • ABSolar
    ABSolar Member Posts: 41
    Fish tanks

    Hey HotRod,

    On those Tilapia tanks, do they circulate salt water through the Caleffi tank coils or the tank body itself?  Is the stainless steel component up to snuff for salt water - i.e. -ss 304 vs ss316?  Wouldn't it be more cost effective for EddieG to utilize existing LARGE tanks for solar storage and just dropping in stainless coils?
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Draining Evac. Tubes

    Thermomax headers don't drain well, and Apricus headers are iffy.

    But 75F maximum temperature isn't really a well-suited application for evacuated tubes. Anybody's glazed flat plate collector will perform really well operating on a big storage tank at 75F. Additional heat storage wouldn't be necessary unless you are trying for a solar fraction of over 50%.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • hot_rod
    hot_rod Member Posts: 19,260
    the water

    I believe this is a fresh water fish. Although I've read they can live in salt or fresh water? There are many different species of tilapi.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Karl_Northwind
    Karl_Northwind Member Posts: 139

    I agree with kevin,

    evacuated tubes seem like a platinum solution to an copper problem.  I would also see if they could insulate the building, if the tanks can't be insulated properly.  this might also protect the building from condensation problems. 

    if the tanks are there,and there is some sort of water distribution system already there (or will be with the boiler system to be installed) using the tanks seems like a good option.

    you should always look at the BTUs that will be produced, and see what sort of effect that will have on the tank water.  if you have 105,000 gallons of water, you may not need any additional storage.  if a full solar day will only heat those tanks 2 degrees, (say about 1600 SF of collector) you'll just need a big HX and a way to clean it of fish poo.

    a single fish tank with coils in it (copper or stainless), and a 120 gallon storage tank will work as DB tank, and the copper coils can be scrubbed with a brush from outside the tank.

    sounds like a good application.  and you could pretty easily put a KWH meter on a single electric heater to get some really good heat load numbers.

    keep us posted.

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