First, let me say I've never done anything remotely like this so I really have no idea what I'm talking about... Although I did sleep at a...oh, wait, no that's not it. Oh, right, I almost did the same thing you're posting about so I researched it for a few months. Anyway...
I think what Dad was saying is that the water will act as a heat sink and therefore, will tend to hold temperature fairly well. While this is generally true, and I agree with his overall point that cooling will be a far greater challenge than heating will be, heating during those cold months could still cost quite a bit. I agree with Garry that heating it via electricity is probably not a very economical solution.
In my research I found a few people that had done similar things -- I'm sure you've already found them and if not, I'd highly recommend doing a google search. I can't seem to find my bookmarks.
Cooling may (will) also require more than just fans. The only way fans have a chance at keeping up is if you can use them to evaporate enough water which may be a challenge since the humidity will be so high.
A heat exchanger (geothermal) might work for you, for both heating and cooling but they have an upfront cost associated with drilling and installing them.
Have you thought much about lighting? I don't think natural sunlight is going to be enough given your location. The research I did showed that supplemental lighting was important, at least depending upon what you are really interested in growing. You may be able to set up a light-rail or similar system so that you don't have to have a lot of lights...the real reason I'm bringing this up though is simply for layout issues. I think for a project like this to be successful, you really, really have to think through all the issues so you make as few 'big' mistakes as possible and layout of the room seems rife with potential 'gotchas'.
I would think maintaining water quality would be easier in a larger system rather than harder. On the other hand, your risk is that much higher if something goes wrong, you lose it all if it is a single, connected system. As a business, I'd say Garry's idea of at least several, smaller and disconnected systems would be a better bet.
In terms of tanks, I think it depends on how you plan to be able to access them. If you can lay out your floorplan so that you have access from both sides, then I'd go with a wider tank (at least 48" and up to 72"). If access is from only one side, I'd go 30"...36" top. I would think shallower tanks would be better; it is easier to shade than it is to light...8-12" (I guess more if you are set on a DSB).
Flow is another critical factor. I'd suggest looking into air lifts and likely building a surge system to provide most if not all of your flow. Air lifts are pretty efficient devices...you can use them to pump water into a surge system that could then feed each of the systems and virtually eliminate the need for most other pumps.
I would try to keep most of your water volume in sumps and the surge tanks. This will allow you to conveniently recover from a situation that resulted in poor water quality.
Calcium (and other) supplementation is another factor to consider... Kalkwasser is a proven, easy way (dump a bunch in a bucket, mix manually once a week..month) to provide calcium supplementation although it may not be sufficient...but that's probably where I would start.
You'll need a very, very beefy RODI system.
Definitely get Calfo's book -- he goes into a lot of details on systems he's been involved in setting up that will no doubt be helpful to you. If I were you, I'd consider visiting a wholesaler in CA to see how they work out there...
Good luck. It is a tough business.
) I'm looking for info on large holding tanks. for lack of a better word.
