NOTE: All links are tinyurls. So, go to tinyurl dot com slash, and then whatever I have in parentheses. Apparently, "You are only allowed to post URLs to other sites after you have made 15 posts or more." but I'm no spammer!!! >.<

Hey, new here. I was hoping you guys could help me with a design I'm working on.

Okay, I know what you're thinking. Another n00b asking for all the answers to design their system for free. I know. I've been on the other end of that, so I don't want it to seem like that's what I'm doing...

I'm primarily a computer engineer. So, electrical engineering plus computer programming, basically. HVAC is a little foreign to me, and even though I've been researching for months, I can't find all the answers by myself. Before I get into the project, let me state again that I'm not asking for someone to design a system for me. After all, I wouldn't really learn anything from that. I'm just asking for advice, tips, dos and don'ts, and how to get started. Don't get me wrong though, the more info you guys will give me, the easier it is for me. :P



Okay, here's the application. This is all going to be just part of a large automation project. I have air and water, heating and cooling needs.

Fifteen gallons of water will need to be kept heated or cooled to ~72 degrees F, +/- maybe 5 degrees, in this tank (2f3lqdh). Method of insulation, if any, is currently unknown. Open to suggestions, but overall budget is of primary concern.

This is an outdoor system that may be used anywhere in the USA. Ambient temperatures may theoretically vary from -10 degrees to 110 degrees, though the client is recommended to keep the unit as shielded as possible.

The system is modular. The "control unit" will host the water tank, all HVAC components and several other unrelated components. Anywhere from 1-8 "grow units" (okay, this is for a hydroponic system... maybe that makes things easier to understand, but I don't want to get too much into unrelated details) may be attached to the control unit for heating and cooling needs.

Each grow unit is 8 feet long, 4 feet wide and 4 feet tall, exterior. Walls are to be 2 inches thick, filled with polyurethane foam. Units will be decently sealed; R-values should be fair. Interior temperatures, I would say, will need to be maintained between 50-75 degrees, though preferably with a bit tighter of a tolerance.

Because of the modular nature of the design, I would like to use radiant heating and cooling, hopefully with a cheap radiator like this (22l2btu) in each grow unit. Possibly with a small DC fan next to the fins...? Not sure if I will need it. Grow units will all be fairly close to the control unit, but will be on casters and able to move around a foot or two any way, so flexible tubing is a must.

If I were designing a forced air system, things would be easier. I know the units are relatively well insulated, and I know that the maximum total cubic feet to heat/cool will be 1,024 (8x4x4 units, up to 8 units), or, if it were a typical room in a house with 8 foot ceilings, a well-insulated 128 square foot room. There are plenty of calculators online to tell me what kind of BTUs I should be looking at as a consumer buying a window A/C unit, but again, because of the modular nature of the design, I do NOT want to use forced air. 6 inch air ducts are a little more cumbersome than 3/4" water lines. So all of those forced air based calculators are worthless to me. This is radiant cooling, which I imagine is completely different, and I can NOT find any decent source material about it. No formulas, no calculators.

I was hoping that a 3926 BTU compressor I have my eye on, with a decent design, would be able to handle my application. I like this little guy (246mlxa), but to be honest, I don't know if this is complete overkill or extremely underpowered.

I have no idea what I'm going to do for my condenser coil. I don't have a clue how large it needs to be, and I don't know how I'm going to build it yet. All parts have to be new, so I can't go to a junk yard and rip a condenser out of a busted window A/C or anything, unfortunately. I'm not sure if I can get a guy to fabricate them for me at a decent price, or how difficult/expensive it would be to build my own. Help. >.<

Anywhere between 1 and 8 grow units may be attached to the system, and they need to be removable/addable. The plan was to have an 8x output manifold, and an 8x return manifold, with an electric solenoid on each output, and check valves on each return. This will allow complete computerized control over which units get heated/chilled water pumped to them, based on temperature sensors in each unit. Just because one unit may be positioned in the sunlight and in need of cooling at any given time doesn't mean the one sitting in the shade needs it too, you know?

I forgot. Make those 9 output/return manifolds. The water tank needs heating and cooling as well. For this, I was thinking coiled copper tubing placed inside the tank would be sufficient. The output and return manifolds are to be connected to a heat exchanger, which will also be be connected to the evaporator, obviously. What exactly my heat exchanger is going to be, I don't know yet. Wouldn't mind some pointers on this either...

For heating, as much as I'd like to design a heat pump so I can just reverse everything and be on my way, I'm told heat pumps are worthless in colder climates without auxiliary heat. Well, I live in Michigan, and most of my customers probably will too... so yeah. If I need to add a resistance heater to the system anyway, I don't see a point in over-complicating the refrigeration system with four-way reversing valves or whatever else I'd need. I was thinking of simply placing an inline water heater in the loop and leaving the refrigeration system offline in the hot months, like this (27ctrmu) with a T, perhaps. Any thoughts about this?

Um... I think that's about all for now. I'm so very sorry about the essay. Again, I'm looking for any help I can get, guides I can read that contain actual useful information for designing a system, with practical figures, examples and formulas, not a bunch of HVAC theory that I've already read over a dozen times. Any tips about anything would be helpful. My budget for this component of the system is... lower than I know it's going to cost me. I was hoping for $500 or less, but I don't see how that's going to happen.

So... Anything? Anything at all? Is this even in the right forum? XD Thanks a lot if you've even read this far...


Don