They probably want you to define the aqueous throughput and the uptake of the lettuce. The material balance will reduce to an open system, with accumulation (i.e. the lettuce), without chemical reaction or heat transfer. You would need to know the watering requirements of lettuce, the optimal spacing of lettuce and the minimum throughput of water required to prevent stagnation. Design the flow rate for the maximum uptake of properly spaced lettuce, and ensure the water is circulated enough to prevent stagnation. Then, design a collection/piping system. Verify your design using Bernoulli’s, or Hazen-Williams provided there are many nodes in the pipe system. Resolve any issues. That’s all there is to it.This seems more like a weekend homework problem than a senior project. In contrast, my senior project was a to design an entire ethylene plant, including a rigorous furnace design (radiant, conductive, and reactive heat balances, mass balances and momentum balances), quench tower sizing, compressor sizing and acid gas removal, column sizing and internals, refrigeration loops, pinch point analysis of heat exchangers, and an initial estimate of total plant costs. I had to define, size and specify the vessels and internals; the splits and recycles, the furnace tubing, pipes and burners; compressor staging and acid removal system, pump and valve sizing, cooling towers, power requirements, a layers of protection (LOPA) safety analysis, hydraulic sizing of all key flows, capital costs and proposed funding. I would like to know more about how this project panned out. Hopefully, the project provided you an interest in gardening, which like home brewing, catalyst manufacture or cheesemaking, is an empirical science. Let me know how it went. Calico Marty, P.E.

The problem with explaining how refrigerators and freezers work is that an even barely sufficient explanation requires knowledge of rudimentary thermodynamics. An insufficient explanation might go like this: Electricity drives a motor that pumps a fluid through the refrigeration plumbing. This fluid, which typically is a gas at room temperature and pressure, has the property that when compressed it gets hot, and when expanded, it gets cold. (This is true of all gases per the Ideal Gas Law.) If the cold gas (now a liquid) is put into contact with a warm surface and allowed to expand to its gaseous form, it absorbs a lot of heat from the surface. When this gas is further pumped and compressed, and then subjected to a surface cooler than it is, it gives up its heat and condenses back to a liquid that is warmer than the exterior ambient. However, when later in the loop expended back to a gas, it gets colder than the interior air and can thus cool it. The expansion part occurs in an expander, and the condensation part occurs in a condenser. The condenser in your refrigerator, like the condenser in your car air conditioning, is a radiator that moves heat to the air. The expander in your refrigerator, like the expander in your car air conditioning (usually buried in ducting and less easy to see) is a radiator operating in reverse by absorbing heat from the air passing through it. The efficiency of this heat transfer loop is mainly determined by three processes: the efficiency of the thermodynamic cycle being used by the system, the motor electrical to work efficiency, and losses from friction moving the gas around. The thermodynamic process prohibits attempts to get something from nothing, or even break even (no perpetual motion machines; no free work). In principle, two separate systems, one for the refrigerator and one for the freezer can be sized and optimized for each such that the total power used in some standard environment is not greater than that used from a freezer only single system that controls the rate of cold air moved to a refrigerator. It could with careful tuning be more efficient. Analyzing such systems is fairly complex and specialized, and designing and building prototype optimal ones (for aerospace applications say) can cost millions of dollars. For residential units, some standardization is expected in selection of compressors, condensers, and expanders such that the last erg of energy savings is not going to be met. One expects for residential units that the efficiency will be as noted on the sticker for some environment, and the buyer has to determine whether differences in electricity cost, differences in purchase cost, and differences in other features make the purchase worthwhile. kas

OK, so if it's a garage, I assume that you don't want to heat that space so you want to insulate the top (under the slab). Again, typically I think extruded polystyrene is the right material for that although I'd be concerned about pressure from the vehicles on the garage floor. Never heard of using an earth box as a heat exchanger. Seems like there's risk of waste unless you insulate the box really well. Also, I don't really like the "one-way" engineering of an earth box (though I've got one of my own, not yet in service, and to be used for space heating, not for heat exchanging - my box is 12 in to 17 in deep and filled with compacted soil, though the pex tubing is embedded in a sand layer at mid-height of the box). If the pex ever gets damaged in that box, there's not way to fix it unless everything is torn out and you start over. I guess this is less of an issue for you since it's a garage. For me it's a finished family room. I didn't use any aluminum wrap - I don't see how that would help much - the heat still needs to get from the sand to the tubing and I don't see that anything will facilitate the process much. The reason why the book you have doesn't give specifics is because there's too much variability in the concepts. Again, a heat transfer calc needs to be done. Why don't you head over to the UC mechanical engineering department and see if there are any ace heat transfer students around who might run a quick calculation for a little extra cash. I think you could find a grad student in search of some extra beer money. I'd get serious with the idea before constructing.

What is happening in 2023? R22 has been in phase out mode for well over 12 years now. The current refrigerant that replaced R22 known as R410a is going to be phased out. California enters this phase first. No new R410a installations in CA starting in 2023. R410a begins it's phase out with strict rules than the aformentioned R22 Freon. (no dry units like with R22). Texas is likely to enter this realm in 2025 at the latest. The refrigerants replacing R410a isn't much better than that of R410a. Two competing versions R32 & R454b both of which are mildly flammable. How flammable? mildly. If you choose R32 solution, that is likely to be phase out sooner because it is mildly more offending than R454b. But either of these choices shelf lifes will be short. Maybe 15 years, maybe 20. R22 is cost prohibitive now. If you have a unit that uses R22 --9 times out of 10-- and you spring a leak -- you buy a R410a unit now. Because? The new units have yet to arrive! ( this is assuming you can even find what you want now.) So in short order anything you buy now will essentially be obsolete "over night". This primarily will only effect you if you spring a refrigerant leak. BUT, refrigerant leaks nowadays are more common than 20 years ago. If you're curious what, where, how and why this is happening? I made a video about it embedded below for your convenience. Note: this video is only a starting point... Part 1.