How Greenhouses Work, Part 2
In our last newsletter in this series, we talked about how we got our “new” energy-efficient greenhouse technology from the Chinese; who developed it at least 800 years ago. Here’s the link to Part 1 in case you didn’t get to read it.
To talk about greenhouses, we need to offer some definitions of our technical terms first. Unfortunately, definitions are a necessary evil, because without them, we wouldn’t be able to talk about greenhouses unless we limited ourselves to a 4th-grade level. If you’re not familiar with these terms, printing out this page to have when reading the articles in this series will help. (Next Part will be interesting and fun, promise!).
Here’s the Glossary of Terms And Definitions, right out of our $998 Family Greenhouse package:
Allelopathic: An allelopathic plant is one that secretes and/or broadcasts chemical compounds that are actively inhibitive to the growth of plants around it. Look under any redwood tree: you will find little growth among the redwood needles because they are allelopathic. An example in aquaponics systems is tomatoes. If any other plant’s roots are touching or nearby a tomato’s roots (except basil, which doesn’t seem to mind), the other plant will do poorly and perhaps even die from the contact.
Alternating Current electricity: or AC, is the kind in your home’s electrical outlets.
Ammonia: A product of the chemical decomposition of organic material and a precursor of nitrogen-bearing compounds that nourish the plants in an aquaponics system: they use them for fertilizer.
Appropriate Technology: This means using materials, resources, and skills that are locally available, affordable, durable, and successful to produce an item or system that fits local needs and requirements; or to solve a problem in a way that makes the locals smile instead of pissing them off. It means killing a fly with a locally made bamboo flyswatter that has no toxic aftereffects on people; instead of killing the fly with a spray of toxic chemicals from an industrial source that pollutes in its own neighborhood as well as in yours (when you spray the stuff on a fly).
Aquaponics: Combining recirculating aquaculture with hydroponics to reduce costs, increase efficiency, and grow both fish and vegetables in the same system.
Aquaculture: Raising fish only using commercial techniques.
Automatic Systems or Controls: A great way to kill all your fish and plants while having a “good excuse” as to why it happened. According to Murphy’s Law, all automatic controls malfunction at the worst possible times, and automatic systems are even worse. If you use timers, thermostatic controls, sensors, or computer control software, just remember to visit the greenhouse every few hours or so; DON’T believe what the readout tells you. See “the farmer’s shadow” also.
Biomass: Means the total weight or amount of an animal or plant in a system.
Biosecurity: Means NOT bringing live stuff into your system from outside that will cause problems. Crawfish, duckweed, vegetarian water snails that eat roots, or piranha in your aquaponics systems would all be examples of poor biosecurity.
CFM: cubic feet per minute; this is a measure of how much air a blower or air pump puts out, and is also a measure of how much air an airstone can blow out into the water. CFM and inches H2O are interrelated, because it takes more work to put out air in deeper water. There is higher water pressure there so you need to provide higher air pressure to overcome it and push the air out of the airstones in deep water.
Charge Controller: a piece of electrical equipment that turns the variable Direct Current voltage coming from a wind generator or bank of photovoltaic panels (PV panels) into the correct voltage of DC to charge your battery bank in an efficient manner.
Chlorine/Chloramine: These are indicators of how much chlorine is in your water; chloramine is a related chlorine compound that has the same effect on fish and plants. Measured with test strips before putting your fish in the water or adding the water to existing systems.
Coir: Ground-up coconut fiber used in potting mix. Used because it is sterile and doesn’t harbor deleterious bacteria and fungi the way (supposedly sterile) peat-based potting mixes often do. Mix 60/40 with vermiculite to make potting mix.
Crud: a technical term for all the varieties of biological “fouling” and deposits that occur in various quantities, with various qualities, in various locations in aquaponics systems. Crud is non-toxic.
Direct Current electricity: or DC, is the kind in car batteries.
DO: Dissolved Oxygen is an indication of how much oxygen is in the water and available for fish to breathe, AND for the plant’s roots (they need oxygen also to grow well). It is measured in ppm or percentage with a DO meter or test strips.
Duck: Depending on what context it is used in, it can mean an amphibious bird of several different species, or just that you should get your head out of the way. We put this in here to see if you were paying attention; it doesn’t have a thing to do with aquaponics or greenhouses.
Dutch Bucket: a bucket filled with potting mix with a hydroponic or aquaponic nutrient drip into it for growing plants, often tomatoes; NOT a part of a recirculating aquaponic system, but a common method of growing in greenhouses.
Energy efficiency: Just means getting the most heating/cooling/power for your money. An energy-efficient device does a LOT of work with a minimum input of energy; and an energy-efficient structure provides heating and cooling with a minimum input of energy.
ETFE: EthyleneTetraFlouroEthylene film is a plastic film used for covering greenhouses and stadiums that is made from flourospar, a mineral similar to quartz. It has better light transmission characteristics than glass, and is capable of lasting from 20 to 50 years in a proper installation.
Experiment: A valid experiment is when you change one thing only in an aquaponics system, and have another identical aquaponics system (except for that one thing) right next to it to act as a control. The control system is your reality check; if something is radically different in the experimental system as compared to the control system, then you can be fairly sure that the one thing you changed was the cause of the difference. If you simply change one thing in your one system, but don’t have a control system, you can’t be sure that the difference in results was due to the change or some other environmental variable that you just didn’t notice.
Farmer’s Shadow: Means you’re out in the greenhouse casting a shadow onto the plants; you can’t do this while sitting at a computer in your house. Actually get yourself out there and in the greenhouse frequently. If you are intimate with your growing operation, it’s much less likely that problems will develop because you will notice them developing and rectify things when they are still relatively OK.
Flow Rate: How much water a pump puts out per minute specified in gallons per minute (GPM) or gallons per hour (GPH), or the rate of flow in a pipe or trough.
GPM and GPH: Gallons per minute, gallons per hour. To get GPH from GPM, multiply by 60. To get GPM from GPH, divide by 60.
Head: The vertical distance a pump needs to lift water. Lifting water to a higher “head” requires a larger-capacity water pump that will use more electricity than lifting water to a lower “head”. If your system is on a hill, you will need to install a higher-capacity pump than the pump that same system would use if installed on level ground.
Heat Exchanger: A device that is designed to transfer heat from one medium to another. An example would be air flowing over heated rocks; a primitive kind of heat exchanger. A more advanced example would be a cooling coil immersed in your aquaponic system water, which transfers cool to the aquaponics water from a cooling source.
Hydroponics: Growing vegetables with water in sterilized soil-less systems (many different kinds are used, some with soil substitutes).
Inches Of H2O: A measure of air pressure at relatively low pressures. For example, if you have 10” H2O air pressure, the air will come out of an airstone that is 10” deep in your water, but NOT out of one that is 12” deep. There is 12” of water pressure at the 12” depth, and 10” of H2O air pressure is not enough to overcome the water pressure at that depth. One pound per square inch (1 PSI) is equal to a pressure of about 27 inches H2O.
Insolation: is the passive heat received by the earths surface (and your greenhouse) from the sun. Not to be confused with insulation, which is quite different (next).
Insulation: is a material or a system that tends to retain heat and/or cool where you want it retained. Insulation is rated in terms of “R” value; the higher the R-value, the better the insulation works.
Inverter: a piece of electrical equipment that turns Direct Current electricity (DC, the kind in car batteries) into Alternating Current electricity (AC, the kind in your home’s electrical outlets).
Mesh Pot: Is a small plastic pot with a RIM (important!), and holes or that is made of mesh that plant roots can drop down through easily into the water when planted in an aquaponics system raft.
Murphy’s Law: As applied to aquaponics and greenhouses, this comes in several flavors, depending on how complex you made your setup: If it can go wrong, it will. If it can’t go wrong, it is even more likely to go wrong. It will go wrong when you’re not there to notice. It will go wrong and the sensors will say that it’s alright. All automatic controls malfunction at the worst possible times, and automatic systems are even worse.
Nitrates: Are the nitrogen-bearing chemical compound that is the primary nutrient for plants in an aquaponics system, and is the product of nitrobacter, a nitrifying bacteria that metabolizes nitrites and excretes nitrates.
Nitrifiers/Nitrifying Bacteria: Nitrifying bacteria that are present in soil and water. These bacteria metabolize (eat) ammonia from decayed organic material and turn it into nitrites (a form of nitrogen that can be used to a certain extent by plants, but is toxic to fish), then into nitrates (a form of nitrogen that is much more usable by plants, and is less toxic to fish than nitrites). Nitrifiers are light-sensitive, that is, too much light kills them or inhibits their growth.
Nitrites: The nitrogen-bearing chemical compound that is the food source for nitrobacter (the nitrifying bacteria that produces nitrates), and is the product of nitrosomonas, a nitrifying bacteria that metabolizes ammonia and excrete nitrites.
PEX: a food-grade plastic water tubing that is UL approved for installation as home plumbing piping. It is cheap, easy to work with, and flexible. It is not as good as copper or stainless steel for earth-contact heat exchanger use, but it costs one-tenth as much, which means you can use ten times as much for the same price.
PPM: A unit of measurement that means parts per million. This is exactly the same as milligrams per liter (mg/L).
PV Panel: PhotoVoltaic panel, which is often referred to as a “solar panel”; it makes DC electricity from sunlight.
Raft: This refers to the 2’ by 4′ of Dow Blue Board Styrofoam sheet used as rafts to hold vegetables in mesh pots for growing in an aquaponics trough that we started with.
Recirculating: A closed system that uses the same water over and over again by pumping it through the tanks/troughs of the system.
Sensor: An electrical or mechanical device whose main purpose is to lie to you and confuse you with numbers when what you need are facts. An example: we have a $400 dissolved oxygen (DO) meter that has an integral thermometer; we have a $200 pH meter that has an integral thermometer; and we have a $5 Ace Hardware store thermometer that we actually USE to measure temperature because the pH meter’s thermometer reads 6 degrees low, and the DO meter’s thermometer reads 6 degrees high.
System: An assembly of different items which adds up to much more than the individual items themselves. A good example is an aquaponic system; it’s just a tank, some plastic troughs, a water pump, an air pump, some styrofoam and small plastic pots, and some fish and water. If it is not assembled in the correct order, or run correctly, it won’t grow fish and plants, and would probably become a stinking mess. But when someone who understands the system runs it, it does amazing things!
Tank: Usually any above-ground vessel made to hold water, and house and raise fish.
Thermal Mass: Any material that is used to store heat or cool in such a manner as to stabilize the temperature of its surroundings.
Thermostatic Control: usually an electronic device that turns a piece of electrically-powered equipment (a fan, a pump, an electrically-opened and closed vent) on and/or off when certain preset temperatures are reached.
Timers: A device that turns equipment on and/or off at preset times. We use Ace Hardware store $15 timers, and they work excellently well. The only problem with them is that if the power goes off, they stop timing, and this can mess up when your intended cycle goes off or on, so check them frequently when you’re in the greenhouse.
Troughs: Usually on-ground (because of their weight of one ton per 8 lineal feet at 4 feet wide and ten inches deep) lined structure of some kind that holds your rafts to grow vegetables on.
Vermiculite: An expanded product made from mica, a naturally-occurring mineral. It is non-toxic, lightweight, and provides aeration in potting mix when mixed 40/60 with coir.
Vertical Growing System: usually an aquaponic or hydroponic system designed to make good use of floor space by “stacking” plants in some sort of vertically oriented structure that holds them and provides means for the nutrient water to reach them and be recirculated.