Talk:Greenhouse - Revision history

RichardWSmith: Discussion of about of energy needed by plants... too low?

2021-04-17T20:18:58Z

Discussion of about of energy needed by plants... too low?

Michel Lamontagne at 02:44, 16 April 2021

2021-04-16T02:44:23Z

Michel Lamontagne at 02:36, 16 April 2021

2021-04-16T02:36:20Z

Michel Lamontagne at 00:24, 16 April 2021

2021-04-16T00:24:54Z

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← Older revision		Revision as of 20:18, 17 April 2021
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		+	Hi Michael L., thank you for your work!
		+
		+	In the Case for Mars, Robert Zubrin said that crops could grow with natural sunlight out to the asteroid belt, but beyond that artificial lights were needed. His calculations were based on Earth farm land. The ASHRAE values seem far too low, using them we could have productive farms on Saturn.
		+
		+	We have the low light vegetables on two pages. Move them to their own page and link to it?
		+
	''From the ASHRAE minimum values, plants might survive even the worst storms. If the illumination goes down from 600 W/m2 to 60 W/m2, then that is significantly above the 3 W/m2 recommended. However the cold might do the plants in. In winter, this might be another good reason to avoid growing plants in greenhouses in the North or southern latitudes. In particular in winter the illuminations times may be too short.''		''From the ASHRAE minimum values, plants might survive even the worst storms. If the illumination goes down from 600 W/m2 to 60 W/m2, then that is significantly above the 3 W/m2 recommended. However the cold might do the plants in. In winter, this might be another good reason to avoid growing plants in greenhouses in the North or southern latitudes. In particular in winter the illuminations times may be too short.''

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-From the ASHRAE minimum values, plants might survive even the worst storms.  If the illumination goes down from 600 W/m2 to 60 W/m2, then that is significantly above the 3 W/m2 recommended.  However the cold might do the plants in.  In winter, this might be another good reason to avoid growing plants in greenhouses in the North or southern lattitudes.  In particular in winter the illuminations times may be too short.
+''From the ASHRAE minimum values, plants might survive even the worst storms.  If the illumination goes down from 600 W/m2 to 60 W/m2, then that is significantly above the 3 W/m2 recommended.  However the cold might do the plants in.  In winter, this might be another good reason to avoid growing plants in greenhouses in the North or southern latitudes.  In particular in winter the illuminations times may be too short.''
-We really need the plant category, or ideally a table or a simple equation that links yields to insolation.  Tonnes per hectare vs watts/m2.
+''The losses through the walls need to be added to the analysis.  Even fairly thin plastics absorb 10-20% of the sunlight.  And that is for thin films on Earth, not holding in 100 kPa!''
 Open issues:

← Older revision		Revision as of 02:36, 16 April 2021
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		+	From the ASHRAE minimum values, plants might survive even the worst storms. If the illumination goes down from 600 W/m2 to 60 W/m2, then that is significantly above the 3 W/m2 recommended. However the cold might do the plants in. In winter, this might be another good reason to avoid growing plants in greenhouses in the North or southern lattitudes. In particular in winter the illuminations times may be too short.
		+
	We really need the plant category, or ideally a table or a simple equation that links yields to insolation. Tonnes per hectare vs watts/m2.		We really need the plant category, or ideally a table or a simple equation that links yields to insolation. Tonnes per hectare vs watts/m2.

@@ Line 1: / Line 1: @@
 Open issues:
 How long can plants survive without sunlight (e.g. during a dust storm)?
 :-Plants can live their entire lives without sunlight if adequate artificial light is provided. Check with your local agricultural extension office to find out how long specific species can survive in total darkness.
 How many persons are needed to work in the greenhouse to produce enough food for a hundred persons?
 :-It depends on what you're growing, as some plants yield more calories per square foot than others. Various gardening writers (John Jeavons and Steve Solomon leap to mind) have calculated how much square footage is needed to feed a person using their gardening methods. Look these up, multiply by 100. Then contact a greenhouse or high-tunnel grower who grows the crops you want to grow, and find out what the area of their greenhouses are and how many employees they have to work that area. Apply that ratio to the area you'd need to grow food for 100 people.
 How much energy is required for heating, especially during long lasting dust storms? This question can not be answered without an experimental setup.
 :-This question most certainly can be answered without an experimental setup, as HVAC technicians routinely calculate the sizes of furnaces needed to heat a given volume. Figure the volume of your greenhouse. Determine what the ambient temperature and high and low windspeeds are (Does NASA have this data?). These figures, along with the R-value of the greenhouse material itself (and surrounding soil, if the greenhouse is earth-bermed or underground), will allow you to determine the rate of heat loss from your greenhouse. If you know the volume of your greenhouse, what the rate of heat loss is, and what temperature you want to maintain, you can determine how many BTUs of heat you need to generate. Look at the energy requirments of an electric furnace that generates that amount of heat.
 What temperature and air pressure do plants need?
 :-Depends on the plant. Again, check with your local extension office. As a rule of thumb, look at plants natural environments. For example, plants that grow high in the mountains do better at lower pressures, while plants that prefer to grow at sea level or underwater need higher pressures. "Coles" (brassicas) like broccoli, cabbage, spincach, kale, and Brussels sprouts can grow in cooler temperatures, whereas tomatoes, peppers, and okra require much warmer temps.
 What air pressure is needed for persons to work in the greenhouse?
 :-The Navy (or any diving instructor) can give you information on human survivability at high temperatures. I'd imagine both NASA and the Air Force would have information on low pressures.
 Do plants need wind? How can it be provided?
 :-Most plants don't need wind for normal development, though many require it for natural reproduction. In the absence of wind, this can be substituted with hand pollination by workers (something that would be necessary anyway in the absence of other pollinators, like bees and flies), but wind is simple enough to create. Just turn on a fan. Fans are standard equipment in greenhouses, both for ventilation (to regulate temperature), and to avoid stagnant, moist air, which can lead to fungal diseases like damping off and powdery mildew. Since a greenhouse on Mars could not be opened. for ventilation, air conditioning, as well as heat, may be needed on sunny days. It depends on your rate of heat loss versus rate of solar heat gain.
 <div style="text-align: center;">

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 Some of these paragraphs seem to contain valuable information that can be inserted into the article. ''Greenhouse'' is a really big topic, which will force us to fork the article sooner or later. -- [[User:Rfc|Rfc]] 20:13, 22 October 2008 (UTC)
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+==Wind comment==
+Wind is needed for plants that disperse their pollen into the air, such as Ragweed.  I'm not sure which food plants are pollinated in this manner; I know that tomato plants started indoors on Earth won't set fruit without using a spray called Blossom Set, which comes in a bottle with a finger pump. [[User:Miros1|Miros1]] 19:30, 30 September 2012 (UTC)

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