permaculture

[Lawrence London <lfljvenaura@gmail.com>]

Reinventing the Greenhouse - LOW-TECH MAGAZINE
https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html

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Reinventing the Greenhouse

[image: Chinese solar greenhouse 1]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b7c7fd2f74970b-pi>The
modern glass greenhouse requires massive inputs of energy to grow crops out
of season. That's because each square metre of glass, even if it's triple
glazed, loses ten times as much heat as a wall.

However, growing fruits and vegetables out of season can also happen in a
sustainable way, using the energy from the sun. Contrary to its fully
glazed counterpart, a passive solar greenhouse is designed to retain as
much warmth as possible.

Research shows that it's possible to grow warmth-loving crops all year
round with solar energy alone, even if it's freezing outside. The solar
greenhouse is especially successful in China, where many thousands of these
structures have been built during the last decades.

A Chinese greenhouse. Picture: Chris Buhler, Indoor Garden HQ
<http://indoorgardenhq.com/2014/07/09/23/passive-solar-greenhouses-chinese-design/>
.
------------------------------
------------------------------

The quest to produce warm-loving crops in temperate regions initially
didn't involve any glass at all. In Northwestern Europe, Mediterranean
crops were planted close to specially built "fruit walls" with high thermal
mass, creating a microclimate that could be 8 to 12*°*C (14 to 22*°*F)
warmer than an unaltered climate
<https://www.lowtechmagazine.com/2015/12/fruit-walls-urban-farming.html>.

Later, greenhouses built against these fruit walls further improved yields
from solar energy alone. It was only at the very end of the nineteenth
century that the greenhouse turned into a fully glazed and artificially
heated building where heat is lost almost instantaneously -- the complete
opposite of the technology it evolved from.

During the oil crises of the 1970s, there was a renewed interest in the
passive solar greenhouse. [7] However, the attention quickly faded when
energy prices came down again, and the all-glass greenhouse remained the
horticultural workhorse of the Northwestern world. The Chinese, on the
other hand, built 800,000 hectare of passive solar greenhouses during the
last three decades -- that's 80 times the surface area of the largest
glasshouse industry in the world, that of the Netherlands.
*The Chinese Solar Greenhouse*

The Chinese passive solar greenhouse has three walls of brick or clay. Only
the southern side of the building consists of transparant material (usually
plastic foil) through which the sun can shine. During the day the
greenhouse captures heat from the sun in the thermal mass of the walls,
which is released at night.

At sunset, an insulating sheet -- made of straw, pressed grass or canvas --
is rolled out over the plastic, increasing the isolating capacity of the
structure. The walls also block the cold, northern winds, which would
otherwise speed up the heat loss of the greenhouse.

[image: Chinese style greenhouse]Chinese greenhouses. Picture:
HortTechnology <http://horttech.ashspublications.org/content/20/3/626.full>.

Being the opposite of the energy-intensive glass greenhouse, the Chinese
passive solar greenhouse is heated all-year round with solar energy alone,
even when the outdoor temperature drops below freezing point. The indoor
temperature of the structure can be up to 25*°*C (45*°*F) higher than the
outdoor temperature.

The incentive policy of the Chinese government has made the solar
greenhouse a cornerstone of food production in central and northern China.
One fifth of the total area of greenhouses in China is now a solar
greenhouse. By 2020, they are expected to take up at least 1.5 million
hectares. [1]

*Improving the Chinese Solar Greenhouse*

The first Chinese-style greenhouse was built in 1978. However, the
technology only took off during the 1980s, following the arrival of
transparent plastic foil. Not only is foil cheaper than glass, it is also
lighter and doesn’t require a strong carrying capacity, which makes the
construction of the structure much cheaper. Since then, the design has
continuously been improved upon. The structure became deeper and taller,
allowing sunlight to be distributed better and ensuring that temperature
fluctuations are decreased.

[image: Different types of chinese greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d1856779970c-pi>

A: The original design from the 1980s with a glass canopy. B: An improved
design from the mid-1980s, with plastic foil, a night curtain, and better
insulated walls. This design is the most widespread. C: An improved design
from 1995. The walls are thinner because they are insulated with modern
materials. Automatic handling of the night curtain. D: The most recent
design from 2007, which has a double roof for extra insulation.

In addition, cultivators are increasingly opting for modern insulation
materials instead of using rammed earth or air cavities for the insulation
of the walls, which saves space and/or improves the heat absorption
characteristics of the structure. Synthetic insulation blankets, which are
better suited for dealing with moisture, are also seeing increased use. The
old-fashioned straw mats become heavier and insulate less when they become
wet.

In some of the more recent greenhouses, the insulation blankets are rolled
up and down automatically, and more sophisticated ventilation systems are
used. Some greenhouses have a double roof or reflecting insulation
installed. In addition, the plastic foil used for the greenhouses —
obviously the least sustainable component of the system — is continuously
being improved, resulting in a longer lifespan.

*Performance of the Chinese Solar Greenhouse*

The performance of the Chinese greenhouse depends on its design, the
latitude, and the local climate. A recent study observed three types of
greenhouses in Shenyang, the capital of the Liaoning province. The city is
at 41.8°N and is one of the most northern areas where the Chinese-style
greenhouse is built (between latitudes 32°N and 43°N).

The research was conducted from the beginning of November to the end of
March, the period during which the outside temperature drops below
freezing. The average temperature in the coldest month is between -15°C and
-18°C (5 to -0.4°F). [1]

[image: Ruined chinese greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d1856a33970c-pi>Air
cavities in a ruined solar greenhouse. Picture: Chris Buhler, Indoor Garden
HQ
<http://indoorgardenhq.com/2014/07/09/23/passive-solar-greenhouses-chinese-design/>
.

The three greenhouses studied all have the same shape and dimensions (60 x
12.6 x 5.5 m), but the walls, the plastic foil, and the transparent layer
vary. The simplest construction has walls of rammed earth and an inside
layer of brick to increase the structures’ stability. The covering is a
thin plastic film that is covered at night with a straw blanket.

The two other greenhouses have a northern wall of brick with extruded
polystyrene foam as insulating material, whereby the width of the wall can
be cut in half. They are also covered with a thicker PVC plastic foil. The
best greenhouse adds to this a reflective coating on the insulation
blanket, further reducing heat loss at night.

[image: Chinese greenhouse with isolating sheet]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d181950b970c-pi>A
Chinese greenhouse. Picture: Chris Buhler, Indoor Garden HQ
<http://indoorgardenhq.com/2014/07/09/23/passive-solar-greenhouses-chinese-design/>
.

[image: Synthetic cover of chinese greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301bb08a1bf84970d-pi>The
night curtain of a solar greenhouse: Energy Farms
<https://energyfarms.wordpress.com/2010/04/05/solar-greenhouses-chinese-style/>
.

In the simplest greenhouse the temperatures dropped below the freezing
point from early December until mid-January. Without extra heating, this
greenhouse cannot grow any produce at this latitude. Only the most
sophisticated greenhouse – with its reflecting insulation layer – succeeded
in keeping the inside temperature above freezing at all times, using only
solar energy.

What’s more, the temperature stayed above 10°C most of the time, which is
the minimum temperature for the cultivation of warm season plants, like
tomatoes and cucumbers. Of course, passive solar greenhouses in more
southern locations would require less sophisticated insulation techniques
to be operated without additional heating.

*Solar Greenhouses in Northern Climates*

If we go further north, similar solar passive greenhouses would require
extra heating during the coldest months of the year, no matter how well
they are insulated. Note that the farther north the greenhouse is located,
the greater its slope will be. The slope of the roof is angled to be
perpendicular to the sun's rays when it's lowest on the horizon.

In 2005, a Chinese-style greenhouse was tested in Manitoba, Canada, at a
latitude of 50°N. A greenhouse that is 30 x 7 meters with a well-insulated
northern wall (3.6 RSI glass fibre) and an insulation blanket (1.2 RSI
cotton) was observed from January to April. During the coldest month
(February) the outside temperature varied between +4.5°C and -29°C (40 to
-20°F). While the interior temperature was on average 18°C (32.4°F) higher
than the exterior, it turned out to be impossible to cultivate plants
without extra heating during the winter. [2]

[image: Cucumbers in a chinese solar greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301bb08a01f95970d-pi>Cucumbers
in a Chinese solar greenhouse. Picture: Energy Farms
<https://energyfarms.wordpress.com/2010/04/05/solar-greenhouses-chinese-style/>
.

[image: Strawberries in chinese solar greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d1870df1970c-pi>Strawberries
in a Chinese solar greenhouse. Picture: wikipedia commons.

Nevertheless, energy savings can be huge in comparison to a glass
greenhouse. To keep the temperature above ten degrees at all times, the
heating system of the Canadian structure must deliver a maximum of 17 W/m2,
or 3.6kW for the building. [2] In comparison, a glass greenhouse of equal
proportions at the same interior and exterior temperatures would require a
maximum capacity of 125 to 155 kW.

Note that these results can't be applied to all locations at 50°N. The
Canadian research shows that solar output has a greater impact on the
inside temperature of the structure than does the outside temperature. The
correlation between inside temperature and sunlight is almost four times
greater than the correlation between inside temperature and outside
temperature. [2] For example, while Brussels lies at the same latitude as
Manitoba, the latter has on average 1.5 times more sun.

Thermal capacity can be further improved by placing black painted water
storage tanks against the north wall inside the structure. These capture
extra solar energy during the day and release it during the night. A
different method to improve the heat retention of a greenhouse is by earth
berming the north, east and west walls. Yet another solution to improve
insulation is the underground or "pit greenhouse". [8] However, this
greenhouse receives less sunlight and is prone to flooding.

*More Space Needed*

The passive greenhouse could save a lot of energy, but a price would have
to be paid: the profits generated by the Chinese greenhouse are two to
three times lower per square meter than those of its fully glazed
counterpart. In the more efficient Chinese greenhouses, an average 30 kg of
tomatoes and 30 kg of cucumbers can be grown per square meter (numbers from
2005), while the average production in a glass greenhouses is about 60 kg
of tomatoes and 100 kg cucumbers (numbers from 2003). [3] [4].

[image: Chinese greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301bb08a0b7c8970d-pi>A
Chinese solar greenhouse. Picture: Energy Farms
<https://energyfarms.wordpress.com/2010/04/05/solar-greenhouses-chinese-style/>
.

A passive greenhouse industry would thus take up two to three times as much
space to produce the same amount of food. This could be viewed as a
problem, but of course what really eats space in agriculture is meat
production. A more diverse and attractive supply of vegetables and fruits
could make it more viable to reduce meat consumption, so land use shouldn't
be a problem.
*Compost Heated Greenhouses*

Another issue with a solar powered greenhouse is the lack of a CO2-source.
In modern greenhouses, operators aim to have a CO2-level at least three
times the level outdoors to increase crop yield. This CO2 is produced as a
byproduct of the fossil fuel based heating systems inside the greenhouses.
However, when no fossil fuels are used, another source of CO2 has to be
found. This is not only an issue for solar greenhouses. It's also one of
the main reasons why geothermal energy and electric heat pumps are not
advancing in the modern glasshouse industry.

In Chinese solar greenhouses, this issue is sometimes solved by the
combined raising of produce and animals. Pigs, chickens, and fish all
produce CO2 that can be absorbed by the plants, while the plants produce
oxygen (and green waste) for the animals. The animals and their manure also
contribute to the heating of the structure. Research of such integrated
greenhouse systems has shown that the combined production of vegetables,
meat, milk, and eggs raises yields quite substantially. [5]

[image: Compost heated greenhouse]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301bb08a11107970d-pi>Detail
of a compost-heated greenhouse: Source: Pelaf
<http://pelaf.com/compost-heating/>.

Justin Walker, an American now living in Siberia, is building an integrated
system using horses, goats and sheep in a monastery in Siberia. Considering
the harsh climate, the structure is partly built below-ground, while its
protruding parts are earth-bermed. Above the barn area is a hayloft that
provides further winter insulation as well as ventilation in the summer
when it is empty. His compost heat recovery system produces hot water that
is piped through radiant floor heating zones in the floor of the
greenhouse. The CO2 is supplied by the animals. [6]

Heating and CO2-production can also be done without housing animals in the
greenhouse. Their manure suffices. As we have seen in the previous article,
the use of horse manure for heating small-scale greenhouses dates back
several centuries in Europe, and in China it was practised already 2.000
years ago. Since the 1980s, several compost heated greenhouse have been
built in the USA. These have shown that a greenhouse can be entirely heated
by compost if it is well-insulated, and that the method drastically
enriches the CO2-levels in the soil and in the greenhouse air. To add to
this, the compost also serves to increase soil fertility. [6]

Kris De Decker
------------------------------

*Sources:*

[1] Energy performance optimization of typical chinese solar greenhouses by
means of dynamic simulation
<http://www.geyseco.es/geystiona/adjs/comunicaciones/304/C02330001.pdf>
(PDF), Alessandro Deiana et al., International conference of agricultural
engineering, 2014, Zurich.

[2] Winter performance of a solar energy greenhouse in southern Manitoba
<http://www.builditsolar.com/Projects/Sunspace/ManitobaGH/WinterGHPerformanceManitoba.pdf>
(PDF), Canadian Biosystems Engineering. 2006.

[3] The solar greenhouse: state of the art in energy saving and sustainable
energy supply
<http://wwwlib.teiep.gr/images/stories/acta/Acta%20691/691_59.pdf>. G. Bot
et al., 2005

[4] Structure, function, application, and ecological benefit of a
single-slope, energy-efficient solar greenhouse in China
<http://horttech.ashspublications.org/content/20/3/626.full>.
HortTechnology, June 2010

[5] Integrated energy self-served animal and plant complementary ecosystem
in China <http://www.fao.org/docrep/t4470e/t4470e0d.htm>, in "Integrated
energy systems in China -- the cold northwestern region experience", FAO,
1994

[6] The Compost-Powered Water Heater: How to heat your greenhouse, pool, or
buildings with only compost
<https://www.amazon.com/gp/product/1581571941/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1581571941&linkCode=as2&tag=lowtemagaz-20&linkId=GIO224NGX6TKWFKC>,
Gaelan Brown, 2014

[7] See for example "The Solar Greenhouse Book
<https://ia800306.us.archive.org/30/items/fe_The_Solar_Greenhouse_Book/The_Solar_Greenhouse_Book.pdf>"
(PDF), published by Rodale Press in 1978

[8] The Earth Sheltered Solar Greenhouse Book
<https://www.amazon.com/gp/product/0960446400/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0960446400&linkCode=as2&tag=lowtemagaz-20&linkId=EN2MO37M5MVTJFEO>,
Mike Oehler, 2007
------------------------------

*Fruit Walls: Urban Farming in the 1600s*

We are being told to eat local and seasonal food, either because other
crops have been tranported over long distances (usually by plane), or
because they are grown in energy-intensive greenhouses. But it wasn't
always like that. From the sixteenth to the twentieth century, urban
farmers grew Mediterranean fruits and vegetables as far north as England
and the Netherlands, using only renewable energy.

[image: Montreuil peaches]
<http://krisdedecker.typepad.com/.a/6a00e0099229e8883301b8d1865a0b970c-pi>These
crops were grown surrounded by massive "fruit walls", which stored the heat
from the sun and released it at night, creating a microclimate that could
increase the temperature by more than 10*°*C (18*°*F).

Later, greenhouses built against the fruit walls further improved yields
from solar energy alone. It was only at the very end of the nineteenth
century that the greenhouse turned into a fully glazed and artificially
heated building where heat is lost almost instantaneously -- the complete
opposite of the technology it evolved from.

Read more: Fruit Walls: Urban Farming in the 1600s
<https://www.lowtechmagazine.com/2015/12/fruit-walls-urban-farming.html>.
------------------------------

Posted on December 24, 2015 at 03:04 PM in Agriculture
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[image: Karyn Schoem]

(1)

Thanks so much for this! Great research, visuals!

Posted by: Karyn Schoem | December 24, 2015 at 09:14 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08a30bb3970d#comment-6a00e0099229e8883301bb08a30bb3970d>
[image: Nils Hjelte]

(2)

Thank you

Posted by: Nils Hjelte | December 25, 2015 at 05:34 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c7feaaa0970b#comment-6a00e0099229e8883301b7c7feaaa0970b>
[image: Yekutiel]

(3)

As usual, you have posted another important and thought provoking article
of extraordinary high quality. Kudos to you!

Have you considered crowdfunding this website via, say, Kickstarter.com or
Patreon.com so that you would have time to write more frequently? Also,
have you considered focusing on obtaining guest posts on this website? In
other words, instead of focusing on writing, if you were to focus on
editing you might be able to leverage your talent for ferreting out
valuable solutions to provide more extraordinarily high quality content for
this website.

In addition, I hope you might consider a follow-on piece about rammed earth
dwellings. They are like kissing cousins of the Chinese greenhouses
discussed in this article. You might think of a rammed earth dwelling as
being very something similar to the Chinese greenhouses. Except instead of
being designed for plants to live in, rammed earth dwellings are designed
for people to live in.

Here are a couple of links on the subject:

*Builder Sylvia Cook Sharing Insights on building with Rammed Earth*
https://www.youtube.com/watch?v=02sr4vyHGC4

*In rural Ontario, a high-tech home built of low-tech dirt*
http://www.theglobeandmail.com/life/home-and-garden/architecture/in-rural-ontario-a-high-tech-home-built-of-low-tech-dirt/article546271/
<https://www.theglobeandmail.com/life/home-and-garden/architecture/in-rural-ontario-a-high-tech-home-built-of-low-tech-dirt/article546271/>

If you want some more links to rammed earth articles and videos please let
me know by responding to this comment.

Posted by: Yekutiel | December 25, 2015 at 09:38 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c7feb75a970b#comment-6a00e0099229e8883301b7c7feb75a970b>
[image: Sherwood Botsford]

(4)

Heating with compost/manure

Some care has to be taken to keep the C:N ratio over 30. If there is too
much N, then the decomposition releases ammonia, which as a gas is tough on
the plants, as well as your sinuses.

That said: For the amount of CO2 needed, a rather small gas flame would
suffice. While not completely solar, this would still be a large step
forward.

In addition, this would be a viable backup for compost heating. If no
natural gas line is available, propane is a somewhat more expensive, but
more portable alternative.

Posted by: Sherwood Botsford | December 26, 2015 at 02:22 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08a34dbf970d#comment-6a00e0099229e8883301bb08a34dbf970d>
[image: Teng Yang]

(5)

Interesting article! I always wondered how modern greenhouses got their
start.

Question, would putting large space blankets over the greenhouse at night,
much in the way the Chinese used straw mats, help to retain the heat better
at night in an all-glass greenhouse?

To borrow again from the Chinese design, would adding a second glass
structure just slightly above the greenhouse to help trap the heat better,
especially if combined with the space blanket design?

I suppose it would take up more space and require more resources such as
more glass, but would it be cost-effective enough in reducing the need to
heat the greenhouse?

Posted by: Teng Yang | December 26, 2015 at 10:45 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b8d188a620970c#comment-6a00e0099229e8883301b8d188a620970c>
[image: Ting Henson]

(6)

In cold but sunny climates like the Manitoba test, would a beer / pop can
furnace be sensible. coupled with a small solar powered / switched
circulating fan and using raised beds to increase the solar mass.
Just a thought.

Posted by: Ting Henson | December 28, 2015 at 08:32 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08a3eece970d#comment-6a00e0099229e8883301bb08a3eece970d>
[image: Lance]

(7)

hemp works great...

http://www.hemp-technologies.com/resources/Thermal-Mass.pdf

Posted by: Lance | December 30, 2015 at 07:24 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c8002a47970b#comment-6a00e0099229e8883301b7c8002a47970b>
[image: Bo Robert Atkinson]

(8)

Thanks and here is my concept-

http://harmoniouspalette.com/EyelidGreenhouse/EyelidGreenhouse.html

Posted by: Bo Robert Atkinson <http://harmoniouspalette.com> | January 01,
2016 at 02:53 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b8d18aed74970c#comment-6a00e0099229e8883301b8d18aed74970c>
[image: Vivi]

(9)

For a moe low-tech CO2-source than the modern gas burner, why not put in a
small wood stove (or even those DIY things you build from cans and feed
with sticks that were designed for cheap and fuel-conserving cooking in
developing countries), or the old charcoal brazier that kept Roman tents
warm on military campaign?

Or a nice old oil lamp with storm-safety features, filled with plant oil
instead of kerosene. The point isn't efficient light, after all, just the
burning. Hell, even a few of those covered storm candles that Catholics put
on graves and leave alone would probably be enough.

Posted by: Vivi | January 07, 2016 at 04:13 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c803fb79970b#comment-6a00e0099229e8883301b7c803fb79970b>
[image: Vivi]

(10)

This principle of rolling blinds can be used to conserve living space
heating and cooling, too. But remember that it is important to install the
blinds on the outside of the window, especially to keep out the heat in the
summer.

Where I come from, many houses have rolling blinds made of wood, metal or
plastic, about a handspan outside the actual window, so they are flush with
the wall. More expensive setups are even automatic and timed or they have
sunlight sensors and go down when the sun sets and up when it rises.

These blinds don't just help keep the house pleasantly cool in summer
(nobody here uses air conditioning), and discourage break-ins (the timed
blinds are mainly to make it look like someone's still in the house when
you're on vacation; and it's just not that easy to open a window from the
outside if there's a sheet of metal or heavy wood infront of it), but put
down on winter nights, they help a lot to keep heating costs down, even if
the windows are already double- or tripple-glazed. Indoor shades or even
thick black-out curtains dont help nearly as much.

Also, is there a particular reason (other than price at large scale) why
the Chinese aren't using bubblewrap foil or similar instead of plain
single-layer PVC? Is it a light refraction issue or something like that? Or
would it get too hot in the summer? 'Cause I've taped a double layer of
simple packaging bubblewrap into some attic windows that don't have outside
blinds and which tended to condense air moisture on the inside when it's
freezing outside, despite being double-glazed.

The bubblewrap stopped that, helped the room retain heat better at night
(when the central heating is switching itself off because the rest of the
house doesn't lose much heat), and it doesn't significantly darken the
room, so I just leave it on all year now. (The brown roof tiles and wooden
construction of the roof mean I always had to keep the windows open 24/7 in
the summer anyway, to keep the room below 35°C most of the time.

Wood framing and a foot of fiberglass insulation can just never be as good
as proper brick walls, which together with the aformentioned heavy blinds,
keep the rest of the house below 25°C.)

I mean, even if bubblewrap really is too costly for large commercial
operations, for small homesteading greenhouses, a transparent insulating
blanket that you can just leave on all winter instead of having to roll it
up and down every day - even when it's wet, covered in snow, or frozen to
the main plastic sheet with a layer of ice - sounds more practical.

The little free-standing, unheated garden greenhouses that I see in
alotment gardens sometimes are also made of some sort of double-layered
transparent plastic with an air space between (hard plastic panes, not
foil), instead of more expensive and fragile glass. (These greenhouses are
mainly used to give cucumbers and such the few extra degrees they need to
grow in our lattitude, even in summer, and to keep tomatoes from dying of
brown rot for another few weeks after the rains start in early September.
They're not meant to actually grow anything wildly out of season, and
they're not frost-free.)

Though after a couple of years, they take on a green sheen - I assume
there's algae growing between the two layers - and that reduces the light
that reaches the inside. So that's not ideal either. Well, maybe if you
take the extra time and a tube of window putty / bathroom silicone sealant
to make these prefabricated plastic panes properly watertight from the
start. Still, plastic foil, and even bubble wrap, is a lot cheaper.

Posted by: Vivi | January 07, 2016 at 05:45 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08a8bbb5970d#comment-6a00e0099229e8883301bb08a8bbb5970d>
[image: Erik Andrus]

(11)

Very cool concept, I have been thinking along similar lines for a
greenhouse on my farm. I have to take issue with one minor point made,
though:

"A passive greenhouse industry would thus take up two to three times as
much space to produce the same amount of food. This could be viewed as a
problem, but of course what really eats space in agriculture is meat
production. A more diverse and attractive supply of vegetables and fruits
could make it more viable to reduce meat consumption, so land use shouldn't
be a problem."

This isn't really how land use decisions are made in agriculture. It is
much more related to supply and demand, and whether investments in
infrastructure can be justified with a rapid payoff. For instance, if a
conventional greenhouse pays for itself more quickly, almost all growers
will have to go that route just to survive economically, pay taxes and
loans and so on. I agree it would be good for a sustainable society to have
a wider variety of fruits and vegetables grown with a low energy cost, but
most farmers have to take their cues from their markets, rather than the
other way around.

For instance I'd like to put in a large greenhouse along these lines to
grow rice seedlings in spring and other stuff the rest of the year. But the
building materials are expensive, and the food competition for anything I
might produce for market, shipped from thousands of miles away to my local
grocery store remains cheap. Once food in general becomes more expensive
we'll likely see a lot more of this kind of creativity on small farms.

Posted by: Erik Andrus <http://www.goodcompanionbakery.com> | February 06,
2016 at 09:04 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b8d19c3507970c#comment-6a00e0099229e8883301b8d19c3507970c>
[image: Andre]

(12)

Hello. Thank you for the great article. Is composting not a viable option
for CO2 production (and heating) inside a greenhouse?

Posted by: Andre | February 18, 2016 at 10:00 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08bc2810970d#comment-6a00e0099229e8883301bb08bc2810970d>
[image: Evan]

(13)

I know I'm late to the party here, but what accounts for the production
drop off in passively heated greenhouses compared to full glass? Is it less
sunlight?

Posted by: Evan <https://urbanverticalproject.wordpress.com> | February 19,
2016 at 07:16 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08bc8f33970d#comment-6a00e0099229e8883301bb08bc8f33970d>
[image: kris de decker]

(14)

@ Evan,

Yes, it's less sunlight

@ Andre

Yes, you can: the last part of the article is devoted to compost heating.

Posted by: kris de decker | February 21, 2016 at 07:29 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b8d1a2931e970c#comment-6a00e0099229e8883301b8d1a2931e970c>
[image: filip]

(15)

https://www.youtube.com/watch?v=pvPVsMGlVVI

Posted by: filip | February 23, 2016 at 02:59 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c819394d970b#comment-6a00e0099229e8883301b7c819394d970b>
[image: J in China]

(16)

@ Evan @ Andre,

I think it's worth pointing out here that the reason the light is reduced
in this kind of greenhouse is that there are opaque walls on the north and
half walls on the east and west sides of the structure, reducing the light
in the early morning and late afternoons, as well as severely restricting
the light in the height of the summer. Basically these greenhouses are only
productive in the wintertime. A solution to this would be to build
permanent walls to only half their height and using removable pieces for
the top halves, allowing you to remove the obstruction when the sun is in
the north. I've been talking to a couple farmers here in China about
exactly that this winter (I live an hour south of Shenyang, the city
mentioned in the story) and I think large papercrete blocks could be a good
compromise between mobility and insulative properties.

Posted by: J in China | March 17, 2016 at 01:20 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c825abd0970b#comment-6a00e0099229e8883301b7c825abd0970b>
[image: Craig]

(17)

I read "CO2-source" + "Thermal capacity can be further improved by placing
black painted water storage tanks"

...and I immediately think of brewing and aquaculture. I'd rather share an
enclosed space with these than with a dung heap.

1) grow carob on more marginal (rocky / hilly / dry) land, and ferment the
pods (which store and transport well) in the greenhouses. Do distillation
through winter, when the waste heat would benefit the greenhouse.

2) raise fish / snails / crayfish, such as the common yabby (Cherax
destructor), which eat algae and dead plant remains. This would turn some
of your cucumber and tomato leaves back into CO2 + tasty flesh.

Posted by: Craig | March 29, 2016 at 05:32 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08cfd0e2970d#comment-6a00e0099229e8883301bb08cfd0e2970d>
[image: Jose]

(18)

Well, I don't know a thing about agriculture... But, what about using
fluorescent/UV lamps?

I remember watching a video that showed how a solar water heater worker
even in cold climates. Could you use hot water to heat the soil and, with
that, the whole greenhouse?

Aquaponics sounds like a better idea, though...

Posted by: Jose | April 06, 2016 at 09:31 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb08d39b47970d#comment-6a00e0099229e8883301bb08d39b47970d>
[image: Leonard]

(19)

What about to use biochar for heating the soil and to increase heating of
bricks?

Posted by: Leonard | July 16, 2016 at 12:58 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301b7c87be881970b#comment-6a00e0099229e8883301b7c87be881970b>
[image: thomas]

(20)

Just found this from 1818 garden magazin https://flic.kr/p/HrPmow

Posted by: thomas <https://twitter.com/peakaustria> | April 03, 2018 at
11:31 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e8883301bb0a00b801970d#comment-6a00e0099229e8883301bb0a00b801970d>
[image: Ben]

(21)

No tech reader 18
http://www.notechmagazine.com/2018/03/no-tech-reader-18.html has a link
about the great nutrient collapse
https://www.politico.com/agenda/story/2017/09/13/food-nutrients-carbon-dioxide-000511.
this article makes reference to increasing the co2 level without mentioning
that may be a bad thing.
Maybe an addendum is called for to point out that increasing co2 in your
greenhouse may not be best?

Posted by: Ben | May 02, 2018 at 09:57 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e888330224e0367ab1200d#comment-6a00e0099229e888330224e0367ab1200d>
[image: Tom]

(22)

https://en.wikipedia.org/wiki/Eliot_Coleman has researched and written
books about passive solar greenhouses.
https://en.wikipedia.org/wiki/French_intensive_gardening and
https://www.chelseagreen.com/2012/history-of-winter-gardening-the-17th-century-french-garden-system
before that used compost, glass enclosures and insulation to extend the
season.

The Chinese greenhouses are in line with what works for farmers, not just
armchair gardners.

I like the idea of including animals in the mix. Chickens can help with
pests as well as provide manure and disposing of some plant waste.

One issue with stand alone, static enclosures is the build up of salts and
pests in the soils. Periodically exposing everything by removing the
covering or moving the structure alleviates this. Perhaps some kind of
movable thermal mass with movable insulated structure for the back wall
could facilitate that.

Posted by: Tom | December 03, 2018 at 03:01 PM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e88833022ad37ec482200c#comment-6a00e0099229e88833022ad37ec482200c>
[image: Rob]

(23)

Tom, I like the movable idea, or possibly better yet, space permitting,
build the same thermal mass structure side by side and move the "glazing"
structure every couple of years? Heck you could even leave in the "ribs" of
the greenhouse and just change the glazing...

Posted by: Rob | January 28, 2019 at 02:55 AM
<https://www.lowtechmagazine.com/2015/12/reinventing-the-greenhouse.html?cid=6a00e0099229e88833022ad3d90ba5200b#comment-6a00e0099229e88833022ad3d90ba5200b>