11210_TheChineseGreenhouse

1 My Introduction to Chinese Greenhouses

In March 2014, I visited a small commercial aquaponics facility, Today’s Green Acres in southern Tennessee, with a couple friends. The owner of the facility gave me and twenty other attendees a free tour of his aquaponics greenhouses and an hour-­long talk about the science and art of aquaponics — ​growing vegetables in nutrient-­rich water from fish tanks.

The first aquaponics greenhouse we toured blew me away. It was a verdant profusion of spinach, lettuce, basil, and other greens, looking absolutely delicious (Figure 1.1). And, what is more, there wasn’t a weed I sight! Our host discussed care of fish, planting, and a number of other topics, including the energy requirements of aquaponics growing compared to conventional agriculture.

One of the chief advantages of growing aquaponically, he noted, is that this system uses much less energy than conventional farming operations. Modern agriculture relies heavily on large machines to grow and harvest produce, and semi-­trucks to ship it long distances to markets throughout the nation. In the process, it consumes an inordinate amount of energy. In fact, way more calories of fossil fuel are used to produce and distribute food than is actually in the final product.

Out of curiosity, I asked how much it cost to heat the tiny greenhouse in which we were standing. His answer: it had cost $700 to $800 a month over the winter (Figure 1.2).

I was shocked by his answer. What made my shock even greater was that we’d experienced an extremely mild winter.

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2 The Chinese Greenhouse

Thinking that I’d like to try aquaponics, but totally turned off by the high energy costs, I immediately began to think how I could set up an aquaponics greenhouse in an even colder environment — ​east central Missouri — ​but greatly reduce, perhaps even eliminate, costly energy bills. Doing so would, of course, help improve the profitability of such an operation. The way I see it, you have to sell a heck of a lot of lettuce and spinach to pay an $800 per month heating bill. If you want to pay for labor, materials, taxes, etc., making a profit would be next to impossible.

FIGURE 1.1. Luscious greens growing in March in an Several novel ways to heat and cool aquaponics greenhouse at Today’s Green Acres in Elora, greenhouses, ideas that I’d been thinking Tennessee in the extreme southern part of the state. about for many years and some of which I’d been experimenting with, immediately came to mind. Let me start with some of my successful endeavors.

FIGURE 1.2. Conventional

greenhouses such as this one at Today’s Green Acres can cost a fortune to heat and cool, making it difficult to generate a profit and to run an environmentally sustainable business.

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16 The Chinese Greenhouse FIGURE 2.3. A passive

solar home, like a Chinese

Ceiling insulation

greenhouse, includes thermal mass, some kind of heat-­absorbing material like stone, concrete,

Insulated Shade Thermal Mass

or adobe that soaks up heat during the day and radiates that heat into the structure at night, helping

Glazing Wall Insulation

to maintain a steady temperature. From my book, The Solar House.

Floor mass

Subslab Insulation

FIGURE 2.4. Notice the

earthen wall (thermal mass) in this Chinese greenhouse.

It looks as if these walls are covered with soil cement, a mixture of cement and soil. These walls can be made with bricks, poured concrete, bin blocks, cement blocks, and rammed earth tires. The north-­facing thermal mass wall and the soil inside the greenhouse store solar heat gained during the day and release it at night. Courtesy of Dr. Sanjun Gu.

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30 The Chinese Greenhouse FIGURE 3.6. First generation

Chinese greenhouse. Although a great growing machine, this design left much to be desired.

The gently sloping south-­facing roof increases heat gain in the summer, causing overheating.

And, the large number of posts made it challenging to use even small equipment. Drawing by Forrest Chiras.

FIGURE 3.7. Second-­generation

Chinese greenhouse. Although

Insulated north facing roof

they look much the same as the first-­generation Chinese greenhouses, second generation greenhouses contained fewer uprights. This made them easier to build and easier to work in with small motorized equipment.

Thermal mass wall

Courtesy of Dr. Sanjun Gu.

Insulated north facing roof Blanket

FIGURE 3.8. Third

generation Chinese

Partial berm Full berm

South roof

greenhouse. A much simpler design whose arched metal roof eliminates the need for posts.

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118 The Chinese Greenhouse

FIGURE 7.6. Steel pipe we

use for solar arrays can be used for solar hot air systems, too.

FIGURE 7.7. Threaded

steel flange for mounting uprights. These guys are pricey but well worth the investment.

Front legs should, in most locations, be about 3 feet (0.9 meters) high.

This height will prevent snow from covering the bottom of the collector, thus compromising its performance. The distance between the ground and the bottom of the collector is determined by typical snow and wind conditions. If you’re in an area blessed with relatively light snow with little snow drifting, 2 feet (0.6 meters) should be fine. If you’re in an area that experiences relatively heavy snow or with strong winds that cause drifting, or the collector is mounted in an area prone to drifting, consider maintaining a distance of 3 to 4 feet (0.9–1.2 meters) between the bottom of the collector and the ground.

Another product you can use to build racks is Unistrut. Unistrut is much like the steel posts that highway departments use to mount road signs. Be sure to use the heavy-­duty Unistrut, known as P1000. Don’t cut corners by using the lighter product.

What’s the Proper Tilt Angle?

Solar hot air collectors can be used to generate heat during the heating season — ​late fall, winter, and early

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