A Chinese greenhouse is an energy-efficient greenhouse that requires no or very little heating to grow warm-season plants year-round, even in areas with extreme temperature drops.
A standard glass greenhouse is an energy-hungry structure. During the winter months, you’ll need to heat the structure and during the summer you’ll need to find a way to keep it cool, or your plants will cook. Even a triple-glazed glass greenhouse loses heat quickly in the winter. However, a Chinese greenhouse is a passive solar greenhouse that stays warm in the winter and comfortable in the summer. The design has the ability to store the sun’s energy.
A Chinese greenhouse uses thermal mass and insulation to stay warm so you can grow crops year-round using only the power of the sun, even if the temperature has dropped below freezing. China has built thousands of passive greenhouses in the last decade to meet the country’s food needs by growing crops year-round with little or no energy use. To date, the Chinese have constructed passive solar greenhouses across over two million acres.
I first became fascinated with Chinese passive solar greenhouses in Oregon where they were growing in popularity throughout the Willamette Valley. Also, many families who want to live off-grid have turned to the design because they can grow warm-season vegetables year-round without any energy needs in most locations.
Understanding What is a Chinese Solar Greenhouse?
Let’s examine what makes the Chinese solar greenhouse so special compared to other greenhouses around the world.
1. Design of the Chinese Greenhouse
A Chinese passive solar greenhouse features three walls on the east, west, and north sides of the structure that are constructed using brick or clay. The south side of the greenhouse is fashioned from a transparent material such as plastic film to let light into the structure and onto the plants.
During the day, the design of the Chinese greenhouse captures the sun’s energy and holds it within the confines of the thermal mass of the walls. When night arrives, the walls start to release the heat to keep the plants warm even if the temperature drops to below zero degrees Fahrenheit.
The bulky walks not only heat the greenhouse space but also block out the winds which can quickly cause heat loss inside the structure if not sheltered.
When sunset arrives, an insulating sheet fashioned from canvas, straw, or pressed glass, is rolled down over the plastic to further provided insulative value inside the greenhouse.
The temperature inside a Chinese passive solar greenhouse stays over 45 degrees Fahrenheit even on the coldest nights.
2. Incentive Programs Fuel the Chinese Greenhouse Craze
Everywhere you look in China, locals are building Chinese greenhouses. The Chinese government launched an incentive program that focused on making the passive solar greenhouse the main component in the country’s food production throughout Northern and Central China. Nowadays, greenhouses span a fifth of the area covered by greenhouses.
Many people are surprised to learn that Chinese greenhouses are not new. In fact, the first one was built in 1978 using transparent plastic film which is much cheaper than glass, lighter, and does not need a costly weight-bearing frame as glass panels do. The construction of a Chinese greenhouse is wonderfully affordable which has fueled the trend.
The Chinese greenhouse design has changed since the 1970s. Today’s greenhouse is much taller and deeper than earlier models. The design lets the sunlight reach throughout the structure and further reduces any temperature fluctuations.
3. Insulative Properties of a Passive Solar Greenhouse
The insulation used in Chinese passive solar greenhouses has improved substantially. Farmers are now using synthetic insulation blankets which are ideal for moist environments. They are replacing the straw mats in such areas because the straw becomes very heavy in the humidity. When wet, the straw has a low insulative capacity.
Some modern designs have ventilation and insulation systems which include automatic roll-up solar blankets. The blanket rolls down automatically when the sun sets.
Another popular option for a modern Chinese greenhouse is a double roof or the installation of reflective insulation. Modern heavy plastic sheeting offers a longer lifespan than previous types.
4. Efficiency Considerations
The leading factors that make Chinese greenhouses so popular include not only the design but also the latitude and the local climate. In order for plants to survive at 42 degrees north, the greenhouse needs a reflective insulation layer to keep the inside temperature above freezing. With such as device, the interior temperature usually stays above 50 degrees Fahrenheit. Passive greenhouses built in southern locations do not require updated insulation.
5. Chinese Greenhouses in the Far North
A Chinese passive solar greenhouse does require some sort of additional insulation and heating to keep the plants warm the further north the greenhouse is built. In regions far north, the roof should be angled. Ensure the slant is perpendicular to the rays of the sun when the sun is at its lowest.
In Manitoba, a 23 by-98-foot Chinese greenhouse was constructed at a latitude of 50 degrees north. The greenhouse has an R-20 fiberglass insulation and an insulative cotton blanket that featured an R-value of 7. In February when the temperature dips down to minus 20 degrees the interior of the Chinese greenhouse averages 32.4 degrees F. In extreme weather, added heat becomes a necessity.
6. Energy Efficiency of a Chinese Greenhouse
The energy savings of a Chinese greenhouse is exceptional compared to a glass greenhouse. Even the greenhouse that was built in Manitoba only required 5.4 British thermal units (Btu) per hour per square foot to maintain the interior greenhouse temperature at 50 degrees Fahrenheit.
A glass greenhouse of equal proportions uses a 125 to 155 kW. This makes the Chinese greenhouse 43 times more energy efficient than a glass model during the most extreme winter weather.
Energy efficiency does vary and depends on the amount of sunlight in the area. Even though Brussels and Manitoba sit at the same latitude, a Chinese solar greenhouse in Brussels will not be as energy efficient as the greenhouse in Manitoba. Manitoba enjoys 1.5 times more sun than Brussels so is more energy efficient in that location.
Growers can also achieve a great deal more energy efficiency if they take additional insulative steps such as placing water storage tanks along the greenhouse’s north wall within the structure. The tanks will capture solar energy during the day and then release the heat at night. You can also create an earth berm along the north, west, and east walls for greater energy efficiency in extreme weather locations.
7. Greenhouse Space Considerations
Even though a Chinese passive greenhouse is wonderfully energy efficient there are problems. A Chinese greenhouse grows around two to three times lower crops per square foot than a fully glazed glass greenhouse. In the confines of a Chinese greenhouse, you can grow around six pounds of tomatoes and cucumbers per square foot but in a glass greenhouse, you can double that number to 12 pounds. To achieve the same production level, you will need to have two to three times more area to produce on the same level as the glass greenhouse.
8. Problems of a Chinese Greenhouse
One major problem with Chinese greenhouses is the lack of CO2. If you want a bountiful harvest then the CO2 level should be at least three times higher than the levels outside the greenhouse. CO2 is gained as a byproduct of the fossil fuel heating systems used within the greenhouse. In a Chinese greenhouse, you must find some other source of CO2 so your plants can flourish.
Some farmers will raise chickens, pigs, or fish to obtain CO2. They create a symbiotic relationship. The animals produce CO2. Their manure can also help heat the interior of the greenhouse. In exchange, the plants produce oxygen for the animals to thrive. Combining production aspects such as vegetables, eggs, milk, and meat gives farmers an even greater yield. The entire process comes full circle. You do not need to house the animals in the greenhouse. Simply use the manure to create heat in the greenhouse. Compost can easily heat a greenhouse that has adequate insulation. Using manure for heat also helps increase the CO2 levels in the air. Even the soil experiences increased CO2 for optimum plant growth and fertile soil.
Another problem with a Chinese greenhouse is the high indoor humidity. When there is no adequate ventilation, the humidity can climb to over 90% which can cause diseases to occur if you are not diligent about proactive disease management.
The last disadvantage of the passive solar greenhouse design is that plants often do not receive sufficient light to flourish in the winter months. Luckily, you can use energy-efficient LED light technology to help plants flourish during the dark days of winter. Even if you have to turn to lighting, you’ll still save a considerable amount with the Chinese greenhouse design and its many benefits.
9. Cost Consideration of a Chinese Greenhouse
A passive Chinese greenhouse does cost more to initially build than standard greenhouses. However, the payback on investment is substantial due to the impressive energy savings. Within the first few years, you’ll experience energy savings which will quickly pay back your initial investment so you can enjoy the profits of the revolutionary greenhouse design.