10.2. History and principle of the integrated energy self-served animal and plant complementary producing system
10.3. The investigation of the problems of the integrated energy self-served ecosystem
10.4. The structure improvement of the energy self-served animal and plant complementary ecosystem
10.5. The study and test of the ventilation system in the E-W form of the ecosystem
Carbon dioxide enrichment in greenhouse has been one of the most important measures for yield promotion and quality improvement since 1960s'. It often maintains through out the entire life cycles of crops in many countries such as the U.S.A., Eastern and Western Europe and Japan, etc., in addition to cold winter when greenhouses are tightly closed. It has been conservatively suggested that doubling of the current level of atmospheric CO2 concentration, i.e., 330ppm, would result in 40-50% increase in photosynthesis for C3 plant, with yield and dry weight increase ranging from 20% and 45%, and 40% increase in primary production.
China has the largest protected cultivation area in the world, but so far there is few economical and safe CO2 enrichment methods that can be accepted by greenhouse farmers. The regular methods for CO2 enrichment, i.e., pure CO2 stored in liquid in steel containers or in frozen state (dry ice), CO2 generated from a carbonate by adding acid, and the normally used method of generating CO2 by the combustion of natural gas, butane, methane, propane or kerosene is neither easily operating nor economically feasible for Chinese greenhouses. Even the utilization efficiency of the CO2 enrichment equipments of the imported greenhouses with environmental computer-control system are rather low or even put aside. So the greenhouses are left with little CO2 enrichment except ventilation and increase the organic materials in the soil. However, by increasing farm fertilizer, the quantity and the period of CO2 production is rather limited, and it is almost invalid for the soilless cultural greenhouse. By ventilating, the maximum CO2 concentration is the atmospheric CO2 concentration, 330ppm, which is much lower than the optimal 800-1500ppm. Moreover, it will inevitably cause the heat loss in winter. In China, most greenhouses are unheated and a few are partly heated during winter, so they are usually tightly closed to avoid heat loss, and the inside CO2 concentration often falls below the photosynthesis complementary points (70-150ppm), which severely influence the crop growth; therefore it is urgently needed that a CO2 source which could meet the requirements of economy, safety and easily operating can be developed to excavate the great potentiality of production increase of greenhouse.
Exploiting CO2 produced or released by other living beings such as animals, fish, mushrooms, etc., as the sources of CO2 enrichment for greenhouse plants (vegetables, herbs, flowers, etc.) is just such a method that could meet the above requirements. Moreover, the oxygen produced by photosynthesis of plants can improve the air quality of the other living beings in turn; therefore plant and the other living beings complement to each other on a mutually beneficial basis and form a benign ecosystem. This kind of integrated complementary producing system does no harm to the environment since it doesn't need any artificial CO2 but can benefit the environment instead. There are mainly three kinds of such systems in China, i.e., plant-mushroom, plant-fish and plant-animal (livestock, poultry and cattle, etc.).
There are three ways for mushroom growing together with vegetables in the greenhouse, intercropping with vegetables, growing under the growing flat of vegetables or growing in an adjacent room which is usually behind the greenhouse. According to the experiment of Wang C.L. et al. (1993), by inter-cropping mushroom with celery, the production of celery increased by 15% and mushroom by 20%. Chen J.S. et al. reported 25% increase in cucumber production in a plant-mushroom complementary system with the mushroom house behind the solar greenhouse.
In some areas of South China, there exist several kinds of vegetable fish (or soft-shelled turtle) ecosystems which are usually related to the farm yard production in a small scale. In many free-standing or lean-to solar greenhouses in the U.S.A. and Canada, water pools are adopted to store solar energy and raise fish. Sanders D.et al. (1988) reported an solar greenhouse in which beans, cucumbers and tomatoes were growing in the sand bed while fish were living in a pool. Bill Makofske et al.(1979) developed an ecosystem in a solar greenhouse in which plants, rabbits, earthworms and fish lived together. CO2-O2; complementary and the recycle of other wastes as nutrition were carried on between plants and other beings and showed better economical and environmental effects.
Although the integrated animal and plant complementary producing system and the energy self-served animal and plant complementary ecosystem in which methane tanks are integrated have developed in China for not more than ten years, they have shown their great potentiality in increasing the productivities of both plant and animal, energy conservation and environmental improvement.
Due to the high capital cost, the traditional permanent animal buildings can only be afforded by state-owned enterprises and other large companies in a large scale. Raising animals, mainly pigs, chickens and cows, in plastic film covered houses with no supplementary heating has been experimented and extended in many regions of North China and it has turned out to be successful. The microclimate of the animal house, especially temperature, is improved considerably and the productivity increases greatly. However, by tightly closing plastic houses to minimize energy consumption in severe winter would often result in high concentrations of moisture and toxic gases (CO2, NH3, H2S, etc.), which hampers further increase of productivity.
So how to ventilate the plastic film covered animal house to modify the air quality while maintaining the minimum optional temperature becomes the most important problem .
To solve the problems of CO2 deficiency in greenhouses and the CO2 excessiveness in animal houses, in the light of complementary characteristics of animal and plant, an integrated plant and animal complementary producing system was developed.
It is a certainty that the methane tanks integrated in the animal and plant complementary producing systems become an indispensable component and increasingly show its importance. How to make the small scaled natural temperature fermentative methane tank in North China work through the severe winter has always been a difficult problem which hampered the methane extension in the countryside. Many methane tanks were going out of work because no or little methane were produced in winter, or the methane producing period was very short, or the tank was damaged by the severe climate. Constructing methane tanks in the greenhouse or the plastic covered animal house can not only assure the methane tanks work through winter but also make it possible to form a complete benign ecosystem which could produce unpolluted or low-polluted vegetables.
10.2.1 The Principle of the Energy Self-Served Ecosystem
As mentioned above, integrating the greenhouse, the animal house and the methane tank together by certain engineering measures like single-slope or tunnel greenhouse forms the system. In this system, the CO2 produced by animals serves as. the CO2 enrichment source for the greenhouse vegetables, so ventilation for CO2 complementary is no longer needed and the heat loss caused by ventilation is avoided; in addition, the sensible heat released by animal is an energy source of the system. In turn, O2 produced by plant can improve the air quality of the animal house and minimize the ventilation rate of the animal house. The methane tanks constructed under the ground of the animal house can work through the winter safely and keep a certain production of methane, and the floor will be the warm bed for the animal. The animal excreta can be put into the methane tank conveniently together with the plant waste as the fermentative material to produce methane. Timely disposal of the animal excreta reduces the production of toxic gases and also contributes to the air modification. For the small family-owned methane tanks with a volume of 6-12m3, the methane is used for cooking and lighting all the year round; for the middle or large methane tanks in farms, it can be used as the main energy resource to meet the requirements of heating, lighting and powering, etc. to varying degrees. The fermentative residue is a kind of organic fertilizer of high quality which can not only replace chemical fertilizer and farm manures to modifying the soil structure and reduce or even eliminate the continuous cropping hamper, but also reduce the physiological diseases of the plant considerably and as a result the using of the agricultural chemicals and pesticides reduce greatly and low polluted or no polluted green vegetables can be produced. Based on the above principles, a green food production demonstrational base has been founded in 1993 in Panjin City, Liaoning Province, which is also the main experimental farm of the authors. The principle is shown in Fig.10.1.
Fig. 10.1 The sketch Map of the Energy Self-Served Ecosystem
10.2.2 The History of The Energy Self-Served Ecosystem
In the year 1984-1986, Liu J.X. et al. designed and constructed a plastic film covered building for producing vegetables and livestocks in Qiqihaer City, Heilongjiang Province, as shown in Fig.10.2. According to the report, the production of both vegetables and livestocks (or poultry) were increased greatly, with 25% increase in cucumber accompanied by 40-60 days prolonged life period in early spring and late autumn, and 11% increase in egg production, 19% in milk production, and 40-80% weight gain increase in fattening pigs in winter compared with the traditional outdoor raising. The extension of this system was very limited because there exist some problems which need further studying.
In the year 1986, an integrated plant-animal-methane system (Fig.10.3) was put into work in Dandong City, Liaoning Province in a farmer's courtyard, and it also showed better economical and environmental effects.
Fig. 10.2 A Plant-Animal Complementary System in Qiqihaer City, Heihongjiang Province
Fig. 10.3 An integrated plant-animal-methane system in Dandong City, Liaoning Province
Fig.10.4 shows another form of plant-animal-methane mixed producing system which was developed in 1986-1989 in Dawa County, Liaoning Province by Wang J.P. et al. and has gained its popularity in many areas of North China in the past four years. Located on 41.2 degrees north latitude with an average temperature of -10.5 °C in January, it has reported a favorable microclimate inside the greenhouses and the animal houses and a satisfactory production elevation by the system . According to the experiment on a typical system in Dawa County, Liaoning Province in Nov., 1992-Apr., 1993, with little or no supplementary heating besides solar energy, the minimum temperature in the greenhouse was 8-10 °C except two or three days around 5°C in extreme climate, so it can ensure vegetable production in the winter. The floor temperature of livestock house was above 10 °C owing to the methane tank in which the fermentative material had a minimum temperature of 12-15 °C. The yield of foliage vegetables (celery, chives, etc.) increased by 40%, the fruit vegetable (cucumber, tomato, eggplant, etc.) by 30-40% and daily weight gain of fattening pig increases by 40%. The methane could supply energy for cooking, lighting of the family all the year round and sometimes can heat the greenhouse temporarily. The use of agricultural chemicals reduced significantly. According to the investigation of an ecosystem in Xinmin City, Liaoning Province, no diseases happened in the winter celery from Nov. 1993 to Mar.1994, so no chemicals was used.
Another vegetable and animal complementary system which has the similar structure of Fig.10.2 has been developed in 1989 in Nei Mongol Province, as shown in Fig.10.5. The production of vegetables increased by 17-20%, the production of egg chicken is normal, the survival rate of the lamb increased by 20%.
In addition, in Huanghai area of Middle China, a few integrated animal and plant complementary systems of varying forms have been employed. There were a few reports on the plant and animal complementary producing systems in Russia, Bulgaria and the U.S.A.. Russian researchers designed a comprehensive solar building to produce vegetables and raising poultry at the same time. The building consists of a greenhouse and a poultry house behind the greenhouse and they are separated by a transparent partition wall. The energy equilibrium of the system was analyzed but nothing mentioned about CO2 and O2 transference between the two parts and the productivity promotion of plants and chickens. The research workers of the Bulgaria made the greenhouse and the poultry house adjacent to each other, which reduced the cost of vegetable and the chicken by one third.
Fig. 10.4 A Plant-Animal-Methane Mixed Producing System in Dawa County, Liaoning Province
Fig. 10.5 The Vegetable-Animal Complementary System in Nei Mongol Province
Generally speaking, the animal and plant complementary system and the energy self-served animal and plant complementary system have just been developed mainly in China in recent years and the theoretical and the experimental research has only been carried out since 1992. Due to the complicated management of the system, it is not fit for the requirement of large scaled intensive production, so the system has been rarely studied in the developed countries. However, it has great potentiality in increasing the productivities of both plant and animal, energy conservation and improving the environment. If the research work can make it fit for the requirement of intensive production, its economical and social significance would be noticeable.
On account of the short history of the system and lacking of further experimental and theoretical studies, many problems are to be solved, mainly as follows.
a. The proportion between various livestocks and the growing area of different vegetables has neither theoretical bases nor experimental studies and is in a state of random. In the system shown in Fig.10.2, the ratio between greenhouse and the animal house is 5: 4, while in the system shown in Fig. 10.3 the ratio is 4-7: 1, so the CO2 concentration is much different in various systems. In the system shown in Fig.10.2, at 07: 30 a.m., Nov.28th, 1985, the CO2 concentration was 12400ppm, and at 13: 30 p.m. the same day, it is 13400ppm. It is necessary to notice that over high CO2 concentration may lead to inhibition on plants or even kill the plants and it is harmful to the livestock as well. Besides, it indicates a rather high toxic gases of NH3, H2S, etc..
The CO2 concentrations in the systems shown in Fig. 10.3 are also much different in accordance with the ratio between the greenhouse and the animal house, the ventilation management and the quantity of farm fertilizer applied in the greenhouse, etc..
Fig.10.6 is the CO2 condition from 9:00 a.m., 9th to 9:00 a.m. 10th of Jan. 1994, in a typical system with a area ratio of greenhouse and animal house 7: 1, in the severe winter with the outside temperature -15-6°C in Weilinzi village, Xinmin City, Liaoning Province, and the system was tightly closed. The CO2 concentration was much lower than 1000ppm from 10:00 a.m.-16:00 p.m. for most part of the greenhouse and the minimum was 180ppm, the maximum was 2667ppm. Fig.7 is the CO2 condition from 8:30 a.m. 8th to 14:00 p.m. 9th of Jan., 1994, in another system with an area ratio of 2: 1 in the same village. The CO2 concentration was rather high most of the day with the max. 7663ppm in the morning and the min. 1552ppm in the afternoon; therefore, it is necessary to study on the proper proportion of animal and plant to provide an optimal CO2 concentration for the plant while avoiding CO2 from too high or too low.
Fig. 10.6 The CO2 Condition in An Energy Self-Served Ecosystem
b. There exists a great gradient of CO2 concentration from the pig house to the end of the greenhouse all the day in a tightly closed system, especially in the daytime when the photosynthesis of plant is high. As shown in Fig.10.6, the CO2 concentration in pig house was 2600ppm, but it was only 180ppm in the east end of the greenhouse at 14: 00 p.m.. So suitable ventilation measures should be studied to carry CO2 from the animal house to the greenhouse and achieve an uniform CO2 concentration in the greenhouse.
Fig. 10.7 The CO2 Condition in Another Energy Self-Served Ecosystem
c. The valid CO2-O2 complementary term of the system is relatively short, which is from Nov. to the middle of Feb. in Liaoning Province when the average ambient temperature is lower than -8°C and the animal house is little ventilated. Fig.10.8 shows the CO2 concentration in a system in Qingshui Farm, Dawa County, Liaoning Province. The CO2 concentration of the animal house was lower than the greenhouse all the day due to the high ventilation rate by the door and the big hole in the plastic film which covered the animal house when the ambient temperature was higher than -8° C and the plastic film covered animal house temperature was higher than 24°C and must be ventilated, this lead to a low CO2 concentration in the animal house. As a result, the CO2 in the greenhouse was even higher than the animal house and some CO2 were lost through the vents in the partition wall and lead to a reversed CO2 concentration gradient, thus the CO2-O2; complementary totally ceased to be effective.
As mentioned in the first part, farm fertilizer is the main CO2 resource of the greenhouse. But too much farm fertilizer will produce much CO2 in a term and may result in a reversed CO2 concentration in the system, especially when the plant is in its early stage. Fig. 10.9 shows the CO2 concentration in a system over fertilized, and therefore fertilizer management in the system should be regulated to promote the efficiency of the system.
Fig. 10.8 The CO2 Condition in A Energy Self-Served Ecosystem With the Animal House Over ventilated
Fig. 10.9 The CO2 Condition in Another Energy Self-Served Ecosystem With Much Fertilizer
d. The structures of the system need to be improved and standardized. There are mainly two forms of the system, one is shown in Fig.10.2 and Fig.10.5 and the other in Fig.10.4. For the former system, the research should be concentrated on the environmental management to ensure a suitable CO2 concentration, temperature and moisture for both plant and animal, and to integrate the methane tank in the system. In fact, the structure form of the later is exactly the same as the popularized plastic film covered single slope solar greenhouse in China, which is suitable for growing vegetables and livestocks through winter, but it is not fit for the livestocks in warm whether. Further more, it is limited on a small scale of 120-200m2 in the courtyard and should be make it suitable for large scale production.
e. There are contradictions in the environmental requirements of animals and plants such as temperature, moisture and toxic gases, which need to be coordinated and prolong the CO2-O2 complementary period as long as possible.
Shown in Fig.10.10, a N-S (North-South) form of the system was designed and has been in construction in the Green Food Producing Demonstrational Base of Panjin City, Liaoning Province and will be put into to use in the autumn of 1994. To satisfy the requirement of separation and connection of the two parts, the greenhouse is placed in the south side and the animal house or the mushroom house in the north side separated by a wall with windows on it. Ventilation should be well managed to get rid of excessive CO2. Under the ground of the north side there are several methane tanks paralleled at a distance of 20m which are also the natural temperature fermentative methane production systems used to dispose the animal excreta and the methane will be the main energy source of the farm. This form is fit for the animal-oriented producing system.
Fig.10.11 shows another N-S form which is reconstructed from a livestock house by adding an attached solar greenhouse to a livestock house, and this form is fit for the reconstruction of the livestock house for conserving energy and improving the environment and promoting the profits.
Fig. 10.10 The N-S Form of the Ecosystem
Fig. 10.11 The Ecosystem of N-S Form With Solar Greenhouse Attached To A Livestock House
Fig.10.12 are three forms of the E-W (East-West) forms of the energy self-served complementary systems improved on the system shown in Fig.3, and it is fit for the plant-oriented producing system, (a) and (c) forms had been constructed and put into use in Nov., 1993 in the same demonstrational base. The CO2 distribution in the greenhouse is uneven. So compulsive ventilation should be employed as discussed above. E-W form can also be used to produce mushroom and plant, which has been carried on in the same demonstrational base. The temperature environment is superior compared with the N-S form for greenhouse.
Fig. 10.12 The E-S Forms of the Ecosystem
As shown in Fig.10.12, a ventilation system is installed in the E-W form of the energy self-served complementary system to get an even distribution of CO2. The ventilation system should be designed on the basis of the equilibrium of CO2 gain and loss in the system consisted of animal house and greenhouse. The CO2 balance equation of the greenhouse is as follows.
AsCs+ ApCb+ Ca+ Ce=ApPn+ Cv
Cs is the CO2 produced by the soil, kg(CO2/m².s;
As is the area of the greenhouse, m2 ;
Cb is the CO2 produced by the respiration of the plant, kg(CO2)/m²s;
Ap is the plant area, m2 ;
Cv is the CO2 from the ambient by ventilation, kg (CO2) /s;
Cais the CO2 from the animal house by ventilation between the two parts, kg (CO2) /s;
Ceis the CO2 from the other resources, such as workers, heating etc., kg (CO2) /s;
Pn is the CO2 consumed by the photosynthesis of the plant, kg, (CO2) / m².s.
Different mathematical models for simulating Pn can be built to different plants and a changing Ca can be computed on this dynamic mathematical models. However, a changing ventilation system is not practical to a practical producing system. So the flow rate of the ventilation system has been designed on the CO2 balance of the animal house with a simplified model shown in Fig.l0.13 (a). On the assumption that the ventilation to the ambient of the whole system is once an hour and the interior ventilation system which consists of a fan and a ventiduct made of plastic film is only for carrying CO2 from the animal house to the greenhouse evenly. Fig.10.13 (b) shows the CO2 gain and loss in the animal house. Then the equation of the CO2 balance is the following:
dv=CtQ*dt+ p* dt-Q* V/Mo* dt
v is the volume of the CO2 at % moment in the animal house, m3;
Vo is the initial CO2 volume in the animal house, m3;
Ct is the CO2 concentration that enters the animal house
through the air return vent, m³(CO2)/ m3;
Q is the flow rate of the fan, m³/s;
Mo is the volume of the animal house, m3;
p is the CO; produced by the animals in a unit time, m³/s.
Fig. 10.13 CO; Gain and Loss in the Animal House
Ct is a variable depending on the CO; concentration in the greenhouse and the photosynthesis of the plant. To simplify the problem and get a general conclusion, it is sensible to take the Ct as a constant C. Then we get a v as follows:
V= (Vo-(Mo/Q)* (C* 0+ p))* exp (-(Q/Mo)* %)+ (Mo/Q)* (C* Q+ p)therefore, the CO2 concentration in the ventiduct Cd (in m³(CO2)/ /m3) is
Cd=V/Mo = (Vo/Mo-(C+ p/Q))* exp (-(Q/MoVt)+ (C+ p/Q)
From this equation, the following conclusion can be deduced:
- when t=0, Cd=Vo/Mo;
- when t=, Cd=C+ p/Q. This indicates that after the ventilation system works for long enough time, Cd will mainly depend on the CO2 produced by the animal, i, e, the number of the animal, and the CO2 returned from the greenhouse. By applying this equation to a typical E-W system, some instructive conclusion can be drawn.
The volume of the animal house is 6* 6* 2 (the average height) m3, the diameter of the fan is 250mm and the flow rate is 0.19m³/s. The pig of 100kg live weight exhales 1.539* 10-5 m3 (CO2) /s. The ventilation rate of the animal house at night, before the fan works and the greenhouse uncovered, is once every one hour. Then Vo is 5.55404m3 when there are 10 pigs in the animal house, or Vo=1.10808m3 when there are 20 pigs. Cd, the air returned to the animal house is assumed to be 330ppm. Then the CO2 concentration in the ventiduct for the two conditions is separately shown in Fig.10.14.
Hence the CO2 transferred to the greenhouse is nearly independent of the flow rate of the fan but merely dictated by the animals and the CO2 concentration in the greenhouse.
Fig. 10.14 The CO2 Concentrations in the Ventiduct with the Simplified Model
This ventilation system has been put into use in the system shown in Fig.7.10. in Xinmin County, Liaoning Province, in an animal and plant complementary system which has a length of 120m, and a mushroom and plant complementary system which has a length of 60m in the Green Food demonstrational base of Panjin City. Fig. 10.15 is the CO2 distribution condition in the system shown in Fig. 10.7.
This ventilation system works well in the severe winter when the system is tightly closed to minimize the heat loss. To prolong the CO2 enrichment term by the animal, the ventilation of the whole system to the outside should be scientifically managed.
Fig. 10.15 CO2 Distribution in the System Shown in Fig.10.7 with the Ventilation System Working
The operation of the ventilation system is divided into three periods. The first period is ventilating in the system between the two parts as shown in Fig.10.16 (a) in the severe winter when the ambient temperature is very low and the system needs little ventilation to the outside. The ventilation could be carried from uncover the thermal insulating cladding material at about 8:00-8:30 a.m. to cover the cladding at about 4:00-4:30 p.m.. This period lasts for less than two months around January. When the livestock house temperature can not to be kept below 24 °C when the thermal cladding is all uncovered in the day time but the greenhouse temperature is not more than 30°C and need not to be ventilated, then comes the second period. In this period, the contradiction is ventilating to the outside to cool the animal house and reducing ventilation for the purpose of accumulating CO2 to enrich CO2 in the greenhouse. Because fattening pig needs a little light which is only enough for eating and acting, the measure then is to partly or even totally cover the animal house with the thermal insulating cladding in daytime of a sunny day to greatly reduce the solar energy gain of the animal house and as a result the temperature of the animal house can be kept at the optimal temperature and the ventilation system can be managed as the first period. Or, ventilate the animal house properly with the outside according to the CO2 requirement of the plant. The third period is to ventilate the system with the outside as shown in Fig.10.16 (b) in the moderate climate when the average ambient temperature is higher than -8°C and the greenhouse temperature is higher than the optimal temperature and also need to be ventilated either. So the CO2-O2; complementary system can be effective for six to seven months in a year from November to the end of April.
Fig. 10.16 Ventilation Management of the E-W System
Another ventilation system has been put into operation in another village, Xijiao Village of Xinmin County, Liaoning Province since Feb.15th, 1994. Shown in Fig.10.17, the ventilation system combines the underground heat exchange system and the air exchange system of the animal house and the greenhouse together. Since the ventilation rate required by CO2 transference from the animal house to the greenhouse is much lower than that of the requirement of heat exchange, so the system was designed according to the requirement of the later. Since the principle of the underground heat exchange system has been expounded in Chapter 9, here we just discuss the effect of the system on the environmental modification and CO2 transference. The interior and ambient air temperature, the soil temperature at the depth of 15cm, relative humidity in the tested greenhouse and the compared greenhouse and the CO2 concentration in the tested system during 8:00 a.m. 25th-8:00 a.m. 27th in Feb. 1994 were measured and the result is shown in Fig.10.18.
From the result, we can get three conclusions. (a) The soil temperature at the depth of 15cm in the tested greenhouse is averagely 6-7° C higher than the compared greenhouse and it is similar to the soil temperature of the compared greenhouse of the 15th Mar. which indicate that it can be 20 days advanced than the others. (b) The day temperature can be reduced by 2-3°C and the night temperature can be increased by about 2°C. (c) The CO2 enrichment can be applied in all the winter and the early spring and late autumn, from Nov. to Apr., but the ventilation system should be properly operated according to the microclimate of the system and the type and the life of the plant. There are also mainly three kinds of operational methods of the ventilation system according to the climate.
Fig. 10.17 A E-W Ventilation System Combines the Underground Heat and Air Exchange System
The first operational method is to control the fan when the temperature is higher than the set maximum or lower than the set minimum and it is used in the severe winter when the ambient temperature is lower than -8°C and the inside temperature lower than 24 °C when the ventilation rate of the system is minimized. The second method is similar to that of the second period of the W-E system and the management of the ventilation system is alike. The third method is used in the moderate climate of early spring or the late autumn and early winter when the maximum greenhouse temperature higher than 28-30 °C while the livestock house temperature is higher than 24 °C and need to be ventilated to get rid of the excessive heat. In this period, the air temperature and the soil temperature are all enough or higher than the optima and the livestock house also need to be ventilated to keep the temperature lower than 24 °C. Since the thermal insulation curtain has been adopted and the minimum temperature can be kept above 12-15°C, the heat exchange system is no longer needed. Thus, the effect of the ventilation system is to enrich CO2 in the greenhouse. For the ambient temperature is still low and the livestock house still need to keep a low ventilation rate at night so the CO2 concentration is still high in the morning, so the fan can be start for a few minutes in the morning to transfer CO2 from the livestock house to the greenhouse. Then for every three hours the livestock house is closed for half an hour or an hour to accumulate CO2 and then start the fan for a few minutes to transfer CO2 to the greenhouse. The vent in the greenhouse should to be as far as possible from the fan to make the full use of CO2. The fan can work continuously to transfer CO2 to the greenhouse with the air entering vent at the end wall of the livestock house and the ail exhausting vent at the greenhouse near the livestock house, meanwhile both the livestock house and the greenhouse is cooled, but the power consumption will be high.
Fig. 10.18 The Miroenvironment Factors of the System
The ventilation system used in the W-E system can be integrated in this system to transfer CO2 continuously and reduce the power consumption in the third period of ventilation management.
The integrated plant-animal (or fish, mushroom) complementary system is an effective, practical and economical way to provide CO2 enrichment for greenhouse vegetables in China and other developing countries.
By using this system, the ventilation rate of both animal house and the greenhouse in winter can be greatly reduced and the heat loss caused by ventilation can be minimized and hence the microenvironment of the two parts can be improved considerably. Moreover, by adopting the structure form of plastic film covered single slope solar greenhouse with thermal insulation curtain, which is the most energy conservative greenhouse, this system can get a high energy conservative efficiency.
By integrating methane tanks in the plant-animal complementary system, not only the methane tank can work through the winter safely and ensure the energy provision of the system but also the animal waste can be disposed timely, which greatly reduced the toxic gases in the animal house and further more the fermentative wastes is a high quality fertilizer which can replace chemical and the other farm fertilizers and promote the disease resistance of plant So with this system, the low pollutant or non pollutant vegetables can be produced. This is of great replace chemical and the other farm fertilizers and promote the disease resistance of plant. So with this system, the low pollutant or non pollutant vegetables can be produced. This is of great significance for China because the water culture in large scale is not practical in the time being and a long term in the future.
Based on the principle of the system, energy self-served green food producing base can be built either by newly constructing or by reconstructing the already existed solar greenhouse bases or the animal houses.
Owing to the short history and lacking of research on the system, there exist many problems that need to be solved. In the present paper, some improved structure forms of the system are developed and put into use.
The CO2 conditions in the practical animal and plant complementary systems have been investigate and the problems of uneven distribution of CO2 in the greenhouse and the short effective term of the CO2 enrichment which no longer than two months are revealed. Several kinds of ventilation systems in the W-E system have been designed and shows great effect in providing an optimal and evenly distributed CO2 for plant. By properly operation of the ventilation system, the CO2-O2 complementary term can be prolonged to six to seven months of a year.
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