| The water source heat pump is a kind of new-type energy-saving equipment in which thermal resource is groundwater with relatively stable temperature and coefficient of performance of up to 3.5- 4, the water source heat pump has widely been used in industry and civil construction as an important energy-saving equipment for heating and cooling in a lot of American-European countries in recent years and increment in its application is by 15% per year. It was a beneficial try and exploration to apply the water source heat pump to multi-span greenhouse heating in summer and cooling in winter to solve such problems, as lower thermal efficiency, higher energy consumption and environmental pollution in greenhouse heating by coal-burning boilers in our country.The greenhouse space design was depended on the demands of crop growth and management, the experimental greenhouse was established according to the designing rule of which reduced heat lost from aperture, increased the thermal resistance of covering materials, decreased the directly-heating space. The experiments were carried out under heating and cooling the greenhouse in summer and winter respectively using the water-air water heat pump during the vegetable growth. The effects of water source heat pump on heating and cooling the greenhouse and the technical and economic efficience were evaluated when the greenhouse was applied as a nursery.The result showed :(1) The experimental greenhouse with heating and cooling by water source heat pump was 6.0m wide of the structure unit span, 4.0m wide of the room, 4.0m high of the ridge , 4.5m high of the outside shade, 2.9m high of the eave, 3.0m wide of the little roof, 1.1m high of the vector of little roof. The greenhouse covered with EVA, and there were two layers of thermal screens above the vegetable plants and the knitted pad with 5.0mm thick hanging by the wall. The wind load of the single film of the small roof greenhouse was dropped by 56.29% compared with that of the big-roof. The ridge height, total height, total volume, directly heating volume, energy consumption of the small-roof greenhouse were reduced by 27.50%, 16.67%, 15.53%,50.00%, 46.5%,respectively, compared with those of the glass greenhouse introduced from Holland in the Yellow River and Huai River Plains. When areas of greenhouse were equial, the energy consumption of the experimental greenhouse was lowered by 69.1% and the coresponding heating cost was just 5.8% higher than the greenhouse introduced from Holland.(2)The light intensity declined from south to north in the greenhouse and it was relatively even in the west-east direction. The light transmission rate was 39.17% in December, and 30.48% in January which was 23.4% higher than those in the greenhouse covered with two-layer films. It was an efficient way to solve the contradiction between the lighting and energy saving using single-layer film coveringat day and 3-layers film covering at night in winter.(3) It was an efficient way to save energy by adding inner covering. The energy-saving ratio was 20.34% , 31.78% , 40.53% higher by adding the first, the second layer film, and hanging the knitted pad by the wall, respectively. Volume heating coefficient of the greenhouse was 4.37W/m3. The temperature gradient inside and outside the greenhouse was kept at 15°C when the designed heating load was 65.55w/m3. In the greenhouse, the temperature from west to east was even, the vertical temperatures were nearly the same, and there was a difference in temperature of 0.9 °C covering a distance of 12.0m from north to south at night. The air relative humidity inside the greenhouse tended to decrease with heating time of the water source heat pump. It was down to 85% during 23:00- 08:00, which was beneficial to prevent vegetable diseases.(4 )The average light transmission rate was 35.7%and 23.7% when covered with single layer film and shade +single layer film in summer. The temperature was even at east-west direction and there was 1.4 °C of temperature gradient covering 15.0m from north to south. The bigest vertical temperature gradient was LIT? from the ground to 2.2m high in the air, which was greater than that in the greenhouse using pad-fan cooling system and it did not result in difference in vegetable growth.(5) The temperature in of the greenhouse was 0.95 *C lower than outdoors when the cooling index per area of the greenhouse was designed as 144.7W/m2 and cooled by shade + forced ventilation + water source heat pump. It was 2.1°C lower when designed as 185.27W/m2. The light intensity inside the greenhouse was improved by 94.6% and the temperature was lowered by 1.5 °C while the greenhouse was cooled... |
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