Apa Itu Greenhouse?Green house adalah sebuah bangunan kontruksi yang berfungsi untuk menghindari dan memanipulasi kondisi lingkungan agar tercipta kondisi lingkungan yang dikehendaki dalam pemeliharaan tanaman. Green House disebut juga "Rumah Kaca", karena kebanyakan green house di buat dari bahan yang tembus cahaya seperti kaca, achrilic, plastik dan sejenisnya.

Dengan greenhouse beberapa kondisi lingkungan berikut dapat dihindari, antara lain:1. Perubahan suhu dan kelembaban yang fluktuatif2. Akibat buruk yang di timbulkkan dari radiasi sinar matahari jenis sinar ultra violet dan sinar infra red3. Kekurangan air pada musim kemarau dan kelebihan air pada musim penghujan.4. Hama dan binatang pengganggu serta penyakit tanaman seperti jamur dan bakteri.5. Tiupan angin kencang yang dapat merobohkan tanaman dan merusak daun6. Tiupan angin dan serangga yang dapat menggagalkan proses penyerbukan bunga7. Akibat buruk dari polusi udara

Kondisi lingkungan yang dapat di ciptakan dengan adanya greenhouse, antara lain:1. Kondisi cuaca yang mendukung pertumbuhan tanaman2. Suhu , kelembaban dan intensitas cahaya matahari dapat di atur sesuai kebutuhan3. Penyiraman tanaman dapat diatur berkala4. Kebersihan lingkungan dapat dijaga dengan baik sehingga terhindar dari penyakit tanaman.5. Kenyamanan terhadapa aktivias produksi dan pengendalian mutu.6. Udara yang bersih dari polutan7. Insklusi (terlindung) terhadap gangguan binatang/hama dan serangga penggangu.

Manfaat dan Fungsi GreenhouseBanyak manfaat & kegunaan dari greenhouse, antara lain:1. Sebagai sarana pembibitan tanaman2. Tempat karantina tanaman   Tanaman yang sedang sakit, terkena hama atau ketika dalam proses tranplantasi (pemindahan tanaman) perlu dirawat dan dipelihara secara intensif atau di karantina. Hal ini dapat dilakukan di dalam green house untuk mendapatkan perawatan khusus dan mengindari kontaminasi terhadap tanaman lain.3. Sebagai wahana budidaya tanaman tertentu   Jenis tanaman tertentu menghendaki pemeliharaan khusus karena tanaman tersebut hanya dapat hidup dan berproduksi pada kondisi khusus. Misalnya beberapa jenis holtikultura (buah, sayur dan bunga), tanaman herbal dan tanaman hias. Dengan adanya green house kondisi lingkungan dapat di manipulasi sesuai dengan kebutuhan tanaman tersebut sehingga produksi dapat berjalan dengan baik, meminimalisir kegagalan produksi dan meningkatkan produktifitas.4. Sebagai sarana Agro Wisata   Green house banyak di jadikan sebagai sarana agro wisata di perkotaan yang memadukan keindahan taman dan fauna seperti angsa, burung dan lainya. Kenyamanan pengunjung dapat di ciptakan dan binatang dapat terjaga dengan baik.5. Sebagai Agromart/AgroshopPenjualan tanaman seperti tanaman hias tidak mungkin dilakukan didalam gedung yang tertutup yang tidak ada cahaya matahari. Dengan adanya green house dapat diciptakan kondisi yang nyaman bagi para pengunjung dan pemeliharaan tanamanpun lebih mudah dilakukan.

       Karena dengan Greenhouse faktor yang berpengaruh seperti suhu, sinar matahari, kelembaban, danudara

disediakan, dipertahankan dan didistribusikan secara merata pada level yang optimal. Untuk tujuan ini

disyaratkan dalam pembuatan greenhouse adalah mempunyai  transmisi cahaya yang tinggi, konsumsi

panas yang rendah, ventilasi yang cukup dan efisien, struktur yang kuat.

                   Greenhouse untuk daerah tropis sangat memungkinkan dan mempunyai banyak keuntungan dalam

produksi dan budidaya  tanaman. Produksi dapat dilakukan sepanjang  tahun, dimana produksi dalam lahan

yang  terbuka tidak memungkinkan karena adanya hujan yang sering dan angin yang

kencang. Strukturgreenhouse di daerah tropis sering menggunakan sisinya untuk melindungi dan mengontrol

suhu denganmenggunakan ventilasi alamiah maupun  terkontrol dengan dilapisi jala (screens) yang mampu

mengurangi serangan serangga dan hama.

*** Sumber: http://www.gemaperta.com

In the electric power industry, megawatt electrical (MWe[17] or MWe[18]) is electric power,

while megawatt thermal or thermal megawatt[19] (MWt, MWt, or MWth, MWth) refers to thermal

power produced. Other SI prefixes are sometimes used, for example gigawatt electrical (GWe).

"watt electrical" and "watt thermal" are not SI units,[20] The International Bureau of Weights and

Measures states that further information about a quantity should not be attached to the unit

symbol but instead to the quantity symbol (i.e.,Pthermal = 270 W rather than P = 270 Wth) and

regards these symbols as incorrect.[21]

For example, the Embalse nuclear power plant in Argentina uses a fission reactor to generate

2109 MWt of heat, which creates steam to drive a turbine, which generates 648 MWe of electricity

(a numerical energy conversion efficiency of 648/2109 = 0.307, or 30.7%). The difference is due

to the inefficiency of steam-turbine generators and the limitations of the theoretical Rankine

cycle.

Definition<p>The watt (symbol: W) is the SIunit of power defined as one joule of energy transferred or dissipated in one second (J/s). Its expression in terms of SI base units is m2·kg·s-3.</p><p>The watt is a common unit of electrical power, in which case one watt of power is expended when oneampere of direct current flows through a resistance of one ohm.Watt electrical (abbreviation: We) is a term that refers to power produced as electricity. SI prefixes can be used, for example megawatt electrical(MWe) and gigawatt electrical (GWe).Watt thermal (abbreviation: Wt or Wth) refers to thermal power produced; again SI prefixes can be used, for example megawatt thermal (MWt) and gigawatt thermal(GWt). </p><p>For perspective, the approximate heat dissipation from an adult human is around 100 Wt. A typical kitchen microwave will be rated around 1000 W (1 kW) and a typical automobile's power output rating will be around 150 kW. </p>

History<p>The unit is named for James Watt (1736-1819), the Scottish inventor, instrument maker and mechanical engineer, renowned for his improvements on the steam engine. </p>

Conversions<p>1 watt = 1 joule/second1 watt = 1 volt ampere1 watt = 1·107 ergs/second1 watt = 2.39006·10-4 kilocalorie (thermal)/second

1 watt = 9.48452·10-4 Btu (thermal)/second</p>

Megawatts electric

Figure 1. The energy input in a heat engine is measured as MWt, and the output energy obtained

as electricity is measured as MWe.[1]

Megawatts electric or MWe is one of the two values assigned to a power plant, the

other being megawatts thermal or MWt. Megawatts electric refers to

the electricity output capability of the plant, and megawatts thermal refers to the input

energy required.[2] Power plants are assigned two values as most are heat engines,

and therefore can't turn 100% of their input energy into electricity. This idea is closely

related tomechanical power, how much power an engine can put out.

For example, a coal-fired power plant rated at 1000 MWe and 3000 MWt will require

supply of 3000 MW of heat from burningcoal for every 1000 MW of electricity it

produces. That's approximately 100 kg of coal every second. This means that it puts

out 2000 MW of waste heat, usually into a large body of water or the atmosphere.

1000 MWe for every 3000 MWt leads to an efficiency of 33%, which is fairly standard

for older plants.

It is good to understand the difference between the two numbers, because, in the

event of a proposed project, you can understand how efficient a plant will be. The

closer a power plant's MWt and MWe ratings are, the more efficient it is.

It is worth noting that not all power plants are heat engines,

specifically hydroelectricity, photovoltaic electricity andwind power are not heat

engines so they have no megawatt thermal rating. These flows of energy have other

types oflosses associated with them though. Likewise fuel cells aren't heat engines,

but are not able to convert energywithout losses.

References

1. Jump up ↑  Made internally by a member of the Encyclopedia team

2. Jump up ↑  R. Wolfson, "Energy and Heat," in Energy, Environment and Climate, 2nd ed. New York, U.S.A.:

Norton, 2012, pp. 86-87

Megawatts thermal

Figure 1. The energy input in a heat engine is measured as MWt, and the output energy obtained

as electricity is measured as MWe.[1]

Most power plants are heat engines, and therefore can't turn 100% of their input

energy into electricity. Because of this, there are two values assigned to a

powerplant: megawatts electric (MWe), and megawatts thermal (MWt). The former

refers to the electricity output capability of the plant, and the latter refers to the input

energy required.[2]

For example, a coal-fired power plant rated at 1000 MWe and 3000 MWt will require

supply of 3000 MW of heat from burningcoal for every 1000 MW of electricity it

produces. That's approximately 100 kg of coal every second. This means that it puts

out 2000 MW of waste heat, usually into a large body of water or the atmosphere.

1000 MWe for every 3000 MWt leads to an efficiency of 33%, which is fairly standard

for older plants.

It is good to understand the difference between the two numbers, because, in the

event of a proposed project, you can understand how efficient a plant will be. The

closer a power plant's MWt and MWe ratings are, the more efficient it is.

It is worth noting that not all power plants are heat engines,

specifically hydroelectricity, photovoltaic electricity and wind power are not heat

engines so they have no megawatt thermal rating. These flows of energy have other

types oflosses associated with them though. Likewise fuel cells aren't heat engines,

but are not able to convert energywithout losses.

References

1. Jump up ↑  Made internally by a member of the Encyclopedia team

2. Jump up ↑  R. Wolfson, "Energy and Heat," in Energy, Environment and Climate, 2nd ed. New York, U.S.A.:

Norton, 2012, pp. 86-87

How to calculate Megawatts thermal from having values of Megawatts electrial (1000MWe) and efficiency (20%)?Best Answer:  The amount of heat an electrical system dissipates is a direct function of the efficiency of the system. Electrical energy either produces power in the load or is dissipated in the form of heat. Therefore: 

MW(thermal) = (1 - %eff.) x MW(electrical) MW(thermal) = 0.8 x 1000 MW = 800 MW