KERJASAMA TRAINING ECOTECT DENGAN PERGURUAN TINGGI

Mulai bulan mei ini studio Gentra memberikan training Ecotec-ESP bekerjasama dengan dua institusi pendidikan yakni Jurusan Arsitektur Universitas Pendidikan Indonesia (UPI) dan Universitas Islam Indonesia (UII) Jogjakarta. Training ini diikuti oleh sejumlah dosen dan mahasiswa dengan cakupan materi : modeling, input properti (material, iklim, internal condition), shading analysis, daylighting and arificial lighting, incident solar radiation, thermal analysis, energy consumption, wind simulation dan kalkulasi OTTV. Bila berminat hubungi : Ismail Zain,081220068733

DIALUX, software gratis untuk analisa pencahayaan

Oleh : Ismail Zain, ST

Tidak seperti Ecotect yang memakai point method, software dialux mengaplikasikan lumens method yang memperhitungkan tingkat reflektansi setiap permukaan interior. Seperti halnya radiance yang memunculkan output illuminance (tingkat pencahayaan) dan luminance (tingkat kecerahan) dalam dialux juga dihasilkan output serupa. Dalam artikel ini akan disampaikan contoh dari dampak pemilihan jenis lampu terhadap tingkat pencahayaan, tingkat kecerahan dan efisiensi lampu.

Ukuran ruang 9.6 m x 9.6 m. Simulasi pertama menggunakan lampu philips LED 342 lumens 5 watt. Kebutuhan tingkat pencahayaan sebesar 300 lux. Saran dari dialux untuk layout lampu adalah 12 baris dan 11 kolom, sehingga jumlah lampu yang dibutuhkan sebanyak 132 lampu. Tingkat pencahayaan rata-rata pada workplane sebesar 432 lux. Tingkat kecerahan terkecil terdapat pada salah satu dinding sebesar 70 cd/m2 sedangkan tingkat kecerahan terbesar terjadi pada lantai sebesar 90 cd/m2. Efisiensi lampu sebesar 7.16 W/m2.

Sedangkan untuk simulasi kedua menggunakan lampu philips LED 1028 lumens 14 watt. Kebutuhan tingkat pencahayaan sebesar 300 lux. Saran dari dialux untuk layout lampu adalah 7 baris dan 6 kolom, sehingga jumlah lampu yang dibutuhkan sebanyak 42 lampu. Tingkat pencahayaan rata-rata pada workplane sebesar 413 lux. Tingkat kecerahan terkecil terdapat pada salah satu dinding sebesar 69 cd/m2 sedangkan tingkat kecerahan terbesar terjadi pada lantai sebesar 96 cd/m2. Efisiensi lampu sebesar 6.38 W/m2.

Dari kedua simulasi dapat disimpulkan bahwa layout kedua lebih hemat dari segi penggunaan listriknya, memenuhi tingkat pencahayaan yang dibutuhkan dan perbandingan kecerahan yang lebih kecil dibanding layout pertama.

BISNIS INTI STUDIO GENTRA

Studio Gentra memfokuskan diri dalam 3 core utama yakni :

1. Kalkulasi OTTV

2. Simulasi Daylight dan Artificial light (illumination level and glares)

3. Simulasi pergerakan udara

OTTV atau Overall Thermal Transmittance Value merupakan parameter awal untuk menetapkan suatu bangunan layak disebut bangunan hemat energi atau tidak, dengan baseline 45 W/m2 ke bawah disebut bangunan hemat energi. Keunggulan hasil kalkulasi dari studio Gentra adalah didasarkan pada worksheet OTTV yang lengkap mulai dari U-value, absorptansi, window to wall ratio (WWR), density, shading coefficient kaca (SC1) dan shading coefficient alat peneduh (SC2). Yang sering dilupakan adalah peranan elemen SC2 dalam perhitungan OTTV, dan Studio Gentra memiliki metode khusus untuk mengkalkulasinya sehingga cukup berperan dalam mereduksi nilai OTTV.

Pengalaman kami dalam menghitung OTTV sudah dilakukan dalam 2 proyek, yakni Rumah sakit Pendidikan Universitas Negeri Surakarta (RSP UNS) yang akan dipromosikan menjadi green hospital pertama di Indonesia dan Lab kedokteran UI. OTTV untuk RSP UNS dapat mencapai 20 W/m2, hal ini dapat dicapai karena yang pertama akibat WWRnya rendah yakni 0,17 (fasad timur), 0,16 (fasad timur laut dan barat), 0,30 (fasad utara), 0,24 (fasad barat laut) dan 0.27 (fasad selatan). Yang kedua adalah penggunaan kaca stopsol supersilver blue green dari asahimas dengan SC1  = 0.43  (memiliki performa termal yang hampir sama dengan kaca low e  sunergy blue green dengan perbedaan pada u-value-nya ). Yang terakhir adalah peranan sun-shading device dan massa bangunan. Sun shading device menggunakan type egg-crate dengan capaian SC2 mulai dari 0,56 hingga 0,96, sedang massa bangunan dimana pada fasad depan lantai 1 & lantai 2 menjorok ke dalam menghasilkan nilai SC2 yang paling rendah yakni 0,47.

Sedangkan OTTV untuk Lab kedokteran UI  mencapai 44.77 w/m2 dengan menggunakan stopsol supersilver green, bila menggunakan kaca low e sunergy green capaian OTTVnya lebih rendah sedikit yakni  44.24 W/m2. Perbedaan yang tipis ini dikarenakan sama-sama memiliki SC1 0.45 namun u-value sunergy green lebih rendah yakni 4,1 W/m2K, ketimbang 5,7 W/m2K  dari stopsol supersilver green. Capaian di bawah 45 W/m2 juga ditolong oleh sistem double skin, dimana cukup menurunkan nilai SC1 total karena dikombinasikan dengan kaca clear indoflot dengan SC1 = 0.87 sehingga secara umum nilai SC1 nya cukup turun banyak menjadi 0.87 x 0.45 = 0.39. Sumbangan SC2 berasal dari shading device pada lantai 3 dan 5, koridor penghubung dari bangunan lama dan secondary skin berlanggam organik.

Keputusan pemilihan kaca sebaiknya didasarkan pada performa antisipasi glare dan tingkat iluminasinya. Pada RSP UNS sebenarnya saat memakai stopsol classic dark blue, OTTV nya memiliki nilai 19.04 W/m2, dan glarenya tidak ada namun capaian tingkat iluminasinya tidak memenuhi syarat. Pada saat digunakan panasap blue green dengan nilai OTTV mencapai 23.3 W/m2 tingkat illuminasinya memadai namun tingkat glarenya melebihi rasio kekontrasan 1 : 3 antara permukaan sekitar jendela dengan jendelanya. Sedangkan saat memakai stopsol supersilver blue green, semua hal memenuhi syarat.

Jika anda membutuhkan jasa kami silakan kontak saya, Ismail Zain, ST 081220068733.

GLASS PERFORMANCES OF ASAHIMAS GLASSES

The glass performance based on the shading coefficient and light transmittance, compare 13 types of glass from Asahimas manufacture for clear, green, blue green and dark blue glasses. The comparison result given as follow :

Picture 1.1  Shading coefficient perfomance

 

Based on shading coefficient performances, there are four categories which refer to four ranges of SC that are  0.30 – 0.39 ,  0.40 – 0.49, 0.50 – 0.59 and > 0.60. The type of the glasses that are included to each categories are given here.

                                                            Table 1.1  Shading coefficient perfomance

SC CATEGORY	TYPE OF GLASSES	SHADING COEFFICIENT	LIGHT TRANSMITTANCE
0.30 -0.39	Stopsol Classic Dark Blue	0.34	0.21
0.40 -0.49	Stopsol Classic Green	0.34	0.27
	Stopsol Supersilver Dark Blue	0.43	0.35
	Stopsol Supersilver Blue Green	0.43	0.39
	Sunergy Blue Green (low e)	0.43	0.42
	Sunergy Green  (low e)	0.45	0.52
	Stopsol Supersilver Green	0.45	0.48
0.50 -0.59	Panasap Dark Blue	0.57	0.48
	Panasap Green	0.58	0.63
	Panasap Blue Green	0.59	0.56
> 0.60	Sunergy Clear (low e)	0.68	0.67
	Stopsol Supersilver Clear	0.76	0.62
	Indoflot Clear	0.89	0.87

 

The stopsol classic dark blue and  stopsol classic green have lowest SC (0.34) than others and  lowest light transmittance (0.21 and 0.27) so they will block the natural lighting significantly.

In the second category (0.40-0.49) the stopsol supersilver blue green and the  stopsol supersliver green are the optimum choices because their light transmittances are not to low (0.39 – 0.45) and not differ significantly with the light transmittance of sunergy blue green  (0.42) but cheaper. The stopsol classic green and stopsol supersilver dark blue have under 0.36 of the light transmittances. But the sunergy  green is the best choice in this category because its light transmittance that is highest (0.52) than others in this category.

In the next category (0.50-0.59)  the all glass indicate the similar  shading coefficient but need to evaluate about the daylight performance. The final category have higher both shading coefficient and light transmittance and have to be located in the shaded areas.

Which category of SC that has to be chosen depends on the OTTV result. If the use of the higher SC still have OTTV value under 45 W/m2 then the next consideration is the optimum of light transmittance of the glass that caused by illumination level and glares.

STRATEGI MENGHITUNG SC KACA UNTUK DOUBLE SKIN

Ismail Zain, ST (studio Gentra)

Nila SC1 sebenarnya tinggal mengambil dari data supplier kaca, namun bagaimana menghitung SC1 pada sistem double glass skin dengan desain tertentu dimana masih ada penetrasi cahaya matahari pada primary envelopenya. Mengkalikan keduanya hanya diperuntukkan bila keduanya ditempatkan pada situsai dimana tidak ada penetrasi langsung pada primary skin.

Logikanya kita harus membagi kapan waktunya suatu penetrasi terjadi pada scondary skin dan kapan hanya terjadi pada primary skin, dengan dibagi seperti itu maka performanya akan tergantung pada posisi matahari pada jam tertentu. Ecotect bisa mensimulasikan kapan suatu performa melibatkan hanya primary skin dan kapan melibatkan kedua skin melalui simulasi persentasi shading dari secondary skin yang menimpa primary skin. Asumsinya adalah secondary skin sebagai shadind device bagi primary skin.

BMKG tidak mendukung gerakan green building?

Ismail Zain, ST (studio gentra)

BMKG tidak mendukung gerakan green building? faktanya iya, karena saat kolega kami ingin mendapatkan data cuaca pada level kedalaman per jam, ada peraturan yang melarang pengeluaran data sedetil itu. Padahal untuk melakukan simulasi terkait green building, tingkat akurasi data sangat diperlukan. Jadi dukungan semua pihak diperlukan agar gerakan green building di Indonesia bisa lebih berkembang pesat, salah satu sektor hulu yang harus mendukung harusnya adalah BMKG. Ada yang salah dari cara berpikir di negeri tercinta kita ini.

 

rumus OTTV dalam SNI, parameter valid?

oleh : Ismail zain, ST (studio gentra)

Banyak yang harus dikritisi dari OTTV :

1. Absorbsi radiasi (α)          

Guideline (yang sering diaplikasikan)  :

Warna dan bahan pada permukaan eksternal fasade maupun atap ternyata memiliki daya serap tertentu terhadap matahari. Absorpsi yang dimiliki bahan tersebut berpengaruh pada panas yang masuk ke dalam bangunan. Semakin mengkilap dan cerah warna suatu bahan, maka daya serap terhadap radiasi akan semakin rendah.

            Absorbsi permukaan yang dicat adalah rata-rata dari absorbsi bahan dinding dan absorbsi cat:

α          =          (α_w  + α _p)/2           

Comment  :

menurut sy perhitungan koefisiennya tidak bisa ditmbah terus dibagi dua seperti di atas. seperti halnya perhitungan SC (sama-sama koefisien) untuk menggabungkan rata-rata antara SC kaca dengan SC alat peneduh rumusnya adalah SC-kaca x Sc-alat peneduh. Mengapa demikian? karena basis yang dipakai adalah koefisien SC mencerminkan tingkat reduksi dari radiasi matahari, misalkan nilai radiasi 100%, dengan SC-alat peneduh berkoefisien 0.60 maka radiasi yang tidak tertahan oleh alat peneduh menjadi tinggal 60%, selanjutnya dari sisa radiasi tersebut direduksi oleh SC-kaca misalnya 0.8 maka radiasi matahari yang masuk kedalam bangun menjadi 0.8 x 60% = 48%. Bandingkan hasil perhitungan dengan mengkalikan kedua SC tersebut, 0.6 x 0.8 = 0.48, hasilnya sama. Maka logika untuk gabungan absorptansi wall dan material harusnya sama, kedua koefisien harus dikalikan, bukannya dirata-ratakan. Itu bila asumsi dasar kita menganggap bahwa terjadi proses ganda dari absorptivity. Pertanyaan selanjutnya adalah apakah memang ada proses ganda seperti itu? Dalam tabel mengenai absorptivity (martin evans), pengkategoriannya selalu disatukan dalam satu kolom misalnya red brick kisaran absorptivitynya 0.65 – 0.8 dengan paints berkisar 0.2 – 0.9. Jadi apakah saat kita menginput nilai α untuk bata yang dicat, kita harus menggunakan α dari cat saja atau gabungan antara α bata dengan α cat? Bila kita memahami definisi mendasar dari absorptivity, kita bisa mencermati bahwa α terkait dengan “surface” atau permukaan. Konsekuensinya, saat kita memakai dinding yang diekspos maka α bata yang kita pakai, tapi bila dinding tersebut dicat maka α cat yang dipakai. Suatu permukaan bata peran permukaannya akan digantikan bila ia diberi lapisan cat. Selanjutnya komponen bata pada susunan material tersebut akan menjadi “inner part” bukan merupakan permukaan lagi. Bila sudah menjadi inner part maka yang berlaku adalah proses “konduksi” bukan absorptivity permukaan. Kita bisa cek dalam rumus solar heat gain (martin evans),

q = α.U.I.ro

q adalah kalor yang diserap, α adalah absorptivity  permukaan, I adalah radiasi yang menimpa dinding, ro adalah resistensi permukaan luar dan U tingkat rambatan panas.

Kita bisa melihat dari rumus tersebut, untuk memperoleh reduksi radiasi yang menimpa dinding terdapat 3 faktor, pertama absorptivity permukaan selanjutnya tereduksi oleh resistensi permukaan luar dan terakhir sebelum merambat masuk ke dalam ruangan direduksi lagi oleh U-value nya.

Jadi cara kita menginput α bergantung pada 2 paradigma awal, apakah proses absorptivity merupakan proses tunggal ataukah ganda, hal ini akan berimbas terhadap cara kita mengambil nilai α. Bila kita memakai paradigma proses tunggal maka hanya α permukaan material terluar saja yang dipakai, tapi bila kita menganggap proses absorptivity tersebut merupakan proses ganda maka pakailah formulasi yang logis, yakni pengalian bukan perata-rataan. Namun karena α terkait dengan permukaan, proses tunggal menjadi lebih logis, sehingga pembagian tabel dalam SNI mengenai OTTV yang menyatakan terdapat dua jenis α untuk warna dan material sebaiknya ditinjau ulang. Pembagian yang betul adalah Tabel α warna merupakan α dari lapisan cat, sedangkan bila dinding tidak dicat maka α yang dipakai adalah α material. Intinya hanya satu α yang menjadi input untuk satu dinding.

Kita akan bergerak lebih dalam lagi, kalau kita melihat rumus asli OTTV, didalamnya tidak terdapat nilai α. Jadi kenapa dalam SNI tiba-tiba muncul nilai tersebut. Mengacu pada rumus q = U.dt dimana dt
merupakan beda temperatur outside dengan inside, dalam dt sebenarnya sudah termaktub nilai  α (martin evans). Jadi penambahan α dalam OTTV merupakan kekeliruan yang cukup fatal. Kalau mau menyertakan α sebagai faktor tidak tetap maka seharusnya dilakukan reformulasi rumus OTTV seperti halnya di malaysia yang bisa dilihat di bawah ini.

OTTV = 19.1α x ( 1 -WWR) x Uw + 194 x WWR x SC

Kekeliruan substansial dan metodologis ini harusnya secepatnya disadari agar kita tidak salah dalam melakukan kalkulasi  OTVV  di Indonesia, sebuah pekerjaan rumah bagi badan standardisasi nasional. 

2. Kalkulasi SC-alat peneduh

Kalkulasi Shading Coefficient (SC) memegang peranan penting dalam menurunkan nilai OTTV. Kalkulasi SC terdiri dari dua komponen yakni SC kaca dan SC alat peneduh. SC kaca merupakan parameter performa kaca dalam merambatkan panas ke dalam bangunan sedangkan SC alat peneduh (selanjutnya disebut SC2)  merupakan parameter performa alat peneduh maupun akibat gubahan massa dalam mereduksi radiasi langsung dalam rentang waktu tertentu.

Untuk mendapatkan nilai SC kaca kita bisa dengan mudah mendapatkannya  dari supplier kaca, sedangkan SC2 harus dikalkulasi secara cermat dengan rumus yang cukup rumit. Logika yang dipakai dalam kalkulasi SC2 adalah nilai 1 untuk kaca tanpa alat peneduh atau tanpa efek peneduhan dari gubahan massa, sedangkan nilai 0 bila alat peneduh maupun gubahan massa mampu meneduhi sepanjang hari.

Untuk menghitung SC2 diperlukan persentase penyinaran pada bidang suatu kaca pada 4 tanggal representatif untuk simulasi matahari yakni 21 Maret, 22 Juni, 23 September dan 22 Desember. Bila suatu kaca pada jam tertentu terjadi peneduhan oleh alat peneduh ataupun gubahan massa sebanyak 50%, maka persentase penyinaran pada kaca tersebut sebesar 50%, sehingga radiasi langsung yang menimpa bidang kaca tersebut harus dikalikan persentase penyinaran untuk mendapatkan perolehan radiasi langsung pada bidang kaca tersebut pada waktu tertentu. Jumlah perolehan radiasi langsung kemudian dijumlahkan setiap jamnya (6-18) untuk mendapatkan total perolehan harian radiasi langsung pada kaca tersebut. Selanjutnya persentase total perolehan harian radiasi langsung terhadap jumlah total harian radiasi langsung dan radiasi pantulan akan menjadi nilai dari SC2  dengan mengubahnya menjadi sebuah koefisien. Rerata tahunan didapatkan bila kita menjumlahkan total perolehan harian radiasi langsung dari 4 tanggal representatif dibagi dengan jumlah total harian radiasi langsung dan radiasi pantulan dari 4 tanggal yang sama.

Di dalam SNI tidak dicantumkan mengenai tingkat radiasi setiap jam pada keempat tanggal representatif tersebut. Jadi proses kalkulasi SC2 menjadi tidak akan pernah bisa dilakukan bila tidak didukung oleh data radiasi pada kota tertentu.  SNI hanya  sampai pada langkah untuk menghitung persentase peneduhan (faktor G) dan itu pun cukup rumit karena melibatkan rumus trigonometri yang cukup memusingkan bagi praktisi arsitektur.

Untuk membantu secara mudah bahkan tidak terbatas, tidak seperti halnya dalam SNI maupun ETTV nya BCA Singapura sekalipun yang memperuntukkan perhitungan nilai G sebatas pada 3 tipe alat peneduh (horizontal, vertikal dan kombinasi keduanya) maka saya mencoba mencari metode yang lebih praktis dengan melibatkan software Ecotect.

Dalam mengkalkulasi nilai G yang diperlukan adalah nilai Horizontal Shading Angle (HSA) dan altitude matahari sehingga kalo kita menemukan nilai HSA dan altitude suatu bidang kaca pada jam tertentu maka akan dapat diketahui persentase peneduhan dan selanjut dibalik agar didapat persentase penyinaran (1-G). Dan Ecotect mampu melakukannya seperti contoh di bawah ini.

Dari dua item di atas maka kita harus meninjau ulang pemahaman kita terhadap substansi dari rumus OTTV dimana di negara-negara tetangga kita, Malaysia dan Singapura, reformulasi perhitungan OTTV dari rumus aslinya sudah dilakukan. Kapankah hal itu bisa dilakukan di Indonesia ? tentunya harus disikapi dengan segera dan serius karena penilaian green building harus berlandaskan pada basis-basis yang jelas tidak tambal sulam.

The Basis for The Green Building Simulations and Calculations in Indonesia – Sun Shading Design, Daylighting, Thermal Comfort, Cooling Load, Air Movement Simulation dan OTTV.

by Ismail Zain, ST – Studio Gentra (Green Building Simulation Studio)

The building performance simulations and calculations are very important things for  the future performance prediction of the building we have designed. The simulation process has been supported by various tools such as Ecotect, Energyplus, etc,  that each software has some specific abilities for some specific simulations. As example for energy simulation,  Ecocect is useful for early stage of the design process, but as the design nears completion it needs Energyplus for  more accurate simulation.  Any building performance  that can’t be simulated yet  had to be calculated manually such Overall Thermal Transfer Value (OTTV) but some parts of the formula can be supported by Ecotect to calculate U-value and shading percentage (G).

In the Greenship rating system of Green Building Council Indonesia (GBCI), the chance for green building simulation has been opened especially on daylighting, air movement  and energy simulation.  For early stage of design process, it is very important to uses a software that enable us to integrate intuitively architect’s ways with an easy understanding simulation result for architects. Ecotect can simulate some building performances with this criteria with a wide range of simulation such as sun-shading design, daylighting, artificial lighting, cfd simulation, thermal comfort, cooling load and electricity consumption. On the contrary, Energyplus is not user-friendly software for architects because it is intended for mechanical engineers.

Nevertheless, Ecotect has some limititations that we have to consider because they can influence the final result of certain simulations. One of the limitations is some data like Time lag and Solar Heat Gain Coefficient (SHGC) have to be calculated outside Ecotect. Recently there is a tool that has abilities to solve the problems, called Ecotect Supporting Program (ESP)  released by Studio Gentra, Bandung. The basis for Time lag and SHGC calculation have been adapted from a book titled House, Climate and Comfort by Martin Evans.

Another limitation that has not been fully supported by Ecotect is weather files for any city in Indonesia. There are some steps to convert the local weather data to be a compatible one with Ecotect. Some data such as temperature, relative humidity and wind can be obtained from local wheater stations . But direct radiaton and diffuse radiation have to be calculated graphically through use of sun-radiation diagram overlaid on sun-path diagram according to a city where the site located.

One of the greenship item that can’t be simulated yet is OTTV calculation. The formula is very specific and has not been supported yet by any simulation tools. It needs extra efforts for us to calculate the OTTV formula because there are some variables such as shading coefficient and U-value have to be calculated with caution for the complexity of the formulas. Ecotect can help simplify the process just for the calculation of U-value and Shading percentage (G).

The Data needed for The Green Building Simulations and Calculations

The green building simulations need various data for the simulation process to be run well. The data types divided into two categories, external data which is weather data and internal data which is inherent to the building we have designed.

For Sun-shading design, the external data needed is the latitude of the site. For daylighting simulation, the external data needed is design sky illuminance for the city where the site is located and the internal data needed are glass transmittance, interior and exterior surface reflectance. For thermal comfort and energy simulation, the external data needed is temperature and sun radiation while the internal data needed are thermal property of the material (thermal conductivity, density, specific heat, solar reflectance, emissivity, time lag, shgc and light transmittance),  type of clothes’s users, room function, room capacity, hours of operation,  type and amount of lamps and appliances.

Meanwhile, for OTTV calculation, external data needed is solar factor that can refer to Standar Nasional Indonesia (SNI)  No. 03-6389-2000 about Energy Conservation on the Building Envelope while the data are aimed only for the city of Jakarta but it can be treated as a baseline for a fair comparison for another cities in Indonesia. The internal data needed are wall’s absorptances, u-value for walls and windows,  density and width of walls, shading coefficient (SC) of glasses and of shading devices and finally, window to wall ratio (WWR).

Sun-shading design

The sun-shading design has to refer to sun-angle that have to be considered when the sun penetration is allowed and when is not. But the sun-shading device is usually intended to block direct radiation which have more radiation intensity  than diffuse radiation that sun-shading device cannot deal with them (unless  we intend to design for it but it will create a trade-off, decreasing daylighting level) . For anticipate the  diffuse radiation, we have to choose some glasses with a best performance on reducing heat affected by sol-air (come from combination of solar radiation and air temperature) .  To avoid the glare, the combination of sun-shading device and glass performance  can be carried out.

The simple guideline for the range of time  we can simulate for sun-shading device simulation on tropical zone are from 10.00 AM to 04.00 PM  which the sol-air are high.  We can activate the sunpath diagram on 3d environment in Ecotect that shows us any sun-position according to time and date on the whole one year. Ecotect has a tool for showing which the areas that still have sun-penetration on this range of time and which is not. Thus we can modify our sun-shading device to cover the problems. But the evaluation is still needed wether our sun-shading device will decrease lighting level or will increase SC for shading device significantly.

Daylighting Simulation

For Daylighting simulation, Ecotect uses The Building Research Establishment (BRE) Split-Flux method that is a slightly more complex but widely recognised technique that is used in many building regulations around the world.

The BRE Split-Flux method is a widely recognised and very useful technique for calculating daylight factors. This method is based on the assumption that, ignoring direct sunlight, there are three separate components of the natural light that reaches any point inside a building:

Sky Component (SC) – Directly from the sky, through an opening such as a window.

Externally Reflected Component (ERC) – Reflected off the ground, trees or other buildings.

Internally Reflected Component (IRC) – The inter-reflection of 1 and 2 off surfaces within the room.

Separate consideration of these three components is justified by the fact that each is affected by different elements within the design. The daylight factor is thus given as a percentage and is simply the sum of each of these three components.

DF = SC + ERC + IRC

However, the original BRE Estimating Daylight in Buildings paper makes a number of assumptions and simplifications which were necessary for quick hand calculations. For more accurate calculation, Ecotect has added the increased accuracy mode which brings some variables to be included such as refractive index of each impacted window and external reflectance value of each surface in the model.

Once the Daylight factor has been calculated, we can convert them into illumination level for each room by multiplied with design sky illuminance (Ecocet will calculate it automatically). Thus the result can be read from the analysis grid which represents various illumination levels at any point in the room.  Design sky illuminance based on the worst-case scenario that is uses the overcast day light level . Design sky illuminace for cities in Indonesia refer to 10.000 lux based on SNI 03-2396-2001 about Code on Daylighting System Planning for Buildings.

Greenship states that 30 % of the floor area  have to achieve the illumination level requirement. Ecotect can integrate daylighting simulation with artificial lighting simulation to increase illumination level at the points that can’t achieve the illumination level requirement for each room.  The Point Method is used for the artificial lighting simulation in Ecotect. This method is aimed to determine direct illumination level  of artificial lighting by use of photometric data. After that,  we can measure the percentage of working  year lighting off for lighting sensor use.

For physically accurate and comprehensive lighting analysis, Ecotect can output  files data for direct input  – vice versa –  into the RADIANCE Lighting Simulation Software developed by Greg Ward at Lawrence Berkeley Laboratories. But  it  should be carried out  when the design  process nears completion.

Two steps have been made that show the balance between the creation of shading device in one side and achievement for  the illumination level requirement (30% of the floor area) in the other side.

Thermal Comfort Simulation

Thermal comfort has been a main issue  for building performance all the time. One of the criterion of thermal comfort is Mean Radiant Temperature (MRT) which means,  the result of surface temperature from sorrounding objects. MRT is a heat sensation comes from the radiation of materials and must be differentiate with air temperatur that is a represent of the temperatur of air molecules.The MRT that can be convert to another criterion for easy reading such as Predicted Mean Vote (PMV)  that scales betwen -4 for coldest one and  +4 for hottest one.

In Ecotect , MRT simulation is applied to a grid analysis thus we can quickly understand which point in a room  that received hotter surface temperature or colder ones. So we can modify the thermal property of the material to achieve better ones. In  Tropical zone , we have to reduce the amount of MRT  in order to give a low contribution to internal temperatur of a room. The Internal temperatur is known as  a dry resultant temperature.

The dry resultant temperature is the temperature registered by a thermometer at the centre of an externally blackened sphere 150 mm diameter, being a function of air temperature, mean radiant temperatures and wind velocity. It is used as an index temperature for comfort where the air velocities are low (CIBSE Guide A, 1999).

This statement indicate a method called admittance  method or steady state method. The method uses idealised (sinusoidal) weather and thermal response factors (admittance, decrement factor and surface factor) that are based on a 24-hour frequency.

Cooling Load Simulation

For air-conditioning buliding, space load  (heating/cooling load)  calculation is very important thing to estimate the capacity of air-conditioning plant. In the tropical zone, only cooling load calculation that is needed. The admittance method is also being used to calculate cooling load.

The admittance method was originally intended to calculate peak internal temperatures in buildings that is affect the peak cooling load to ensure that it would not become uncomfortably hot during sunny periods.  But This method frequently over exceed on its prediction. So, it is useful only in early stage of design process for comparing various design alternatives.

The validation is needed to have more accurate calculation as recently a new method called a dynamic simulation has been implemented  in order to solve the problems. Energyplus have adopted this method on its simulation engine.

In Ecotect, the results of cooling load simulation are shown as a graphic that represent monthly cooling load for a year.

Electricity  Consumption

For a comprehensive energy modeling, Ecotect have a tool that enable us to display the monthly electricity  consumption in one year that comes from use of various applliances and lamps. we just insert 3d applliances and lamps into the model  and Ecotect will calculate automatically for the result.

The electricity consumption for one year can be easily converted to the amount of emmission of CO2 that correspond with. But for the effective of the design process, just the lamps and certain applliances  that should be incorporated into the model because it is just aimed for comparing various design alternatives. For more accurate estimation of electricity consumption, Energyplus is needed to deal with.

In greenship, energy modelling is encouraged with the potentiality of high scores that can achieve maximum scores about 20 points. Based on Energy Efficient Index (EEI) standar for a certain building type as a baseline,  then our building model  is being calculated for its electricity consumption. Finally we have to calculate the percentage of the reduction of the electricity consumption based on the baseline.  The high scores will be  granted  if the percentage of the reduction achieve 60 %.

Air Movement  Simulation

Introducing the outdoor air is important for occupants to conncet with the nature for healthy reason.  One of the good criteria for the indoor air movement  is to have inlet and outlet openings to achieve a cross ventilation. The simulation for this can be carried out in Ecotect alongside with Winair as the cfd engine.

Initial setting for this simulation is conducted by including the prevailing local wind – their  directions and speeds. Then we can run the simulation in Winair  and displayed it back into Ecotect.  The results show which points in a room that have a good ventilation or not.

OTTV Calculation

In Greenship, OTTV is one of the prerequisite item in Energy Efficient and Conservation category. OTTV or Overall Thermal Transfer Value, is one of the parameters to measures the efficiency of the building energy  which a building envelope performance  have to achieve ≤ 45 W/m2.

The calculation refer to SNI 03-6389-2000 about Energy Conservation on the Building Envelope.  The formula is :

OTTV = α [(Uwx (1- WWR)] x TDeq + (SC x WWR x SF) + (Uf x WWR x ΔT)

where

OTTV          = overall thermal transfer value of the external wall (W/m2)

α              = wall absorptance (dimensionless)

Uw              = U-value of opaque wall (W/m2.K)

TDeq          = equivalent temperature difference (K)

Uf               = U-value of fenestration (W/m2.K)

DT               = temperature difference between interior and exterior (K)

SC               = shading coefficient of fenestration (dimensionless) = SCwin x SSF

SCwin         = shading coefficient of window glass (dimensionless)

SSF             = solar shade factor of external shading devices (dimensionless)

SF               = solar factor of fenestration (W/m2)

WWR         = window-to-wall ratio (gross wall area)

To obtain the data that will be included to this formula is comes from any sources and many techniques.  Solar Factor and DT can be obtained directly from The SNI. To have a TDeq value, we have to insert the density and the width of a material. SCwin can refer to technical data from any glass manufactures. The WWR is found out directly from the building drawing.

Another data such as Uw, Uf and SSF need further calculation.  To find out the Uw or Uf, many steps have to be conducted. First we have to find out the resistance value by divided the thickness of the material with its thermal conductivity.  Then we sum all of the resistance values of the material and the external and internal surface resistances.  The U-value is the reciprocal of the sum of the resistances.

SSF has a number of complex calculations, unfortunately  the formulas are very specific according to the shape of the given shading device type. In SNI , there are no calculation examples related to the formula and no additional information about ID or Direct radiation and Id or diffused radiation. For comparison of how  the formula is excercised, we have to refer the guideline of Envelope Thermal Transfer Value (ETTV) calculation realesed by Building and Construction Authority (BCA) , Singapore.

The formulas are given below ,

Q = Ae x ID +A  x Id

where

Q   = solar heat gain (W/m2)

A    = total area of window or Ae + As  (m2)

Ae    = exposed area of window (m2)

As = shaded area of window (m2)

ID   = direct radiation (W/m2)

Id   = diffused radiation (W/m2)

to find SC fenestration,

SC = G x ID + Id

IT

where

SC = shading coeficient fenestration (dimensionless)

G    = the fraction of area exposed to direct solar radiation or Ae / A  (dimensionless)

ID   = direct radiation (W/m2)

Id   = diffused radiation (W/m2)

To determine the effective SC of a shading device, theoretically, the computation has to be carried out for 12 months of the year. However, as the computation involved is rather tedious and the degree of accuracy required is not a critical factor, it is deemed sufficient to base the SC computation on 4 representative months of the year, March, June, September and December. The representative days of these 4 months are March 21, June 22, September 23 and December 22. Further, since the solar data for March 21 and September 23 are almost identical, it suffices to compute the solar heat gain for March and double it to take account of the heat gain for September. Mathematically, the effective SC of a shading device is given by:

Effective SC = ∑M(G x ID x Id) + ∑J(G x ID x Id) + ∑S(G x ID x Id) + ∑D(G x ID x Id)

∑M IT + ∑J IT + ∑S IT + ∑D IT

where

M   denotes March

J     denotes June

S    denotes September

D    denotes December

To determine G value there are a number of different formulas depend on the type of shading. But there are limitations for calculate SC of more complex types. In Ecotect, there is a feature to simulate G-value,  the fraction of area exposed to direct solar radiation. The feature that enable to simulate G-value present the hourly percentage of  shading.  By this feature we can simulate any type of shading device easily.

Summary

Use of  a computer simulation, especially that suitable for an architect’s workflow in early stage of design process,  can help architect to judge his work effectively without manually excercise a number of the formulas that too complex to dealing with.  The other hand, a combination with any simulation tool that encourages a more accurate result is very important in a final stage of the design process. But there are a number building performance calculations that have not been supported by computer simulation and hopely  one by one can be adapted to be a computer program, especially an architect-friendly one.

 

REFERENCES

Olgyay, V., (1962), Design With Climate: Bioclimatic approach to architectural regionalism, (Princeton: Princeton University Press).

Marsh, A., (2008), Ecotect 2010 Help, ( – : Autodesk, Inc).

Lippsmeier, G., (1994), Bangunan Tropis, (Jakarta: Erlangga).

Egan, D., (1983), Concepts in Architectural Lighting, (New York: McGraw-Hill Book Co).

Badan Standardisasi Nasional, (2000), Konservasi energi selubung bangunan pada bangunan gedung - SNI 03-6389-2000, (Jakarta: BSN).

Badan Standardisasi Nasional, (2000), Tata cara perancangan sistem pencahayaan alami pada bangunan gedung – SNI 03-2396-2001, (Jakarta: BSN).

Priatman, J., (2006), Building Information for ASEAN Energy Efficient Award 2006 : Graha Wonokoyo Surabaya Indonesia, (Surabaya: – ).

Evans, M., (1980), Housing, Climate & Comfort, (London: The Architectural Press).

Thomas, R., (1997), Environmental Design, (London: Chapman & Hall).

Building and Construction Authority, (-), Code on Envelope Thermal Performance for Buildings, (Singapore: BCA).

Green Building Council Indonesia, (2012), Greenship untuk Gedung Baru Versi 1.1, (Jakarta: GBCI).

KERJASAMA TRAINING ECOTECT-ESP DENGAN PENTA ARCHITECTURE

Studio Gentra pada bulan Januari 2013 mengadakan training ecotect – esp di kantor Penta Architecture, Bandung. Training ini diikuti oleh 7 peserta, dilaksanakan setiap sabtu dengan jumlah pertemuan 5 sessi.

2012 in review

The WordPress.com stats helper monkeys prepared a 2012 annual report for this blog.

Here’s an excerpt:

600 people reached the top of Mt. Everest in 2012. This blog got about 5,400 views in 2012. If every person who reached the top of Mt. Everest viewed this blog, it would have taken 9 years to get that many views.

Click here to see the complete report.

SIMULASI BIOKLIMATIK GEREJA OIKUMENE

KALKULASI OTTV dengan BANTUAN ECOTECT

OTTV telah sekian lama menjadi parameter bangunan hemat energi melalui perhitungan rumus di bawah ini:

Menyelesaikan rumus di atas tidaklah mudah, harus melalui pemahaman yang mendalam mengenai variabel-variabel juga perhitungan yang cukup rumit untuk sejumlah variabel seperti menghitung U-value dan SC. Demikian pula mengenai tingkat variasi fasad akan menambah kerumitan perhitungan OTTV. Untuk itu Studio Gentra telah merilis Worksheet OTTV, yang bisa mengakomodasi hingga tiga jenis fasad baik untuk opaque maupun glass.

13.1.  Memahami rumus OTTV

Pada rumus OTTV di atas terdapat tiga bagian utama, yakni :

1. α.Uw.(1-WWR).Tdeq
2. Uf.WWR.∆T
3. SF.SC1.SC2.WWR

Bagian pertama adalah perolehan panas melalui material opaque yang bersifat konduktif (perpindahan panas melalui rambatan antar molekul benda padat) dengan elemen-elemen α (absorptansi dinding), Uw (U-value dinding), 1-WWR (luas dinding per luas fasad), Tdeq ( Beda Temperatur ekuivalen).

Bagian kedua adalah perolehan panas melalui material kaca yang bersifat konduktif  dengan elemen-elemen Uf (U-value kaca), WWR (luas kaca per luas fasad), ∆T (Beda kondisi perencanaan Temperatur luar dan dalam).

Bagian ketiga adalah perolehan panas melalui material kaca yang bersifat radiatif (perpindahan panas melalui gelombang radiasi matahari) dengan elemen-elemen SF (Solar factor), SC1 (Shading coefficient kaca), SC2 (Shading coefficient alat peneduh), WWR (luas kaca per luas fasad).

13.2.  Input untuk variabel OTTV

Ecotect dan ESP mampu membantu untuk menghitung sejumlah variabel yakni U-value, baik Uw maupun Uf (lihat Bab 3 – modul Ecotect-ESP part 1) dan SC2 (lihat Bab 12 – modul Ecotect-ESP part 2v3). Untuk WWR ecotect juga mampu menghitung luasan atau bisa juga dengan manual dimana nilai WWR didapat dari perbandingan luas kaca suatu fasad terhadap luas keseluruhan fasad. Sedangkan α didapat dari data supplier pabrikan cat dan SC1 didapat dari pabrikan kaca.

SF, Tdeq  dan ∆T didapat dari SNI 03-6759-2002 mengenai Tata Cara Perencanaan Konservasi Energi pada Bangunan Gedung, dimana pada Worksheet telah disertakan sehingga akan  secara otomatis muncul sesuai inputnya (kecuali ∆T, dengan nilai defult 5^oC), misalnya ketika kita mengetik U maka nilai SFnya akan otomatis menjadi 130 W/m2, atau pun bila densitas dan tebal material berubah maka akan mempengaruhi berat per m2 nya sehingga akan mempengaruhi nilai Tdeq-nya.

13.3.  Worksheet  OTTV

Dengan adanya Worksheet OTTV maka perhitungan OTTV akan lebih mudah, selain fitur utama kalkulasi OTTV, juga ada fitur tambahan untuk menghitung SC2 (Bab 12).  Untuk menghitung OTTV terdapat 4 tab untuk 4 orientasi/fasad dengan tab akhir sebagai tab kalkulasi total.

OTTV per fasad dapat dilihat pada gbr di bawah ini.

Sedangkan  OTTV total dapat dilihat pada gbr di bawah ini.

Untuk dapat memenuhi syarat sebagai bangunan hemat energi maka nilai OTTV harus ≤ 45 W/m2.

13.4.  Contoh

 

Untuk worksheet terdapat contoh perhitungan OTTV dengan acuan bangunan di atas yang memiliki 3 jenis selubung bangunan:

Podium 1  -      Fasad selatan :  dinding beton, kaca tunggal

Fasad timur :  dinding beton, kaca tunggal

Fasad utara :  dinding beton

Fasad barat :  berbatasan dengan bangunan lain (tidak disertakan)

Podium 2,3  -  Fasad selatan :  balok beton+kaca, kaca double, parapet bata+kaca

Fasad timur :  balok beton+kaca, kaca double, parapet bata+kaca

Fasad utara :  dinding beton

Fasad barat :  berbatasan dengan bangunan lain (tidak disertakan)

Menara  -        Fasad selatan :  balok beton+kaca, kaca double, parapet bata+kaca

Fasad timur :  balok beton+kaca, kaca double, parapet bata+kaca

Fasad utara :  balok beton+kaca, kaca double, parapet bata+kaca

Fasad barat :  balok beton+kaca, kaca double, parapet bata+kaca

KERJASAMA STUDIO GENTRA DENGAN KONSULTAN ARSITEKTUR

Saat ini studio Gentra sedang melakukan kerjasama dengan salah satu konsultan di Jakarta bernama PT.North Artchitecture, kerjasama difokuskan untuk melakukan simulasi passive/bioklimatik design dan energy effecient building dengan menggunakan Ecotect dan software lainnya seperti Winair dan ESP.

Studio Gentra dalam hal ini memberikan pelayanan berupa pembuatan framework dan workflow yang diterjemahkan dalam bentuk worksheet. Selanjutnya dari pihak PT.North Artchitecture akan memakai worksheet tersebut sebagai panduan untuk menjalankan prosedur simulasi. Acuan ke depannya akan diarahkan untuk mengejar rating Green Mark Singapore.

Contoh dibawah merupakan salah satu  worksheet untuk melakukan simulasi shading device.

Worksheet lainnya adalah building envelope, area hijau, material kaca, simulasi daylighting, opaque material, roof, hardscape non-roof area, simulasi mean radiant temperature/PMV/PPD, simulasi local urban heat island, cfd simulation (croos ventilation).

Bagi anda yang berminat bekerja sama dengan pihak studio Gentra dalam kaitannya dengan simulasi energy-efficient building, silakan menghubungi :

Ismail zain, ST 081220068733

DAYLIGHTING AND GLARE SIMULATION

PRIEVIEW OF GLARE SIMULATION

DAYLIGHTING AND GLARE SOFTWARE (RADIANCE & EVALGLARE)

DIVA FOR RHINO

CFD SIMULATION

The fundamental basis of almost all CFD problems are the Navier–Stokes equations, which define any single-phase fluid flow.  In physics, the Navier–Stokes equations, named after Claude-Louis Navier and George Gabriel Stokes, describe the motion of fluid substances. These equations arise from applying Newton’s second law to fluid motion, together with the assumption that the fluid stress is the sum of a diffusing viscous term (proportional to the gradient of velocity), plus a pressure term.

Newton’s laws of motion are three physical laws that form the basis for classical mechanics. They describe the relationship between the forces acting on a body and its motion due to those forces. They have been expressed in several different ways over nearly three centuries, and can be summarized as follows:

1. First law: The velocity of a body remains constant unless the body is acted upon by an external force.
2. Second law: The acceleration a of a body is parallel and directly proportional to the net force F and inversely proportional to the mass m, i.e., F = ma.
3. Third law: The mutual forces of action and reaction between two bodies are equal, opposite and collinear.

The three laws of motion were first compiled by Sir Isaac Newton in his work Philosophiæ Naturalis Principia Mathematica, first published in 1687. Newton used them to explain and investigate the motion of many physical objects and systems.

The second law states that the net force on a particle is equal to the time rate of change of its linear momentum p in an inertial reference frame:

where, since the law is valid only for constant-mass systems, the mass can be taken outside the differentiation operator by the constant factor rule in differentiation. Thus,

where F is the net force applied, m is the mass of the body, and a is the body’s acceleration. Thus, the net force applied to a body produces a proportional acceleration. In other words, if a body is accelerating, then there is a force on it.

Any mass that is gained or lost by the system will cause a change in momentum that is not the result of an external force. A different equation is necessary for variable-mass systems (see below).

Consistent with the first law, the time derivative of the momentum is non-zero when the momentum changes direction, even if there is no change in its magnitude; such is the case with uniform circular motion. The relationship also implies the conservation of momentum: when the net force on the body is zero, the momentum of the body is constant. Any net force is equal to the rate of change of the momentum.

Newton’s second law requires modification if the effects of special relativity are to be taken into account, because at high speeds the approximation that momentum is the product of rest mass and velocity is not accurate.

velocity field

The Navier–Stokes equations dictate not position but rather velocity. A solution of the Navier–Stokes equations is called a velocity field or flow field, which is a description of the velocity of the fluid at a given point in space and time. Once the velocity field is solved for, other quantities of interest (such as flow rate or drag force) may be found. This is different from what one normally sees in classical mechanics, where solutions are typically trajectories of position of a particle or deflection of a continuum. Studying velocity instead of position makes more sense for a fluid; however for visualization purposes one can compute various trajectories.

Nonlinearity

The Navier–Stokes equations are nonlinear partial differential equations in almost every real situation^[2][3]. In some cases, such as one-dimensional flow and Stokes flow (or creeping flow), the equations can be simplified to linear equations. The nonlinearity makes most problems difficult or impossible to solve and is the main contributor to the turbulence that the equations model.

The nonlinearity is due to convective acceleration, which is an acceleration associated with the change in velocity over position. Hence, any convective flow, whether turbulent or not, will involve nonlinearity. An example of convective but laminar (nonturbulent) flow would be the passage of a viscous fluid (for example, oil) through a small converging nozzle. Such flows, whether exactly solvable or not, can often be thoroughly studied and understood.

steady state

A system in a steady state has numerous properties that are unchanging in time. This implies that for any property p of the system, the partial derivative with respect to time is zero:

The concept of steady state has relevance in many fields, in particular thermodynamics and economics. Steady state is a more general situation than dynamic equilibrium. If a system is in steady state, then the recently observed behavior of the system will continue into the future. In stochastic systems, the probabilities that various states will be repeated will remain constant.

In many systems, steady state is not achieved until some time has elapsed after the system is started or initiated. This initial situation is often identified as a transient state, start-up or warm-up period.

While a dynamic equilibrium occurs when two or more reversible processes occur at the same rate, and such a system can be said to be in steady state, a system that is in steady state may not necessarily be in a state of dynamic equilibrium, because some of the processes involved are not reversible.

For example: The flow of fluid through a tube, or electricity through a network, could be in a steady state because there is a constant flow of fluid, or electricity. Conversely, a tank which is being drained or filled with fluid would be an example of a system in transient state, because the volume of fluid contained in it changes with time.

incompressible flow of newtonian fluids

A simplification of the resulting flow equations is obtained when considering an incompressible flow of a Newtonian fluid  (A Newtonian fluid -named after Isaac Newton- is a fluid whose stress versus strain rate curve is linear and passes through the origin. The constant of proportionality is known as the viscosity).  In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric flow) refers to a flow in which the material density is constant within a fluid parcel – an infinitesimal volume that moves with the velocity of the fluid. An equivalent statement implying incompressibility is, that the divergence of the fluid velocity is zero.

An isochoric process, also called a constant-volume process, an isovolumetric process, or an isometric process, is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition.

Incompressible flow does not imply that the fluid itself is incompressible. It is shown in the derivation below that (under the right conditions) even compressible fluids can – to good approximation – be modelled as an incompressible flow. Incompressible flow implies that the density remains constant within a parcel of fluid which moves with the fluid velocity.

The assumption of incompressibility rules out the possibility of sound or shock waves to occur; so this simplification is invalid if these phenomena are important. The incompressible flow assumption typically holds well even when dealing with a “compressible” fluid — such as air at room temperature — at low Mach numbers (even when flowing up to about Mach 0.3). Taking the incompressible flow assumption into account and assuming constant viscosity, the Navier–Stokes equations will read, in vector form:

Navier–Stokes equations (Incompressible flow)

Here f represents “other” body forces (forces per unit volume), such as gravity or centrifugal force. The shear stress term becomes the useful quantity ( is the vector Laplacian) when the fluid is assumed incompressible, homogeneous and Newtonian, where is the (constant) dynamic viscosity.

It’s well worth observing the meaning of each term (compare to the Cauchy momentum equation):

nozzle. Though individual fluid particles are being accelerated and thus are under unsteady motion, the flow field (a velocity distribution) will not necessarily be time dependent.

Another important observation is that the viscosity is represented by the vector Laplacian of the velocity field (interpreted here as the difference between the velocity at a point and the mean velocity in a small volume around). This implies that – for a Newtonian fluid – viscosity operates in a diffusion of momentum, in much the same way as the diffusion of heat seen in the heat equation (which also involves the Laplacian).

If temperature effects are also neglected, the only “other” equation (apart from initial/boundary conditions) needed is the mass continuity equation. Under the assumption of incompressibility, the density of a fluid parcel is constant and it follows that the continuity equation will simplify to:

This is more specifically a statement of the conservation of volume (see divergence and isochoric process).

These equations are commonly used in 3 coordinates systems: Cartesian, cylindrical, and spherical. While the Cartesian equations seem to follow directly from the vector equation above, the vector form of the Navier–Stokes equation involves some tensor calculus which means that writing it in other coordinate systems is not as simple as doing so for scalar equations (such as the heat equation).

Turbulence

Turbulence is the time dependent chaotic behavior seen in many fluid flows. It is generally believed that it is due to the inertia of the fluid as a whole: the culmination of time dependent and convective acceleration; hence flows where inertial effects are small tend to be laminar (the Reynolds number quantifies how much the flow is affected by inertia). It is believed, though not known with certainty, that the Navier–Stokes equations describe turbulence properly.

The numerical solution of the Navier–Stokes equations for turbulent flow is extremely difficult, and due to the significantly different mixing-length scales that are involved in turbulent flow, the stable solution of this requires such a fine mesh resolution that the computational time becomes significantly infeasible for calculation (see Direct numerical simulation). Attempts to solve turbulent flow using a laminar solver typically result in a time-unsteady solution, which fails to converge appropriately. To counter this, time-averaged equations such as the Reynolds-averaged Navier–Stokes equations (RANS), supplemented with turbulence models, are used in practical computational fluid dynamics (CFD) applications when modeling turbulent flows. Some models include the Spalart-Allmaras, k-ω (k-omega), k-ε (k-epsilon), and SST models which add a variety of additional equations to bring closure to the RANS equations. Another technique for solving numerically the Navier–Stokes equation is the Large eddy simulation (LES). This approach is computationally more expensive than the RANS method (in time and computer memory), but produces better results since the larger turbulent scales are explicitly resolved.

In fluid dynamics, turbulence kinetic energy (TKE) is the mean kinetic energy per unit mass associated with eddies in turbulent flow. Physically, the turbulence kinetic energy is characterised by measured root-mean-square (RMS) velocity fluctuations.

Generally, the TKE can be quantified by the mean of the turbulence normal stresses:

TKE can be produced by fluid shear, friction or buoyancy, or through external forcing at low-frequency eddie scales(integral scale). Turbulence kinetic energy is then transferred down the turbulence energy cascade, and is dissipated by viscous forces at the Kolmogorov scale. This process of production, transport and dissipation can be expressed as:

where: ^[1]

• is the mean-flow material derivative of TKE;
• is the turbulence transport of TKE;
• is the production of TKE, and
• is the TKE dissipation.

The full form of the TKE equation is

computational fluid dynamics (CFD), it is impossible to numerically simulate turbulence without discretising the flow-field as far as the Kolmogorov microscales, which is called direct numerical simulation (DNS). Because DNS simulations are exorbitantly expensive due to memory, computational and storage overheads, turbulence models are used to simulate the effects of turbulence. A variety of models are used, but generally TKE is a fundamental flow property which must be calculated in order for fluid turbulence to be modelled.

Reynolds-averaged Navier–Stokes (RANS) simulations use the Boussinesq eddy viscosity hypothesisto calculate the Reynolds stresses that result from the averaging procedure:

where

The exact method of resolving TKE depends upon the turbulence model used; k-ε (k–epsilon) models assume isotropy of turbulence whereby the normal stresses are equal:

This assumption makes modelling of turbulence quantities (k and ) simpler, but will not be accurate in scenarios where anisotropic behaviour of turbulence stresses dominates, and the implications of this in the production of turbulence also leads to over-prediction since the production depends on the mean rate of strain, and not the difference between the normal stresses (as they are, by assumption, equal) .

shear velocity

Shear velocity, also called friction velocity, is a form by which a shear stress may be re-written in units of velocity. It is useful as a method in fluid mechanics to compare true velocities, such as the velocity of a flow in a stream, to a velocity that relates shear between layers of flow.

Shear velocity is used to describe shear-related motion in moving fluids. It is used to describe:

• Diffusion and dispersion of particles, tracers, and contaminants in fluid flows
• The velocity profile near the boundary of a flow (see Law of the wall)
• Transport of sediment in a channel

Shear velocity also helps in thinking about the rate of shear and dispersion in a flow. Shear velocity scales well to rates of dispersion and bedload sediment transport. A general rule is that the shear velocity is about 1/10 of the mean flow velocity.

Where is the shear stress in an arbitrary layer of fluid and is the density of the fluid.

Typically, for sediment transport applications, the shear velocity is evaluated at the lower boundary of an open channel:

Where is the shear stress given at the boundary.

Shear velocity can also be defined in terms of the local velocity and shear stress fields (as opposed to whole-channel values, as given above).

law of the wall

In fluid dynamics, the law of the wall states that the average velocity of a turbulent flow at a certain point is proportional to the logarithm of the distance from that point to the “wall”, or the boundary of the fluid region. This law of the wall was first published by Theodore von Kármán, in 1930. It is only technically applicable to parts of the flow that are close to the wall (<20% of the height of the flow), though it is a good approximation for the entire velocity profile of natural streams.

ISOTHERMAL CONDITION

An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange.

SOFTWARE UNTUK CFD SIMULATION

Apakah WinAir merupakan valid software untuk simulasi aliran angin? untuk mencari rating di Green Mark, WinAir tidak bisa memenuhi syarat ukuran grid hingga 0,2 meter  (limitasi jumlah cell pada WinAir terbatas).

Alternatif lain bisa dijajaki, coba Phoenics dan Ansys Fluent

Phoenics

• Problem dimensionality: one, two and three dimensions.
• Time dependence: steady state and transient processes.
• Grid systems: Cartesian, cylindrical-polar and curvilinear co-ordinates; rotating co-ordinate systems; multi-block grids and fine grid embedding.
• Compressible/incompressible flows.
• Newtonian/non-Newtonian flows.
• Subsonic, transonic and supersonic flows.
• Flow in porous media, with direction-dependent resistances.
• Convection, conduction and radiation; conjugate heat transfer, with a library of solid materials and automatic linkage at the solid fluid interface.
• A wide range of built-in turbulence models for high and low-Reynolds number flows; LVEL model for turbulence in congested domains and a variety of K-E models, including RNG, two- scale and two-layer models.
• Multi-phase flows of three kinds with a variety of built-in interphase-transfer models:Finite-volume approach on staggered or collocated grids, with 13 choices of discretisation schemes for convection.
  1. Inter-penetrating continua, including turbulence and modulation;
  2. Particle tracking, including turbulence dispersion effects;
  3. Free-surface flows.
• Combustion and Nox models, with a range of diffusion and kinetically controlled models including the unique Multi-Fluid Model for turbulent chemical reaction.
• Chemical kinetics including multi-component diffusion and variable properties. Built-in interface to the CHEMKIN chemical database.
• Advanced radiation models, including surface-surface model with calculated view factors, a six-flux model and composite radiosity model for radiative heat transfer, known as IMMERSOL
• Mechanical and thermal stresses in immersed solids can be computed at the same time as the fluid flow and heat transfer.

Ansys Fluent

The vast majority of industrial flows are turbulent, so ANSYS Fluent software has always placed special emphasis on providing leading turbulence models to capture the effects of turbulence accurately and efficiently.

For statistical turbulence models, ANSYS Fluent provides numerous common two-equation models and Reynolds–stress models. However, particular focus is placed on the widely tested shear stress transport (SST) turbulence model, as it offers significant advantages for non-equilibrium turbulent boundary layer flows and heat transfer predictions. The SST model is as economical as the widely used k-ε model, but it offers much higher fidelity, especially for separated flows, providing excellent answers on a wide range of flows and near-wall mesh conditions. ANSYS Fluent complements the SST model with numerous other turbulence modeling innovations, including an automatic wall treatment for maximum accuracy in wall shear and heat transfer predictions and a number of extensions to capture effects like streamline curvature.

ANSYS Fluent also has innovative capabilities for laminar-to-turbulent transitionl. Using CFD to predict the location where the laminar boundary layer becomes turbulent is critical to improving efficiency and/or longevity of equipment in turbomachinery, aerospace, marine and many other industries. The Menter–Langtry γ–θ laminar–turbulent transition model™ gives users a powerful tool to capture various types of transition mechanisms in CFD simulation.

In addition, ANSYS Fluent provides a number of scale-resolving turbulence models, such as large- and detached-eddy simulation (LES and DES) model. The development of the novel scale-adaptive simulation (SAS) model is a highlight. This model provides a steady solution in stable flow regions while resolving turbulence in transient instabilities, such as massive separation zones without an explicit grid or time-step dependency. The SAS model has shown excellent results on numerous validation cases. It provides a good option for applications in which resolution of turbulence is required.

In ANSYS Fluent, an embedded-LES (E-LES) option allows computation of an LES solution for the subdomain in which unsteady (resolved) turbulence is required for accuracy, with a RANS model used to model the rest of the flow domain. For flows were wall effects are important but cannot be captured by a full LES simulation, the wall model LES (WM-LES) model was developed.

Sejarah singkat CFD simulation, Klik disini.

ALUR ALIRAN PANAS (HEAT FLUX) PADA MATERIAL NON-TRANSPARAN

Aliran panas pada material non-transparan (opaque material) memiliki 2 tahapan :

1. Pada permukaan luar material
2. Pada bagian dalam material

Proses aliran panas pada permukaan luar material melibatkan dua properti termal yakni reflectivity dan emmisivity. Kontrol untuk mereduksi sinar radiasi  matahari yang masuk ke dalam bangunan dapat dilakukan dengan menggunakan material yang memiliki tingkat reflektansi yang tinggi (reflectivity) dan memancarkan balik radiasi yang diserap (emmisivity) sehingga mampu melepaskan panas dari bangunan. Namun proses pemancaran balik tidak akan terjadi bila permukaan lahan sekitar bangunan lebih panas.

Contoh :

Dinding bata yang dicat putih memiliki nilai reflectivity-nya 0,71. Misalnya irradiasi matahari pada jam tertentu sebanyak 100 W/m2. Berarti sinar matahari yang diserap menjadi panas sebanyak 29 W/m2. Dengan tingkat emmisivity 0,89 maka panas yang dipancar balik 25,81 W/m2 dan yang akan merambat tinggal 3,19 W/m2. Namun bila permukaan lahan di sekitar bangunan lebih panas, maka panas yang akan merambat tetap  29 W/m2.

Bandingkan dengan dinding aluminum yang memiliki reflectivity 0,85. Pada irradiasi matahari 100 W/m2, panas yang diserap lebih kecil yakni 15 W/m2. Namun dengan emmisivity 0,08 panas yang dipancar balik hanya 1,2 W/m2, sehingga panas yang merambat lebih tinggi yakni 13,8 W/m2. Pada lingkungan dengan permukaan lahan lebih panas, dinding aluminum lebih baik dibandingkan bata putih karena merambatkan panas 15 W/m2.

Untuk memudahkan penilaian saat ini sudah ada parameter gabungan antara reflectivity dan emmisivity yang diistilahkan dengan Solar Reflectance Index yang sudah diterapkan oleh BCA Singapore pada sistem rating green buildingnya yakni Green Mark. Perhitungan SRI mengacu pada ASTM Designation: E 1980-01

Pada bagian dalam material terdapat dua properti termal yang terlibat, yakni resistance-insulation dan capacity-insulation. Resistance-insulation terkait dengan U-value, semakin kecil nilai U-value suatu material maka akan semakin kecil aliran panas yang bisa masuk ke dalam bangunan. U-value sendiri dipengaruhi oleh nilai thermal conductivity, tebal material, resistan permukaan luar dan resistan permukaan dalam.

Sedangkan capacity-insulation mempengaruhi waktu tunda aliran panas atau dikenal dengan istilah Time lag atau Thermal Lag. Nilai Time lag dipengaruhi oleh thermal conductivity, tebal material, resistan permukaan luar, specific heat dan density suatu material.

Dalam bukunya Design With Climate, Victor Olgyay merekomendasikan kombinasi resistance-insulation dan capacity-insulation pada bangunan untuk setiap tipe iklim.

Tipe Iklim                                             resistance-insulation                      capacity-insulation

Tropis (0^o -15 ^o L)                               low                                                         dinding ringan

Kepulauan Tropis (10 ^o -20 ^o L)     low                                                         dinding ringan

Hot Humid (15 ^o -25 ^o L)                  low                                                         no lag

Hot Arid (15 ^o -30 ^o L)                       high                                                       dinding tebal

Temperate (35 ^o – 42 ^o L)               low di sisi lainnya                              dinding tebal di sisi barat

Cool (45 ^o – 50 ^o L)                             high di sisi barat                                dinding tebal di sisi barat

Cold (di atas 50 ^o L)                           low di sisi luar                                    dinding tebal

Dengan kombinasi resistance-insulation dan capacity-insulation seperti di atas maka material yang harus dipilih pada bangunan Tropis ataupun Hot Humid adalah material dengan U-value rendah agar rambatan panas yang masuk ke dalam bangunan menjadi rendah, dengan nilai timelag yang rendah agar dapat dengan segera melepaskan panas dari dalam bangunan pada malam harinya. Namun pada iklim Hot Arid dimana suhu siang hari bisa mencapai 45 ^o C sedangkan pada malam hari bisa sangat dingin hingga mencapai 5 ^o C maka U-value harus tinggi agar panas yang merambat masuk tetap tinggi dengan nilai time lag yang tinggi juga agar rambatan panas dapat ditunda sampai malam hari sehingga pada siang hari ruangan tidak panas dan pada malam harinya ruangan menjadi hangat. Pada iklim Temperate dan Cool dimana suhu cukup dingin, panas matahari dari barat perlu dimanfaatkan untuk malam hari sehingga dinding pada bagian barat harus memiliki U-value yang tinggi dengan time lag yang tinggi sedangkan dinding utara, selatan dan timur harus memiliki U-value yang rendah agar panas tidak lepas dari bangunan. Pada iklim Cold semua dinding harus tebal dan U-value rendah di bagian luar agar berkurang panas yang keluar dari bangunan.

Untuk menghitung nilai U-value bisa dilakukan oleh software Ecotect keluaran Autodesk, sedangkan untuk menghitung Timelag bisa memakai software ESP keluaran studio Gentra Bandung.

Ref :

Olgyay, V., (1962), Design With Climate: Bioclimatic approach to architectural regionalism, (Princeton: Princeton University Press).

Lippsmeier, G., (1994), Bangunan Tropis, (Jakarta: Erlangga).

BCA Green Mark for Landed House Version 1.0

OPEN SOURCE ENERGY SIMULATION SOFTWARE

Klik di sini

PROGRAM PENGEMBANGAN KOTA HIJAU (P2KH)

Kota hijau merupakan kota yang ramah lingkungan, yang memanfaatkan sumber daya air dan energi secara efektif dan efisien, mengurangi limbah, menerapkan sistem informasi terpadu, menjamin kesehatan lingkungan, serta mensinergikan lingkungan alami dan buatan.

Sebanyak 60 kabupaten/kota, yang terdiri atas 34 pemerintah kabupaten dan 26 pemerintah kota saat ini telah menyiapkan Rencana Aksi Kota Hijau (RAKH) sebagai bagian dari keikutsertaan dalam prakarsa Program Pengembangan Kota Hijau (P2KH). Program tersebut tahun 2011 ini mulai diinisiasi oleh Kementerian Pekerjaan Umum (PU) dengan tujuan untuk meningkatkan kualitas ruang kota agar terjamin keberlanjutannya, sekaligus dapat responsif terhadap perubahan iklim.

Pada tahap inisiasi, P2KH difokuskan pada tiga atribut, pertama perencanaan dan pencanagan kota yang ramah lingkungan. Kedua, perwujudan ruang terbuka hijau 30 persen dan ketiga peningkatan peran masyarakat melalui komuniatas hijau. Namun sesungguhnya, masih terdapat beberapa atribut selain RTH yang juga perlu segera dikembangkan dalam Kota Hijau, seperti Green Waste, Green Water, GreenTransportation, Green Building, dan Green Energy.

Kota hijau memiliki makna strategis karena dilatarbelakangi beberapa faktor, antara lain tingginya tingkat urbanisasi dan menurunnya kualitas ruang perkotaan. Saat ini, sekitar 52,03% penduduk Indonesia tinggal di perkotaan, dan diperkirakan akan meningkat menjadi kurang lebih 68% pada tahun 2025. Pertumbuhan kota secara cepat tersebut secara langsung berimplikasi terhadap timbulnya berbagai permasalahan kota seperti kemacetan, banjir, permukiman kumuh, kesenjangan sosial, dan berkurangnya luasan ruang terbuka hijau.

Panduan pelaksanaan P2KH

http://www.pu.go.id/uploads/services/infopublik20120426103859.pdf

Manual DED P2KH

KOTA-HIJAU-IV-manual-DED

Contoh Green Open Space

Ecopark kab. Tasikmalaya

DATA IKLIM DI INDONESIA

Download Gratis Data iklim kota-kota di Indonesia

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Titik koordinat geografis kota-kota di Indonesia