Upload
vulien
View
215
Download
0
Embed Size (px)
Citation preview
Your partner for fansin the field of technical building equipment
1
Ventilation and smoke extraction
Formore than 130 years,wehavebeensub-stantially parti-
cipating in thede-velopment of ven-
tilation engeneeringwith our pretentiousproducts.
By a numerous pioneering steps andtrend setting product developmentswe offer consistentlymarvellous pro-ducts to our costumer and user.
Our competence reflects in our so-phisticatedproducts.While taking intoaccount every economical aspect, wedevelop innovative technical solutions.
Especially in the field of preventivefire protection and the correspon-ding smoke exhaust fans for thema-chanical smoke extraction,we againand again set standards.
Our self understanding is to be apartner to companies active in thefield of technical building equip-ment. TLT smoke exhaust fans offergreatest security.
They all have been tested acordingto all valid Building rules and posessthe CE-marks for smoke extractingfans.
This affects the different tempera-ture sectors as well as the differenttypes of constructions of thesesmoke exhaust fans.
It eases work especially with majorprojects. As a matter of fact it is pos-sible for the planner and the execu-tive company to react at any time onthe situation of installation and re-quests within the complete productprogramm without changing theproducer.
Udo Jung,Vice President
We offer our professional help andsupport in finding solutions for yourproblems at any time with help ofour experienced office work andfield work. Because we want you tobe successful with our products.
We offer innovative solutions, technicalcompentence and reliability
Your partner for fansin the field of technical building equipment
1.2
Tradition and improvement
When Benno Schilde and AugustBüttner – independently from eachother, founded their factories in1874, none of them both thoughtthat 125 years later BadHers-feld would be one of themost modern product fa-cilities for fans.
Startingwith the„Exhaus-tors“, which in the beginning were
mainlymade of cast-iron and that af-terwards because of the use of steelsheets, became much lighter and
cheaper , our engineers develo-ped fans of higher quality andreliable technique.
This tradition developed intoa very successful companywith innovative products.
Our fans are used in a varietiy of ver-sions in nearly all industrial branches.
For more than 130 years: Construction of fans in Bad Hersfeld
Today we offer a range of pro-gramms for the technical buildingequipment sectors fire protection,ventilation, heating and industrialapplications.
Benno Schilde factory
A big impeller with a diameter from 4500mm (1910) First dynamic wheel balancingmachine (1925)
Exhaust air fan at potashmining (1920)
Your partner for fansin the field of technical building equipment
1.3
Quality in the production process from the beginning
Each product unit undergoes an in-tensive test run according to DINISO EN 9001 before leaving thefactory.
We not only want to be good, butefficent. We not only want to cor-respond to the expectations of ourcustomers but we want to thinkahead. Also in the future we willtake care for TLT products to hold aworldwide top technological posi-tion.
Above all there ist he qualiy of ourproducts. Our efficent and modern
production process, as well as highqualified staff, guarantee highestpossible quality.
Our customers take profit especi-ally from high operational safetyand efficiency of our fans and sys-tems.
The departments of research anddevelopment continue optimisingour products and test constantlynew methods.
The synchronized fan-production: safe, reliable and economical.
TLT-Turbo GmbHhold all importantnational and international qualitycertificates.
Pulverbeschichtungsanlage als 200˚C-Schleuse
Präzise Schweißarbeiten an einem Laufrad für Dachventilatoren Hans-Georg Gluth,Fertigungsleitung
Your partner for fansin the field of technical building equipment
1.4
Research,Development andQuality assuranceMore security by qualityassurance
The TLT quality assurance systemguarantees the same high qualiylevel for all products with regard tomaterial,working process, techniqueand functionality as well as to appli-cation and operational safety.
The quality of a product is alreadydecisively influenced during its de-velopment. As a matter offact our quality assurancebegins at that stage,
Our staff understand qua-lity as being an integralpart of their daily work.
An important part of their task ist hedaily controll of our quality assu-rance system and its update if neces-sary.
Thus its permanent quality can beguaranteed.
Our quality management accordingto DIN ISO EN 9001 guarantees thatall material processed and all parts,components, products and systemsproduced completly fulfil all strin-gent requirements at any time.
The strict observation of nationaland international standards as wellas all contractual obligations is self-evident for us.
Bei Forschung,Entwicklung und Qualitätssicherung setzen wir die Maßstäbe
Ein Garagen-Jetventilator auf dem Prüfstand in der TLT-Forschungs- undVersuchsabteilung Messarbeiten in der Versuchshalle
Your partner for fansin the field of technical building equipment
1.5
Smoke extraction in case of fire in buildings
into the concept of preventive fireprotection and informs planner andexecutor about conceptional andtechnical news in the field of smokeextraction from buildings.
The AGE stands for complete smokeextraction for the personal and pro-perty security as well as for the sup-port of foreig rescue with regard tothe applicability and the economicconversion in buildings.
TLT- Supply Program
•• roof-mounted smoke exhaust fans• axial smoke exhaust fans• wall-mounted smoke exhaust fans• centrifugal smoke exhaust fans• smoke exhaust-jet fans• Comprehensive range of • accessories
TLT smoke exhaust fans are availablefor 200, 300, 400 oder 600 degreeswith an endurance of 120 minutes.
Smoke exhaust fans for preventive fire protection.Fire smoke is very dangerous and isoften deadly. Enormous volumes ofsmoke may fil a room within a few mi-nutes and thus hinder the rescue ofhuman beings as well as the fire-fighting activities.
All TLT smoke exhaust fans are ap-proved and secure and have beentested by the Munich Technical Uni-versity according to EN 12101 part 3,CE certificated and admitted to theBuilding rules List of the German In-stitute of Building Technology (DIBt).
TLT is a leading memberof the German Smoke
extraction Association (AGE) .
The AGE introduces the subject of anall comprehensive smoke extraction
With our smoke exhaust fans youcan very quickly and efficently con-trol and extract this dangeroussmoke from the premises.
Der Entrauchungsventilator ist immer das Herzstück einer jeden Anlage
Großbrand mit starker Rauchentwicklung
Stabile Rauch-Schichtenbildung für Fluchtwege
Entrauchungs-Axialventilatoren
Entrauchungs-Dachventilatoren
Your partner for fans in the field of technical building equipment
1.6
Ventilation and air exhaust to and from buildings
TLT centrifugal roof units are used toextract used or polluted air from in-dustrial or commercial premises aswell as in halls or houses where theyserve for normal air extraction.
Equipped with silencers our acousti-cally optimised fans fulfil the highesrequirements for lownoised service.
TLT Supply Program
•• roof units• axial fans• centrifugal fans• plastic fans• comprehensive range of • assescories
TLT centrifugal roof units offer asimple an competitive way of me-chanical ventilation.
They may be used for decentralizedas well as centralized air extraction.
TLT-Dachventilator am Flughafen in BudapestWir bieten ein komplettes Programm an Lüftungsventilatoren für nahezu jeden Anwendungsfall
Dachradialventilatoren bieten eine einfache und kostengünstige Art der mechanischen Lüftung
TLT-Radialventilatoren mit einem Hochleistungs-Laufrad und rückwärts gekrümmten SchaufelnTLT-Lüftungs-Axialventilator
Your partner for fans in the field of technical building equipment
1.7
Air-heating and plant constructionComponents for the air-heating marketRequirements for industrial compo-nents used in air-heating have in-creased constantly.
Our products again and again setnew standards concerning accustic,
power requirement and design.
With help of our roof mounted heatrecuperation the heat recuperationmay be very efficiently realized.
TLT air-heaters Thermon® are produ-ced in a compact construction andare available in different versionsand with a large range of accessories.
These air-heaters are mostly used incommercial premises as for exampleshops, show-rooms, shopping mallsbut also open-plan offices, restau-rants and in warehouses and assem-bly halls.
TLT Supply Program
• air-heaters• roof mounted heat recuperators• thermovent• controls and accessories
acoustics, production and tests ofnewly developed appliances on ourtest rigs makes TLT the ideal partnerfor mechanical contractors
Our clean room components arebeing used in micro-electronics, me-dicine, food-technology, pharma-ceutical industry, automobileproduction as well as in the opticsand the clean room industry.
Our experience in fan application in-tegrated into drying equipmentlead to the development of plug-infans for the most diverse application
The near contact to our customers,together with a comprehensiveknowledge of fluid mechanics ,
concepts.
Due to the use and production ofimpellers we developed „free-run-ning impellers“ with very high effi-ciency rates, and in a next stepcentrifugal plug-in fans.
These plug-in fans are very success-fully used in air handling units anddryers, but also in the constructionof waggons, locomotives and ships.
TLT Supply Program
• Clean room components• Impeller sets• Centrifugal plug-in fans
Industrial components for plant construction
From our range of fans we develo-ped components for industrial ap-plication.
Kompakt-Thermon® mit AusblasdiffusorBeheizung von Gebäuden: Dach-Wärmerückgewinner für eine Produktionshalle
Radiallaufrad für industrielle Einsatzzwecke
Your partner for fans in the field of technical building equipment
1.8
Metro- and Tunnelfanspropulsing jet and remaining quantityof air, on the other hand as axial fans
in an operational buil-dings connected tothe ventilation ductwork. An escaperoute can also beprotected against in-coming smoke withthe help of over-pressure. The jet and
metro fans are equipped with a 100 %reversible blade. As a matter of fact,the air can be transported in both di-rections.
External air can be introduced forcooling or for air regeneration inmetro property as well as the pollu-ted air or smoke can be drawn offoutwards to the atmosphere.
Due to the modular casing construc-tion, the fans can be optimally adap-ted for difficult access conditionsduring the mounting, retrofit or du-ring the exchange of existing fans. :
The successful story of these fansstarted at the beginning of the 70’swith the implementation of the mostfamous Alp transit-routes and hasbecome more important today, intimes of increasingly rapid urbaniza-tion and relocation of infrastructurein subterranean areas.
TLT-Product range
• Metro fans• Tunnel-Axial fans• Jet fans• Pressure fans escape tunnel• Additional accessories
The fan line tested in accordance to12101 – 3 give the essential safety fortunnel operators. Specially selectedmaterials, high temperature motorsand the precision design from TLT
combine “your” safety with high effi-ciency.
Good flow features guarantee lowconnected loads and also lower in-stallation costs. They help also tokeep the acoustic emission low.
On the one hand the fans can beused in the section reservedfor traffic as jet fans which areused for supplying fresh air by meansof exchange of impulses between
Smoke is the major dangerous me-dium for human beings in subterra-nean tunnel sections. Our metro & tunnel fans ensuresmoke free escape routes in case offire.
Airventilation of metros and tunnels
Mit Strahlventilatoren der neuesten Generation sorgen wir immer für frische Luft im Straßentunnel
Tunnel-Axialventilator in Bad GodesbergHöchster Wirkungsgrad und beste Aerodynamik
Metro-Ventilatoren in einer U-Bahnanlage
Your partner for fans in the field of technical building equipment
1.9
Representations tunnel fans
TLT-Turbo GmbH Büro WienAm Stadtpark 31030 WienFon +43 17134030Fax +43 17134030 30E-Mail: [email protected]
TLT-Turbo GmbH Büro Moskauul. Profsojusnaja 45117 420 MoskauFon +7 - 9 57 18 72 31 Fax +7 - 9 57 18 73 31E-Mail: [email protected]
Hansa Engineering ABBäckvägen 20192 05 SollentunaFon +46 (8) 594 770 50Fax +46 (8) 585 797 50E-Mail: [email protected]
ZAG EngineeringHauptsraße 965064 WittnauFon +41-62 871 8 383Fax +41 62 871 83 86E-Mail: [email protected]
Pasch y Cia, S.A.C/Capitan Haya, 9-1°28020 MadridFon +34 (91) 598 3760Fax +34 (91) 555 1341E-Mail: [email protected]
Joseph B. Johnson, LLC62 Deer Path Lane, P.O. Box 562Mansfield, MA 02048Fon +1 774 719 2108Fax +1 774 719 2216E-Mail: [email protected]
Austria
Russia
Sweden
Switzerland
Spain
USA
Benelux
Brasil
Greece
Iran
Italy
Markhoven Engineering b.v.Nieuwe's Gravelandseweg 91405 HJ BussumPostbox 11 211400 BC Bussum / NiederlandeFon +31 35 698 2211Fax +31 35 691 9100E-Mail: [email protected]
Ventiladores Bernauer S.A.Avenida do Oratório, 2635 03221-100 - Parque Sao LucasSao Paulo - SPFon +55 11 6101 1855Fax +55 11 6918 0493E-Mail: [email protected]
Reimex Ltd. International Trading Co & RepresentativesStasinou Ave & 2, St. Elena str. 1514P.O. Box 21 884Nicosia 1514 / CyprusFon +30-10 98 12 352Fax +30-10-98 37 271E-Mail: [email protected]
Touphan Machine Co.No. 73, Mirzai Shirazi Ave,Corner of 11th st.,Tehran, IranFon +9821-8840 102Fax +9821-8845207E-Mail: [email protected]
NME s.r.l.Via F. Dell'Orto, 824126 BergamoFon +39 035-320030Fax +39 035-312022E-Mail: [email protected]
Your partner for fans in the field of technical building equipment
1.10
Training and further education
Only innovative products don’t beenough: You must be able to handlethem, too. And to be able tohandle them, we shareopenly and comprehen-sivly our know-howwith you.
Training, furt-her educa-tion an symposiasfor planner are veryimportant to us.
Therefore we have an own trainingcenter at our plant in Bad Hersfeld,including an affilliated productshowroom..
Here we offer product trainimg onthe basis of the fan manual as well astraining measures for different sub-jects like fluid mechanics for fantechnology, acoustic, or trainuigmeasures for extremly complex ap-plications e. g. smoke extraction sy-tems for buildings, garages andtunnels.
The advantage of our „inhouse-trai-ning“ is, that the gained knowledgecan be examined during practise.
As a matter of fact, a tour throughour plant complements the trainings.
But the fans of the product show-room can be used as well for de-monstrations, e. g. for smoke-free
escape routes.
We don’t want to overflowyou with theoretical and
technical details, mo-reover we want tooffer our precisesupport when
handling our pro-ducts in practice.
During our product training we im-part information about production,
materials, product variety, possibleapplication and of course tips forpractice.
Our competent and well trained staffoffer you qualified product trainings.
Other information, details and ap-pointments are availale under:++49(0)6621 - 9500
During our product training we im-part information about production,materials, product variety, possibleapplication and of course tips forpractice.
Qualified training and further education in Bad HersfeldIm TLT-Werk in Bad Hersfeld finden regelmäßig Produkt-, Service- und Vertriebsschulungen statt Entrauchungssymposium im Schulungszentrum
Anhand praktischer Beispiele vermitteln wir Informationen und wichtige Tipps für die Praxis
Your partner for fans in the field of technical building equipment
1.11
Sorted incoming mail adresses and fax numbers
We want to process your demands, commands and wishes as fast as possible. Therefore we have arranged direct mailadresses and fax numbers for your incoming mail. Please use our sorted mail adresses and fax numbers
Sector E-Mail Fax Remarks
Order [email protected] 950-5600 your order arrives our customer center for ist attention
Comission [email protected] 950-5610 Questions about confirmation of the order or amendmends to the contract
Dispatch [email protected] 950-5620 Questions or indications abot delivery to construction zones
Project [email protected] 950-5630 Questions about project elaboration or about the elaborated offer
Technique [email protected] 950-5640 Questions about the whole fan technique
Information [email protected] 950-5650 Documents, suggestions or a visit of our field service
Export [email protected] 950-5670 Questions from abroad directly redirected to our export departement
Contact person customer centerBirgit GermerothTel. 06621-950-165Email: [email protected]
Martin ArendTel. 06621-950-166Email: [email protected]
Walter Wurmnest Tel. 06621-950-162Email: [email protected]
Ingrid Döll Tel. 06621-950-161Email: [email protected]
Jörg Quanz (Teamleiter)Tel. 06621-950-160Email: [email protected]
Christina Till Tel. 06621-950-191Email: [email protected]
Beate ZeretzkiTel. 06621-950-182Email: [email protected]
Contact person technical sales and distribution
Jörg SpichalskyTel. 06621-950-185Email: [email protected]
Detlef HeineTel. 06621-950-183Email: [email protected]
Horst HölscherTel. 06621-950-163Email: [email protected]
Gabriele Wagner Tel. 06621-950-164Email: [email protected]
Oliver HolsteinTel. 06621-950-184Email: [email protected]
Manfred KümpelTel. 06621-950-190Email: [email protected]
Alfred Lapp (Teamleiter)Tel. 06621-950-180Email: [email protected]
Jochen BartlTel. 06621-950-158Email: [email protected]
Dirk DeiningerTel. 06621-950-181Email: [email protected]
Your partner for fans in the field of technical building equipment
1.12
Representations in GermanyHamburg
Bremen
Berlin, Brandenburg
NRW Nord
Kassel
Saarland
Bayern Nord
Bayern Süd
Hillo-Wilfried Markert Vogelsang 12 A 22926 Ahrensburg Fon: +49 (0) 4102 - 5 11 44 Fax: +49 (0) 4102) - 5 04 36E-Mail: [email protected]
Aike LoudoviciSchützenstr. 3521720 SteinkirchenFon: +49 (0) 4142 - 89 88 89Fax: +49 (0) 4142 - 89 88 90E-Mail: [email protected]
Friedrich GestDr.-Manasse-Straße 315370 PetershagenFon: +49 (0) 33439 - 1 61 73Fax: +49 (0) 33439 - 1 61 75E-Mail: [email protected]
Hans-Peter MüllerHavensteinstraße 4646045 OberhausenFon: +49 (0) 208 - 88 22 69 80Fax: +49 (0) 208 - 88 22 69 87E-Mail: [email protected]
Armin BelikSchloßbergweg 2 34587 Felsberg Fon: +49 (0) 5662 - 13 32 Fax: +49 (0) 5662 - 54 32E-Mail: [email protected]
Holger ReulGoethestr. 635510 Butzbach OstheimFon: +49 (0) 6033 - 92 78 60Fax: +49 (0) 6033 - 92 78 61E-Mail: [email protected]
Hans GassauerLaub 7497357 Prichsenstadt Fon: +49 (0) 09383 - 9 98 50 Fax: +49 (0) 09383 - 9 98 52E-Mail: [email protected]
Thomas SchusterBreitenbergstraße 686807 BuchloeFon: +49 (0) 8241 - 9 11 97 40Fax: +49 (0) 8241 - 9 11 97 41E-Mail: [email protected]
Martin KulinnaSeestraße 7a 17034 Neubrandenburg Fon: +49 (0) 395 - 5 69 42 10 Fax: +49 (0) 0395 - 5 69 42 03E-Mail: [email protected]
Gerhard OelzeOtto-Lilienthal-Str. 1031535 Neustadt Fon: +49 (0) 05032 - 95 45 0Fax: +49 (0) 5032 - 95 45 20E-Mail: [email protected]
Kersten ZeitfuchsObstgutgarten 6A 06842 Dessau Fon: +49 (0) 340 - 2 20 30 98 Fax: +49 (0) 340 - 21 22 47E-Mail: [email protected]
Werner PüllenHavensteinstraße 4646045 OberhausenFon: +49 (0) 208 - 88 22 69 80Fax: +49 (0) 208 - 88 22 69 87E-Mail: [email protected]
Bernd Oefler Auerweg 101445 RadebeulFon: +49 (0) 351 - 7 95 63 44Fax: +49 (0) 351 - 8 95 64 40E-Mail: [email protected]
Peter BraunVeldenzer Weg 1355288 ArmsheimFon: +49 (0) 6732 - 93 88 91Fax: +49 (0) 6732 - 93 88 92E-Mail: [email protected]
Jürgen Dolder Glockenturmstraße 12 71229 Leonberg-Warmbronn Fon: +49 (0) 7152 - 4 10 63 Fax: +49 (0) 7152 - 4 31 82E-Mail: [email protected]
Questions, wishes, suggestions? Thancontact us. We are pleased to help you!You can find all our contact datesunder: www.tlt.de
Neubrandenburg
Hannover
Leipzig
NRW Süd, Siegerland
Dresden
Frankfurt
Stuttgart
Your partner for fans in the field of technical building equipment
1.13
Representations in Europe
Denmark
France
Greece
Netherlands
AustriaSlovenien
Poland
TLT-Turbo GmbH office Moskau ul. Profsojusnaja 45117 420 MoskauFon +7 - 9 57 18 72 31 Fax +7 - 9 57 18 73 31E-Mail: [email protected]
Sefovent Lundbergs Pla t ABBox 10 20 S-55111 Jönköping Fon +46 - 36 30 13 50Fax +46 - 36 90 13 90E-Mail: [email protected]
Tobler AGIndustriestraße 176CH-8957 Spreitenbach Fon +41 - 5 64 18 13 00Fax +41 - 5 64 18 13 01E-Mail: [email protected]
BSH - Klima CZ, s.r.o. U Trojice 1042/2 CZ 150 00 Praha 5 Fon +420 2 511 77 DW 369 Fax +420 2 511 77 343E-Mail: [email protected]
IMCO Ventilation Systems Ltd.Inonu Cadessi Ozan Sokak No. 5/1T-81090 Kozyatagi Istanbul Fon +90 - 216 411 45 95 Fax +90 - 216 411 24 21E-Mail: [email protected]
BSH Hungaria Legtechnikai Kft.Ferto u. 8H-1107 BudapestFon +36 1 203 0690Fax +36 1 204 28 21E-Mail: [email protected]
Hammer Ventilation A/SFroselevvej 81 CDK-6330 PadborgFon +45 (746) 73329Fax +45 (746) [email protected]
Lennox France1, rue Raoul FollereauF-77608 Bussy-Saint-Georges Cedex 3Fon 0033-1-64 76 23 12Fax 0033-1-64 76 35 75E-Mail: [email protected]
Clima Comfort Components Ltd.Vrasida 11GR-115 28 AthenFon +30 210 7255 925Fax +30 210 7255 927Email: [email protected]
Inatherm B. V. Vijzelweg 10NL-5145 NK WaalwijkFon +31 (0)416 317830Fax +31 (0)416 342755 Internet: www.inatherm.nl
BSH Luft- und Klimageräte GmbHPuchsbaumgasse 25-27 A-1100 Wien Fon +43 1 485 15 11-0 Fax +43 1 486 36 28E-Mail: [email protected]
BSH Klima Polska Sp. z o.o.ul. Kolejowa 13, St. Iwiczna05-500 PiasecznoFon +48 22 737 18 58 Fax +48 22 737 18 59E-Mail: [email protected]
Russia
Sweden
Switzerland
Czech Republica
Turkey
Hungary
Entrauchungs-Dachventilatoren auf dem Hallendach der Kölnarena
Partner für die in der technischen Gebäudeausrüstung tätigen Firmen
Your partner for fans in the field of technical building equipment
1.14
Product selection in the internet
Increase efficiency in the process of offer and sales
Your advantage: You can contact usat any time. With our internet offer,we want to provide a good sevice.
Butt he contact via internet shalloffer you, as welll, new and effi-cient services during the infor-mation search.
Therefore you can find impor-tant and current information
about the company and the pro-ducts on our TLT-Webside, as well asthe TLT product configurator, withwhich you are able to arrange, indi-
With help of our product configura-tor you can use quickly and precislythe TLT product range.
Via structure, branche, applicationarea, way of ventilation, location andfans type, you will find very comfo-rably and quikly the suited fan foryour application out of our compre-hensive product range.
After the entry of the product speci-fic design parameter like operationpoint, engine auxiliaries, installationcircumstances, equipment etc., thepossible fans are calculated and li-sted in a clear table.
You can sort and compare the quali-fied fans with help of these tables byyour decision criterions, like nominalsize, efficiency factor, engine perfor-mance, acoustic, delivery time, priceetc.
After choosing a fit you come to a re-sult area. Here, your configurationwill be completed with the choise ofthe needed component and the in-dication of the quantities.
We provide all information and do-cuments about the configured fan,like specification, text for invation toenter, acoustic information, charac-teristics, dimension sheet, in the re-sult area.
Your configurations are collected un-der a project.Each of yourprojects maycontain anynumber of con-f i gu ra t i ons .While saving,the project, all its contained configu-rations are always retained.
To prevent invalid combination, theproduct configurator has an auto-matical validity check with the nes-secary attribution. Our productconfigurator is constructed multilin-gually. In this process, you can regu-late, independently from each other,the dialogue language and the prin-ting language.
�www.tlt.de/configurator
vidually and independently fromtime, our fans.
The download area, with its techni-cal documentation, tarifs, text for in-vation to tender,our professionelarticles and acomprehensivepicture library, isvery importantfor the information area.
�www.tlt.de/downloads
Gaining information: For you at any time, comfortably with your computer
The time for creating your offerscan be reduced explicitly, possiblemistakes can be minimized.
Mit dem Produktkonfigurator können Sie unser Produktangebot schnell in Kundennutzen umsetzen