《专业英语》课件Unit_35.pptx
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1、Unit35Mechanical Engineering Design ProcessTextThe decisions made by the designers of the buildings heating,ventilating,and air-conditioning(HVAC)system are crucial in determining thermal comfort,the quality of the indoor air,and the efficiency of energy use by the building.Air exchange rates affect
2、 the amount of energy used to heat or cool fresh air,and the energy lost when used air is exhausted.The American Society of Heating,Refrigerating,and Air-Conditioning Engineers(ASHRAE)requirements for ventilation include minimum rates for replacing previously circulated air in the building with fres
3、h air.Energy costs can be reduced or eliminated by improving building insulation,lighting design,and the efficiency of HVAC and other building equipment.Buildings that allow natural ventilation,and those that employ such techniques as heat reclamation,thermal-storage systems,and flexible air handlin
4、g and chiller units lower energy use and reduce costs.The architect and engineers usually make the decisions on what systems to employ,but the responsibility for finding appropriate solutions depends on creativity and integrated efforts of the entire design team,in which the interior designer should
5、 play a significant role.TextThe mechanical systems of the building have their own model codes,which are geared toward professional mechanical engineers and installers.They are based on three model codes:the Building Officials Code Administrators International(BOCA)National Mechanical Code(NMC),the
6、Standard National Mechanical Code(SMC),and the Uniform National Mechanical Code(UMC).These model codes are revised every three years.As an interior designer,you will rarely need to refer to the mechanical codes,but you should be familiar with some of their general requirements and terms,especially t
7、hose affecting energy conservation requirements.In buildings where there is a minimum of mechanical work,the mechanical engineer or contractor will work directly off the interior designers drawings.For example,the interior design drawings may be the source for information in a renovation project whe
8、re a few supply diffusers or return grilles are being added to an existing system.In any event,you may need to coordinate your preliminary design with the mechanical engineer or contractor to make sure you leave enough room for clearances around HVAC equipment.TextThe mechanical engineer,like the in
9、terior designer,is trying to achieve an environment where people are comfortable,and to meet the requirements of applicable codes.By calculating how much heating or cooling is needed to achieve comfort,the engineer is able to develop design strategies that affect both the architecture and the mechan
10、ical systems of the building,such as the optimal size of windows,or the relative amounts of insulation or thermal mass.The engineer will figure out how big the UVAC system components should be to provide enough heating and/or cooling for the most extreme conditions the building is likely to experien
11、ce.The engineer will calculate the amount of energy used for normal conditions in a typical season and adjust the design to reduce long-term energy use.The number of people using the building both seasonally and hourly is also taken into account.The amount of heat gained or lost from the outside env
12、ironment will be considered.The materials,areas,and rates of heat flow through the buildings envelope affect this calculation.The amount of fresh air introduced into the system also influences these calculations,so the engineer will look at the volumes of the spaces in the building and the rates of
13、fresh air exchange.The engineer will suggest window locations and other design elements that minimize the heat gain within the building.TextPHASES OF THE DESIGN PROCESSThe phases of the engineering design process are similar to those of architects and interior designers:preliminary design,design dev
14、elopment,design finalization and specification,and the construction phase.During the preliminary design phase,the engineer considers the most general combinations of comfort requirements and climate characteristics.The schedule of activities that will take place in the space is listed,along with the
15、 conditions required for comfort during performance.The engineer analyzes the sites energy resources and lists strategies to design with the climate.Building form alternatives are considered and discussed with the architect.Available systems are reviewed,including both passive(nonmechanical)and acti
16、ve alternatives.Then the engineer figures out the size of one or more alternative systems using general design guidelines.In smaller buildings,the architect may do the system design.For larger,more complex buildings,the mechanical engineer will work as a team with architects,landscape architects,and
17、 the interior designer.The team approach helps to assess the value of a variety of design alternatives arising from different perspectives.When mutual goals are agreed upon early in the design process,this team approach can lead to creative innovations.TextThe more that the siting,layout,and orienta
18、tion of the building reduces heat loss,the less energy the healing and cooling equipment consumes.Opportunities may arise for the design of the HVAC system to be expressed in the form of the building.Creative teamwork can lead to new designs that offer better environments with less energy use,and th
19、at can be applied to many other buildings later on.During the design development phase,one alternative is usually chosen as presenting the best combination of aesthetic,social,and technical solutions for the buildings program.The engineer is given the latest set of drawings and programming informati
20、on for the building.The architect and engineer then establish the design conditions by listing the range of acceptable air and surface temperatures,air motions,relative humidities,lighting levels,and background noise levels for each activity to take place in the building.A schedule of operations for
21、 each activity is also developed.By considering these activities and their schedule,the amount of heat that will be generated by the activities,and the buildings orientation,the engineer then determines the HVAC zones for the building.Each of these zones has its own set of functional,scheduling,and
22、orientation concerns that determine when and how much heating,cooling,or ventilation is needed.TextFor each zone,the engineer establishes the thermal load(the amount of heat gained or lost)for the worst winter and summer conditions,and for average conditions during the majority of the buildings oper
23、ating hours.An estimate of the buildings annual energy consumption may also be made at this time.With all this detailed information in place,the engineer next selects the HVAC systems.More than one system may be used to meet different conditions in a large building.For example,one system may serve z
24、ones that are completely within the interior of the building,with a separate system for perimeter zones.Next,the engineer identifies the components of the HVAC system,and locates them within the building.Mechanical rooms,distribution trees(vertical chases and horizontal runs of ductwork),and compone
25、nts like fan-coil units(FCUs)under windows and air grilles within specific spaces all have to be selected and located.Sizes for these components are also specified.Once the engineer lays out the system,it is time to coordinate conflicts with other building systems,such as the structure,plumbing,fire
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