《专业英语》课件Unit-35.pptx

1、TextThe 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 the amount of energy used to heat or cool

2、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 fresh air.Energy costs can be reduced or elimin

3、ated 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 handling and chiller units lower energy use and re

4、duce 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 play a significant role.TextThe mechanical

5、 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 Standard National Mechanical Code(SMC),and

6、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 those affecting energy conservation requirem

7、ents.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 where a few supply diffusers or return grilles

8、 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 interior designer,is trying to achieve an env

9、ironment 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 mechanical systems of the building,such as the op

10、timal 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 experience.The engineer will calculate the amount o

11、f 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 environment will be considered.The materials,a

12、reas,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 fresh air exchange.The engineer will sugges

13、t 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 development,design finalization and specificat

14、ion,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 conditions required for comfort during per

15、formance.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 active alternatives.Then the engineer figures o

16、ut 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 the interior designer.The team approach he

17、lps 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 orientation of the building reduces heat loss,the

18、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 that can be applied to many other buildings l

19、ater 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 information for the building.The architect and engin

20、eer 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 each activity is also developed.By conside

21、ring 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 orientation concerns that determine when an

22、d 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 operating hours.An estimate of the buildings an

23、nual 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 zones that are completely within the interio

24、r 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 components like fan-coil units(FCUs)under windows

25、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 safety,and circulation.TextBy drawing sect

26、ions through the building,architects and engineers can identify clearance problems and see opportunities to coordinate the HVAC system with other building systems.The process of design finalization involves the de-signer of the HVAC system verifying the load on each component and the components abil

27、ity to meet this load.Then the final drawings and specifications are completed.During construction,the engineer may visit the site to assure that work is proceeding according to design,and to deal with unanticipated site conditions.TextTHERMAL COMFORT ZONESThe way zones for heating and cooling are s

28、et up by the mechanical engineer has implications for the architecture and interior design of the space.Zones may occupy horizontal areas of a single floor,or may be vertically connected between floors.The function of a space affects both its vertical and horizontal zoning(Fig.1).Some functions may

29、tolerate higher temperatures than others.Some functions require daylight,which may add heat to the space,while others are better off away from the buildings perimeter.In some areas,such as laboratories,air quality and isolation is a major concern.The input of the interior designer can be an importan

30、t component in making sure that the clients needs are met.Fig.35.1Thermal zones based on activity patterns.TextZones also take into consideration the schedule of use of the space.Spaces that gain heat from daylight or electric lighting during the day only may be able to flush that heat to another sp

31、ace for use at night.An isolated activity with a different schedule from the rest of the building may need a separate mechanical system.The buildings orientation will also affect the HVAC zones.Exposure to daylight direct sun,and wind all create specific heating and cooling requirements.Perimeter sp

32、aces have different needs from interior spaces.In multistory buildings,interior spaces on inter-mediate floorsthose spaces not at the buildings perimeter or on the top or ground floorsmay be able to use ventilation air as their only heating load source.These areas are so well shielded from the build

33、ings exterior that they may not need additional heal,and can be served only by cooling.The amount of electrically generated heat,plus that produced by human activity and other heat-generating sources,usually outweigh the cooling effect of the amount of outdoor air supplied by minimal ventilation,eve

34、n in winter weather.In the summer,most of the interior cooling loads are generated inside the building.The perimeter areas of the building are much more weather sensitive.TextHEATING AND COOLING LOADSHeating and cooling loads are the amounts of energy required to make up for heat loss and heat gain

35、in the building(Fig.2).The rate of flow of hot or cold air coming into the building from ventilation and infiltration influences the amount of heating or cooling load.It is also dependent upon the difference in temperature and humidity between the inside and outside air.The amount of outside air com

36、ing in is expressed in liters per second(cubic feet per minute,or cfm).Fig 35.2Heat gains and losses in buildings.TextHeat Loss and Heating LoadsA heating load is created when a building loses heat through the building envelope.Cold outside air entering a building through ventilation,such as an open

37、 window,or as a result of infiltration,as when air leaks through cracks in the building envelope,also add to the heating load.Convection,radiation,or conduction of heat through the buildings exterior walls,windows,and roof assemblies and the floors of unheated spaces are the main sources of heal los

38、s in cold weather.Wind passing the building both draws warm air out and forces cold air in.Infiltration of cold air through cracks in the exterior construction,especially around doors and windows contributes significant heat loss.This heat loss places a heating load on the buildings mechanical syste

39、m,which must make up heat in spaces that lose it through cracks and poorly insulated areas.Energy auditors use equipment to locate air leaks and areas with inadequate insulation.They know what to look for in new and older buildings,and the cost of an energy audit is a good investment for a building

40、owner.Some utilities will supply basic energy audits for free.Trained experts,sometimes called house doctors or home performance contractors,look at the building as a system and evaluate safety,comfort,energy efficiency,and indoor air quality.You can get a listing of qualified,trained energy auditor

41、s from your stale energy office or cooperative extension service.TextThe most common sources of air leaks are where plumbing,wiring,or a chimney penetrates through an insulated floor or ceiling,or along the sill plate or band joist on top of the buildings foundation wall,fireplace dampers and attic

42、access hatches are other likely suspects.Anywhere that walls and ceilings or floors meet or where openings pierce the buildings exterior is an opportunity for air to infiltrate.Air can leak where the tops of interior partition walls intersect with the attic space and through recessed lights and fans

43、 in insulated ceilings.Missing plaster allows air to pass through a wall,as do electrical outlets and switches on exterior walls.Window,door,and baseboard moldings can leak air,as can dropped ceilings above bathtubs and cabinets.Air can also leak at low walls along the exterior in finished attics,es

44、pecially at access doors,and at built-in cabinets and bureaus.Gaps under 4 mm(1/4 in.)wide can be scaled with caulk,which is available in a variety of types for different materials.Specify caulks with 20-year flexibility lifetimes and select either colored or paintable caulk for visible use.Avoid us

45、ing the cheapest caulks,as they dont hold up well.Larger cracks and holes that are protected from the sun and moisture can be filled with expanding one-part polyurethane foam sealant.Look for a safe-for-ozone label for foam sealants without chlorofluorocarbons(CFCs).TextFor even larger cracks and fo

46、r backing in deep cracks,specify backer rod or crack filler,usually in the form of a round 4-to 25-mm(1/4-1-in.)diameter coil made of a flexible foam material.The crack is then scaled with caulk.Rigid foam insulation or fiberglass insulation wrapped in plastic can be used for very large openings lik

47、e plumbing chases and attic hatch covers.Avoid using plastic in places with high temperatures,as it may melt.Metal flashing with high temperature silicone sealants may be permitted around chimney by some building codes.Heat Gains and Cooling LoadsBuildings gain heat from occupants and their activiti

48、es.Cooling loads are defined as the hourly rate of heat gain in an enclosed space,and are expressed in Btu per hour.Cooling loads are used as the basis for selecting an air-conditioning unit or a cooling system.Cooling loads represent the energy needed to offset the heat gained through the building

49、envelope in hot weather or from hot air entering by infiltration or ventilation.Peoples body heal,showering,cooking,lighting,and appliances and equipment use also create cooling loads.TextThe heat generated by lighting is often the greatest part of the total cooling load in a building.All types of e

50、lectric lighting convert electrical power into light plus heat.Eventually,the light is also converted to heat within the space(think about a lamp shining on a desk and the desk becoming warmer).All the electrical power that enters a lighting fixture ends up as heat in the space.Some of the heat from