ASHRAE HVAC APPLICATIONS SI CH 1-2015 Residences.pdf

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1、1.1CHAPTER 1RESIDENCESSystems 1.1Equipment Sizing. 1.2Single-Family Residences . 1.3Multifamily Residences . 1.7Manufactured Homes 1.8PACE-CONDITIONING systems for residential use vary withSboth local and application factors. Local factors include energysource availability (present and projected) an

2、d price; climate;socioeconomic circumstances; and availability of installation andmaintenance skills. Application factors include housing type, con-struction characteristics, and building codes. As a result, many differ-ent systems are selected to provide combinations of heating, cooling,humidificat

3、ion, dehumidification, ventilation, and air filtering. Thischapter emphasizes the more common systems for space condition-ing of both single-family (i.e., traditional site-built and modular ormanufactured homes) and multifamily residences. Low-rise multi-family buildings generally follow single-fami

4、ly practice becauseconstraints favor compact designs; HVAC systems in high-rise apart-ment, condominium, and dormitory buildings are often of commer-cial types similar to those used in hotels. Retrofit and remodelingconstruction also adopt the same systems as those for new construc-tion, but site-sp

5、ecific circumstances may call for unique designs.1. SYSTEMSCommon residential systems are listed in Table 1. Three gener-ally recognized groups are central forced air, central hydronic, andzoned systems. System selection and design involve such key deci-sions as (1) source(s) of energy, (2) means of

6、 distribution and deliv-ery, and (3) terminal device(s).Climate determines the services needed. Heating and cooling aregenerally required. Air cleaning, by filtration or electrostatic de-vices, is present in most systems. Humidification, when used, isprovided in heating systems for thermal comfort (

7、as defined inASHRAE Standard 55), health, and reduction of static electricitydischarges. Cooling systems usually dehumidify air as well as low-ering its temperature. Typical forced-air residential installations areshown in Figures 1 and 2.Figure 1 shows a gas furnace, split-system air conditioner,hu

8、midifier, and air filter. Air from the space enters the equipmentthrough a return air duct. It passes initially through the air filter. Thecirculating blower is an integral part of the furnace, which suppliesheat during winter. An optional humidifier adds moisture to theheated air, which is distribu

9、ted throughout the home via the supplyduct. When cooling is required, heat and moisture are removed fromthe circulating air as it passes across the evaporator coil. Refrigerantlines connect the evaporator coil to a remote condensing unit locatedoutdoors. Condensate from the evaporator is removed thr

10、ough adrain line with a trap.Figure 2 shows a split-system heat pump, supplemental electricresistance heaters, humidifier, and air filter. The system functions asfollows: air from the space enters the equipment through the returnair duct (or sometimes through an opening in the equipment itself),and

11、passes through a filter. The circulating blower is an integral partof the indoor air-handling portion of the heat pump system, whichsupplies heat through the indoor coil during the heating season.Optional electric heaters supplement heat from the heat pump duringperiods of low outdoor temperature an

12、d counteract indoor airstreamcooling during periodic defrost cycles. An optional humidifier addsThe preparation of this chapter is assigned to TC 8.11, Unitary and RoomAir Conditioners and Heat Pumps.Table 1 Residential Heating and Cooling SystemsCentralForced AirCentralHydronic ZonedMost commonener

13、gysourcesGasOilElectricityGasOilElectricityGasElectricityDistribution mediumAir WaterSteamAirWaterRefrigerantDistributionsystemDucting Piping DuctingPiping orFree deliveryTerminaldevicesDiffusersRegistersGrillesRadiatorsRadiant panelsFan-coil unitsIncluded with product or same as forced-air or hydro

14、nic systemsFig. 1 Typical Residential Installation of Heating, Cooling, Humidifying, and Air Filtering System1.2 2015 ASHRAE HandbookHVAC Applications (SI)moisture to the heated air, which is distributed throughout the homethrough the supply duct. When cooling is required, heat and mois-ture are rem

15、oved from the circulating air as it passes across theevaporator coil. Refrigerant lines connect the indoor coil to the out-door unit. Condensate from the indoor coil is removed through adrain line with a trap.Minisplit and multisplit systems, which are similar to split sys-tems but are typically duc

16、tless, are increasingly popular worldwide.A typical two-zone, ductless multisplit system installation is shownin Figure 3. In this example, the system consists mainly of two parts:an outdoor condensing unit and two indoor air-handling units thatare usually installed on perimeter walls of the house.

17、Each indoor airhandler serves one zone and is controlled independently from theother indoor unit.Single-package unitary systems, such as window-mounted,through-the-wall, or rooftop units where all equipment is containedin one cabinet, are also popular. Ducted versions are used exten-sively in region

18、s where residences have duct systems in crawlspacesbeneath the main floor and in areas such as the southwestern UnitedStates, where rooftop-mounted packages connect to attic duct sys-tems.Central hydronic heating systems are popular both in Europe andin parts of North America where central cooling h

19、as not normallybeen provided. New construction, especially in multistory homes,now typically includes forced-air cooling.Zoned systems are designed to condition only part of a home atany one time. They may consist of individual room units or centralsystems with zoned distribution networks. Multiple

20、central systemsthat serve individual floors or the sleeping and common portions ofa home separately are sometimes used in large single-family resi-dences.The energy source is a major consideration in system selection.According to 2009 data from the U.S. Energy Information Admin-istration (EIA 2013),

21、 for heating, about 49% of homes use naturalgas, followed by electricity (34%), fuel oil (6%), propane (5%),wood (2.5%), and kerosene or other fuel (1%). Relative prices,safety, and environmental concerns (both indoor and outdoor) arefurther factors in heating energy source selection. Where variouss

22、ources are available, economics strongly influence the selection.Electricity is the dominant energy source for cooling.2. EQUIPMENT SIZINGThe heat loss and gain of each conditioned room and of ductworkor piping run through unconditioned spaces in the structure must beaccurately calculated to select

23、equipment with the proper heatingand cooling capacity. To determine heat loss and gain accurately, thefloor plan and construction details, including information on wall,ceiling, and floor construction as well as the type and thickness ofinsulation, must be known. Window design and exterior door deta

24、ilsare also needed. With this information, heat loss and gain can becalculated using the Air-Conditioning Contractors of America(ACCA) Manual Jor similar calculation procedures. To conserveenergy, many jurisdictions require that the building be designed tomeet or exceed the requirements of ASHRAE St

25、andard 90.2 or sim-ilar requirements.Proper matching of equipment capacity to the building heat lossand gain is essential. The heating capacity of air-source heat pumpsis usually supplemented by auxiliary heaters, most often of the elec-tric resistance type; in some cases, however, fossil fuel furna

26、ces orsolar systems are used.Undersized equipment will be unable to maintain the intendedindoor temperature under extreme outdoor temperatures. Someoversizing may be desirable to enable recovery from setback and tomaintain indoor comfort during outdoor conditions that are moreextreme than the nomina

27、l design conditions. Grossly oversizedequipment can cause discomfort because of short on-times, wideindoor temperature swings, and inadequate dehumidification whencooling. Gross oversizing may also contribute to higher energy useby increasing cyclic losses. Variable-capacity equipment (heatpumps, ai

28、r conditioners, and furnaces) can more closely matchbuilding loads over broad ambient temperature ranges, usuallyreducing these losses and improving comfort levels; in the case ofheat pumps, supplemental heat needs may also be reduced.Residences of tight construction may have high indoor humidityand

29、 a build-up of indoor air contaminants at times. Air-to-air heatrecovery equipment may be used to provide tempered ventilation airto tightly constructed houses. Outdoor air intakes connected to thereturn duct of central systems may also be used when reducinginstalled costs is important. Simple exhau

30、st systems with or withoutpassive air intakes are also popular. Natural ventilation by operablewindows is also popular in some climates. Excessive accumulationof radon is of concern in all buildings; lower-level spaces should notbe depressurized, which causes increased migration of soil gases intoFi

31、g. 2 Typical Residential Installation of a Split-System Air-to-Air Heat PumpFig. 3 Example of Two-Zone, Ductless Multisplit System in Typical Residential InstallationResidences 1.3buildings. All ventilation schemes increase heating and coolingloads and thus the required system capacity, thereby resu

32、lting ingreater energy consumption. In all cases, minimum ventilation rates,as described in ASHRAE Standards 62.1 and 62.2, should be main-tained.3. SINGLE-FAMILY RESIDENCESHeat PumpsHeat pumps for single-family houses are normally centrallyducted unitary or split systems, as illustrated in Figures

33、2 and 3.Most commercially available heat pumps, particularly in NorthAmerica, are reversible, electrically powered, air-source systems.The direction of flow of the refrigerant can be switched to providecooling or heating to the home.Heat pumps may be classified by thermal source and distributionmedi

34、um in the heating mode as well as the type of fuel used. Themost common classifications of heat pump equipment are air-to-airand water-to-air. Air-to-water and water-to-water types are also used.Heat pump systems are generally described as air-source orground-source. The thermal sink for cooling is

35、generally assumed tobe the same as the thermal source for heating.Air-Source Systems. Air-source systems using ambient air asthe heat source/sink can be installed in almost any application andare generally the least costly to install and thus the most commonlyused.Ground-Source (Geothermal) Systems.

36、 Ground-source sys-tems usually use water-to-air heat pumps to extract heat from theground using groundwater or a buried heat exchanger. As a heatsource/sink, groundwater (from individual wells or supplied as autility from community wells) offers the following advantages overambient air: (1) heat pu

37、mp capacity is independent of ambient airtemperature, reducing supplementary heating requirements; (2) nodefrost cycle is required; (3) although operating conditions forestablishing rated efficiency are not the same as for air-source sys-tems, seasonal efficiency is usually higher for heating and fo

38、r cool-ing; and (4) peak heating energy consumption is usually lower.Two other system types are ground-coupled and surface-water-coupled systems. Ground-coupled systems offer the same advan-tages, but because surface water temperatures track fluctuations inair temperature, surface-water-coupled syst

39、ems may not offer thesame benefits as other ground-source systems. Both system typescirculate brine or water in a buried or submerged heat exchanger totransfer heat from the ground or water. Direct-expansion ground-source systems, with evaporators buried in the ground, also areavailable but are seld

40、om used. Water-source systems that extractheat from surface water (e.g., lakes or rivers) or city (tap) water aresometimes used where local conditions allow. See Chapter 49 of the2012 ASHRAE HandbookHVAC Systems and Equipment for fur-ther information.Water supply, quality, and disposal must be consi

41、dered forgroundwater systems. Caneta Research (1995) and Kavanaugh andRafferty (2014) provide detailed information on these subjects.Secondary coolants for ground-coupled systems are discussed inCaneta Research (1995) and in Chapter 31 of the 2013 ASHRAEHandbookFundamentals. Buried heat exchanger co

42、nfigurationsmay be horizontal or vertical, with the vertical including bothmultiple-shallow- and single-deep-well configurations. Ground-coupled systems avoid water quality, quantity, and disposal con-cerns but are sometimes more expensive than groundwater systems.However, ground-coupled systems are

43、 usually more efficient, espe-cially when pumping power for the groundwater system is consid-ered. Proper installation of the ground coil(s) is critical to success.Add-On Heat Pumps. In add-on systems, a heat pump is added(often as a retrofit) to an existing furnace or boiler/fan-coil system.The hea

44、t pump and combustion device are operated in one of twoways: (1) alternately, depending on which is most cost-effective, or(2) in parallel. Bivalent heat pumps, factory-built with the heatpump and combustion device grouped in a common chassis and cab-inets, provide similar benefits at lower installa

45、tion costs.Fuel-Fired Heat Pumps. Extensive research and developmenthas been conducted to develop fuel-fired heat pumps. They havebeen marketed in North America. More information may be foundin Chapter 49 of the 2012 ASHRAE HandbookHVAC Systems andEquipment.Water-Heating Options. Heat pumps may be e

46、quipped withdesuperheaters (either integral or field-installed) to reclaim heat fordomestic water heating when operated in cooling mode. Integratedspace-conditioning and water-heating heat pumps with an addi-tional full-size condenser for water heating are also available.FurnacesFurnaces are fueled

47、by gas (natural or propane), electricity, oil,wood, or other combustibles. Gas, oil, and wood furnaces may drawcombustion air from the house or from outdoors. If the furnacespace is located such that combustion air is drawn from the out-doors, the arrangement is called an isolated combustion system(

48、ICS). Furnaces are generally rated on an ICS basis. Outdoor air isducted to the combustion chamber (a direct-vent system) for man-ufactured home applications and some mid- and high-efficiencyequipment designs. Using outdoor air for combustion eliminatesboth infiltration losses associated with using

49、indoor air for combus-tion and stack losses associated with atmospherically induced draft-hood-equipped furnaces.Two available types of high-efficiency gas furnaces are noncon-densing and condensing. Both increase efficiency by adding orimproving heat exchanger surface area and reducing heat loss dur-ing furnace off-times. Noncondensing furnaces usually have com-bustion efficiencies below 85% and condensing furnaces havecombustion efficiencies higher than 90%. The higher-efficiencycondensing type recovers more energy by condensing water vaporfrom combustion products. Condensate is forme