ASHRAE HVAC SYSTEMS AND EQUIPMENT IP CH 34-2012 RESIDENTIAL IN-SPACE HEATING EQUIPMENT.pdf

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1、34.1CHAPTER 34RESIDENTIAL IN-SPACE HEATING EQUIPMENTGAS IN-SPACE HEATERS. 34.1Controls 34.2Vent Connectors . 34.3Sizing Units 34.3OIL AND KEROSENE IN-SPACE HEATERS . 34.3ELECTRIC IN-SPACE HEATERS 34.3Radiant Heating Systems . 34.4SOLID-FUEL IN-SPACE HEATERS . 34.4Fireplaces. 34.4Stoves . 34.5GENERAL

2、 INSTALLATION PRACTICES . 34.6N-SPACE heating equipment differs from central heating in thatI fuel is converted to heat in the space to be heated. In-space heat-ers may be either permanently installed or portable and may trans-fer heat by a combination of radiation, natural convection, andforced con

3、vection. The energy source may be liquid, solid, gas-eous, or electric.GAS IN-SPACE HEATERSRoom HeatersA vented circulator room heater is a self-contained, freestand-ing, nonrecessed gas-burning appliance that furnishes warm airdirectly to the space in which it is installed, without ducting (Figure1

4、). It converts the energy in the fuel gas to convected and radiantheat without mixing flue gases and circulating heated air by trans-ferring heat from flue gases to a heat exchanger surface.A vented radiant circulator is equipped with high-temperatureglass panels and radiating surfaces to increase r

5、adiant heat transfer.Separation of flue gases from circulating air must be maintained.Vented radiant circulators range from 10,000 to 75,000 Btu/h.Gravity-vented radiant circulators may also have a circulating airfan, but they perform satisfactorily with or without the fan. Fan-typevented radiant ci

6、rculators are equipped with an integral circulatingair fan, which is necessary for satisfactory performance.Vented room heaters are connected to a vent, chimney, or single-wall metal pipe venting system engineered and constructed todevelop a positive flow to the outdoor atmosphere. Room heatersshoul

7、d not be used in a room that has limited air exchange with adja-cent spaces because combustion air is drawn from the space.Unvented radiant or convection heaters range in size from10,000 to 40,000 Btu/h and can be freestanding units or wall-mounted, nonrecessed units of either the radiant or closed-

8、fronttype. Unvented room heaters require an outdoor air intake. The sizeof the fresh air opening required is marked on the heater. To ensureadequate fresh air supply, unvented gas-heating equipment must,according to voluntary standards, include a device that shuts theheater off if the oxygen in the

9、room becomes inadequate. Unventedroom heaters may not be installed in hotels, motels, or rooms ofinstitutions such as hospitals or nursing homes.Catalytic room heaters are fitted with fibrous material impreg-nated with a catalytic substance that accelerates the oxidation of agaseous fuel to produce

10、heat without flames. The design distributesthe fuel throughout the fibrous material so that oxidation occurs onthe surface area in the presence of a catalyst and room air. Catalyticheaters transfer heat by low-temperature radiation and by convec-tion. The surface temperature is below a red heat and

11、is generallybelow 1200F at the maximum fuel input rate. The flameless com-bustion of catalytic heaters is an inherent safety feature not offeredby conventional flame-type gas-fueled burners. Catalytic heatershave also been used in agriculture and for industrial applications incombustible atmospheres

12、.Unvented household catalytic heaters are used in Europe. Most ofthese are portable and mounted on casters in a casing that includes acylinder of liquefied petroleum gas (LPG) so that they may be rolledfrom one room to another. LPG cylinders holding more than 2 lb offuel are not permitted for indoor

13、 use in the United States. As a result,catalytic room heaters sold in the United States are generally perma-nently installed and fixed as wall-mounted units. Local codes and theNational Fuel Gas Code (NFPA 54/ANSI Z223.1) should bereviewed for accepted combustion air requirements.Wall FurnacesA wall

14、 furnace is a self-contained vented appliance with grillesthat are designed to be a permanent part of the structure of a building(Figure 2). It furnishes heated air that is circulated by natural orforced convection. A wall furnace can have boots, which may notextend more than 10 in. beyond the horiz

15、ontal limits of the casingthrough walls of normal thickness, to provide heat to adjacentrooms. Wall furnaces range from 10,000 to 90,000 Btu/h. Wall fur-naces are classified as conventional or direct vent.Conventional vent units require approved B-1 vent pipes andare installed to comply with the Nat

16、ional Fuel Gas Code. Some wallfurnaces are counterflow units that use fans to reverse the naturalflow of air across the heat exchanger. Air enters at the top of the fur-nace and discharges at or near the floor. Counterflow systemsreduce heat stratification in a room. As with any vented unit, a min-i

17、mum of inlet air for proper combustion must be supplied.Vented-recessed wall furnaces are recessed into the wall, withonly the decorative grillwork extending into the room. This leavesmore usable area in the room being heated. Dual-wall furnaces aretwo units that fit between the studs of adjacent ro

18、oms, thereby usinga common vent.The preparation of this chapter is assigned to TC 6.5, Radiant Heating andCooling.Fig. 1 Room Heater34.2 2012 ASHRAE HandbookHVAC Systems and Equipment Both vented-recessed and dual-wall furnaces are usually naturalconvection units. Cool room air enters at the bottom

19、and is warmedas it passes over the heat exchanger, entering the room through thegrillwork at the top of the heater. This process continues as long asthe thermostat calls for the burners to be on. Accessory fans assist inthe movement of air across the heat exchanger and help minimizeair stratificatio

20、n.Direct-vent wall furnaces are constructed so that combustionair comes from the outdoors, and all flue gases discharge into theoutdoor atmosphere. These appliances include grilles or the equiv-alent and are designed to be attached to the structure permanently.Direct-vent wall heaters are normally m

21、ounted on walls with out-door exposure.Direct-vent wall furnaces can be used in extremely tight (well-insulated) rooms because combustion air is drawn from outside theroom. There are no infiltration losses for dilution or combustion air.Most direct-vent heaters are designed for natural convection,al

22、though some may be equipped with fans. Direct-vent furnaces areavailable with inputs of 6000 to 65,000 Btu/h.Floor FurnacesFloor furnaces are self-contained units suspended from the floorof the heated space (Figure 3). Combustion air is taken from the out-doors, and flue gases are also vented outdoo

23、rs. Cold air returns at theperiphery of the floor register, and warm air comes up to the roomthrough the center of the register.United States Minimum Efficiency RequirementsThe National Appliance Energy Conservation Act (NAECA) of1987 mandates minimum annual fuel utilization efficiency (AFUE)require

24、ments for gas-fired direct heating equipment (Table 1). Theminimums (effective as of January 1, 1990) are measured using theU.S. Department of Energy test method (DOE 1984) and must bemet by manufacturers of direct heating equipment (i.e., gas-firedroom heaters, wall furnaces, and floor furnaces).CO

25、NTROLSValvesGas in-space heaters are controlled by four types of valves:The full on/off, single-stage valve is controlled by a wall ther-mostat. Models are available that are powered by a 24 V supply orfrom energy supplied by the heat of the pilot light on the thermo-couple (self-generating).The two

26、-stage control valve (with hydraulic thermostat) fireseither at full input (100% of rating) or at some reduced step, whichcan be as low as 20% of the heating rate. The amount of time at thereduced firing rate depends on the heating load and the relative over-sizing of the heater.The step-modulating

27、control valve (with a hydraulic thermo-stat) steps on to a low fire and then either cycles off and on at the lowfire (if the heating load is light) or gradually increases its heat outputto meet any higher heating load that cannot be met with the low fir-ing rate. This control allows an infinite numb

28、er of fuel firing ratesbetween low and high fire.The manual control valve is controlled by the user rather thanby a thermostat. The user adjusts the fuel flow and thus the level offire to suit heating requirements.ThermostatsTemperature controls for gas in-space heaters are of the follow-ing two typ

29、es.Wall thermostats are available in 24 V and millivolt systems.The 24 V unit requires an external power source and a 24 Vtransformer. Wall thermostats respond to temperature changesand turn the automatic valve to either full-on or full-off. Themillivolt unit requires no external power because the p

30、ower isgenerated by multiple thermocouples and may be either 250 or750 mV, depending on the distance to the thermostat. Thisthermostat also turns the automatic valve to either full-on orfull-off.Built-in hydraulic thermostats are available in two types: (1) asnap-action unit with a liquid-filled cap

31、illary tube that responds tochanges in temperature and turns the valve to either full-on orfull-off; and (2) a modulating thermostat, which is similar to thesnap-action unit, except that the valve comes on and shuts off at apreset minimum input. Temperature alters the input anywherefrom full-on to t

32、he minimum input. When the heating require-ments are satisfied, the unit shuts off.Fig. 2 Wall FurnaceFig. 3 Floor FurnaceTable 1 Efficiency Requirements in the United States for Gas-Fired Direct Heating EquipmentInput,1000 Btu/hMinimumAFUE, %Input,1000 Btu/hMinimumAFUE, %Wall Furnace (with fan) Flo

33、or Furnace42 74 37 57Wall Furnace (gravity type)46 6546 65Residential In-Space Heating Equipment 34.3VENT CONNECTORSAny vented gas-fired appliance must be installed correctly tovent combustion products. A detailed description of proper ventingtechniques is found in the National Fuel Gas Code and Cha

34、pter 34.SIZING UNITSThe size of the unit selected depends on the size of the room, thenumber and direction of exposures, the amount of insulation in theceilings and walls, and the geographical location. Heat loss require-ments can be calculated from procedures described in Chapter 17 ofthe 2009 ASHR

35、AE HandbookFundamentals.DeWerth and Loria (1989) studied the use of gas-fired, in-spacesupplemental heaters in two test houses. They proposed a heatersizing guide, which is summarized in Table 2. The energy con-sumption in Table 2 is for unvented, vented, and direct vent heatersinstalled in (1) a bu

36、ngalow built in the 1950s with average insula-tion, and (2) a townhouse built in 1984 with above-average insula-tion and tightness.OIL AND KEROSENE IN-SPACE HEATERSVaporizing Oil Pot HeatersThese heaters have an oil-vaporizing bowl (or other receptacle)that admits liquid fuel and air in controllable

37、 quantities; the fuel isvaporized by the heat of combustion and mixed with the air inappropriate proportions. Combustion air may be induced by naturaldraft or forced into the vaporizing bowl by a fan. Indoor air is gen-erally used for combustion and draft dilution. Window-installedunits have the bur

38、ner section outdoors. Both natural- and forced-convection heating units are available. A small blower is sold as anoption on some models. The heat exchanger, usually cylindrical, ismade of steel (Figure 4). These heaters are available as room units(both radiant and circulation), floor furnaces, and

39、recessed wallheaters. They may also be installed in a window, depending on thecabinet construction. The heater is always vented to the outdoors. A3 to 5 gal fuel tank may be attached to the heater, or a larger outdoortank can be used. Vaporizing pot burners are equipped with a single constant-levela

40、nd metering valve. Fuel flows by gravity to the burner through theadjustable metering valve. Control can be manual, with an off pilotand variable settings up to maximum, or it can be thermostaticallycontrolled, with the burner operating at a selected firing ratebetween pilot and high.Powered Atomizi

41、ng HeatersWall furnaces, floor furnaces, and freestanding room heaters arealso available with a powered gun-type burner using No. 1 or No. 2fuel oil. For more information, refer to Chapter 31.Portable Kerosene HeatersBecause kerosene heaters are not normally vented, precautionsmust be taken to provi

42、de sufficient ventilation. Kerosene heaters areof four basic types: radiant, natural-convection, direct-fired, forced-convection, and catalytic.The radiant kerosene heater has a reflector, while the naturalconvection heater is cylindrical in shape. Fuel vaporizes from thesurface of a wick, which is

43、immersed in an integral fuel tank of upto 2 gal capacity similar to that of a kerosene lamp. Fuel-burningrates range from about 5000 to 22,500 Btu/h. Radiant heaters usu-ally have a removable fuel tank to facilitate refueling.The direct-fired, forced-convection portable kerosene heater hasa vaporizi

44、ng burner and a heat-circulating fan. These heaters areavailable with thermostatic control and variable heat output.The catalytic type uses a metal catalyst to oxidize the fuel. It isstarted by lighting kerosene at the surface; however, after a fewmoments, the catalyst surface heats to the point tha

45、t flameless oxi-dation of the fuel begins.ELECTRIC IN-SPACE HEATERSWall, Floor, Toe Space, and Ceiling HeatersHeaters for recessed or surface wall mounting are made withopen wire or enclosed, metal-sheathed elements. An inner liner orreflector is usually placed between the elements and the casing to

46、promote circulation and minimize the rear casing temperature. Heatis distributed by both convection and radiation; the proportion ofeach depends on unit construction.Ratings are usually 1000 to 5000 W at 120, 208, 240, or 277 V.Models with air circulation fans are available. Other types can berecess

47、ed into the floor. Electric convectors should be placed so thatair moves freely across the elements.Baseboard HeatersThese heaters consist of a metal cabinet containing one or morehorizontal, enclosed, metal-sheathed elements. The cabinet is lessthan 6 in. in overall depth and can be installed 18 in

48、. above the floor;the ratio of the overall length to the overall height is more than twoto one.Table 2 Gas Input Required for In-SpaceSupplemental HeatersHeater TypeAverage AFUE,%Steady State Effi- ciency,%Gas Consumption per Unit HouseVolume, Btu/h per ft3Outdoor Air Temperature, FOlderBungalowaEne

49、rgy-Efficient Houseb5 30 50 5 30 50Vented 54.6 73.1 6.5 3.8 1.6 2.8 1.6 0.7Unvented 90.5 90.5 6.0 3.5 1.5 2.6 1.5 0.6Direct vent 76.0 78.2 5.9 3.4 1.5 2.1 1.2 0.5aTested bungalow total heated volume = 6825 ft3and U 0.3 to 0.5 Btu/hF.bTested energy-efficient house total heated volume = 11,785 ft3andU 0.2 to 0.3 Btu/hF.Fig. 4 Oil-Fueled Heater with Vaporizing Pot-Type Burner34.4 2012 ASHRAE HandbookHVAC Systems and Equipment Units are available from 2 to 12 ft in length, with ratings from100 to 400 W/ft, and they fit together to make up any desired con-tinuous length or rating. Ele