ASHRAE HVAC SYSTEMS AND EQUIPMENT SI 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 3 to 22 kW.Gravity-vented radiant circulators may also have a circulating airfan, but they perform satisfactorily with or without the fan. Fan-typevented radiant circulators ar

6、e 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 heatersshould not be use

7、d 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 from 3 to12 kW and can be freestanding units or wall-mounted, nonrecessedunits of either the radiant or closed-front type. Unvented room

8、 heat-ers require an outdoor air intake. The size of the fresh air openingrequired is marked on the heater. To ensure adequate fresh air sup-ply, unvented gas-heating equipment must, according to voluntarystandards, include a device that shuts the heater off if the oxygen inthe room becomes inadequa

9、te. Unvented room heaters may not beinstalled in hotels, motels, or rooms of institutions such as hospitalsor 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 heat without flames.

10、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 is generallybelow 650

11、C 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.Unvented household ca

12、talytic 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 0.9 kgof fuel are not permitted for indoor use in the United S

13、tates. As aresult, catalytic room heaters sold in the United States are generallypermanently installed and fixed as wall-mounted units. Local codesand the National Fuel Gas Code (NFPA 54/ANSI Z223.1) should bereviewed for accepted combustion air requirements.Wall FurnacesA wall furnace is a self-con

14、tained 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 250 mm beyond the horizontal limits of the ca

15、singthrough walls of normal thickness, to provide heat to adjacentrooms. Wall furnaces range from 3 to 26 kW. Wall furnaces are clas-sified as conventional or direct vent.Conventional vent units require approved B-1 vent pipes andare installed to comply with the National Fuel Gas Code. Some wallfurn

16、aces 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-imum of inlet air for proper combus

17、tion 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 rooms, thereby usinga common vent.Th

18、e preparation of this chapter is assigned to TC 6.5, Radiant Heating andCooling.Fig. 1 Room Heater34.2 2012 ASHRAE HandbookHVAC Systems and Equipment (SI)Both vented-recessed and dual-wall furnaces are usually naturalconvection units. Cool room air enters at the bottom and is warmedas it passes over

19、 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 stratification.Direct-vent wall furnaces ar

20、e 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 mounted on walls with out-door

21、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,although some may be equipped wi

22、th fans. Direct-vent furnaces areavailable with inputs of 2 to 19 kW.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 outdoors. Cold air returns at theperiphery of

23、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)requirements for gas-fired direct heating equip

24、ment (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).CONTROLSValvesGas in-space heaters are con

25、trolled 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-stage control valve (with hydraulic the

26、rmostat) 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 control valve (with a hydraulic thermo-s

27、tat) 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 number of fuel firing ratesbetween low and h

28、igh 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 types.Wall thermostats are available in 24

29、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 power isgenerated by multiple thermocoupl

30、es 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 capillary tube that responds tochanges in t

31、emperature 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 the minimum input. When the heating requi

32、re-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,kWMinimumAFUE, %Input,kWMinimumAFUE, %Wall Furnace (with fan) Floor Furnace12.3 74 10.8 57Wall Furnace (gravity type)2.9

33、59 Room Heaters2.9 to 3.5 60 13.5 6513.5 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 Chapter 34.SIZING

34、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 ASHRAE HandbookFund

35、amentals.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 bungalow built in

36、 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 quantities; th

37、e 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 burner section out

38、doors. 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 recessed wallhe

39、aters. They may also be installed in a window, depending on thecabinet construction. The heater is always vented to the outdoors.An 11 to 19 L fuel tank may be attached to the heater, or a larger out-door tank can be used. Vaporizing pot burners are equipped with a single constant-leveland metering

40、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 Atomizing HeatersWa

41、ll 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 provide sufficien

42、t 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 immersed in

43、an integral fuel tank of upto 7.6 L capacity similar to that of a kerosene lamp. Fuel-burningrates range from about 1.5 to 6.5 kW. Radiant heaters usually havea removable fuel tank to facilitate refueling.The direct-fired, forced-convection portable kerosene heater hasa vaporizing burner and a heat-

44、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 that flameless oxi-datio

45、n 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 topromote circulation a

46、nd 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 berecessed into the floor. El

47、ectric 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 150 mm in overall depth and can be installed 460 mm above thefloor; th

48、e ratio of the overall length to the overall height is more thantwo to one.Table 2 Gas Input Required for In-SpaceSupplemental HeatersHeater TypeAverage AFUE,%Steady State Effi- ciency,%Gas Consumption per Unit HouseVolume, W/m3Outdoor Air Temperature, COlderBungalowaEnergy-Efficient Houseb15 0 10 1

49、5 0 10Vented 54.6 73.1 67.1 36.9 16.8 28.6 15.7 7.1Unvented 90.5 90.5 61.7 33.9 15.4 26.3 14.4 6.6Direct vent 76.0 78.2 60.7 33.4 15.2 21.1 11.6 5.3aTested bungalow total heated volume = 193.3 m3and U 1.7 to 2.8 W/(m2K).bTested energy-efficient house total heated volume = 333.7 m3andU 1.1 to 1.7 W/(m2K).Fig. 4 Oil-Fueled Heater with Vaporizing Pot-Type Burner34.4 2012 ASHRAE HandbookHVAC Systems and Equipment (SI)Units are available from 610 to 3700 mm in length, with ratingsfrom 300 to 1300 W/m, and they fit together to make up any desiredcontinuous length or rating. Electric hy