Document w8JmJmBO1KmZ45Z69B3BgjxV

Heating Ventilating Air Conditioning Guide 1939 around a drum or heating section, and out of the heater at or near the ton ? These heaters cause a continuous circulation of the air in the room durin jfe the time they are in operation. The burner or burners are located in `I base at the bottom of an enclosed combustion chamber. The products of j combustion pass up around baffles within the heating element or drum 1 and out the flue at the back near the top. They are well adapted not only y for residence room heating but also for stores and offices. y RDadJi.a----n--it heate---r--s---m--- a*ke ad, m.irab. l.e auxiliary heating appliances to be used during the occasional cool days at the beginning and end of the heating season when heat is desired in some particular room for an hour or two, i The radiant heater gives off a considerable portion of its heat in the form S of radiant energy emitted by an incandescent refractory that is heated by * a Bunsen flame. They are made in numerous shapes and designs and in J sizes ranging from two to fourteen or more radiants. Some have sheet- iron bodies finished in enamel or brass while others have cast-iron or brass '! frames with heavy fire-clay bodies. An atmospheric burner is supported i near the center of the base, usually by set screws at each end. Others j have a group of small atmospheric burners supported on a manifold J attached to the base. Most radiant heaters are supported on legs and are | portable; however, there are.also types which are encased in a jacket which fits into the wall with a grilled front, similar to the ordinary wall if register. Others are encased in frames which fit into fireplaces. `jj Gas-fired steam and hot water radiators are popular types of room heating i appliances. They provide a form of heating apparatus for intermittently ' heated spaces such as stores, small churches and some types of offices and ; apartments. They are made in a large variety of shapes and sizes and are - similar in appearance to the ordinary steam or hot water radiator con- ? nected to a basement boiler. A separate combustion chamber is provided j in the base of each radiator and is usually fitted with a one-piece burner. ? They may be secured in either the vented or unvented types, and with steam pressure, thermostatic or room temperature controls. ' Warm air radiators are similar in appearance to the steam or hot water f radiators. They are usually constructed of pressed steel or sheet metal f- hollow sections. The hot products of combustion circulate through the '' sections and are discharged out a flue, or into the room, depending upon whether the radiator is of the vented or unvented type. # Garage heaters are usually similar in construction to the cabinet | circulator space heaters, except that safety screens are provided over all | openings into the combustion chamber to prevent any possibility of explosion from gasoline fumes or other gases which might be ignited by an open flame. They are usually provided with automatic room tem- i perature controls and are well suited for heating either residence or i. commercial garages. Conversion Burners | Residence heating with gas through the use of conversion burners in- | stalled in coal-designed boilers and furnaces represents a common type | of gas-fired house heating system. In many conversion burners radiants or refractories are employed to convert some of the energy- in the gas to radiant heat. Others are of the blast type, operating without refractories. Many conversion units are equipped with sheet metal secondary air 228 Chapter 11- Automatic Fuel Burning Equipment ducts which are inserted through the ashpit door. The duct is equipped with automatic air controls which open when the burners are operating and close when the gas supply is turned off. This prevents a large part of the circulation of cold air through the combustion space of the ap pliance when not in operation By means of this duct the air necessary for proper combustion is supplied directly to the burner, thereby making it possible to reduce the amount of excess air passing through the com bustion chamber. Conversion units are made in many sizes both round and rectangular to fit different types and makes of boilers and furnaces. They may be secured with manual, push-button, or room temperature control. Ho Combustion Process Because of the varying composition of gases used for domestic heating it is difficult to generalize on the subject of gas burner combustion; Refer to the section on Gas Classification, in Chapter 9. Combustion Adjustments Little difficulty should be experienced in maintaining efficient com bustion conditions when burning gas. The fuel supply is normally held to close limits of variation in pressure and calorific value and, therefore, the rate of heat supply is nominally constant. Since the force necessary to introduce the fuel into the combustion chamber is an inherent factor of the fuel, no draft by the chimney is required for this purpose. The use of a draft diverter insures the maintenance of constant low draft condition in the combustion chamber with a resultant stability of air supply. A draft diverter is also helpful in controlling the amount of excess air and pre venting back drafts which might extinguish the flame. Measurement oi the Efficiency oi Combustion It is possible to determine the results of combustion by analyzing the gases of combustion with an Orsat apparatus. 11 is desirable to determine the percentage of carbon dioxide (C02), oxygen (02) and carbon monoxide (CO) in the flue gases. While ultimate C02 values of 10 to 12 per cent may be obtained from the combustion of gases commonly used for domestic heating, a combustion adjustment which will show from 8 to 10 per cent COi represents a practical value, Under normal conditions no CO will be produced by a gas-fired boiler or furnace. Limitations as to output rating by the A.G.A. are based upon operation with not more than 0.04 per cent CO in the products of combustion. This is too small an amount to be determined by the ordinary flue gas analyzer. Controls Gas burner controls may be divided into two parts: (a) devices to regulate burner operation so that the desired house heating results may be obtained, and (b) devices for the safety of the.boiler and burner. Control devices are treated in detail in Chapter 37. A room thermostat may be used as a control of house heating effect. These may be obtained in a number of types. Some central heating plants are equipped with push button or manual control. Class (b) controls include a device to shut off the burner if the gas fails to ignite, a device actuated by boiler pressure, 229