Document 2NqL0bkwVz0kBdbgRVnV4VODR

504 CHAPTER 19 : , ' !1958 Guide CROUP 7. REGISTERS (INCLUDING LOSSES IN SJACKHEAD. AND VELOCITY PRESSURE). i Table A. Equivalent Length for Registers Deflection Angle A - .0' 15 . 22 30 45" Baseboard, lligh or Low Sidewall Registers Floor Registers with Box only Eq. Ft. ` 35 25 40 45 . 60 1X5 ' For 2^way deflection registers, add the vertical and horizontal-deflection angles together and multiply by 0.7. Select closest angle A in Table A. For diffuser type registers see manufacturers' catalogs. Fig. 7. Equivalent Length of Fittings (Concluded) i i i 8. Selection of Blower. *'1. i i , -;A. Determine total cfm air delivery (the sum of all branch cfm values). ; ! 1B. Determine static pressure requirement. . - ;i | .... a. For furnace blower combination units it is the sum of bonnet pressure i : and suction.pressure. b. For blower's separately selected from the furnace it is the sum of bonnet; i : pressure, suction pressure, filter loss, casing loss, losses through air wash- ,ers, coils, and other.devices.,......- . , 9. Selection of Furnace. '..J;'- -:- ! ' A. Determine register delivery (the sum of room Btu losses). ; B. Determine bonnet capacity. ; Bonnet capacity = (total cfm) X (temperature rise) X 1.089. C. Determine allowance for pick-up load. For buildings which are heated in termittently, such as churches and auditoriums, .it is customary to add from 10 to 25. percent extra furnace capacity for warming of the structure. AUTOMATIC CONTROLS I Air stratification, high bonnet temperatures, excessive flue gas tempera-. : tures, and heat, overrun or lag in a properly designed system, can be largely . i eliminated through proper care in the planning, and! installation of the con- < j trol system.10 Best results are obtained when the fan is operated as con- i tinuously as possible, coupled with frequent, short- cycles of burner opera-j < tion. Controls usually employed are: , . ]i , j -- * .. 'll': ... T- - ; 1. -A room thermostat located in the occupied space at a'point where there is-good[ air-.circufi^iph-ahd^fiere the temperature is representative of the area being con-, ! trolled .-'Iti.sthe operating control which initiates the starting and stopping of the | burner. 11 is frequently of the timed, two-position type. -Refer to Chapter 38 for,- ! -inbre information on types of room thermostats. ! 2. A fan thermostat located in the bonnet of the furnace to start the fan at a bon- j net temperature between 110 and 130 F and stop the fan at about 15 deg below the: cut-in point. The lower settings are used for high sidewall register installations and . the higher settings for baseboard register installations. For most satisfactory per- formance these settings should be as low as is feasible without resulting in drafts.. 3. A high limit control, also in the bonnet of the furnace, to stop the burner inde- = pendently of the room thermostat if the air temperature exceeds 175 F. The fan thermostat and high limit control are sometimes combined into a single unit. Warm Air Heating Systems 505 4. A humidistal to regulate the moisture supplied to the rooms on systems which are equipped with humidifying'means. This may be of the room type, usually located adjacent to the room thermostat, or it may be of the insertion type located in the main return air duct. 5. Primary and limit controls for the various types of gas burners, oil burners and coal burners (stokers) should be provided as required, and; are discussed in Chapter 38. ADJUSTMENT OF SYSTEM More even room temperatures, will result if the controls are'adjusted to produce long period fan operation. This is accomplished in automatically- fired forced warm air heating systems when, the control arrangement is of the type where the room thermostat .controls the fire, and the blower con trol (fan switch) controls the blower operation. This procedure1 as out lined in detail in Manual-6 of the National Warm Air Heating and Air Con ditioning Association, is as follows:3 .? ; 1. Adjust the fuel input in proper relation to the heat loss of the structure.. - 2. Determine the temperature rise through the furnace. 3. Adjust the air volume to produce a temperature rise through the furnace of about 90 deg. ;i 4. If adjustable, set the fan switch differential to a minimum of about 15 deg. 5. Adjust the fan switch cut-out point as low as practicable. 6. Balance the system by adjusting dampers to produce even temperature distri bution between rooms. 7. Set the room thermostat at the desired room temperature. Close control of room temperature is facilitated by. theruse of a room thermostat having a narrow operating.differential. The heat anticipating, thermostat is an example of such a device. WARM AIR CEILING PANEL SYSTEMS ! Warm air ceiling panel heating systems utilize a false ceiling suspended 3% in. from the ceiling joists which have previously been covered on the bottom with sheets of plasterboard. Special hangers are used to suspend the false ceiling or heating panel from the joists. Steel supporting rods Tb 1fs*'a^e<* trough these hangers and metal lath is attached.to the rods. I he lath is then plastered toa thickness of % in., making a completely sealed air space above the ceiling. Warm air is delivered to this sealed space through a standard warm air duct, installed in the usual manner. The - 611 ohculated over the entire ceiling being guided by sheet-metal baffles. After the air has passed over the ceiling, it is returned to the fur nace through a return air duct for reheating. The system is- closed, and no air is introduced into the heated space from the panel. (See also Chapter . , Panel Heating.) Because a warm air ceiling panel system involves a different type of e mg construction, its installation is practically -limited to new construc- Li n" ^nly automatically-fired and thermostatically-controlled furnaceheat-61 uuits may be used with this system. ' The standard automatic trol conteols consisting of a room thermostat, temperature limit con- quired 0VwvOn*ro^ ^an swltch), and. primary control are all that are re` While warm air ceiling panel heating has particular advantages onp- f utillty room houses, it canr be- just as" effectively installed in nd two-story houses with basements. ' ; .....;