DIRECT-FIRED GAS AIR MAKE-UP UNITS - powellhvac.com

1 DIRECT-FIRED GASAIR MAKE-UP UNITSM odels FCBT & BIBTB uilt to ANSI & StandardsMay 2004 BULLETIN 8722 Aerovent Bulletin 872 Introduction .. 2 Application Considerations .. 3 Construction Features.. 4 Accessories .. 5 Standard Temperature Controls .. 6 Control Panel .. 7 Pipetrain .. 7 Sequence of Operation Gas Burner.. 8 Typical Specifications .. 9 Performance Data Forward Curved .. 10 Performance Data Backward Inclined .. 11 Dimensional Data .. 12-23 Pressure Drop Curves for Accessories .. 24-27 2004 Aerovent, Twin City Fan Companies, illustrations cover the general appearance of products at the time of publicationand we reserve the right to make changes in design and construction at any time without is MAKE-UP air? MAKE-UP air is outside air tempered and introduced intoa building to eliminate negative pressure and provide apositive operating pressure within a do you need MAKE-UP air? Fans and blowers used in spray booths, hoods, ovens,dust collectors, ventilators, and other plant equipmentexhaust air to the outside.

2 Without a controlled intro-duction of MAKE-UP air an air-starved environmentwill do you know you need MAKE-UP air? MAKE-UP air is required when: Gravity stacks from unit heaters and processes back-vent. Exhaust systems do not perform at rated volumeleading to poor control of contaminants. The perimeter of the building is cold due to a highinfiltration rate. There are several indrafts at exterior doors, windows,and building openings. Exterior doors are hard to open. Heating systems are not able to maintain uniformcomfort conditions throughout the building. Theouter core area is cold due to infiltration while thecenter core is much does MAKE-UP air cost? MAKE-UP air doesn t cost money. It actually savesmoney by: Extending the life of heat exchangers on combustionequipment. Providing more uniform temperatures throughoutthe building, reducing overheated areas and colddrafty areas. Allowing exhaust systems to operate at designedcapacity, reducing the need for additional equipment.

3 Minimizing the damage to materials from contami-nates which may exist in the the local atmosphere. Reducing employee turnover and absenteeismbecause of better health conditions and plant clean-liness. Improving products with fewer rejects because fur-naces operate at designed much MAKE-UP air do you need?The recommended procedure to determine the amountof MAKE-UP air needed is to total the CFM capacity ofall the exhaust fans and blowers in the plant and add10% to create a positive pressure the data is not available, the following equationscan be used as a means of determining how muchmake-up air is Spray Booth:125 to 175 CFM per square foot offace Exhaust:One air change per minute of ovenvolume in cubic Exhaust:CFM = area of discharge pipe insquare feet xvelocity (3,000 fpm average).Roof Ventilator:CFM = area of discharge pipe insquare feet xvelocity (3,000 fpm average).Dust Collector:Area of discharge pipe in square feetx velocity (4,000 fpm average).

4 Canopy Hoods:100 to 300 CFM per square foot ofhood open Air For Furnaces: CFM = fuel consumedin Btu per hour divided by 6, , Baking, or Curing Ovens:100 CFM persquare foot of both cross or Cleaning Tanks:150 CFM per square footof door opening or 200 CFM per square foot of hoodface Bulletin 872 Air BalanceExhaust fans cannot work properly without an ade-quate supply of air. If provision for air supply is notmade, the vacuum created reduces the effectiveness ofmechanical ventilation. Negative pressure also causesexcessive infiltration, making it difficult to heat proper-ly. These conditions can be corrected by replacing theexhausted air with clean, fresh, pretreated air. The pri-mary purpose of MAKE-UP air is to temper outside airand supply it in sufficient quantities to bring about thecondition of balanced upon the quantity of MAKE-UP air in rela-tion to the exhaust, the heating system will shut downduring the working day allowing the MAKE-UP air sys-tem to handle the entire load.

5 The heating system thenfunctions only to maintain satisfactory temperatures atnighttime and other plant shutdown you add an air MAKE-UP system to an existingplant it is necessary to make a detailed analysis of theoverall situation in order to determine what the rela-tionship might be between the heat added by make -upair and that supplied from the plant heating exhaust systems already exist, the installation ofmake-up air usually will not increase the heating loadand can bring about a reduction of overall heatingcosts. This may be understood by considering that infil-trated air, warmed at least partially by the plant heatingsystem, is ultimately mixed with room air and exhaust-ed through the ventilating fans. Infiltration of unheatedair results in a decline of heating efficiency. Most heat-ing systems are not adequately rated to cope with infil-tration when appreciable negative pressures exist. Airmake-up UNITS provide a systematic method of heatingentering air and supplying it in controlled the proper balance of supply and exhaust, infiltra-tion is eliminated and negative pressures are properly tempering supply air, the heating system isrelieved of this abnormal load.

6 The results are uniformspace heating, effective ventilation, and improved with fresh air heating systems has shownthat it is practical and economically sound to heatindustrial plants and even warehouses with fresh question of whether to use 100% fresh air or recir-culate some portion is debatable, and engineers areusing both methods in their DIRECT-FIRED systems were first used someauthorities felt that positive exhaust was necessary toassure a balance and prevent the possibility of productsof combustion buildup. It is now generally recognizedthat air can be supplied into most buildings having nomechanical exhaust and in quantities sufficient to heatthem without building up a positive pressure of morethan a few hundredths of an inch water gauge. It is thereverse of infiltration and this principle can be used todesign fresh air plant standard air MAKE-UP unit is used for industrialspace heating with 100% outside air or with a fixed per-centage of recirculation, and in some designs with acombination of these.

7 Your Aerovent representative canassist you in determining application requirements forgeneral air MAKE-UP and for fresh air heating. They cansupply detailed information as it may apply to Considerations4 Aerovent Bulletin 872 Construction FeaturesThe BT series DIRECT-FIRED gas air MAKE-UP unit is a com-plete air supply system in a self-contained package withfan, burner, and controls. The unit is ready for connec-tion to the gas line and power source. Heavy duty forward curved or backward inclinedDWDI centrifugal blower with pillow block bearings ANSI and FM approved gas manifold design Heavy duty 16 gauge galvanized steel housing Large access door for internal accessibility Lifting eyes for ease of unit installation Venturi monitored airflow supervision 0 to 92 degree temperature rise 120 volt fused control circuit with 230/460 to 120 voltcontrol transformer Number-coded wires and terminal strips Dual fuel burner (Maxon) Factory assembled and tested Weatherproof control enclosure Remote operating station unit support/mounting channels Maxitrol Series 14 temperature control Honeywell series 7800 flame safeguard protection Ultraviolet detection system Safety shutoff valves Discharge temperature sensor Drives rated for 150% of motor nameplate rating High temperature limit Single point gas and electrical connections Non-recycle system with low fire start protectionwith main flame supervision 25.

8 1 temperature control modulation Pilot gas pressure regulator High and low gas pressure switchStandard FeaturesThese systems are for use in industrial or commercialapplications where supplying tempered outside air Bulletin 872 V-bank filter section Intake hood with bird screen 90 degree discharge elbow Roof curb Curb mount construction Inlet bird screen Modulating room temperature control (MaxitrolSeries 44) Digital temperature controls (Maxitrol Series 94) IRI pipe train manifolds Directional discharge grille, single and doubledeflection Circuit analyzer Insulated construction Vertical support stand Two speed operation Mild weather thermostat Service platform Main gas regulator Vibration isolators ( unit mount) Tamper proof remote station Reset module Disconnect switch OSHA Belt guard Motor operated damper (inlet or discharge) Freeze protection thermostat Door switch interlock Painted unit and accessories Extended grease linesAdditional OptionsAccessories80/20 RecirculatingThe 80/20 recirculating system allows 80% recirculationand is designed to insure that a minimum of 20% of thedesigned performance is outside air.

9 Recirculated air isnot allowed to flow across the burner. Manual setpointis standard. Room pressure control available as anoption. V-Bank Filter SectionThe standard filter is a 2" Farr 30/30 disposable typewith washable as an option. MODULATINGPROFILEBURNERRETURN AIRDAMPER6 Aerovent Bulletin 872 Standard Temperature ControlsTwo standard systemsfor temperature controlare available offering achoice of functions forthe regulation of air tem-perature. The outlet tem-perature control (OTC)system senses only thedischarge air tempera-ture at the unit . Thesensing device is locatedin the airstream. It aver-ages the temperatureand sends a signal to theservomechanism in themodulating regulator in turn modulates the gas pressure in theburner manifold, and the gas flow is varied to maintainthe air temperature constant at the sensor. The OTC sys-tem is used where the volume of air supplied is rela-tively small compared to the volume of the building,which usually means that it is not intended for the airmake-up unit to pick up an appreciable part of thebuilding most installations, room temperature control isdesirable.

10 Two controllers are available for this opera-tion. The simplest and least expensive control is a ther-mostat added to the OTC system (OTC-RO) and locat-ed to sense the room temperature. The contacts closeon a call for heat and cause an increase in the dischargeair temperature. The air MAKE-UP unit delivers air at thehigher temperature until the room thermostat is satis-fied; full control is then returned to the discharge sen-sor. The limited amount of temperature increase elimi-nates excessive discharge air temperature. The temper-ature setting is usually 5 below the outlet temperatureset modulating room temperature control (MRTC) isslightly more sophisticated. Instead of a thermostat, athermistor is used to sense the room temperature. Thesignal actuates the modulating regulator to provide anincremental increase or decrease of the discharge tem-perature, providing closer control and preventing anabrupt change in the temperature of the air at the out-let of the unit or outlets of a distribution system.