Technical Development Program

Transcription

1 Technical Development Program PRESENTED BY: James Parker Insert your logo here AIR HANDLERS Coils: Direct Expansion Chilled Water and Heating

2 Menu Section 1 Introduction Section 2 Typical Coil Applications Section 3 Coil Terminology and Construction Section 4 Types of Coils Section 5 Heat Transfer and Coil Formulas Section 6 Application Topics Section 7 Cooling Coil Design Parameters Section 8 Coil Selections Section 9 Summary

3 SECTION 1 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Introduction Section 2 Duct Design Drivers

4 Objectives Identify where coils are used in HVAC Describe the various types of heating and cooling coils Define the component parts and terminology Identify the heat transfer formulas and properties Coil applications Describe methods to control water and direct expansion coils Identify coil selection criteria and factors affecting performance Section 1 Introduction

5 What is a Coil? A coil is a heat transfer device that adds or removes heat to the entering air Types of coils: Chilled Water Airflow Hot Water Direct Expansion (DX) Steam Electric Water Coil Return Header Supply Header Section 1 Introduction

6 SECTION 2 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Typical Coil Applications (Five General Categories)

7 Residential Coils Cased Uncased Section 2 Typical Coil Applications

8 Small Commercial Packaged Unit Coils Installed in duct A coil design, installed on twinned furnaces 6-10 Tons Section 2 Typical Coil Applications

9 Large Commercial Packaged Unit Coils DX or chilled water DX COOLING COIL IN ROOFTOP UNIT DX COOLING COIL IN PACKAGED AIR HANDLER Section 2 Typical Coil Applications

10 Duct Mounted Coils Drive Slip Casing Section 2 Typical Coil Applications

11 Duct Mounted Coil Ducting Flange Flanged Casing Ducting Section 2 Typical Coil Applications

12 Terminal Mounted Heating Coils Unit Mounted Hot Water Coil Fan Powered Box VAV Single Duct Box Section 2 Typical Coil Applications

13 Draw-Thru and Blow-Thru AHU Coil Coil Diffuser Plate Horizontal Draw-Thru Horizontal Blow-Thru Draw-Thru Fan downstream of cooling coil Fan draws air through coil Most common type Fan motor heat travels to conditioned space adding to the room BTUH load Advantages: Even airflow assured over the coil Shortest length required Coil Vertical Draw-Thru Blow-Thru Fan upstream of cooling coil Fan blows air through coil Diffuser plate needed which adds length Advantages: Motor heat becomes coil load NOT ROOM LOAD Less cfm required with smaller ducts and less fan energy Section 2 Typical Coil Applications

14 Coil Banks For applications requiring large volumes of air, one may opt for using multiple coils in a stacked configuration, instead of one very large coil. Arrangements can vary from just two coils stacked, to multiple banks four or more coils high. Note each coil requires its own drain pan, and there is a primary drain pan underneath the bottom coil. All the condensation from the upper coils is directed into the primary drain pan. Section 2 Typical Coil Applications

15 SECTION 3 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Coil Terminology and Construction

16 Coil Terminology Tubes Tubes The tube is a small-diameter conduit through which the heating or cooling medium passes as it rejects or absorbs heat Airflow Outlet 3/8, 1/2, and 5/8 inch Header Inlet Section 3 Coil Terminology and Construction

17 1/2-in. Tube vs. 5/8-in. Tube Coils You can achieve the same or lower pressure drop using a 1/2 in. coil with different circuiting. Section 3 Coil Terminology and Construction

18 1/2-in. Tube vs. 5/8-in. Tube Coils Section 3 Coil Terminology and Construction

19 Tube Wall Thickness Manufacturers may offer varying choices in tube wall thickness. One manufacturer s 1/2 tubes are.016 /.025, and the 5/8 tubes are.020 /.035 inches thick. Tube Wall Thickness Section 3 Coil Terminology and Construction

20 Fluid enters the coil counterflow to the air direction Coil Rows Airflow Rows Section 3 Coil Terminology and Construction

21 Rows and Fins Fin - The coil fin is a thin metal plate attached to the tube to improve the heat transfer efficiency from medium to air-stream Coil Fin Section 3 Coil Terminology and Construction

22 Coil Terminology H Finned or Face Area The working area of the coil is defined as the height length of the finned area. We need to know this in order to determine the face velocity across the coil. L This area does not include the extra dimensions for the casing. Face area or tube face area or finned area Section 3 Coil Terminology and Construction

23 Face Velocity Limitations (FPM) Face Area = Length * Height Length and height measured from inside edges of casing Length Height Face Velocity= CFM / FACE AREA Finned Area Section 3 Coil Terminology and Construction

24 Face Area Calculation The relationship between airflow volume (cfm), velocity (V) and area (A) is: cfm = VA or A = cfm/v Where: A = H * L H Example: 25,000 cfm AHU A = cfm / V A = 25,000 cfm / 500 fpm A = 50 ft 2 cooling coil required (nominal size 50 unit would be selected) L Section 3 Coil Terminology and Construction

25 Face Velocity Limits Section 3 Coil Terminology and Construction

26 Bypass Factor Causes ROWS BYPASS FACTOR AIR VELOCITY BYPASS FACTOR fpm 400 fpm 500 fpm 600 fpm FINS PER INCH BYPASS FACTOR AIR VELOCITY 300 fpm 400 fpm 500 fpm 600 fpm BYPASS FACTOR Section 3 Coil Terminology and Construction

27 Header, Inlets and Outlets Header A large diameter pipe to which several tubes are connected Chilled Water Coil Inlet and Outlet Pipe stubs on the header where the heating or cooling medium enters and leaves the coil In steam coils, the inlet is always the higher stub, allowing condensation to drain out of the lower stub Section 3 Coil Terminology and Construction

28 Construction Materials Header Steel or Non-Ferrous (copper) Casing Galvanized or Stainless Steel. Drain Pan Condensate drain pans can be galvanized or stainless steel. Section 3 Coil Terminology and Construction

29 Refrigerant Distributors Suction Headers Refrigerant Distributors Feeder Tubes Tube Sheet Suction Connections Section 3 Coil Terminology and Construction

30 Chilled or Hot Water Coil Hand RH COIL LH COIL Section 3 Coil Terminology and Construction

31 Direct Expansion Coil Hand Suction Header LH COIL RH COIL Section 3 Coil Terminology and Construction

32 DX Coil Face Split Face Split Coils Split horizontally Subdivisions within the coil Parts of coil can be deactivated to alleviate low-load problems Face Split Allow more flexibility Can match with dual-circuit or multiple condensing units Section 3 Coil Terminology and Construction

33 DX Coil Row Split Row Split Coils (full face active) Intertwined Subdivisions within the coil Parts of coil can be deactivated to alleviate low-load problems Allow more flexibility Can match with dual-circuit or multiple condensing units Section 3 Coil Terminology and Construction

34 Vent And Drain Connections Vent and Drain Connections: Used on water coils Located on supply and return stubs Vents on top of coil allow purging of air from coil Periodic venting to maintain proper coil performance Air Vent Drains needed for: Freeze protection in cold climates Service drainage Section 3 Coil Terminology and Construction

35 Return Bends, Hairpins, Passes Return Bends or Hairpins Hairpin OUTLET Header Airflow Tubes in Face = 6 Passes = 4 Rows = 4 INLET Feeder Tubes Section 3 Coil Terminology and Construction

36 Coil Circuiting Cooling or heating medium path of travel. Varies heat transfer performance Outlet Airflow Inlet Rows Section 3 Coil Terminology and Construction

37 Full Circuiting Airflow All of the tubes in face are fed from the header For 4-row coil shown: Circuits Passes = 4 Circuit length = One for each tube in face = 4 * coil length Rows Section 3 Coil Terminology and Construction

38 Half Circuiting Airflow Half of the tubes in face are fed from the header For 4-row coil shown: Circuits Passes = 8 Circuit length = ½ * of tubes in face = 8 * coil length Fluid velocity in tube: 2 * full circuit tube velocity Fluid pressure drop: ~ 4 * full circuit Rows Section 3 Coil Terminology and Construction

39 Quarter Circuiting Airflow ¼ of the tubes in face are fed from the header For 4-row coil shown: Circuits Passes = 16 Circuit length = ¼ * of tubes in face = 16 * coil length Fluid velocity in tube: 4 * full circuit tube velocity Fluid pressure drop: ~ 16 * full circuit Rows Section 3 Coil Terminology and Construction

40 Double Circuiting Airflow All tubes in face of two rows are fed from the header For 4-row coil shown: Circuits Passes = 2 Circuit length = 2 * of tubes in face = 2 * coil length Fluid velocity in tube: ½ * full circuit tube velocity Rows Fluid pressure drop: ~ ¼ * full circuit Section 3 Coil Terminology and Construction

41 More Than One Circuiting Can Work Airflow GPM: A < B Tube Velocity: A > B Airflow Pressure Drop: A > B More than one circuit will satisfy job Rows Rows Pick circuit that meets capacity, meets pressure drop limits, affords lowest cost, and gives good control range Section 3 Coil Terminology and Construction

42 Coil Circuiting Impact

43 Selection Options: (Highest to Lowest): Face area Rows Fins per inch Coil circuiting Coil Cost Factors Section 3 Coil Terminology and Construction

44 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Break

45 SECTION 4 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Types Of Coils

46 DX Coil Relationship To The System Exhaust Damper Return Air Fan Return Duct Supply Duct Return Damper HEAT Supply Air Fan Air Handler DX Coil Interconnecting Refrigerant Piping Air-Cooled Condensing Unit Section 4 Types of Coils

47 DX Coil Showing TXV Three limiting factors for capacity reduction: 1. Thermostatic Expansion Valve (TXV) 2. Distributor Nozzle 3. Evaporator Circuit Connects with TXV Feeler Bulb TXV Thermostat Expansion Valve Suction Header Distributor Assembly Airflow Liquid Line from Condenser To compressor suction TXV Feeler Bulb Distributor Nozzle Feeder Tube (one per refrigerant circuit) External Equalizer Line Section 4 Types of Coils

48 Evaporator Circuit Low Load Limit Refrigerant velocity in tubes must be maintained between prescribed minimum and maximum limits Maximum limits ensure reasonable pressure drop and efficient operation at design load Minimum limits ensure oil return to compressor at part load Low velocity may be caused by compressor unloading in response to load reduction The term tons per circuit is used to define velocity and represents how many tons of cooling are flowing through each circuit of the coil One manufacturer recommends 0.8 to 2.0 tons per circuit for ½ inch tube coils. Minimum s may vary by slightly by manufacturer. Section 4 Types of Coils

49 Split Coil Control Example LIQUID LINE Filter Drier Capacity Control Solenoid TXV Distributor Sight Glass Application: Match coil at right (8 circuits) with a 15-ton condensing unit which has two steps of unloading: (100%, 67%, 33% ) Section 4 Types of Coils

50 Chilled Water Coil Relationship To The System Exhaust Damper Return Air Fan Return Duct Supply Duct Return Damper HEAT Coil Supply Air Fan Cooling Tower Air or Water-Cooled Chiller (shown) Section 4 Types of Coils

51 Typical Chilled Water Coil 4 to10 Rows Available Vent Copper Tubes Aluminum or Copper Fins Fin Spacing 8 to 14 fins/inch Water Outlet Cap unused water connections Non-ferrous or Steel Header Water Inlet Section 4 Types of Coils

52 Hot Water, Steam, Electric Heating Coils Hot Water Steam Electric Section 4 Types of Coils

53 Hot Water Coils Outlet Copper Tubes Aluminum or Copper Fins Hot Water Feeder Tubes Inlet Drain Section 4 Types of Coils

54 Inner Distributing Tube Steam Coil Inlet Outlet Copper Tubes Aluminum Fins Section 4 Types of Coils

55 SECTION 5 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Heat Transfer and Coil Formulas

56 Heat Given Up By Air Air Total Heat Transferred (Change in enthalpy): q t = 4.5 * cfm * (h e h l ) Sensible Heat Transferred (change in temperature): q s = 1.10 * cfm * (t e t l ) Latent Heat Transferred (Change in moisture): q l = 0.69 * cfm * (gr e gr l ) Section 5 Heat Transfer and Coil Formulas

57 Overall Coil Heat Transfer Where: q t = U * A * LMTD U = 1 / (R A + R D + R M + R F + R HTF ) A = Total Coil Effective Surface Area LMTD = Log Mean Temperature Difference between the air and water Section 5 Heat Transfer and Coil Formulas

58 Chilled Water Coil Heat Transfer Heat Flow Resistant Layers Air Film External Fouling Metal Tube Fouling Water Fluid Film

59 Air Dt Per Row Row Air Dt % Total Heat TOTAL 22.0 F Section 5 Heat Transfer and Coil Formulas

60 Parallel vs. Counter Flow Parallel Flow Counter Flow Entering Water Temperature Leaving Water Temperature Leaving Water Temperature Entering Water Temperature Section 5 Heat Transfer and Coil Formulas

61 Heat Absorbed By Water Air Outlet Q Q Inlet = 500 * gpm * Rise = The total heat absorbed by the water (Btuh) 500 = 60 min/hr * 8.33 lb/gal * specific heat of 1.0 Btu/lb-F gpm = gallons per minute Rise = The water temperature increase as if flows through the coil Section 5 Heat Transfer and Coil Formulas

62 SECTION 6 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Application Topics

63 Glycol Effects On Cooling Coil Section 6 Application Topics

64 Corrosion-Resistant Coil Options Mild Coastal Severe Coastal Severe Industrial Pre-Coat Fins Copper Fins E-Coat Coils Most Economical Choice Most Durable Option Best Baked-on coating applied to fins before coil is assembled. Inhibits galvanic corrosion. All copper construction. Corrosion-inducing bi-metallic joints eliminated. Eliminates galvanic corrosion. Best choice for seacoast. Precisely controlled epoxy dip process for entire assembled coils and headers. Impermeable coating best protects entire coil in harshest environments. Section 6 Application Topics

65 Coil Maintenance and IAQ Chemical treatment of fluid being circulated Sloped Drain Pan Section 6 Application Topics

66 Stacked Coils Header Baffle Hairpin Baffle Intermediate Sloping Drain Pan ¼ /ft min Side Enclosure Clamps Side Enclosure Bottom Sloping Drain Pan ¼ /ft min Floor Enclosure Curb Drain Pipe To Approved Drain Section 6 Application Topics

67 Water Coil Methods 2-Way Valve Supply Return Shutoff Valve Shutoff Valve Control Valve (2-Position On/Off, 2-Way Modulating) 2-Way Control Valve Open/close applications where tight temperature control is not required Commonly used in variable flow applications Balancing Valve Pete s Plug (Typical) Air-Handling Unit Coil Flange or Union Drain Valve Section 6 Application Topics

68 Water Coil Methods 3-Way Mixing Valve Supply Return Shutoff Valve Shutoff Valve Control Valve 3-Way Mixing 3-Way Control Valve Constant flow systems Balancing Valve Balancing Valve Pete s Plug (Typical) Air-Handling Unit Coil Flange or Union Drain Valve Section 6 Application Topics

69 Typical Steam Coil Piping Detail Shut-Off Valve Strainer Control Valve Steam Coil Steam Union (Typical) Float and Thermostatic Trap Assembly Vacuum Breaker Condensate Return Dirt Pocket Section 6 Application Topics

70 SECTION 7 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Cooling Coil Design Parameters

71 Load estimating and Coil Selection A good load estimate is the foundation for good coil selection It establishes the capacity requirements for the HVAC system It is used to develop the psychometric analysis necessary to determine coil selection parameters Ensures that the system will meet sensible and latent load requirements of the building to maintain both temperature and humidity Section 7 Cooling Coil Design Parameters

72 Cooling Coil Process Coil process line typical 6 row coil: First few rows provide mosty sensible capacity Last rows produce more latent capacity Air leaves coil close to saturation line Proximity to saturation depends on bypass factor Bypass factor function of: Face velocity Rows Fin spacing Coil Process Line Coil Leaving Air 2 t ra t ma oa Coil Entering Air Air Side Coil Performance t Section 7 Cooling Coil Design Parameters

73 SECTION 8 COILS: DIRECT EXPANSION, CHILLED WATER, AND HEATING Coil Selections

74 Select a Chilled Water Coil Air System Sizing Summary for Typical Floor all zones Project Name: Example 9 Story office 04/29/2004 Prepared by: 04:39PM Air System Information Air System Name...Typical Floor all zones Equipment Class. CW AHU Air System Type VAV Number of zones Equipment Class ft 2 Sizing Calculation Information Zone and Space Sizing Method: Zone cfm.. Peak zone sensible load Space cfm..individual peak space loads Calculation Months.... Jan to Dec Sizing Data... Calculated Central Cooling Coil Sizing Data Total coil load Tons Total coil load MBH Sensible coil load MBH Coil cfm at Aug CFM Max block CFM at Aug CFM Sum of peak zone CFM CFM Sensible heat ratio ft 2 /Ton BTU/(hr-ft 2 ) Water 10.0 F rise gpm Load occurs at. Aug 1500 OA DB / WB / 74.0 F Entering DB / WB 82.3 / 66.2 F Leaving DB / WB / 55.1 F Coil ADP F Bypass Factor Resulting RH.. 42 % Design supply temp F Zone T-stat Check.. 12 of 12 OK Max zone temperature deviation F Indicates data used for coil selection Section 8 Coil Selections

75 COIL SELECTION BROWSE MODE FPM < 500 TC = 280,000 BTUH SHC = 234, 200 BTUH EAT = 82.3 F. / 66.2 F. LAT = 56.0 F. / 55.1 F. GPM = 59.6 TEMP RISE = 10 F.

76 Altitude Effects Example

77 Direct Expansion Coil Selection AHU Builder Selection Software Data Inputs: Select Condensing Unit Program will balance coils with condensing unit Input Coil Selection Parameters from Load Estimate: Coil split type Condensing unit data Section 8 Coil Selections

78 Direct Expansion Coil Selection AHU Builder Selection Software Results: Compare performance to load requirements: TC = MBtuh SHC = MBtuh Coils meet capacity requirements: Tons/circuit (Optimum range (0.8 to 2.0)) Half Circuit better Better for low-load 4/14/HF and 6/8/HF meet specs and is most economical Section 8 Coil Selections

79 Direct Expansion Coil Selection Check Final Selection: 4 row, 11 fins per inch, half circuit coil Design tons/circuit = 1.73 TXV quantity =2 Condensing Unit Unloading Capability: Unloading Capability: 67% of full load Check Part Load Operation: To establish coil split control requirements Tons / circuit Tons / circuit Tons / circuit * Minimum Unloading * Total = Number of TXVs active 1.73 * 0.67 * 2 = 2 = 1.16 (OK without staging) #TXVs If result was below minimum, one TXV must must be closed when compressor unloads Section 8 Coil Selections

80 Hot Water Coil Selection Entering Air Temperature (EAT) and Entering Water Temperature (EWT) should be entered prior to running performance Enter the fluid flow and allow the performance software to run the coil capacity based on that flow Enter the system airflow and the maximum allowable coil water pressure drop (WPD) Section 8 Coil Selections

81 Hot Water Coil Selection Best available shows a heating capacity of 347 MBH (Btuh) and 90.3 F. leaving air temperature. This is short of our requirements. Section 8 Coil Selections

82 Hot Water Coil Selection 2 Row coil displays heating capacities much higher (451 MBH) than the required 350 MBH. Section 8 Coil Selections

83 Hot Water Coil Selection Reducing EWT from 180 F. to 160 F. Section 8 Coil Selections

84 Hot Water Coil Selection Change fluid temp difference for 20 F. to 30 F. (lowering GPM). Section 8 Coil Selections

85 Summary Identified where coils are used in HVAC applications Defined the component parts of coils and typical coil terminology Described the various types of heating and cooling coils Identified the heat transfer formulas and properties of coils Demonstrated the proper use of coils in a variety of applications Described methods to control water and direct expansion coils Identified key coil selection criteria and factors affecting performance Chilled water, DX and Hot Water selections Section 10 Summary

86 Technical Development Program Thank You This completes the presentation. TDP 614 Coils: DX, Chilled Water, and Heating Artwork from Symbol Library used by permission of Software Toolbox