HVAC Applications. VFD considerations for HVAC systems...

Transcription

1 HVAC Applications VFD considerations for HVAC systems... 1

2 COMMON TERMINOLOGY VFD (VARIABLE FREQUENCY DRIVES) AFC (ADJUSTABLE FREQ. CONTOLLER) ASD (ADJUSTABLE SPEED DRIVES) VSD (VARIABLE SPEED DRIVES) FREQ. DRIVE INVERTER DRIVE Inverter Duty Motors =?? = New motors meet NEMA MG 1, Part 31 = peak voltage of 1600 volts and a minimal rise time of 0.1 microseconds 2

3 Typical Large HVAC System Cooling Tower Fans Secondary Hot/Chilled Water Pumps Systems don t necessarily have all components. Supply Fan Condenser Water Pump Primary Hot/Chilled Water Pumps Return Fan 3

4 Good Retrofit Candidates Large energy cost saving possibility Large motors Poor present efficiency Flows manually throttled back Malfunctioning mechanical flow modulation Inefficient control methods High energy costs Easy retrofit 4

5 Why Flow Control? HVAC systems are designed for worst case situations. Most of the time they have excess capacity. Controlling flow Saves energy Improves occupant comfort 5

6 Methods of Flow Control Air flow Inlet guide vanes Outlet dampers Variable pitch in motion fan Adjustable speed Fluid flow Throttling valve (two-way) Bypass valve (three-way) Adjustable speed 6

7 Why Adjustable Speed? Energy savings Secondary pumping example 7

8 Energy Requirements Important Curves Pressure Setpoint Pressure F low Pump Curve Operating Point Control Curve System Curve P P 8

9 Energy Requirements Pressure Power a Flow x Pressure Flow 9

10 Energy Requirements Pressure Flow Desired Flow 10

11 Energy Requirements Two-Way Valve (Throttling) Power Pressure Flow 11

12 Energy Requirements Three-Way Valve (Bypass) Pressure Flow Power Balancing Valve 12

13 Energy Requirements Adjustable Speed Pressure Power Flow 13

14 Why Adjustable Speed? Energy savings System control Reduced maintenance Sound control 14

15 Why Adjustable Frequency Drives? High efficiency Easy retrofit Replace the existing motor starter Flexible mounting Simple control Minimum maintenance 15

16 Typical Large HVAC System Heat Rejection Section Cooling Tower Fans Chiller Condenser Water Pump 16

17 Cooling Tower & Fluid Cooler Fan Cooling Tower Fan 17

18 Cooling Tower Fan Fan Motors 18

19 Cooling Tower Fan Notes Traditional Control Methods None Poor efficiency Staging cells in multi-cell towers Poor efficiency High mechanical stress Dual-speed motors Moderate efficiency High mechanical stress 19

20 Cooling Tower Fan Notes, continued Traditional Control Methods, continued Variable pitch in motion fans Good efficiency, when functioning High maintenance, often don t function Other Concerns Wasting highly treated water Audible noise 20

21 Condenser Water Pump Cooling Tower Fan Condenser Water Pump 21

22 Condenser Water Pump Cooling Tower Pump Pump Motors 22

23 Condenser Water Pump Cooling Tower From Cooling Tower Strainer Differential Pressure Switch (Flow Proof) Motor To Chiller Pump Motors 23

24 Condenser Water Pump Notes Traditional Control Methods No active control It is important to maintain design flow for Proper cooling tower operation Proper chiller operation However the pump is often over-sized to compensate for pipe scaling later on Manually close a valve to reduce flow If the valve is closed a lot, a drive can save significant energy 24

25 Condenser Water Pump Cooling Tower Fan Chiller Condenser Water Pump 25

26 Heat Rejection Section Chiller Chillers 26

27 Chiller Notes While the chiller has a large motor, Inaccurate control can cause major problems Some chillers require constant torque Less energy savings Be sure you know its design and operation before considering retrofitting a chiller with a drive 27

28 Rooftop Units 28

29 Rooftop Units Notes Rooftop units generally don t have cooling towers and condenser water pumps They are often direct exchange (DX) heat with the outside air It can be economical to retrofit drives in the DX section 29

30 Typical Large HVAC System Chiller Secondary Hot/Chilled Water Pumps Boiler Primary Hot/Chilled Water Pumps 30

31 CHW, HW (Water Source Heat Pump Circulating & Booster) Primary Pumps Boilers or Chillers Primary Hot/Chilled Water Pump 31

32 Primary Pumps From Chillers Primary Pumps 32

33 Primary Pumps Air Separator From Chillers To Chillers Secondary Pumps Primary Pumps 33

34 Primary Pump Notes Traditional Control Methods No active control The pump is often oversized Flow is reduced by Trimming the pump s impeller Closing a pressure reducing valve When a valve significantly reduces flow, a drive can provide large energy savings 34

35 Primary Pump Notes Although some modern chillers can accept some amount of flow variation, be careful about attempting to actively control flow through either part of the chiller 35

36 Secondary Pumps Automatic valves at each coil control the flow of water to the coil. Boilers or Chillers Secondary Hot/Chilled Water Pump Primary Hot/Chilled Water Pump Variable flow in the secondary loop. Constant or Variable flow in the primary loop. 36

37 Secondary Pump Valve Motor Secondary Pump 37

38 Secondary Pump Secondary Pumps Valves Motors 38

39 Secondary Pump Notes Traditional Control Methods Valves control flow through each coil Two-way throttling valve Three-way bypass valve For proper operation, drive systems require two-way valves Therefore, retrofitting systems with threeway valves is more expensive 39

40 Secondary Pump Notes Tertiary pump systems are much like secondary pump systems Because the size of the motors is generally quite small, energy savings may also be small 40

41 Single Pump Loop Boilers or Chillers 3-Way Valve Total flow is constant. Variable flow through the coils. Constant or Variable flow through the boiler/chiller. Hot/Chilled Water Pumps 41

42 Single Pump Loop Notes Pumping systems that do not have separate primary and secondary loops present unique problems It will take significant work to convert it to a primary/secondary system Vary the flow through a chiller based manufacturers specifications Approach such systems with caution 42

43 Typical Large HVAC System Air Supply Section Supply Fan Return Fan 43

44 Air Supply Section Supply Fan Supply Fan 44

45 Air Supply Section Supply Fan 45

46 Air Supply Section Supply Fan Fans Drive Belt Motor Sheaves 46

47 Supply Fan Notes Traditional Control Methods Constant air volume systems have no direct method of reducing air flow The flow of water through the coils determines the temperature of the conditioned space Variable air volume systems use VAV boxes to restrict or redirect air when less flow is needed 47

48 Supply Fan Notes Methods of reducing fan capacity Outlet dampers Low efficiency Require maintenance Inlet guide vanes Moderate efficiency Require maintenance Variable pitch in motion fans Better efficiency Very high maintenance/costs Often multiple dampers per fan One per fan 48

49 Supply Fan Notes Old methods of reducing fan capacity Variable speed belt drives Low efficiency High maintenance Eddy current drives Low efficiency at low speeds High maintenance 49

50 Supply and Return Fans Supply Fan Return Fan 50

51 Air Supply Section Return Fan Fan Belt Drive Disconnect Switch Motor 51

52 Return Fan Notes Notes Traditional Control Methods Not controlled Controlled like the supply fan The method of providing the control signal depends on the control system A fixed amount less than supply flow A fixed difference between building and outdoor air pressure 52

53 Return Fan Notes Notes The main purpose of the return fan is to keep from over-pressurizing the building Not all systems require return fans 53

54 Examples of Some Air Supply Systems A wide variety of systems are used to control air flow Some are easy to retrofit with drives Others require more work to retrofit with drives The following are a few examples 54

55 VAV System with Fan Capacity Control The sensors and control signals for drives are already present. 55

56 Open Loop VAV System The sensors and control signals for drives are already present. 56

57 VAV System with Perimeter Terminal Reheat Static Pressure Sensor The sensors and control signals for drives are already present. 57

58 Dual Duct VAV System One drive for each fan. The sensors and controls are already in place. 58

59 VAV System with Bypass Boxes Add Static Pressure Sensor Close bypass part of VAV boxes. Add static pressure sensor to control fan. 59

60 Dual Duct System Terminal units designed for constant air flow make fan speed control less attractive. 60

61 Multi-Zone System Constant volume, multi-zone system. Requires adding VAV boxes and pressure sensors. 61

62 Terminal Reheat System Constant volume, multi-zone system. Requires adding VAV boxes and pressure sensors. 62

63 Induction Reheat System The induction units require high air velocity to function properly. 63

64 CAV Fan & Clean Room Supply Fan Air Filter Conditioned Space Pressure Sensor Supply Fan Drive

65 Garage and Tunnel Fan Vent. Fan Smoke Sensor CO Sensor Vent. Fan Drive

66 Fume Hood Fan Fan Damper Positioning Motor & Limit Switch Fume Hood Fan Drive

67 Outside Air Damper Smoke Extraction Supply Fan Conditioned Space Close this damper Return Air Damper Return Fan Reverse this fan Smoke Sensor Relief Air Damper Supply Fan Drive

68 Stairwell Pressurization Fan Pressure Sensor Fan Drive

69 Exhaust Fan Fan Pressure Sensor Fan Drive

70 Application Interfacing Operator s controls Plain language for Operation Fault display Programming Manual speed control Remote mounting Application MACROs Hand/Off/Auto control Auto OFF HAND

71 Single Motor Bypass Circuit Breaker, Bypass & Output contactors and fuses to service the drive while running Points to consider Can the system run at full speed? Drive fusing Safety interlocks Automatic bypass Run permissive circuit

72 Application Interfacing Operator s controls Bypass Single motor Multiple motor

73 PI and PID Controller (Closed Loop / Set Point) Compares the desired process variable with the set point value Proportional to the error Integral function adds errors over time Derivative function considers the rate of change of error (only for fast response systems) PID Speed Control Reference Set Point Feedback Sensor Controlled System

74 Other Considerations Environment Enclosure type NEMA 1 NEMA 12 Circulating dust Dripping non-corrosive liquid NEMA 3R Outdoor

75 Other Considerations Environment 1-50 HP: NEMA 1 & 12, & 3R Outdoors = -15 to 50ºC (5 to 122ºF) No De-rate 60 HP HP: NEMA 1 & to 40 C (5 to 104 F) Not exceed 10% 122 F

76 Harmonics What? Non-linear loads draw non-sinusoidal current from a sinusoidal line (current doesn t look like voltage): Non-incandescent lighting Computer Equipment UPS (Uninterruptible Power Supplies) Telecommunications equipment Copy machines Variable Frequency Drives Electronic/Controls for Facility Elec. Equip. / Systems, Security, HVAC / Mech. equipment Any load with a solid state AC to DC power converter 76

77 Harmonics Why worry? Harmonic Voltage Distortion Increased heating in motors and other electromagnetic equipment Noisy operation of electromagnetic equipment Malfunctioning of sensitive electronics Nuisance tripping of electronic circuit breakers Overheating of PF correction capacitors Tripping of PF protection equipment Equipment downtime Premature component failures Failed motors and capacitors 77

78 Harmonics Why worry? Harmonic Current Distortion Added heating in transformers and cables, reduces available capacity May stimulate a resonance condition Excessive voltage Shutdown / damage to electronic equipment May cause telephone or electronic interference Failed transformers, equipment Not in Compliance with CODES, STANDARDS, REGULATIONS, IEEE, GOOD DESIGN PRACTICE 78

79 Include: Reactors (Chokes) Least expensive when specified to be included with base drive package 5% impedance AC line reactors -or- DC link reactors Both types provide similar harmonic benefits Also Suppress voltage transients that can cause equipment damage Harmonic Distortion Calculations = only VFD contribution 79

80 RFI / EMI RFI = RADIO FREQ. INTERFERENCE conducted through the air EMI = ELECTROMAGNETIC INTERFERENCE conduct through AC power line EFFECTS SIMILAR TO HARMONIC DISTORTION! 80

81 RFI / EMI Hardware RFI / EMI FILTERS: WILL BE INCLUDED IN ALL VFD SIZES ACH 550: Meets EMC PRODUCT STANDARD EN FOR THE FIRST Environment restricted level BENEFIT: VFD will not interfere with other electronic equipment Other electronic equipment will not interfere with VFD 81

82 Serial Communications BAS / DDC Company Alignment BACnet ALC (Automated Logic Corp.) Andover Controls Novar American Auto-Matrix Alerton Trane Delta Controls Teletrol Tridium JCI (Johnson Controls, Inc.) Honeywell KMC LonWorks Honeywell Invensys Distech Novar TAC (formally CSI) JCI Trane Staefa Circon ModBus RTU ASI Controls KMC Reliable Controls 82