How to use VSD in existing HVAC installations ■ Comparison Traditional AHU controlled by IGV ........................... 3 AHU controlled by VLT 6000 HVAC ........................ 3 ■ Considerations Steps to be taken to retrofit by drives .................... 4 The electrical installations ........................................ 4 Sizing the drive ........................................................ 4 Connecting the control system ............................... 5 Before choosing a drive .......................................... 6 Cons ider motor derating ......................................... 8 Consider short-circuit capabilities of the drive ......... 8 Consider capabilities of switching on the output ..... 8 Consider user friendliness ........................................ 9 Consider galvanic isolation ...................................... 9 Consider other important features ........................ 10 Zero inrush current ................................................ 10 Catches spinning motor without tripping .............. 10 Acoustic noise ....................................................... 11 Serial communication .......................................... 11 MC.60.E1.02 - VLT is registered Danfoss trademark 1 Table of contents ■ Introduction Where can drives be applied ................................... 2 Function and mounting place ................................. 2 Before choosing a drive .......................................... 2 Introduction How to use VSD in existing HVAC installations ■ Where can drives be applied For energy saving the great advantage lies in installing variable speed drives on applications using centrifugal fans and pumps. Such typical installations in buildings are: ❖ Air handling units and ventilating plants, cooling towers used in most buildings and extract fans (extract fans are widely used in kitchens, production areas or underground car parks, tunnels etc.). ❖ Water pumps for cooling towers, chilled water pumps or pumps for potable water. ■ Function and mounting place When using a drive the flow of air or water will be controlled by varying the speed of the fan or pump. Hence the function of damper, guide vane, by pass or motorised valves will no longer be necessary. These parts should either be removed or blocked in the fully open position. Existing BMS signals, previously used for controlling guide vanes, motorised valves or contactors, may all be used as input (e.g. feedback and start/stop for the drive(s). The best place to mount a drive is next to the motor it is controlling. Choosing a drive in IP54 enclosure makes it possible to use the drive in dusty or wet areas. For panel mounting an IP20/IP21 version should be chosen. 2 Standard low-cost sensors/transmitters for temperature, air or pressure will be needed to make the drive increase or decrease speed in order to maintain a given setpoint. These transmitters, however, may typically already exist in the installation. ■ Before choosing a drive If the drives are correctly retrofitted, the building will both be more energy efficient and become a more comfortable place to work in. To obtain that, however, the correct selection of drives is important. The most critical issues are discussed in the following. ■ Installation Retrofit installation of drives should be let to professional control companies or HVAC contractors, in order to ensure correct installation. Fig. 1 shows a traditional VAV-Airconditioning plant using Inlet Guide Vane, IGV, to control the airflow as well as three port valves to control the heating/ cooling liquid. Fig. 2 shows a VLT 6000 HVAC frequency converter controlled plant. For a comparison between the two systems, see overleaf. MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations Comparison Fig. 1.Traditional AHU controlled by IGV Fig. 2. AHU controlled by VLT 6000 HVAC MC.60.E1.02 - VLT is registered Danfoss trademark 3 Considerations How to use VSD in existing HVAC installations ■ Steps to be taken to retrofit the installation See Figs. 1 and 2 ❖ The motor only needs a three-wire cable for connection to the VLT 6000 HVAC drive (3 wires of existing cables can be used). The existing star/delta starter is no longer required and can therefore be removed. ❖ Bypass loops incl. 3 port valves on pump systems are not required. If dificult to take out, the valves can be blocked in fully open forward position. If necessary a NRV (Non-Return-Valve) can be applied instead of the existing 3-port valves. ❖ The Inlet Guide Vane (IGV) is no longer required, as flow in controlled directly by changing fan speed. If too troublesome to remove, it should be blocked in fully open position. The IGV actuator signal and motor signal are no longer required, but the signal can be re-used as a control signal for the drive. The same considerations should be made when using a damper. ❖ No Power Factor Correction (PFC) equipment required, as it will have no influence on the power factor of drives. NB: The use of some brands of VSDs, with low power factor, may damage PFC capacitors. Dedicated drives provide a power factor better than >0.9/cosϕ ~ 1.0. ■ Considerations on electrical installations The existing motor cable can be cut where most convenient and the VLT 6000 HVAC drive connected directly to the cable ends. The VLT 6000 HVAC drive comes in an IP54 enclosure and can therefore be mounted close to the motor or where best suited depending on space. If the drive is to be mounted in a panel, it can also be supplied in an IP00 or an IP20/21 enclosure. The Danfoss VLT 6000 HVAC drives are supplied with built-in filter and are fully EMC tested and certified to qualify for the CE marking. For more detailed description, see below. Drives not including galvanic isolation to VDE 0160 (PELV) have to be fitted with isolators, according to standards, between BMS system and drive. VLT 6000 has fully galvanic isolation according to PELV requirements. ■ Sizing the drive In retrofit applications determining the size of a drive to a given motor should cause no problems. However, some drive brands require the motor output power to be derated: Drives using standard sine wave controlled PWM principle cannot give full voltage to the motor at 50 Hz, unless a third harmonic voltage is introduced. This results in a non-sinusoidal output waveform from the drive, which will cause additional heat loss in the motor, resulting in higher motor temperature and shortened motor life. Do not forget to check the drive manufacturers’ recommendations on this. For use of the motor’s full 100% output power, it is necessary either to choose a motor one frame size larger, to get more surface and material to compensate for the additional heat loss, or to use a motor rated for temperature class F. For retrofit applications this is often not realistic, as the motor is already installed. When using a Danfoss VLT 6000 HVAC drive the motor temperature will not significantly exceed that of a motor connected directly to the mains (<+1°C). That is because Danfoss’ specially developed VVC (Voltage Vector Control) principle ensures full voltage at 50 Hz, without any distortion. Besides it provides fully optimised magnetising voltage for the motor at any lower frequencies (speeds). No motor derating is required with VLT 6000 HVAC drives. Danfoss has this certified by third party (Western Electric Australia PTY. Ltd.) EMC (Electro Magnetic Compatibility) is an important issue in order not to interfere with computers and BMS systems. Please carefully follow the instructions given by the manufacturer on EMC correct installation of control and motor cables. 4 MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations Read the nominal full load motor current on the motor name plate and choose the Danfoss drive that meets or exceeds that value. Should you want Danfoss to match the drive for your motor and applications, just give us a call. ■ Connecting to the control system The drive can be easily connected to an existing BMS control system or it can be self-contained. For most fan and pump applications the speed control is based on temperature or pressure feedback signals. If connected to a BMS system, the BMS will provide the speed control and the start/stop signals for the drive. Either analogue or digital signals can be used. If self-contained, the Danfoss VLT 6000 HVAC drive will take a signal (e.g. 0/4 - 20 mA) directly from a temperature/pressure transmitter, or differential pressure transmitter, and control the fan or pump application using the built-in PID controller *) (IEC Publ. 34-1. (IInternational Electrotechnical C ommission). Smooth Control No need for any neutral zone known from ON/OFF control. Temperature or pressure will be kept constant. Fig. 3 MC.60.E1.02 - VLT is registered Danfoss trademark 5 Considerations As no motor derating is required with VLT 6000 HVAC drives it is possible to use standard IEC*) specified AC induction motors of class B insulation together with any Danfoss VLT 6000 HVAC drive. And it is easy to choose the right drive for retrofit applications: Considerations How to use VSD in existing HVAC installations ■ Before choosing a drive The reason for choosing a drive in HVAC applications is to gain energy savings and reduce maintenance costs. None of this may be achieved if the wrong type of drive is chosen. (Many industrial drives are not recommended for HVAC use). Danfoss VLT 6000 HVAC drives are equipped with integrated factory tested RFI filters as standard (see fig. 5) and when following the instructions in the manual, RFI suppression to EN 55011 is achieved. Danfoss has this certified by third party: TELEDANMARK, The tele communication authorities of Denmark. The drive must comply with your specifications. A drive’s immunity to interference from electrical disturbances from mains or other equipment connected to the same mains phases is specified in EN 50082, - 1 & 2 2.. (See also paragraph “Input surge protection” page 7 and “Galvanic isolation”, page 9). All Danfoss drives comply with this norm as the tests are carried out in accordance with the standards IEC 1000-4-2 / 5 and VDE 0160. Can your supplier prove that his product does meet some minimum requirements? Some of the most important issues are: Electro Magnetic Compatibility) covering 1) EMC (E RFI (R Radio F Frequency Interference) filtering, Immunity and low frequency harmonics. ■ 2) Derating of the Motor (should not be required) See paragraph “Sizing the drive”, page 4. Harmonics Interference (on supply transformer) 3) Short Circuit Capabilities of the Drive An electric motor connected to mains draws sine wave current and is considered a linear load. No harmonics arise from that. A VSD does not draw sine wave current because of the rectifier in the mains input and is therefore considered a non-linear load. Fig. 4 shows the conventional PWM frequency converter. 4) User Friendliness 5) Galvanic Isolation 6) Other Important Features ■ EMC (Electro Magnetic Compatibility) The term EMC covers the ability of an electrical device to keep high frequency disturbances inside the device and to withstand disturbances from the outside, preventing malfunction or damage to other equipment or the device itself. The degree of compatibility is now specified in a new set of European Norms, EN (e.g. EN 55011 Group 1, Class A and B, EN 50081, 50082 etc.) Harmonics are unavoidable and comprise multiple integers of the fundamental frequency of 50 Hz or 60 Hz. 5th, 7th and 11th harmonics of 50 Hz will thus be 250Hz, 350 Hz and 550 Hz, respectively. The harmonics will cause an increase in the total current consumption IRMS of the VSD, but will not add to the useful torque on the motor shaft. If the amount of harmonics gets too high, cables, the supply transformer as well as other connected equipment may overheat and eventually be damaged. All VSDs produce a lot of above mentioned disturbances called RFI (Radio Frequency Interference). In order to comply with the new norms, often referred to in customers’ specifications, the drive must be equipped with a suitable “filter” preventing this noise from disturbing the environment. Most manufacturers can provide this filter as an external option. Besides, many drive manuals are not very informative on EMC correct installation, so whether sufficient RFI suppression is achieved or not may be accidental. Fig. 4 Conventional PWM frequency converter 6 MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations AC reactors have the disadvantage that they can cause a voltage drop across them of up to 5% of the mains voltage, causing the output voltage to drop by 5%. Most drives will tolerate up to a ±10% deviation of the mains voltage level designed for. Outside of this range they often trip. When using AC reactors half of this range then cannot be used and these drives become much more sensitive to mains sags or “brown outs” (dip in mains voltage). Danfoss drives have DC link coils integrated as standard. When using DC link coils, there is no significant voltage drop. Danfoss VLT 6000 HVAC drives ensure (guarantee) full rated motor voltage and torque within ±10% deviation of the mains voltage and will tolerate deviations of up to ±20% (or more, depending on drive size), before a trip occurs. Fig. 5: VLT 6000 HVAC Frequency Converter There is no risk of damaging power factor correction capacitors, PFC capacitors or other electrical/ electronic equipment, or of overheating the supply transformer when using Danfoss VLT 6000 HVAC drives. MC.60.E1.02 - VLT is registered Danfoss trademark Many drive brands will damage power factor correction capacitors and other electrical /electronic equipment due to low power factor (0.5 - 0.6), caused by harmonics. Power factor correction capacitors cannot compensate for a low drive power factor. Danfoss VLT 6000 HVAC drives have a full rated DC link filter built in as standard (See fig. 5). Suggested limits for harmonics disturbance are set in the recommendations G5/3 and IEEE 519. Norm VDE 0160 specifies approximately the same levels. The Danfoss drives observe the normed VDE 0160 specifications. This ensures good suppression of harmonics and improves the power factor to above 0.9. Please bear in mind, that power factor and Cos ϕ are not the same thing, when drives with bridge rectifiers in the input are used. In order to find the true power factor, multiply the fundamental current I1 (1st harmonic) by Cosϕ1 and divide by the total rms current, IRMS . Usually the rms current is difficult to establish as it demands more sophisticated instruments than an ordinary ammeter. ■ Input surge protection All Danfoss VLT 6000 drives are input surge protected according to IEC 1000-4-4 and -5 as well as protected against other disturbances according to IEC 1000-4-2 and -3. 7 Considerations To suppress harmonics and at the same time improve the power factor, most manufacturers supply AC line reactors (coils to mount in the AC supply lines) or DC coils (coils to mount in the DC link circuit), as optional extras to be mounted outside the drive cabinet. Considerations How to use VSD in existing HVAC installations ■ Motor derating This issue is already discussed in “Sizing of Drive” page 6, but there are a few more words to it: Danfoss VLT 6000 HVAC drives can run a motor without derating, because of the advanced VVC (Voltage Vector Control) principle developed by Danfoss. It is based on a 60° switching pattern controlled by the software and an ASIC, to give optimum magnetising of the motor under any operating condition, taking load and speed into consideration. Used in the VLT 6000 HVAC drives, the software control ensures close resemblance with the centrifugal characteristic of fans and pumps. ■ Short circuit capabilities of the drive What precautions are made to prevent damages because of short-circuits between motor phases or motor phase to earth? * The quality of motors and cable used for motors may vary. Low quality plastic insulation may become crisp and eventually cause short circuits. * Accidents may happen causing damage to motor cable, which then short circuits. * By accident water can get into electrical systems and that may cause short-circuits. * The application may block the rotor of the motor. If so, the motor will take up much current and eventually overheat. * The environment may cause even good products to fail and eventually to short circuit. ■ Switching directly on the drive output * In many applications a service switch, mounted between the drive and the motor, is desirable. In this way any repair work in the installation can be carried out safely, even if voltage is connected. * It may be relevant to connect more than one motor in parallel to a drive and then switch the motors in and out during operation as required. The situations mentioned may cause an open circuit between the motor and the drive or rapid load changes, when motors are switched in and out. Most drives will not tolerate the motor to be switched on or off between the drive and the motor (service switch or parallel operation of motors) during operation. The drive and motor should always be switched off/brought to standstill to avoid damages to the drive. Shock loads may also damage the drive. Make your supplier prove that his drive can withstand such situations during operation, before you make your choice. With a Danfoss VLT 6000 HVAC drive, unlimited ON/ OFF switching of the motor, between the drive and the motor is allowed. The drive may trip but it will not be damaged. The VLT 6000 drives can run without a motor connected and still not be damaged. The VLT 6000 HVAC drives have extremely fast current sensors built into all three motor phases. The problems mentioned are just a few of many possibilities of short circuits between motor phases, shorts to ground (earth) or over-current situations that a drive will have to deal with. Most drives will not tolerate to be short circuited directly between the output phases or between an output phase and ground (earth) and especially not when it is running. Make your supplier prove that his drive can withstand such situations without any limitation or damage, before you make your choice. The Danfoss VLT 6000 HVAC drives tolerate direct, solid short-circuit of the output phases or phase to ground under any condition, loaded or unloaded. 8 MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations Programming: Many drives are difficult to set up or programme and often they communicate with the user in codes. The manual briefly shows what to do, but there is often a lot to do before the drive is running. The drives can be programmed to many different applications, situations and operating conditions, which are used in industrial applications. In HVAC applications, however, most of the functions are superfluous or even wrong. The Danfoss VLT 6000 HVAC drives are dedicated for HVAC applications including relevant I/Os. The Danfoss VLT 6000 HVAC drives have a 3-line alphanumeric display explaining the drive conditions chosen. The Danfoss VLT 6000 HVAC drives have Hand/Off/Auto functions that can be selected directly from the keyboard as well as remotely. That makes it very easy to control the application e.g. during commissioning, both on site and from the control room. Hand function can be disabled, if necessary. VLT 6000 HVAC is preprogrammed from the factory with HVAC relevant settings. VLT 6000 HVAC has a Quick Set-up menu in which you only need to record motor data: voltage, current and frequency to make the drive run. Ten parameters are maximum in the quick set-up menu, but sufficient to adapt to most applications. VLT 6000 HVAC have RFI and harmonic filters integrated in compliance with the standards for building services. ■ Galvanic isolation Considerations ■ User friendliness Control terminals must be safe to touch during installation, commissioning and operation. Any standard signal source should connect to the control terminals without the use of signal isolators. Many drives do not have proper galvanic isolation between the high voltage power section and the low voltage control section. This means that the low voltage control terminals can be “riding” on a high voltage level and problems can arise when connecting signal sources, if they are not “floating signals” or not referring to the same ground potential as the drive. Damage can even occur if signal isolators are not used. Some drives do have opto-couplers as signal separators in the control input, but the optocouplers used, are usually not certified to any standards. They must comply with VDE 0884 or UL 508. the norms may also specify certain demands as to how the opto-couplers are mounted on the circuit boards, leakage path etc. and high voltage testing of the finished assembly. Make your supplier prove that his drive has true galvanic isolation in accordance with international norms, before you choose your frequency converter. Danfoss VLT 6000 HVAC drives provide full galvanic isolation between control terminals and power section, according to the norms VDE 0106 and VDE 0160, PELV (Protective Extra Low Voltage). The isolation is for example provided by transformers. The norms demand three layers of insulating material. The lacquer on the copper thread is not regarded as a layer! The control terminals of VLT 6000 HVAC are safe to touch and no external signal isolator will be necessary between drive and source. MC.60.E1.02 - VLT is registered Danfoss trademark 9 Considerations How to use VSD in existing HVAC installations ■ Other important features Zero inrush current In pump applications it is important to avoid water hammer, which will damage pipes and valves. Water hammer comes from the shock wave that arises in the pipe system every time a pump is started or stopped. DOL (Direct On Line) start and Star/Delta starters both cause water hammer and high inrush currents from the mains. The inrush current can be 5-7 times the rated motor current (name plate current). See fig. 6. Soft starters limit the water hammer but the inrush current on mains is 2.5 to 3 times higher than the rated motor currrent. The VLT 6000 HVAC drives ensure that there will be no inrush current at start, as the motor is ramped up to desired speed in a smooth and controlled way. On stop, the motor is ramped down to zero speed in the same smooth and controlled way. Together with the variable torque characteristic the ramp up and down function will prevent any water hammer. Catches spinning motor without tripping In for example ventilating plants, several fans could be installed, but not all of them are used all the time. They are cut in or out as required. When cutting in a fan, it will probably be rotating in the opposite direction as intended, because of the existing air flow (wind-milling). A fan in an Air Handling Unit may be swtiched off intentionally or the mains may simply disappear. When power is switched on again, or mains reappears, the fan may still be rotating due to inertia. Drives connected to fans in such situations should be able to detect the direction and actual speed of the fan and bring the fan back to desired speed and rotational direction, normally without the use of injected DC voltage. However, wind-milling fans may have to be brought to standstill by means of DC injection before some drives will connect without tripping. The VLT 6000 HVAC drives can detect the speed of a disconnected, but already/still spinning motor, catch it and control it back to desired speed, no matter in which direction it was spinning. Unidirectional fans can thus be brought back to correct direction, if they should be windmilling, without tripping. 1 = VLT 6000 HVAC 2 = Star-Delta 3 = Soft Starter 4 = Direct-on-line Fig. 6 10 MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations Serial communication Making the motor completely noiseless over the full frequency range may be desirable, but recent investigations have revealed that this cannot be achieved without cost: An installation with many drives require a lot of control cables and wires to be connected between PLCs, Building Management Systems, transmitters, transducers etc. Controlling the drives via serial communication requires only two wires and a PC software program. The motor bearings will usually erode because of circulation currents in the motor frame, caused by high switching frequencies or high du/dt. (Note that du/dt is the rate of voltage rise over a period of time, usually defined as the change in voltage in one microsecond). This can be overcome by replacing the normal bearings by insulated ones, that will prevent the flash-over from the outer bearing ring to the inner bearing ring, via the rollers. But this is an expensive operation, which should not be necessary. The VLT 6000 HVAC drives operate completely noiseless in the lower output freqeuncy range (up to 25 Hz). Then , as fan or pump noise increases, the drive will allow the switch frequency to come down to the preset value, which is reached at 50 Hz output frequency. This is ensured with ASFM (Automatic Switch Frequency Modulation). If necessary, drive and motor can be made noiseless up to 50 Hz output frequency, by running at high switch frequency all the time. However, that requires the output power to be somewhat reduced. Because of the Danfoss VVC control system, no damage is made to the motor bearings, when running high switch fr equency with a VL T 6000. frequency VLT Further energy savings Most HVAC applications only require some monitoring and not so much controlling. Such applications can be run with RS 485 serial communication. More demanding applications would require faster communication systems which can handle higher data rates. The VLT 6000 HVAC drives have RS 485 serial communication built in as standard. Up to 99 drives can be addressed via a PC and repeaters for programming, monitoring and control, by means of the communication software VLSTM Dialog 2. Should more intelligent serial communication be of interest, Danfoss can offer solutions with PROFIBUS, Modbus+, LONWorks & Metasys N2. Contact Danfoss for further technical information covering Design Guide, References, Application and Feature Notes. The booklet Why Why... use VSD in existing HVAC installations MA.60.D1.02, Retrofit Guideline Part I, describes the advantages of fitting VSDs in existing installations. It deals with the benefits, fully described with energy saving and pay back time calculations. When drives are running a HVAC application and steady conditions are achieved, it should be possible to reduce the energy consumption according to load, by allowing the motor voltage to drop to lowest possible value and still running the application safely and reliably. The VL T 6000 HV AC drives have an AEO (Automatic VLT HVAC Energy Optimising) function built in as standard. When the drive has reached the set speed, the motor voltage is adjusted to an optimum value that will ensure reliable operation, optimise efficiency and reduce energy consumption further by 5-10% depending on the application. MC.60.E1.02 - VLT is registered Danfoss trademark 11 Considerations Acoustic noise For your notes/calculations How to use VSD in existing HVAC installations 12 MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations For your notes/calculations MC.60.E1.02 - VLT is registered Danfoss trademark 13 For your notes/calculations How to use VSD in existing HVAC installations 14 MC.60.E1.02 - VLT is a registered Danfoss trademark How to use VSD in existing HVAC installations For your notes/calculations MC.60.E1.02 - VLT is registered Danfoss trademark 15 How to use VSD in existing HVAC installations For your notes/calculations 16 MC.60.E1.02 - VLT is a registered Danfoss trademark
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