Compensação de Vazão com VLT®HVAC Drive
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Compensação de Vazão com VLT®HVAC Drive
- 1. CCoo mmppeennssaaççããoo ddee VVaazzããoo Confidential / Property of Danfoss Drives A/S
- 2. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 2 Compensação de Vazão A Necessidade para Compensação da Vazão
- 3. VLT®HVAC Drive Ponto de Operação Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 3 0 100 200 300 400 500 600 Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Curva da Bomba Curva de Controle Vazão
- 4. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 4 0 100 200 300 400 500 600 Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Potência a Vazão x Pressão Vazão
- 5. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 5 0 100 200 300 400 500 600 Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Vazão Desejada Vazão
- 6. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 6 0 100 200 300 400 500 600 Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Potência Potência Gasta Vazão
- 7. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 7 Compensação de Vazão
- 8. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 8 0 100 200 300 400 500 600 Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Potência P Vazão
- 9. e a perda de pressão na tubulação? VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 9 Compensação de Vazão É mais barato colocar o sensor de pressão aqui
- 10. Pressão em Vazão Plena 0 100 200 300 400 500 600 VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 10 P Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Potência Potência Gasta Vazão
- 11. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 11 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Flow (%) Power (%) Vazão (%) Sem Controle da Pressão Sensor de Pressão Próximo a Bomba Sensor de Pressão Através da carga Potência do Motor (%)
- 12. 0 100 200 300 400 500 600 VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 12 P Flow 50 45 40 35 30 25 20 15 10 5 0 Pressure Set Point de Pressão Potência Pressão sem Vazão Curve Aprox. Quadrática-Linear Vazão
- 13. Compensação de Vazão Ajustando o Drive – Velocidade de Projeto Conhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 13 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência
- 14. VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 14 Compensação de Vazão Ajustando o Drive – Velocidade de Projeto Conhecida 22-80 Compensação de Vazão Ativada 22-82 Cálculo do Ponto de Trabalho Inativo 22-83/4 Velocidade na Falta de Vazão 15 Hz 22-85/6 Velocidade no Ponto de Projeto 45 Hz 22-87 Pressão na Velocidade de Falta de Vazão 25% 20-21 Setpoint 1 (pressão no ponto de projeto) 75% 22-81 Aproximação da Curva Quadrática-Linear 100% - 0%
- 15. Ajustando o Drive – Velocidade de Projeto Conhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 15 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência 20-21 22-87 22-84 22-86 Flow Compensation
- 16. Ajustando o Drive – Velocidade de Projeto Conhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 16 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência 20-21 22-87 22-84 22-86 22-81 100% Flow Compensation
- 17. Ajustando o Drive – Velocidade de Projeto Conhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 17 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência 20-21 22-87 22-84 22-86 22-81 100% Flow Compensation
- 18. Ajustando o Drive – Velocidade de Projeto Desconhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S Freq., Vazão & Pressão Conhecidas October 22 – 26.2007 LAM HVAC Training 18 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência Freq. & Pressão Desconhe. Vazão Conhecida Compensação de Vazão
- 19. Flow Compensation Ajustando o Drive – Velocidade de Projeto Desconhecida A maioria dos parâmetros são como antes, exceto: 22-82 Cálculo do Ponto de Trabalho VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 19 Ativo 22-88 Pressão na Velocidade Plena 93% 22-89 Vazão no Ponto de Projeto XXX (determinado da curva da bomba) 22-90 Vazão na Velocidade Plena XXX (determinado da curva da bomba)
- 20. Flow Compensation Ajustando o Drive – Velocidade de Projeto Desconhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 20 Compensação da Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência 22-88 22-90 vazão 22-89 vazão 22-82 Cálculo do Ponto de Trabalho
- 21. Ajustando o Drive – Velocidade de Projeto Desconhecida VLT®HVAC Drive Confidential / Property of Danfoss Drives A/S October 22 – 26.2007 LAM HVAC Training 21 Compensação de Vazão 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% 0 5 10 15 20 25 30 35 40 45 50 Hz Referência 22-81
- 22. CCoo mmppeennssaaççããoo ddee VVaazzããoo Confidential / Property of Danfoss Drives A/S
Hinweis der Redaktion
- Name/department Page <number> VLT®HVAC Drive An adjustable frequency drive avoids this large pressure drop by controlling the speed of the pump. While there are a number of different ways of accomplishing this, the simplest and most common is to measure the differential pressure across the most distant significant load. A setpoint controller is used to adjust the speed of the drive to maintain the required system differential pressure. The concept here is that, if the required pressure is maintained here, sufficient pressure will be available throughout the system. As the valves in the system are closed due to a reduced demand for flow, the pressure in the system will tend to increase. The differential pressure sensor will indicate this and the setpoint controller will slow down the drive to maintain the desired pressure. The opposite happens when the demand increases.
- Name/department Page <number> VLT®HVAC Drive Details of the way that drives are interfaced with the building’s HVAC system have a major impact on the amount of energy that can be saved. In some cases, the simple relocation of a sensor or the changing of a setpoint can be critical to achieving maximum energy savings. This portion of the presentation considers factors that are critical to maximizing energy savings. While this example deals specifically with a pumping system, the same concepts apply to fan systems. The Pump Curve determines the relationship between the flow and pressure that the pump can produce. The Control Curve determines the same relationship for the controlled system. Where these two curves intersect determines the pressure and flow that will result.
- Name/department Page <number> VLT®HVAC Drive It helps to be able to visualize the amount of power that is associated with any particular combination of pressure and flow. Since power is proportional to the product of pressure and flow, the area of the rectangle that is formed between the axes of the pressure-flow graph and the operating point represents the power that is associated with the flow. It should be noted here that this describes the power associated with the flow from the pump. It does not take into account the inefficiency of the pump, the motor, or any other portion of the system. While consideration of these inefficiencies will be important for a precise analysis of the total power requirements of the system, these do not need to be considered for this discussion.
- Name/department Page <number> VLT®HVAC Drive Since the system will seldom need to operate at its full design flow, it is important to consider how to reduce the flow to the level that will be required under less severe conditions.
- Name/department Page <number> VLT®HVAC Drive The traditional method of reducing the flow from a pump is to close a throttling valve. This increases the pressure that the pump needs to produce. The operating point is said to “ride up” the Pump Curve. An examination of this situation shows that the power associated with this flow, as shown by the area of the purple rectangle, has decreased. However, only the bottom portion of this rectangle represents the flow and pressure delivered to the load. The rest of the rectangle represents power that is lost through the pressure drop across the partially-closed valve.
- Name/department Page <number> VLT®HVAC Drive An adjustable frequency drive avoids this large pressure drop by controlling the speed of the pump. While there are a number of different ways of accomplishing this, the simplest and most common is to measure the differential pressure across the most distant significant load. A setpoint controller is used to adjust the speed of the drive to maintain the required system differential pressure. The concept here is that, if the required pressure is maintained here, sufficient pressure will be available throughout the system. As the valves in the system are closed due to a reduced demand for flow, the pressure in the system will tend to increase. The differential pressure sensor will indicate this and the setpoint controller will slow down the drive to maintain the desired pressure. The opposite happens when the demand increases.
- Name/department Page <number> VLT®HVAC Drive Instead of following the Pump Curve for a fixed speed, the operation of the system follows the Control Curve. As the required flow decreases, both the pressure and the flow decrease. As a result, the reduction in power is significant. If the setpoint pressure was zero, the pressure would be proportional to the square of the flow. As a result, since power is proportional to pressure times flow, the power would be proportional to flow cubed. This is the familiar centrifugal fan or pump affinity law. When projecting the energy savings possible by using an adjustable frequency drive, it is important to remember that this only applies when the setpoint pressure for the Control Curve is zero. It is also important to remember to consider the efficiencies of the various devices in the system.
- Name/department Page <number> VLT®HVAC Drive Unfortunately, a major mistake is too frequently made when such a system is installed. In order to reduce the initial installation costs, it is tempting to place the pressure sensor at the pump. While this reduces the installation cost somewhat, it makes it impossible for the control system to measure the pressure that is being delivered to the most distant significant load. As a result, the system can’t directly compensate for the variable pressure loss associated with producing pressure in the system.
- Name/department Page <number> VLT®HVAC Drive As a result, a simple fixed setpoint control system must use a setpoint that is high enough to provide for the maximum pressure drop in the piping system. Although the pressure loss in the piping will decrease at reduced flows, the control system doesn’t account for this. Therefore, the pump will produce excess pressure at all flows that are less than maximum. This significantly increases the power required to produce reduced flow in the system. While it is possible to mathematically model the Control Curve and provide the system with a setpoint at the pump that varies with flow, this adds complexity to the programming of the system and can’t directly take into account all of its related dynamics. It is always best to directly measure the quantity this is to be controlled.
- Name/department Page <number> VLT®HVAC Drive These measurements were taken on a small model pumping system in our laboratory in Milwaukee. In a large system, where the variable losses play an even more significant role, the energy savings from proper location of the feedback sensor would be even more dramatic.
- Name/department Page <number> VLT®HVAC Drive As a result, a simple fixed setpoint control system must use a setpoint that is high enough to provide for the maximum pressure drop in the piping system. Although the pressure loss in the piping will decrease at reduced flows, the control system doesn’t account for this. Therefore, the pump will produce excess pressure at all flows that are less than maximum. This significantly increases the power required to produce reduced flow in the system. While it is possible to mathematically model the Control Curve and provide the system with a setpoint at the pump that varies with flow, this adds complexity to the programming of the system and can’t directly take into account all of its related dynamics. It is always best to directly measure the quantity this is to be controlled.