Starting Current Reduction of Residential HVAC System and Peak-Load Impact of Power System: A Case Study

Transcription

1 Starting Current Reduction of Residential HVAC System and Peak-Load Impact of Power System: A Case Study By Paul I-Hai Lin Professor of Electrical and Computer Engineering Technology P.E. (State of Indiana & State of California) For WaterFurnace Inc. September 9, 2009 Initial Meeting: 2:00 PM, July 14, 2009, WaterFurnace Inc., Attendees: John Groulik, Executive Vice President, WaterFurnace Inc., Carl F. Huber, Vice President Corporate Quality, WaterFurnace Inc., Sean Ryan, Director of University Engagement, IPFW Jean Eisaman, Project Manager, Office of University Engagement, IPFW Paul I. Lin, Professor of Electrical and Computer Engineering Technology, IPFW Meeting Minutes: John Groulik made a presentation entitled Reduces Starting Current of PSC Motor using IntelliStart. and showed many innovative features of this new product, a single-phase motor starter, for HAVC applications. These features include Capability of reducing, up to 66 percent, the inrush or starting current of a single-phase 208/230V PSC (Permanent Split Capacitor) motor of a residential HVAC system during an average start-up duration of 0.13 sec (or about 8 cycles). Reduced the HVAC supply voltage drops experienced during the start-up Light flicker reduction And many others such as line impedance tolerance, better protect the compressor motor from potentially damage by low voltage sags, randomly restarting time, etc. John asked IPFW to help to conduct a study that could identify the magnitude of impact on peak load reduction during hot summer days in the time period from 4:00 PM to 6:00 PM if this soft starter is widely used by consumers of electric utilities (power grid). Paul Lin pointed out that that this is an innovative device with a potential impact on reducing the peak-load of power system (distribution system), and suggested that the scope may be reduced to just considering a smaller number of residential HVAC system in a subdivision that connected to a distribution transformer of utility company. In an to John, a few days later, Paul said that he will start his research for preparing a project proposal for review. After the meeting, Paul Lin allocated many hours for initial research on related products and works to assess the significance of the problem.

2 Initial Assessment of Significance of Problem 1. Initial Research on Related Works and Soft Start Products Power Distribution Apparatus: Transformers, Primary-unit substations, Secondary-unit substations Electrical Energy Management (HVAC related) o Load management, Load Control, Load Shedding o Types of demand controllers: Instantaneous, Ideal rate, Converging rate, Predictive rate, Continuous interval Soft Starters and PSC Motor Starters o IntelliStart Soft Starter o RapidStart Motor Starters (current sensing, voltage sensing) o I-Start Single Phase AC Motor Soft Starters o CI-Tronic Single-Phase Compressor Soft Starters o SIRIUS Soft Starters o Square D LH4 Modular Soft Starters o Altistart Soft Starters o PSC Single-Phase Motor Start Assist, Vishay 305C series Motor Starting Methods and Short Cycle Protection Techniques o Inrush Current/Locked Rotor Current, Voltage Drop o Positive Temperature Coefficient (PTC) thermistors o Start relay/ Capacitors HVAC Control Systems and Applications Conducted an Initial Power System Modeling of PSC motors using IntelliStart for HVAC applications, see Figure 1 below. Terms related to Demand, Maximum Demand, Coincident Demand, Demand Factor, Critical Load, Connected Load, Gross Demand Load, Load Factor, Diversity Factor, Peak-Load, etc [1][2]. o Demand (or demand load) demand is expressed in kw, kva, kvar, Amperes or suitable units. If there are 100 5hp PSC compressor motors of HVAC systems are connected to the utility s power system, then the demand load is 500 hp. o Connected Load If there are 100 5hp PSC compressor motors of HVAC systems are connected to the utility s power system, then the demand load is 500 hp; but if only 50 HVACs are operating at any time, the connected load is 250 hp. o Maximum Demand (Peak Demand) The greatest of all the demands that have occurred during a specific period of time; determined by measurement over a prescribed utility s demand metering time interval (15 min, 30 min, or 1 h). Penalty fee will be charged if the peak demand occurred. o Peak Load The maximum load of a specific unit or groups of units in a stated period. It may be the maximum instantaneous load or the maximum average load over a designated period of time. o Coincident Demand Any demand that occurs simultaneously with any other demand; also the sum of any set of coincident demands. o Gross Demand Load The summation of the demands for each of the several group loads.

3 o Demand Factor The ratio of the maximum demand of a system to the total connected load of the system. Since the demand load cannot be greater than the connected load, the demand factor cannot be greater than unity. o Diversity Factor The ratio of the sum of the individual maximum demands of the subdivisions of the system to the maximum demand of the complete system. Basics of Soft Starters and Inrush Current Reduction Electricity Consumption by End Use in U.S. Households, 2001, 2005, The Residential Heating and Cooling Load Calculations o HVAC Sizing Energy Use and End-Use Load Characterization - Transformers o Transformer Loading o Hourly Load Model o Monthly Load Model o Electrical Load Modeling Load-Side Management, Demand-Side Management, Residential HVAC Direct Load Control HVAC System Related Peak-Load Reduction Technologies o By using thermo-stat (classical regulator that maintain the temperature in a specified value carried out by a thermostat for a HAVC unit containing two AC single-phase motors: one for Air Fan runs continuously and one for the compressor runs on an ON/OFF cycle mode); this can cause an excess of peakload if too many HVACs operates at the same time) o By using air-conditioning regulators exercising demand control during periods of power shortage and adapted to the permissible power. o By Soft Starters: Extremely short duration of peak-load reduction based on typical HVAC cycling (15 min ON/ 15 min OFF) may not be able to generate sufficient peak-load reduction that could justify the further research.

4 Utility Lines Desired Temp Set Point Temp F Adj Thermostat error PI + Controller Feedback Temperature Sensor Actuator KWH Meter Main NFB NFB Outdoor House Branches Load 1 Load 2 Load n... Indoor unit Fan/Motor Magnetic Switch Coil IntelliStart M Compressor/ Motor Outdoor unit Figure 1. Initial Power System Modeling of PSC motors using IntelliStart for HVAC applications 2. Initial Project Feasibility Assessment of Peak-Load Reduction through the Use of Soft Starters for PSC motor of HVAC System. For the industrial and commercial users, peak-load is normally defined as the maximum load consumed by a unit or group of units in a state period of time. Using a soft starter such as IntelliStart, the Peak-load can be reduced for only a fraction of HVAC cycle time (say for a cycle pattern of ON-time for 15 minutes, OFF-time for 15 minutes). This can be calculated as 0.13 sec/900 sec or about 1.4 percent of the 15 minutes on-time period; or 0.7 percent of 30 minutes of ON-OFF cycle time. Soft-starters ramping up the voltage to the PSC motor, cut abrupt inrush current that accompanies full-voltage starting. The inrush current will be reduced to 34 percent of regular Locked Rotor Current (66 percent reduction). The soft starters do not reduce the amount of energy (in terms of KWH) necessary to start a motor, but spread it over a longer period rather than fractions of a second. 3. Conclusion Based on the initial research, Paul Lin found that there are similar soft starters with less innovative features available in the market. All those products claim starting current or inrush current reduction but not peak load reduction. The IEEE Std and IEEE Std define peak load as The maximum load of a specific unit or groups of units in a stated period. It may be the maximum instantaneous load or the maximum average load over a designated period of time. The recognized minimum period of time for peak-load calculation is 15 minutes.

5 Distribution transformers are sized with certain peak-load consideration and installed by utility companies. While there is proven data showing that the IntelliStart soft starter can reduce the starting current (Inrush current) of a single-phase, 208/230V, PSC motor with HVAC compressor load to 34 percent of its regular Locked Rotor Current (66 percent reduction), however, based on initial research findings and from IEEE Standards, Paul Lin concludes that the 0.13 sec time period for this inrush current reduction during the HVAC ON-OFF cycle time is too short to make an impact on the Peak-Load of distribution transformers owned by utility companies. The soft starters do not educe the amount of energy (in terms of KWH) necessary to start the PSC motor with HVAC compressor load, but spread it over a longer period rather than fractions of a second (without soft starter). Therefore, a suggestion is not to continue this research project or ask WaterFurnace Inc. to find other experts to continue this research. References [ 1] IEEE Recommended Practice for Electric Power Systems in Commercial Buildings, IEEE Std , Institute of Electrical and Electronics Engineers, Inc. [ 2] IEEE Recommended Practice for Electric Power Distribution for Industrial Plants, IEEE Std , Institute of Electrical and Electronics Engineers, Inc.