Variable Frequency Drive Retrofit Opportunities. Michael Kuk CERx Solutions LLC

Transcription

1 Variable Frequency Drive Retrofit Opportunities Michael Kuk CERx Solutions LLC

2 Speaker Introduction» Founder / owner of CERx Solutions LLC» Veteran Owned Small Business Enterprise founded in 2013» 27+ years of energy efficiency experience» Performing State of Illinois / Illinois Utility efficiency studies since 2005» Commissioned 95 new buildings» Re-commissioned 35 existing buildings» Conducted 100 s of Energy Efficiency Evaluations» Instructor in MEEA Building Operator Certification (BOC) program throughout the Midwest

3 Agenda The overall goal of this presentation is to 1. present the energy saving potential for variable frequency drives 2. present alternative opportunities for VFD retrofits Preface on Variable Frequency Drives and Affinity Laws Issues / Opportunities Seen in the Field Case Studies Tweaking and Tuning Existing VFD installations for additional savings Rebates and Incentives Questions

4 Preface on VFDs / VSDs» Variable frequency drives (VFDs) / Variable Speed Drives (VSDs) reduce motor speed by changing the frequency of power supplied to the motor» Reducing a pump or fan speed can dramatically reduce its energy consumption» A VFD typically doesn t go lower than 20% speed (12 Hz) for a pump or fan, but could possibly go lower under the right circumstances

5 Preface on VFDs / VSDs-continued» A VFD can be used to increase speed faster than 60 Hz if needed» A VFD can be used for soft start to extend life of a motor» A VFD rated motor is suggested to ensure maximum life of the motor and bearings. Shaft grounding can be used in lieu» A VFD is the most energy efficient means for reducing fan / pump speed» VFD costs have gone down dramatically in recent years

6 Fan and Pump Affinity Laws Modified Fan Affinity Law % Savings using modified calc. Modified Pump Affinity Law % Speed BHP BHP Savings % 100% 100% 0% 95% 88% 12% 90% 77% 23% 85% 67% 33% 80% 57% 43% 75% 49% 51% 70% 41% 59% 65% 34% 66% 60% 28% 72% 55% 22% 78% 50% 18% 82% 45% 14% 86% 40% 10% 90% 35% 7% 93% 30% 5% 95% 25% 3% 97% 20% 2% 98% This is all geek talk what you need to know is that a little speed reduction = Big Energy Savings! Source: Wikipedia, Basic pump parameters and affinity laws, Greenheck Fan Law Calculator Mobile App Source: Nexant Calculation and M&V Guidelines

7 Traditional applications of VFDs in HVAC Traditional applications are common in new construction Retrofitting a CAV system to VAV in traditional method could involve expensive modifications of equipment and controls VARIABLE AIR VOLUME VARIABLE FLOW PUMPING Source: Advanced VAV system Guide California Energy Commission, Oct pg 152 Source: Ground Source Heat Pumps: Design of Geothermal Systems for Commercial and Institutional Buildings, ASHRAE 1997, figure 5.10

8 4 sample Issues and (VFD retrofit) Opportunities Seen in the Field Issue Typical Cause Opportunity ( take your foot off the brake ) Pumps Oversized Circuit Setters Substantially Closed ( quit spinning your wheels ) Too much flow: Trends show minimal differential temperature between supply and return water or air temperatures Initial Design Seasonal variations, over sized system Install VFD to reduce flow, open circuit setters Install VFD and control to maintain higher differential temperature ( get rid of the muscle car ) Motor Oversized for Load ( close the window the AC is on ) Over ventilating or over exhausting Initial Design Initial Design, Change in Building Use Right size motor / sheave Install VFD and control on schedule, or on sensor feedback

9 Issues and (VFD retrofit) Opportunities Seen in the Field (Continued) Issue Typical Cause Opportunity ( take your foot off the brake ) Pumps Oversized Circuit Setters Substantially Closed Initial Design Install VFD to reduce flow, open circuit setters» Circuit setters are used to reduce pump flow by increasing restriction to flow ( driving while still putting on the brakes )» Required if pumps are over-sized (common)» Energy Code requires trimming impeller or reducing pump speed to reduce flow if pump is oversized

10 Issues and (VFD retrofit) Opportunities Seen in the Field (Continued)» Steps for reducing flow by installing VFD Review previous history TAB reports Changes in operation Verify motor loading, flow requirements Determine savings potential Apply for AMEREN Illinois EE Incentive Install VFD Set your desired pump flow, and lock out this speed on the VFD Protect your motor from over-amperage (program in limits on VFD, or motor limit relay)

11 Issues and (VFD retrofit) Opportunities Seen in the Field (Continued) Issue Typical Cause Opportunity ( quit spinning your wheels ) Too much flow: Trends show minimal differential temperature between supply and return water or air temperatures Seasonal variations, over sized system Install VFD and control to maintain higher differential temperature» Typical engineering design is 10F differential temperature (DT) between Hot water or chilled water supply vs. return temperature» Low differential temperature indication that likely overpumping» Can potentially vary water flow to keep differential temperature higher and save on pumping energy» Need to be careful not to starve some systems of flow, especially during below freezing conditions. Need to tweak and tune.» Low differential temperatures in a constant air volume flow system is also an indication of opportunities to reduce flow» Best applied when using HW/CHW air handling units

12 Issues and (VFD retrofit) Opportunities Seen in the Field (Continued)» Can potentially vary water flow to keep differential temperature higher and save on pumping energy» Need to be careful not to starve some systems of flow, especially during below freezing conditions. Need to tweak and tune.» Low differential temperatures in a constant air volume flow system is also an indication of opportunities to reduce flow» Best applied when using HW/CHW air handling units

13 Issues and (VFD retrofit) Opportunities Seen in the Field (Continued) Issue Typical Cause Opportunity ( get rid of the muscle car ) Motor Oversized for Load Initial Design Right size motor / sheave» Per DOE Motor Master program 50% of Motors = 75%-100% loaded 25% of Motors = 50% - 75% loaded 25% of Motors = less than 50%» Best loading is between 75% and 100%» Motor efficiency drops substantially below 50% load» If you end up installing a VFD, this % load will drop even further» The larger the motor HP, the more costly the VFD» So, it makes sense to right-size a motor before implementing a VFD retrofit» Right sizing a motor can substantially improve the payback of a high efficiency motor upgrade» Potential custom incentive from Ameren Illinois?

14 Issues and (VFD retrofit) Opportunities Seen in the Field (Continued) Scenario 1 (60 hp with 60 hp) Scenario 2 (60 hp with 30 hp) Base Case Horsepower 60 HP Op. Load 24 HP Op. Load 34.3 kw % Load 40 % Efficiency 53 % Energy Use/Year 300,468 kwh Energy Cost/Year $15,554 Scenario 1 Scenario 2 Horsepower 60 HP 30 HP Op. Load 24 HP 24 HP Op. Load 30.1 kw 19.2 kw % Load 40 % 80 % Efficiency 60 % 94 % Energy Savings/Year 36,569 kwh 168,536 kwh kw Saved 4.2 kw 15.1 kw $ Savings/Year $1,893 $8,719 Motor Cost $2,856 $2,495 Payback 1.5 years 0.29 years

15 Issues and Opportunities Seen in the Field (Continued) Issue Typical Cause Opportunity Over ventilating or over exhausting Initial Design, Change in Building Use Install VFD and control on schedule, or on sensor feedback» Calculated load for Springfield = 5.4 ton hr cooling, 214 kbtu heating per CFM. This equates to $2-$5/ CFM if ran continuously» ASHRAE ventilation standards have changed throughout the years» You may be providing more ventilation air than is required

16 Issues and Opportunities Seen in the Field (Continued)» Outside air intake may be able to be scheduled off, or reduced based upon building pressure, temperatures, or CO2 concentrations by controlling fan speed and/or dampers» Some exhaust fans may be able to be scheduled off, or controlled based upon building pressure, temperatures, or CO2 build up» Make-up air units especially have high potential for savings, and can be synchronized with the operation of exhaust fans» These measures may qualify for custom and standard AMEREN Illinois Incentives

17 Case Study 1: CAV to VAV Conversion of AHU» Background: WIU Student Recreation Center Had seven constant air volume air handling units with hot water heat, chilled water cooling» Solution: Converted Constant Air Volume fans to Variable Air Volume Installed two-20 HP VFDs, and five- 5.0 HP VFDs Programmed the BAS to vary the speed of the fan in proportion to deviation from space temperature setpoint No ductwork or other system modification necessary Installed cost: $5,300* Annual Energy / Cost Savings: 242,762 kwh / $19,400 Economics: 0.27 yr simple payback, 370% ROI *Original Installed cost Estimate = $19,000. Customer used internal labor for programming and some other tasks to bring down the cost dramatically.

18 Case Study 2: Variable Flow Pumping Conversion- Differential Temperature Controlled» Background: N. Illinois Middle School (Winston Campus- CCSD15, Palatine, IL) Two pipe constant speed chilled water-hot water distribution system serving unit ventilators and air handling units Trends showed minimal differential temperature (at 32F OAT, DT was only 6F, and was only 0.5F 3.5F at 56F OAT) Circuit setters were partially closed» Solution: Installed 50 HP variable speed drives on the two HW/CHW dual temperature pumps Opened circuit setter and rebalanced flows using the VFD for balancing BAS programmed to keep differential temperature approximately 6-10 F (adj) Speed not allowed to drop <50% No other modifications made to system

19 Case Study 2: Variable Flow Pumping Conversion-Differential Temperature Controlled Installed Cost: $14,800 Verified Annual Energy Savings: 129,000 kwh / $8,100 (5.5% of total) Economics: 1.8 years simple payback, 55% ROI

20 Case Study 3: Variable Flow Control: Schedule Based Background: N. Illinois grade school (F.C. Whitely CCSD15 Palatine IL) 40 HP constant speed condenser water pumps serving water loop heat pump system Circuit Setter closed 40% Total system flow requirements 565 GPM 416 GPM for heat pumps (72% total flow) 71 GPM for water cooled air conditioner (AC1) serving gym (14% total flow) 78 GPM for water cooled air conditioner (AC2) serving multipurpose rooms (14% total flow)

21 Case Study 3: Variable Flow Control: Schedule Based Heat pumps were NOT equipped with motorized valves to shut off condenser flow when compressor wasn t running. Needed continuous flow. (Not typical in new construction.) Retrofitting heat pumps with motorized valves was cost prohibitive AC units needed condenser water only when operating in cooling mode. AC units were equipped with motorized valves, but remained open continuously

22 Case Study 3: Variable Flow Control: Schedule Based (continued)» Solution: Install VFD on condenser pumps Open up circuit setter and rebalance flow at pump via VFD Initial recommendation was to control pumps based upon outside air temperature and status of two large AC units Customer implemented a more simple SOO They now Control speed of pumps based upon system status 100% speed when AC1 and AC2 calling for cooling 80% speed when AC1 not calling for cooling 65% speed when AC2 not calling for cooling (runs this way all heating season)

23 Case Study 3: Variable Flow Control: Schedule Based (continued)» Currently in measurement and verification. Initial savings look better than first estimated. Seeing 50% 100% speed (surprising), 65% savings at 80% speed, and 82% savings at 65% speed!» Installed Cost: $15,152 (lower than initially estimated $23k)» Initial Est. Annual Savings: 199,000 kwh (15% of total), $12,900» Economics: 1.17 yr simple payback, 85% ROI

24 Tweak and Tuning Existing VFD Installations for Additional Savings If you already got them, make them better Issue Typical Cause Opportunity Minimum speed settings too high on VFD Initial Setup Reduce minimum speed settings continuously, or seasonally Circuit setter closed on variable flow system Static pressure reset not being utilized Static pressure setpoint not changed for major changes in seasonal load Improper water balancing procedure Initial setup Initial setup Open up circuit setter. Rebalance to meet flow requirements without circuit setter pump losses Reprogram BAS to implement static pressure reset for water / air systems based upon changes in load requirements Reprogram BAS to change static pressure reset for major changes in seasonal load (IE: summer and winter settings)

25 General Recommendations / Cautions» Always be cautious in making any changes to existing system» Utilize the services of AMEREN Illinois Retro-commissioning Service Providers(RSP) to evaluate your unique situation and identify the potential energy savings» Consult with engineer of record, or manufacturer before changing flows to a system. Especially boilers, chillers, DX cooling systems, AHU s with electric heat» Be very careful when opening up circuit setters so as not to potentially over load motor. Protect from potential over-load» In general, if unsure, ask an expert» Apply for custom or standard efficiency incentives from AMEREN Illinois.

26 Rebates and Incentives» Custom Incentives (Large HVAC projects) 2018: $0.12/kWh, $1.20/therm saved/yr capped at 80% of project cost 2019: $0.08/kWh, $1.20/therm saved/yr capped at 60% of project cost» Standard Incentives HVAC VFD on HVAC Motor: $125/hp controlled (capped at 80% of project cost) Demand Control Ventilation: $0.17/SF controlled

27 Thank you! Questions?

28