Geothermal Alliance of Illinois

Variable Speed Pumping Control Strategies for ECM Pumps Geothermal Alliance of Illinois March 11, 2019 Tom Wyer, Geo-Flo Products Corporation

This presentation will provide an overview of the control strategies used with modern ECM pumps in closed-loop geothermal systems, with a focus on installation and commissioning simplicity, and energy efficiency. Constant and proportional pressure control modes will be explained and compared. This information will be useful for contractors and engineers installing multiple geothermal heat pumps on a common ground loop heat exchanger. Overview

Review the benefits of variable speed pumping on geothermal systems • Review PSC, VFD, and ECM pumps • Review basic control strategies for modern ECM pumps • Learn to read pump performance and power curves for ECM pumps • Understand the two common differential pressure control modes including advantages/disadvantages of each mode Goals

Drivers for Geothermal Heat Pump System Efficiency Review benefits of VS Pumping • Geothermal heat pump unit efficiency • Duct design and installation • Ground loop design and installation • Pumping efficiency

Variable Speed Pumping Advantages Review benefits of VS Pumping • Increased system efficiency (next slides) • Lower operating costs • Added start-up/service benefits • Some systems display one or more • Pump speed (RPM) • Power (W) • Head (Feet or PSI) • Flow rate (GPM) • EWT/LWT • HE/HR read-out

Pumping Contribution to System Efficiency Review benefits of VS Pumping • Manufacturers catalog data for COP/EER does not include pumping watts • AHRI/ISO/ASHRAE 13256-1 certified data for COP/EER includes pump watts based on the following formula: • Pump power correction (W) = (gpm x 0.0631) x (Press Drop x 2990) / 300 • Where "Press Drop"is the pressure drop through the unit’s heat exchanger at rated water flow in feet of head • Example: 4 ton system with 11 ft of head @12 gpm • Pump power correction = 83 Watts • This is incredibly low, and causes AHRI efficiency to be overstated in most cases (if using constant speed pumps)

Pumping Contribution to System Efficiency benefits of VS Pumpingsystem efficiency • COP = [Heating Capacity/Power Input] ÷ 3.412 • EER=[Total Cooling Capacity/Power Input] • Pumping watts can be significant, and will affect system COP/EER • Manufacture’s performance data: Full Load • COP= [Heating Capacity/Power Input]÷3.412 • Actual System COP=[Heating Capacity/(Power Input+ Pump watts)]÷3.412

Pumping Contribution to System Efficiency benefits of VS Pumpingsystem efficiency • For more information, see: New Technologies That Are Increasing Geothermal System Efficiencies-MNGHPA Jan 2013.pdf • Variable speed pumps lead to greater system efficiency, and in some cases, are required. • ASHREA 90.1 (2013)

PSC,VFD, AND ECM PUMPS Review ECM technology • PSC= Permanent Split Capacitor • Motor that uses AC to generate a magnetic field in the stator to spin the pump’s rotor • Typically single or multiple constant speed settings • Advantages • Simplest installation and setup • Low first cost • Disadvantages • No control (over pumping) • Highest operating costs • Cannot be used on large systems (per ASHREA standards)

PSC,VFD, AND ECM PUMPS Review ECM technology • VFD=Variable Frequency Drive • Controller that drives the pump motor by changing the frequency • Advantages • Lower operating costs than PSC • Capable of scaling to very large systems (high head-high flow) • Disadvantages • Highest complexity installation and setup • Higher installation cost • Limited turn-down (20-30% of full speed)

PSC,VFD, AND ECM PUMPS Review ECM technology • ECM=Electronically Commutated Motor • Permanent magnet rotor • Advantages • Low complexity installation and setup • Lowest operating cost • Lower first cost than VFD • Lower sound levels than VFD • Disadvantages • Higher first cost than PSC • Limited capacity (head/flow) • Must design loop for these pumps • Limited voltage ranges (208-230V) • Can be overcome with transformer

ECM CONTROL STRATEGIES OVERVIEW Control strategies • Modern ECM pumps have built-in controls that allow simple setup. • ECM pump manufactures include: • Grundfos (Magna3) • Taco (00e Series) • Wilo (Stratos) • Bell & Gosset, Armstrong, others • NOTE: This presentation is not intended to cover all control strategies or ECM pump options. • See Magna3 Installation and Setup- 2016 FEB.pdf for a discussion of control options offered by one pump manufacturer.

ECM CONTROL STRATEGIES OVERVIEW Control strategies • Constant/fixed speed ECM (i.e. no control ) • Can be used in central, primary/secondary, and one-pipe systems • Generally higher efficiency than PSC pumps due to ECM technology • External control • Can be used on any system type • NOTE: See “New Technologies Increasing Geothermal System Efficiencies” (IGSHPA 2015) for detailed description of system types.

CONTROL STRATEGIES OVERVIEW Control strategies • Delta-T; Δ-T (Differential Temperature) • Typically used on primary/secondary systems • Must use external controller if more than on set point is required. • Delta-P; Δ-P (Differential pressure) • Constant pressure • Proportional (variable) pressure • More on next slides • NOTE: Avoid “black box” automatic modes for geothermal systems

CONSTANT PRESSURE CONTROL Control strategies • Constant differential pressure (Δp-c) • Pump maintains a constant differential pressure based on the programmed setpoint • Output pressure of the pump is constant • Pump adjusts speed (RPM) to maintain this differential pressure • Power consumption can be determined from corresponding power curves

CONSTANT PRESSURE CONTROL Control strategies • Like constant speed pumps, the pump can only run at the intersection of the system curve, and the pump curve. • Unlike constant speed pumps, ECM pumps have more than one curve. • If system curve/duty point is beyond the max pump curve, the differential pressure will be less than desired.

CONSTANT PRESSURE CONTROL Control strategies • If system curve/duty point is below the constant pressure setpoint, the pump will run at the constant pressure setpoint. • Result: Flow may be higher than required/desired, and/or additional pressure drop will be created by system devices (such as circuit setters or flow control valves)

PROPORTIONAL PRESSURE CONTROL Control strategies • Proportional (variable) pressure (Δp-v) • Pump maintains a differential pressure between the setpoint, and ½ of the set point. • Pump adjusts speed (RPM) to maintain this differential pressure. • Output pressure varies linearly between setpoint and ½ setpoint • Power consumption can be determined from corresponding power curves.

PROPORTIONAL PRESSURE CONTROL Control strategies • Like constant speed pumps, the pump can only run at the intersection of the system curve, and the pump curve. • Unlike constant speed pumps, ECM pumps have more than one curve. • If system curve/duty point is beyond the max pump curve/speed, the differential pressure will be less than desired.

PROPORTIONAL PRESSURE CONTROL Control strategies • If system curve/duty point is below the proportional pressure setpoint, the pump will run along the H to ½ H curve. • Result: Flow may be higher than required, and/or additional pressure drop will be created by system devices (such as circuit setters or flow control valves)

COMPARING Δ-P MODES Control strategies Δp-c Δp-v ✔ ✔ Easy to understand Easy field troubleshooting Predictable flow when zone valves close Lower power consumption Lower noise ✔ ✔ ✔ ✔ = Advantage

COMPARING Δ-P MODES Control strategies • EXAMPLE SYSTEM: 3 heat pumps, customer wants VS & 100% redundancy 1 – 5 ton heat pump 1 – 3 ton heat pump 1 – 2 ton heat pump 10 tons total 20 % methanol See next slide for details 2” HDPE 410’ total ¾” loops, 650’ total

COMPARING Δ-P MODES Control strategies • COMPONENTS AND DIAGRAM FOR AN ECM PUMP SYSTEM WITH TWO PUMPS IN PARALLEL

COMPARING Δ-P MODES Control strategies • EXAMPLE SYSTEM: • 10 tons of equipment; 3 heat pumps (5, 3 and 2 ton packaged units) • Unit 1= 5 ton + unit’s piping: 18.5 ft-hd@15 GPM • Unit 2= 3 ton + unit’s piping: 10 ft-hd@9 GPM • Unit 3= 2 ton + unit’s piping: 8.5 ft-hd@6 GPM • Common loop pressure drop • 25 ft-hd@30 GPM (all units running-max) • 1st duty point: 43.5 ft-hd@30 GPM (all units running) • 2ndduty point: 17.5 ft-hd@15 GPM (units 2 and 3 running) • 3rd duty point: 10 ft-hd@6 GPM (unit 3 only) • NOTE: See Understanding Pressure Drop Calculations and Pump Sizing For Large Residential-Light Commercial Geothermal Systems-Iowa Geo Conf 2015.pdf

COMPARING Δ-P MODES Control strategies • 1st duty point: 43.5 ft-hd@30 GPM (all units running) Proportional Constant 539 W 539 W 53.9 W/ton 53.9 W/ton

COMPARING Δ-P MODES Control strategies • 2nd duty point: 17.5 ft-hd @15 GPM (units 2 and 3 running) Proportional Constant 419 W 289 W 84 W/ton 58 W/ton

COMPARING Δ-P MODES Control strategies • 3rdduty point: 10 ft-hd@6 GPM (unit 3 only) Proportional Constant 352 W 179 W 176 W/ton 89.5 W/ton

COMPARING Δ-P MODES Control strategies • Selecting the Δp control mode to use • One manufacturer’s recommendation ?

COMPARING Δ-P MODES Control strategies • Selecting the Δp control mode to use • Another manufacturer’s recommendation ?

COMPARING Δ-P MODES Control strategies • Simplified recommendation for selecting the control mode • Design the system based on constant pressure mode • Commission the system with proportional pressure mode • If proportional pressure does not give you the flow you need at full load, switch to constant pressure

CONCLUSIONS Control strategies lessons • ECM pumps integrate simple, yet powerful, pumping controls into a small, easy to install package • Proportional/variable differential pressure results in decreased energy consumption at part load • “H” setpoint has the biggest influence on pump energy consumption at full and part load • Consider setpoint at manufacturer’s minimum recommended values at full load for maximum energy savings • Use proportional pressure control whenever possible

Questions? Geothermal Alliance of Illinois Tom Wyer, Geo-Flo Products Corporation

Geothermal Alliance of Illinois