1. 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

2. Overview
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.

3. Goals
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

4. Review benefits of VS Pumping
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
Main drives from a product standpoint
Items 3 and 4 are closely related

5. Review benefits of VS Pumping
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

6. Review benefits of VS Pumping
Pumping Contribution to System Efficiency
Review benefits of VS Pumping
Manufacturers catalog data for COP/EER does not include pumping watts
AHRI/ISO/ASHRAE certified data for COP/EER includes pump watts based on the following formula:
Pump power correction (W) = (gpm x ) 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 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)
Repeat bullet 1 for emphasis
Pressure drop is through the unit only; does not include loop

7. benefits of VS Pumping system efficiency
Pumping Contribution to System Efficiency
benefits of VS Pumping system 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

8. benefits of VS Pumping system efficiency
Pumping Contribution to System Efficiency
benefits of VS Pumping system 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)

9. 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)

10. 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)
May require controls contractor, depending on system complexity

11. 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 ( V)
Can be overcome with transformer

12. 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 FEB.pdf for a discussion of control options offered by one pump manufacturer.

13. 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.

14. 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

15. 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

16. 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.

17. 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)

18. 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.

19. 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.

20. 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)

21. 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

22. COMPARING Δ-P MODES Control strategies
April 29, 2014
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

23. COMPARING Δ-P MODES Control strategies
April 29, 2014
COMPARING Δ-P MODES
Control strategies
COMPONENTS AND DIAGRAM FOR AN ECM PUMP SYSTEM WITH TWO PUMPS IN PARALLEL

24. 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 GPM
Unit 2= 3 ton + unit’s piping: 10 GPM
Unit 3= 2 ton + unit’s piping: 8.5 GPM
Common loop pressure drop
25 GPM (all units running-max)
1st duty point: 43.5 GPM (all units running)
2nd duty point: 17.5 GPM (units 2 and 3 running)
3rd duty point: 10 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
Assume 20% methanol
10X 650 ft of ¾” HDPE u-bends
410’ of 2” HDPE (plus two elbows)

25. COMPARING Δ-P MODES Control strategies
1st duty point: 43.5 GPM (all units running)
Constant
Proportional
Side NOTE: at the duty point of each of these units, a two-pump flow center would be required. Each would consume around 320, 350, 390-watts (total of 1060 W)
539 W
539 W
53.9 W/ton
53.9 W/ton

26. COMPARING Δ-P MODES Control strategies
2nd duty point: 17.5 GPM (units 2 and 3 running)
Constant
Proportional
Notice higher pressure than duty point on each.
419 W
289 W
84 W/ton
58 W/ton

27. COMPARING Δ-P MODES Control strategies
3rd duty point: 10 GPM (unit 3 only)
Constant
Proportional
Notice higher pressure than duty point on each.
352 W
179 W
176 W/ton
89.5 W/ton

28. ? COMPARING Δ-P MODES Control strategies
Selecting the Δp control mode to use
One manufacturer’s recommendation
Notice higher pressure than duty point on each. ?

29. ? COMPARING Δ-P MODES Control strategies
Selecting the Δp control mode to use
Another manufacturer’s recommendation ?
Notice higher pressure than duty point on each.

30. 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
Notice higher pressure than duty point on each.

31. Control strategies lessons
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
Assume 20% methanol
10X 650 ft of ¾” HDPE u-bends
410’ of 2” HDPE (plus two elbows)

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