1. PERFORMANCE EVALUATION Economizer Enthalpy Sensors
Presented by: Xiaohui Zhou
Iowa Energy Center
Acknowledgement:
Based on experimental evaluation and
product testing conducted by the
National Building Controls Information Program

2. Outline Background Economizer Sensor Testing Summary Apparatus
Procedure
Performance Charts
Summary

3. Background What Is An Economizer?
A system of sensors, dampers, actuators and control logic devices arranged to use outside air under the appropriate conditions to provide cooling to the conditioned space

4. Background Evolution of Economizer Sensor Types
Economizer Enable Logic
Strategy
Conditions to Enable Economizer
Fixed Dry Bulb
OA temp is less than controller setpoint
Differential Dry Bulb
OA temp is less than RA temp
Fixed Enthalpy
OA enthalpy is less than controller setpoint
Differential Enthalpy
OA enthalpy is less than RA enthalpy
Electronic Enthalpy
OA enthalpy is less than a curve on the psychrometric chart
Evolution of Economizer Sensor Types
1950’s – Temperature Sensor Based
1970’s – Electromechanical Electronic Enthalpy Sensor Based
1980’s – Solid State Electronic Enthalpy Sensor Based
1990’s – Solid State True Enthalpy Sensor Based

5. Economizer Control Devices
Discharge Air Temp Sensor
Damper Actuator
Electro-Mechanical Enthalpy Switch
Mixed Air Temp Sensor
Solid State Economizer Logic Module
Enthalpy Sensor
Solid State Economizer Logic Module
Enthalpy or Temperature Sensor

6. Economizer Sensor Testing
Devices Under Test – (Enthalpy Based)
Device
Device Number
Avg. Cost
Enthalpy Sensor
(Analog Output corresponding to enthalpy change)
#1 (Solid State – electronic enthalpy)
$ 46
#2 (Solid State – true enthalpy)
$ 82
Enthalpy Switch
(Digital Output
– ON/OFF)
#3 (Electro-Mechanical,
electronic enthalpy)
$ 332
#4 (Electro-Mechanical,
$ 139
#5 (Solid State,
$ 109
#6 (Solid State - true enthalpy)
$ 88

7. Economizer Sensor Testing
Testing Apparatus
Laboratory grade “Two-Pressure” Humidity Generator
Laboratory grade power supply and data acquisition equipment
0.5% RH accuracy from 10% – 98% RH and 32ºF – 158ºF
0.06 Deg C (0.11 Deg F) accuracy for chamber temperature
Enthalpy calculation using formula from ASHRAE standard
Courtesy Thunder Scientific

8. Test Procedure
Economizer Enthalpy Sensors – Step Increase In Temperature
For each temperature, condition 10%RH and 90%RH for one hour before proceed
Slowly 10%RH/Hour rate
Fast change, not included in data analysis
Humidity generator temperature set points

9. Test Procedure
Economizer Enthalpy Sensors – Step Decrease In Temperature

10. Performance – Enthalpy Sensor #1
Manufacturer’s Published Performance Data
Electronic enthalpy sensor

11. Performance – Enthalpy Sensor #1
Actual Test Data – Manufacturer reference to mA
Max BTU/lb
Hysteresis
2.6% of rdg
Output w/ increasing RH
Output w/ decreasing RH

12. Performance – Enthalpy Sensor #2
Manufacturer’s Published Performance Data
True Enthalpy sensor
Output proportional to Enthalpy
4~20 mA = 0 ~ 50 Btu/Lb

13. Performance – Enthalpy Sensor #2
Actual Test Data
Max BTU/lb
Hysteresis
1.9% of rdg
Output w/ increasing RH
Output w/ decreasing RH

14. Performance – Enthalpy Sensor #1 and #2
Actual Test Data
Different curve and range between sensor #1 and #2

15. Performance – Enthalpy Switch
Manufacturer’s Published Performance Data
Typical electronic enthalpy switch action curve
Economizer Disabled
Economizer Enabled

16. Performance – Enthalpy Switch #3
Manufacturer’s Published Performance Data
Enthalpy switch action curve
Action Curve plotted
Continuously variable adjustment
A and D position tested
(min/max)

17. Performance – Enthalpy Switch #3
Actual Test Data
Economizer Disable (A)
Economizer Enable (A)
~ 2 BTU/lb
Deadband
~ 10%
same temp
Economizer Disable (D)
Economizer Enable (D)

18. Performance – Enthalpy Switch #4
Manufacturer’s Published Performance Data
Enthalpy switch action curve
Action Curve plotted
Fixed A,B,C,D positions
A and D position tested
(min/max)

19. Performance – Enthalpy Switch #4
Actual Test Data
~ 4 BTU/lb
Deadband
~ 5 Deg
same RH%
Economizer Disable (A)
Economizer Enable (A)
Economizer Disable (D)
Economizer Enable (D)

20. Performance – Enthalpy Switch #5
Manufacturer’s Published Performance Data
Enthalpy switch action curve
Action Curve plotted
Continuously variable adjustment
A and D position tested
(min/max)

21. Performance – Enthalpy Switch #5
Actual Test Data
Enthalpy switch action curve
~ 4 BTU/lb
Deadband
~ 20%
same temp
Economizer Disable (A)
Economizer Enable (A)
Economizer Disable (D)
Economizer Enable (D)
Economizer Disable
Economizer Enable

22. Performance – Enthalpy Switch #6
Manufacturer’s Published vs Actual Test Data
Enthalpy switch action curve
~ 1 BTU/lb
Deadband
Disable Line from Published Data
Enable Line from Published Data
Economizer Disable
Economizer Enable

23. Only use with certain logic controllers Fixed enthalpy switchover
Summary
Device
Device Number
Accuracy / Hysteresis
Comments
Enthalpy Sensor
#1 (Solid State, electronic enthalpy)
< 1 Btu/Lb
/ < 1 Btu/Lb
Only use with certain logic controllers
#2 (Solid State, true enthalpy)
~ 1 Btu/Lb
Accuracy / Deadband
Enthalpy Switch
#3 (Electro-Mechanical,
electronic enthalpy)
~ 4 Btu/Lb
/ ~ 2 Btu/Lb
#4 (Electro-Mechanical,
~ 3 Btu/Lb
/ ~ 4 Btu/Lb
#5 (Solid State,
#6 (Solid State, true enthalpy)
/ ~ 1 Btu/Lb
Fixed enthalpy switchover

24. Summary
Electronic enthalpy sensors / switches are not intended to measure true enthalpy
Some enthalpy switches may have poor accuracy and/or large enthalpy deadband, resulting in energy penalty

25. Questions ??? Thank You !!!
Contact Information
Xiaohui Zhou
Curtis Klaassen