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

Outline Background Economizer Sensor Testing Summary Apparatus Procedure Performance Charts Summary

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

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

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

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

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 41.6-1994 Courtesy Thunder Scientific

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

Test Procedure Economizer Enthalpy Sensors – Step Decrease In Temperature

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

Performance – Enthalpy Sensor #1 Actual Test Data – Manufacturer reference to mA Max. 0.53 BTU/lb Hysteresis 2.6% of rdg Output w/ increasing RH Output w/ decreasing RH

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

Performance – Enthalpy Sensor #2 Actual Test Data Max. 0.36 BTU/lb Hysteresis 1.9% of rdg Output w/ increasing RH Output w/ decreasing RH

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

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

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)

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

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)

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

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)

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

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

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

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

Questions ??? Thank You !!! Contact Information Xiaohui Zhou xhzhou@energy.iastate.edu Curtis Klaassen curtk@energy.iastate.edu