Interview - March 2003
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EMAIL INTERVIEW  Rob Kapinos & Ken Sinclair

Rob Kapinos, Senior Design Engineer, ACI Rob Kapinos is the Senior Design Engineer for Automation Components, Incorporated (ACI). ACI is a manufacturer of humidity, temperature, and pressure sensors for various HVAC/R applications. Rob has an extensive background in Customer Service and has been working in the HVAC industry for 16 years. Rob has designed Humidity and Enthalpy sensors for ACI which can be viewed at

Any questions about these products can be directed to

An Enthalpy Sensor that works with Economizers

Sinclair: Does the humidity sensor or element used in peripheral devices make a difference?

Kapinos: The sensor really does make a difference depending on the application. When specifying or buying humidity sensors, there are a number of specifications that should be taken into consideration such as Accuracy, Repeatability, Interchangeability, Long Term Stability, Recovery from Condensation, Recovery from Chemical and Physical Contaminants, Operating Temperature Range, and Response times. All of the humidity sensors on the market are limited in some way, as to the applications in which they can be used. When choosing a humidity sensor, make sure to decide which one of the above specifications are the most important to your application and choose the type of sensor that best fits.

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Sinclair: Is sensor interchangeability important?

Kapinos: In my opinion sensor interchangeability is an important feature in the selection of a relative humidity transmitter, since it allows you to replace the sensor without having to return the unit. As long as you are looking for accuracies of +/- 3 to +/- 5% then this shouldn’t be a problem depending on the type of sensor used. I do think that there are times when the interchangeability is not properly used such as replacing the sensor instead of recalibrating the transmitter due to sensor drift. When designing a relative humidity transmitter, there are a number of different solutions that may be used in order to eliminate the need for having to replace the sensor. In time, both the electronics and relative humidity sensor will drift and the best solution would be to recalibrate the transmitter and the sensor together so as to eliminate as much of the error as possible. If the sensor needed to be replaced due to failure or some other circumstance, I would still recommend calibrating the sensor to a known standard or reference.

Sinclair: Why are more manufacturers offering field calibration/validation of humidity transmitters?

Kapinos: I think that field calibration is becoming much more prevalent, due to the advances in technology and the increased need to reduce the energy consumption due to the increasing energy costs. I also believe that a greater emphasis is being placed on Customer Service and/or Service Contracts than in the past, since the HVAC market is highly competitive and service can distinguish one company from another. If done correctly, field calibration and validation will increase not only the life of the humidity sensor but it will also help in the prevention of mold, bacteria, property damage, and other problems that occur due to an extremely low/excessive amount of moisture in the environment. Humidity calibration can be done accurately in the field, but the most important thing to understand is that you need to have a reference that is highly accurate such as a Chilled Mirror. Please note that a Sling Psychrometer shouldn’t be used in the calibration of humidity transmitters, since there are a number of things that could affect the overall accuracy of the wet bulb temperature such as dirt, oil and contamination on the wick, and insufficient water flow. Sling Psychrometers also tend to lose accuracy at humidity levels below 20% RH and temperatures below 32oF. When using a Sling Psychrometer to verify that a transmitter is working correctly, remember to take into consideration the tolerances of both of the devices before doing any recalibration.

[an error occurred while processing this directive]Sinclair: Can humidity be controlled to within +/- 1% accuracy?

Kapinos: Humidity transmitters with an overall accuracy of +/- 1% can be achieved, but it will cost dramatically more due to the increased calibration time. Some factors that play an important role in being able to maintain accuracies of +/- 1% are the accuracy of the sensor, drift, temperature dependence, and overall accuracy of the calibration equipment. In applications such as Clean Rooms, Museums, Document Storage Facilities, and some Manufacturing Processes, the operating temperature and humidity ranges are known upon the design of the BAS (Building Automation System). Therefore, I would recommend that when ordering a relative humidity transmitter with an accuracy of +/- 1% from the manufacturer that you specify both the operating temperature and humidity range. In order to maintain an overall accuracy of +/-1%, it is recommended to check the transmitter every 6 months and to recalibrate them if necessary. Remember that in order to maintain or verify the accuracy, it is recommended to use a calibration reference or standard that is NIST certified.

Sinclair: How does Humidity and Enthalpy Measurement help to save money?

Kapinos: Humidity and Enthalpy are similar but differ in the way that they are calculated. Humidity is calculated using both the actual temperature and measurement of the amount of moisture in the environment. Whereas in order to calculate the Enthalpy, you need to know the Relative Humidity and Barometric pressure of the atmospheric air, since both temperature and pressure will vary considerably with altitude. Humidity and Enthalpy can both be used to determine when you can use the Outdoor Air as your first stage of cooling, thus reducing the overall amount of mechanical cooling or dehumidification that is needed. In “Demand Ventilation” you want to use the outdoor temperature and outdoor humidity/enthalpy to determine when you can use the outdoor air as the first stage of cooling. As either the outdoor temperature or enthalpy increases, there is a point in which you can’t use the outdoor air to effectively cool the space and mechanical cooling or air conditioning is necessary. This is where a significant energy savings takes place, since you only use the amount of mechanical cooling or staging that is necessary to maintain the space temperature and humidity. The money is saved by not having to dehumidify or cool the outside air.

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