Harnessing the power of relative humidity

Nicola Brittain

How Relative Humidity monitoring can increase energy efficiency through improved climate control.

Continually rising energy costs are a burden for everyone and have significantly contributed to recent increases in inflation. These higher costs have particularly impacted the manufacturing industry with estimates of US$113bn spent annually on energy inputs (1). Climate control of commercial buildings accounts for 19% of this total energy usage, presenting a substantial cost but also an opportunity for costs savings (2). In many manufacturing warehouses, climates levels are tightly specified and variation from these levels can lead to product waste or recall due to failure.

Effective climate control

The key to effective climate control is the strategic deployment of relative humidity and temperature (RH/T) sensors and connecting them to a central controller system. The readings from these sensors provide feedback to the controller system to turn the HVAC system on and off.

While RH/T sensors can be beneficial to effective climate control, they can also be detrimental to energy savings if their performance is not accurate and consistent. The dependence on sensors for effective HVAC control mean that they are critically important, this is something that has not received enough attention (2). Their operation is of particular importance in spaces where humidity levels are required to be higher than ambient - such as indoor agriculture or cheese manufacturing. Same applies to comfort climate conditions such as cleanrooms or production facilities.

The cost of humidification is high while the impact on product quality of incorrect humidity control can lead to product waste, so even small deviations from the ideal humidity and temperature can be costly.

Cost savings in climate control

Consequently, the difference between an RH/T sensor that is accurate to 4% RH and one that is accurate to 0.4% RH could result in thousands of dollars in energy savings from climate control accuracy. Further, if the readings of an RH/T sensor are constantly shifting due to drift and a need for calibration, it will result in the HVAC system trying to respond to sensor drift resulting in additional energy use.

The important role sensors play in energy savings is reflected in the US Department of Energy identifying HVAC sensors as the highest priority among energy savings research with the potential to make a difference in energy usage (3).

Summary

Many older manufacturing facilities are using outdated climate control systems that may operate from a single thermostat. With energy costs typically being one of the top 3 operating expenses, it behooves these companies to invest in better climate control, the savings from which will ultimately pay for the updates and provide further income. The key, but often overlooked component of an effective climate control system are the RH/T sensors feeding data to the system. Electrolytic RH/T sensors, with their unmatched accuracy and reliability, should be the sensor of choice to ensure climate control is delivering maximum energy savings.

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References

1.  https://fred.stlouisfed.org/series/MPU9900641 https://fred.stlouisfed.org/series/MPU9900641

2.  Yeonjin Bae, Saptarshi Bhattacharya, Borui Cui, Seungjae Lee, Yanfei Li, Liang Zhang, Piljae Im, Veronica Adetola, Draguna Vrabie, Matt Leach, Teja Kuruganti. 2021. Sensor impacts on building and HVAC controls: A critical review for building energy performance. Advances in Applied Energy Volume 4, 100068 https://doi.org/10.1016/j.adapen.2021.100068.

3.  Goetzler W, Shandross R, Young J, Petritchenko O, Ringo D, McClive S. 2017. Energy savings potential and R D & amp; D opportunities for commercial building HVAC Systems. U.S Dep. Energy. https://www.osti.gov/biblio/1419622/.

4.  Carter, BP. 2022.  Why Electrolytic Resistive Sensors Solve the Root Cause of RH Sensor Problems. Novasina Application Note.

Climate control with electrolytic RH sensors

Most RH/T sensors utilise a common technology based on capacitive (hygroscopic polymer) sensors to recognise changes in relative humidity and temperature. While these sensors can perform adequately for certain applications, their accuracy is limited to 2% RH or worse and they all suffer from saturation and drift when exposed to high humidity or contaminants in the air.

Resistive electrolytic RH/T (4) sensors provide an alternative technology to polymer-based sensors (4). For this type of sensor, humidity is tracked by the change in resistivity of an electrolyte solution. The advantage of this approach is that the sensor has a fast response time and does not experience drifts in changing or challenging environments. Consequently, the accuracy of the electrolytic sensors is 0.4% for RH and 0.1K for T across the entire specified humidity and temperature range possible in a manufacturing facility including at humidities higher than 85%. This accuracy is an order of magnitude better than can be achieved with polymer-based sensors.

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