Saving Energy in Climate Control
Importance of Relative Humidity and Temperature Sensing for Energy Savings in Climate (HVAC) 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 where margins are tight. With prices constantly increasing, the only way to secure margins is through cost savings created by increased efficiency. With estimates of $113 Billion USD spent annually on energy inputs by manufacturing, reducing energy usage is a strong candidate for realizing cost savings.
In many manufacturing warehouses, to meet quality and safety requirements, climate levels are tightly specified and variation from these levels can lead to product waste or recall due to failure. Climate control of commercial buildings accounts for 19% of total energy usage, presenting a substantial cost but also an opportunity for costs savings. Let’s discuss the key elements of climate control and where it is possible to affect energy reductions.
Effective Climate (HVAC) 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 a programmable logic controller system to turn the HVAC system on and off. When these sensors are strategically placed throughout a manufacturing facility, they can provide critical data about microclimates and the capability of the HVAC system to eliminate spatial differences.
These large data sets collected from the sensors can ultimately be used in combination with other deployed sensors and machine learning to anticipate climate changes and allow preventative adjustments to be made before more expensive large fluctuations can occur. 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.
The Cost of RH/T Sensor Failure
While RH/T sensors can be beneficial in effective climate control, they can also be detrimental to energy savings if their performance is not accurate and consistent. The impact of sensor accuracy and reliability is a critical factor that has not received enough attention when considering the impact of sensors on effective HVAC control.
This is of particular importance for spaces that must be maintained to humidity levels higher than ambient such as indoor agriculture or cheese manufacturing. The cost of humidification is high while incorrect humidity control can lead to product waste, so even small deviations from the ideal humidity and temperature can be costly.
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 tens of thousands of dollars in energy savings per year from superior climate control.
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Example on how to save energy with efficent HVAC Control
We use the example of a small facility that has tolerance range of +/- 6% RH to produce a quality product and meet climatic requirements.
To effectively keep the climate controlled within that 6% range, we can assume that the accuracy of the RH sensors being used to track humidity should be a factor of 6 to 8 better than the control range to achieve effective control. That means that for a +/- 6% relative humidity tolerance, the accuracy of the RH sensors must be +/- 1% or better. Otherwise, the sensors will be continually telling the control system that it needs to activate when it doesn’t.
Each time the system is activated, the life span of each part of the HVAC system (controlling units, air humidifiers, fan filters, etc.) is reduced while energy use is increased.
These recurring costs are often not sufficiently considered as expenses as this, occur over time and not as one capital expense. However, these monthly savings can add up to over $13,000 of unnecessary expenses per year compared to next best sensors and over $23,000 compared to the worst sensors, all due to RH sensors that don’t meet the accuracy requirements for tight climatic control. These are the savings for a small area, so the savings will be even more for a larger area. With climate control using 19% of the energy, these savings will quickly pay for the initial cost of deploying high accuracy sensors and make significant contributions to reducing overhead and increasing profitability.
Table 1. Calculation of cost saving potential using the optimal sensor technology. Sensor A is a Novasina nSens RH sensor with +/- 0.4% accuracy, Sensor 2 is a high-quality capacitive sensor with +/- 2% accuracy and Sensor C is a low cost resistive sensor with +/- 4% accuracy.
Importance of RH/T Sensor Technology for HVAC Control
The unfortunate challenge of the example presented in the previous section is that most RH sensors do not have accuracy better than +/- 1%. That is because common RH/T sensors detect relative humidity changes by tracking the electrical conductivity of a hygroscopic polymer as the polymer equilibrates with the relative humidity conditions of its environment. 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. In fact, these types of sensors are never specified for accuracy or repeatability at humidity levels higher than 85% due to this known weakness. Finally, the electrical properties of the hygroscopic polymer are subject to hysteresis after multiple wetting and drying cycles, leading to a need for constant calibration adjustment.
Resistive electrolytic RH/T sensors from Novasina provide an alternative technology to polymer-based sensors. 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, does not become saturated at high humidity, and does not experience hysteresis during adsorption and desorption events. Consequently, the accuracy of the electrolytic sensors is 0.4% for relative humidity and 0.1K for temperature 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 and will result in much tighter humidity control in manufacturing facilities.
Summary
Many older manufacturing facilities are using outdated climate control systems that may operate from a single thermostat/humidistat with limited accuracy. 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 the maximum energy savings.
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