Humidity sensors are devices that measure the amount of water vapor in the air. They are essential for maintaining indoor air quality and comfort, especially in homes with whole-house dehumidifiers and ventilation systems. However, humidity sensors can sometimes malfunction or drift out of calibration, resulting in inaccurate readings and poor performance. In this article, we will explain how to troubleshoot and calibrate your humidity sensors using some common tools and methods.
We will focus on the case of a homeowner who installed an UltraAire 120 whole-house ventilating dehumidifier along with a new heat pump in November 2023. The UltraAire 120 is a high-efficiency unit that can remove up to 121 pints of water per day and provide fresh air ventilation and air filtration to the entire home. The homeowner also installed a Honeywell T10 Pro Smart Thermostat with RedLINK Room Sensor and a Santa Fe DEH 3000 Digital Controller to monitor and control the temperature and humidity in the house. The Honeywell T10 is a WiFi-connected thermostat that works with Smart Room Sensors to adjust the temperature and humidity in different rooms. The Santa Fe DEH 3000 is a digital controller that integrates with the UltraAire 120 and allows the homeowner to precisely monitor and control the moisture levels, manage the fresh air ventilation, and activate the air filtration from the living space.
The homeowner noticed that the DEH 3000 and the T10 were not showing the same relative humidity (RH) and temperature readings. The DEH 3000 was showing 12% lower RH than the T10 and three AirThings monitors (two Wave Mini’s and a Wave Plus) that were installed next to the T10 and the DEH 3000. The AirThings monitors are smart indoor air quality monitors that measure radon, particulate matter, carbon dioxide, temperature, humidity, airborne chemicals, and air pressure. The homeowner also observed that the DEH 3000 would change its RH reading by 2% while standing in the hall. The homeowner wondered if the DEH 3000 was faulty or out of calibration, and if there were any other options for controlling and scheduling the fresh air ventilation with the UltraAire 120.
Troubleshooting the DEH 3000
The first step in troubleshooting the DEH 3000 is to check the specifications and the manuals of the devices involved. According to the specifications, both the T10 and the DEH 3000 have a +/-5% accuracy on RH and a +/-2°F accuracy on temperature. The AirThings monitors have a +/-3% accuracy on RH and a +/-2°F accuracy on temperature. This means that there could be some variation in the readings among the devices, but not as large as 12%. Therefore, the DEH 3000 seems to be out of calibration or defective.
The manuals of the T10 and the DEH 3000 provide instructions on how to recalibrate the devices. For the T10, the homeowner can access the advanced settings menu and adjust the humidity offset by up to +/-10%. For the DEH 3000, the homeowner can use the calibration mode and adjust the humidity offset by up to +/-10%. The homeowner should follow the steps in the manuals to recalibrate the devices and see if the readings match.
If the recalibration does not solve the problem, the homeowner should contact Santa Fe and request a replacement or repair of the DEH 3000. The DEH 3000 could be faulty due to a defective sensor, a loose connection, or a damaged component. The homeowner should also check the warranty and the return policy of the device.
Calibrating the DEH 3000
To calibrate the DEH 3000 more accurately, the homeowner can use a reference standard of known humidity and compare it with the readings of the DEH 3000. One method to create a reference standard is to use a saturated salt solution in a sealed container. Different salts produce different levels of humidity when dissolved in water. For example, table salt (sodium chloride) produces a humidity of about 75%, while potassium chloride produces a humidity of about 85%. The homeowner can use a table of salt solutions and their corresponding humidity levels to choose the desired reference standard.
To prepare the salt solution, the homeowner needs a glass jar with a lid, a small dish, some distilled water, a paper towel, and the chosen salt. The homeowner should fill the dish with the salt and add enough water to moisten it, but not dissolve it. The dish should be placed inside the jar and the paper towel should be placed on top of the dish to prevent salt crystals from falling into the jar. The lid should be tightly closed and the jar should be left undisturbed for at least 24 hours to reach equilibrium. The homeowner should also label the jar with the name of the salt and the expected humidity level.
To calibrate the DEH 3000, the homeowner should insert the sensor probe of the device into the jar through a small hole in the lid. The sensor probe should not touch the salt solution or the paper towel. The homeowner should wait for at least 15 minutes for the sensor to stabilize and then read the RH value on the display. The homeowner should compare the RH value with the expected humidity level of the salt solution and calculate the error. The homeowner should then use the calibration mode of the DEH 3000 and adjust the humidity offset by the same amount as the error. For example, if the salt solution produces a humidity of 75% and the DEH 3000 reads 63%, the error is -12%. The homeowner should enter the calibration mode and increase the humidity offset by 12%. The homeowner should repeat the process with different salt solutions to verify the accuracy of the DEH 3000 at different humidity levels.
Controlling and scheduling the fresh air ventilation
The UltraAire 120 has a built-in fresh air ventilation system that can bring in outdoor air and dilute indoor pollutants and maintain high oxygen levels. The amount of fresh air ventilation can be regulated by a variety of dampers and controls. The DEH 3000 can control the fresh air ventilation by using a 24-volt damper that is wired to the dehumidifier. The homeowner can set the desired ventilation rate and schedule on the DEH 3000.
However, the DEH 3000 does not have a sensor for measuring the outdoor air quality or the demand for ventilation. Therefore, the homeowner may want to consider other options for controlling and scheduling the fresh air ventilation with the UltraAire 120. One option is to use a smart ventilation controller that can monitor the outdoor and indoor air quality and adjust the ventilation rate accordingly. For example, the Aprilaire 8126X Ventilation Control System is a device that can be connected to the UltraAire 120 and the DEH 3000 and provide smart ventilation control. The device has sensors for temperature, humidity, and VOCs, and can also use data from the AirThings monitors and the T10 thermostat. The device can calculate the optimal ventilation rate based on the indoor and outdoor conditions and the homeowner’s preferences. The device can also provide feedback and reports on the ventilation performance and energy consumption.
Another option is to use a smart home system that can integrate the UltraAire 120, the DEH 3000, the T10 thermostat, and the AirThings monitors and provide smart ventilation control. For example, the Samsung SmartThings system is a platform that can connect various smart devices and create automation rules and scenes. The homeowner can use the SmartThings app or a voice assistant to control the ventilation system and set schedules and routines. The homeowner can also use the SmartThings app to monitor the air quality and the energy usage of the ventilation system.
