Why Indirect Gas-Fired? Clean Heat, Controlled Drying, and the Case Against Outside Air
Product Highlight
One of Nyle’s claims about the HT-Series is that it’s accessible to operators at all experience levels. That’s not just a comment on the drying process; it’s a statement about the control system. The control is designed to give operators real-time visibility into exactly what’s happening inside their kiln, with an interface that makes adjustments straightforward and a data logging system that keeps a complete record of every cycle.
The foundation of the control is a PLC with a built-in Ethernet switch, 24VDC power supply, and RTD-based temperature module. That’s industrial-grade control hardware, the kind of platform that handles complex automation reliably and consistently. The interface on top of that hardware is a 7-inch color touch screen that presents kiln conditions clearly and gives operators access to every function they need without requiring them to understand the PLC logic underneath.
The HT-Series uses two types of sensors to build a complete picture of conditions inside the kiln chamber: dry bulb sensors and wet bulb sensors. Understanding what each measures is helpful for understanding how the system makes its decisions.
The dry bulb sensor measures the true thermodynamic temperature inside the kiln, the actual air temperature. The control uses the dry bulb reading to control the exhaust vents and the heat system. If the dry bulb falls below the set target, the heat turns on. If it rises above, the vents open to bring it back down.
The wet bulb sensor is equipped with a water wick that cools through evaporation. The temperature it reads, always lower than the dry bulb, reflects the humidity level in the chamber. The gap between dry bulb and wet bulb (called the depression) tells you how dry the air is. The control uses the wet bulb reading to control the compressor and the spray system. When the wet bulb drops below the setpoint, the compressor turns on to remove moisture. When it rises above, the spray system activates to add humidity.
Two dry bulb sensors, one at the front and one at the rear of the chamber, give the system front-to-rear temperature visibility across the full length of the lumber pile. The manual recommends a thermal lag buffer on the dry bulb sensor to prevent short-cycling, and Nyle provides these with the unit.
The 7-inch HMI touch screen is the operator’s primary window into the kiln. The Status Screen is the main view during a running cycle. It displays the forward and rear dry bulb temperatures, the wet bulb temperature, the depression, the wet bulb setpoint, and the dry bulb setpoint, all updated in real time. It also shows the kiln start time and cumulative runtime, and gives direct access to the five equipment screens along the bottom: fans, heat, vents, spray, and compressor.
The Trend Screen lets operators view graphical data from the current cycle in either a 24-hour or 7-day view, so you can see how conditions have tracked over time rather than just the current moment. If something looks off in the finished lumber, the trend data is often where you find the answer.
The Setup Screen is where a new drying cycle begins. You name the data log file, set your target dry bulb and wet bulb temperatures, and select the operating mode. Mode options include WB/DB (wet bulb and dry bulb control), DEP (depression-based control), and CONV (conventional). From setup, you can also navigate to the Schedule Screen.
The Schedule Screen is one of the most practically useful features in the control. A drying schedule is a multi-step program that automatically adjusts wet bulb setpoint, dry bulb setpoint, depression setpoint, estimated moisture content, fan speed, and duration across as many steps as your schedule requires. Once a schedule is programmed and saved, you can load and run it for any future cycle of the same species and thickness.
For operators drying the same species repeatedly, schedules mean the kiln essentially runs itself. You load the lumber, start the schedule, and the system moves through each step automatically. Schedules can be saved and loaded by name, and the control includes pre-loaded reference schedules organized by wood group and lumber type to help operators get started without building every schedule from scratch.
Every cycle logged by the controller creates a data file that records the kiln’s conditions over time, forward and rear dry bulb temperatures, wet bulb temperatures, system states, and more. These logs can be retrieved directly from the controller and are stored under the file name you assigned at setup. For operations that track drying performance across loads, these records are the raw material for understanding what’s working and what to improve.
Remote access via VNC and a web browser allows operators to monitor a running cycle from a computer or mobile device on the same network. You can check real-time conditions, review trend data, and verify that a cycle is running as expected without being physically present at the kiln. The manual walks through the VNC configuration process, and password protection is available to control who has access.
The control is built on the same platform used across Nyle’s product line, which means the skills operators develop running an HT-Series kiln transfer directly to other Nyle systems. It’s a control platform designed not just for today’s operation but for wherever your drying business goes from here.
To learn more about the HT-Series or the controls, contact Nyle at (800) 777-6953 or kilnsales@nyle.com.