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Dry Kiln Control / Re: Wet bulb and air flow
« Last post by MichaelM on October 25, 2016, 08:41:38 AM »
Yes - low airflow causes an artificially high Tw.  This makes the vents open more so the measured Tw comes to setpoint while the real TW (if measured with an accurate wet-bulb) would be lower.

I've always figured this part of the reason two identical kilns dry differently.  The sensor placement is a little different and they read differently so that the actual conditions in the kilns differ.  Ever hear of a schedule working well for one operator, but not working at another mill?  This could be the reason.

Wet-bulb sensors are placed away from the wall to help with airflow.  In some situations we have (in measurements at OSU) placed out wet-bulb and dry-bulbs inside of a blower to have good airflow.  This was not in a kiln application.

Dry Kiln Control / Re: Wet bulb and air flow
« Last post by HencoV on October 25, 2016, 12:37:47 AM »
Ok, so we need 500ft/min (2.5m/s) or more over the wet bulb probe to get a constant accurate reading.

From your description of what happens to the air around the bulb at lower (too low) air speed, can one deduce that at lower air flow over the WB:
- the less the evaporation...the higher the WB reading and that radiation and conduction comes into play more (possibly pushing it up further) than at ideal air flow?

This will mean that the condition shows a smaller WB depression than what it actually is, while the drying condition is much harsher than what the control system is showing or trying to control at. This will result in more active venting or vents staying open for long periods for open/close vents or proportionate vents being open more (bigger %) than what is required. Both cases will result in more energy used, possibly more downgrade due to harsher conditions and longer drying times where energy supply is an issue.

Consider that when vents are open, it actually becomes the air's path of least resistance, possibly reducing the amount of air flow through the stack....further reducing energy transfer to the timber and prolonging drying times while drawing more energy from the boiler to maintain DB Setpoint
Training / Events / Production Planning Course 10/17 - 12/12
« Last post by admin on October 24, 2016, 01:44:26 PM »
Production Planning

The Centre for Advanced Wood Processing will be offering the  Production Planning Course starting on October 17th for eight weeks.  For more details see our Management Skill Training Program

Start date:  October 17th

End Date:    December 12th

Cost:           $495

Contact Info:  Jason
Training / Events / Timber Building Technical Tour and Conference
« Last post by admin on October 24, 2016, 09:52:17 AM »
Timber Building Technical Tour and Conference to Switzerland, Austria, Germany

CAWP, in partnership with UNBC, is organizing a technical tour for architects, construction and wood builiding products manufacturers, public sector officials and policy makers. The tour will begin in Zurich, Switzerland on Saturday 3rd of December and end in Munich on Saturday 10th of December, including three days at Holzbau Forum, the world’s largest wood building conference. A group of 15-20 industry participants, accompanied by ‘tour guides’ from CAWP, will visit state of the art production facilities of innovative producers of prefabricated homes and building systems, world renowned timber structures, and building component manufacturers.

Start:    December 2, 2016
End:    December 10, 2016
Venue:    Zurich
Address:  Zurich, Switzerland   
Cost:    2195

For more information see our Holzbau 2016 Agenda

Holzbau Forum Program: Holzbau_22

To register follow this link: Holzbau Registration

AIBC Approved Credits: 33.5
Dry Kiln Control / Re: Wet bulb and air flow
« Last post by MichaelM on October 23, 2016, 12:11:05 PM »
The wet-bulb measurement is independent of airflow above a certain point.  A figure of 500 ft/min is often cited as the minimum.

Water evaporating from the wet-bulb cools it.  As it cools, heat transfer occurs from the air to the bulb.  The rate of evaporation slows as the bulb cools.  Simultaneously, the rate of heat transfer increases as the bulb cools (more heat moves from the surrounding air to the bulb).  At a certain temperature these two factors balance and the temperature becomes steady.  At the wet-bulb temperature, the energy reaching the bulb by convection just equals the energy carried away by the evaporating water molecules.

The two factors (heat transfer and evaporation) are both controlled by the insulating effect of an air layer at the surface of the bulb.  When airflow increases or decreases, the layer is affected and both factors are similarly affected.  For this reason, the wet-bulb temperature is not affected by airflow (above a certain point).  Heat transfer by the moving air is called convection.

High airflow is desirable to minimize the impact of things (radiation and conduction) that affect amount of heat or energy reaching the bulb.  For example, the metal in an rtd conducts (conduction as opposed to convection) some energy from the rtd mount to the tip.  Also, heating coils in view of the bulb can radiate (radiation instead of convection) energy to the bulb.  Hence, dry- and wet-bulbs may have heat shield in some locations.

Below a certain air velocity, the mode of convection changes from turbulent to laminar.  This depends on the bulb diameter and other factors.  This is why most books say 500 ft/min and up is ok. 
Dry Kiln Control / Wet bulb and air flow
« Last post by HencoV on October 20, 2016, 08:32:14 AM »
@ the forum experts...

What is the effect of more or less air flow over the wet bulb (WB) on the WB reading, and the consequent effect on drying controls. Put differently - will higher or lower air speed effect the evaporation rate and temperature of the WB? Will lower air flow result in a higher WB reading, same for higher air flow result in a lower reading?
Job Postings / Boiler/Kiln Operator, Moyie Springs, ID
« Last post by admin on October 17, 2016, 03:22:32 PM »
Boiler/Kiln Operator, Moyie Springs, ID

Built on Tradition

From its Coeur d'Alene, Idaho headquarters, the closely held, family-owned company continues to be "Idaho Grown" and the first recipient of the Idaho Pacesetter Award.  The company is now one of America's largest lumber producers, with capacity for nearly one billion board feet per year and markets around the globe.  The company founders hold high standards when it comes to product, process and company objectives.  This is a healthy, growing company big enough for its national and international markets, but with hometown ethics and pride in a job well done. Excellence is the goal in caring for our team members, customers, and natural resources.


A Boiler/Kiln Operator operates/maintains a wood fueled boiler and to produce lumber with specified moisture content by kiln drying while meeting our high product quality standards. They also maintain lumber flow from the sawmill out feed through the kilns.

  • Follow key safety processes for the facility
  • Operates boiler maintaining required pressure and steam flow.
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  • Dry lumber of all sorts using computer to control kiln
  • Operate forklift to load and unload kilns, change kilns, and dump hoppers
  • Monitor kilns all throughout shift and make adjustments as needed
  • Cover sawmill/planer drivers when necessary
  • Clean work areas
  • Help with new hire training and cross training of existing team members
  • Other duties as directed by supervisor


  • Have a good safety record and the ability to work in a team
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  • Ability to lift 100 lbs., climb stairs, repetitive bending, kneeling, stretching, pushing and pulling, continuous walking and/or standing
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For more information or to apply click here

NOTE: Job postings on Kilndrying.org are provided as a free service. We do our best to keep all postings current. However, if you discover a job listed on our forum is no longer available, please send us a message to that effect and we will remove from the board. Thank you.
Dry Kiln Control / Re: Steam Management
« Last post by HencoV on October 10, 2016, 01:48:46 AM »

It can be done, in fact it is standard in the control system I have designed where my Vent set point is dynamic based on DB temperature and evaporation rate

Standard schedules, be it time or MC% based works on the assumption that you can achieve and run at set point - so when steam supply runs low - so will your DB temperature. The vent set point stays constant and your vents stays closed for this time. The ideal is to reduce the vent set point when "energy in" is reduced...to keep on removing moisture, although at a slower rate. The opposite when steam pressure is restored again...vent set point must be increased.
Dry Kiln Control / Steam Management
« Last post by TILLAMOOK on October 04, 2016, 03:34:22 PM »
How about building a better schedule that is better suited to your available steam?
Drying Defects / Controlling moisture variability
« Last post by TILLAMOOK on September 28, 2016, 03:44:13 PM »
Are you drying different species or dimensions in the same kiln charge?
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