Develop better lumber drying schedules


As a kiln operator your primary job is to maximize the efficiency of the kilns under your supervision in order to allow your company to provide better drying quality to your customers plus help reduce the drying costs and waste (degrade).
-- For every 1 unit of lumber damaged during the drying process, you will have to dry 10-20 units to make up for the loss (break even).

As raw material/lumber has become increasingly costly and sometimes hard to get, we have seen an attitude change in the amount of waste/degrade your kilns can be allowed to produce. In addition, increased competition in the lumber industry is also putting more pressure on the kiln operators to maximize production, reduce costs, and minimize degrade. In the early days of kiln drying it used to be said that you were drying it too slow if you had less than 10% degrade, whereas today a company can barely accept 2-3% degrade in order to remain profitable.
-- Remember lumber drying is all about maximizing profit by increasing the value of the lumber together with minimizing the cost of drying. (Cost of drying = Energy cost + Degrade + Depreciation + Maintenance).

This procedure for improving a drying schedule has been compiled in a rather simple format and we hope it explains the general approach a kiln operator should take in optimizing the kiln performance. First and foremost it is important to understand that:

"Not all kilns are created equal"


Most lumber kilns have similar layouts; however, the devil is in the details. You will often find great variation in the venting, heating and fan capacity depending on design, manufacturer, and time of construction. Consequently, you may have to develop variations in certain drying schedules depending on which kiln you intend to dry a certain species and thickness in. This is all part of the job as a kiln operator. We have worked hard to provide the tools needed for making intelligent and educated evaluations for maximizing your kiln operation and we hope you will consider our kiln controllers and components for your next kiln upgrade or new kiln.

We hope this information and these guidelines meet with your expectations and approval. We always welcome your opinion and suggestions. You can email, fax, or call us. 


Before you begin experimenting with new and hopefully much better kiln drying schedules and programs, which will offer faster drying times; more energy efficiency; and/or better drying quality, it is important to structure your research. This is best done by setting clear and singular goals. By singular we mean, that we should only set one goal and try to change the drying process to achieve this goal. By setting only one goal we will know the cause and effect of the changes we make, which will provide clear results and help us make better decisions. If we were to try and solve two or more goals at once, we would probably need to change several parameters. With more parameter changes and several goals we will make it difficult to analyze the collected data for exact cause and effect. In addition, by changing one parameter to achieve a modest goal we would not be running as big a risk. Since it is easier to predict the effects of changing one parameter versus changing many parameters.


A few examples of "singular" goals:


-- Lower the electrical energy consumption without increasing drying time or degrade.
-- Drying a certain species at lower temperatures without increasing the drying time (in order to create a lighter color).
-- Reduce the drying time by 5% without increasing degrade.
-- Prevent excessive case-hardening (and checking) during the length of the drying process by using the interval fan operation.



A multiple goal could be:


-- Reducing drying time and decreasing drying temperatures without increasing the degrade.

The last example has conflicting goals, which will be difficult to incorporate into the same test run; however, you may get there by dividing the test into two or three experiments. You would then be able to monitor the effects of your program improvements more exactly and then later combine the two new test schedules into a third (and hopefully final) schedule.

Be sure to establish exact and clear "singular" goals for your kiln drying experiment, it will make it much easier to learn valuable lessons and gain a precise understanding of the changes and their effect. This kind of knowledge will help you build and develop better schedules in the future.

When developing improvements to your drying schedules it is best to change as few parameters as possible. This is similar to the idea of setting singular goals. By studying the effect of lowering only the temperature, it is fairly easy to see the exact change. Whereas studying a change in the temperature, relative humidity and air flow will not provide a similarly clear picture, since three factors were changed and it may be unclear which ones helped improve the drying quality and which ones may have hurt the drying quality.

Let's imagine an example where we would like to dry a load of maple with a lighter color result than the schedules used in the past. It could be argued that by lowering both the temperature and the relative humidity setting you would get a brighter color. However, the lessons from an experiment where both the temperature and relative humidity is reduced will not be as educational as two test runs (one with lower temperature and one with lower relative humidity). By making two test runs you will learn what each change accomplishes.

Remember that you must have an accurate method establishing a benchmark to measure you improvements.

Learn about how adjustments in temperature, relative humidity, and air flow changes drying rate of the lumber.

Once the new drying schedule has been developed and the actual drying process initiated it is very important to collect information for later study in order to evaluate the result (good or bad). If you do not already have computerized controllers with data collection capability (and preferably networkable to a central computer), your best option is to invest in one.

The old style kiln controllers with circular graphs can tell you many things and was very valuable before the recent development in information technology; however, they generally fall short when compared to the information gathering of networked and computerized kiln controllers available from several kiln controller manufacturers.

In addition, the kiln control system you invest in (or maybe already have) should make it easy to share the collected information with others. Our software allows you to easily email this information to any person, thereby allowing you maximum access to the kiln drying knowledge. Maximum sharing ability can help you obtain the best possible help and opinions from any person with kiln drying knowledge. This person could be a consultant, a university professor, or a friend, who has experience similar problems or faced similar challenges.

Once the information has been collected from a kiln charge, we are ready to make sense of how our changes/adjustments made a difference, both positive and negative. We believe you will find that using analysis programs, such as a spreadsheet, can help you present the data in a way which clarifies how the changes impacted the kiln drying process. We are currently working on features, which will allow you to transfer the data from one of our kiln drying snap-shot reports directly onto a spreadsheet or similar program. It should be noted that the data found in our snap-shot report presents the data in a general way to troubleshoot and optimize the kiln process.

In many cases you will find it most pratical to eliminate several types of data and focus on a few parameters. Let's consider an example where we are trying to reduce the electrical operating cost. In this case, we would probably focus on three key figures with a secondary eye on two more from the snap-shot report plus two newly generated (calculated) figures:


Three key figures:


-- Average moisture content for each interval.
-- Main fan speed for each interval (only if you have frequency controls).
-- Main fan operation (percent operating time in each period).

Two secondary figures:

-- Actual temperature in kiln chamber.
-- Actual relative humidity in kiln chamber (or wet bulb temp.).

New calculated figures:


-- Average moisture content drop per interval (calculated).
-- Moisture content drop compensated for fan activity. (MC drop divided by fan percent value) (Higher number less energy consumption per MC% drop).

We should generate above numbers/figures (and maybe a graph) from one or several earlier kiln schedules and the new "improved" kiln schedule. Raw numbers can show trends and help you improve the process, but using specifically calculated figures makes it much easier to compare and evaluate the results. As with the example above the last number can become a key figure that you can be used as a benchmark for future improvement and a type of "energy watch dog", which will alarm you when your energy cost exceeds a certain level per one percent moisture drop. By having the ability to set clear goals where none were before, you will have the ability to push further ahead in the right direction without the usual guess work.

Actually, one could take the data one step further, which would allow one to compare the energy performance between individual kilns. If you were to take the last figure (MC drop compensated for fan activity) and compensate this for:
-- Installed fan capacity (kilowatt or horsepower) and
-- Loading capacity (cubic meter or boardfoot)

This new benchmark number would allow you to compare the energy performance of kiln 2 against kiln 5 on a certain specie/thickness. We are certain you can see the possibilities of arranging and manipulating the data from a drying report.


Comparing the results sounds like a simple task after all the hard work is done of:
-- First,
figuring out your goals.
-- Second,
finding the right adjustment to the drying schedule.
--Third, running one or several kiln loads with the new schedule.
-- Fourth, collecting information from the test kiln charges, and
--Fifth, arranging the collected information in a meaningful way.

How can comparing the result be any significant task? Well, in theory it is simple; however, lumber is not a uniform material like steel, plastic, aluminum, etc. Instead we find that the structure and drying characteristic varies greatly within the same specie. The actual value of a specie often depends on its geographical origin. You will even find that the time of year the logs were harvested has a noticeable effect on the drying process. This means that during your testing you have tried to eliminate as much of the variations as possible, but you will never be able to eliminate it completely. Hence the reason that several test charges can help create an average effect, so you do not make permanent changes based on an "abnormal" charge.

The key task here is to determine which type of information to compare. The information chosen for the comparison should have had a significant impact on the changes you have tried to accomplish (or not accomplish by design).

Let's take the abstract idea of achieving a goal with accomplishing a change in the drying result. Considering the goal for an experiment which attempts to reduce the energy consumption without changing the drying conditions, drying time, or quality. There could be times for reducing the fan operation (either by interval operation or reducing fan speed) without extending the drying time or increasing the degrade.


In most cases evaluating the result becomes a judgement between achieving a balance between contradictory goals. The obvious two contradictory goals are:
-- Drying quality versus drying time.


Now it should be understood that there are two types of evaluation:


-- Evaluate the best way to use the existing equipment in the most profitable way. This is very much related to improving drying schedules.
-- Evaluate the best way to invest in future upgrades, kilns, predryers, fansheds etc. This is more related to evaluating how capital investment can be put to the best use possible.

The first type of evaluation has a short distance from collecting the data to its usage and implementation; in addition, a bad change can easily be undone for the next kiln charge. The second type of evaluation is more the kind where you have collected data and information for some time, which you will look back upon to determine the most efficient use of upgrades and expansion.

The decision about expansion and upgrade are generally non-reversible. If you have purchased a kiln that was poorly designed at a high price you are normally stuck with it.

In the end all the changes you decide to enact should increase the profitability of the kiln operation. In some of the more precious species avoiding drying degrade becomes one of the most important goals, whereas on construction pine some degrade can be justified. This does not mean in the latter case that significant degrade can be accepted when looking down the road. It could very well be that an investment in additional kiln capacity could reduce the degrade by increasing the drying time, for example by 25% and this reduction in "wasted" lumber/degrade could pay for the new kiln in 18 months. You would have to run the number and make trial kiln charges to make an educated estimation and generate the information needed for a cost/benefit study.

Re-evaluation of earlier results may also be beneficial in changing market conditions. Consider as an example that a slow down in the lumber market allows you to increase the drying time on an average of 10%. You could slow the drying process across the board. However, you would probably benefit by looking at earlier collected data and determine that it is more profitable to pick a few species and only change these few schedules. Again, profitability is the key to deciding when and what changes should be enacted.

Enacting permanent change to your drying schedule is the reward for a long process (if done correctly), where you have decided that the changes will improve your kiln's profitability. In addition, you have gained valuable knowledge for making better and more educated guesses in the future.

It is important to keep a very close eye on the next couple of kiln charges to insure that the results are in line with your earlier findings.

We hope this information and guidelines meet with your expectation and approval. We always welcome your opinions and suggestions and are more than willing to receive email from you.
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