Through all the phases of a lumber mill, controlling moisture is key to producing a quality end product. Ironically, despite being where moisture is altered the most, kilns are also often the most overlooked.
West Frasers Thermal Energy Supervisor Martin Andres has been with the company for more than 42 years, and knows the importance of kilns as well as anyone. With wets, you will obviously get claims, Andres said. Even though we dont get a claim for over dries, it degrades the wood and youll end up with more end and surface checking. The lumber shrinks just that much more so you end up with skip on your wood.
Understanding how wood dries is crucial to developing effective drying schedules. Finding the right mix of temperature control, air flow and relative humidity improves the quality of the boards sent to the finishing stage. By finding the correct mix, mills can lessen problems such as wet claims, checks, warping, and unnecessary transportation costs due to excess water weight.
Previous methods of measuring included weight sensors that were used to chart the drying process of sample boards. Using that data, it was possible to develop calculations for estimating moisture content. However, this provided more of an educated guess than reliable, repeatable results.
As more advanced technology produced more reliable methods, the process improved. Two types of metering sensors took readings directly from the lumber charges. The first in-kiln sensors developed detected the resistance between two probes inserted into the edge of boards. The data was collected by a handheld meter. Resistance values were extrapolated to indicate moisture content.
While this was a vast improvement, giving more accurate data from inside the kiln, there were limitations. First, the data came from a single representative board. While several probe sets could be used, the number of data collection points was limited. The second limitation was probe placement. Driven into the edge of the board, not the face, the probes could not measure at the optimal point for moisture release.
Used primarily in batch kilns, the probes were inserted before charge placement. Hot checks at various stages of the drying schedule were used to gather data for calculation. Real-time measurement could not be gathered, particularly during the early development of this type of sensor. Additionally, hot checks required shutting down the kiln and bringing it to human-friendly temperature levels. In a direct-fired kiln, this also meant venting noxious fumes. After measurement was complete, the kiln was restarted, resulting in lost time and wasted energy.
Other problems occurred with hot checks, primarily that there were less people to do them. As mills looked to reduce costs, many experienced kiln operators were transferred to other parts of the mill, or given added responsibilities that diverted their attention. With this loss of knowledge, technology was needed to pick up the slack.
Initially, wired radio frequency (RF) sensors were developed for batch kilns. These sensors use RF to determine capacitance, another method of determining moisture. Plates are non-invasively inserted between the stickers. With a plate near the top of the stack and the other near the bottom, a more representative value of the entire charge package is possible. Instead of a limited number of data collection points, moisture content value of up to 17 cubic feet, per sensing unit, are tracked. Cables connected the sensor plates to computer-based monitoring hardware, and software, outside the kiln. The data can be displayed, allowing the operator to manually make changes, or integrating with the kiln controls for automation. Especially with southern yellow pine, the variability of guessing when to shut down was removed.
With the development of continuous dry kilns (CDKs), static sensors were no longer feasible, leading to the development of wireless RF sensors. With no cables to tie them down, the sensors travel with the charge. These sensors also integrate with the kiln controls for either manual or automated operation. Up to 100 sensors, monitoring moisture and temperature sets can be used per kiln, meaning the operator gets a more complete view of whats going on inside the kiln, and can adjust the schedule accordingly.
At a particular division, we were in need of replacing aged control equipment so we evaluated the [RF sensors] to ensure they would provide the right moisture content, Andres said. So far we have experienced time savings and consistent results using the moisture sensing system. We have not had wet lumber since it was installed.
With the data capturing system integrated with the controls, there is another potential benefit. Using kiln systems connected to each other via network or Internet, multiple kilns can be monitored and controlled from one location, also helping to offset the lack of operators.
According to Tony Nadeau, Sechoir MECs Dry Kiln Automation and Control Director, We worked with a customer that bought kilns for two different sites. We installed KilnScout systems for each kiln with eight sensors per system. MECs sensor system was modified so the customer was able to monitor both sites from one location. The RF sensors and data collection units allowed the mill to monitor and modify the drying schedule for each kiln.
Despite providing several benefits including additional throughput, grade recovery and remote monitoring, in-kiln sensors are continuously being improved to keep up with the needs of modern lumber mills. The most pressing need for these mills is up-time. The sensors are now being built with Internet of Things (IoT) predictive maintenance features that actively notify the operator when there are upcoming issues, such as low battery strength. This allows action to be taken, before issues, and loss of data is prevented. Additionally, software has been built so that the kiln no longer needs to be relied upon as the sole manager of moisture it can be monitored from the beginning of the process from sawmill to the kiln.
Wood-Mizer dehumidification and solar wood kilns range from 300 to 35,000 board feet capacity for drying lumber. Kiln drying lumber is a simple, cost effective method recommended for anyone who wants to increase profits by selling dried lumber. Kiln dried wood typically sells for a third more than green lumber and eliminates the need for customers to incur costs associated with drying lumber before use. The Wood-Mizer KD series of lumber kilns feature 100% corrosion resistant aluminum cabinets and specially coated dehumidification coils to ensure quality lumber drying performance and an extra-long life. The KS solar wood kiln is a simple and economical system for starting to kiln dry lumber. Download a free Introduction to Kiln Drying Guide that provides basic information on how to dry wood and the many advantages of drying your own lumber. Kiln chamber diagrams are also available. Review our complete range of lumber drying wood kilns below.
We use an iDRY Vacuum kiln. All iDRY models promise the same fast, reliable and efficient drying , using a combination of heat and vacuum, iDRY Turbo dries lumber and squares from 4/4 to 16/4 ten times faster than conventional kilns, while the iDRY and iDRY PLUS dry about 5 times faster.
Because wood has been kiln dried does not mean it is sterilized, as most DH kiln cycles top out at 120 degrees, not high enough to properly sterilize. It takes special effort, time and expense to do so. If you purchase wood from other sources, ask them if they perform a dedicated sterilization step. Most likely they will give you a What? look.
Air dried wood is not sterilized, no matter how long it has been drying, and since the incubation period for certain insects can take years, not seeing bugs when you buy air dried wood doesnt mean they arent in there. As an interesting observation, I have never kiln dried and sterilized live edge slabs where there werent dead bugs on the wood when the cycle was finished. Never. Live edge slabs will always have bugs under the bark or in the cambium layer. The only way to kill them is with heat, and we sterilize every single load of wood that comes out of our kilns.
All iDRY kilns use a vacuum to create a pressure gradient between the shell and the core of the wood. Conventional drying methods rely on moisture differential or gradient to move the water from the wetter core toward the dryer shell. This can be a slow process since the operator must be careful not to over dry the shell or degrade will result. The iDRY achieves its fast drying rates by maintaining a small differential between the shell and the core moisture contents throughout the drying period. Typically, the core of the wood is essentially at atmospheric pressure, while the shell of the wood is at a much reduced pressure, causing the water to flow toward the shell more rapidly.
When drying lumber it is necessary to increase the temperature while maintaining a vacuum. This causes the environment within the dryer to become superheated and therefore the equilibrium moisture content is reduced causing the moisture from the wood to convert to water vapor at the reduced pressure. The moisture from the wood can then be condensed and removed from the pressure vessel and drained via the floor drain or vacuum pump.
If you own a sawmill or a furniture business you know how important quality lumber drying is. You also know what it is worth. What would your business look like if you didnt have to wait more than a week for your wood to dry? How would your cashflow change?
We currently have five kilns with a sixth planned for service in early 2017. We offer the following kiln drying services: Dry from green or partially dried lumber in one of our Nyle Dehumidification or VT Solar kilns, lumber sterilization. Prices depend upon species, lumber dimension, moisture content %, quantity. We can take your 15% MC air dried lumber and dry it down to 6% - 8% MC and sterilize it.
General Info Wood in log form typically has a very high moisture content between 60% to 100% - and it must be dried before it is suitable for most woodworking or construction uses. Because wood is hygroscopic, once milled the boards will lose their high level of moisture content until they reach equilibrium with their environment. Typically lumber used out of doors will acclimate to a MC% between 12% - 18% (framing lumber is typically dried to this level), and wood used inside a modern, climate controlled home or commercial building will acclimate to 6% - 8% MC.
Lumber will shrink and distort as it dries. The distortion is typically referred to as "cup, twist, bow, warp and/or crook". The ultimate quality and yield of the milled boards is greatly impacted by drying practices, as well as the quality of the log and skill of the sawyer.
The rate that lumber dries is based upon it species, thickness, initial moisture content (IMC% or MC%), and environmental factors (temp, RH%, and air flow rate). Dry kilns are typically used in order to control and in some instances accelerate the drying rate of milled lumber. Kilns can be divided into four broad categories, and there are notable differences between the various technologies. The different types of wood kilns include conventional, or steam kilns, dehumidification kilns, solar kilns, and vacuum kilns.
Steam or conventional kilns are most commonly used by large volume lumber producers, and they are most economical when drying 30,000 50,000 board feet of similar species, thickness and moisture content lumber. Kilns this size are not practical for smaller producers, who frequently use solar and dehumidification kilns (or a combination of the two) for producing high quality kiln dried lumber in smaller quantities. Vacuum kilns are typically use by specialty manufacturers for products such as baseball bat blanks, lumber prone to stain such as holly, or thicker slabs.
Thick boards are frequently air dried for a period of time before being "finished" in a dry kiln. For every inch that you increase the thickness of a board beyond one inch, the kiln drying rate decreases exponentially by approximately 60% per inch. For this reason, it costs much more to dry thicker boards and planks as opposed to thin ones and the increased drying cost is reflected in the price for the lumber. There an old adage amongst woodworkers that lumber requires "one year per inch of thickness" to air dry. Unfortunately, this "rule" is inaccurate except for certain slow drying species such as oak. Species such as pine, poplar, and cedar dry very quickly. In the summer time in the Southern US a 1" thick pine board will frequently air dry from green to 14%MC within 60 - 90 days. A poplar board will air dry in about 90 days. Species such as maple and walnut dry at an intermediate rate, ie a 1" walnut board air dried in the Southern US in the summer time will dry in about 120 days, and species such as oak, mesquite, and hickory dry very slowly (ie 1" per year). It is best to store lumber "in the tree" until you are ready to mill it. When lumber is stored "in the log", it will degrade by attracting bugs and stain while it is waiting to be milled, especially during a hot summer. Certain decay resistant species such as eastern red cedar, white oak and black walnut may be successfully stored in log form for 1 3 years, but the sapwood will decay and the heartwood may develop some stain. Soft species such as pine and poplar will start decaying quickly. Lumber dries very poorly in "log" form. It is best to dry lumber as dimensional boards. Rounds, or "cookies" as they are called in the industry, almost always crack severely during the drying process unless they are treated with a preservative such as Pentacryl. Air Drying and Stickering Info Green lumber can be successfully dried by a hobbyist as long as some basics are observed. To dry properly, a stack of lumber needs gentle airflow across it. Thus, the best location to air dry lumber is where it is under cover but with good access for air flow. Open sided carports or carport structures can be excellent places to dry lumber because they offer cover from the weather but good air flow through the stack. Totally green lumber does not dry well in an enclosed space where it does not have airflow, nor does it dry well out of doors if the stack is placed longitudinally near the side of a building or anything else that may impede air flow through the stack. As mentioned before, wood is hygroscopic, which means that it will absorb and release moisture based upon the surrounding relative humidity and it is always trying to reach equilibrium with its environment. In most parts of the US lumber dried and/or stored in a non-climate controlled environment such as outdoors or a non-climate controlled warehouse will air dry down to 12% - 16% moisture content (MC%). This is called "equilibrium moisture content" and is based upon temperature and relative humidity. Lumber destined for interior use should be dried between 6% - 10% MC, with 6% - 8% being ideal. Stickers are small strips of wood that separate the boards while they are drying. Industry standard kiln drying stickers are 3/4" thick and 1-1/4" wide and are a dry hardwood material. Softwood such as pine, cedar, etc has also been successfully used for stickers. A good "store bought" sticker are "furring strips" or "1 x 2's". They are typically around 3/4" thick and 1-1/2" wide and come in 8' strips. Cut them in half to make 48" long stickers and you are good to go. A 1" thick sticker is a good choice for air drying. The width should be about 1/2" wider than the thickness so that they are not accidentally placed on edge (which is easy to do with a 3/4" x 1" sticker). It is important to protect the top of the stack from rain and snow during the drying process. If left uncovered on top (or not placed under cover), rain/snow will cause excessive degrade on the boards - especially the top boards in the stack. Many air driers use old roofing tin or make a simple flat panel that they will place on top of the stack. Overhang the panel on all four sides of the stack at least 12", and 24" is better. Do not tarp the sides of a stickered stack of green lumber while it is drying (unless it is on a very short term basis such as during a rain storm). Stickered lumber requires air flow in order to dry, and tarped lumber may develop severe surface mold. Using proper stickering techniques will make a significant difference in the quality of air dried lumber. Adding weight to the top of a stickered stack of green lumber will promote flatter boards. Ratchet straps can be successfully used to maintain pressure on a stack of stickered lumber. If you go this route, you will want to make "Spreader boards" that are a few inches wider than the stack for your ratchet straps to go over. They allow the pressure from the strap to be equally distributed across the entire width of the stack. Because lumber shrinks as it dries, you will want to tighten your ratchet straps about "one click" per week to maintain pressure as the stack dries. Using green stickers (the spacers used to separate the layers of boards in a drying stack) can often lead to "sticker stain" which is a discoloration on the board where the sticker was located. It is important to use dry stickers to prevent sticker stain. With some hard to dry (without stain) species like maple, sticker stain and gray stain (an enzymatic oxidation reaction in the wood that occurs when the wood is exposed to air, high temp, and high humidity) is a big problem. So, it is key that there be good air exchange around the drying stack so that the evaporated water vapor from drying is removed from between the layers of the wood to lower the humidity. Air dring wood in an enclosed space where there is no air exchange will typically lead to poor results. For example, a basement is a poor place for drying green lumber. The water vapor from the drying wood has to go somewhere, and you will be amazed by how much water will result from drying wood. All that water ends up in your basement. Not good. The closer that you space the stickers, the flatter the resultant lumber will be. A lot of good lumber has been ruined because of poor stickering. Boards will take on the shape of the foundation of your sticker stack. If the foundation is not consistently level, your boards will not turn out flat. The stickers in a layer need to line up with each other as you build subsequent layers. There should also be good support in the foundation under each line of stickers. It is extremely important that stickers line up with each other, layer, to layer, and also that the stickers line up vertically over a support in the foundation
End Sealers Ideally lumber should be dried from the face of the boards, as opposed to the ends of the boards. Due to the cellular structure, lumber loses moisture much more quickly through the ends of the boards than the face of the boards; however rapid moisture loss from the ends of boards can result in unequal shrinkage rates between the end of the board and the portion of the board 1' or so from the end. This rapid shrinkage frequently results in "end checks" on the lumber and reduces the yield from your boards. End sealers were developed to reduce the loss of moisture from the ends of the boards while not damaging post processing equipment such as jointers and planers. One of the most predominantly used end sealers isAnchor Seal Classicavailable from US Coatings or an authorized reseller. Bailey's also sells an excellent end sealer. Store your end sealer where it wont freeze. If this is not an option then purchase "winter formula" sealer which won't freeze. Many hobbyists use other forms of end sealer, such as latex paint, parafin wax, roofing tar, etc. While these may be effective in reducing excessive moisture loss from the ends of the boards, it is best to trim the ends of the boards after drying before they are run though your equipment. Latex paint may cause accelerate dulling of planer and jointer knives, and the residue from roofing tar may be difficult to remove (and transfer to your other boards if not removed quickly from your equipment). Anchorseal does not need to be removed and thus you will usually yield more lumber and have less time spent in post processing. If you don't use an end sealer, one of the best ways to minimize the growth of end checks is to sticker your boards within an inch or so of the ends of the stacks. Kiln Dried versus Air Dried Lumber Kiln dried lumber has two primary advantages over air dried lumber. These are that the kiln drying process will allow the operator to dry the lumber down to 6% - 8%, the ideal range for interior wood, and also that the kiln operator can heat sterilize the load at the end of the kiln cycle and kill any unwanted pests in the lumber. Kiln drying also allows the operator to safely dry the lumber more quickly than ambient environmental conditions would allow for air drying. In some instances, such as when drying thick slabs of a slow drying species such as white oak, use of a kiln can allow the operator to slow down the drying rate to that which will provide less surface degrade in the lumber There are four different types of kiln drying processes. 1 Conventional kilns which use high temperature steam to dry, 2 - Dehumidification (DH) kilns which use low temperature (90 120 degree) drying methods, 3 - vacuum kilns, and 4 - solar kilns.The only one of these four drying process that will change the color of black walnut is conventional kilns that use steam. Black walnut dried in solar, DH or vacuum kilns does not change color. Solar kilns will usually get hot enough to sterilize lumber in the summer time, but not in the winter. Lumber shrinks as it dries; typically 5%- 6% in thickness for flat sawn lumber and up to 12% for quartersawn lumber. Width shrinking is opposite of face shrinkage; a flat sawn board will shrink 12% or so in width as it dries, and a quartersawn board will shrink 6%. For this reason a 1" flat sawn board is typically milled green at 1-1/16" 1-1/8" to allow for shrinkage. Longitudinal shrinking is minor - typically around 1%. Boards will distort during the drying process due to several factors, including stresses that preexisted in the tree, sapwood stress, poor stickering and knots. For this reason typically a board will require at least 1/8" of face jointing / planing per side in order to remove the rough sawn marks. Boards wider than 8" may require 3/16" 1/4" per side to clean up, and boards wider than 24" even more. A good rule to use when having lumber custom milled for you is to allow 10% for drying related shrinkage, and 1/4" per 8" of board width for surfacing both sides. Boards milled within a few inches of the center of the log will cup more in the center than boards milled further away. When brought into a climate controlled environment (50% RH and 75 degrees F), lumber that has been stored in a non-climate controlled environment will continue to dry as long as it is stickered and has good exposure to ambient air on the faces of the boards. Usually lumber will acclimate within a few weeks. Conversely, lumber that has a low MC% will gain moisture if stored in an environment with a higher RH%. The average hobbyist can sterilize lumber at home by using a simple foam board built chamber and a space heater. There is an article in FWW magazine about this. Air dried lumber may be susceptible to insect infestations such as termites and powder post beetles. The best method of prevention is to store kiln dried lumber in a controlled environment and away from air dried lumber. Heat is the best sterilization method for lumber. When this is not practical, boric acid based solutions such as Timbor (for green lumber) or Bora-care (for dry lumber) have been used successfully for treatment. Fumigation methods have also been reported to be successful. If you will be drying thick slabs for an extended number of years, it would be a wise investment to treat them green with Timbor or something similar.
Oftentimes, hardwood lumber drying begins with exposure to an uncontrolled outside environment in a process called air drying. At times, loss of quality in this process can be in excess of 10 percent. Yet, with well managed air drying, including the use of plastic mesh and open sheds, quality losses can be under 2 percent. Almost all defects in lumber drying occur at very high moisture contents (MCs). After air drying, the lumber is put into a kiln to achieve the low final MCs desired. Quality losses in air drying cannot be repaired in the kiln-drying process.
Kiln drying of grade hardwood lumber is carried out in a closed chamber or building in which heated, humidity-controlled air is rapidly circulated over the surface of the wood being dried. Defects that might develop in drying are minimized by controlling the temperature, RH and velocity.
Temperatures. Conventional dry kilns commonly use initial drying temperatures, when the lumber is more than 50 percent MC, from 100 to 130 degrees F. As the lumber dries, temperatures are gradually raised. When the lumber is under 15 percent MC, temperatures, depending on species, range from 150 to 200 degrees F; although 160 degrees F maximum is preferred in most cases.
Air Flow. Air velocities through the load in drying hardwoods generally are between 200 and 650 fpm; the lower velocity values (250 fpm maximum) are for refractory or difficult-to-dry species such as oak and beech when at higher MCs, while the higher numbers are for the white species like maple, ash, and basswood. Velocity is not a critical factor for well air-dried lumber.
Humidities. Control of RH or EMC during kiln drying is necessary to avoid creating shrinkage associated defects, such as cracks, as well as to equalize and condition the wood with a high degree of precision. Today, many kilns use computerized recorders and controls.
A kiln schedule, which indicates the desired temperature, humidity, and velocity in the dryer depending on the MC of the lumber, is a carefully worked-out compromise between the need to dry lumber as fast as possible and the need to avoid severe drying conditions that will cause drying defects. It is a series of dry- and wet-bulb temperatures that establish the temperature and RH in the kiln and are applied at various stages of the drying process. Temperatures are chosen to strike this compromise of a satisfactory drying rate and avoidance of objectionable drying defects. One of the key defects is discoloration; another is checking and cracking.
As lumber is dried using kiln schedules, which are combinations of temperature and RH applied at various MC levels during drying, some means of estimating MC of the lumber, especially the wettest and driest pieces of lumber, in the kiln during drying is necessary. These MC values are determined by using 12 carefully chosen kiln samples. The samples chosen must represent the lumber and its variability. The main principle of selection is that the kiln samples be representative of the wettest and driest lumber in the kiln. (A large kiln might have 10,000 pieces of lumber. So "to put all your eggs in one basket" by using only 12 pieces of lumber to determine what is happening to all 10,000 pieces is risky. Poor sampling means low lumber quality when the customer tries to process the lumber.
Traditionally, kiln samples have been removed from the kiln periodically and weighed manually for MC estimates. This manual procedure is still used in the majority of hardwood operations, but automated methods are available.
The selection, preparation, placement, and weighing of kiln samples, if properly done, provides information that enables a kiln operator to 1) reduce drying defects, 2) control of the final MC of the charge better, 3) reduce drying time while maintaining lumber quality, 4) develop time schedules, and 5) locate kiln performance problems. All these advantages add up to lower drying costs and lower secondary manufacturing costs due to dried lumber that has a consistent MC, is uniformly conditioned, and free of drying defects.
After the lumber achieves the correct moisture content, it must be equalized and conditioned. That is, equalizing and conditioning (also called stress relief) are two quality-control measures necessary to complete the drying of high-quality hardwoods. Having the lumber at the desired final MC with little variability and free of drying stresses is critical in today's manufacturing and supplier/purchaser environment.
Frequently, near the end of the drying run, the MC of lumber varies considerably. This is because of natural variability in drying rate (such as the ends of the lumber versus the center of the lumber), initial MC, heartwood and sapwood and bacterial wet pockets. Variability can also result due to variability in drying conditions (temperature, humidity, or velocity) in various parts of the kiln. Variation in final MC can cause serious problems in the subsequent processing and use of the lumber. The purpose of equalizing is to reduce this variation in MC without over-drying.
Residual drying stresses (often called casehardening although there is no actual hardening of the surface) can cause problems with immediate warp when machining, various gluing problems, and pinching the saw blade when ripping or resawing. Drying stresses should be removed (that is, the lumber should be conditioned) in most hardwood lumber before the lumber is cut-up. The purpose of conditioning is to relieve the residual compressive drying stresses in the shell by exposure to high temperature and high RH. Conditioning can also have the beneficial effect of producing more uniform MC throughout the thickness of the boards. Effective equalizing is necessary before satisfactory conditioning can be accomplished because the effectiveness and length of the conditioning treatment depends on MC.
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Freshly milled lumber requires about a year to dry and cure before you can use it in construction. Even firewood takes at least six months before its ready to burn. If your lumber needs are more consistent, a home firewood kiln can cut this wait time down to a week or less. X Research source Solar kilns or smaller boiler-based models will be the most accessible for home users. Commercial kilns are very large and can cost thousands of dollars.
There are many types of kilns and each type is defined by the way in which the temperature and humidity are controlled. In fact, the most commonly used kilns are conventional and dehumidification kilns. Vacuum and solar kilns also are used for special applications and conditions.
Conventional kilns have pipes that radiate heat into the kiln chamber. This heat is forged from steam or by hot water coils. The water extracted from the wood is converted into vapor and then released from the kiln through the hot air.
This type of kiln can typically dry 1-inch-thick (25 mm) green wood in 10 hours down to a moisture content of 18(1). However, 1-inch-thick green red oak takes almost 28 days to dry down to moisture content of 8%(2).Generally, cool dry air is found at one end of the kiln while warm water is discharged at the other. Conventional kilns require a considerable amount of energy as constant heating of air is needed.
Dehumidification kilns have been used extensively in the lumber industry due to their recycling based characteristics. In fact, these types of kilns have a heat pump system that removes moisture from wood as the majority of the evaporated water is condensed on the refrigeration coils of the dehumidifier then drained as cool liquid instead of being ventilated away from the kiln. Even though dehumidification kilns use electricity, which can be more expensive than gas, they are still economically practical because they constantly conserve energy by recycling heat and as a result the amount of electricity demanded by the system is minimal.
Vacuum kilns are known for their high-drying speed systems. However, they are more costly than either conventional or dehumidification kilns since the heat of vaporization is being provided by electricity instead of local fossil fuel. In addition they have limited drying capacity in the chamber.
The temperature at which water boils is determined by atmospheric pressure. For example, the higher up a mountain you go, the less pressure the atmosphere exerts, so water boils at a lower temperature up the mountain than at its base. So unless you can haul your vacuum kiln to the top of the Himalayas, its going to take more energy down where us commoners live.
A solar kiln relies on solar collectors to provide the heat energy that is needed for the water evaporation. Drying times in a solar kiln depend on the weather and are therefore unpredictable. Solar kilns usually use electric-powered fans to enable the air to freely circulate through the wood. However, the cost of running these fans is high and because of the long drying times, youve got to run the fans for a long time making solar drying quite expensive and inefficient.
We welcome you to make an appointment to come by our manufacturing facility to witness our kilns in action. We have a few conventional kilns at our facility: two big units names Nyle l500 and one smaller unit, the Nyle l200. You could say we dry lots of wood!
You may think that air drying is better than kiln drying in terms of saving money since it is a natural process that doesnt need advanced technology . However, this natural process has its hidden drawbacks.
Well, in the case of air-drying the logs are not only left at the mercy of the weather and the climate fluctuations, but there are also other associated costs including costs of storage as the air drying processgenerally takes a minimum of 12 months under optimum conditionsin order for the wood to be ready. And air drying will never bring the humidity level down to the needed 6-8% for flooring applications.
We cannot also forget that the wood would be absolutely susceptible to bacteria andinsects during that long period of storing. The cost averages between$.35-$.60 per board foot(3)so in reality, air drying is not as cheap as people think.
Instead of waiting several months,your lumber can be ready within only a few weekswith kiln-drying. In fact,advancements in wood drying technology have reduced the time it takes, lowered the risks of damaging your lumberand reduced other costs.
Kiln-drying is the ultimate way of ridding timbers of mold and insect infestation. As temperature can reach176 F (80 C) on the last days of drying, it automatically kills any insects, sanitizes the lumber from any kind of fungus or even eggs.