Kiln Drying Forum
Wood Drying Topics => Dry Kiln Control => Topic started by: fbushaw on January 25, 2012, 12:49:33 PM
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I am trying to figure out how to set up my WF schedules so the kilns will get up to temp on time. I was wondering if anyone has ever tried setting the intake vent limit to 0 for a whole charge. Seems to me, this would have to help, you would still be letting the moisture out of the other side, and you wouldnt be pulling in cool air from the intake side.
Any suggestions???
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Francis,
Are the valves fully open? If so the heating rate is limited either by the boiler, the coil area, or some other mechanical factor.
I suggest closing the vents completely for the first few hours until the kiln gets to temperature. The kiln vents something like 10 or 15 pounds of air for every pound of water removed at a wet-bulb of 110 to 130F. At a wet-bulb of 150F, this reduces to about 5.
Try not to let the structure cool too much between charges.
Stagger kiln startups.
Higher fan speeds can remove more heat from the coils and might help, but I suspect you already run at full amperage.
Are the coils baffled (assuming you can do this without choking airflow)?
I can't say more without knowing more about the system and the problem.
Mike M.
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Higher fan speeds WILL remove more heat from the coils. However, at higher fan speeds (and consequently higher flow rates through the lumber), the lumber will remove that heat.
Actually, this is a good thing....what do you want hot lumber or hot air? Hot Lumber!
Higher air flow rates will always cause the kiln to take longer to get to temperature if steam availability is limited, however the total drying time will be less.
If, you have unlimited steam availability then the increase in air flow will not lengthen your time to temperature.
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It seems you don't know the heat capacity of your kiln. As a rule thumb, you can use the following procedure to determine your start temperature: Cold start the kiln with a full load of wet lumber, run a heating phase as you normally would, eg. open heat valves to max, introduce steam spray/humidification and keep all vents 100% closed for the first 4 hours. Note the DB temperature. The max DB temp you can reach at this stage is a good guide temperature to use throughout. If you cant reach the DB after drying has commenced, reduce the DB setpoint by 1 Deg C until it can be maintained and set your desired EMC/RH with your WB setpoint. In an energy starved system, you will see that you can reach higher temps when the lumber MC goes below ±20%.