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Calculating fan air speed for your curing chamber....

Discussion in 'Curing' started by daveomak, Aug 20, 2018.

  1. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    Air Speed Air speed is a factor that helps remove moisture and stale air, and of course it influences drying. Sausages will dry faster at higher temperatures, but in order to prevent the growth of bacteria, drying must be performed at lower levels, generally between 59-53º F, 15-12º C. The speed of drying does not remain constant, but changes throughout the process: it is the fastest during the beginning of fermentation, then it slows down to a trickle. At the beginning of fermentation humidity is very high due to the high moisture content of the sausage. When starter cultures are used, the temperature is at the highest during fermentation which speeds up moisture escape from the sausage. The surface of the sausage contains a lot of moisture which must be constantly removed otherwise slime might appear. If the sausages are soaking wet during fermentation, the humidity should be lowered. At the beginning of fermentation the fastest air speed is applied, about 0.8 - 1.0 m/sec. The speed of 3.6 km/h (2.2 mile/hour) corresponds to the speed of 1 meter/second. Ideally, the amount of removed moisture should equal the amount of moisture moving to the surface. To control air speed in improvised chambers such as a refrigerator is surprisingly easy. The most reliable device is a computer cooling fan as it is designed for working 24 hours a day. There is a huge variety of these fans and they come in different sizes, shapes and power outputs. They can be obtained at Radio Shack® or at any computer store. The current draw of a typical 3” 12 VDC, 1.9 W fan is only 0.1 A. It runs from a 115 VAC adapter and the beauty of the design is that the adapter’s output can be set to 12, 9, 7.5 or 6 VDC with a built in mini switch. Each voltage setting lets the fan run at a different speed and quite a sophisticated system is created. If only a fixed DC output voltage adapter is available, a simple, inexpensive and universally available device called a “potentiometer” can be attached between the fan and the adapter. The device will control the fan’s speed.

    Marianski, Stanley. Home Production of Quality Meats and Sausages (Kindle Locations 9648-9664). Bookmagic LLC. Kindle Edition.
    as an example, I used the fan below......
    uxcell 50mm x 25mm 12V DC Blower Cooling Fan, Long Life FDB Bearings
    • 50mm Blower Fan, comes with 2 bare wire; Rated Voltage: DC 12V, Current: 0.1A
    • Bearing Type: FDB Bearing, Speed: 3000 RPM, Air Flow: 3.09CFM
    • Lead Wire Length: 25cm (9.8 Inch), Fan Noise Level (dB-A): 33 dB-A
    • This fan is made of special and premium materials, it is high temperature resistant and extremely durable
    • Containing long life dual ball bearings, guaranteed to continuously run 30,000 hours under normal temperature
    Roughly, a 2" fan putting out ~3 CFM...

    2x2= 4 sq. in.
    A cu. ft. is 1728 sq. in. .... / 4 sq. in. = a 432" long 2x2 column = 1 cu. ft...
    At 3 CFM, the air has moved 432x3= 1296 inches in a theoretical flow... mind you the flow will spread out in a cone pattern but we are theoretical here... so... I will use a linear flow not spreading out....
    1296 in. in one minute / 12 = 108 ft. min.. / 60 = 1.8 ft. sec.

    1.8 ft. sec. = 1.23 M.P.H. or 0.55 Meters per second

    If you use the ~ 1"x1" square opening, the air flow will be 4X's the estimated.. equaling 4.9 M.P H. or 2.2 Meters per second..

    This is the fan I chose for my ~4 cu. ft. dorm fridge... I do have 2 of them...
    With time delay and run time adjustments, being the dummy I am, I think these fans will work well and I should not get any case hardening...

    Soooooo, this thread is put up so you can estimate the fan in your chamber...
    My computer has these wonderful calculators and converters so I don't need to think when crunching these numbers...

    I don't particularly agree with the temperature range of 53-59 deg. F for drying... Temps above 50 ish. start growing pathogens faster... some "experts" recommend temp range of 45-50 F to avoid bacteria etc. problems... That's the range I will be shooting for in the drying stages...
    Last edited: Aug 20, 2018
  2. AllAces

    AllAces Meat Mopper SMF Premier Member

    Are you using refrideration to maintain 45-50F? Any thoughts on how to control/manage intake air humidity?
  3. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    There are temp controllers and humidity controllers ... There are many recommendations from members on this forum.... Pick your poison.. from a few bucks to many bucks..
    The only thing I can recommend is.... Thermal mass.... fill your chamber with water containers... as many as is practical... have the water acidified with white vinegar to prevent bacterial growth...
  4. Holly2015

    Holly2015 Master of the Pit OTBS Member

    I can concur thermal mass is paramount controlling temperature fluctuations and the amount of refrigeration cycles. This also helps eliminate excess air moving from condenser fan running with refrigeration cycles.

    One of the best thermal masses I have encountered is 6-packs of beer. Another thing to remember no matter what thermal mass you are using do not initially add it all at once.

    I also pre cool the thermal mass and let the chamber bring the temperature up as apposed to putting in warm thermal mass and the chamber working to bring the temp down.
    daveomak likes this.
  5. I have a question. Is it 100% necessary to have a frost free refrigerator? The refrigerator I plan on using for my build has a separate freezer compartment on top and no direct air exchange between the freezer and the lower compartment. I do have Stanley & Adam Marianski's book (The art of making fermented sausages) and I believe it doesn't say frost free is required. Because you have a strong understanding of the air flow situation I am wondering about your opinion.
  6. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    Morning Polyj.... No, frost free is detrimental in my opinion.... Frost free heats up to evaporate the frost, then cools off again.. When you are trying to get to ~80% humidity and hold it there for 3 months, using frost-free you end up chasing your tail continually adding moisture... The cooling plates suck the moisture out of the air and it turns to ice on the plates... then the refrigerator turns off.. now the ice melts and goes back into the air as humidity...
    Using a dehumidifier is a much better option... along with a humidity measuring sensor that can turn the dehumidifier on/off..
    Refrigerators have chilling coils in them... the coils suck moisture out of the air and have the same effect as frost free...
  7. Holly2015

    Holly2015 Master of the Pit OTBS Member

    Using an external controller to regulate the temperature takes the defrost cycle out of the equation or at least enough where it can have a drastic effect.

    Over 99% of the time there will be no power supplied to the refrigerator and it'll sit there unpowered so the defrost cycle cannot run. Only when the external controller calls for cooling will it allow power to the refrigerator allowing it to run until set point is reached (1 to 3 minutes typically) then all power is again cut to the refrigerator.

    If you are going to try and use the refrigerators integral thermostat to control the temper of the chamber then you run the risk if it going into a timer activated defrost cycle. But before this ever happens you'll also experience drastic inaccurate temperature swings as fridge thermostats are usually bimetal and not accurate from ne cycle to the next and also slow to react. They are good enough to hold a range of temperatures but a digital controller can hold a much tighter range.

    Humidification and dehumidification are as important as the temperature setting. Fortunately that an easy work around as well with the proper equipment and controls.

    Here is a tutorial I put together on building a chamber. My chamber I can hold setpoint no mater what the air temperature is. My garage see's temperature swings of over 100 degrees summer to winter.

    daveomak likes this.
  8. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    Holly, EXCELLENT description ......
  9. Holly2015

    Holly2015 Master of the Pit OTBS Member

    Thanks, Dave.


    The only thing I'd caution is if using a combination refrigerator/freezer is if you don't cut out at least some of the divider between the two the freezer is going to end up being a science experiment as the freezer section will sit sealed with very stagnant air and very minimal airflow.

    The benefit of cutting out the divider is you gain some of the freezer space to use as part of the chamber. Best scenario is if you get a bottom freezer/top refrigerator is you cut out the divider and put the humidifier, dehumidifier and heater in the freezer space then hang the meat in the refrigerator portion.

    The down side is you will need to seal the cut edges where you cut out the divider. Foil backed tape, bent metal sealed with silicone are viable options.
  10. Thank you for your time and opinion.

    This particular refrigerator has the evaporator coils in between the two compartments(I think so anyway).
    What is wrong with maintaining temp and humidity in lower refrigerator compartment and cutting a hole in the side , install the uxcell 50mm x 25mm 12V DC Blower Cooling Fan as you discussed and keep the humidifier down in the crisper draw area? As long as the freezer can maintain temperature via. the external temperature controller?
    By the way how are your casings since you installed the the uxcell 50mm x 25mm 12V DC Blower Cooling Fan?
    Thanks again

    Attached Files:

  11. daveomak

    daveomak Epic Pitmaster OTBS Member SMF Premier Member

    I have the fan on a timer... Amazon

    Century Short Period Repeat Cycle Timer Day/night, or 24 Hours Operation
  12. Holly2015

    Holly2015 Master of the Pit OTBS Member

    I am not a fan of using a fan to control humidity. Its like riding around in your car with A/C on full blast and rolling the windows up/down to modulate the humidity or temperature level inside the vehicle. It'll work but it not accurate and repeatable as outside conditions continually change.

    Mechanical humidification/dehumidification on their own separate controller is the best, easiest and most accurate way to set and maintain very specific Relative Humidity levels in a curing chamber. The chamber is also a small enough space whereas the RH/temp levels won be differ form the top to the bottom of the chamber or at least not enough to be a concern or to add a fan.
  13. Thanks for the input