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"Espresso! My Espresso!"
An Ongoing Internet Novelette
by Randy Glass - Copyright 2012 - All rights reserved

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Cold Weather Roasting

Sunday, December 16, 2012

    It was cold today. If it hit 40 F, that was about as warm as it got. For some, weather like that is a signal to don short sleeves and take a walk in the park before it gets cold. But I needed to roast a batch so I layered-up, went out to the garage, and as I watched the snow fall out the garage window, I plugged the laptop into the roaster and started RoastLogger. This was the first really cold day on which I used the HTC + TC4C + RoastLogger set up to control and monitor the Hottop roaster, and things were interesting right from the start.
    Once RoastLogger was in communication with the roaster I noticed two things. The first was that both the BT and ET temperatures were within a few tenths of each other at 38F. The second was that the Hottop KN8828B-2K was displaying 52F. Normally the Hottop displays a temperature that is about the average of the BT and ET temperatures which RoastLogger reports particularly before adding beans. I assume that the Hottop's lowest displayed temperature is around 50 F., and since the specified range of K thermocouples is usually lower than that, I have to think that it is the programming of the electronics controls that displayed range. That is just a guess, but the temperature in the garage was around 38F. so I had to assume that this was the source of the difference.
    Once the roast got underway it was clear that the cold ambient temperatures were having an effect. As the roast progressed the effect was dramatic. Easily seen in this crop of the roasting graph (note that graphed data is gathered from the low-mass thermocouples I installed and not the Hottop displayed data):

cold roast

    At the seven minute mark after charging the roaster the BT was about 25 F. degrees cooler than what I experienced previously during roast which were in the “normal” 50-70 ambient temperatures. Normally I would keep the heating element at 100% and the fan at 0% as I had this cold afternoon. Seeing the discrepancy on the real-time graph continue (and even increase) I manually set the the fan to 50%. Here is what happened at that point:

cold roast

A - The graph line from a previous roast which reflects about the same behavior I have seen in over 30 previous sessions using the HTC+TC4C system.
B - Today's roast in cold weather. That is the point at which I turned on the fan.

    As you can see. The BT responded quickly to the change in fan speed. The ET also showed a change in the graph line, smoother, but echoing what we see in BT.
    So I assume that the heat was being more evenly circulated once the fan came on. With so few data streams, and all of them coming from the same area of the roast chamber (the back wall) I can only guess as to the cause.
    The educational value of this simple chapter is that having accurate telemetry is valuable, but only if you put it to use. Additionally, sometimes experimentation can lead to discovery, even if the experiment seems counter-intuitive.

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