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  1. #1
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    Default Workshop Humidity Control

    With the cold weather approaching we are moving into the time of year where we are getting nights where the temperature drops below the dew point causing condensation.

    The workshop is pretty well insulated, so the internal temperature stays up about 5 or 6 degrees above outside temperatures.

    That's no guarantee that on those really cold frosty foggy mornings that there won't be condensation inside the workshop. So the solution is a humidity control system.

    A cheap fan heater is mounted up under some overhead storage shelves, The fan heater seems pretty solid and only cost $49.95

    New 2in1 Industrial Electric Drum Fan Heater Workshop Floor Dryer Standing 2000W | eBay

    IMG_2128.JPGIMG_2127.JPG

    It's connected to a power point controlled by a Sonoff wifi controller https://www.itead.cc/smart-home/sonoff-pow.html
    The power point has a couple of USB ports and I've rewired it so that the USB ports are powered independantly of the double power point.

    The USB double power point is this one 5x Dual USB Australian Power Point Home Wall Power Supply Socket SAA Approval AU | eBay

    The USB is needed to power the sensor.

    The Sonoff POW, gives not only remote on/off control via the wifi network, but measures voltage/ current and power factor. I'm using the TASMOTA firmware.

    The sensing is done by a Sonoff SC module, https://www.itead.cc/smart-home/sonoff-sc.html

    IMG_2129.JPG

    The module costs less than $20, and gives you temperature, humidity, light level, air quality and noise level over the wifi network.

    Stuck on with some velcro till I figure out something better.

    The web interface to the Sonoff SC, via phone, pc or tablet, it's all the same.
    SonoffSC.jpg

    The power on/off switch is similar.

    SonoffPOW.jpg

    That's the hardware, total cost less than $100, the firmware that comes with the Sonoff units is replaced with the popular https://github.com/arendst/Sonoff-Tasmota
    Which is open source and very actively developed, the control is done via mqtt and node red.
    Node Red is a web based graphical programming environment, easy to visualise and use.

    I won't go into the gory details, look up some of the node red on-line tutorials. The final result is that the fan heater switches at the psychological moment to the keep the temperature a degree or so above the dew point.

    It's not really a workshop heater as such, it's not intended to be, it just has to bump the temperature a degree or two at the critical time during the night.

    So far this year it hasn't even had to switch the heater on, ( apart from testing of course ) but we have had condensation outside a couple of times in the last week, so it's only a matter of time.

    PS. I've never seen the Sonoff SC air quality ever ready anything other than 100%, I couldn't figure out what it was supposed to be for, till I looked at the air quality levels in Beijing. Then it all made sense.

  2. #2
    BobL is offline Member: Blue and white apron brigade
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    The Sonnof looks like an interesting gizmo so I looked it up and was amused by a statement by a seller that wrote ;

    "This is more a TOY than a final product. Please take it as a product for hobbyist."

    but for $20! hey that's still a bargain and I'm tempted to get one just to play with it.

    As it supposedly measures dust particle concentrations I wondered if it could be useful for monitoring woodworking.
    I tracked down what it uses for air quality monitoring and it's a GP2Y1010AU0F Sharp dust sensor that uses an IR diode and an photo transistor.

    The response of that sensor is pretty limited.
    Presumably voltages close to zero are rated as clean, between 1 and about 3.5V that's intermediate and above that is bad?
    WW dust OHS levels 1 and 5 mg/m^3 for hard and softwood respectively. For MDF it's 0.5 mg/m^3 so it would be useful good for MDF workers.

    Would you mind get a pinch of wood dust or talcum powder and fluffing it in its general direction and see what it does?

    Thanks

    Screen Shot 2017-05-09 at 7.12.26 PM.png

  3. #3
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    Hi Bob,

    I'm using it for temperature and humidity, and it comes as standard with the DHT-11 sensor, which is not especially accurate, so we replace the DHT-11 with DHT-22 and it performs pretty well temperature wise it is within +-0.25 C of my good thermocouples.

    Don't know about the air quality sensor, I'd think it more for bad days in Beijing than a wood work shop, but you never know.

    I'll try that talcum powder test and see if it responds.

  4. #4
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    Ray, is the high mounted fan positioned there to mix and stir the air in an effort to minimise stratification, in other words to avoid having all the hot air in the higher parts of your workshop? If so, has it worked well to even out the heat distribution?
    Rob.

  5. #5
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    Quote Originally Posted by Ropetangler View Post
    Ray, is the high mounted fan positioned there to mix and stir the air in an effort to minimise stratification, in other words to avoid having all the hot air in the higher parts of your workshop? If so, has it worked well to even out the heat distribution?
    Rob.
    Good question, although it's mounted up high, I've got it angled down, the reason is to get the airflow over the machines and cover a wider area, down at ground level there is too much obstruction for good airflow. We did a test run the other night, ( you have to do it when everything is cold ) and running the heater for about 30 minutes raised the average air temperature about a degree. But there's a lot of thermal mass in there, 3 tons of granite makes a good heatsink. This was on a night when there was condensation on the car windows outside.

    My recollection of the few times in the past when there's been condensation inside the shed is that it drips down from the rafters, so that's another reason to keep the air flow higher.

  6. #6
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    Ray, I think that the effect of a fan mounted high up but angled down would be to drag the surrounding air into the stream coming from the fan, with the result that there should be little stratification, and a fairly even temperature from floor to ceiling after the fan has run for some time. In the community shed (like a mens shed) I am a member of, the summertime condition (temperature profile wrt height above floor) is generally fairly even unless you climb a ladder on the mezzanine floor. Within the top 6' or so the temperature would be 5 - 7º higher than the rest of the shed, you can feel the transition point if you reach up with a bare arm. The shed is about 24X12X6m to the gutter height, and the roof is a medium pitch of 10 to 15º. It has aluminised foam insulation under the roof, and the same on the walls, but with rockwool insulation between the foam and the walls in addition. We use no heating or cooling winter or summer and the building is always a very comfortable environment.
    Good luck with your project, hopefully you have the humidity problem sorted. It is my understanding that a dehumidifier needs a fairly warm ambient temperature to work efficiently, possibly somewhat warmer than your winter time shed temperature, but I may not have that correct, so it might be another avenue worth investigating. Cheers,
    Rob

  7. #7
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by RayG View Post
    Hi Bob,

    I'm using it for temperature and humidity, and it comes as standard with the DHT-11 sensor, which is not especially accurate, so we replace the DHT-11 with DHT-22 and it performs pretty well temperature wise it is within +-0.25 C of my good thermocouples.

    Don't know about the air quality sensor, I'd think it more for bad days in Beijing than a wood work shop, but you never know.

    I'll try that talcum powder test and see if it responds.
    Thanks.
    I've ordered one and will have a bit of a play with it.

    I realise this is not your area of interest but there are a couple of issues I can see with it for dust detection. The first is the dust sensor relies on dusty air to diffuse over to and simply fall though the sensor which means it will have a slow response time to some dust making activities. I was thinking perhaps (a bit like your own fan heater used to equilibrate the heat) a small fan could be used to gently circulate air so that it reaches the sensor more rapidly. The other problem is that it seems like it will be very easy to flood the sensor with too much dust which will change the measurement characteristics and there are warnings to this effect in the literature provided with the sensor. However it might be useful as a general dust sensor that sits in a shed corner (away from really high dust concentrations) and maybe even switches an exhaust fan on/off as needed.

    When I get it I will check it against a particle counter.

  8. #8
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    Quote Originally Posted by BobL View Post
    Thanks.
    I've ordered one and will have a bit of a play with it.

    I realise this is not your area of interest but there are a couple of issues I can see with it for dust detection. The first is the dust sensor relies on dusty air to diffuse over to and simply fall though the sensor which means it will have a slow response time to some dust making activities. I was thinking perhaps (a bit like your own fan heater used to equilibrate the heat) a small fan could be used to gently circulate air so that it reaches the sensor more rapidly. The other problem is that it seems like it will be very easy to flood the sensor with too much dust which will change the measurement characteristics and there are warnings to this effect in the literature provided with the sensor. However it might be useful as a general dust sensor that sits in a shed corner (away from really high dust concentrations) and maybe even switches an exhaust fan on/off as needed.

    When I get it I will check it against a particle counter.

    I don't think it will work as an effective dust sensor without a few modifications.

    IMG_2131.JPGIMG_2130.JPG

    The case obstructs the airflow through the sensor, and the sensor itself is oriented at right angles to any possible airflow.

    It might work if the sensor was re-oriented so that a small fan could circulate a bit of air through it. It seems sensitive enough when you can get airflow to it.

    In the above pictures you can see how we have moved the temperature and humidity sensor closer to the top and away from the main cpu board, I think we were picking up a small temperature offset from the pcb self heating.
    Also, in that picture, that's the DHT-22 upgraded from the supplied DHT-11.

    Josh reflashed the Atmel chip that does the interfacing to the sensors, and tells me that the timing of the software driving the dust sensor is critical, the IR led is pulsed for about 300 us, and the analog input from the photodiode read at about 200 us, I can post the code if you are interested in hacking it any further.

    All in all it's a brilliant little gizmo, for $20 it's a bargain.

  9. #9
    BobL is offline Member: Blue and white apron brigade
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    Thanks Ray.

    Quote Originally Posted by RayG View Post
    I don't think it will work as an effective dust sensor without a few modifications.
    The case obstructs the airflow through the sensor, and the sensor itself is oriented at right angles to any possible airflow.
    I reckon that has been done deliberately so it doesn't get flooded wth too much dust which could ruin it.
    My guess is it relies on plain old diffusion for the dust to reach the sensor.

    It might work if the sensor was re-oriented so that a small fan could circulate a bit of air through it. It seems sensitive enough when you can get airflow to it.
    Thanks

    All in all it's a brilliant little gizmo, for $20 it's a bargain.
    Sounds like it - Im looking forward to playing with it - more time wasting - but hey that's what retirement is for.

  10. #10
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    Quote Originally Posted by Ropetangler View Post
    It is my understanding that a dehumidifier needs a fairly warm ambient temperature to work efficiently, possibly somewhat warmer than your winter time shed temperature, but I may not have that correct, so it might be another avenue worth investigating. Cheers,
    Rob
    That is true of heat-pump type dehumidifiers. For cooler temperatures the desiccant type work well. I have one of each of these to dehumidify the bedrooms in winter:

    Ionmax ION612 Desiccant Dehumidifier Reduce Moisture Remove Mold Spots | eBay
    Ionmax ION 632 Desiccant Dehumidifier 10L-Voted No.1 By Choice-Reduce Mould | eBay

    The problem with a heater is that it doesn't remove the moisture from the air. It's still there the next night waiting to condense again. These use a lot less than 2000W too.

  11. #11
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    Quote Originally Posted by jack620 View Post
    That is true of heat-pump type dehumidifiers. For cooler temperatures the desiccant type work well. I have one of each of these to dehumidify the bedrooms in winter:

    Ionmax ION612 Desiccant Dehumidifier Reduce Moisture Remove Mold Spots | eBay
    Ionmax ION 632 Desiccant Dehumidifier 10L-Voted No.1 By Choice-Reduce Mould | eBay

    The problem with a heater is that it doesn't remove the moisture from the air. It's still there the next night waiting to condense again. These use a lot less than 2000W too.

    Thanks for that, yes that's the sort of thing that comes to mind when talking about humidity control. What I'm trying to avoid is condensation.

    Here's last night's data.

    May12WeatherData.jpg

    So far the heater hasn't had to even switch on, the coldest it got inside the workshop was 11 C 60% RH when the outside temp was 5 C, 99% RH.

    But the BOM data shows the air temperature was around the dew point for most of the night, lowest was 2.7 C. No frost.

    Based on the way the insulation seems to be keeping the temperature 5 or 6 degrees about outside air temp, the heater might never even turn on

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