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  1. M

    PID or Relay for Circulating Shower

    I am considering using PID (autopid arduino lib), in order to control the heat, with PWM and a 50amp mosfet heating a 40amp 24v heating element in a 3litter tank, but I am thinking, that since the water is going to be circulating, and sometimes losing heat to a person, sometimes falling straight...
  2. M

    LiFePO4 battery heater project (makes sure battery doesn't freeze)

    I have a 700watt array now. I get about 8 hours of sun a day(this time of year), often overcast The BMS on the battery will not let the charge start if the battery is under 0. So a heater is required.
  3. M

    LiFePO4 battery heater project (makes sure battery doesn't freeze)

    and if i leave my camper parked for 2 weeks on its own in my backyard? This is part of what im trying to solve also. But great outside of the box thinking with the water though! It just wont last long enough.
  4. M

    LiFePO4 battery heater project (makes sure battery doesn't freeze)

    While freezing is a concern, charging below zero is a totally different concern. In this battery chemistry it creates dendrites and overtime these can severely reduce the capacity of the battery.
  5. M

    LiFePO4 battery heater project (makes sure battery doesn't freeze)

    I think PID is overkill (but would consider it). I am thinking of setting up an array of thermistors around the battery to make sure that they are all above T? Maybe two on top, two on the sides. The battery is about 8"x20". I am building an r10 insulation box around the battery, which will...
  6. M

    How can you determine if a fan is better at blowing or sucking?

    wow checking back on this thread months after posting it. I really like where it went :D
  7. M

    How can you determine if a fan is better at blowing or sucking?

    I see so the main consideration is just contamination effecting performance, and that all fans perform equally well sucking/blowing if their position is reversed in the same system, lets say a long tube. I tested this out with a 7' pipe and i got different results for CFM measurement from...
  8. M

    How can you determine if a fan is better at blowing or sucking?

    I am being vague because its not specific to any one system, I am working on many, and so just looking for a general rule on determining if a fan is better for pulling or pushing air.
  9. M

    Applying desiccant to surfaces (aluminum sheet or PLA/PETG)

    Thanks for your suggestion. Also a descant wheel is not an ERV wheel (which is why I specified I need to apply it to aluminum or a plastic capable of heat transfer). They do different things and are manufactured differently.
  10. M

    How can you determine if a fan is better at blowing or sucking?

    I am trying to determine if they are better placed in positions where they suck or blow. Is there a rule to determining this?
  11. M

    Applying desiccant to surfaces (aluminum sheet or PLA/PETG)

    Thank you but im not seeing any relevant (how its made) info on either of those links. I hope i didnt miss anything.
  12. M

    Applying desiccant to surfaces (aluminum sheet or PLA/PETG)

    I think i just thought of a great way to do this. I will try to get silica powder, and then surround my 3d printed part in the powder, and then I bake it, this way it will maintain its shape and a thin film of silica will stick to the printed part. people are already doing this with salt in...
  13. M

    Applying desiccant to surfaces (aluminum sheet or PLA/PETG)

    and would i just use pure silica powder? I would have to toss it around in a bag of it or something because the channels in the wheel will probably be around 1-2 inches deep and extremely narrow. It would be much better if i could make a solution of it that i dip the part into
  14. M

    Applying desiccant to surfaces (aluminum sheet or PLA/PETG)

    I will either be using aluminum strips wound up, or 3d printing it out of PLA or PETG. How can I apply a coating of silica to the surface of either of these materials so that it can hold and release the moisture of the incoming air/outgoing air? This is to manage heat and humidity in my...
  15. M

    B How long will it take to reach 1000ppm CO2 from 2000ppm

    Thanks for the response! What is dt? is it delta time? and what is p(t)? A human adds 5000ppm co2 in one hour. So me being alone will add that to the room I dont know, there is no constant rate to this because the fresh air is being mixed in with the inside air, and that mixture is being...
  16. M

    Two computer fans on top of each other

    If I have a computer fan that provides 50 cfm, and x static pressure. By stacking two of the same type of fans together, in the same direction, will it maintain the cfm but increase the static pressure to ~2x?
  17. M

    B How long will it take to reach 1000ppm CO2 from 2000ppm

    would this be a quadradic equation since its dealing with half life? I think in 500/50 = 10 minutes, the fan would have brought 500 CF of fresh air, but the out fan would have been taking out the same amount of air which includes the fresh air, so at 10 minutes, it should have less then half the...
  18. M

    Air to Air heat exchanger

    Assuming the above ERV has 50 CFM, I calculated 95% efficiency. inside: 77.5 outside: 105 supply: 79 exhaust: 96 x = 97.2 = 1.8 deg F / deg C * 50 CFM * 0.018 BTU / ft^3 / deg F * 60 min/hr 77.5-105 * x = 2,673 BTU/H (supply - outside) 79-105 * x = 2527 BTU/H 2527/2,673 = .95 I think I...
  19. M

    Air to Air heat exchanger

    Yes i just looked into adopting an already made HRV like that, and its a really good option. I am trying to see how efficient they are but I haven't had much luck trying to find data on it. I then also came across ERV's which would actually even be better for the campervan since humidity is big...
  20. M

    Air to Air heat exchanger

    Also if material doesnt matter, then would 3d printing an exchanger with a much larger surface area and "nuances" to break up the air film be a much better approach? I also found there are thermal conductive filaments e.g. GRAFYLON 3D and TCPOLY I think this is the way to go, now I just need...
  21. M

    Air to Air heat exchanger

    Is it related to the Thermal boundary layer? So would some aluminum fins attached radially around the outside and inside of the inner pipe, which would cause the air to vortex, improve this, by breaking up this film/layer? Or am I misunderstanding this.
  22. M

    Air to Air heat exchanger

    Thank you for that jrmichler! 40% is not that great :( What is the air film (didn't find much on it online), and how could I improve it?
  23. M

    Air to Air heat exchanger

    I built a basic counter flow prototype. It was a warmer day today so I didn't get to test it in negative temperatures ( I will over the next few days). It is a 3"x8' flexible aluminum tube, inside a 4"x8' pvc pipe. using two fans. one fan sucking from out to in, and another fan sucking from in...
  24. M

    Calculating air flow through a tube

    I understand the Friction Head Loss in Air Ducts - Online Calculator provided .0979 with those parameters, and so i see how you got 0.1, but i dont understand where you got the 0.9 from. I dont understand the size reduction at the begging part you mentioned. I also tried looking up velocity...
  25. M

    Air to Air heat exchanger

    not sure what an economizer is. Yes the reason for exhausting the warm air is to make room for fresh outside air (co2 being the main concern). the source of heat is a 5kw diesel heater. it has a powerful fan (for the space), and i have some aux fans (high static pressure) ill be using. which...
  26. M

    Air to Air heat exchanger

    Came across this: https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node131.html would "18.5.2 General Counterflow Heat Exchanger" give me what i need?
  27. M

    Air to Air heat exchanger

    75% would be great, but is there any hint that it would be around that? is there a way to do some educated guess at that? And i did seal it as best i could with sprayfoam and foam panels. I have a co2 sensor in there. It can maintain the co2 level for days if i don't open a vent. Here is a...
  28. M

    Air to Air heat exchanger

    Removing heat is not the objective, but a consequence of removing co2, which im trying to mitigate through an exchanger.
  29. M

    Air to Air heat exchanger

    I am considering building this type of heat exchanger, as I have seen several youtube videos on the build. The inside tube is aluminum, I am planning on building one from the top of my roof to nearly the floor, so ill say 5 feet. I am thinking of using a 1.5" inch aluminum tube, and bringing in...
  30. M

    Calculating the coldest outside temperature my campervan can be in and still be warm inside

    Yep thats what i was thinking also. So maybe something for later. thanks!
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