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Soliciting advice on a "Smart" fan to move conditioned air through both sides of basement.


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Adding the extra ductwork to the street side basement to mitigate high freeze risk areas has worked well (see Cold temperature data thread), but it is dependent on propane and the furnace.  I still want an all-electric backup to the furnace solution where cabin air warmed by a space heater could be moved around the ducts in the basement to accomplish the same thing.  In addition to having a backup to the furnace I hope I never need while camping, the main reason I want this type of solution is to be able to use all electricity rather than propane/electricity to keep everything above freezing while my trailer is in "semi-hibernation".

I'm toying with the idea of using a 4" smart duct fan (or 2) like this (https://terra-bloom.com/collections/ec-inline-duct-fans-speed-adjustable-pwm-0-10v-wireless-controls) to pull conditioned air from the cabin.  This particular fan has a wireless speed controller and can also be paired with a programmable thermostat.  It uses technology that enables it to move 160 CFM using only 18 watts (120V). 

As a bonus, this solution could also be used in the summer to move cooled cabin air around in the basement if needed (cooling street-side electronics and the battery bay for example)!

I have 3 primary options and maybe some folks will chime in with thoughts to help me decide which would work best (or maybe not at all).  Right now I think these are in order of expense, with the cheapest first and the most expensive last.

1.  1 fan on the STREET SIDE ONLY with a new vent tied directly into the existing 4" ducts using an airflow damper.  Efficient for the cabin as the ducts will restrict the amount of air exchange.  Only requires one new hole.  Will enough conditioned air make it to the curb side?

2.  1 fan on EACH side, each with a new vent, but NOT tied into the ductwork.  This would just "flood" the basement(s) with conditioned air.  Flexibility to run one or both fans.  This may be overkill as we don't necessarily need all of the basement air to be mixed into the cabin air.  Also requires 2 new holes in the cabin.

3.  1 fan on each side, both tied into the existing ductwork.  Flexibility to run one or both fans (only need the street side in the summer).  More efficient for the cabin as it restricts and focuses the air exchange.  

Thoughts?

 

John and Anita

2020 Oliver Elite II, Hull 688

Tow Vehicle:  2006 Silverado 2500HD Crew Cab.  6.6L Duramax

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I think this could be a very cool solution (pun intended) for when you are on shore power. I actually don’t think it needs to be inside a furnace duct at all. The spaces under the floor are all essentially tied together by the huge gaps at the front and rear of the water tanks. You already have a great big air inlet at the curb side, for the furnace air. How about this....?

Mount your fan under the front dinette seat, if you can tolerate a loss of storage, or alternately under the rear one (use plastic ductwork because of the high voltage there). Leave its intake wide open and duct the outlet air into the cabin through a 4” hole cutout.  

Put your space heater on the floor in the middle, facing backwards. Warm air will tend to pool near the back and will get sucked into the furnace grill. It will then flow all around the basement, through your new fan and out the front grill. No dampers needed. It might be fine with the furnace running (the suction could disrupt air entering the furnace box), but OTH I don’t think it would at all be needed when you are heating with propane.

In summer it will suck out the hot air from under the floor and cabinets and provide some extra cabin air circulation, as you commented.

I do think you should add holes in your battery box for the lithium battery area to ventilate. It consists of two closed and nested cubes and traps heat if the door vents are sealed.

I don’t think you need nearly as much as 160 cfm for heating, but in summer it would provide a nice blast of air. Research “bilge blower” in some power boat forums for some ideas, that is what essentially you are building. Look at 4” marine blower fans, I am not sure what is available in 120 volts AC, maybe there are some.

Good luck.

John Davies

Spokane WA
 

 

 

Edited by John E Davies
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"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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John, I did basically the same thing you’re thinking a couple of years ago. I took two low amperage 12 volt computer fans and mounted them to the inside of the furnace return grill. Now that I have removed the problematic propane fridge, I use the fridge fan switch by the entry door to operate these fans. I don’t use a thermostat but just turn them on and let them run. They are able to take the conditioned cabin air and force it into the basement. Not a lot of flow but I can feel a slight bit leaking thru the converter grill under the dinette. A higher capacity fan(s) would be great but I would be careful not to have so much that you run the risk of activating the furnace sail switch. 

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3 hours ago, John E Davies said:

In summer it will suck out the hot air from under the floor and cabinets and provide some extra cabin air circulation, as you commented.

I do think you should add holes in your battery box for the lithium battery area to ventilate. It consists of two closed and nested cubes and traps heat if the door vents are sealed.

Good luck.

John Davies

Spokane WA
 

 

 

While the battery blanket solves the problem of warming lithium batteries in freezing temperatures, a recent post brought up the question of how to keep the batteries cool in extreme heat.  

So, you are saying that running a fan in the cabin will circulate cool air below.  Will this be enough to keep the battery compartment cool?  Unless outdoor temps are above 90 degrees, is overheating the batteries a problem, or can the heat inside the hull exceed the outdoor temperature?  With average daily temps in the 40's in our PNW, it will be several months before we can determine whether overheating of the batteries is a problem in our case.

Regarding holes in the battery box, are you referring to adding holes in addition to the four already present in the battery compartment hatch, like holes allowing air to enter the battery box from inside the cabin?  If a fan is the solution, it would be nice if it were thermostatically controlled.  Could this somehow be connected with the heat blanket thermostat that monitors the internal temperature of the lithium battery: battery temp drops below 35 degrees, heat blanket turns on; battery temp exceeds upper threshold, fan engages?  

I know either the Xantrex Pro 3000w or the power converter/charger (I'm not real clear on the components of the power system) already has a fan, as we hear it running when we first connect to shore power. 

More possibilities to ponder.

 

Ray and Susan Huff

Elite II Twin "Pearl" - Hull#699; delivered December 7, 2020

2013 F350 3.2l diesel Super Duty 4x4 long bed crew cab

2017 Leisure Travel Van Unity Twin Bed (sold)

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3 hours ago, John E Davies said:

I think this could be a very cool solution (pun intended) for when you are on shore power. I actually don’t think it needs to be inside a furnace duct at all. The spaces under the floor are all essentially tied together by the huge gaps at the front and rear of the water tanks. You already have a great big air inlet at the curb side, for the furnace air. How about this....?

Mount your fan under the front dinette seat, if you can tolerate a loss of storage, or alternately under the rear one (use plastic ductwork because of the high voltage there). Leave its intake wide open and duct the outlet air into the cabin through a 4” hole cutout.  

Put your space heater on the floor in the middle, facing backwards. Warm air will tend to pool near the back and will get sucked into the furnace grill. It will then flow all around the basement, through your new fan and out the front grill. No dampers needed. It might be fine with the furnace running (the suction could disrupt air entering the furnace box), but OTH I don’t think it would at all be needed when you are heating with propane.

In summer it will suck out the hot air from under the floor and cabinets and provide some extra cabin air circulation, as you commented.

I do think you should add holes in your battery box for the lithium battery area to ventilate. It consists of two closed and nested cubes and traps heat if the door vents are sealed.

I don’t think you need nearly as much as 160 cfm for heating, but in summer it would provide a nice blast of air. Research “bilge blower” in some power boat forums for some ideas, that is what essentially you are building. Look at 4” marine blower fans, I am not sure what is available in 120 volts AC, maybe there are some.

Good luck.

John Davies

Spokane WA
 

 

 

Thanks! Great idea to give a try!  I can test how this works with a fan mounted on a piece of plywood that fits over the access hatch under the dinette seat.  I'll set it up and see how it moves the temps around the basement.  If there are still some dead areas that stay cold I may be forced to use the ducts as I have those set up and targeted specifically at the problem areas.  The entire basement really needs some heat all around as the plumbing wraps around 3/4 of the trailer.

The battery compartment is staying surprisingly warm and looks like it won't need any venting specifically for heat.  I have the Oliver provided heat pad in there anyhow as a last resort.  Trying to keep the battery compartment cool(er) is a different problem than trying to keep all of the basement plumbing from freezing.  I may be able to leverage some of this work I'm doing on the heat, but I don't necessarily have to.  I'm going to wait and see how hot it gets in that compartment - I'm in NC and I won't have to wait long for some steamy temps - then I'll figure something out.  You should have some great data on your venting project by then too!

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John and Anita

2020 Oliver Elite II, Hull 688

Tow Vehicle:  2006 Silverado 2500HD Crew Cab.  6.6L Duramax

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Well, I gave JED's idea a try and the results were "mixed".  I used a 400 CFM inline fan mounted on a piece of plywood that fit over the dinette seat hatch.  I ran the fan for 10 minutes once per hour and monitored my temp sensors around the Ollie.  In general, the cabin temp dropped dramatically and the humidity came up just as dramatically.  The cabin dropped about 8 degrees each time I ran the fan and the humidity came up about 25% each time as well (expected as temps go down).  In addition, the basement temps came up (dramatically) in the curb side basement (warm air was being pulled in) and the front street (where the fan was pulling from).  The rest of the basement didn't budge much though (the other two corners) and the bathroom vanity actually got a few degrees colder each time I ran the fan.  I suspect if I kept running the fan longer, eventually the basement and cabin air would equalize.  I'm not really keen on making the basement and cabin the same temp though (super inefficient for the cabin) - just keeping the basement above freezing.

Bottom line is there's a LOT of cold, humid air in the basement and mixing it around with a big fan doesn't accomplish what I'm after and mitigate "cold" spots in the basement.  Furthermore, it significantly brings the cabin temp way down and the humidity way up.

So...  back to the drawing board.  I'm going to test running some cabin air through the ducts now to see if the "targeted" approach works at all.  This may not work well at all if the cabin isn't 90 degrees first!  There may not be a feasible way to keep the trailer safe in freezing temps with electric only.  😞

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John and Anita

2020 Oliver Elite II, Hull 688

Tow Vehicle:  2006 Silverado 2500HD Crew Cab.  6.6L Duramax

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Interesting. Did you have the warm duct air running into the basement at the same time as the fans? Do you think that the moist air in the basement can be “drier” if the temperature is increased by the air from the ductwork?

if the object is to keep pipes from freezing using electricity, it might be worth trying running an extension cord with a clamp light equipped with a 150w bulb into the basement.. 

There are crawl spaces under old houses  throughout Maine that use that technique to prevent pipes from freezing.. might help an Ollie in NC🙂

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Mark & Deb..2020 Elite II..Dearie..Hull #685..2016 Tundra

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2 hours ago, NCeagle said:

Well, I gave JED's idea a try and the results were "mixed".  I used a 400 CFM inline fan mounted on a piece of plywood that fit over the dinette seat hatch.  😞

Interesting test, but I suspect your results may be due to your choice of fan. 400 cfm is a whole lot of air. My medium Vornado portable is about 300 cfm. Their large model for a 100 ft wide room is 500. In summer that might work great for making a breeze in the cabin, but for heating, a low flow will work better. Can you repeat your experiment with a much much smaller fan running all day? I don’t know enough about the physics to be able to predict the results, but I do know that plastic (your water lines and tanks) is a really poor heat conductor. Blowing high velocity air across them for a short time will not do much to raise their temperature. Here is an interesting article. 

https://sciencing.com/drink-metal-can-plastic-bottle-5518851.html

Your water filled fresh tank is a VAST reservoir of heat. It takes a long time to adjust its temperature, and it tends to hold onto that heat. I wonder if an in-tank electric water heater could help with maintaining the under floor temp in winter. A regular RV tank heating pad located under the tank would do the same, but the Ollie design doesn’t allow for that. An automotive engine block heater with built in circulator pump would probably be excellent, if you could find one that worked at a lower temperature. Most car units run hot enough to damage pex tubing.

An Alde hydronic heating system  would be 100% perfect for this! Just add a little radiator coil wherever it is needed. Unfortunately you can’t buy a kit, it is for OEM builders only. I did check😢 I would love to be able to retrofit one in my Ollie. With the double wall hull it should work magnificently (and completely silently), but you would have to drill a whole bunch of holes for air circulation.

I am pretty sure that heating the water inside  the fresh tank to say 40 degrees F would work, but engineering a safe, reliable, affordable system may be a real hassle. Try the small fan, running all day, to see if that might work OK. The computer fan I am mounting under the batteries is 35 cfm (12 vdc, 70 milliamps) and I will probably just let it run all the time when it is needed. It comes with two inline resistor cables to drop rpm if needed. Good luck.

John Davies

Spokane WA

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Edited by John E Davies
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"Mouse":  2017 Legacy Elite II NARV (Not An RV) Two Beds, Hull Number 218, See my HOW TO threads: https://olivertraveltrailers.com/topic/john-e-davies-how-to-threads-and-tech-articles-links/

Tow Vehicle: 2013 Land Cruiser 200, 33" LT tires, airbags.

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42 minutes ago, Mcb said:

Interesting. Did you have the warm duct air running into the basement at the same time as the fans? Do you think that the moist air in the basement can be “drier” if the temperature is increased by the air from the ductwork?

if the object is to keep pipes from freezing using electricity, it might be worth trying running an extension cord with a clamp light equipped with a 150w bulb into the basement.. 

There are crawl spaces under old houses  throughout Maine that use that technique to prevent pipes from freezing.. might help an Ollie in NC🙂

Hi Mcb, no - this was a strictly an all electric test to see how effective it would be at keeping the pipes from freezing.  I used just a space heater to warm the cabin air and then the big fan to do this "blast" test.  I suspect JD is correct in saying that a fan running on low constantly would be a better test, but my goal is not to heat the entire basement - just the highest risk areas of the plumbing. 

Everything I'm trying is non-intrusive so far.  Easy to test since I have the sensors set up and happened to have a fan I could try.  I've been thinking low watt heat strips would be the best (similar to the light bulb approach), but I haven't gotten access to all the plumbing yet (some tough spots left).  Blowing out the lines and putting some antifreeze in them is always an option too. 😃

John and Anita

2020 Oliver Elite II, Hull 688

Tow Vehicle:  2006 Silverado 2500HD Crew Cab.  6.6L Duramax

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53 minutes ago, John E Davies said:

Can you repeat your experiment with a much much smaller fan running all day?

Hey John, If I come up with a way to test a low velocity approach I'll do it, but I don't have a low velocity fan at the moment.  I do agree that low velocity kept on or run longer should work better. 🤔  I'll try a similar test (with the same fan) using the ductwork as that's not hard to do either, but my guess is that's not going to be effective at moving the temps that much either - just good to have a comparison.   

Ultimately, as @Mcb alluded to with the light bulb approach, heat strips might be the optimal way to solve this particular problem but I will have to take my time with that as it's more involved than these simple air/fan tests.  Working with electricity is nowhere near as fun for me!

Thanks again for the suggestions.  I'm having a blast (pun intended) trying this stuff!

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John and Anita

2020 Oliver Elite II, Hull 688

Tow Vehicle:  2006 Silverado 2500HD Crew Cab.  6.6L Duramax

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I would suggest making it as simple as possible and based on 12V with three temp sensors, one each in both basement sides as well as the coach.

Using an Adruino unit or Raspberry pi one could program the device to turn each side on/off independently when the basement temps are either high or low and the coach temp is in a beneficial range.

An automated control could be done with < 3watts when idle and 5-10 watts when all of the fans are running.

 

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