Mechanical Ventilation Heat Recovery

[Rory_Heath]

Hello everyone. This would have links in it but I’m a new user!

I’m in the planning stages and am considering ventilation options.

I’m planning to have wet things in the van often - wetsuits, mountain bikes, wet boots etc.

Ventilation is certainly an important system to get right to prevent condensation and mould from these damp items - but I also don’t want to waste heat or have stale air hanging around.

I have learned that ‘passive houses’ use Mechanical Ventilation Heat Recovery (MVHR) systems. They feed in fresh air from the outside and run it in a countercurrent direction against outgoing warm internal air to allow heat exchange. e.g passivedesign .org/ mvhr

There are big units for houses and smaller units for bathrooms, the latter likely the best bet for a van.

The smaller units could have the external vents through the side of the van, the main MVHR sitting in cabinetry and ducting hoses positioned to have a vent near the cooking area and in the garage. Paired with an electric heater (ebay 2-2kw-Micro-Heater-12v-Vehicle-Marine-Boat-Van-Camper-Race-Rally-Kit-Car ) to circulate hot air around, I hope to have a system that provides and recycles hot air.

My intended van is a L2H1 Trafic.

Has anyone considered using MVHR/ implemented it into the van/ have any tips (for and against!)

Expensive waste of time? Large problem I have overlooked? Better options?

Thanks!

[Axel]

You might be overthinking it.

Vent fan for the summer, and a heater with the intake and exhaust isolated from the interior for the winter (dry heat).

I use a solid fuel heater for winter, and in summer a couple small vent fans in the roof to draw the stale/hot air out of the van.

Trying to heat or cool with battery power, aside from fans, is a huge drain on battery resources. You either have to have a very big battery bank with a very big way to charge it (expensive), or be connected to shore power all the time (limits your freedom).

[Van_Dweller]

Greetings & Welcome!

My van has windows all the way around, that I don’t insulate & my van has absolutely no added insulation, yet it still holds the heat very well. No recovery methods needed in the summer either.

I’ve seen home built systems attempting what you’re suggesting, but I can’t justify the time or expense for myself.

Cheers!

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"Be the reason someone smiles today!" ~ Van_Dweller

[Fabricator]

The answer is yes to the OP’s question, I’ve thought, and even done something about it. (was looking for somewhere to post. Coincidenty also even have a L2H1 Trafic van).

I got to thinking the same way about ventilation. It seems most people take for granted burning whatever fuel is necessary to keep things warm in the winter (house or van), including heating all the fresh air. Obviously good insulation is a first step, but once you’ve got all that nice warmth penned up inside your space, whats the point in pumping it straight out and replacing with stock cold air? (And theoretically the reverse in summer if you have air con working, even if fresh air is often good enough). With such small inhabited spaces, good ventilation is critical, and the decent flow of air necessary for this, equals a lot of potential energy loss.

I was also given a kerosene heater as well, which tends to smell a bit, can be cooked on as well, and requires a good oxygen supply, so that helped spur me to come up with a more efficient ventilation system. A heat exhanger seemed the way to go.

To cut a long story short, (my mind went through various design implementations, trying minimise the impact on available space, but keep it still easy enough to build), I ended up with a design using a single 70mm hole through the lower rear corner panel of the van, behind the corner plastic bumper trim. I mean, why make a hole in the roof? The drawbacks to a roof chimney are added vehicle height- risk of getting hit by low things, wind and rain ingress, and in this case the impossibility of fitting the exchanger duct discreetly along the top edge panel pressings. The system is going to have to be fan driven anyway so a traditional convection chimney is not relevant. The stale air can be ‘pumped’ down out of the bottom, through the one hole, just far enough away from the intake to avoid mixing.

The principle is pretty simple: Counter flowing air ducts with a common, thermally conductive skin between. There are lots of ways to implement this, but simplicity is key! For me, I ended up with some ~40mm flexible aluminium ducting, centered inside a 68mm PVC rain pipe running about 1.5 metres together. The design is dependent on the configuration of the vehicle/space. You need to locate the interior inlet/exhaust vents in places which you can most easily run the ducting to/from, bearing in mind that they both have to run through the common heat exchange section. You’d typically want the exhaust vent up near the ceiling, and the inlet nearer to the floor.

Here’s a picture of the result before fitting:

(As a newbie I’m only allowed to post one photo. Will wait for responses…)

[Van_Dweller]

Greetings!

Many step vans have closable side vents strategically placed both high and low, and capable of opening facing either forward or back. These options work well for either hot or cold weather, moving or parked, and require no power.

Cheers!

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"Beat Murphy's Law with a KISS! (Keep It Stupidly Simple)" ~ Van_Dweller

[Rory_Heath]

@Fabricator
Thanks very much for your reply!
Happy to see that this has been done, and without having to buy a MVHR designed for bathrooms!

Would like to see more photos - how did you split the air entry and exhaust?
Where does the heating element lie in your circuit?
Did you vent the bumper as well?

Cheers

[Fabricator]

Heres another photo: (…)

I chose the size of pipe(s) so it would fit between the inner and outer skin of the van. First made a strategic ~90 degree slow bend over the wheel arch in some rigid PVC rain pipe (using the hot sand (and blowtorch) technique, not too difficult really). Then after cutting the 70mm hole in the van corner panel, I positioned and trimmed the PVC to size. WHen I was happy it would all work ok, I proceeded with the exchanger…

[Fabricator]

@Rory_Heath I didnt make any holes in bumper, the end is just cable tied up to the chassis. You could maybe put some mesh around the inlet as a simple bug filter. I havent so far, but nothing much is going to get in upwards I think.

Will post a picture (eventually…) of the elbow I used to separate piped at the interior end. Exterior as you can seen is just as the pipes end.

[Fabricator]

There’s no heating element with this design (I just use a kerosene heater internally ) . Its true, there are such things as water air heat exchangers, which can be used for heating etc, but the point of this is to provide fresh air, without too much heat loss.

This is the elbow joint I used to separate the inlet from the outlet inside the van. And just put a bit of silicone arount the hole drilled through it at around 45 degrees.

(To be honest, my aluminium ducting could be a bit smalller, to give a more equal cross sectional area each way. I ended up with 45mm I/D, whereas 40mm would be better, shouldn’t make too much difference though)

[TangerineVanGreece]

Hi guys, great stuff, I’m also going to be loading wet downhill bike and snowboard gear in the van. I have a small propane heater, thought of the kerosene one you can also cook with, is it called the Buddy Heater? I only have a vent in the upper back corner of the van, it was there when I got it so went with that. I was originally only going to put a small bathroom style motorized fan on it to drive stale air out. The van has a vent on its own down on the step of the side door and I have also seen people just crack a driver or passenger window open for intake. I have insulated the heck out of the van (armaflex rubber, aluminum and mineral wool, plus the plywood but I like the idea of no heat loss. If you put the system to work let us know how it did.

Cheers!

[Van_Dweller]

Greetings & Welcome!

In the winter, I keep all the upper vents closed, and only the foot well ones open. In the summer I also open the top vents for automatic, electricity free cooling/ventilation.

Cheers!

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"God bless the nomads, all of us!" ~ Nature Lover

[Trevor_Potter]

I use a 4" vent in the floor right behind the driver seat which naturally draws air from the cooler underside of the van and it moves through the van to exhaust out the roof fan at the back. For heat and cold ventilation I use a Propex heater that is ducted to the center of the van and can produce heated or unheated air

[Aldous]

Thanks for posting this, a very interesting idea. Are you pumping air out via an internal fan in the inner ducting?

I’ve just installed environmental sensors in my van and it has brought it home to me how important ventilation is!

I’d be interested to see the temperature of incoming air vs internal and external air temps.

[Fabricator]

Yes, I used a small centrifugal fan on the ceiling plus another one down near the floor on the inlet. All the pipe work was fitted behind the panelling, and insulated where appropriate and possible. Here is one another picture: (as a newbie I can still only post one at a time)

This photo shows the heat exchanger in position. The inner tube was extended up to the ceiling in the end with some 30mm corrugated plastic hose, and the outer was extended with another bit of pipe and elbow to a floor level entrance.

Results:
Not as good as I was hoping for although it basically worked. I made a blurry video of a test I did on a cold night (-0.6C) with the heater on inside the van providing 40C at the ceiling outlet. The inlet air temperature was about 17C. So the difference between inlet and outlet was still about 23C.

Conclusions:
Does work, but takes a fair bit of effort. Some thought required for the layout of the exchanger section and connecting pipes. I was trying to think of a way to increase the surface area of the exchanger using these tubes, but not that easy. The exchanger section is basically too short. I think maybe various other types of cross flow, box designs might be better, if you can make them fit. It should theoretically be possible to achieve high efficiencies of say 90% recovery…

[Fabricator]

This is how I centred the inner pipe inside the outer, using ‘castellated’ bent, springy wire wrapped helically around the inner foil pipe, prior to inserting it all into the black pipe. This went quite well. I thought it would get stuck etc but not really, and came out nice and centred. As I said before, the inner pipe should have been 5mm or so smaller diameter, although I think there still isn’t really enough heat transfer area with this design.