Heat Recovery Ventilators

[IdaSHO]

Isn't that exactly what the ventilator is for? I mean... you can open all the windows and crank up the exhaust fan, and that would surely take care of the moisture problem...? But then you'd have a heat problem. The heat exchanger warms the incoming air so you can be warm and dry at the same time. Seems like it should be a common item.

Read my previous post. Again, its not a heat issue. Though you could split hairs about efficiency all day.
In my book the amount of heat you are loosing, and the little amount of heat needed to replace it is so small
that adding complexity, cost, and weight of a fancy setup simply isn't justified.

In most instances, the overall volume of a true 4-season camper is so small that when you add occupants, you need VERY little heat to maintain comfortable temps.
So little that, with two adults and a doggo or two in -20 degree weather with a tiny gravity fed 6kBTU furnace we still have windows cracked, all the while easily maintaining 65 degrees.

 

[yamaha225]

I thought I would chime in on this thread since I have a bit of real world experience with HRV’s and specifically ones made by Lunos. While I haven’t yet put one in a camper, my partner and I use the Lunos E2 system in the tiny house we built and live in full time.

The house is 32’ x 8’ or about 256 square feet. We have one pair of the E2 HRV fans. One is at each end of the house. The E2 work in tandem and switch direction every 50 seconds. So one will pull inside air out for 50 seconds while the other pulls outside air in. Then they switch. As a result you always have one pulling air in and one pulling air out. In the winter the core in the unit is heated while it pulls inside air out, and it then transfers that heat to the outside air when it pulls it in. Then the opposite is true in the summer.

We have the short version which has slightly lower efficiency at 83% heat recovery, but works in a thinner wall. I don’t have a lot of specific real world numbers, but I may start trying to gather some. I just took a quick reading while one of the units was pulling air in to see what the temp was. At about 30F outside, I saw about 65 degrees at the start of the pull down to about 57 at the end of the pull. That’s with an inside air temp of about 68 degrees.

For reference we live in Maine and see down to -20F on occasion in the winter. If the temp gets below -10F Lunos recommends that you turn the fan speed down to low, which we do and we have never had any issue with them or with frost build up. We’ve been in the house almost 2 and a half years and they have run steady without issue. If memory serves they have a 10 year warranty.

We built the house extremely airtight for energy efficiency, so the air exchange is crucial for humidity control and air quality. There are numerous accounts of moisture problems with tiny homes, especially in cold climates and we have had none. With the lunos on we never have any condensation build up, even on the insides of the windows. However, I have tried turning them off and the windows get condensation buildup very quickly in the winter. Especially after showers or cooking. We do have an exhaust fan as well that we run during those times to pull moist air out quicker.

While I see your point about the complexity Idasho, it’s a pretty simple system (the Lunos ego) is even simpler) and I think the energy recovery is worth it. I do see that in a smaller camper, that you’re spending less time in, it isn’t as necessary but the thought of keeping a window cracked at -10F is less than appealing.

If anyone has any questions about the system, I’d be happy to answer them. 475 High Performance Building Supply is where we got ours. They are very helpful and a fantastic resource for stuff like this.

 

[Trail Talk]

Thanks for sharing your real world experience 👍

 

[yamaha225]

Happy to!

 

[simple]

I thought I would chime in on this thread since I have a bit of real world experience with HRV’s and specifically ones made by Lunos. While I haven’t yet put one in a camper, my partner and I use the Lunos E2 system in the tiny house we built and live in full time.

The house is 32’ x 8’ or about 256 square feet. We have one pair of the E2 HRV fans. One is at each end of the house. The E2 work in tandem and switch direction every 50 seconds. So one will pull inside air out for 50 seconds while the other pulls outside air in. Then they switch. As a result you always have one pulling air in and one pulling air out. In the winter the core in the unit is heated while it pulls inside air out, and it then transfers that heat to the outside air when it pulls it in. Then the opposite is true in the summer.

We have the short version which has slightly lower efficiency at 83% heat recovery, but works in a thinner wall. I don’t have a lot of specific real world numbers, but I may start trying to gather some. I just took a quick reading while one of the units was pulling air in to see what the temp was. At about 30F outside, I saw about 65 degrees at the start of the pull down to about 57 at the end of the pull. That’s with an inside air temp of about 68 degrees.

For reference we live in Maine and see down to -20F on occasion in the winter. If the temp gets below -10F Lunos recommends that you turn the fan speed down to low, which we do and we have never had any issue with them or with frost build up. We’ve been in the house almost 2 and a half years and they have run steady without issue. If memory serves they have a 10 year warranty.

We built the house extremely airtight for energy efficiency, so the air exchange is crucial for humidity control and air quality. There are numerous accounts of moisture problems with tiny homes, especially in cold climates and we have had none. With the lunos on we never have any condensation build up, even on the insides of the windows. However, I have tried turning them off and the windows get condensation buildup very quickly in the winter. Especially after showers or cooking. We do have an exhaust fan as well that we run during those times to pull moist air out quicker.

While I see your point about the complexity Idasho, it’s a pretty simple system (the Lunos ego) is even simpler) and I think the energy recovery is worth it. I do see that in a smaller camper, that you’re spending less time in, it isn’t as necessary but the thought of keeping a window cracked at -10F is less than appealing.

If anyone has any questions about the system, I’d be happy to answer them. 475 High Performance Building Supply is where we got ours. They are very helpful and a fantastic resource for stuff like this.

That's interesting that you are pulsing them rather than running continuous. How did you come up with that idea?

 

[Buddha.]

That's interesting that you are pulsing them rather than running continuous. How did you come up with that idea?

I think they work that way, in/out cycles. It’s how it transfers the heat through the heat sink part.

 

[IdaSHO]

We built the house extremely airtight for energy efficiency, so the air exchange is crucial for humidity control and air quality. There are numerous accounts of moisture problems with tiny homes, especially in cold climates and we have had none. With the lunos on we never have any condensation build up, even on the insides of the windows. However, I have tried turning them off and the windows get condensation buildup very quickly in the winter. Especially after showers or cooking. We do have an exhaust fan as well that we run during those times to pull moist air out quicker.

As I have said, and exactly why I will hold my stance on these units in campers.
Its a moisture issue, NOT a heat issue.

And all this speak about "real world" and your assumption that leaving a window cracked in cold temps is the end of the world...
We do it all the time. And I can assure you, its not the end of the world.

One window cracked back of the camper, one cracked in the overhead.
The moment that air enters the back window it is diluted by already heated air. 6" from the window you can hardly feel it. Further, nothing at all.
Window in the overhead is exhausting warm air, so no cool air entering. Its not rocket science.

As mentioned, these units do have their place in "tight" homes.
Its well know that "tight" homes introduce a pile of both health and structural problems that require units like this.
I know, I've been in residential and commercial construction in one form or another for 30+ years. You know, real world.

 

[yamaha225]

As I have said, and exactly why I will hold my stance on these units in campers.
Its a moisture issue, NOT a heat issue.

And all this speak about "real world" and your assumption that leaving a window cracked in cold temps is the end of the world...
We do it all the time. And I can assure you, its not the end of the world.

One window cracked back of the camper, one cracked in the overhead.
The moment that air enters the back window it is diluted by already heated air. 6" from the window you can hardly feel it. Further, nothing at all.
Window in the overhead is exhausting warm air, so no cool air entering. Its not rocket science.

As mentioned, these units do have their place in "tight" homes.
Its well know that "tight" homes introduce a pile of both health and structural problems that require units like this.
I know, I've been in residential and commercial construction in one form or another for 30+ years. You know, real world.

I understand your perspective. I just thought I’d offer my experience since I’ve lived with the units in question for a couple of years. Ultimately folks have varying degrees of appetite for complexity in their campers.

I’m frankly not sure if we’ll put an HRV in our camper when we get around to building it, but we’re certainly considering it. I do get your point about the heat loss not being a big deal in a small space. Due to the size of our house, you could make the same argument, but I’ve tried having a window open when it’s 20F out and it sucks. If you’re anywhere near it you can feel the cold air coming in. Maybe it would be different in a camper with the furnace running, since it’s even smaller, but I still think I’d prefer the HRV.

I’ve looked through a lot of your build information Idasho and have gained a ton from it. We’ll likely be using some of your construction techniques when we build our camper. It has clearly worked well for you and held up awesome. I’ll also be doing something similar to your 3-point bed mounting system. I have a lot of respect for your experience, but there are also multiple ways to do things and different folks have different tolerances for complexity and cost and different priorities with their rig.

 

[yamaha225]

I think they work that way, in/out cycles. It’s how it transfers the heat through the heat sink part.

Yes, you’re correct. We use the Lunos E2 system which would be a little harder to package in a camper, but totally possible. The unit has a heat sink and a fan inside of a tube. In the winter, the fan pulls inside air out for 50 seconds, which heats the core up. Then the fan reverses pulling outside air in for 50 seconds, using the stored heat to warm the cold outside air. The two units work in tandem with one always pulling out and one always pulling in.

This is a little different than the Lunos EGO unit that was referenced earlier. That is one unit with two fans that accomplishes the same thing.

Conventional HRVs in larger houses typically have one fan that always pulls out and one that pulls in. Inside the unit the air streams are crossed, transferring the energy from one air stream to the other.

Basically the goal is to heat the incoming cold outside air with the warm inside air that’s being exhausted. That’s obviously in the winter. The energy transfer is opposite in the summer and transfers cold air conditioned air to warm incoming outside air.

 

[Trail Talk]

Looking at the Lunos website there is a single unit, the Ego, with split intake and exhaust that might be worth considering for campers. A short version requires 200mm depth space.

Edit: it was the Ego that Victorian installed in a Total Composites build

 

[IdaSHO]

I understand your perspective. I just thought I’d offer my experience since I’ve lived with the units in question for a couple of years. Ultimately folks have varying degrees of appetite for complexity in their campers.

No worries! And to be clear, I do feel like there is benefit to such a device, regardless of cabin/home size.
However, IMO there is a serious question of justification. And I simply do not see the justification, considering the drawbacks.

Cost and cost of install
Complexity
More weight
Needs power (must add battery to compensate... more weight)

If you can justify all of that, instead of just cracking windows, by all means.
Ill continue to keep things simple, light, and efficient.

 

[dstefan]

keep things simple, light, and efficient

This ↑↑ !!

I also live in the photography world, which is what led to off-road and overlanding a long time ago. There’s a serious disease rampant there called GAS (Gear Aqcuisition Syndrome), which I contracted years ago — don’t ask me how many heavy, expensive lenses I have, that I rarely use!

I’m pretty sure the overlanding world is experiencing an epidemic of GAS too, as well as its related disease — TMF (Too Many Farkles). 😁

I’m certainly as prone to both as the next person, but it’s sure worth the reminder to"Make everything as simple as possible, but not simpler” as Einstein supposedly once said.

Rant off. Back to our regularly scheduled programming . . .

 

[Trail Talk]

By now the Transglobal Car Expedition is becoming well known to overlanding enthusiasts: Transglobal Car Expedition. I've been following the build of their 2nd Total Composites cabin (the 1st cabin was built to support the 2022 Pole To Pole EV expedition as preparation for this main event) by Off Grid Customs. It appears they are incorporating an HRV into the build, specifically the Lunos Ego two-way unit. I've reached out to OGC for confirmation and will update here if details are forthcoming. I sure hope so as we can all learn from their experience with HRV in this extreme RV application.




Three Ford F350 6x6 conversions by Arctic Trucks will carry the team from Yellowknife NWT up to Cambridge Bay Nunavut before switching to Yemelya amphibious vehicles for the Arctic Ocean ice crossing enroute to the geographic North Pole. Two will carry cabins and one flat deck will transport the spares.

 

[IdaSHO]

Definitely interesting, though pretty far removed from essentially near any camper built on this forum, let alone the typical camper usage.
For the given use-case though, Id say it should be worthwhile from a simple fuel efficiency standpoint.
Though time will tell as it is obviously completely untested at this point.

We use ours in cold temps more than most on the forum, with the coldest as I recall being -24 degrees F.
As I was digging for a photo for another thread I found this example...

Then I noticed the open window in the cabover

 

[Trail Talk]

We use ours in cold temps more than most on the forum

Same here Our lowest temps experienced with this camper has been -36F/-38C more than once.

There are endless discussions about AC for hotter climes, we have a similar need at the other end of the spectrum.