Key Findings;
- Shiftpods are not significantly better than cheap alternatives.
- No tent performs well in direct sun.
- No matter what kind of tent you have, putting it under a shade structure is the most important thing for keeping it cool inside during the day.
- Evaporative “swamp” coolers are not as helpful as simple ventilation.
- Thermal mass batteries are a simple and very effective tool for normalizing temperature throughout the day.
The Experiment
Lots of people spend time in tents. As a Burner, I am one of them. There is a big problem which anyone who has ever slept in a tent can relate to. That problem is Thermodynamics.
Thermodynamics is a law of physics which basically says that the heat from the sun will eventually get into your tent. What this means for campers is that even on a day where the outside temperature only gets to 80, it’s going to be 100-120 degrees inside your tent. There are basically two ways to fight back against thermodynamics in this case; put barriers in the way which will slow but not stop the heat getting in, or put something in place to absorb or remove the heat.
For a Chemistry honors project, I am studying the effect of various techniques and materials on prolonging that magical sleeping time in the morning before the temperature inside the tent gets too high to keep sleeping.
I will also be comparing fancy expensive tents to the cheapest alternatives in order to see if fancy expensive tents are actually any better. In this case, I have chosen the very popular Shiftpod v2.0 to compare with a cheap tent of similar design from amazon. I have taken to referring to the blue fishing tent as “Blueshift” for simplicity’s sake.
One thing to keep in mind is that this is not the playa. We do have partly cloudy days here in Sacramento, so there may often be sudden spikes and dips in temperature. These cloud effects will reach both tents, so it will be interesting to see how they each fare with them.
Disclaimers
This experiment was done in Sacramento, not at Burning Man. Results will vary but systemic error should be low, since both situations include similar variables such as humidity, sunlight, etc and impact from the different mitigation strategies. I’m planning to do a future version of this experiment at the playa during fourth of juplaya which includes more tent types such as a hexayurt and a pup tent.
The tents are not exactly the same size. There may be some differences in amount of heat reaching each tent. That said, Shiftpods are 1200% the price of the cheaper tent. If it’s worth that, this trivial difference should not matter.
Some of the links on this page are affiliate links. I”m a starving student trying to pay for this expensive experiment. It doesn’t add to your cost if you choose to buy things with these links. I just get a small cut to help cover my costs. If you don’t want to use the affiliate links, you can open them in incognito or something like that in order to remove the tracking code.
Sensor Equipment
I am using a custom built multi-zone temperature logger to track the data. The full details of that can be found here.
Phase 1: The Naked Sun
Phase 2: Loose Aluminet
Aluminet is a very interesting material which has found wide adoption among burners, just like Shiftpods. It’s both a radiant barrier and wind-permeable. This solves several interesting problems.
The idea of a radiant barrier is that heat and light will be reflected rather than absorbed, as would be the case with a tarp. The problem with past radiant barriers is that they were solid like a tarp, and with high winds, they become a sail that tries very hard to blow away. Many radiant barrier materials such as mylar are very delicate and will tear themselves to shreds with even the slightest wind.
Aluminet is made of a similar material to mylar, but it is reinforced and braided, so it forms a very strong barrier in the wind, which wind can actually pass through. It comes a wide range of opacities which allow different amounts of light through. I go with 80% Aluminet.
As I mentioned before, Shiftpod has recently started giving out free radiant barriers called “blast shields” which are basically just a non-breathable mylar -like material. The blast shield is basically a cheap and inferior alternative to Aluminet, and the fact that they are now giving them away for free seems to indicate that the makers of Shiftpod are aware of a potential design flaw in this very expensive tent.
Thermodynamics sometimes has a problem with both mylar and Aluminet, especially when they get dusty. Sure radiant barriers will reflect much of the light and heat, but dust will not. If the dust is touching the radiant barrier, then it doesn’t stop the heat from the dust conducting through the barrier and into the tent. Aluminet and mylar are not conductive barriers, only radiant barriers. This means that a dusty piece of Aluminet or mylar will conduct some heat through to anything they are physically touching. For this reason, if the radiant barrier is touching the tent, and it’s dusty, then it will not block as much heat as it would if it were several feet away from the tent, suspended from another structure. This will be expanded on in a future phase of the experiment.
This photo was taken in the afternoon. As you can see, the Aluminet is hanging from the two tents and tied to the fences. For the purposes of this experiment, the Aluminet is covering the east sides of the tents. This means it will block morning sun, and to a lesser degree the noon sun. The south and west sides of the tents are not covered. (This entire experiment focuses on the morning time.)
The addition of Aluminet pulls the curves closer together, and we see the Shiftpod performing much better after an initial heating-up period. But the thickly insulated Shiftpod is still much warmer than the thin and breathable Blueshift. The Shiftpod has two humps when the sun is hitting it straight on, first thing in the morning and then again at mid-day. Between these times, the sun is hitting its edges at an angle. This seems to impact the heat absorption as shown above.
Once we pass noon, the Shiftpod’s thickly insulated roof absorbs the conducted heat from the loose Aluminet, and traps that heat inside the tent. In contrast, the Blueshift’s breathable and un-insulated roof lets the heat escape. Right at noon, we see the Shiftpod suddenly jumps to nearly twenty degrees warmer than the Blueshift. This could be the problem that the makers of Shiftpod were trying to solve by giving everyone free blast shields to block the mid-day sun from cooking their thickly insulated roofs. By comparing the first and second phase data, we see that adding a radiant barrier op top of the Shiftpod does mitigate this problem to a certain extent, but not completely. Eventually the heat gets through since the barrier is touching the roof.
Phase 3: Passive Thermal Mass Batteries
Water as a molecule has a lot of interesting properties. One of these properties is that it’s really good at storing heat energy. In fact, my understanding is that no known material has a higher density of heat storage than water.
This gave me the idea of placing lots of water inside the tent to store and release heat. This would theoretically have the effect of flattening out the temperature curves so that they are closer to the average value throughout the day. I decided to use four five-gallon buckets of water as my passive thermal mass battery. These buckets would be easy to transport and store, and even use as storage for other gear. You could also fill one or two of those large 27 gallon totes and use that as your battery, but that seems like overkill and it would be a lot of water.
As you can see in the photo below, I also put one of my temperature probes into one of the buckets to monitor the temperature of the water so we will see that in the graph.
In order to accurately compare the performance of the two tents, I decided to split this phase into three parts and compare each tent’s performance against the other, then both together. Therefore Phase 3A will test the performance of the Shiftpod with a 20 gallon passive thermal mass battery. During this phase, the Blueshift will just be normal and without any thermal mass battery. Then during Phase 3B, they will be switched. The thermal mass battery will be placed in the Blueshift, and the Shiftpod will just be normal. Then we can compare the performance of each with the addition of the batteries. Lastly, during Phase 3C, both tents will contain the same thermal mass batteries.
In order to get the most accurate data, I let the tents and their thermal mass batteries sit for a full 24 hours before collecting the data as shown. This way we can see the data once the batteries have been well adjusted to the conditions we are observing.
Phase 3A: Shiftpod Only
I was a little surprised by this data. In the first graph above, we see that the thermal mass battery starts absorbing a great deal of heat long before we see a significant change in air temperature inside the Shiftpod. To really see the impact, compare the difference chart to previous phases of the experiment. Only in the pre-dawn hours does the Blueshift take the lead. I am amazed. With the simple addition of a passive thermal mass battery, the Shiftpod now performs better than the Blueshift all throughout the day.
Phase 3B: Blueshift Only
Now let’s look at the next part of the experiment, where the passive thermal mass battery is placed only in the Blueshift and the Shiftpod is just normal without any help from the batteries.
We see that the difference curve swings the other way. This is not surprising since the Blueshift is not insulated. I think this test should be compared to the first test in the experiment since that’s the same conditions the Shiftpod is under during this test. In the first test, both tents eventually reached essentially the same temperature, and the Shiftpod was slightly warmer for most of the day. In this test,we see that both tents follow very similar curves, but that for most of the day, the Blueshift is a good 10-12 degrees cooler than the more expensive Shiftpod.
It’s interesting to note that we don’t see precisely the same effect from the previous test (3A) where the thermal mass battery absorbs the heat that would otherwise constitute the curve of it’s surrounding tent. Instead we see a gradual warming throughout the day, and a reduced warming in the surrounding tent.
Phase 3C: Both Together
During this phase of the experiment, we saw that thermal mass batteries significantly improved the effectiveness of the Shiftpod, while not significantly improving the effectiveness of the Blueshift. Four buckets of water has a footprint of just a few square feet. You would barely notice these in the tent, and they seem to provide an enormous benefit. Probably you would see similar effects from filling an empty tote with water. This would be an interesting topic for a future experiment.
Phase 4: Active Thermal Mass Battery
In order to increase the efficacy of the thermal mass battery, it seems logical to test adding a fan, pump, and heat sink. This would mean you would need to supply constant power to it, but if it provides enough of a benefit, then this may be worthwhile. I removed three of the buckets for this phase of the experiment, using only five gallons of water in a single bucket. Expanding on this may prove worthwhile but at this point, connecting buckets would be complex. If we wanted to do a larger active battery, then probably a larger container would be more appropriate. This would also allow you to add ice to your container, etc in order to cool the tent even more.
Hanging this from the ceiling also has the added benefit of potentially mitigating that pesky heat-trapping effect in the Shiftpod.
Pictured above are a 240mm heat sink with two c. I hung the heat sink and fans from the roof of the Shiftpod and put the pump and hose into the bucket. Here is what it looked like in the early evening. (You can see the sun reaching behind the Aluminet to hit the Shiftpod from the afternoon side. This time of day is not part of the experiment.)
Here is the data on the active thermal mass battery in the Shiftpod only;
As you can see, the smaller thermal mass battery just isn’t able to keep up. Being active seems to make little difference in terms of absorbing the heat in the tent. This is an unexpected result; very interesting data.
Because we see such a limited effect even with the insulated Shiftpod, and because the larger thermal mass battery had essentially no effect on the Blueshift, it does not seem worthwhile to test an active thermal mass battery in the Blueshift.
Phase 5: Ventilation
As you can see in previous experiments, the temperature inside the tent can be as much as twenty degrees hotter than the outside temperature for much of the day. This suggests a simple solution; ventilation. This can be a problem in dusty environments at Burning Man. In other environments, this may be a better option.
Ventilation & Dust mitigation
I did some experimentation this year at the burn based on Nikola Tesla’s patents for solid state check valves as well as the closely related concept of vortex filtration. The basic principle is that when you have a fluid such as the air, and there is something in suspension, such as the dust, you can encourage the dust to fall out of suspension by forcing the fluid to suddenly change directions.
My idea was to take a section of about eight or ten feet of aluminum duct and hang it so that at least a few feet were hanging loosely and free to flap around in the wind. The other end of the duct would go into the tent, where a powerful fan would suck air into the tent. I set up some other ducts (pic) to maintain constant slightly-negative pressure and pull the hot air out from the top of the tent. This meant that no dust would blow in through these other ducts. The theory was that because the outside piece of duct was free to flap around, the open end would never be facing into the wind. This means that when air is sucked into the duct and drawn into the tent, that air would have to change direction 180 degrees in order to get into the duct. This means the dust would fall out of that air. As far as I can tell, this worked perfectly. I would definitely recommend trying this at the burn.
Phase 5a: Ventilation (Shiftpod Only)
The basic idea is pretty simple. We will have a fan drawing the air out of the top of the tent at 200CFM 24/7. Then an open vent will allow fresh air to enter the tent. This means all the air in the tent will be replaced every five minutes. This is generally considered to be the ideal ratio for ventilation, especially with evaporative cooling as we will see in the next experiment.
As you can see above in the photo, I have used the same hose from the previous experiment as well as the same 200CFM fan. The direction of the airflow is out of the tent. You can see the duct drawing the hot air from the roof area of the Shiftpod and then pushing it outside the tent. A window is open to allow fresh air to enter the tent, replacing the hot air being pushed out. This photo is for simplicity’s sake, but having the open window be close to the exhaust duct doesn’t make sense. In the actual experiment, only the window opposite the exhaust duct was left open.
As you can see, just like the passive thermal mass batteries in Phase 3A, ventilation swings the difference curve in the direction of the Shiftpod. Also just like Phase 3A, this puts the Shiftpod ahead by about ten degrees. Recall that with no assistance, the Shiftpod is a few degrees warmer than the Blueshift. Knowing that these two methods each impart a ten degree advantage plus the unaided difference, we will likely see large advantages when we pair these methods together in a later trial.
Phase 5B (Blueshift Only)
This is the same experiment with a 200CFM fan drawing the air from the center of the ceiling of the Blueshift and blowing it outside while fresh air comes in from another vent.
Here you can see the same fan and ducts going out through a window which is covered with cardboard for this experiment. Let’s see the data…
As you can see, adding ventilation did make the Blueshift cooler than the Shiftpod, but only by a few degrees. I was surprised to see how little impact was measured in phase 5 of the experiment.
Phase 6: Hung Aluminet
From the beginning, I suspected this would be the most impactful phase of the experiment. The idea here is that the Aluminet is suspended a few feet away from the tents in order to eliminate any potential heat conduction between the radiant barrier and the tents. This seems like the most logical step to take in order to see a really dramatic change. This is where the Aluminet will really shine.
Flat top shade structures are expensive! But they don’t need to be. Check out this post about how I cut the cost in half and eliminated most of the hardware involved while still getting all the benefits of a normal flat top shade structure.
As you can see, this material has a big impact versus the previous phase. The Shiftpod never hits one-hundred (as an average of its floor/ceiling temperature), though the temperature at the ceiling briefly does. The radiant barrier on the Shiftpod seems to really shine in this phase, with the highest temperature difference between Blueshift and Shiftpod we’ve seen so far.
Phase 7: Evaporative Cooling
Evaporative cooling (AKA swamp coolers) add humidity to the air in order to reduce its temperature. This works best in dry climates. The maximum temperature difference is a function of the dew point under the given conditions. This means the best case is a 40 degree temperature difference if there is 0% humidity, and less of an effect with higher humidity, with no effect at 100% humidity.
For this phase, I used the evaporative coolers I designed in this post. In both cases, the coolers burned about three gallons of water during the period shown.
Phase 7A: Shiftpod Only
Based on comparison of the data from Phase 6 to Phase 7A, there does not appear to be any significant temperature difference in the Shiftpod with the addition of the evaporative cooler. On the day the data was collected, humidity was 68%. This is probably why there was no significant temperature difference. Despite that, the evaporative cooler did burn through three gallons of water during this period, so it was working and cooling the Shiftpod despite the unimpressive results.
These values would likely be different if there was a significantly lower humidity. This was a problem at the burn this year, where the humidity was uncharacteristically high, and evaporative coolers were not working very well.
Phase 7B: Blueshift Only
As I suspected, evaporative cooling was basically useless in the Blueshift as well. This matches my experience from on-playa this year. By the end of build week, I threw my swamp coolers in my camp’s dumpster.
Phase 8: All Or Nothing
In this final phase of the experiment, each tent will take a turn with all or nothing. Based on comparing the results of Phases 5 and 7, there is no reason to include useless evaporative cooling in this phase. Instead, the more compelling phase 5 results will be included and simple ventilation will take the place of evaporative cooling. The more I think about it, the more sense this makes. If it’s twenty or more degrees cooler outside than inside, then simple ventilation is guaranteed to accomplish that or something close to it. This also parallels my playa experience, where ventilation is often the best and easiest option.
Phase 8A: Shiftpod Only
For this phase, the Shiftpod will be under hung Aluminet with the 20 gallon passive thermal mass batteries, and ventilation. The Blueshift will have none of these things, and be sitting out under direct sun.
Here we see the effectiveness of the ventilation system sucking the hot air out from the top of the inside of the Shiftpod. For much of the day, the ceiling is actually cooler than the floor.
Phase 8B: Blueshift Only
For this phase, the Blueshift will be under hung Aluminet with the 20 gallon passive thermal mass batteries, and ventilation. The Shiftpod will have none of these things, and be sitting out under direct sun.
As with several previous phases, there seems to be a critical tipping point when the Shiftpod suddenly becomes much warmer. My going theory is that it is related to the angle of incidence of the sun. I found the results of this last phase very surprising. I would have expected the difference curve to be much flatter and to stay below zero all day.
Final Thoughts
In the naked sun or with loosely draped Aluminet, it’s actually hotter than the cheaper Blueshift. Both tents perform a lot better under a shade structure.
Simple ventilation is more effective and comfortable and less complicated than evaporative cooling.
The Shiftpod is over ten times the cost of the Blueshift. Does it perform ten times better? No. In general, the tents perform pretty similarly. The Shiftpod excels in a few situations with some help. If I was choosing a new tent today, I would pay more attention to getting a good shade structure than to getting any certain kind of tent.