Greenhouse container experiment

Here are the final results of my container experiment. It was originally designed to see whether black painted containers were better or worse than containers with black ink. It was expanded to include different types of paint, different painting techniques, and a container in a black plastic bag. I took a total of 4 sets of measurements, but I excluded a couple when I realized that the container was inadvertently shadowed. To further minimize any biases based on the positions of the containers, I rotated the containers through different positions on the south end of the greenhouse. I measured the morning temperature, then measured again in the evening. By subtracting the two, we have the heat gained and stored in the container, and this is the heat released at night. I calculated this difference (DIF) for each day, then I averaged the DIF. The chart below shows the average increase in temp for each of the different containers. The higher the number on the chart, the more effective that container treatment was.

This is the key:
#1 ACE Black enamel, 1/2 gal, painted completely
#2 ACE Black enamel, 1 gal painted completely
#3 Kryon Black, 1/2 gal, painted completely
#4 Kryon Black, 1/2 gal, 3 sides painted
#5 Kryon Black, 1/2 gal, 1 side painted
#6 Kryon Black, 1 gal completely painted
#7 1/2 gal clear, blue food coloring
#8 1/2 gal clear, black ink
#9 1/2 gal clear
#10 1/2 gal clear in black plastic bag

I draw these conclusions:
ACE black enamel worked better than the Kryon. Therefore, there are clearly differences between paints.
The container in the black plastic bag was inferior to both paints.
Blue food coloring is inferior to black ink or any paint.
Covering a container with a black plastic bag is better than nothing, but inferior to most black paint treatments.
Black ink was inferior to all of the painted containers except for the one painted only on one side.

Here is the data presented slightly differently. In this chart I took the average gain in temp for each container and subtracted the gain of the clear, unpainted container. This chart then shows how much better each container is over a clear, unpainted, 1/2 gallon container.

So the clear, unpainted 1/2 gallon container increased an average of 28.67 degrees from morning to day end. The best performer, #2, the ACE black enamel 1 gallon container, increase on average 38.67 degrees from morning to day end. Several container readings exceeded 105*F and one reading hit 110*F. This was about 20-25*F higher than the maximum GH temperature.

A BTU is the energy required to raise one pound of water one degree Fahrenheit. If I do the math correctly, then, container number two reemitted an average of 309 BTU each day of the experiment.

I hope these results are useful. Comments, critique, and questions welcome!

SB

This message was edited Oct 29, 2006 7:49 PM

Out of curiosity, do you keep the caps/tops on or are they open to the air for evaporation?
I read on the other thread your experiement and it sounded very interesting.
Carol

Caps were left on to prevent evaporative cooling and contamination of the water.

SB,

Would you say that this points to bigger containers being more energy efficient than many smaller ones?

MollyD

Molly, I don't know that bigger containers are necessarily better. With one paint, the 1 gal was a bit better, but with the other paint, the two were about equal. I think you would have to repeat the experiment with a much larger container. I suspect that the larger container would be slower to gain heat during the day because of a lower ratio of surface area to volume. On the other hand, it would hold more heat because of the larger thermal mass (greater volume of water).

Efficiency with regard to the size of the containers, in my mind, really just means getting thermal mass anywhere you don't have plants, regardless of the size of the container...with black enamel on any of them that are exposed to the sun!

What a great thread! How scientific! I MUST a can of ACE Black enamel and spray paint the dozens of pop bottles we have around the house (my hubbie LOVES pop).

Stressbaby and Molly... you guys are everywhere on the internet! http://forums2.gardenweb.com/forums/load/strucs/msg1023514613401.html?2736

Only on the plant forums heebeejeebee (LOL)

MollyD

what other forums do you guys frequent other than those two?
I also hang out at organicgarden.com sometimes

Well, there is the citrus forum that nobody knows about: http://citrus.forumup.org/

Mostly it is Tropicals, Tropical fruit, Trees and Shrubs, Container gardening and GH here at DG.

I tend to stay around daylilys and greenhouse areas.

MollyD

Hey Stressbaby..I think I asked this on the other thread so please forgive me because I cna't find that one.. but I was wondering if you took your measurements from the water inside the containers ? thanks

JP, yes, the temps are of the water in the containers. SB

Thanks Pal

What about in the winter Time ?

I don't follow your question, phicks.

stressbaby, I put a 55gal black plastic drum in the center of my little hoophouse and put a small electric heater a few inches facing the drum, the results are heat radiated in all directions in the GH. It works for me. John