Wednesday, January 29, 2014

Update: Flower Pot Heater

The last few days, I experimented a bit with the flower pot heater... actually, I turned the one heater into two! All experiments were done whilst my central heating was set to "frost protection".

From a physics point of view, the 4 pots, as shown in the previous post, are a rather large thermal mass. And of course, physics does not lie. Despite the 4 candles, it took some time to build up noticeable radiant heat, which than lasted for quite a while. In this respect, the 4 pot solution is more of a constant heater than an "on demand" device.

At some stage, I removed one inner pot and tried with 3 pots bolted together. This has proven to be a little bit faster in heating up, satisfactory it was not. The mass of the big pot takes too long to warm up appearently.

The next experiment was to use the second to largest pot and the 2 smaller ones. I also removed the brick at the opposite end, since I noticed that the candles were not getting enough oxygen. Well, some improvement, but still not really up to scratch.

In the next iteration of experiments, I used only 2 pots, the smallest and the second to largest. Also, I reduced the amount of metal inside by using a shorter bolt. The reduced circumference of the setup allows for a smaller soucer to hold the candles. The bricks set flat now, the distance between the flame(s) and the thermal mass is reduced, speeding up the warm-up. Noticeable difference!
Some remark here, it seems that in particular when using more than 2 tealight candles, the soucer I used was filled up with cold CO2 so quickly that one candle always fainted. It seem that the heat-transfer is very effective, so effective that the CO2 fall straight down on the candle(s). When the setup is warmed up a bit, this effect is gone.

Radiant heat is kinda cool (warm that is), however, what about heating air? And yes, this works well, however, it slows down everything again. What works well, you may ask...
I used 4 candles in the 2 pot heater mentioned above and placed the big flower pot on top. Since this time the big pot is not connected to the bolt, the hole in the pot is open. Heat builds up between the bolted 2 pot setup and the outer loose pot, which due to the chimney effect is drawn upwards through the big pots hole. In the course of time, also the big pot heats up such that it radiates heat.
Such a setup creates heat by convection and at some later stage also radiant heat.

Latest experiment: two 2 pot heaters.
I believe you understand where I am going from here. The big pot was loose already, and the second to smallest was not used at all.
Some considerations about the 2 heaters I have presently available. The biggest pot will have a large thermal mass, which stores heat for a while. The smaller pots (less mass) will heat up fast and start radiating relatively quickly.
Since a couple of days I experimented successfully with the following scenario. The smaller heater is in my study, where I do stuff in the late afternoon, just when I returned to home. This room needs quick heating, so I use the smaller FP-heater with 2 or 3 TL-candles, to get radiant heating asap. At the same time, I would light a single TL-candle in the big pot heater to create a certain baseline warmth in my bedroom. Halfways into the evening/night, I might have to replace this single TL-candle with a fresh one. The big pot does not get very, it is warm to the touch at the top and cold at the lower side, however, my bedroom feels just right with this amount of heating.

Again, this is not radio related... sorry for that! However, I believe that this could be of some interest to some of my audience.
2 tealight candles per night to keep your bedroom comfortable... how cool (ergh warm) is that?!

BTW: There are some critics writing rather negatively about this particular way of warming a room. And honestly said, they have point!
We, including me, are talking about "heaters". Of course this evokes the impression that those things are really hot, creating a lot of "heat", litereally. But than, those devices are not up to such expecations for very simple reasons. Here is one: tealight candles are designed to keep a pot a tea warm for some while... that's all! The idea is not to create an amount of heat so that the tea will evaporate in a couple of minutes. So, should we expect the very same candle to be as hot as a Bunsen-burner?! It is the constant flow of a small amount of energy that keeps your bedroom cosy... not more than that!

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