Greenhouse heating

[illahe]

Hi Peter,

Have you looked into these phase change tiles? They seem to offer a higher btu benefit than passive solar capture like water barrels in in a much smaller footprint. You could line a greenhouse bench or insulate a sun gathering wall with them. I'm hoping to give them a try in my new high efficiency climate battery greenhouse design i'm working on. link here: phase change tiles

Interesting! A quick browse shows relatively high temperature phase change, do they come in lower temperature ones for keeping a greenhouse over freezing? And what is the approximate price per 2'x2' panel?

Robert, 
It looks like they have a range of temperatures available, so maybe a lower temp pcm than the 72 degree they offer is available. I come up with around $19.44 for a 24" tile. I would love to see other brands/options, but it looks to be a pretty novel new concept being marketed for greenhouses. 

Mark

[Robert_Parks]

Robert,
It looks like they have a range of temperatures available, so maybe a lower temp pcm than the 72 degree they offer is available. I come up with around $19.44 for a 24" tile. I would love to see other brands/options, but it looks to be a pretty novel new concept being marketed for greenhouses.

Mark

That's actually pretty reasonable pricewise, but even their 62F/17C is way too high...I mean, when I would want supplemental heat transfer, the greenhouse is unlikely to spend much time warmer than that. I suspect demand would be much lower for 40F/5C or 50F/10C tiles.

[CG100]

I do not see how these PCM tiles can work as they give up all their energy at one temperature as the temperature is reached - it will not be absolutely precise but once a temperature is reached the change happens and the heat is given out.

What happens as the temperature rises slightly? Presumably the panels chill the air as they change back? Which is not what you want at all.

They don't seem to provide anything like enough joules either.

I accurately measured what it took to keep the large cloche that I am using, inside my greenhouse, an average of 6C above outdoor temperature, over-night (15 hours). The cloche is made from bubble-wrap, two layers to the outside wall of the greenhouse, around 3 cubic metres/cubic yards - near enough the same for this exercise. That was around 4.5kWhr, which is around 16MJ - 16000kJ

When I was heating the entire 12 x 8 greenhouse, I needed a bare minimum of 1kW of heating to cover most frosty nights. In reality, there was far better distribution of warmth and a good margin for extremes, by using two 1kW fan heaters, one at each end of the greenhouse, controlled by a solid state thermostat with a bare sensor. From memory, 1kW would give a temperature difference of around 8? 10?C outdoors v. within the greenhouse when running all the time. That is 3600kJ/hr.
The greenhouse was completely lined with bubble-wrap.