Idea: Solar water storage heater for greenhouse

pauln

We were talking about Polytunnels and a greenhouse I'm working on over here and it reminded me of another idea I was having.

I was trying to figure a way to average out the temperature differences between day and night inside the greenhouse without an electrical or fuelled heating system.

What I was thinking of was building something similar to a solar water heater collector out of plywood, black piping some insulation and perspex and putting it outside the greenhouse. Then running the piping back to a copper water cylinder inside the greenhouse that's higher then the collector (Hot water rising and all that).

During the day the heated water in the collector would circulate up to the collector and then at night release the heat back into the greenhouse. In effect a solar powered storage heater.

If you've stuck with this so far, any comments, suggestions or ideas?

Macy

Would the cyclinder in the greenhouse not be heated by being in there in the first place? I have seen it suggested to have a barrell of water in the greenhouse to store water, so no reason why a more complex way of doing it couldn't work.

The other thing that strikes me is that during sunny days you'll be trying to reduce the greenhouse heat, so would the tank being in there increase the heat at time's you're trying to reduce it?

pauln

Macy wrote:

Would the cyclinder in the greenhouse not be heated by being in there in the first place? I have seen it suggested to have a barrell of water in the greenhouse to store water, so no reason why a more complex way of doing it couldn't work.

Yes it would but I was thinking that with the additional collector I might be able to get the water hotter then just sitting inside on it's own.

Macy wrote:

The other thing that strikes me is that during sunny days you'll be trying to reduce the greenhouse heat, so would the tank being in there increase the heat at time's you're trying to reduce it?

I really don't know what kind of temperatures to expect inside in the summer. I'm guessing it would work by leaving windows and doors open during the day and watering to cool things down. Then as summer nights can get pretty cold due to a lack of cloud cover, close all the windows and doors and let the heat stored in the water tank heat the greenhouse.

What you think?

Macy

pauln wrote:

I really don't know what kind of temperatures to expect inside in the summer. I'm guessing it would work by leaving windows and doors open during the day and watering to cool things down. Then as summer nights can get pretty cold due to a lack of cloud cover, close all the windows and doors and let the heat stored in the water tank heat the greenhouse.

What you think?

Haven't got my greenhouse yet - still looking at options (can't decide whether I want to cough up for toughened glass), but I think greenhouses can get up to very high temps - hence the shading in summer. It'd be worth experimenting with at least, especially if you can scavege materials like the copper cylinder. At the very least, if you did it in conjunction with a thermostatically controlled heated, you'd reduce the amount of electricity you'd use.

patrido

hi pauln
this is a very interesting idea... it's a complex area and i only have a limited knowledge of it.

passive solar houses use a variety of techniques to store up solar energy when it's at it's peak, and release it slowly after it fades... there are lots of good books on the subject - the passive solar house, and the passive solar chapter in ecohouse 2 and are two i can recommend.

your suggestion will certainly add heat to the greenhouse, but i'd say it will start to release very quickly. it is likely to prolong and intensify the peak temperature, and make no difference to the lowest temperature, just before dawn.

you could build a large water store made of concrete and half filled with stones... these will absorb and store the heat for longer, and should provide heat to the greenhouse for longer during the night/cold periods.

some passive solar houses use a south facing water wall as a thermal mass. in your case this will reduce the solar energy hitting the inside of the green house during very sunny days and release that energy slowly later.

pauln

patrido wrote:

You could build a large water store made of concrete and half filled with stones... these will absorb and store the heat for longer, and should provide heat to the greenhouse for longer during the night/cold periods.

I was thinking the water might release its energy too quickly alright, suppose that's why the electric storage heaters use bricks as their thermal stores.
I'm restricted to using water as the collecting and distribution medium but I like the idea of the concrete water container and the bricks.

patrido wrote:

Some passive solar houses use a south facing water wall as a thermal mass. in your case this will reduce the solar energy hitting the inside of the green house during very sunny days and release that energy slowly later.

I'm with you. I'll have the collectors outside to the south but not obstructing the greenhouse. I'd like to maximise both methods of collection.


Something else I was thinking about for this was would it be an idea to run piping with the heated water in it through the soil the plants are in? Is soil temperature something that's more important then air temperature when it comes to veg?

Hector's House

In the seven years since this thread was launched you've probably sorted your issue out, but I did see one US book that had a lean to greenhouse with the entire back wall kitted with a rack containing old jerry cans painted black. The black surface warmed up, the water similarly got warm, then kept the heat at night to reradiate it out in the greeenhouse. Haven't tried it, but it looked very impressive!