Heating greenhouse ideas?

[rickw]

Has anyone tried the heat sink method, or tried heating their greenhouse from a compost bin/wormery?

[CeeBee]

Has anyone tried the heat sink method, or tried heating their greenhouse from a compost bin/wormery?

No - but greenhouse heating certainly interests me - 8x20 (ft) greenhouse with as many cacti and other strange things as will fit inside.

I'd ideally like to maintain 7 degrees C (or maybe 5). Heating is just electricity, with double-sided bubble-wrap insultation in the roof in winter. At present, I have a maximum of 1.4kW heating installed (OK - it could probably go a bit higher with thermostat-tweaking, but that's the max it's used on very cold nights), and I'm not really willing to put any more in - rather spoils my 'green' credentials. Suspect that's very little for a greenhouse this size (in most people's terms). Doubt that heat-sinks or compost etc. would do the job - like solar-thermal panels it would do least when you most need it, but then any contribution helps offset the electricity.

Probably got down to about 2 degrees C at times this winter, and some of the cacti are showing it - many are quite happy with that, but equally some aren't (those from e.g. most of Brazil, or the hotter lowland parts of Peru). Some I've had for 20-30 years are struggling, but I'm adapting - that's a good lifetime for some cacti in habitat, and I just won't bother growing anything that's very cold-sensitive.

I keep thinking a heatpump would be a good idea, but no time to progress the idea - and wouldn't want to spend a fortune on it - it's only a greenhouse after all. Afraid I'm coming to dislike some of the greenhouse-fraternity who almost seem proud of how much energy they've pumped into their many greenhouses maintaining very high temperatures...

[martin]

Here's an earlier post on the subject - http://www.navitron.org.uk/forum/index.php/topic,9146.0.html

[dhaslam]

I am about to  put up a greenhouse in the next few weeks using heat sink.    It would have been very suitable for the last month or so with temperatures down to -6C at night and very sunny during the day.   In a normal winter it wouldn't be as cold at night or as warm during the day so  I will probably use some soil heating as well.    A few hundred watts  at night rate  electricity  isn't a significant cost.   I have a small heated porch for propagation so the greenhouse doesn't  need to be warm all winter.   

[guydewdney]

I would think about a thermal store type system - water has the highest thermal capacity of almost any material. I would be tempted to put some large bore pipes underground, and pump water in on a hot day etc etc..

[billi]

another  read about that subject http://www.navitron.org.uk/forum/index.php/topic,9866.0.html

Billi

[Ivan]

If I were looking to heat my greenhouse to 10C or less, I'd look very seriously at circulating air underground. At a depth of 1.5-2m, the air is going to be 10C or thereabouts, most of the year. So all you need to do is to bury a large diameter (4-6") plastic pipe, with ducted up to the greenhouse floor. With some ingenuity, it might be possible to thermosyphon effectively (think chimneys), in which case no power would be required. Include a fan which could be switched on in hot conditions to act as air-conditioning for the greenhouse.

If you're clever, you can probably get some useful information out of this program - http://nesa1.uni-siegen.de/index.htm?/softlab/gaea_e.htm

[dhaslam]

I would think about a thermal store type system - water has the highest thermal capacity of almost any material. I would be tempted to put some large bore pipes underground, and pump water in on a hot day etc etc..

How would you transfer heat from air to water?   It is possible to  circulate water on the  roof of a greenhouse for cooling  but it  tends to work by evaporation rather than heating the water much.   The direct air system has the advantage of simplicity, just two thermostats and a fan.   

[guydewdney]

I was assuming a basic solar type panel - a black radiator. A pump would transfer heat to tank for storage and use later. a second pump (or valves) would then transfer the heat to the soil at night / cold times. I dont see how you can do that with air.

[dhaslam]

The black radiator would take heat by radiation but not very much from the  air in a greenhouse.    In summer  high air  temperatures when the sun comes out is just as much a problem as  low temperatures at night.   

[guydewdney]

OK - lorry radiator and a fan.....

[dhaslam]

Probably would get water up to 30C or so but the heat exchange might not be very good since radiators normally work at about 80C.  Could be more useful for an existing greenhouse in that water could be stored  in an insulated container overground.   

[dhaslam]

Finally got started on this project.  The greenhouse is  8'X14'  with polycarbonate.   I have to buy   the pipe tomorrow,   land drainage pipe 110mm costs 97 cent per metre and I will need to use  about 40 metres.     I plan on using  computer case  fans for both this and  the seasonal heat store so this project is a dry run for the other.    I will use a small amount of insulation near ground level to reduce cooling,  except into the greenhouse.

I wonder if I should split the pipe up into two or more pieces.   There are a lot of rocks to fit back into the space  which could flatten the pipes a bit  and I am not sure  how far one of these fans will carry heat.   Anyone done something similar?