Solar is a possible if you look at solar water systems there is some interesting stuff around. About the best seems to be sydney tubes these are are glass tubes made of pyrex with an inner tube which is metal coated inside a vacumn sealed clear outer tube being circular they always face the right way. The heat captured is quite incredible and can boil water.
while domestic water systems can be very expensive. The tubes themselves can be quite cheap. (i've seen smallish tubes on the internet at $99 for 10 only problem import duty) Theres a couple of methods for transfering the heat the simplest just requires a pipe leading down from a tank the hot water in the tube will rise into the tank while cooler water replaces it , thermo syphoning. another type of transfer is the heat pipe where a sealed pipe has water under low presssure. This causes the water to boil at relatively low temperature and rise up the pipe where it is again into a tank of water which cools the water vapour releasing latent heat and heating the water in the tank. Once the sun goes down the hot water generated in the day could be used to provide heating at night. I'm still at the experimenting stage but i was quite impressed with the heat pipe i made even thou i was forced to test it with a fire. I'm looking at ordering a small sydney tube for experimenting with from canada tomorrow. Its about €15 plus postage but i'm not expecting to heat much water with it. I just want to see how hot it can get on these cold days.
We've actually got a solar water heater on the house, it works surprisingly well. Even in the middle of winter if if the temp is -5 outside as soon as the sun comes out you start getting plenty of hot water generated.
Problem with a greenhouse heater based on solar i guess is when you really need it you won't have solar power, ie cold wet, dark winter months. As unlike solar leccy, we don't seem to get much when it's dull.
In the summer you'll have to watch overheating, as the water litterally just keeps getting hotter and hotter very fast. Our boiler has a safety trip but the temp in the pannel can very quickly hit boiling once the tank is hot.
I'm embarking on a project in the next few months, I have used a gas heater (very efficient in the very cold), I have the luxury of a power supply that has an oil filled radiator on frost stat in case the gas runs out. My idea is a bit different and there are pages here and there on the net that describe this more than I will here.
Step 1: (the biggest job)
Lift greenhouse and dig 1metre deep trench through centre where the greenhouse stands. (although I'll be making the trench almost as wide as the greenhouse). Line the base with plastic guttering tube with holes in the tube, have 90degrees at each end to route the tube above ground level. Then fill the hole with pebble (pea gravel), I'm researching the best here. It seems the volcanic type is the best. It needs to be full of holes to be most efficient. Refit the greenhouse (probably buy more glass as well).
Step 2
On one side I will still have a border, however, I'm thinking of hydroponics this year to grow my peppers and chilli and maybe tomato. The tubes from underground need to be joined to either end of the routing underground, one goes up in one corner just above the ground and then along the length of the greenhouse on one side (with holes in it), and the other the opposite corner all the way to the very top of the greenhouse.
Step 3
I'm mad on solar power and have several solar panels dotted around that power lighting in my garden at night, All the batteries for these panels are in the greenhouse so the power is there for this step. I'll be fitting a fan, probably a 120mm pc fan that can run on 12v on each end of the routing at the top of each 'chimney'. One push and one pull. I have done some maths on this (I'm a mechanical design engineer by trade), and this should work easily.
Result
According to my calculations, during the summer the auto vents open fully to let all the heat out during the day. This system should drag hot air from the very top, through the cool pebbles underground and blow out cooler air into the greenhouse, at the same time, they will warm the pebbles. During the night, the same warmed pebbles will keep the greenhouse warmer with the same flow. Winter would have a similar effect, however, not as much. I have seen my vent open on a very cold day shortly after the sun comes out and generally the greenhouse is warm enough on a bright day (unless it's covered in snow). This system should ease the yearly cost (£80 LPG for the gas alone).
Conclusion
I guess it's not an ideal solution for winter heating, however, for the summer it's ideal. I'm expecting good results in spring and starting things early. I have trialled a few things and was surprised on the poor results of bubble wrapping the inside of my greenhouse, I tried the black water containers and that gave some results. I have trialled a small scaled model with the brown pea gravel in a large bucket and it gave fairly good results. I also have a problem of water, when it rains heavy the pea gravel will fill with water and that would not transmit heat well, so maybe I will have to come up with a way of moving air around just above the flood line and drill some drainage holes. I would also think that the movement of air would be good for the greenhouse.
Posts
Solar is a possible if you look at solar water systems there is some interesting stuff around. About the best seems to be sydney tubes these are are glass tubes made of pyrex with an inner tube which is metal coated inside a vacumn sealed clear outer tube being circular they always face the right way. The heat captured is quite incredible and can boil water.
while domestic water systems can be very expensive. The tubes themselves can be quite cheap. (i've seen smallish tubes on the internet at $99 for 10 only problem import duty) Theres a couple of methods for transfering the heat the simplest just requires a pipe leading down from a tank the hot water in the tube will rise into the tank while cooler water replaces it , thermo syphoning. another type of transfer is the heat pipe where a sealed pipe has water under low presssure. This causes the water to boil at relatively low temperature and rise up the pipe where it is again into a tank of water which cools the water vapour releasing latent heat and heating the water in the tank. Once the sun goes down the hot water generated in the day could be used to provide heating at night. I'm still at the experimenting stage but i was quite impressed with the heat pipe i made even thou i was forced to test it with a fire. I'm looking at ordering a small sydney tube for experimenting with from canada tomorrow. Its about €15 plus postage but i'm not expecting to heat much water with it. I just want to see how hot it can get on these cold days.
We've actually got a solar water heater on the house, it works surprisingly well. Even in the middle of winter if if the temp is -5 outside as soon as the sun comes out you start getting plenty of hot water generated.
Problem with a greenhouse heater based on solar i guess is when you really need it you won't have solar power, ie cold wet, dark winter months. As unlike solar leccy, we don't seem to get much when it's dull.
In the summer you'll have to watch overheating, as the water litterally just keeps getting hotter and hotter very fast. Our boiler has a safety trip but the temp in the pannel can very quickly hit boiling once the tank is hot.
I have found a cheap free method to heat a greenhouse and it's so simple.
cut the grass. Stuff clippings into a compost or coal bag put bag(s) in the greenhouse.
you might want to just pile them up initially to get them brewing.
Grass as it rots generates heat, once your into the first few inches the heat is massive. google "jean pain method"
http://www.youtube.com/watch?v=-Jm-c9B2_ew
This is a bit extreme but this guy is actually generating hot water from compost, basically running about a 100 foot of pipe through his compost pile.
I guess once the pile cools off it can become part of your regular compost heap or used as a mulch or soil enricher...
Late addition here.
My issue
Too cold in winter, too hot in summer.
I'm embarking on a project in the next few months, I have used a gas heater (very efficient in the very cold), I have the luxury of a power supply that has an oil filled radiator on frost stat in case the gas runs out. My idea is a bit different and there are pages here and there on the net that describe this more than I will here.
Step 1: (the biggest job)
Lift greenhouse and dig 1metre deep trench through centre where the greenhouse stands. (although I'll be making the trench almost as wide as the greenhouse). Line the base with plastic guttering tube with holes in the tube, have 90degrees at each end to route the tube above ground level. Then fill the hole with pebble (pea gravel), I'm researching the best here. It seems the volcanic type is the best. It needs to be full of holes to be most efficient. Refit the greenhouse (probably buy more glass as well).
Step 2
On one side I will still have a border, however, I'm thinking of hydroponics this year to grow my peppers and chilli and maybe tomato. The tubes from underground need to be joined to either end of the routing underground, one goes up in one corner just above the ground and then along the length of the greenhouse on one side (with holes in it), and the other the opposite corner all the way to the very top of the greenhouse.
Step 3
I'm mad on solar power and have several solar panels dotted around that power lighting in my garden at night, All the batteries for these panels are in the greenhouse so the power is there for this step. I'll be fitting a fan, probably a 120mm pc fan that can run on 12v on each end of the routing at the top of each 'chimney'. One push and one pull. I have done some maths on this (I'm a mechanical design engineer by trade), and this should work easily.
Result
According to my calculations, during the summer the auto vents open fully to let all the heat out during the day. This system should drag hot air from the very top, through the cool pebbles underground and blow out cooler air into the greenhouse, at the same time, they will warm the pebbles. During the night, the same warmed pebbles will keep the greenhouse warmer with the same flow. Winter would have a similar effect, however, not as much. I have seen my vent open on a very cold day shortly after the sun comes out and generally the greenhouse is warm enough on a bright day (unless it's covered in snow). This system should ease the yearly cost (£80 LPG for the gas alone).
Conclusion
I guess it's not an ideal solution for winter heating, however, for the summer it's ideal. I'm expecting good results in spring and starting things early. I have trialled a few things and was surprised on the poor results of bubble wrapping the inside of my greenhouse, I tried the black water containers and that gave some results. I have trialled a small scaled model with the brown pea gravel in a large bucket and it gave fairly good results. I also have a problem of water, when it rains heavy the pea gravel will fill with water and that would not transmit heat well, so maybe I will have to come up with a way of moving air around just above the flood line and drill some drainage holes. I would also think that the movement of air would be good for the greenhouse.
Any comments appreciated.
Simon