Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 10:24am 27 Mar 2020
Copy link to clipboard
Print this post
I need to clear out my shed, lots of accumulated junk that might be useful one day, now that we are locked down for the next 4 weeks (no it will be 6 weeks min ) with limited travel after, its time to use some of it on another project.
We want to build a tunnel house with a heated propagation table for striking plant cuttings, as the site is totally off grid and I don't want to consume battery storage energy for heating, figured hot water storage would be a good option and easily build by DIY. So the 200L copper open vented low pressure hot water cylinder taking up space in my garage may be put to good use. I built solar hot water panels for our house approx 10 years ago and have enough stuff left over to make a suitable panel approx 4 sqm, this should be enough to heat up a 200L cylinder quite quickly, when the sun is shining. The HWC still has its element, another option is to get about 4Kw of PV panels and dump that energy into the element, may be easier than building a water heating panel.
Here is a rough block drawing:
The main HWC tank will be heated as high as possible around 90c, water from this tank will heat a small insulated tank via a copper coil heat exchanger to approx 10 degrees hotter that the propagation table requires; 12 vdc magnetic drive pump M3 circulates the warm water through rubber tubing in a thick sand bed sitting within a thick polystyrene layer. Plant pots sit on this and are warmed by the heated sand, drip pot irrigation is tightly controlled so watering doesn't loose too much heat.
This is not going to work well in the dead of winter, but any sun at all will be of help to raise the root temperatures in cooler periods (mornings, night) either side of the winter months.
Here is the schematic, uses a Picaxe 20M2, monitoring is by either by serial or I2c LCD display, with a connection to our supervisory 1-wire network. DS18b20 temperature sensors and the small keypad are multiplexed by transmission gates, speed isn't required here.
Cheers Mike Edited 2020-03-27 20:32 by Solar Mike
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 11:07am 27 Mar 2020
Copy link to clipboard
Print this post
I can barely see let alone understand your schematic Mike but it's certainly over my head.
I have a tiny play greenhouse I used last winter very successfully. I didn't loose one plant right thought the season. At first I used a regular 3.6 KW element in the side of a 100L plastic drum direct connected to some panels. attached a lot of panels in the end before realising how inefficient it was and put the panels back on the GTI. I then got a 1500W submersible heater and put that on a thermostat and let the water sit at about 45oC.
I had some styrofoam under the tank and a sheet on top of the open tank which I sat the seedlings on. The water drum was an excellent thermal mass and the temp inside the greenhouse never fell below 120C even on -5 Nights. The heater was connected to one of those daylight modules on a relay so did not heat at night.
I found that through the day, even if the temp inside the enclosure got up to 50oC, as long as the humidity was running down the sides, the plants were fine. If I let things dry out a bit, then they keeled over. Keeping things humid also meant watering was minimal. The evaporation from the tank worked well as long as I left some open area for the moisture to escape more easily.
For seed propagation, I use an old fridge. I have 3 x 190W panels on a mains element in a 25L drum of water for heating and an LED light bar for radiation. The seeds don't need any light to sprout though. You can get a lot of trays and seeds in a fridge and the insulation is good and doesen't need much to power it.
If your green house is large, you may be better off with a different type of heater in a Burner. I make waste oil burners and I remember one guy who used one of my designs was heating a greenhouse with his. He had a commercial size operation in Canada and had an LPG tank out the front of the place that looked like it was made from a surplus submarine.
The guy built a burner which he ran on waste oil in the same enclosure as the gas burner which heated water that circulated through several structures. He ran the burner at a bit over 200Kw output and it worked very well. he had 6000L of water for thermal storage. His brother was a foreman at a big truck service place in town so he would come bring him IBC's full of oil. He brought it all year and they saved and filtered it through summer and then used it in winter. Saved the guy tens of thousands in gas cost and transformed his business. because the oil was free he was able to start earlier on certain plants and grow them when normally it cost too much and they were left later in the season. This alone gave him a BIG advantage. I make these things for fun and games but he sure made good use of them.
He also bled some of the flue gasses off to increase the Co2 levels in the growing areas instead of buying bottled Co2.
If you used something like water heater tanks, You could do a burn every few days, store the heat and then use the pump to circulate and distribute it as needed. Like you say, solar heating is near useless in winter and it doesn't matter how many panels you have. For a small amount of water like 200l, a couple of kilos of panels on a controller will probably be enough for a small setup but heating a tunnel is going to be something else again.
I was just saying to the mrs on my way to sit down here, I wanted to get a bigger greenhouse for this winter. It might be a wise thing the way the world is going. Already said to her wont be putting anything inedible in this year. Was also thinking it might be smart to put the greenhouse in the shed. Save a lot of heat that way. Either that Or I'll cover it with with tarps at night and on bad days and leave a couple of light bars in there for illumination.
I was thinking for something bigger, to use a 200L drum of water and have a fan Blow on the drum on a thermostat to keep the air an even temp off the one simple " radiator". I could boil the water as well if I wanted. the fan would keep the temp in the greenhouse even and I could part insulate it so not too much heat was released at once.
What are you intending growing?
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 01:50am 28 Mar 2020
Copy link to clipboard
Print this post
Woody shrub or plant cuttings, they root up much quicker if the media temperature they are in is at a consistent temperature; so the heated thermal mass is in the insulated sand bed that they sit upon. I'm not an expert on this, however the requirement from the experts is hopefully met by this solution. Not heating a whole tunnel house here, just a 4 sqm sand bed.
I'm also pulling an old tunnel house apart 2.5 x 5m and relocating it to my back section, hopefully to grow tomatoes in tubs on the soil. We get strong winds here in Wellington that blows the garden to bits at times, think a bit of shelter and extra warmth will do wonders.
Cheers Mike
Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138
Posted: 03:00am 31 Mar 2020
Copy link to clipboard
Print this post
Here is the pcb layout, 100x100mm size. Specs: 8 x 18DSB20 inputs, 4 x mosfet 4 amp outputs, 1 x I2c or Serial LCD output, 1 x beeper.
Can be used for any generic temperature control applications, however I will be using it to control 3 x 12 vdc magnetic drive pumps, 1 x water solenoid valve and 6 x temperature control sensors.
Will send off the gerbers, last lot took 1 month to get back by airmail post.
Cheers Mike
Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1024
Posted: 03:14pm 31 Mar 2020
Copy link to clipboard
Print this post
Some good ideas here, I think a lot of us will have to grow our own food or at least as a supplement if need be. So far there haven't been much in the way of frost over the years but this a heated grow-shed would certainly help keep a few veges growing.
The biggest issue I have had is during the summer months apart from the complete lack of water there's was so much heat the plants could not grow, keeping them alive was difficult, the hot westerly wind fried them on one side, then for several days there must have been more UV or something, all the plants were sunburned it even totalled the avocado tree.
There is a white UV resistant shade cloth that might help stop them from getting burned next time, if I get time to build some sort of frame for it.
I have heard of poly tunnels weather that would be big enough to drive a tractor inside I don't know.
Mike, what is that grow shed made out of?
A friend was growing fodder for their animals I think it had some sort of sheet set up on a gentle slope for a grow bed, it had a simple drip system that was run from a solar powered pond pump that just recirculates during a sunny day and off all night no batteries required.
We had an old 5000 gallon water tank that was split at the top, cut the thing in half around the middle and berried it 2/3rd's in the ground, forgot what for...but anyway a friend was moving and had some fish that needed a home. Fitted up a pump and big aerator then a bath tub with gravel as a filter and recirculates, turns out that made an excellent grow bed, plants had terrific growth but with a drastic increase in water consumption...during the drought. Having the tank in ground I did not need to run a chiller as the water temp was still ok unlike any above ground tank, however winter is still a bit harsh and will need heating on some occasions already have some HW panels that will help, even the dam has been as low as 15c and the small tubs down to about 3c that's deadly for Redclaw.
Don't have the water supply for this sort of thing at the moment but when we did we could get a good feed, fresh too. Always try to have gravity feed from tanks and have the solar pumps refill them when necessary.
Anyway, nice circuit.Cheers Aaron Off The Grid
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 12:23am 01 Apr 2020
Copy link to clipboard
Print this post
I built a structure out of scaffolding over a bit of garden I wasn't using ( planning to asphalt) before summer. Put in about 50 of the tomato seedlings I had. They all went nuts and well surpassed my expectations. Was pulling 2-3 Kg every second day off them.
The rain actually knocked them over in the end but then they started to come good but the weeds have Over taken them. I wanted to leave them there and see how they went over winter with things the way they are but weather is fast cooling off and the setup looks an eyesore.
I wanted to get a bigger greenhouse but the thought struck why not just cover what I have with plastic and use the scaffold? Certainly a lot stronger than any of those kit things and with the wind here, I don't think they would stand a chance. The scaffold otoh wouldn't budge.
Clear Builders film is MUCH cheaper than the proper greenhouse film and while I don't think it would last near as long, for the price I can buy a roll, I'd get at least 5 coverings with it so the price would not be bad in reality. IF it lasts one winter, good enough. I have used the black Builders plastic for a pool covering and that was good for better than 3 years.
Got too look how I can attach and hold the plastic. I have wooden formwork beams and solar rails now on the top suspending the tomatoes. I'm thinking of using that again with some Improvements and putting solar panels on the south side on the top. I'd tilt them up and use them to heat a drum of water to provide heat at night. Might also run some LED lamps at Night to help with the growing and a fan to Circulate the heat.
This time I'll put down black plastic on the ground as I was going to before but forgot till it was all done to keep the weeds away and dig a hole in a corner and sink a drum so it catches any run off water. That way I can put fertiliser in it and not loose it. I'll grow most of it in pots or halved drums and anything I want to put in the ground I can just cut a slot for. I'll get the plough and turn all the weeds and plants in before I start then cover it all with the black plastic.
The black should help heat the enclosure through the day as well. The setup is 5 x 2.5 x 1.8 so a decent amount of room. I already have a stack of tomatoes coming up from where I dumped some that got hit by birds in the garden. They were dormant for a couple of months but now with the rain, are going nuts.... Like all the weeds that have been in hibernation for a year. I must have 2-300 Plants that have come up and are looking very strong. They are thicker than the grass on the lawn areas atm.
The mrs is getting a bit annoyed. We have tomatoes coming up everywhere like weeds. They have got in the pot plants, one is doing well in the water lillys, they have come up in the front ornamental garden. Quite funny. They will probably just start to fruit and the frost will wipe them all out. When I came here I brought an almost 3 Yo tomato plant I had growing in a drum. I went away and no one watered it on a couple of hot days and I lost it which I was annoyed about.
I have an aeroponic drum I built that uses a pump on a timer to spray water on the roots of the plants growing in net pots. This works awesome for Lettuce. I use a tea from my daughters rabbit in the water and some sea sol. there are expensive Hydroponic fertilisers around but I have had no problems with what I have done. I mix the sea sol weak but add it ever day more or less rather than the full strength every fortnight. I could put that setup in the big greenhouse and that would add to the thermal mass of the enclosure at night.
I was thinking doing a double plastic wrap, Maybe black plastic on the south side wall of the setup may help with heat retention at night as well like double over single glazing... sort of.
Day temps aren't bad at all here, it's the well sub zero mornings that are the problem. 1250W of panels may not be enough to get the water drum where I want. Would be interesting to try and work out if the plants prefer more warmth or more light. I could put another string of panels up there covering the top and just letting the light from the sides come in. Winter sun angle is 34o here anyway. Might be cheaper to run the LED lights all night to make up for the light shortfall than run the heater off the mains.
Alternately Put in an IBC and heat that ton of water with an oil burner every 2-3 Days. An IBC could be good but take up a lot of space. Then again, I could put things on top to use the footprint and I'd only loose vertical space which wouldn't be a problem with every crop. Putting it in the middle might be the best position even to one side.
Could probably wrap the IBC in insulation I have up the back and put a pump on a radiator with a fan and a thermostat so the heat was retained and only was used when needed.
Starting to sound like a lot of work already.
Better look at potential crops first. Most winter things take forever to grow but in a hot house summer crops like tomatoes would probably be OK I think.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
