Backyard Aquaponics
A place to discuss aquaponics

I'm about to buy a greenhouse (pictured) and have done a fair bit of reading and that also took me into greenhouse heating, the budget controls everything here and I'm at the bottom end of that scale and it's a lot harder to find heating efficiency down there without having an open cheque book.

Even thinking about a heater is a mine field and the cost involved in running heating is also a bigger concern, so the plan is not too run heating 24/7 or during the day, but to only run on extremely cold nights just to take some of the chill off the air on those colder nights.

By using a bottled Propane Gas heater I can monitor the heating budget and not have any unexpected gas bills occur, and only run according to my budget.

The heating I'm thinking of using is a Biogreen Mi 300/GB 300W Frostbuster unit, I know it's not going too be the ideal setup a will not produce anywhere near sauna like conditions, but I'm hoping it will make some small difference. I could always look at building a small rocket heater, but the gas would be a far easier option than having to light it each time and keeping the fuel up.

It would be nice too know how efficient this heater is without having to buy it and find it's a waste of money.

http://www.ebay.com.au/itm/Biogreen-Mi- ... 48671f505b

Has anyone used this heater?, the only reviews I've found for it are from Amazon and they would only have the positive reviews posted so it's not a true indication.

http://www.amazon.co.uk/product-reviews/B005N96RN2

Joe

have you bought the greenhouse? Is it a double layer type? You'll lose alot of heat at night if it is not. Can't comment on the heater, though I've just built a single skin hoophouse and that almost tracks ambient temp at night.

Matt I haven't bought anything yet, and have tossed up between building a green house and buying one.

The price of building anything these days is expensive, and Bunnings make sure it will stay that way, plus freight and labor, it's cheaper to bite the bullet and buy one.

That greenhouse is in my price range and has 6mm polycarbonate sheets, not the thickest polycarbonate sheeting but it's thicker than the normal 4mm, it would probably do a little better your single skin.

Thanks for the heads up on the single skin tracking the ambient temp at night, I assumed any hoop house would do slightly better than the ambient temperature by retaining some of the thermal mass of what the garden beds were made from and their contents.

My wife has always wanted to house her 2 Moringa plants in a greenhouse and now she also wants to grow ginger in it, the original idea of the greenhouse was just too keep the frost off the Moringa at night and a bit of warmth during the cooler days.

Joe

The heater is going to be as efficient as any other heater because you are just burning gas and if you do that in the GH then all the heat will go into the GH but...

The heat loss through your GH walls will be significant. If you could rig up some movable blanket over the top of your plants (assuming they are all low plants) then that will shrink the volume of the GH that you need to heat and reduce the amount of heat you loose through the GH roof. You could further reduce your heat loss by insulating the walls. However,...

You seriously need to think about ventilation because burning gas in your GH all night could very easily deplete your GH of O2 and add way too much CO2.

Don't plants need co2 ?
The blankets sound like a good idea You could put the on wires, I think Tom 77 has shade cloth in a similar manner.
Of course shade cloth is lighter than blankets.
Bunnings have a heavy blanket that's like a packing / removal blanket, nor real heavy but dense.
Good luck.

Just thought of it, you could use milar reflective space blankets they reflect heat realy well. That's why they use them for survival blankets. Light and easy to move. Just a bit fragile

the heat loss from the greenhouse at night is conductive, reflective surfaces don't help much with conductive heat loss. Pool covers work well - I'd ideally like to come up with something that does not need to be put up/down every night/morning though.

also plants need CO2 when photosynthesizing, so won't need it at night, unless artificially lit.

I recon you would be better heating your water than the whole green house

Not at night.

Plus if there is no oxygen in the house what is going to happen to your fish and bacteria?

You could use an air pump out side the GH to inject air into your FT but if you had an air pump inside the GH it wouldn't help.

Thanks for the replies guys, in my case there wont be any fish in the greenhouse, just plants and it's mainly to keep them frost free and do a bit better than they would out in the elements.

I'm going to try a combination of bubble wrap, propane heat and a little water heat next winter. I would much rather have wood or elec heat to cut down on condensation. I have seen some videos of using Christmas lights to knock the frost off.

Rairdog I like the idea of Christmas lights, I've had a string of solar powered Christmas lights running in my fernery for many years, they were put up one Christmas and just haven't been taken down.

I think the ferns love them, we'll there's been no complaints

A few strung around the greenhouse might take a little bit of sting out of the air and cheer the plants up as well

Seriously I think a propane heater or rocket stove would be the way to keep the running expense down and if you had any worries about ventilation or fumes, you could run your heating pumped through a copper coil from outside the greenhouse, circulating into large PVC barrels as a controlled thermal mass source.

I've seen the special effects movie guys make up an instant water heater from a copper coil with a small gas flame up the centre and it was very efficient, in this case it would need a large volume of water so your water didn't get too hot.

Controlling a pump to turn over enough water volume and keep the temperature at a reasonable range wouldn't be that hard.

A small rocket stove with copper tube coiled around the flue pumped into the greenhouse would be cheap and efficient.

As long as the other end is a heat exchanger not made of copper. When heating a GH from inside the GH the heat that you transfer into the system will always be 100% efficent. Same with electric heaters. Rocket stoves that are outside the greenhouse will not be because only a portion of the heat will be transferred from the rocket stove to the system and no matter how efficient some heat will be lost out the flu.

The biggest challenge with heating a system is not heating the water of the system. It is holding the air at a temperature such that the heat transfer from the water to the air is relatively slow. So if your target water temp is 18c then you need to keep the air temperature as close to 18c as you can. This means insulating the air about the system in some way is a big part of the solution. Screens and blankets shrink the volume that needs to be heated but more importantly insulates the space above the system slowing the rate at which the heat is leaving the GH.

Once you have that sorted all you need to do is put heat in at a rate that is faster than it is leaving. Which is still rather fast.

Ground temperatures around the world are generally in their high teens and at depth are very stable. Go deep enough and you can't actually detect any change between summer and winter. Tying your system into the ground can really help keep your system stable but that is only useful if you want to keep your system close to the ground temp.

If the temp that you want to keep your system at is lower or higher than the ground temp then you need to insulate your system from the ground as well.

It is unlikely that you will want to keep your system at a temp lower than the ground temp but everyone that wants to keep warm water fish will want their temperature to be higher than the ground temp. Often you see people writing about burying tanks to "insulate" them. This doesn't work. Burying a tank ties it close to the ground temp and since dirt is a relatively good conductor of heat burying a tank or sump helps to keep your system closer to the ground temp. For trout this is almost always a good thing but for warm water fish it is almost always a bad thing. For warm water fish you would be better off insulating the floor of your GH.

This is relevant to the above discussion because in a tiny GH like the one above you are also going to get a lot of heat loss through the floor. Around the edge of the GH heat is going to exit through the 6" of heated soild near the wall. This problem can be fixed by burying insulation in a trench under the GH wall. Alternatively for a system for cool water fish add a skrit of insulation out from the wall. This will increase the amount of dirt that is contained within the thermal envelope of the GH. For warm water fish cover the entire floor with insulation so that it is easier to keep the GH temp above ground temp.

Stuart thanks for the reply.

Sorry Stuart my statement "Controlling a pump to turn over enough water volume and keep the temperature at a reasonable range wouldn't be that hard.",was a little confusing.



What I meant too say was:

Controlling a pump to turn over enough water volume and keep the "WATER" temperature at a reasonable range wouldn't be that hard.

Meaning the water temperature of the thermal mass not the greenhouse air temperature, I wont have any fish tanks or aquaponics in the greenhouse, I'm just trying too take some of the chill out of the air.


I don't know how much difference it would make and I know it would be minimal, I've even thought of running a horizontal flue from a rocket stove along the full length inside the greenhouse with the rocket stove situated outside.

I think there would be a fair amount of heat come off the flue too make some sort impact on the air temperature in the greenhouse and no exhaust or fume problems.

Stuart I value your comments highly and take it all on board, thanks for your time.

Yes a flu running through the GH will transfer a lot of heat into the GH great way to improve the efficiency but...

As the smoke cools down it will loose its buoyancy. Long flues that loose a lot of heat to their surrounds can make ovens/heaters/fireplaces hard to get to burn well. If the fire is hard to light then it can help to add a secondary fire box for getting the fire started.

For example your flu will turn out of the firebox and run horizontal through the GH and then turn again to go vetical and up and away from the GH. If the fire won't light and draw properly you can add a hatch in the vertical section of the flu after the GH. Inside the hatch have a minimal grate on which you place a "bunch" of screwed up newspaper or something else that will burn fast. You light the primary fire and when it starts to struggle you then light the secondary fire and close the hatch (preferably the air tight hatch). The secondary fire heats the vertical exit flu and sucks air through the horizontal flu in the GH and kick starts the primary fire.

Depending on your setup and skill you may need to do this several times until the primary fire is well lit and providing enough heat through the entire length of the flu to get the fire to draw properly.

Your welcome.