Backyard Aquaponics
A place to discuss aquaponics

To be accurate its electromagnetic radiation..a radio wave

So, if you installed reflective window tint backwards on the greenhouse it would let the good stuff in during the daylight hours and try to keep it in during the night?

nope,the backside of the barrier would act as an absorber and heat up, once the radiant energy becomes heat, its subject to conductive and convective losses

Everything above absolute zero radiates energy, the trick is to trap it inside the greenhouse so it cant get to anything outside which is likely to be a lot cooler than anything inside.. especially at night. When some object (plant,gravel bed etc) inside the greenhouse gets cooler than another it receives energy from all objects that are warmer, warmer being a relative term as it could be subzero

In a green house we are dealing with several forms of heat gain and loss: radiant, conducted, convected and air leaks.

Radiant is where most of the gains and losses are made, the trick is controlling the amount of radiant heat entering and leaving the building. Triple wall polycarbonate and reflective curtains for night, foil side down under the roof, are best for heat retention as most losses are at the highest point due to convection currents and conduction - foil dealing with some of the radiant losses by reflecting back into the building. For summer shade cloth on the outside of the roof is generally used.

Conducted heat is where most of the stability comes - when the radiant heat is absorbed and conducted into thermal mass. Dark surfaces absorb radiant heat better than light ones - matt black being best. Thermal bleed (conduction) also occurs when using aluminium framed structures in particular - easily solved using a less conductive material eg. wood.

Convection (like cold draughts) where the heat rises, cools, and then falls in loop is best fixed by insulation. The triple walled polycarbonate and even the roof curtains will help.

Air leaks seem pretty obvious, but an airlock entry would help a lot in a smaller structure like yours.

My two cents worth, in such a climate as yours, and money being no problem, I would minimise all of the above losses and maximise the radiant gains and thermal mass, edge insulate the structure with foam down to 1 metre (or under the whole floor), running hydronic coils under the FT if not the whole structure and couple this to an evacuated tube solar heater, all backed up by a wetback wood heater (or a dedicated LPG, nat gas, oil, elec water heater) for the coldest of days. It would be a lovely place to spend time on a cold winters day, being 'productive'.

From memory someone on the forum, possibly emsflojo, had a similar problem and was looking at the twin skinned greenhouses with polystyrene beads being pumped between the skins at night.
Hex think the phase changes of water are not particularly helpful at night. the move from a gas to a liquid happens very quickly (condensation) and then becomes a problem. And between a liquid and a solid at temps which are too low. Water appears to be a fairly good emitter of IR.

From memory McFarm many of the acrylics are invisible to IR so triple wall poly may be good for conduction loss but possibly of no benefit for radiant loss.

It may be useful if we knew whether we were dealing with a clear sky low humidity cold or an overcast windy cold

I was thinking along the lines of using phase change (and every other mode) to increase the rate of heat storage during the day. A knock on effect of the phase change energy transfer is cooler and drier air absorbs more heat and water.
If you use direct sunlight alone to heat the mass you dont get the bonus, its just heating not cooling
Once you have heat in the mass you can remove it by any method, the hard part is getting enough of it into the mass

Got the reverse problem over here in summer plus water's going to get a lot more expensive along with power
Going to start playing with heat pipes, small scale for another application don't know whether there will be any spin off for ap though.

Thank you Hex... confirms an idea I have in mind...

is it classified top secret Rupe?
Sleepe, the phase change of the water happens underground during the day in mine.
It won`t be running run at night as cold air picks up moisture from the mass as latent heat which is likely to increase the RH without a rise in air temp. The growbeds are sitting directly on the mass so they will gain heat mainly by conduction from below.
We don`t get as much sun as you guys but its surprising how hot the air in a greenhouse can get even on a fairly dull day. I have a plan B add-on for the winter, a large (20m2) solar air heater on the south facing fence to bolster the daily gains into the mass.The oversized main fan should be capable of driving everything.
The heatpipes sound interesting, you can never have too many strings on your bow

Some products that are already available that might be useful to this discussion.

I'm using Aluminet shade cloth. It has reflective mylar woven into the strands so when used over plantings in the summer, it provides a slightly more difuse light and helps keep things cooler under the shade cloth. The bonus is the reflectiveness of it gives a slight temperature advantage on cold nights helping to reflect some of the warmth back down to the plants rather than letting it all escape to deep space. Now I know the effects the aluminet has are really quite minor but as we all know a minor benefit is sometimes very important to the plants. My shade cloth is only 40% by the way.

Another item I've seen in catalogs but never in person is this water wall stuff. Basically framing a big black plastic bag as part of a greenhouse wall or divider. It will take on heat during the day and give off heat at night. Basically added thermal mass is all that is.

Now in the pacific northwest, do you get enough sun to really make the solar heating options worth the cost of them?

Hi Sleepe, already dealt with in previous previous post - "Triple wall polycarbonate and reflective curtains for night, foil side down under the roof, are best for heat retention as most losses are at the highest point due to convection currents and conduction - foil dealing with some of the radiant losses by reflecting back into the building."

The reflective and retractable curtains are often made from vapour deposited aluminium and Mylar - the higher the spectral reflectivity index the better for night time heat retention. Others are designed to filter light and reflect it within the structure with foil side down bonded to a thin shade cloth in hit and miss strips, when placed other way up they allow light in and restrict / slow heat gains (used in conjunction with roof vents). Some curtains are for maximum restriction of air flow and reduce convection currents as well as reduce radiant losses. There is even a silver foil bubble wrap roll out ceiling, along the lines of a double sided pool cover, for better insulation. Horses for courses.

Oh, and the clear polycarbonate offer up to 98% IR/light transmission but only 1% UV. I guess this is a straight arithmetic progression too, so twin wall 96% and 0.5% and triple wall 94% and 0.25% ?? All I know is that you can get very bloody hot under clear polycarbonate and not get sunburnt.

Other ideas for thermal mass is to put the grow beds on 44 gallon drums painted black and filled with water and anti freeze, laid on side and restrained from rolling. The anti freeze is mainly for the corrosion inhibitors. The other thing I've seen used to good effect are trombe walls. Sun facing high density masonry walls painted black for absorption, heat gain in summer controlled by foil curtains. I could imagine trombe walls being the grow bed stands.
cheers, mcfarm

Barrels come up alot for thermal mass but at best you`ll can only get half the surface area in direct sun, so around an 8F rise in the water temp per hour assuming its irradiated at 1kw/m2.
If they are shaded under the growbeds they get less energy as only the air/water temperature difference will be driving the process. With a 30F air/water differential you could see a 1.5F rise in the water temp per hour. Maintaining a 30F differential for the whole day wouldnt be easy.

the Human brain , our reason for success and perhaps our demise.
Those in cold environ want tropical fish living in thermal centred ice-cubes,..... those in tropical enivorn want cold water fish growing in ice centred deep fryers
Don't get me wrong , it can be done ,, but it takes ENERGY , power / cost.
If you desire to grow fish "out of ideal" conditions then please face the fact it is going to be expensive . As with most thing the MORE out of ideal the more expense.
Cairns does not supply salmon to tasmania ,, tasmania does not supply barra to cairns.
The ability to do both at minimal costs , exist in a small area ,, somewhere on the coast between Sydney and Port Maquarie.

+1 Chappo
Its the only way really. Its definitely easier to acheive a few degrees of temp shifts for native species than attempt 30deg rises or more over several months for tropicals.
Its the worst time of the year to rely on collecting solar energy too

Wouldn't happen to be centred somewhere in the "shire" would it Chappo.....