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Author Topic: Silly solar project No. 1: Greenhouse solar air heater  (Read 5360 times)

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Bigrich

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #15 on: January 23, 2015, 12:04 »
What makes it all complicated is I'm going to need 3 timers to run it all
1 for the fan on the solar heater (the fan is a 140mm pc fan which is 12 volt) - to run in the mornings
1 for the "in" on the heatink to pull warm air into the underground box(a 80mm PC fan in an enclosure on the pipe) - to run mid morning till late afternoon

Would it be enough to hook this fan up to a solar PV panel - if there is sun it will run, if not it won't?
I'm wanting that small fan to run in the evenings as well to help pull the warm air back out of the heatsink, so that's got to be on a battery & timer. Though I'm definitely thinking of doing that for the main solar heater in fan

Quote
1 for the "out" fan pipe (a 40mm PC which I've bodged into the 40mm waste out pipe to pull warm air out of the box at night (and maybe help the in fan pull warm air in by creating a bit of negative air pressure)

I wonder if this could be achieved with a short vertical pipe to, say, staging height.  Would cold air "sink" into the store and drive the warmer air out, up the vertical pipe?

I can give it a whirl, but I'm figuring the small elbow fan will work more efficiently - though maybe not: it's all an experiment, and I'm not investing much cash into this since most of the materials were already in the shed


I'm being realistic about it in that I know that expecting to get heat from November to late March will be a waste of time as there's not enough sunshine about. But April to Mid June, and September to October will hopefully be a success


Bigrich

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #16 on: January 23, 2015, 12:08 »
I think more than the sunlight hours, the insolation is important. That is a measure of the "power" of the sun - e.g. used by installers of Solar PV panels

First site I found that came up in Google was this:
http://www.efficientenergysaving.co.uk/solar-irradiance-calculator.html

and putting in London and facing due South I got (Measured in kWh/m2/day onto a horizontal surface):

Jan   0.75   15%
Feb   1.37   28%
Mar   2.31   48%
Apr   3.57   73%
May   4.59   94%
Jun   4.86   100%
Jul   4.82   99%
Aug   4.2   86%
Sep   2.81   58%
Oct   1.69   35%
Nov   0.92   19%
Dec   0.6   12%

Percentage is a comparison with the June figure, so in January only 15% of summer "strength" and February a quarter.

Here are the sunshine hours, from the earlier link, for comparison:

Jan   01:21   20%
Feb   02:07   31%
Mar   03:36   52%
Apr   04:54   71%
May   06:11   90%
Jun   06:52   100%
Jul   06:17   92%
Aug   05:56   86%
Sep   04:34   67%
Oct   03:03   44%
Nov   01:42   25%
Dec   01:15   18%

The hours, on their own, look like there is 1/8th in January and 1/3rd in February, but I think "sun power" will be less, as per insolation values above.

Storing the heat from Summer to Winter would be a different proposition, bit more of an engineering challenge though!

Interesting numbers in that you get a near doubling from Feb to March, and then a fall off a cliff from September to October.

But if it helps increase heat as the growing season kicks off and extends it at the other end I'll deem it a success.

I'm also getting a thermometer to put in the solar heaters in-pipe so i can get some comparison values for heat output - 2 quid from ebay so hardly breaking the bank

Kristen

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #17 on: January 23, 2015, 13:47 »
Quote
1 for the "out" fan pipe (a 40mm PC which I've bodged into the 40mm waste out pipe to pull warm air out of the box at night (and maybe help the in fan pull warm air in by creating a bit of negative air pressure)

I wonder if this could be achieved with a short vertical pipe to, say, staging height.  Would cold air "sink" into the store and drive the warmer air out, up the vertical pipe?

I can give it a whirl, but I'm figuring the small elbow fan will work more efficiently

I agree, bound to work better like that, its just a question of whether you have energy available to drive the fan during the night - more hassle to set up battery / charger etc. circuits IF you could get away with direct driven off a solar panel to "store" the heat, and "convection" to extract it.
My Blog last major update 30th December 2012

Headgardener22

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #18 on: January 23, 2015, 13:58 »
What about a simpler system?

Put some pipes under the soil and pump the air from the top of the greenhouse through the pipes when the sun is shining and let convection release the heat overnight?

In March, my polytunnel regularly gets up to 40C when the sunshines on it but drops quickly overnight. Circulating the air would have an additional benefit.

Its still going to be nigh on impossible to work out if there's any benefit but might be fun to try.

Bigrich

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #19 on: January 23, 2015, 16:00 »
What about a simpler system?

Put some pipes under the soil and pump the air from the top of the greenhouse through the pipes when the sun is shining and let convection release the heat overnight?

In March, my polytunnel regularly gets up to 40C when the sunshines on it but drops quickly overnight. Circulating the air would have an additional benefit.

If I've understood it right, that would be simpler, but that's a lot of mass to heat, without digging everything out & creating some sort of undersoil insulation layer to stop the heat bleeding down and being lost.





Its still going to be nigh on impossible to work out if there's any benefit but might be fun to try.

True - Though I might chat to my plot neighbour who has a greenhouse in a similar position and ask he can measure his temperatures at the same time to see if there's a difference

If I get really into it, I could paint the paving slabs and graven in the greenhouse black to store heat as well  :D

Quote
1 for the "out" fan pipe (a 40mm PC which I've bodged into the 40mm waste out pipe to pull warm air out of the box at night (and maybe help the in fan pull warm air in by creating a bit of negative air pressure)

I wonder if this could be achieved with a short vertical pipe to, say, staging height.  Would cold air "sink" into the store and drive the warmer air out, up the vertical pipe?

I can give it a whirl, but I'm figuring the small elbow fan will work more efficiently

I agree, bound to work better like that, its just a question of whether you have energy available to drive the fan during the night - more hassle to set up battery / charger etc. circuits IF you could get away with direct driven off a solar panel to "store" the heat, and "convection" to extract it.
I've got the clobber anyway, makes sense to use it. Though I might mess around with the more low-tech options if it does work in the first place. Which is not a given

Headgardener22

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #20 on: January 23, 2015, 16:31 »
If I've understood it right, that would be simpler, but that's a lot of mass to heat, without digging everything out & creating some sort of undersoil insulation layer to stop the heat bleeding down and being lost.


Agree. However, you're not trying to heat the soil (whether it be your heat sink or just the soil in the greenhouse), you're just trying to allow some of the heat from the atmosphere to be stored for a relatively short period of time and then to be radiated when the air is cooler. So even if the heat bleeds downwards, I assume that it wouldn't go very far. The reason (if I remember right) that the Not Easy Being Green demo used ground glass (other than showing off a fancy glass pulverising machine) was to have a large surface area to absorb the heat.

Overall I guess it depends what you are trying to do. Are you trying to make a small area of the greenhouse significantly warmer all night (like a propagator) or are you trying to generally raise the temperature of the greenhouse a bit overnight. If the former, then yes, you'll need to concentrate the heat into a small area but its probably easier to buy a propagator  :D.


Bigrich

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #21 on: February 09, 2015, 18:41 »
Time for a little update:
Not got a huge amount done on it since it's been so cold of late, but I've got a few bits of progress to report

I've sorted out a way of getting the warm air into the greenhouse - have taken a spare bit of polycarb sheet and stiffened it with a sheet of 6mm marine ply, I'll then swap it h#out for a sheet of glasss, and drill a hole in the polycarb/ply for the pipe to fit through



I've also build a sort of protective enclosure for the fan to keep it as dry as possible, and mounted it onto a bit of timber. The whole assembly will then be bolted onto the polycarb/ply sheet over the "in" hole to draw the warm air in. Nowt flash as I've no idea if the thing will work anyway, but it should work


I've also got hold of a 5 watt 12v solar panel, and tested direct connecting the fan to it. The good news is that the fan doesn't run unless the panel is in direct sunlight, which is good asn it means it'll only draw air through when the heater gets hot when the sun shines

Next job is to connect it all up  :)

In heatsink news, I've got the fan for drawing air into the heatsink built, tested and fitted. When the weather gets a bit warmer I shall give it a test

tinyallotment

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #22 on: February 09, 2015, 20:58 »
FANTASTIC post

This is the sort of thing I am going to build into my geodesic dome project. I want to try and use the hot air from the top of the dome to heat the water in the fish tanks of the aquaponics system which will then release that heat at night.

It will be an experiment

Keep up the good work dude

paul

jrko

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #23 on: February 18, 2015, 18:00 »
Lfe all this info and ingenuity!

I must say though, I think the grey stones will provide more heat storage (as long as you don't damp down)
Hello.  My name is James, the builder of Evil Shed mkII and The Greenhouse of Doom.  Please enjoy the madness of my Plot Diary here:
http://chat.allotment-garden.org/index.php?topic=107298.0

Bigrich

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Re: Silly solar project No. 1: Greenhouse solar air heater
« Reply #24 on: February 22, 2015, 15:04 »
Yesterday it was warm and sunny so I had a large bonfire, today it was raining and about 2 degrees so stupidly decided to go and fit the ducting and fan for the heater  :blush:

Removed the glass and fitted the new custom sheet of polycarb/ply, then worked out where the ducting (bit of drainpipe) would enter the greenhouse; removed and drilled a hole through the polycarb attached the fan housing and refitted it.


Then attached the ducting to the "out" of the heater and the "in" on the greenhouse and sealed it all up with some silicone




So all the remains now is to fit the solar panel up next month and see how it works  :) :)



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