Passive solar heating/cooling for conservatory

[thegreenman]

Here's something I have been pondering for a while.

My southish facing conservatory gets very hot in Summer and very cold in winter.

Temperatures typically max at 40c and go pretty close to freezing on cold Winter nights.

The floor is concrete with tiles covering it. During the Summer they do give off noticeable heat at night.

I have been looking at using a large black container of water to help stabilise the temperature as used here http://www.growingspaces.co.uk/features.html

I am looking for something low cost and low tech, any ideas if this would work or would the water mass needed be far too great as I have no idea on how to work out the sums for this.   

[A.L.]

hello,

a 1000litres of water will store 1.16KWh per degree centigrade rise in temperature.

a store physically in the conservatory could even out temps spring to autumn but will not heat the conservatory in winter

the lowest cost solution would be a water wall at the back of the conservatory or a low one at the front

[EccentricAnomaly]

OK, back of the envelope time.  Suppose in summer the net inflow of heat is 800 W/m² of the sun-facing aspect of the conservatory (allowing somewhat less than 1 kW/m² for heat loss, particularly through assumed ventilation) and we want to soak up, say, 4 hour's worth of heat (i.e., effectively the warmest part of the afternoon though, of course, actual absorption would spread over more of the day).

Total energy to store is 800 × 4 × 3600 = 11'520 kJ/m².

Suppose the temperature of the water rises from 20 to 25°C (trying to keep the air temperature to, say, 30°C instead of 40°C) the energy absorbed by the water (with a heat capacity of 4.2 kJ·kg⁻¹·K⁻¹) is 5 * 4.2 = 21 kJ·kg⁻¹.

Dividing the second number into the first we need 548 kg of water for each square metre of the conservatory facing towards the sun.

In other words, with these assumptions the tank would need to have a capacity equivalent to one 548 mm thick across the north facing side of the conservatory.  That's big but not totally implausible.  Still, it shows that something of only a few hundred litres is not likely to help much.

Another consideration is the rate at which heat can be moved in and out of the tank.  This might be of interest:

http://njhurst.com/blog/01165734373

and look for "wootank" in the middle of this post:

http://njhurst.com/blog/01163886516

[thegreenman]

So basically lots of water or a bit less water with the addition of an active system to speed up heat absorption.

You both mention a wall of water about 50 cm thick, I presume that means from ground to roof.

Will container colour/material make much difference?

I guess plastic would be the most cost effective solution, painted black!

Would the effectiveness differ from a single mass or many smaller water vessels.

I'm thinking either plastic milk cartons or baby food tins (metal), that's what we get through most.

I'm also looking at underground greenhouses to reduce winter heating demand, apparently it's already been used http://www.rnw.nl/english/article/growing-vegetables-4000-metres

I love those low cost passive design ideas.

I wonder if it would work on a commercial scale?

   

[billi]

Hi

Our 3 m3  or ca 5 ton rammed clay store wall in our conservatory does a good job so far

I  am hoping to extend the passiv heating/ cooling effect one day and connect the  "wallheating " pipes to an active heating idea   ( sitting in there without heating in the momant in underpants at 5 30 in the morning  

Here is a photo of the clay plastered rammed earth wall with underfloor heating pipes

[Baz]

Putting barrels of water in an apple store to even out the temperature goes back to Roman times I think.
I put 3 litre bottles of water between rows of pots in my cold frame. I also put a bucket of water next to my garage tap.
The victorians built sunken heated greenhouses. You sometimes find them, normally delapidated, when going round garden scheme open days.

[EccentricAnomaly]

I'm thinking either plastic milk cartons or baby food tins (metal), that's what we get through most.

Good thought.  As I mentioned, the problem is getting the heat in and out of the store quickly enough to be useful on a daily cycle.  Lots of small containers increases the surface area available.

Try Googling "Laren Corie".  He's a house designer/builder in the American mid-west (near the Great Lakes) who uses lots of small containers (2 litre (or American equivalent) soft drinks bottles, as I remember) for heat storage within the thermal envelope of solar houses.  Unfortunately, his writings on the subject are rather scattered - incomplete web pages plus postings to various groups (particularly the Yahoo Tiny House group).  It was largely thinking about his systems which switched me from thinking about heavy-weight earth-bermed designs to lighter-weight buildings with water heat stores within the thermal envelope.

Where I don't follow him is his storage of the water high in the building and use of passive convection to store the heat.  From a purely practical point of view I'd prefer the water lower down and use of active circulation (fans) if required.

Going back to the conservatory, I wouldn't worry about the colour of the containers if they're plastic.  Metal tins painted black exposed to the sun sounds like a good idea but plastic containers probably should be kept out of direct sunlight unless anybody knows of paint that will really do a good job of stopping them going brittle through UV exposure.

[A.L.]

I guess plastic would be the most cost effective solution, painted black!

Or coloured ink in the water! 

[thegreenman]

Lots of great ideas.

Been trawling the net and as it always happens getting distracted. Found an interesting bubble greenhouse, they literally use bubbles to insulate the greenhouse at night. Pure genius.

Billi - Do you have any more info on your wall, would be interested to know how it works and how much it cost you.

Off topic It seems a shame so many things are built cheaply to last such as short time when more robust designs that can be easily maintained would do so much better. I purchased some solar christmas lights last year, this year they need new rechargeable batteries, I open up the box to find the batteries soldered to the circuit board   

[billi]

Billi - Do you have any more info on your wall, would be interested to know how it works and how much it cost you.

i cant tell, really what the costs were ,cause i swapped a lot of material and service and just used our subsoil


 so its only subsoil /studs and ply ..... and my/our labour

i  like thermal mass , insulation and passive solar

Billi