Greenhouse Heat-Sink

@philomel thanks for your time

@fat controller thanks for filling in the survey. Nice to have a reply from a mod and please ask their thoughts. This is something we feel a lot of people can benefit from and build on as we are doing this on a budget.

My intention is not to steal thunder from this forum, but the amount of data, images, technical details and findings will need to be posted on a separate website and at some stage maybe post a link here? (If not then I will respect the rules of the forum 100%).

In answer to your question yes we aim to store the heat energy generated by the sun during the day and then release this at night or over as long a period as possible, therefore trying to maintain a better mean average temperature. Not a new idea, but what is new is controlling the fan speed so a more controlled release of the energy is possible.

We did some material testing today with a small 5L plastic container, then we filled it with 3 types of materials: Fractured tempered glass, Granite chips (10~20mm) and broken concrete slabs of irregular sizes no bigger than 60mm approximately. These material all have good thermal conductivity properties, particularly the granite and glass, they are also different shapes and sizes, the glass is irregular but has 2 flat sides etc. Considerations will be made for availability and cost of materials as well, but this gives us a good data set to work with.

The box (materials testing box from my original post) had a pipe at the bottom with holes and a 40mm*10mm fan pushing air in, then there was a hole at the top the same size as the pipe and we also inserted a temperature sensor. The materials were all outside for over 8hrs to let them acclimatise to 5C, we then placed the box containing each material type at room temperature 19C (in this case) and had the fan running for 1 hour at full speed, then cooled them in a freezer (-20c) for 1 hour. All the time my laptop was recording the temperature every second, so we have a good data set from that. We also measured the volume of each material, free air space etc, this then allows us to look at the temperature variation data and make some conclusions against the materials volume, free air space etc.

lots of data to go through just from today, but some interesting stuff like the free air space in the granite chips was around 40% (we all thought 15-20%)

My question I guess is would the mods mind if I posted a link to a website, where all this information can be viewed in a more organised manner?

 

Survey done......very interesting Anthony. I hope the mods won't mind you posting a link.

 

@Fern4 thank you for contributing to the survey

@fat controller that is great news and very encouraging. I have dedicated a small section of my website to the project for the time being, this maybe moved at a later date but will serve perfectly well for sharing our findings. The link is below and I will also update the original post to reflect this. Not much information there at the moment but I will try and add weekly updates.

http://coder-tronics.com/greenhouse-heat-sink/

 

Just a quick update as not had time to place anything further on the website, but it will be coming!

Ok we are re-doing the material box testing for a bit longer this time, and introduced a few extra 10 minute fan rest periods, so we can see the temperature in the chamber when the fan is off. This allows us to see the true temperature not affected by any wind chill factor. The graph image attached shows the data from the fragments of concrete, the yellow bars mark three 10 minute fan rest periods and the large red and light blue lines mark 2 hours of warming (2C fridge to 19C room temp) and 2 hours of cooling (19C room temp to -20C freezer). We need to get the other 2 materials completed again and can then draw some conclusions, we don't have an air flowmeter unfortunately as that would provide some useful information.

We have also calculated the volume of our test greenhouses, basically each chamber is 1.15m(cubed) i.e. 1150 litres, so dug a hole to make the heatsink exactly 10% or 115 litres. This would make quite a large hole if scaled, but should be an easy scaling factor and also should provided some measurable effects. We will build a box and then insulate this, so the final hole was made 560mm(W) * 600mm(L) * 600mm(D), this then allows for the extra insulation etc. Another image attached.

I am waiting for some PT100 temperature sensors as we intended to have 7 sensors, but as we need to start testing next week, we will just place 2 temperature sensors in each greenhouse. The key data is really the control greenhouse temperature which forms the reference, then the heat sink greenhouse temperature can be measured against that.

Cheers,
Ant

 

Survey done.

 

Survey completed, good luck with the project

 

Thank you M and Adendoll, we are now closing the questionnaire as it has served it's purpose but I really appreciate all the input.

Firstly sorry for not coming back with an update sooner, we have all been very busy and I have a number of projects I am working at the minute. Not had time to update the website either, so posting updates here for now.

The volume inside the control and heatsink greenhouse is approximately 1150 litres each, so the heatsink was scaled to 10% 115 litres. We used an insulated box as this all needs to be removed in May, but a DPM lining with insulation is probably the best option.

A few photos attached showing the hole we made, the insulated box and the box and electronics inside the the greenhouse. Additionally a graph showing the initial 96hrs of test data.

We have also completed a initial 96hrs test with the heatsink in operation and have collated the data. It looks good so far with the heatsink keeping the temperature approximately 1C above the control greenhouse at night, as well as clipping high temperature extremes. We obviously need to carry out more testing, before drawing final conclusions but this is promising. I just removed this data this afternoon and we will be carrying out a prolonged test of 1-2 weeks.

Data filtered to show average over 30 minute intervals. Data start is around 14:16 on 26th of March, Data end is 15:25 (with clock adjustment 16:25) on 30th of March

Best regards,
Ant

 

Hi Antscran
I arrived a bit late for your survey unfortunately, but very nice project just the same.
Fwiw, i`ve had 60m of 80mm perforated drainage tubing buried 4ft deep under my greenhouse for the past 5 or 6 years. The heatsink it influences consists of approx 30 tonnes of clay soil that was already in situ. I just had to do a bit of digging


and after wrestling this weird looking critter into the ground


it was pretty much done



Hi John
I suspect Dick never followed up on his heatsink project because the results were less than great, a computer fan wouldnt push much air through the 40mm pvc pipe and it would take the path of least resistance up through the rubble..
.

 

Hi John
It gets frosty on the outside but havent seen any inside over the winter. I dont think its been all that cold this year and it seems like we`ve a few more sunny winter days than usual, which helps.

I vaguely remember Dick`s son having a go at NFT in the greenhouse. He used a mix of soil and water as a diy "organic" nutrient, so it wasnt a great success .He could have turned it around by buying a bottle of organic hydro nutrients but he decided several hundred quid on two 250w growlights was the way to go

 

Sorry for last response, we have been head down writing reports and exams. The original intention was to have 4 sensors; 2 in the greenhouse located near the apex and one mid level around where most of the plants are, then 1 buried inside the heatsink and the last externally for ambient temperatures.

However we order 7 but they never arrived so had to make do with just 2, not ideal but we only had a limited time with the prototype. It's all been dismantled now as Jen's (one of my colleagues) whos garden had the construction, was only allowed to have it there until mid May.

 

Hi Hex,

Sorry for late response, our heads have been down with reports and exams.

That is quite a construction and looks like a lot of work, are you pushing air through all that or water?
Regards,
Ant