Monday, December 23, 2013

Liquid mass fridge/night cooler experiment

Inspired by the night cooler design by Mike Reynolds of Earthship fame I decided to build a cold storage box that doesn't rely on electricity.

The original design uses full beer cans for liquid mass plus reinforced  concrete to contain the cold once captured.

I decided to try and use as many recycled materials as possible in my modified Kimberly safe and it wasn't long before the bulk of the materials came to me by way of various jobs!

Being a Handyman certainly helps when it comes to sourcing things to reuse and the first thing I did was look in my workshop for something which might serve as the framework for the walls and floor of the fridge.

marine ply with membrane paint

I found some off cuts of marine ply left over from a possum nesting box project I did a couple of years ago so I painted them with bitumen paint and put these aside and drew up some plans of what else I might need.

A week after deciding to make my  cold box I was asked to clean up under a house where the floor had recently been insulated with large blocks of polystyrene and there was plenty of this stuff to use in my project so I filled the van up, took it home and put the polystyrene next to my marine ply.

polystyrene foam

A few days later and I found myself replacing half a dozen ceiling tiles in an office where the roof had leaked and stained some of the tiles, seeing that the tiles were made from pumice or vermiculite, both excellent insulative materials, I decided to use these too.

ceiling tile

I gave the ceiling tiles that were only marginally damaged a coat of bitumen membrane paint and added them to my collection.

ceiling tile with membrane paint
The basic idea for this type of cooler is to take advantage of the colder nighttime temperatures by installing a chimney on the top of the cooler and opening an operable hopper box at night allowing the air to pass through and cool the contents of the fridge.

Having a removable insulated damper between the chimney and the top of the box allows the space to be kept cool during the day by shutting out the warmer daytime temperatures.

By using the thermal mass of the insulated walls plus liquid mass as an internal skin, the contents of the night cooler can be kept cold until the sun sets and the cold air is once again admitted.

I picked up some esky ice bricks cheap and proceeded to put all my materials together...

ice brick inside skin of walls

After gluing the ceiling tiles to the marine ply I wrapped these panels in 0.3mm aluminium flashing, then I used silicone to attach the ice bricks and finally I wrapped the them again with more aluminium.

I made three panels like this for the back and two sides of the cooler.

solid liquid mass top with vent

I used some thicker ice bricks to make the top and I put a vent all the way through to let the chilled night air pass through to the inside of the box as well as chilling this solid block of liquid mass, again wrapping the whole thing in aluminium flashing.

floor with drain hole for condensation and air draw

For the bottom of the box I only used the marine ply and ceiling tile wrapped with aluminium as I want to be able to place items in the floor of the cooler without freezing them.

I did however put two layers of the polystyrene insulation under the floor because cold air sinks and this is one of the most likely places where it could escape.

Note the drain hole to draw the cool air through.

I framed all of the panels including the door with steel channel usually used for stud wall framing just to give everything a nice clean edge.

For the door I used one piece of the polystyrene with marine ply for the outside and panelscape plastic for the inside with heavy duty self closing hinges and a latch I had left over from one of my door hanging jobs.

For the seal on the door I used silicone extrusion generally used for replacing the seal on car boots .

insulated damper open for cold air entry to unit

The insulated damper on top of the unit slides in and out like a drawer for allowing the cooler night time temperatures and shutting out the day time heat.

insulated hood for top

I built a box similar to a range hood for the top after deciding to experiment with horizontal air flow coming from under ground rather than the vertical chimney I was originally going to use, this would allow me to use the range hood to allow cool air into the Earthship by opening the operable skylight in the green house and creating a convection engine thus serving two purposes.

cooling tubes built into hood

I incorporated four short tubes with insulated screw on lids for allowing the air through.

insulated damper in closed position

of course the damper to the cooler remains in the closed position on those hot days when this air flow may be needed.

cooling tubes open for convection engine

This project will be incorporated into the design of the Earthship I intend to build in sunny Tasmania in 2014 so stay tuned for results on how it performs!

The night cooler is now installed in the Earthship with a change in design.

the pipe which will run to the woodstove can be seen at the bottom left of this picture, note the use of a milk crate as the base.

I decided to scrap the sliding damper from the original design because the cooler will only be used in winter when the air temperature is cold enough for it to work and the days will be cold too so as long as I am using the woodstove for cooking etc, the cold air will continue to be drawn through.

I also decided to get rid of the range hood cowling because I installed cooling tubes in each of the earthship rooms and these will be enough to cool the building.

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