Cold Weather, The Coop and Heat Transfer


_DSC6863-2A few weeks ago, we bought a new waterer for the coop.  There was nothing wrong with the current waterer other than being an energy hog.  Throughout December, we struggled with keeping the coop’s battery charged enough power the waterer.  The waterer’s 100 watt heating element was just too much. Think of it like this: the waterer’s draw (outflow) on the battery is greater than the solar panel’s ability to recharge (inflow) the battery.

\(Outflow > Inflow\)

_DSC6854-2The new waterer, branded as Cozy Hen Waterer, is from Neora Inventors, LLC. From a cost perspective, it was expensive.  Around $70 for the waterer, a hanging chain, and a heater.  The waterer consists of two buckets – one ¾ gallon bucket nested within a larger pail. Inside the larger pail, there is a layer of thin insulation.  The outer pail is only used as a convenient way to capsulate the inner pail in insulation.  The water, contained in the inner pail, is able to get out to the chickens byway of a chicken nipple (pictured to the right).  The other interesting bit of engineering is the encasement of the chicken nipple in an aluminum pipe.  The pipe extends into the water pail by several inches.  This is subsequently encased in a bit of insulation with an outer shell made of a PVC plumbing part.  Finally, inside the water pail, there is a 15 watt aquarium heater.  It will keep the water at around 77°F.

The aluminum pipe is clever because of what it allows: heat transfer.  Although not entirely analogous (it is a pipe and not a rod), you could get a sense of the heat transfer by using a partial differential equation (Partial Differential Equations for Scientists and Engineers is also a good place to look).  There are actually several energy-flows going on in these coop-systems if you think about it.

The heat is transferred from near the center of the water pail down to the chicken nipple byway of the aluminum pipe.  This allows for the nipple to stay mostly ice-free on those -20°F days.

A bit of welding - the new waterer needed a bracket to hang on.
A bit of welding – the new waterer needed a bracket to hang on; rebar scraps that I had laying around.

If you recall from a previous post, the first-replacement waterer had a thermostatic switch that kept the water at 35°F.  In my mind, that seems like a valid temperature for water – it would minimize the energy consumption.  The new waterer with the aquarium heater and its 77°F temperature seems, on the surface, like it will use too much energy.

But, there are a few things that make the new waterer-system much easier on the consumption of electricity.  First, the larger waterer has 1.⅔ times the surface area as that of the new, insulated waterer.  More surface area results in faster transfer of energy from the warm water to the cold air.  Second, and this is likely the most important factor, the new waterer is insulated.  Top, bottom and sides – it is all insulated.  The one direct exception is the chicken nipple area, but that has the aluminum pipe to assist with heat loss (with the assumption that the heat transfer from the water + pipe is greater than the heat transfer from the end of the nipple to the air).

The more I have thought about the larger waterer and how it appears to be inefficient, the more I kept thinking of its design in comparison to the new waterer.  The larger waterer has the heating element on the bottom – the three gallons of water sit on top of the element.  This means that only one side of the element in contact with a surface that has water touching it.  That other side is hanging out in the air; sometimes, well-below-zero air.  What is the likelihood that the thermostatic switch actually switches off for any significant length of time?

A better design would be have the heating element have more contact surface with the water.  Perhaps, instead of being encased in a disc in the base of the waterer, the element would be a more rod-shaped protrusion from the base into the center of the water  reservoir.  Secondly, insulate, insulate, insulate.  The choice of insulation material is possibly debatable – the new waterer uses foil covered bubble insulation – this might be sufficient; it would certainly be better than nothing.