Thursday, March 27, 2014

Storing Excess Daytime Solar Energy to Heat Greenhouse at Night

Russell has a unique and effective solar heating system for his greenhouse. On sunny days, the system takes excess heat from the peak of the greenhouse that would normally just be vented outside and uses a water to air heat exchanger to transfer this this heat to a large heat storage water tank. 

The heat stored in the water tank provides heat to the greenhouse on cold nights and cold cloudy days. The same water to air heat exchanger that stores heat is used to distribute heat to the greenhouse.

The solar greenhouse
In Russell's North Carolina climate, the system is doing quite well and is able to weather cold and cloudy days on stored heat.

The fan at the top of this picture pushes heated air down the duct and through the water to air heat exchanger that is just visible under the bench.  A pump circulates the warmed water to a 275 gallon heat storage tank behind the wall.

 The heat storage tank lives in the yellow structure that adjoins the greenhouse.

At night when the greenhouse temperature falls below a set value, water is circulated back to the water to air heat exchanger, and the same fan that pushes hot air through the heat exchanger now pushes cold greenhouse air through the heat exchanger to warm it up.

The full article gives more details on the greenhouse design, construction, schematics, and performance (which has been very good)...

March 27, 2014

Tuesday, March 18, 2014

Night Radiation Cooling of Water Flowing Over Roof for Space Cooling

David lives in Castlemaine, Victoria, Australia with hot and dry summers. He is working on a simple and inexpensive and very energy efficient space cooling system that uses water cooled via radiation to the night sky.

The roof spray tube and the collection gutter at the bottom of roof.
At night water is pumped from a tank to the roof where a spray tube trickles the water down the roof corrugations.  The water cools by radiation and evaporation as it makes its way down the roof.  At the bottom of the roof, a gutter collects the cooler water and returns it to the tank.  The next day, when cooling is needed the cooled water in the tank is used for space cooling.

Closeup of the spray tube in action.  Water is cooled as it flows down the roof.

The "coolth" storage tank.  In the final system, the tank will be located inside the living space.
In this trial system, the tank is a 275 gallon IBC tote located outside on the ground, but in the final system the "coolth" storage tank will be located in the living space so that it can directly cool the living space.

David is interested in hearing your thoughts on both how the roof cooling system might be improved, and how the cooling distribution inside the living space would best be handled.  He would like to avoid an active cooling distribution system and just let the tank (perhaps with a fan) radiate and convect  cooling into the room.  Will this work?  Comment here...

March 18, 2014

Thursday, March 6, 2014

A Simple Solar Water Heating System for the Tropics

Peter lives in a remote and beautiful area of  Costa Rica and was looking for a simple solar water heating system that could be built with locally available and affordable materials.

Costa Rica home for the new water heater.
Peter worked out a simple thermosyphon collector design that heats water in an elevated tank.  The tank gravity feeds to showers. A float valve arrangement at the tank automatically keeps the tank topped up with water.

Because copper is very expensive locally, he used CPVC pipe for the collector.  Normally CPVC would not be a good choice for a glazed collector that sees this much sun because of the potential for overheating damaging the CPVC pipe, but Peter has worked out a couple of reliable mechanisms to keep the collector temperatures down.  He allows for some circulation of air under the collector glazing, and the thermosyphoning of water from the collector to the tank coupled with the un-pressurized tank insures that the water temperature will not exceed 212F.  Both of these protection methods are reliable and don't depend on electrical power or pumps or controllers (which are all subject to failure).

The collector absorber before painting

The gravity feed hot water tank with float valve

The completed system.

Peter provides a detailed description of the design and build and the challenges in finding suitable materials ...

March 6, 2014

/* Start Analytics ---------------- */ /* End Analytics ---------------- */