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)...

Gary
March 27, 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...

Gary
March 18, 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 ...


Gary
March 6, 2014

Gordon's Deep Energy Retrofit - After 5 Years Report

Back in 2009 Gordon and Sue did a full deep energy retrofit of a 1963 brick schoolhouse making it into a very energy efficient home.

The retrofit include R40 Larsen Truss walls, triple glazed R6 windows, a passive solar window scheme, a new solarium, solar water heating, and a hand crafted masonry heater.

The new solarium

They have been in the home for five years now and this full report describes on how things have worked out along with a well kept record of energy savings -- all the details after five years here...

The whole retrofit project is described in detail here...

The Larsen Truss Walls

Thanks very much to Gordon and Sue for providing the update.

Gary
February 27, 2014

A Solar Heated Loo

Michael has developed this simple and elegant solar heated version of Arbor Loo that has many advantages as well as offering a little more comfort on those cold mornings.

The Arbor Loo provides a efficient and sustainable solution to the poop problem, saving thousands of gallons of water a year and providing useful tree planting compost.

I really like the nice simple space heating system.  It is a drain back system with the collector nicely integrated with the roof.  An IBC container is used for heat storage.  And, by leaving the insulation off the parts that face the "living space", the IBC also provides the heat distribution.

The only moving part is the pump -- no controller, no antifreeze, no heat distribution controls or pumps -- very simple.

I think that this kind of design could be applied to other simple space heating needs.

The loo under construction with the IBC container at the back (providing a heated backrest for the toilet seat).   I like the way the structure integrates the standard size door, collector, IBC and toilet seating area with no wasted space.

Full details on the build and performance of Michael's solar heated loo ...

Thanks very much to Michael for providing this material!

Gary

DIY Ground Source Heat Pump + PV Array -- No Heat Bills!

In this very ambitious project, Jerry goes through all the details on installing a 5000 watt PV system and a 2 ton Ground Source Heat Pump. Together they provide all of the space heating and cooling and hot water.  

No heat bills and very low emissions.

The ground loops for the Ground Source Heat Pump

Jerry started by installing a 5000 watt PV system on his garage roof.

5 KW grid tie PV array on garage roof.

The PV system is grid tied and uses an Aurora 6000 watt grid tie inverter to produce house power and to interface with the grid. Jerry is paid 14 cents per KWH generated via the net metering agreement with his utility and is also able to sell SRECs to the utility to allow them to meet their renewable energy generation requirements with the state of NJ.

The 6000 watt grid-tied string type inverter for the PV system.

Once the PV system was installed, Jerry installed a Ground Source Heat Pump to efficiently use the PV generated electricity to both heat and cool his house. The GSHP installation involved digging a 300 ft long 8 ft deep trench, laying out the ground loops in the trench, installing the 2 ton heat pump.

The 300 ft long trench for the three GSHP ground loops.

The 2 ton ClimateMaster water to air heat pump.

In addition to installing the 2 ton heat pump, Jerry also designed and installed a duct system to distribute heating and cooling to the house.

All the details on the DIY GSHP + PV system in a 26 page pdf...


Gary
January 22, 2014

Building Large Cylindrical Tanks for Solar Heat Storage

Alan Rushforth of Rushforth Solar provides detailed information on building large cylindrical water tanks for storing heat. These tanks are commonly used to store heat generated by an array of solar collectors in space and water heating applications.

One of Alan's tanks

The tanks that Alan makes typically range from a thousand gallons up 4000+ gallons, but the design could certainly be used for smaller tanks that would be typical of residential solar applications.

This design is very structurally efficient, light weight, and material efficient.

The tanks consist of aluminum  sheet wrapped into a cylinder, which is then lined with rigid foam board insulation.  

The outer aluminum sheet wall with layers of insulation inside.

An EPDM liner is then installed to contain the water.

The EPDM tank liner being installed

Alan also includes some very helpful material on building heat exchangers for these large tanks.

Thanks very much to Alan for providing this material!

Stainless steel pipe coil heat exchanger.

Alan's full description on building these tanks ...

Gary

Home Power Digital Subscription Deal

I don't usually do deal announcements, but could not pass up this one.

Home Power Magazine is doing 50% off their digital subscription rate for a while.  So, a 3 year digital subscription that also includes access to 20+ years of back articles is now $11.95 -- what a deal!!

https://www.homepower.com/subscribe-and-save?template=subscribe

If you are not familiar with Home Power, its probably the best source out their for detailed articles on DIY solar and other renewable energy projects -- aside from Build-It-Solar of course :)

Gary

Backup Heating for the $2K Solar Space and Water Heating System

Our $2K solar space and water heating system provides solar water heating and also space heating to part of our house.  Until recently the backup heat for this part of the house was a propane forced air furnace that came with the house.  But, last winter the furnace died and the replacement cost was $6000.  So, instead of replacing the furnace, we added a backup heat system that just adds heat to the large solar heat storage tank when there is not enough sun to keep the solar tank warm.  This approach cost about $300 (pretty good saving), and has the advantage that we no longer have a noisy and potentially unsafe gas furnace hung from the floor just below our bed.

The new backup heat system is pretty simple.  Its just an electric hot water heater that sits next to the solar tank with a small pump to circulate hot water from the electric tank to the solar tank when the solar tank temperature drops below a setpoint.  The heat is distributed to the room above by the same radiant floor pex tube system as before.

The backup heat source electric hot water tank

The TopsFlo pump that circulates water between the backup tank
and the solar tank is at the bottom of the picture -- only 15 watts.

Diagram of the new backup heat system -- really simple.

I've added a new page that describes the backup system here...

And, updated a few pages for the project to reflect the new backup heat system...

There is also some discussion of other alternative backup heating systems -- I'd be interested in hearing any ideas on a better way to do it.

Gary

The Passive Solar Bird Bath is Back

We lost Jim's very nice passive solar bird bath for a while, but is back now.

The passive solar bath provides some unfrozen water in the winter for the birds to drink.  Its a nice simple design that is easy to build and has worked well for Jim.

Thanks very much to Jim for documenting this project!

The solar collector on the bottom heats the drinking dish on the top.

If you have any ideas for improvements or any questions, or have a design of your own that you would like to report on -- please use the Comments section on this page...

All the details on Jim's passive solar bird bath...

Gary