A Unique, Passively Cooled Home in the Tropics

Kotaro Nishiki built a passively cooled home in Leyte Philippines at 11 degs north latitude that incorporates a number of unique cooling features that allow the home to be cooled passively and without electricity.  Definitely worth a look if you live in a hot, low latitude climate.

In this area, most homes are constructed of concrete, and the concrete structures tend to absorb solar heat during the daytime, and then retain that heat through the night making the homes uncomfortable. Kotaro's design is centered on eliminating these daytime solar gains.

Leyte is quite warm summer and winter, so solar heat gains is to be avoided all year long.  At 11 degrees north latitude, the  winter sun shines on the south side of the house, and the mid summer sun actually swings into the north and shines on the north side of the house.  He keeps the whole house shaded using these techniques:

• The south facing single slope roof has on overhang on the south that keeps the south wall in shade most of the day.
• The north side of the house is shaded by an roof extension sloped down to the north that shades the north side of the house most of the day.
• The roof is double layered with airflow between the well spaced layers.  This greatly reduces solar heat gain through the roof.
• The east and west walls of the house are double wall construction with a couple feet between the walls.  The shading that the outer wall offers plus airflow between the double walls keep the wall temperatures low.
• In addition, he has worked out ways to take advantage of the night temperature drop and to use thermal mass on the basement to provide some cooling.

I think that even homes that are mechanically cooled could utilize some of the Kotaro's techniques to reduce heat gain and AC energy use.

Kotaro's website provides more detail, diagrams and pictures of the house ...

Gary

Update and Thoughts on Treated Lumber PV Array Mounts

Back in 2009 I built a ground mounted PV array for my house. The mounting system used treated 4 by 4 treated lumber for the mounts.

There was some concern expressed that the treated lumber would not have a good life. So, I've put up a page that covers:

• How things are going so far with the treated lumber mounts
• Results of a little research on various types of treated lumber.
• Ongoing maintenance.
• A design detail change for better timber decay resistance.

The treated lumber PV array supports

One of the posts after 4 years.

The new page gives some detail on types of treatment you want to use, ongoing maintenance,  better design details, ...

Gary

A Highly Reflective White Roof Coating for Home Cooling

I've received reports from two people now who have applied a coating of reflective white hydrated lime to their roofs in order to  lower attic and living space temperatures and reduce cooling costs.

While you might expect the lime to wash off in the first rain, it does not, and appears to last for several years.  It is cheap, readily available, and easy to apply.  

According to David and Wolfgang it is quite effective in reducing attic temperatures and AC bills.

David's Experiment
David reported on his white roof experiment back in 2010.  

On performance, David reports:
- House temperature with AC off 87F to 92F before, and 79F to 82F after coating.
- Attic temperatures before 120F to 140F, and 90F to 97F after coating.

This has resulted in much less AC run time.

All the details on David's white roof coating...



Wolfgang's White Roof
Wolfgang after looking at a number of potential coatings for his roof decided to give the hydrated lime a try.  
The house is located in Texas.

Reflective hydrated lime roof coating

Wolfgang's records indicate:
- Average summer day saving of 10 KWH per day
- Attic temperatures drop from as high as 150F to just a few degrees above ambient
- Estimated drop in AC runtime of 40%
- Payback period of 60 day


All the details on Wolfgang's white roof coating...


If the hydrated lime is not appealing, there are commercial white coatings available that can be applied.  I'd like to hear from anyone has tried one of the commercial coatings.

Gary

DIY Solar Air Heating Collectors: Pop Can vs Screen Absorbers

DIY solar air heating collectors are one of the better solar projects. They are easy to build, cheap to build, and offer a very quick payback on the cost of the materials to build them. They also offer a huge saving over equivalent commercially made collectors.

Two of the more popular designs are the pop can collector and screen absorber collector. 

The pop can and screen collectors being tested side by side

The pop can collector uses columns of black painted pop cans for the absorber with the air pumped through the columns.  The screen collector use 2 or 3 layers of ordinary black insect screening for the absorber.  The air flows through the layers of screen to pick up the solar heat.

In this test, a pop can collector and a screen absorber collector are run side by side with the temperature rise and airflow being noted for each.

There are also details on building each of the collectors and on the cost of materials.

Building the pop can collector.

In addition to measuring temperature rise and flow, thermal images were taken of the collector glazing and absorber.

Thermal image of glazing on the two collectors.

For all the details on how each collector did go here...

Gary

Two new resources on the web for the DIY solar crowd

A couple brand new resources available on the web for the DIY solar and renewable energy crowd:

Ask the Renewable Engineer

This is Nick Pine's new blog site.  Nick is a long time solar and renewable energy analyst, designer and innovator.  He is posting solar and renewable energy questions along with answers that include a full analysis.

Nick in his new, 3 story, Low Thermal Mass Sunspace

Hot and Cold TV

For several years, Tom Gocze hosted a TV show in Maine called Hot and Cold TV. 

In each show, Tom goes into a project of interest to DIYers.  Often the topics are renewable energy related.

The shows are factual, down to earth, practical, DIY oriented, innovative, and often funny -- a hard to beat combination.  The unfortunate thing was that if you did not live in Maine the shows were not available.  Now that has changed -- Tom has started a Youtube channel for Hot and Cold TV and has put up a number of the past shows with more to come.

Tom re-plumbs his shop using the Manablok system 

Tom covers the ins and outs of picking a good used pellet stove.

Lots more on the Hot and Cold TV Youtube channel...

Gary

A Test of Reflective Surfaces In Front of Vertical Solar Collectors to Improve Performance

I like my 100 sqft vertical collector that is integrated with the south wall of the house.  It provides our solar water heating and also some solar space heating. It provides excellent performance all winter, and does not have any tendency to overheat in the summer.  The boss says it looks nice.

The one downside of this collector is that in the late spring, the sun is getting up higher in the sky, which reduces the effective area of the collector, and there is still some need for space heating.  So, it would be nice if it could put out a bit more heat in the late spring.

This test looks at adding several types of reflective material on the ground in front of the collector to improve late spring and summer output.  A near horizontal ground reflector works well under these circumstance because the sun is hitting the collector nearly straight on.

The reflective materials include bright white rocks, a white painted reflector board, and at a flat board covered with highly reflective aluminized Mylar.  The results for each of these was measured -- the chart at the end shows how the did.

White reflective rocks

The radiation intensity was measured at each of the blue tape squares on the collector.

White painted board as reflector

The aluminized Mylar reflector was made by just applying the Mylar film over the white board.

This chart shows how the materials compared.

How each of the materials compared as reflectors

The first black bar is a baseline and was done with black weed fabric on the ground in front of the collector.

As expected, the aluminized Mylar does the best, but the white board also does well, and even the white rocks provide some useful gain.

For all the details on using these materials and actual percentage improvements...

Gary

Using Reflectors to Improve Collector/Window Solar Gain

I've added a new section that covers using reflectors to improve the performance of solar collector  or passive solar gain windows.

The section covers:

• Design tables that allow you determine the benefit of reflectors of various sizes and to optimize the placement of the reflector.
• An easy to build earth-sun simulator that allows you to see how a reflector of a given size and shape will perform for any location at any time of the year at any hour of the day.
• Examples of the use of reflectors to improve collector performance.

Reflectors offer a uniquely effective way to increase the energy produced by a collector in that they increase the solar energy incident on the collector without increasing the heat losses from the collector -- so, you get both an increase in solar input and an increase in collector efficiency -- see the new section for more on this.

This earth-simulator allows reflector performance to be seen  for
any location and for any time of year and for any time of day.
A quick spin of the turntable shows the reflector light pattern for a full day.
Can also be used for shading and lighting studies.
Lots of fun!

Example of reflector performance table.

The new section on reflectors is here...

Gary

A Design Challenge: Help ClubRust with Solar Heating Low Income Homes

ClubRust builds several low cost homes for families in northern Mexico each year. They would like to work out a way to insulate and solar heat these homes. The very small budget for these homes makes this a difficult design challenge.

So, here is your chance to help out with some ideas for solar heating and insulating these homes on a tight budget.

The ClubRust crew and one of their homes 

What's Needed:

Most cost effective means to insulate and heat small houses in mild winter climate with little or no electricity.

Ideally the solution would provide heat thru a few cloudy days and cost less than $700.

Typical house is 320sf wood-frame construction on concrete slab -- see the link below for full details.

ClubRust home under construction.

Full details on the the home construction, heating goals, climate, etc. are provided here...

Take some time to think over this solar heating and insulation challenge, and contribute your ideas and  comments at the link just above.

Gary

Building a Solar Heated Well House

This is a very nice and well documented project on the Alt. Build Blog that covers building a freeze resistant well house.  The idea is to keep the well plumbing and tanks above freezing with a passive solar heating system.

The well house and Trombe wall solar heater.

The well house is built from dry stack concrete blocks that are insulated with rigid foam insulation on the outside and then stucco for the outer weather surface.

A Trombe wall solar collector covers most of the south face of the structure -- the south wall concrete blocks are used for the mass of the Trombe wall, and twinwall polycarbonate is used for the Trombe wall glazing.

The advantage of using a Trombe wall for this situation is that the wall absorbs heat when the sun is on it, and this stored heat is released over the night time period to keep the structure above freezing for the full day.  The mass of the other wall concrete block walls should also help in maintaining a more even temperature -- putting the insulation on the outside of the block allows the wall mass to be effective in regulating the temperature of the space.  The mass of the water in the tanks should also help to even out temperature variations.

Trombe wall opening surrounded by stucco walls.

The entire project is described in 9 blog entries covering the whole build in a great deal of detail.  To my eye, the overall design and details are well thought out and executed -- a really nice job.

For colder climates, some changes that might be considered -- 1) use thicker insulation to reduce the heat loss out the roof and walls (possibly polyiso), 2) add insulation under the floor to reduce heat loss to the ground.  For really challenging climates, you  could consider going to a drain back solar collector on the outside that heats water in a relatively large unvented water tank on the inside that stores heat.  The heat loss from the heat storage tank would then heat the well house so that it stays above freezing.  The tank insulation could be set at a level such that the tank loses heat at a rate that keeps the inside of the structure above freezing all day -- even with some cloudy days.   The drain back circulation pump could be something like a PV powered TopsFlo pump, so that no separate differential controller would be needed.  While the drain back solution is more complicated and more expensive than the Trombe wall, the advantage is that its about twice as efficient as the Trombe wall collector -- so, it may payoff for cold climates.

All the details on the solar heated well house here...

Lots of interesting article on the  Alt. Build Blog -- have a look.

For hundreds more solar space and water heating ideas and projects...

Inside the well house.

Gary

A Simple and Inexpensive High Lift Solar Pumping Setup

Stan was faced with a difficult garden watering problem in which he had to get water from a spring to a greenhouse that was located several hundred feet away and 50 ft uphill from the spring. The flow requirement was relatively small at about 3 gpm for for an hour and half a day about 3 times a week.

Using a conventional AC powered pump would have meant running a lot of wire, and the 800ft distance would have meant a larger than normal wire gage to keep the voltage drop from being excessive.

Using one of the submersible well pumps that are made to run directly from solar PV panels is a nice solution, but the pumps are expensive and they require quite a bit of PV panel area to drive. So, this would have been an expensive solution for the relatively low flow required.

PV panel at spring -- green bucket covers pump and battery.

Stan's solution was to use a relatively inexpensive 12 VDC Shurflo pump that is intended for spraying and RV applications. The pump draws about 8 amps, so, to drive it directly with PV panels would have required at least 100 watts of PV array, and perhaps a linear current booster for startup. Instead of direct PV drive, Stan incorporates a deep cycle 12 volt battery to drive the pump, and then uses a small (30 watt) PV panel to charge the battery over the course of the day. This works well because the run time for the pump is not very long and can be handled by the battery, and the PV panel has all day to recharge the battery.

Pump, battery and charge controller under PV panel.

All the details on building and sizing this system...

More on solar water pumping...

Gary