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

Backdraft Dampers for Solar Air Heating Collectors

Solar air heating collectors provide a nice stream of heated air during the day when the sun is shining on them, but at night, the flow often reverses and brings unwanted cold air from the collector into the room.

Backdraft dampers are added to prevent this reverse flow of cold air.  There are several types of dampers -- both DIY and commercial.

I've added a section that lists the ones I know about -- if you know of others, please let me know.

New section on backdraft dampers for solar air heating collectors...

A example DIY backdraft damper

PV Powered Pool Pump Installation

When Bruce looked at where his electricity was going, he found that about a quarter of his total electricity use was to run his pool pump. He decided to install a new pump that would be run from PV modules.

Bruce's report gives details on the design and installation of the new pump, and on how the economics is working out. The drop in PV module prices in the 6 years since the system was installed, the payback period would now be substantially shorter.

Two 170 watt PV panels in series drive the DC motor pool pump

The installation is simple consisting of only the two 170 watt PV panels (above), a controller, and the DC powered pool pump itself.  Given the efficiency of DC pumps and the minimal losses its a very efficient setup.

The new pool pump -- the controller is visible on
the wall behind the pump

An alternative to Bruce's approach would be to retain the existing AC pool pump and add a grid-tie PV system for the whole house that would power both the pool and the rest of the house loads.  This is appealing in that one system does both jobs, but the low efficiency of typical AC pool pumps appears to require a much larger PV array (perhaps a 3000 watt PV array just to drive a 1.5 hp AC pool pump 8 hours a day).  So, the dedicated PV array to drive the DC pool pump appears to be the more cost effective solution -- do you agree?

Two speed AC pool pumps run for longer periods at lower speeds also appear to offer a larger saving in electricity at a modest initial cost.

I've added a small section on powering pool pumps efficiently that includes Bruce's PV powered pump as well as some other ideas on efficient pool pumps.  If you have any other ideas or thoughts, lets hear them.

Gary

Our Low Thermal Mass Sunspace Project in Home Power Magazine

I did an article for Home Power on the Low Thermal Mass Sunspace concept -- its in the Dec 2013 issue, which is just coming out.

William's Minnesota LTMS 

I'm a big fan of the Low Thermal Mass Sunspace (LTMS).  In a nutshell, this is an attached sunspace in which the design is optimized for providing maximum heat to the attached house.  The main design characteristics are:

• Double glazing with tilt angle optimized for winter collection
• Unglazed surfaces in the sunspace are dark in color to absorb sun well
• Unglazed surfaces are well insulated to reduce heat loss
• Unglazed surfaces are low in mass so that they don't suck up heat you want to go to the house
• A high capacity fan/duct system delivers heated air to the house as fast as the sunspace makes it

Some of this may seem strange at first compared to the usual sunspace design guides, but its all aimed at maximizing heat production and in getting as much of the heat as possible to the house. 

It turns out that if you follow these design guides, the LTMS will produce heat for the house just as efficiently as a good commercial collector with the same glazed area -- AND it will give you all the benefits of a sunspace as well.  Benefits include: great place to have cup of coffee in the sun, great playroom or family hangout, all season clothes line drying, wood drying, ...  

About the only downside of the LTMS is that when the sun goes down it goes cold quickly, so its not a space to hang out in after sunset, or go grow plants in cold climates.

The performance is impressive.  My test LTMS with 200 sf of glazing produced 200K BTU of heat for the house on one sunny winter day -- equivalent to nearly 3 gallons of propane burned in a typical furnace.

The test LTMS under construction.

I also tested the performance of my test sunspace when it was closed in, but not insulated and with a dirt floor -- in this configuration it only delivered 1/3 of the heat to the house than the finished sunspace with insulated low mass surfaces.

The finished test LTMS

I've done a section on LTMS's that goes into quite a bit of detail on on the design, performance testing, and includes some great LTMS examples contributed by Mike, Nick, and William. 

Mike's example LTMS -- heating the house and solar drying clothes!

Nick's 3 story LTMS that provides most of the heat for his
very difficult to heat old home.

The Home Power article covers everything in the LTMS section in one place and the Home Power editors have worked it into something that is clear, easy to read, and still quite detailed.

Gary
November 9, 2013

Looking for an Improved Over Window Collector

There is a lot of interest in solar air heating collectors that work with an existing window.  One of the more popular ones has been the Mother Earth News Heat Grabber.  These collectors don't require punching new holes in your wall, are simple to build, and they can be seasonally installed.

This work is an attempt to go a step further with collectors that work in conjunction with an existing window.  The hope is to both improve the aesthetics and to include more collector area.

Clearly there is plenty of room for improvement, so lets hear your ideas.

One think I want to make clear up front is that solar collectors that just fit over or in an existing window without increasing the collection area of the window do not work -- they do not end up collecting any more heat than the window alone.  There are kits out there for collectors that fit in the window -- they are ineffective.

Collector on left window -- regular window on right

This first cut prototype sits over the window and extends out to both sides and on the top and bottom.  It increases the collection area from 12 sf for the window alone up to 45 sf -- a pretty good increase in heat gathering area.

Outlet manifold on top supports screen absorber and pulls in
the hot air across the collector width, and sends it
down the vertical pipe and into the room
The room air inlets are on the right and left at the
bottom of the window.

Inside view -- inlets on right and left -- outlet with fan in middle.

Some of the outstanding questions...

• How to make it look nicer and how to better integrate the collector with the house design
• How to improve the efficiency of the collector.
• How to get even more collector area.
• How to make it easy to install.

For more details and to contribute suggestions ...


Gary

Replacing Our Power Hungry DVR Saves 310 KWH a year

We have been working for the last few years on reducing our electricity use.  So far we have cut our electricity use about in half using these projects.  We started at right around 1000 KWH per month, and got down to right around 500 KWH per month using the simple projects listed above.  We also did a 2.2 KW home built PV system that generates (on average) about 270 KWH a month, so our average electricity bill is around 250 KWH a month -- 1/4 of what it was when we started.

But, one thing that has bugged me for several years is that our DISH DVR uses 53 watts all day every day day and night.  This adds up to 464 KWH and 750 lbs of CO2 emissions a year -- its actually more energy than our fridge uses.  It is possible to turn it off at night, but then you lose any recordings that were to be made and have to wait through the boot up process in the morning.  I've kept track of new DISH DVR offerings in the hope that they would address this problem, but, according to DISH, the power usage on the new offerings is about the same as the one I have.

It came to our attention that Direct TV has done some work on this problem with considerable success.  Most of the DVRs  they now offer are Energy Star compliant, and use far less power than our DVR.  So, we decided to drop DISH (after 12 years) and go to Direct.

We ordered their Genie DVR which is a "whole house" DVR in that it will allow TV's in different rooms to watch different shows. It also has 5 tuners and will record up to 5 shows at one time.  So, the new DVR offers some feature gains as well as reduced power usage.

The power usage on the new DVR is 18 watts.  Compared to the old DVR, this is a saving of 310 KWH and 500 lbs of CO2 emissions a year.  All for a DVR with much more functionality than our old one.

New DVR on the Kill A Watt meter.

The new DVR also has a "sleep" feature in which after 4 hours of no activity it goes into a lower power consumption mode.  In the few days we have had the DVR, I've not seen it go into this mode at all and the power consumption over the first few days as measured by the KillAWatt meter indicates that it is not spending any significant time in this mode.  Perhaps shows recorded late at night kick it out of this mode?
But, given that the base power usage is so low, it does not make a lot of difference.

The new receiver/DVR

Anyway, I guess the message is to check the power consumption of everything that uses power in your house -- you may find that some of those innocent looking boxes are using a lot more energy than you think.

Gary

Solar Space Heating System in Virginia

This is a very nicely planned and executed solar heating project in Virginia. Lots of detail on all phases of the project with sections on planning, installation, costs, and performance.

The system is modeled after our $2K system, but with many adaptations and innovations to suit Kevin's home and climate.

Thanks very much to Kevin for documenting the project and sending it in!

Nearly vertical collectors positioned for good solar access.

250 gallon tank tucked into a corner of the garage

Kevin managed to tuck the radiant floor distribution manifold into a closet

All the details in a 25 page pdf here....

Gary October 8, 2013

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

Waterbag Solar Water Heating Collector Using Inflatable Film Cover and Soap Bubble Insulation

This is an innovative new wrinkle on the Integral Collector Storage (ICS) design from Nick Pine.

With ICS solar water heaters, the collector and the storage are combined into a single unit. Basically they consist of a water container that typically sits inside of of a glazed enclosure. Solar radiation heats the water container during the day. This is an example of a commercial ICS design.

One of the downsides of the nice simple ICS design is that it tends to lose quite a bit of heat at night through the glazing. Nick has addressed this problem by filling the area between the water container and the glazing with soap bubbles at night. The soap bubbles are good insulators and greatly reduce the night heat loss.

The design has several other innovations:

• A film bag is used to hold the water, which reduces the cost of the water container.
• A greenhouse polyethylene film cylinder is used for the glazing and is inflated to hold its shape -- a significant cost saving over conventional glazing. Similar to a hoop style greenhouse.
• The north half of the glazing cylinder is reflectorized to reflect more solar onto the water bag.

One upshot of the inexpensive materials used in Nick's design is that it is not expensive to build a solar water heater with a large collection area and a large storage capacity -- this increases the solar fraction.

Thanks to Jay Burch for this diagram.

To transfer the heat stored in the bag to the domestic water, a large coil of PEX pipe is immersed in the bag, and the cold water from the house takes ones pass through this large coil of PEX and is heated by the water in the bag. This heat exchanger scheme has been used quite successfully on the $1K solar water heater.

Be the first on your block to build one!

All the details here....

If you have any thoughts or ideas on this design, please leave them at the link above.

Gary

Dave's £900 Homemade Solar Water Heating System

David lives at 52 degree North latitude in the UK -- a pretty tough location for solar water heating, but his homemade system works quite well.

This is a really nice build with lots of good ideas and details to learn from.

The system is loosely modeled after our $1K system, but has a number of noteworthy features:

• Very nice workmanship and details.
  
• Solar heat is stored in the existing house thermal storage tank (which is used for both space and domestic water heating).
  
• An aesthetically pleasing collector and mounting arrangement.
  
• A pumping station that is mounted in a weather protected box on the back of the collector.
  
• A freeze protection system that takes into account his unique circumstances.

Dave is a professional plumber who now teaches plumbing, and this shows in the attention to detail in the design and the careful workmanship.

Thanks very much to David for sending this in!

All the details in a 25 page pdf...

The copper riser, aluminum fin collector under construction.

The pump was located at the collector in the box as there was no
space near the tank.

This is the existing thermal storage tank for the house that
is used for space and water heating and now stores solar heat as well.

Gary April 26, 2013