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