Build-It-Solar Blog

I added a couple new entries in the Heat Pump Water Heater Section. 

The first is a Tom Gocze video that describes installing a Geyser Heat Pump Water Heater -- a good video -- informative and funny in places.  Tom is a long time friend of Build-It-Solar and has contributed a lot of helpful information.  He does some radio and TV work in Maine, so if you are in place where you can get these, they are very good.  Tom knows renewable  energy well, and has a good, practical approach to energy matters.



Heat pumps in general remove heat from one place and "pump" (transfer) it to another place.  For the heat pump water heater, the heat is removed from the household air and transferred to the water in the water heater tank.  The efficiency of the whole process is about 200% (that is they have a Coefficient of Performance (COP) of about 2).  This compares to a regular hot water heater which has a heating efficiency of nearly 100%.  In addition, during the summer they have the added benefit that they provide some free air conditioning -- that is, they cool and dehumidify the household air some. 

The cost of the units are around $700 to $1400.  Some of them (but not all) qualify for the 30% federal tax rebate, and some states may also offer some incentives.

On the down side the cool air they provide, which is a plus in the summer becomes a negative in the winter.  In the winter the cooled air has to be heated back up by your space heating system, and this is a cost.  It seems to me that in effect it will reduce the efficincy back to about what a regular electric water heat is for the winter.  
This paper on a Building America demonstration home shows a way to hook up the heat pump water heater in such a way that in the summer, the cooling air is used to cool the kitchen area, but in the winter the ducts are switched around so that the heat pump air is taken from the crawl space and does not cool the house air (or at least not as much).  This seems like a worthwhile improvement, but does complicate the installation.

Does anyone have any ideas on a winter hookup that would not steal warm air from the house?  Seems like there ought to be a way to do this?

From a carbon emissions point of view, I get these numbers -- the
- Regular electric water heater:  1.5 lbs CO2 per KWH heat out
- Heat pump water heater: 0.75 lbs CO2 per KWH heat out (COP of 2)
- Regular NG gas (EF0.65):  0.75 lbs CO2 per KWH heat out
- Tankless NG gas water heater (EF0.85): 0.6 lbs CO2 per KWH heat out

So, they are substantially better than a straight electric water heater, about the same as a conventional gas water heater, and not quite as good as a tankless gas heater.
These numbers are based on the 1.5 lbs of CO2 per 1 KWH of electric power (the US grid average), and 0.5 lbs of CO2 per 1 KWH of heat output from NG.


Gary

Energy Alternatives has come up with a new design for heating domestic water.  Their design pipes water/antifreeze through several PEX pipes that are suspended in the attic ridge roof vent. 



The water heated by the PEX tubing is passed through a heat exchanger coil in a domestic water preheat tank.  The domestic water is preheated in this tank before it goes on to the regular water heating tank.

No real data is given on performance, and I suspect that for many climates, this is a three season heater at best, but it does offer an interesting alternative to solar, and it keeps the external look of the roof unchanged.

One article suggests that the cost of a 40 ft section of the PEX ridge vent assembly might be around $300, and that a full kit including the preheat tank with heat exchanger might be about $3100.

Here are some thoughts about DIY implementation of the ridge vent design that could (I think) be done for less than $1000 -- maybe substantially less.

Thanks very much to Chris for finding this and suggesting it!

Gary

I've been collecting material on the idea of extracting heat from compost piles and adding it to this section...

At first, this was a "that's kind of interesting" idea to me, but it has become more and more of a "that might really work" sort of idea.

Basically these schemes (there are several shown) start with a carefully constructed, large pile of biomass.  The biomass heats up as it goes through the composting process.  Pipes running through the pile pick up heat which can be used for domestic water heating and/or space heating.  Some schemes simultaneously collect bio-gas, which can be used for cooking fuel or even running a vehicle or generator.


Marc's compost furnace under construction.

A lot of work was done on this in the 70's by Jean Pain in France.  The section has some good descriptions of Pain's work, including two newly added videos (thanks to Curbie for these).

Marc's compost furnace work is very interesting, and includes some results from his first winter of operation.

The MB-Soft work in this area is interesting, if a little hard to decipher.

The New Alchemy papers are also quite good.

The attraction of this approach to me is that it holds the promise of a carbon neutral way of generating useful amounts of heat over long periods of time.  Some of the Pain piles are said to have been still generating useful heat after 18 months.  It is quite a bit of work to build one of the structured compost piles and set up the heat extraction plumbing, but then you may be able to get useful heating from the pile for an entire heating season.
The efficiency is claimed to be of the same order as burning the biomass -- maybe even a little better.  In many cases, the biomass can be material that would just be left to rot in place.

Does anyone have more useful information on this area?
Any thoughts on how useful and idea this might be?

Gary

I've been trying to get the new PV system in the last week or so, and as a result I'm falling behind on getting new entries up on the website.  Thought I would just give a short progress report on the PV system. 

I do plan to do a new section with a lot of detail on the whole PV system process with lots of detail on design, site survey, mount construction, wiring, installation, ...   probably a lot detail more than you ever wanted to see :)

After much looking at a lot of options, I chose the type of system that uses one Enphase micro inverter for each PV panel.   In this kind of system, each PV panel gets its own grid-tie inverter, which is mounted right at the PV panel.  Each inverter takes one PV panel's DC output and converts it to 240 VAC that is grid compatible.  Each inverter plugs into the next inverter in the array, and you end up with all the power from up to 15 PV panels being available as 240VAC at the last panel/inverter in the string of panels.  My system has 10 PV panels at 215 watts each for a nominal total of 2150 watts. 

I bought the system as a "kit" from Wholesale Solar -- this one...

The more common approach on grid-tie systems is to wire several PV panels in series so that the they produce a high DC voltage.  This string of PV panels are then wired to an single inverter which takes the several hundred volts from the string of PV panels and converts to grid compatible 240 VAC. 

There are pros and cons to each approach, but (I think) both are pretty simple systems that can be DIY projects as long as you are VERY careful to mind the safety precautions. 

In my system, the PV panels are mounted on the ground and are located about 100 ft from the house out in the weeds.  The wires are run underground from the PV panels to the area where power comes into the house, and the grid-tie is made there.


I rented a power trencher to dig the trench for the wires.  In our hard soil, this saved a lot of time and effort.

After some debate with myself, I settled on a rather robust mounting system made from 4X4 treated lumber.  I wanted something that would withstand the high winds we get occasionally, and that would last 30 years.  Treated lumber may not be the best choice for long life in some areas, but around here, if properly installed it lasts a very long time.


This shows the framework that the PV panels will be mounted on. 
Anchored in about in 3200 lbs of concrete!



Running the wire (in conduit) from the house to PV array.


I clamped the PV support rails and a PV panel in place just to get the spacings
right and to plan where the inverters would go (they mount to the same rails as the PV panels)

This is where I am -- just waiting for a day or two of descent weather to finish it up.

Gary

The Solar Decathlon is here!  Its going to be from October 9 to October 18.

This is a terrific event.  Here is a good description shamelessly copied from the DOE Newsletter:

20 Solar Homes Take Shape on the National Mall for the Solar Decathlon

Construction is underway at the Solar Decathlon, which opens to the public on October 9. Enlarge this photo. Credit: Richard King, DOE Solar Decathlon

The assembly of 20 solar homes on the National Mall in Washington, D.C., is rapidly approaching completion, as the 2009 Solar Decathlon prepares to open, free to the public, on October 9th. The Solar Decathlon is an international event in which DOE challenges university teams to design and build homes that run entirely on solar energy. The teams ship their partially constructed homes to the National Mall, assemble them, and then compete in ten contests. This year, the 20 teams came from universities in Arizona, California, Illinois, Iowa, Kentucky, Louisiana, Massachusetts, Minnesota, Missouri, New York, Ohio, Pennsylvania, Texas, Virginia, and Wisconsin, as well as Puerto Rico, Canada, Germany, and Spain. Trucks rolled onto the National Mall just after midnight on the morning of October 1, and since then, the teams have been steadily working to assemble their solar homes. See the DOE press release and the Solar Decathon Web site.

This is the fourth running of the Solar Decathlon, and for the first time, the competition features a stand-alone electrical microgrid to which each team will have to connect their home. Starting on October 8, each home will be monitored for its performance in five areas relating to performance and livability: comfort (maintaining comfortable temperature and humidity in the home), hot water (producing a sufficient quantity at a high enough temperature), appliances (such as keeping refrigerated items at the right temperature), home entertainment (running a television, computer, lights, and other devices), and net metering. For the net metering competition, homes must use zero net energy over the course of a week, and teams receive a bonus for producing more energy than their home consumes. Other contests rate the teams for their communications with the public and for the architecture, engineering, and market viability of their homes. The overall winner will be announced on October 16. See the Solar Decathlon's Contests and Scoring page.

DOE is the primary sponsor of the 2009 Solar Decathlon, which is also sponsored and managed by DOE's National Renewable Energy Laboratory. Homes will open to the public beginning on October 9, and will be open for tours weekdays from 11 a.m. to 3 p.m., and from 10 a.m. to 5 p.m. on weekends, through October 18 (with the exception of October 14). Not able to come to D.C.? You can keep up with the Solar Decathlon online through daily journals posted by DOE's Richard King, the Solar Decathlon director; photos of the day from the event; YouTube videos; time-lapse photos from three cameras at the event; blogs from the teams; the Solar Decathlon Facebook page (become a fan!); and even a Twitter feed!

Gary

The first full year of performance for the $1K Solar Water Heating system is in the books.  The graph below shows Solar Fraction by month.

All the details, and detailed plots that show collector, tank top, tank bottom, and ambient temperature are here...



So, this is the end of the promised one year of logging -- I now get my loggers back for other projects!

I've also a added a page that describes how I estimate Solar Fraction, and considers some sources of error, and describes how my method differs from the SRCC ratings of solar water heating systems.

Gary

This is a really interesting solar space heating collector design.  It is built as a single unit that is 24 ft wide by 8 ft high.  Compared to building a bunch of separate collectors, the single unit construction saves some time, effort, and materials, and looks very nice.



The absorber is an extra wide variation on the PEX/aluminum absorber.

For more on the collector, including a link to Scott's site with all the construction details, and a few of my thoughts on the collector...

This is a good example of the kind of freedom to try new things and fit your design to your situation that building your own system gives.

Scott is a founder of the Yahoo SimplySolar group -- a good place to discuss your new solar ideas.

Gary

Three New Content Items

1. Lee's Solar Mower
Some time back, Lee sent in the details for his solar lawn mower.  The article basically tells you how to convert a gasoline powered mower to a battery powered electric mower with solar charging.
One issue with doing this is finding a good electric motor.  The one that Lee originally used is no longer available.  So, Lee has found a new source of motors that should work well and are cheap and easy to find....



2. Performance Update for Marc's  Compost Furnace

I added a section on methods of heat distribution for solar heating systems.  The new section provides links to a number of ways to distribute heat to a house for a solar heating system with an emphasis on DIY approaches.

Distribution of heat for solar heating systems is complicated by the fact that solar heating systems are more efficient when producing water that is not hot by boiler standards -- that is, boilers can easily produce 160F (or more) water, while solar heating systems are going to be more efficient when producing 120F (or less) water.  This makes the heat distribution more challenging, and makes some of the conventional systems difficult to use  because of their reliance on high temperature water.

If you have any additional ideas, please let me know. 

The new section is here....


A rather neat homemade radiator for heat distribution at the Dawson Creek, YT Visitors Center.

I also updated and added some material to the Heat Exchangers for Solar Heating Systems section...  Again, the emphasis is on DIY approaches.

Gary

Marc has worked out a what appears to be a very nice design for extracting heat from a large compost pile for space heating.



Marc's design includes a blower and air supply manifold system to aerate the pile, a pipe network to add water to the pile as needed, a pipe network to extract heat from the pile, insulation to increase the efficiency of the composting process, and a nice containment and cover system.

Link to Marc's blog entry on heat from compost...

Other heat from compost schemes on Build-It-Solar...

Judging from the emails I get, there is a lot of interest in using compost to generate heat, but there is not a lot of detailed information out there on how to actually build such as system.  I think Marc has taken a good cut at it.  What do you think?

Gary