Saturday, July 28, 2012

Solar Thermal for the Masses

For a few years now, I've independently been trying to solve the problem of solar domestic hot water (SDHW) systems that are too expensive.  Here's what I've come up with: a simple and cheap solar hot water system design that at the very least should give manufacturers food for thought.

The Problem:  Even small SDHW systems cost way too much ($6-$8k on average)
Since gas heated water is still very cheap, the average family can only save $30/month with solar.

My Opinion:  The US SDHW industry is in deep trouble now, and will remain so until $2000 systems are available. 

A Solution?:  Bring back Recirculation for Freeze Protection (RFP) in all but the coldest climates in the US.

History:  RFP is still used in many non-freezing climates, so it's still a free option on most solar thermal controllers. It's reliability took a hit in the 80s when many systems froze because power failures often accompanied freezing weather. (Freezing rain will often take down power lines) Because of this, most installers eschewed this method for most climates. Historically, it can't be used with flat plate collectors because in the winter it takes too much energy to prevent the collectors from freezing. (They are pointed at the night sky which is usually colder than -100F on a clear night)

Why This Solution Can Work: A. If Evacuated Tube (ET) collectors are used, the heat required for freeze protection is almost negligible, and B. In case of a power failure, the system will self-freeze-protect by thermosiphoning. C. The outdoor piping is freeze and stagnation tolerant hose.

Yes, the ET collector header can still freeze and break, but the probability will prove to be too low to worry about. (Drainback systems have a few failure modes including freezing, but we still use them because the Mean Time Between Failures (MTBF) is long enough.)

I've tested this system for two winters now, and it works great in Denver. Here's a link to the YouTube tutorial about the system.

For more info and pricing, here's a link to my presentation at the 2012 ACEEE Hot Water Forum.

100% Off-the-Shelf:  Only  five of the items required must be purchased somewhere besides Home Depot:

1.   The pump:
2.   The Pump Controller:
5.   A 110V SPDT relay is also needed to control the ECV just right.

Tuesday, July 17, 2012

Just Say No to Twitter

It's an annoying fad that is a complete waste of time for the average person.   And time is your most important dwindling resource.  So cut it out.

Sunday, July 1, 2012

Plumbing Efficiency in New Construction: Using a Little Pipe to Save a Lot of Water and Energy

All of us have had the annoyance of waiting for hot water.   Whether it's to do a good job of hand washing or to get the morning shower over quickly, you know the feeling.

The conventional wisdom has always been to install a recirculation pump.   The best one available is probably from ACT:
It's a good solution, I guess the only problem is the cost, which is about $200 plus labor.

However if you pipe your hot water directly to each fixture with 3/8" pex, you have solved the problem.  But now you have to convince your plumber.

Gary Klein has developed a plumbing strategy that eliminates the need for a recirculation pump if the house you're designing isn't too damn big.  The strategy is called Structured Plumbing.  The reason it works is that there is very little water in the hot lines going to each fixture.  It's similar to "home run" piping.

Michael Chandler at Green Building Advisor has sketched for us what it means.   (Michael is uniquely qualified for that since he is a master plumber who designs and builds green custom homes)

Somewhat non-intuitively, it requires more pipe, which would be expensive with copper, but with PEX it's very easy and cheap.  PEX is very easy to work with,  especially in the 1/2" and 3/8" sizes, and is color coded.   Since it bends easily, you rarely need an elbow.   So you wind up using less fittings and more pipe.  That's OK, since the pipe is very cheap and should last 100 years.   In a small house, this extra cost is less than the $200 for the ACT pump, and it shouldn't need replacing during the life of the house.  Home Depot now sells the manifolds that make it even easier.

So thanks to Gary and Michael for giving us what will become the new standard method in residential plumbing.   If you're a builder, just hand this sketch to your plumber.  He may be a little reluctant at first, but if he's used to PEX he'll understand it quickly.   If he's not used to PEX, get a new plumber NOW.

Do you still need to insulate all the hot water pipe? Yes.   With insulation, the second person in the shower has instant hot water if there is less than 30 minutes between showers.