Solar Hot Water Heaters

Plumbing Engineer - Columns: February 2011: Solar Solutions


Solar Solutions

Stranded heat recovery using software controls
By Bristol Stickney, technical director,
Cedar Mountain Solar Systems, Santa Fe, N.M.
?In a well-designed solar heating system, the solar collectors provide most of the heat throughout the year, and the conventional boiler or other familiar heat source becomes the “backup system.” Even in the sunniest climates, there are days when the heat provided by the sun is not enough to satisfy the entire heating load. Whether this is due to extreme weather or extreme heat demand, even if the situation is rare or intermittent, the need for heat must be satisfied to keep the users satisfied. This is why no contemporary solar heating system is complete without a backup system that is reliable, fuel-efficient and properly controlled.

In a solar water heater, the backup can be as simple as an electric heating element that only turns on when the water drops below “shower temperature.” In solar combisystems installed in recent years, condensing boilers have become very popular backup burners because of their small size and high fuel efficiency. A typical backup boiler might burn propane, natural gas, electricity or fuel oil. The controls must prevent the burner from firing whenever solar heat is available at a useful temperature, either directly or from the solar heat storage.

Figure 31-1 shows the typical piping configuration that I have installed many times to provide these functions in a solar combisystem. Using a primary/secondary “flow center,” the solar collectors, heat storage, backup boiler, domestic hot water (DHW) and space heat zones can all be connected in a standard plumbing pattern. Notice that there are three heat sources and three heat loads. Solar combisystems always include multiple heat sources and loads. Even in this simple home heating design, the solar collectors, the boiler and the heat storage can provide heat (sources), while the heat storage, DHW and living spaces may demand heat (loads). The heat storage system can act as a source or as a load.

Unconventional backup heat

One major benefit of using a flow center design is that any source (and any load) can be “plugged-in” with two pipes. In some installations this has worked out nicely using alternative heat sources; some of them have been unconventional. When designing for energy efficiency, “waste heat” and convenient local fuel sources are hard to ignore, especially when they are expedient, plentiful and inexpensive. If you have multiple local resources, you might want to connect three or four heat sources, or even more, if the connection is relatively easy and if the potential for savings is real.

These resources generally come in two flavors: On demand and Intermittent. Figure 31-2 shows how other sources of heat can be easily added to a primary loop using two pipe connections at closely spaced tees. In a primary loop, the heat sources are best placed in order of lowest temperatures first and higher temperatures last, around the loop.

On demand

Alternative heat sources that can be started and stopped on demand (only when heat is needed) can be installed, similar to a “boiler” and controlled similar to multiple boilers. This is done most often to take advantage of alternate fuels, as the price of fuel changes over time or the performance of the equipment changes seasonally. So, for example, a ground-source heat-pump or an electric boiler might be placed just before a propane boiler in Figure 31-2 so that these fuels can be used exclusively or combined to achieve the best backup fuel costs from month to month. Solar heat, when placed upstream in the loop, is used for fuel offset by preheating any of these units and shutting them down during good, sunny weather.

Intermittent

Heat is sometimes generated out of sync with the need for heat and not controlled by the need for heat. Some typical examples would be Solar, a wood stove with heat coil, fireplace with heat coil, wood fired hydronic boiler, other multi fuel hydronic boilers (coal, pellet fuel, small biogas digester) and waste heat from other mechanical equipment such as generators or large refrigeration compressor systems). These sources can be used, stored and controlled in much the same way as solar heat is treated and can be a nice complement to the solar heat. When installed upstream of the solar heat storage system (as seen in Figure 31-2), non-solar intermittent heat can be stored in the solar storage as well.

Example: Wood-fired hydronic backup

In 2006, a homebuilder near Santa Fe found that the building site provided an ample supply of firewood that was essentially free. The only other backup fuel in that location was propane. The construction of the home was planned in two stages; solar collectors were to be added in the second stage. This meant that the house would be occupied for several years before the solar collectors were installed. The house was well insulated with radiant floor heat, using mostly concrete floors.

The homeowner chose to install a large wood-fired hydronic boiler (outdoors) that came with a built in 600-gallon tank. This was used as both a heat storage tank and as an intermittent alternative heat source. A primary loop was installed in the mechanical room with the wood-fired hydronic heat connected with two pipes upstream of a condensing propane boiler. The piping connections were done in the same order as labeled in Figure 31-2.

The homeowner could make one large wood fire on a cold day and run the heating system (using standard automatic home heating solar controls) on the heat stored in the water tank. When that was depleted, the condensing boiler would kick in. When the solar collectors were eventually installed both wood and propane usage was reduced significantly, and more heat was stored in the mass floors by the control system. The two-pipe, primary-loop connections allowed each heating device to be easily installed and controlled in a modular way over time.

Example: “Waste” heat from a generator

An off-grid home built around 2007 near Cerrillos, N.M. gets most of its electricity, which is stored in batteries, from photovoltaic panels. During extreme weather, an Onan generator fires up (on propane) to recharge the batteries when the solar cannot supply all the electrical needs in the home. This house was built from the ground up with solar heated warm mass floors, solar hot water and condensing boilers. When we realized (in 2009) that most of the propane heat from the generator was heating the great outdoors in winter, we decided to capture it. The top rubber hose on the automotive-style radiator was diverted to a stacked-plate heat exchanger. This allowed the automotive “water pump” in the engine to pump hot antifreeze from the engine through the heat exchanger before returning to the engine. The heat exchanger was treated like a solar collector, with controls that pumped heat away from the engine into the primary loop whenever the engine was hot enough. In this way, the “waste heat” from the propane burned by the generator is allowed to contribute to heating the floors, the DHW and even the swimming pool. The primary loop in this home was connected in a similar configuration to the labels shown in Figure 31-2.

These articles are targeted toward residential and small commercial buildings smaller than ten thousand square feet. The focus is on pressurized glycol/hydronic systems, since these systems can be applied in a wide variety of building geometries and orientations with few limitations. Brand names, organizations, suppliers and manufacturers are mentioned in these articles only to provide examples for illustration and discussion and do not constitute any recommendation or endorsement.
Bristol Stickney, partner and technical director at Cedar Mountain Solar Systems in Santa Fe, N.M., has been designing, manufacturing, engineering, repairing and installing solar hydronic heating systems for more than 30 years. He holds a Bachelor of Science in Mechanical Engineering and is a licensed Mechanical Contractor in New Mexico. He is the Chief Technical Officer for SolarLogic LLC and is involved in training programs for solar heating professionals (visit www.cedarmountainsolar.com or www.solarlogicllc.com for more information.)

 

Thanks CC

Nearly everyday as I take a shower, the thought comes to mind that I've got to get to work on a solar water heater. But I've got sooooo many other projects that I have to do first. However, your work on this thread has been extremely informative and provides a good template for a do-it-yourselfer like me, and has saved me much time in research. I appreciate and thank you for the unsolicited work, as I realize that you spent quite a bit of time on this post.

 

Hawaii now requires all new homes to have a solar hot water system. http://hawaiienergy.com/

40 years ago Israel did the same thing.

Changing Cities: Ending Hawaii’s Oil Addiction


7/16/2012 Filed under Press Releases
When you think of the most innovative places around the world for clean-tech, Denmark, where 50 percent of the energy comes from wind, might come to mind. Or maybe you’d think of Iceland, which is almost nearly 100 percent powered off geothermal, or perhaps Germany, which recently set a new world record in power generated from solar, but Hawaii?
U.S. Pacific Command is working closely with Hawaii, the most oil addicted state in the nation, to ensure that the Hawaii Clean Energy Initiative, a plan launched in 2008 to reduce the state’s consumption of fossil fuels by 70 percent by 2030 is a success.

“Pacific Command accounts for 20 percent of the island’s energy demand, so Hawaii needed Pacific Command to sign on to make the Clean Energy Initiative work,” Joelle Simonpietri senior analyst to U.S. Pacific Command Energy Office joint innovation and experimentation division told ABC News.

The military is using the Hawaiian islands as a test bed for new green tech innovation — everything from algae-based jet fuels and hydrogen fuel cell technology to smart-grids that can resist cyber terror.

Some of these efforts will be showcased on July 18, when the Navy tests a carrier strike force using alternative fuels during the six-week, 22-nation Rim of the Pacific exercises, the largest annual global naval maneuvers.

The ships and aircraft will be powered by alternative fuel, either nuclear or advanced biofuel blends. The biofuel blends are 50-50 mixtures of biofuel (made from used cooking oil and algae) and petroleum-based marine diesel or aviation fuel.
The new “Green Fleet” is not without its critics.

Conservative lawmakers came out this month in opposition to the U.S. military’s use of advanced biofuels, claiming that they are concerned about the cost of these new, nonoil fuels. Sen. John McCain, R-Ariz., the ranking Republican on the Senate Armed Services Committee, said, “I don’t believe we can afford it.”

The Navy purchased 450,000 gallons of biofuels for $12 million in 2011 for the maneuver — $26 per gallon.

Pacific Command contends that the need to invest in biofuels is evident.

“The Department of Defense’s military expenditures on fuel is about $15 billion, 3 billion of that was unbudgeted simply because of the change in the price of fuel,” Simonpietri said. “The reasons for using biofuels, from a military utility point of view, is for national economic security, it’s part of the interest of the nation, and really having different options that can address price volatility.”

Connecting the Islands
Beyond the military’s efforts, the state — which currently imports 90 percent of its energy in the form of oil — is proposing a mega-construction project to build an underwater cable connecting renewable energy projects on the islands.

“Hawaii is taking on renewable energy and using that as a solution to really reduce our vulnerability to imported oil,” Mark Glick, Hawaii’s energy administrator, told ABC News.
“Our (current) power generation comes from low sulfur fuel oil powered plants,” Glick said. “We’re trying to replace power generation which accounts for 30 percent of our energy with renewable energy sources.”

Hawaii Gov. Neil Abercrombie signed the undersea cable bill into law on June 27. The measure puts in place a regulatory framework that would pave the way for the islands to share power through an undersea high voltage network connecting the islands’ renewable energy sources including wind, solar, geothermal and tidal power.

According to a Department of Energy study, the high-voltage undersea cable interconnection project will cost $16 billion to complete, most of which is projected to come from the private sector. To put it into perspective, Hawaii currently spends $5 billion a year importing oil.
Critics of the underwater sea cables between the islands argue it would turn neighbor islands into industrial areas serving Honolulu’s population and that Oahu should look at energy conservation as a first step.

Becoming the Model for Energy Innovation
Since Hawaii’s goals of a 70 percent reduction of fossil fuels was announced, dozens of renewable energy projects have been proposed and employment and jobs in the clean-tech sector have sharply increased.

“Twenty percent of construction jobs in Hawaii are now in the installation of solar photovoltaics,” Glick said.

Several factors have allowed the state to forge ahead. A law that requires all new homes install solar hot water heating, and great tax rebates are helping Hawaii move toward a cleaner energy grid.

Hawaii has the second most solar photovoltaic systems, as well as the most EV’s and charging spots per capita in the country, and it’s also forging ahead on its efforts to increase the percentage of its electrical production with renewable power.

“Looking at all the options her in Hawaii, we have the sun, we have geothermal, wind, possibly wave, all the resources for us available in Hawaii,” Kekoa Kuluhiwa, director of external affairs for First Wind, a wind power company based in Hawaii told ABC News. “I sincerely hope there will be a day when we are completely free from importing fuel for our energy needs.”

Source: abcnews.go.com/blogs/technology/2012/07/changing-cities-ending-hawaiis-oil-addiction/

 

I've done panels with copper tubing and a cabinet with a tank inside .
Double wall glass is most important on these applications .
Ambient air/wind has more power to remove heat than one might expect.
Though in my experiment the panel produced hotter water ,the tank provided more volume .
I never did , but combining the two would have been golden.
Not having a heat exchanger at the time, the tank was the more practical application .
I have books on solar, and one home design used 55 gallon barrels stacked like wine bottles and their space in the house, was glassed and faced south so it had the full advantage of the sun through out the day.
Building one's home to BE solar takes a lot of thought concerning ;
weight, the over all structure through out the seasons including snow and unusual snow/wind conditions.
exposure, through out the year
access, for; building, service, and repairs.

I have seen expensive homes built with zero attention to weather conditions, an insult to this day and age , being that the knowledge of solar is older than recorded time. stupid home builders.

 

Solar water heaters are awesome. Until they freeze and bust.

 

NAW You did't build it correctly !!
I have 3 solar collectors , one polyglycol , two back drain
Sloth

 

I put a 48 tube system ( 3-16 tube headers in series) on our hoop house. Heat the tank well, but not near enough BTU to do much in the hoop house, so I think I'll move it up to the house and use ahead of the propane water heater we have now. Did this as an experiment, but I think it would take at least twice the tubes to do much good in the hoop house.

Built a frame out of 2" galvanized pipe, and ran 2" gal angle across it to mount the solar header/frame.


Frame/header mounted:



Tubes installed, outside done. Bed below, we use for garlic and onions.



Inside setup is a 50gal tank with a glycol loop between the panel headers and tank coil, then I draw water out of the tank with the little B&G red pump and pump it thru pipe in the slab and beds.

 

The commercial available units have "freeze protection" usually rated down to any where from 20°F down to around 0°F it looks like most people just run the hot water through the heater, single pass style.

 

I'm saying it's reasonable to expect people wI'll use them with water in a single pass configuration.
All you have to do is shop around a little to find ones where the manufacturer recommends "for area where freezing is uncommon" or has a freeze temperature rating.
I think glycol is better but not everyone uses glycol.

 

Why is my soft start post so funny?
All testing shows that it is going to work.
I guess it is funny since some people told me it wouldn't work yet I have been able to reduce starting amps from more than 45 amps down to as little as 10 to 12 amps.

I'm not a know it all I just know a lot and like to point out when people are wrong.

 

I think thermal application of solar for heating air, water, glycol is the most effective way to use it.
I used to not like photo electric panels, mainly because of the power produced versus power produced but they are so cheap now that's no longer the case.

 

I look at every contribution as an asset.
Even a small solar water heater before the regular gas water heater is an asset .
Ground temperatures are an average of 45 degrees and your conventional water heater has to bring that up to 100 or so.
So even if the solar panel brings the temp 40 degrees more, your that much ahead in the lack of gas/electric consumption required to top it off. Even if you happen to have an on demand water heater the principal is the same.

 

The only problem I see with putting solar before say a tankless water heater is the manual on my gas fired tankless water heater says that it will not kick on if the inlet water temperature is above 95°F.
I lose between 8 and 12°F between the water heater and the shower head.
My wife wouldn't like that.

But, add in some kind of thermostatic mixing valve before the tankless water heater to keep the inlet temperature below the cutout and you should be all set.
I don't know if electric tankless heaters suffer this inlet temperature lock out.

 

Hello

 

good bump