Solar Gain
By Bob ‘hot rod’ Rohr
A loud buzz in our industry right now centers around solar thermal. Every trade show and Expo I attend presents another handful of “players” entering the solar thermal business. Designers, installers, homeowners, and yes, even politicians are seeing the future of solar thermal. Many of us who deal in hydronics and radiant systems understand the use of low temperature fluids to provide a portion of our domestic hot water, warm our homes, provide pool or spa heat and maybe melt some snow or ice. It is a very small step for hydronic-knowledgeable designers or contractors to transition into the solar thermal business. All you need are some collectors (a heat source), storage, a pump and controller. Looks a lot like a hydronic heating system except the boiler, per say, is on the roof or the ground outside the building.
Many contractors have embraced the technology, attended the seminars and have multiple system installations under their belt. The solar thermal focus currently, with a weak residential housing market, seems to be commercial and industrial systems. Driving around your service area, you should be able to pick out the prime solar domestic hot water SDHW candidates. Look for businesses with large domestic hot water loads. Hotels, car washes, laundromats, fast food or any restaurants are the usual suspects.
I encourage you to look deeper into your surroundings to find commercial and industrial potential. Food processing uses a large amount of DHW. One manufacturer I met recently at the annual Colorado Solar Energy Industries Assoc. (COSEIA) event has his sights set not only on food processing but one big name player with hundreds of plants across the country. He has studied their operations and unique hot water needs and pitches his products and services directly to their plants. Yet another supplier I know has packages for a specific brand of fast food restaurants.
I returned just this week from a military base that is installing 1,900 square feet of collectors for a large housing application in the deep South. Big money, our money really, is being spent to upgrade mechanical systems and add alternative energy components to government projects.
But what keeps tugging at me is the imbalance of solar radiation available from summer to winter. In many Southern and Sunbelt areas, the summertime incoming water temperatures rise, and the amount of radiation available may even triple. What you may find when you run the calculations is the SDHW load may be covered early in the day in a sunny summer condition. Now what? You have designed a system to provide a solar fraction on a yearly basis. Summertime conditions may provide more DHW than you can possibly use. The million-dollar question is: How do you deal with the excess energy you will harvest?
The reality is “you get the most amount of solar energy when you need it the least.” Here are some websites that help you determine the solar radiation available at your location throughout the year:
http://eosweb.larc.nasa.gov/cgibin/sse/sse.cgi?+s01#s01
http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/atlas/
So, a missing component might be a means to use solar thermal energy to condition or cool spaces. Air conditioning, if you will. Turns out the technology to accomplish this has been used for many years here in the U.S. of A. Recall the refrigerator in a recreational vehicle. Fired by a propane LP flame, the unit cools your food. And maybe, more importantly, your beer. Large-scale refrigeration units can be found powered by district steam in cities that create and distribute energy this way.
So the next logical step would be to design residential and light commercial cooling equipment to be powered by solar thermal collectors. Currently, these systems seem to favor the evacuated tube type of collectors for higher temperatures required to drive the absorption cycle.
As we wish, these products are starting to become available. Japan has been manufacturing and installing absorption chillers and some data indicates as much as 40% of their commercial air conditioning equipment is powered by absorption cycle equipment.
While small residential systems, solar thermal-powered ones are starting to show up in the market, look at other options that are currently available, too. If you attended the AHR show in Orlando recently you may have noticed a small direct current powered residential split system air conditioning unit powered by photovoltaic panels. Solar Panels Plus was displaying an 18,000 BTU system. This could be a good option for off-gridders looking to keep their cool. A bank of deep cycle batteries provides the power after the sun goes down. The battery bank can be sized to provide cooling after the solar drops off. Solar Panels Plus out of Virginia has been developing this product and testing it for several years now.
Yet another interesting approach was a system that used a Sterling engine powered by a parabolic dish. The Sterling spun a generator to supply electricity. It is interesting to see this technology, discovered many, many years ago, getting another look.
Stay cool and keep your eyes open for new and exciting solar-powered cooling products.
Mining the sun’s energy in the Utah Rockies
Park City, Utah was born as a mining town. Silver was mined there and has created a lot of work and wealth over the years. If you get the opportunity to hike or ski the surrounding mountains you, will spot evidence left behind by prospectors. Many of the old buildings and equipment, some dating back to the 1800s, can be seen on the mountainside. Park City Mountain Resort (PCMR) — (see opening image on opposite page) — has maintained and upgraded some of the original mining buildings for continued use. One example is the Mid Mountain Lodge. This building originally housed the miners who worked in the area. As a resort property, it has housed the U.S. Olympic team, and served as a warming location and restaurant. Over its 100-year history, this building repeatedly updated, and even relocated. Most recently, the building has benefited from a $1 million renovation for the 2008-09 season. It has been a popular gathering place for skiers for many decades.
The resort is currently operated by Powdr Corporation. Over the years, pcmr has received many awards from the industry. PCMR is very proud of the Save our Snow initiative. In 2006, PCMR commissioned a study of global warming effect on the resort and the Utah snow sport industry. In 2008, the resort received the “Green Power Leadership Award” from the EPA. The resort is the largest purchaser of renewable energy in the travel and leisure category. The resort ranks #15 of all U.S. corporations that purchase 100% renewable energy. Brent Giles is the director of Environmental Affairs at the resort. He is constantly seeking way to position the resort at the forefront of environmental initiatives and concepts.
So it came as no surprise when PCMR contacted Harris Dudley Mechanical, Inc. of Salt Lake City to investigate a solar thermal hot water system for the Mid Mountain Lodge. As you would imagine, the lodge has a large DHW load. Bob Dudley and his team put together a proposal to supplement the DHW system with a solar thermal drainback system. Solar designer, Aaron Cook, took the challenge for the Harris Dudley team. He ran some simulation calculations on the retScreen software. He quickly realized the payback challenge with a seasonal use building. The lodge is closed at the end of the ski season and the DHW load disappears along with the skiers. The solar thermal system has a short 4-5-month season to work. This is also the coldest time of year to provide solar thermal energy. Bob Dudley nervously approached the PCMR with their proposed design, including the long payback projection numbers, under current seasonal use conditions.
The PCMR board acknowledged the payback period and moved on to the details of the design. The decision was based on the environmentally friendly approach to producing DHW, and in staying true to the PCMR goal of being a leader in the environmentally friendly resort initiative. Also, Jordan Gates was a major player in the Harris Dudley team on this unique job. Jordan worked closely with the building department getting permits, and helping them establish some solar guidelines. Jordan was responsible for seeing that the job was completed professionally and in a timely manner on a very site-difficult job. Jordan also worked closely with the resort on the design and presentation of the proposal.
Team Harris Dudley was given the go ahead to install the solar thermal domestic hot water system (SDHW). Knowing the unusual conditions and seasonal use, a pressurized drainback system was designed. When not in use, the collectors drain back and are designed to withstand years of service in this type of operation.
This system comprised of ten Caleffi flat plate collectors 32 square feet each. The 10 collectors were arranged in two 5-collector groups and positioned on the roof with the two 5-collector arrays sloping to the center. This mounting method provided an attractive look, as the system will be viewed by perhaps millions of visitors over the course of its projected lifetime. The system also uses a 40-gallon drainback tank and a 120-gallon Caleffi SolarCon insulated storage tank. The whole package is controlled by a Caleffi I-solar drainback control. The system feeds the solar pre-heated water to and electric boiler and two additional 80-gallon storage tanks. A pipe insulation upgrade was also included in the job to limit the standby loss from piping and tanks.
Mounting the collectors proved to be a challenge for the crew. The roof had a substantial build-up from years of remodeling, and locating adequate structural members took some time. A rough terrain crane was used to safely place the collectors on the steep pitch. This installation was one of the first in the Park City area to be permitted and the Harris Dudley team worked closely with the Park City Building department. Providing roof loading and structural data was required for the permit and inspection.
Harris Dudley has chosen to walk the solar walk, as well as talk the talk. A well-positioned solar thermal array greets all that visit their Salt Lake location. It is a nice addition to their world-class hydronic showroom. The display shows how well radiant and solar thermal can exist together. A data logger on the solar enforces the work-ability of solar thermal energy harvest in the Utah Rockies.
Instead of mining silver, with the help of Harris Dudley Co., the resort is mining sunshine in the Utah Mountains.
Bob “hot rod” Rohr has been a plumbing, radiant heat and solar contractor and installer for 30 years. A long-time RPA member, and columnist for Phc News, Bob has joined Caleffi North America as manager of Training and Education.