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The Power of the Sun Within Reach

Solarex Solar Panels
Eighteen Solarex VLX80s power the Hoovers' home, including the fan, pump, and igniter for the air conditioning system.

ill and Carol Hoover live in a remote California mountain canyon, isolated from the hubbub of city streets and highways. Their concrete house is cut into the canyon wall, overlooking a stream and pond. Wildlife regularly visits this sanctuary, especially deer, raccoon, wild pig, and bird life of all sorts. The Hoovers' home has been independent of the utility grid since it was built. They chose renewable energy sources to avoid ugly and expensive power lines intruding into the canyon.

In trying to cool the house, the Hoovers tried some portable swamp coolers. These helped some, and for more improvement, they changed to window-mounted swamp coolers powered by Siemens solar panels. These worked just well enough to be teasers. The water source had enough mineral salts to rapidly build deposits (mostly magnesium). Maintenance was a problem, so they decided to search for something better.

In 1998, Bill came to me asking about air conditioning. For several years, I have been his consultant on their renewable energy system, and I designed the original power system for their home. When Bill discovered an Internet company selling air conditioning that could run on solar panels, I was skeptical, thinking of the energy demands of a typical compressor.

After some research, I found the Servel name on three to five-ton chillers using a gas absorption process. (By definition, the standard ton of refrigeration is defined as

288,000 British thermal units per day, or 12,000 BTU per hour, or 200 BTU per minute.) With this system, a significant portion of the energy demand was transferred to natural gas or propane.

Feasible? Yes! Gas refrigerators have been doing this for years. The Servel name is well known. Bill and Carol already had a 500 gallon (1,900 l) propane tank for the gas appliances in their home. Gas chillers have been serving the air conditioning demands of commercial installations for a long time.

The Servel three-ton gas-fired cooling unit behind the house.

The upshot of this is that Bill and Carol now have a three-ton air conditioning unit powered by solar energy and propane. House temperatures are now in the comfort zone, despite outside temperatures that are typically in the 90s during summer days, sometimes reaching as high as 110°F (43°C).

Air Conditioning System

The air conditioning system has two major components—the chiller and the cooling coils. Robur Corporation, using the trade name Servel, manufactured the Air Cooled Absorption Water Chiller model ACD 36-00, a three-ton unit with a delivered capacity of 36,000 BTU/h. It uses up to 75,000 BTU/h of propane together with 875 watts of electrical power at 120 VAC. It delivers 45°F (7°C) chilled water at 7.2 gpm (27 lpm), and is mounted outside the house.

The heat exchanger to cool the house was provided by Edwards Engineering, Inc., and consists of cooling coils mounted along internal walls adjacent to the ceilings. These valance cooling coils are completely passive, requiring no fans to move the air. The air is circulated throughout the rooms by natural convection currents.

Edwards Engineering sells these valance units in a number of configurations, each cut to the desired length. They consist of parallel finned copper pipe enclosed in a sheetmetal cover ducting warm air in at the ceiling and cooled air down the wall.

The valances are well made and attractive. The configuration we received has two rows of finned 1/2 inch (13 mm) pipe—one row of five and one row of four. To our knowledge, this is the first usage of valance cooling coils with the Servel chiller. Connected to the chiller, this air conditioning system operates quite effectively.

The Servel three-ton gas-fired cooling unit behind the house.

One unexpected side benefit of the valance system has to do with the family cat. Before the installation, he used to climb up on the bookshelves and get into the dropped ceiling. The valances block his access, so the Hoovers no longer need to worry about him getting up there. Only one other significant feline problem remains. The cat likes to play with the new thermostat

Inside the Servel air-cooled absorbtion water chiller.

The Hoovers' all-concrete house, in the mountains of California.

The House

The Hoovers' house is of poured concrete construction—floors, walls, and roof—and has approximately 1,440 square feet (134 m2) of floor space. A second tile roof is fitted above the basic concrete roof, with an air space separating them. The original roof was flat concrete. When some leakage started to occur, a second sloping tile roof was installed above the original. This solved the problem of the leaky roof, and increased the total roof insulation value as well.

Approximately 40 linear feet (12 m) of valance cooling coils were installed. The back half of the house receives little cooling when the doors are closed, but it is not as critical there since it is not the main living area and is mostly below ground.

Planning the System

In planning this air conditioning system, the big question was the heat load and losses of the house, which would dictate the size of system required. Bill Hoover did this study, and I cross-checked his data. Bill acquired a couple of recording thermometers, and monitored the internal and external temperatures. We then had the temperatures and the time lag between the two environments, as well as the heat conductance of building materials and contents. From this, we could make the calculations to give us the information we needed.

A three-ton air conditioning unit was called for. From the data sheets of the Servel unit, the gas and electrical demands were established. The existing propane tank would be adequate, though Bill was prepared to upgrade to a 1,000 gallon (3,800 l) tank if necessary.

The solar-electric system needed to be enlarged if it was still to meet other electrical demands placed upon

Floor to ceiling double-pane windows and sliding glass doors take up much of the front, which faces south. The front half of the house is partitioned into the kitchen, dining room, living room, and master bedroom. Down the middle of the house is a lengthwise partition with doors leading to rooms in the back half of the house.

Though it is normal to install hydronic heating and cooling around the perimeter, the floor to ceiling glass precluded this. So the valance cooling coils were installed along the top of the center partition, with exposure to the dining room, living room, and master bedroom.

The valence hides the hydronic cooling coils—Bill Hoover likes how it looks.

Looking down from the ceiling—the cooling fins create surface area for maximum air contact.

Nine finned copper pipes carry cool water through the heat exchanger.

Looking down from the ceiling—the cooling fins create surface area for maximum air contact.

it. The valance cooling coils required some study, since they were new to us. Edwards Engineering was very helpful in giving specifications based on our household dimensions and heat load data.

Solar-Electric System

The objective was to remain completely independent of the grid, and with no supplemental generator. The six Solarex MSX-53 50 watt panels were replaced with eighteen Solarex VLX-80 80 watt panels, a nearly fivefold increase. The eight Trojan 205 AH golf cart batteries were replaced with sixteen 350 AH Trojan L-16s, an increase of nearly three and one-half times the capacity.

The wiring was changed from a 12 VDC to a 24 VDC configuration. The Trace U2012 inverter was replaced with a Trace DR3624. The Trace C-40 controller is now operating at its maximum. All wiring, disconnects, and

Nine finned copper pipes carry cool water through the heat exchanger.

fuses were upgraded to the new capacity. The wiring from the powerhouse to the main house, a 150 foot (46 m) run, was changed from #12 to #6 (3.3 to 13.3 mm2).

The Trace DR3624, C-40, fuses, and disconnects.

The Trace DR3624, C-40, fuses, and disconnects.

The Harris system was corroded beyond repair.

A new circuit breaker panel at the house was added, with two 20 A circuits, one feeding the new chiller. We changed the motor in the water pump (a Dankoff 1305 Slowpump) from 12 to 24 VDC. Water is pumped from a spring to a tank up the hill that gravity feeds the house.

Ancient History

The powerhouse started out life as an 8 foot (2.4 m) diameter steel culvert turned on end and set into the ground. A concrete floor with drains was added, along with a wooden roof covered with asphalt roofing. A hatch and a ladder provided access through the roof. A Harris Hydro Pelton wheel driving a Delco alternator provided 12 VDC output to charge a battery bank through an Enermaxer diversion load controller. The battery bank used eight GNB 6 V golf cart batteries. A Dynamote square wave inverter provided 120 VAC to the house.

All of this equipment was located together below ground in the powerhouse. Several problems soon became apparent. The hydroelectric system was quite troublesome, largely because the water pickup was designed for a rather docile summer stream. High water from winter storms, coupled with surges of debris, sand, and gravel plagued the system from the pickup point all the way to the jets for the Pelton wheel. Tapping the stream, which ranged from a dry bed in summer to a raging torrent in the winter, became too much of a fight. The intake had been rebuilt several times, but with no long-term success. The original 50 watt solar panels were only installed to augment the hydro, but proved to be far more reliable.

Fumes from the battery bank immediately started to corrode virtually all equipment in "the hole." For three or four years, we cleaned the hydro intake every season, sometimes multiple times, until we started looking for another source of energy. The corrosion told us, "Get those batteries out of the hole," so we built an aboveground battery box.

The square wave inverter was very bothersome to radios and audio equipment. It was also getting very corroded, so we replaced it with the Trace U2012. Though it was not a sine wave inverter, everything worked better thereafter.

With temperatures ranging from just below freezing in winter to well over 100°F (38°C) in the summer, the batteries were hard to regulate. So the controller was changed to a temperature-compensated Trace C-40, since the Harris Hydroelectric system was by then out of service. The C-40 also provided a periodic equalization charge, which previously had to be done manually.

The new array of six MSX-53, 50 watt Solarex PV panels replaced the hydro system and the older PVs. These changes proved quite stable. The GNB batteries lasted about six years, before being replaced with equivalent Trojans and new battery cables.

Corrosion finally got the best of the Slowpump on the water system, so Dankoff sold us a new one. At one point, the Trace U2012 inverter had to be flushed with distilled water and baked dry before resuming its operation. The Harris Hydroelectric system was yanked in the spring of 1999, prior to upgrading for the air conditioning system. It was so badly corroded that it was unsalvageable.

A Sola power conditioner was necessary to operate the Servel igniter on mod-sine power.

A Sola power conditioner was necessary to operate the Servel igniter on mod-sine power.


Numerous delays plagued the hardware acquisition phase of the air conditioning project. In the end, we worked with Edwards Engineering's main office in New Jersey. Within days after we sent our check, they shipped exactly what we wanted. Shipping this large unit was also troublesome, and took some special arrangements. Finally, after over eight months of trying to get the air conditioning system, we got it and were able to use a local contractor to do the installation.

Meanwhile, we were working on the solar-electric installation. We first received a quote from a respected Arizona company. They had been involved in a number of home air conditioning installations in Mexico using the Servel chillers, but with supplemental gasoline generators. Their proposal looked good, and only needed minor changes, since it was designed for a 4 ton chiller and used an auxiliary gas-driven generator. The quote also specified a 230 VAC system, and a full sine wave inverter. The engineers at Trace felt that we could get by with a modified sine wave inverter, which would save about a thousand dollars.

The three-ton chiller used 120 VAC, as compared to the four and five-ton units that required 230 VAC. Rather than going with the Arizona outfit, I went to a California solar distributor I had been using for years and gave their rep a complete order for what we wanted. This was a mistake! The California company was in the middle of changing ownership, and the rep I liked so well had left the company. The order was lost.

Regardless, I stubbornly stuck with this distributor, and re-ordered. The parts came piece by piece, each with its own billing. Every week I had to call them again and check on or re-order the next components. After over six months of continual negotiations, we finally got most of what we wanted, though we had to go to a second distributor to get cables and some other minor components.

A number of substitutions were made. Instead of the twelve 120 watt Solarex MSX-120 modules we had ordered, our supplier shipped eighteen 80 watt VLX-80 modules. The mounts for these were delayed over two months, and arrived short on parts, which took another week to arrive by air.

Installation Problems

The system was installed piecemeal as components arrived, and went together without significant problems. The chiller did not appear to have an installation manual with it, and we had to make minor plumbing changes after seeing what we had. Without directions, we initially overcharged the system with antifreeze solution and had to drain some.

Air Conditioning Performance Measurements



Temperatu Outside

re (degrees Fa Input Water

renheit) Output Water


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