The Solar System at 1043 Dodge Avenue

Brian Slator

The short story is this: by repairing and re-engineering the solar hot water system that came with the house, we were able to reduce average monthly electric usage, in terms of Kilowatt Hours by 30.77%.

The Components of the System

According to the U.S. Department of Energy publication FS 119, 3rd edition, "Passive and Active Solar Domestic Hot Water Systems", the solar system at 1043 Dodge Avenue is of the active, indirect type. "Active" means that heated fluid is pumped through the system rather than rising and falling through convection as the fluid is warmed and cooled. "Indirect" means the solar energy is transferred into the hot water system by means of a "heat exchange" where a heated fluid, like anti-freeze, passes heat into the water through copper tubes. The specifics of the solar system are detailed below.

At 1043 Dodge Avenue, on the roof, there are 3 solar panels each 4 feet by 8 feet. The solar panels are fairly simple: a plate of glass, an air space filled with coiled copper tubing, and a back panel covered with black paint. There is also a sensor that reports the temperature of the rooftop fluid.

The copper tubing is filled with pressurized Propylene Glycol (non-toxic anti-freeze) at 20 pounds per square inch (PSI) of pressure. When the sun warms the anti-freeze, the sensor detects this heat, and the fluid is pumped down into the basement where the copper tubing passes through the hot water heater. The copper tubing coils around itself inside the water heater; this coil of tubing is called a "heat exchange". The heat from the anti-freeze is transferred by the heat exchanger into the water, and then the anti-freeze is pumped back up to the roof for more solar energy.

In the basement there is a large hot water heater (115 gallons) with a 3000 watt electric element (this element is now controlled by a switch). There is also a small (35 gallon) natural gas water heater. When water is delivered to a faucet, it comes from the gas water heater. The gas water heater is filled from the solar water heater, and the solar water heater is filled from the city's water pipes. (Sometimes this arrangement, where the solar system's water tank is used to feed another water heater, is called a "temper system" or a system with a "temper tank" -- the water is "tempered" by the solar system before it is fed into the conventional water heating system).

How the Water is Heated

The large solar water heater gets cold water from the "ground" (i.e. the city water pipes). Inside the tank, there is a coil of copper tubing called the "heat exchanger". As hot anti-freeze is pumped down from the solar panels, the heat passes into the water. When a hot water tap is turned on, water is delivered from the small natural gas water heater, and the small tank is refilled from the large solar water heater. This way, the gas water heater is always getting warm water put into it, rather than the cold water from the "ground". This arrangement is sometimes called a "temper tank" system. The cold water is pre-warmed, or tempered, before passing into the conventional natural gas water heater.

Here is where the savings come in. Instead of heating the water that enters the house at 50 degrees to the usual 135 degrees, the gas water heater is is heating water that is already warmed by the sun. In the winter, on a sunny day no matter how cold, the solar heated water will get up to at least 100 degrees. On March 11, 1996, for example, the outdoor temperature was about 40 degrees, and the sun was shining through a clear, hazeless sky: the solar water heater showed a temperature of 135 degrees. In the summer, on a sunny day, the solar heated water has reached 155 degrees (you have to be careful with the water). During the summer, there is virtually NO cost for heating water -- the natural gas heater almost never burns any gas.

Background

The Slator family bought and moved into 1043 Dodge Avenue at the end of April, 1994. At that time, there were solar panels on the roof and a large,115 gallon, electric water heater in the basement. Off to the side was a small, 35 gallon, natural gas water heater, not hooked up.

An attempt was made to learn about the system: when was it installed and who did the work? The story, from the sellers (Herbert and Rose Longsworth), was that the solar system was one of 17 installed by the city of Evanston as part of an experimental energy-savings program in the 1970s. We were unable to verify this.

Several phone calls were placed to Evanston city government, including the Evanston Assessors Office, the Evanston Department of Building, Planning, and Zoning, and Evanston Central Records. These calls yielded absolutely nothing. There was apparently no such experimental solar program, and there was, in fact, no record of a solar system ever installed at 1043 Dodge Avenue -- no work permit, construction permit, or any other record.

We also visited the Evanston Historical Society, Dawes House, 225 Greenwood St., Evanston IL 60202 (ph. 847-475-3410). There, on record, we found a building permit for the garage, constructed in 1954, and another for the roof replacement in 1977, and some record of a water heater replacement in 1978. In addition, an inspector visited the house in 1967 and noted the WC in the basement had no vent, and that the front yard of 23 feet was less than the new minimum of 27 feet (as a consequence the inspector issued "zoning exception certificate #3278).

Unfortunately, despite all these efforts at searching the official record we were unable to find any documentation to authenticate the history of the solar system. Nor were we able to find a description or rationale of its original design.

In the spring of 1995, we contacted Brandon Leavitt at Solar Service (P.O. Box 31430, Chicago, IL 60631, ph. 708-677-0950, the area code is now probably "847") who was contracted to put the system into working order. These repairs were completed by the end of May, 1995.

At this time we learned that the solar system was not working at all, nor had it worked for some months or years. We learned that the hot water in our house was being produced by the large electric element inside the solar tank as a backup. This explained why our electric bills seemed so high.

Results

For the first year, the system remained untouched (that is, it was NOT functioning as a solar system, it was an electric hot water system), and electric bills ranged from $121.96 (1420 Kilowatts) to $201.45 (2515 Kilowatts) per month (with an average of $156.95 and 1799.42 KW).

In the year following the repairs (that is, the solar system was made to work, the small gas hot water heater was installed, and the electic element was put onto a switch that was turned off), electric bills ranged from $99.14 (882 Kilowatt Hours) to $194.15 (1647 Kilowatt Hours) per month (with an average of $140.13 and 1245.78 KWH).

Bear in mind that we were HEAVY users of electricity: multiple stereos, multiple televisions, multiple air filtering devices running at all times (because of allergies and asthma in the family), a fish tank, and multiple computers. Your bills will almost certainly be lower.

Average electric usage, in terms of Kilowatt Hours, was reduced from 1799.42 KWH to 1245.78 KWH, a reduction of 30.77%.