Millions live around the world without access to hot water. Whether it is for drinking or showering, having sufficient hot water should not be a luxury. We looked at economic ways to provide hot water for showering and cleaning, and as a preheater to produce clean water.
This document shows how to construct a simple solar based water heat exchanger. The heat exchanger consists of a long length of copper tubing with water being continuously cycled through it to be heated by the sun.
We also show how to construct a simple sun tracker that follows the sun as it moves across the sky to ensure the heat exchanger receives the maximum amount of solar energy each day.
Note: The instructions provided are very general with the hope of illustrating the concept and the idea rather than providing detailed steps to replicate our design. There are many improvements that can be made and some of these are listed in the “Improvements” section. We give permission and encourage readers to improve upon our design in any way, as long as it is not for commercial use and credit is given to this document.
Step 1: Materials
- Masking tape
- Duct Tape
- Solar Absorption “Coil” ½ inch outer diameter Copper Tubing (13 ft or longer, preferably soft tubing that can be hand-bent)
- Copper bending tools (optional for soft tubing, mandatory for hard tubing)
- Matte Black Paint/Spraypaint (Needs to be able to adhere to the copper. In this case we used black “Rust-oleum Painter’s Touch” primer)
- Plastic Zip-Ties (various sizes)
- Aluminium foil
- Aluminium foil tape
- Material for making the risers for copper tubing (we used foam, can use wood or other metal clamps)
- Plastic food wrap (for clear cover). Could also use a sheet of acrylic or glass
- Housing for copper coil. We used a cardboard box as a prototype, however, we recommend a wooden box that is resistant to rain and moisture
- ⅜ inch inner diameter rubber tubing (8ft or more, we used Tygon® tubing)
- Bucket (preferably insulated). Food safe is required for potable water, but optional if water is not for consumption e.g showering
- Steel wool/scotch brite/sandpaper for roughing up bucket. Also used to clean copper tubing
- Foam for insulation
- Submersible Pump - we used a 7 watt AC aquarium pump with a flow rate of 227.8L/hr
- Heavy wood base approximately 1m x 1m
- Thin wood platform approximately 0.8m x 0.8m (enough to support the solar collector). This will be the top rotating platform
- Vertical rotation shaft (obtained from a printer or similar, or suitably sized metal rod in general)
- 4x 8mm ID standard skateboard bearings
- 4x 8mm bolt and nut1x Motor (we used the following https://solarbotics.com/product/gm3/) and motor mount (https://www.thingiverse.com/thing:972223/#files)
- Bearing holder (https://www.thingiverse.com/thing:972223/#files)This and the motor mount can be made from metal, wood, or other suitable material since 3D printers are not yet widely available in developing regions.
- motor gear (and corresponding larger gear) (https://www.thingiverse.com/thing:972223/#files)Different sized gears of different materials can be used by moving the motor mount on the top board to the correct location.
- Various wood screws and washers
- Arduino or similar microcontroller
- Adafruit Motor Shield
- Battery - Rechargeable e.g Lithium Polymer, NiMH etc. Ideally lightweight (not a car battery).
- 2x LDR light sensors
- 2x 10kΩ resistors
Step 2: Making the Copper Heat Exchanger - Bending
The first step is to bend the copper into a coil.
- This can be done by hand for softer copper tubing (careful as not to kink the tubing) or with copper bending tools
- Bend very slightly with even spacing to introduce a curve. repeat with more bends until the copper is in a circular coil shape
- Keep in mind that the coil must fit the housing that you intend to place the coil in.
Step 3: Making the Copper Heat Exchanger - Painting
Next, the copper heat exchanger is painted matte black to increase the absorption of solar energy. We used a spray-painted primer.
- Clean the coil with water and steel wool or suitable soft abrasive such as scotch brite pads
- Cover 1cm of each end with painter’s tape to prevent paint entering the tubing
- Follow instructions specific to the paint for details. We used very short bursts from about 30cm away to provide even paint coverage. start with a very thin layer of paint and allow to dry. repeat until there is a thin even layer of coverage with no visible copper
- Remove tape from ends after final layer dries.
Step 4: Making the Copper Heat Exchanger - Fittings
Finally, it is time to install the pump fittings and tubing.
One end of the copper pipe will attach to the outlet of the pump and the other end will connect to the return tubing.
- Slip on tubing onto each end. May require placing in hot water for a few seconds to soften and stretch
- Attach pump fitting to the opening of the tubing that will be closer to the ground when it is installed.
- Attach a zip-tie or hose clamp to fasten tubing
The copper heat exchanger is complete.
Step 5: Making the Housing
The housing for the copper exchanger should be constructed at an angle appropriate for the latitude to maximize solar absorption (ideally so that the coil is perpendicular to the angle of sunlight for as much of the year as possible). The housing will be lined with foil and covered with a clear food covering.
Lining the housing with foil
- Cover inside box with large pieces of foil being careful not to wrinkle the smooth surfaces
- Use aluminium foil tape at the edges of the foil
Constructing the foam risers
- Cut out foam blocks of approximately 10cm x 5cm x 8cm
- Mark out and cut grooves into the foam to fit the tubing as shown.
- The cuts should be slightly narrower than the outside diameter of the tubing and slightly deeper than the diameter for a tight fit
Covering the housing with a clear cover
- Plastic food wrap was used as the cover over the box
- Use long vertical lengths of the cover and hold in place with tape on the ends and edges of the box
Insulating the box with foam is recommended to retain the warmth of the water.
Step 6: Water Reservoir
We used a 5 gallon water bucket as the water reservoir. Originally, the bucket was painted black to passively heat the water, however, we decided to make it a reservoir instead and added insulation to the bucket to prevent heat loss. Theoretically, this should lead to a decrease in heating performance when the temperature of the water is below ambient air temperature, and an increase in performance when the temperature is above the ambient air temperature.
Step 7: Making the Solar Tracker
The solar collector is most efficient when it is directly facing the sun. This poses a problem as the sun moves from east to west during the day. To mitigate this problem, we built a rotating platform upon which the solar collector can automatically rotate to always face the sun.
- Drill two holes in the centre of both the support and rotating platform to fit the vertical shaft
- Put in vertical axle
- Screw in larger gear centred on the axle onto the base board
- Drill holes and attach the motor (with the motor mount) onto the underside of the rotating platform. This allows for the rotation of the top platform around the larger gear while keeping motor wires as part of the rotating platform
- Attach the bearing supports
- Connect the two light sensors to analog pins 4 and 5 on the arduino
- See appendix 1 for the Arduino code
Step 8: Testing and Results
- Attach pump to pipe inlet and place into the insulated black bucket fill bucket ¾ of the way with cool water.
- Face the solar heater towards the sun
- Turn on the tracker
- Turn on the pump and let water run through the pipe
- Leave apparatus in the sun for several hours (or until to desired temperature )
We conducted several tests, both with and without the solar tracking system. The results are shown here. The first graph is a water temperature and solar insolation over time of the solar heater without solar tracking. The temperature is shown in blue, with the starting temperature being 20°C, and a final temperature of 40°C after 5 hours. Time 0 on the graph was 11:00am, with the ambient temperature being an average of 18°C through the 5 hours. The total volume of water heated was 15L. It can be seen that despite a drop in insolation early on (insolation shown in red), it reached approximately the peak temperature of 40°C after 4 hours, reaching a plateau.
The second graph is a graph of water temperature, actual insolation, and expected insolation had the solar tracking mechanism not been used. It shows the results of of 4 hour test with the solar tracking mechanism. The temperature is shown in yellow, with a starting temperature of 20°C, and reaching 41°C, with the volume being 15L once again. The average ambient temperature was 25.5°C. While the ambient temperature was higher than the previous test without the solar tracking system, it can also be seen that the water reached the previous peak of 40°C after only 3 hours, and increased to 41°C after 4 hours. By comparing the graph of actual insolation (blue) and insolation without the tracking mechanism (red), it can be seen that aside from a period of time where they converge - when both the tracker and the non-tracking heater faced the same direction - there is a noticeable increase in solar energy received by the heater. The solar tracking worked to stabilize the rise and fall of solar insolation by continually orienting towards the sun as opposed to remaining in a fixed position. This increased the rate of which water can be heated compared to the non-tracking scenario.
Step 9: Improvements
Many improvements can be made to our concept design.
- Length - longer lengths of copper tubing will allow more energy to be transferred to the water.
- Serpentine shape - allows for a more compact shape for the copper pipes, such as the design from http://mondodesigno.com/ben/serpentine.html
The plastic zip ties along with the tubing used soften in the heated water. The use of metal hose clamps would be preferred to the zip ties.
Replacing plastic wrap top cover with acrylic or glass
The plastic wrap is a cheap and fairly effective, but a proper acrylic or glass cover would be more robust, easier to clean, and have higher efficiencies.
Better housing material
- Plastic - Waterproof with good thermal insulating properties, but can be fragile compared to other materials and may not last long in outdoor conditions
- Insulated metal - sturdy and waterproof, but heavy, and requires good insulation to prevent rapid heat loss getting the water into and out of the storage bucket Another pump to pump the water into/out of the bucket instead of manually filling/emptying
Getting the water into and out of the storage bucket
Another pump to pump the water into/out of the bucket instead of manually filling/emptying the reservoir bucket is a possible improvement.
Solar powered pump, tracker
Since the pump and the tracker are both very low power, it is possible to power them off of a solar panel and battery. This, however, will add a decent amount to the cost.
Step 10: Arduino Code
Attached is the arduino required for the tracking.
The code will tracking from east to west during the day and return back to the east position after it is dark.
Step 11: Acknowledgements
This project was conducted by M. Tong and A. Wang at the University of Calgary. We would like to thank Associate Dean, Marjan Eggermont and Dr. Ed Nowicki of the University of Calgary, Schulich School of Engineering for the opportunity, help, and resources necessary for this project. We would also like to thank Associate Dean Dr. Ron Hugo for providing us with the necessary equipment for data collection.