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Abstract

This spring 2011 semester, we constructed a passive thermosyphon solar shower system that utilizes natural temperature stratification to heat and store water without natural gas or electricity. Constructed at the Manila Eco-Hostel, this is an educational piece that seeks to inspire travelers of the area to recreate such a project in their own community.

Background

Continuing on the design for the Samoa Hostel Thermosyphon Solar Shower System, designed by previous Engineering 215 students at Humboldt State University, we have constructed a solar shower at the Manila Eco Hostel. This shower uses a solar water heating panel to heat water for an outdoor, enclosed shower, providing visitors with an ascetically pleasing, functioning way to shower sustainably.

Opportunity Definition

The objective is to demonstrate, educate, and inspire an alternative way of heating water to visitors of the eco-hostel.

Solar Water Heating Basics

Solar water heating is a growing and innovative field that takes advantage of the suns energy to heat water. [1][2]. Solar water heating is a growing market, as Israel, China, Australia, and Austria continue to expand the field.

Types Solar Water Heating

Generally there are two types of solar water heating: passive, and active[3] heating.

Passive Solar Water Heating

  1. Integrated Collective Storage: This simple and relatively cheap design is a storage tank that also collects heat from the sun. The disadvantage of this tank is that you need to be in a hot climate for it to be effective. [4]
  2. Convection Heat Storage Unit: Using the properties of convection and thermosyphoning, this system uses a solar water heater panel to collect heat and move water against gravity into a insulated water tank.[5][6]

Active Solar Water Heating

Active solar water heating systems use electricity to pump fluid from the panel to the storage tank.[7] The advantage of an active solar water heating system is that it has the capability to run at higher efficiency with the installation of a pump and controller. [8] These items allow the water to be circulated faster, allows for storage of the water tank lower than the panel, and also reduces the risks of overheating from increased circulation. There are three classifications for Active Solar Water Heating systems[9][10]:

Direct System

Water is the medium which is heated up in a solar collector and is then actively pumped into an insulated storage tank. Concern for freezing should be considered in places with seasonal cold climates.

Indirect System

Anti-freeze circulates through the solar collector, collecting heat. The Anti-freeze is then circulated through a heat exchange device to transfer the heat to water without mixing. This system is a good alternative for the Direct System if freeing is a concern.

Drain-Back System

Similar to that of the Indirect system, except the Drain-back system allows for fluid to drain out of the solar collector when not in use, which allows for variation in design from the Indirect System. This is also a good candidate for cold weather climates.

Implementation Cost

The materials needed for this specific project are listed below. Included is the item name, the quantity needed, the cost per unit item, the cost at which we received the item (at the quantity needed), and an estimated retail cost should someone care to build a system modeled after this page. Several items have been donated and others have been previously obtained by another group working on this project. Items that are labeled NA are items that were not required for the testing phase, but would be needed for an lasting final result. The variability for the final cost is due to the large range of price a solar water heating panel can have and it should be noted that our range is a modest one.

Materials Quantity Unit Cost($) Actual Cost ($) Retail Cost ($)
2x4 (8 feet) 8 $3.79 $30.32 $30.32
4x4 (8 feet) pressure treated 5 $8.96 $44.80 $44.80
Redwood Fence Boards 56 $3.25 donated $182.00
Concrete cubic yard 1 $130.00 $130.00
Fencecrete 5 $3.99 $19.95 $19.95
Thompson's Water Sealer 2 $15.99 $31.98 $31.98
Latch 1 $1.99 $1.99 $1.99
Hinges 2 $2.99 $5.98 $5.98
Shower Head 1 $12.99 $12.99 $12.99
2.5" Screws 5 lbs $2.99 per lbs $14.95 $14.95
Shower Pan Drain 1 $9.99 $9.99 $9.99
Hot Water Heater 1 $80.00 donated $80.00
Copper Pipe (feet) 30 $3.00 NA $90.00
Solar Water Heating Pannel 1 $500-1,000 donated $500-1,000
Total Cost $302.95 $802.95-$1302.95

Evaluation Criteria

This section includes all possible aspects thought up by the group members for this project as well as the partners of the Manila eco-hostel. These criteria were chosen to evaluate the project based on ease of use, educational capacity, and aesthetic. These criteria helped us to determine how much time, money, and effort should be invested in each aspect of the system based on its importance to our clients.

Criteria Constraints Our weight (0-10)
maintainability must be able to maintain functionality on less then .5 human labor hrs a week 7
safety must be able to function with out possible injury to users or observers 9
effectiveness must be able to power a device for the full duration of its intended function 8
ease of use must be useable for adults without struggle 7
social justice 50 % of materials must be donated or reused 5
educational value must be able to provide an understanding of the functionality and use of the device, within a two minute viewing span 9
aesthetics must be pleasing to the eye and look professional 6

Proposed time line

Week: Tasks:
Week 6 (3/7/11) Collect Materials: Fencing
Meeting with "Truth Window" Team to Confirm Measurements

Meeting with "Water Boys" Team to confirm measurements Confirm Measurements

Week 7 (3/14/11) Survery Job Site

Data Collection: Solar Pathfinder
Solidify Design: Greywater
Confirm Measurements
Collect Materials: Plumbing/Copper piping

Week 8 (3/21/11) Solidify Design: Shower
Confirm Measurements

Create Project Site Map
Timesheet #4 Due 3/25

Week 9 (3/28/11) Construction Assembly

Create Signage for thanking donaters
Create Signage for safe soaps

Week 10 (4/4/11) Construction Assembly

Timesheet #5 Due 4/8

Week 11 (4/11/11) Construction Transport Shower,
Install Shower

Start Final Draft Project Report

Week 12 (4/18/11) Construction Transport Greywater, install greywater

Work on FDPR
Timesheet#6 Due 4/22

Week 13 (4/25/11) Testing, adjustments to System

Work on FDPR

Week 14 (5/2/11) Testing, adjustments to System

Work on FDPR
Make thank you notes to donaters
Timesheet #6 Due 5/6

Week 15 (5/9/11) Turn in FDPR

Gallery

Results

On a warm 21°C day with full sun in Manila, we managed to heat 15°C water to 47°C as measured from the output of the panel. After 10 minutes, the water coming from the shower head was 20°C, but did not heat significantly more after 50 minutes. Ideally, this system will have several hours to heat and allow for temperature stratification in the water heater tank and the tank will be better insulated then it was during our tests.

Next Steps

Over the summer of 2011, a cradle will be constructed at the crest of the north side of the shed roof to house and insulate an electric water heater tank. Also, the solar water heater panel will be fastened to the south side of the shed roof and the permanent plumbing will be installed. After that is done, the Samoa Hostel Truth Tank could be connected for natural grey water treatment and education on grey water treatment.

References

  1. Patterson, J. (2010). “Solar Hot Water Basics.” Homepower Magazine. <http://homepower.com/basics/hotwater/>
  2. Basics of thermosiphon flow.
  3. Ramlow, Bob (2006.) "Solar Water Heating." A Comprehensive Guide to Solar Water and Space Heating Systems, New Society Publishers, Gabriola Island, Canada.
  4. Keisling, Bill. (1983). “The homeowner’s handbook of solar water heating systems.” Rodale Press, Emmaus, Pa.
  5. J. Cadafalch (2009) A detailed numerical model for flat-plate solar thermal devices. Solar Energy, Volume 83,157-2164
  6. W.M. Rohsenow, J.P. Harnett, Y.I Cho (1998). Handbook of heat transfer 3rd Ed.. McGraw-Hill, Chicago, USA.
  7. AEF solar water heater
  8. RCEA Solar thermal vs Heat pump
  9. Findley, David S. (2010). "Solar power for your home" . New York: McGraw-Hill, Print.
  10. [[Kang, J., ITT Residential and Commercial Water. "An Introduction to Solar Water Heating". http://www.Bellgossett, PDF.
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