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Bayside Park Farm solar hot water

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Bayside Park Farm's appropriate tech projects:
Info Kiosk | Food Dehydrator | Greywater (en Español) | Photovoltaics | Solar Water Heater | Spiral Herb Garden


Solar Hot Water Heater

Abstract[edit]

Our project was to rebuild the Bayside Park Farm solar hot water heater[1] that was disassembled during construction of the new dish washing/vegetable washing station. We started our project by assessing how we wanted to set the system back up, how we wanted to improve it, and by doing research on the system. Once we knew what we wanted and understood the heater fully, we began construction and completed it in steps. Step 1 was to fix the broken sink plumbing. Step 2 was to build a rack for the solar collector. Step 3 was to complete solar intake and output plumbing. Step 4 was to connect the heater to the sink for cold water intake and hot water output. Step 5 was to get the old solar panels onsite to run the water heater pump. Throughout all of the project we were testing the system and looking for the simplest and cheapest ways to complete it. We also tried to provide the farm with educational materials on the system as well as give them some guidance for maintenance.

Background[edit]

Bayside Park Farm is a local CSA, (Community-Supported Agriculture establishment) which is supported by the community and provides fresh organic produce to members and shareholders. Bayside was formed by Humboldt State University Professors, started farming in 1993 and was the first CSA in Arcata. It is also a community park and demonstration site for permaculture farming and appropriate technology. Bayside Park Farm is located on 930 Old Arcata Road, in Humboldt County, California.

Our Engr305 Appropriate Technology team (Trevor, John, and Annika) chose to help the farm rebuild their solar hot water heater for the outdoor sink and vegetable washing station. It was disassembled and never rebuilt; we determined what parts were in working order and tried to improve the system where possible.

Problem statement[edit]

The objective of this project is to reassemble the Bayside Park Farm solar hot water heater and connect it to the sink in the new wash station in a way that it will be easy to maintain and will be effective to the farm's needs.

Criteria[edit]

The following criteria are based off of a scale from 1 to 5, 5 being the most crucial and 1 being the least.

Criteria, Constraints, and Weights for the Bayside Park Farm solar hot water project
Criteria Constraint Weight
Water temperature Warm enough to wash vegetables with, not hot enough to scald hands 5
Hot water duration /

Total heat capacity

At least 30 minutes of continual usage 5
Washing station

efficiency

Must be more efficient than the current kitchen sink 2
Maintenance /

documentation

Must be easy to understand by farm staff with no prior solar hot water experience and provide some trouble shooting information 5
Educational physical infrastructure Should provide signs and additional information on the project that the farmers can reference when giving tours. 4
Cost Should remain within budget. 3

Literature Review[edit]

This is a review of the available literature pertinent to the solar hot water heater at the Bayside Park Farm.

Solar hot water basics[edit]

Solar water heating collectors capture and retain heat from the sun and transfer this heat to a liquid. Solar thermal heat is trapped using the “greenhouse effect,” which is the ability of a reflective surface to transmit short wave radiation and reflect long wave radiation. Heat and infrared radiation (IR) are produced when short wave radiation light hits a collector’s absorber, which is then trapped inside the collector. Fluid, usually water, in contact with the absorber collects the trapped heat to transfer it to storage. [2] The core of a solar water heater is a solar collector and a storage tank. A solar collector is basically a glazed, insulated box with a dark-colored interior and, usually, a bunch of tubes or passageways for water flow. The solar collector turns the sun's radiation into heat. The storage tank does the job of holding the water. [3]

Solar hot water concerns[edit]

There are a few concerns with the use of solar hot water, the main one being that hot water is not always guaranteed. The sun does all the heating, so without sun the water will not be heated. Cloudy days can still produce warm water but it will not be hot. Also, early in the morning the water will not be hot, the tank could still have retained some heat from the previous day but it will not be hot. Solar hot water had a peak in use in the 1980s, but with the cost of energy going down people opted for the traditional water heater. The solar hot water heater is still not making much of a come back, but there are really high quality systems being made. A problem is that the systems worth owning are not cheap, they are expensive, and requires a skilled crew to install. They cost more then a traditional water heater and the initial investment is hard for people to pay. With the combination of efficiency and the cost of energy relatively cheap, the market for solar hot water in United States is not as big as it could be.[4]

Types of solar hot water heaters[edit]

All solar hot water heaters use collectors, which are the "panel-like" components of the system that are heated by the sun, and storage tanks, which hold the domestic water. Solar hot water heaters have these basic components, but otherwise are separated into active and passive. Active systems use circulating pumps, while passive systems do not. [5] Systems can also be closed loop or open loop. Closed loop systems "continuously circulate an isolated fluid... from which heat is extracted via a heat exchanger" and open loop systems run the same water that would come through your tap through the collector. [6] Open loop systems should only be used in warmer climates, due to fear of the water freezing up in the collector. [7] However, collectors can also be mounted inside the house to prevent freezing, while in warmer climates solar collectors can be placed on the roof. [8]

Type 1: Active[edit]

There are two types of active solar hot water heaters:

  • Direct circulation system
    • Pumps circulate water directly through collector to be heated up and then hot water is passed on to the house/faucet. This is considered an open loop system.
  • Indirect circulation system
    • Pumps circulate a "heat transfer fluid" through the collector to be heated up. This can be a variety of fluids such as, water, refrigerants, silicones, and even air can be used. After the heat transfer fluid is warmed by the sun, it is carried into the storage tank to heat the domestic water itself. The transfer fluid does this by traveling through a "heat exchanger", which is normally made of copper or another good conductor. Within the heat exchanger, the heat transfer fluid is passed by the potable water so as to transfer thermal energy. This is accomplished through multiple means; by running a coil through the water storage tank, and shell-in-tube/tube-in-tube designs. The shell/tube-in-tube designs run the transfer fluid and potable water past each other in tubing so that they are in thermal contact with one another. This is a closed loop system.[5]

Type 2: Passive[edit]

Passive solar hot water heaters do not use pumps and therefore are cheaper, but possibly less efficient. There are two types of passive solar hot water heaters:

  • Integral collector-storage passive system
    • Also known as a batch system, the integral collector-storage system has domestic water run straight through the collector and into a storage tank. This is often used alongside a normal gas/electric water heater and may have to be drained and out of commission during cold winter months. This is an open loop system. [6]
  • Thermosyphon system
    • The collector is positioned underneath the water storage tank. Water from the collector is heated up and then naturally flows into the water storage tank. From there, the cold water sinks to refill the collector. This is an open loop system.[5]

Construction[edit]

Step 1[edit]

Fixing PVC

When we first started the project we were informed that the PVC pipe that brought cold water to the dish washing sink had broken during a winter frost. We needed to fix this first so that a) the farm could have use of the sink again and b) we could run a PVC pipe to the heater for cold water intake.

Broken PVC

We started by cutting off the pipe as far back as it was cracked. Upon further inspection, we realized the break was not only from the cold, but also from the pipe having been placed in a way that it was twisted and had a lot of pressure applied to it. We tried to improve the plumbing by putting in the new PVC pipe so that it sat correctly. We also improved the system by putting a ball valve on the heater's cold water intake. This was so that if there is ever something that needs fixing in the hot water heater, the farmers could shut off water flow to it, but still use cold water at the sink.

We figured out how the PVC piping needed to go as we went along and used cord wood to hold the pipe in place as it was free and available.

Step 2[edit]

Finished Product

The next step of our project was to set the heater where we wanted it to go and put the collector over it. We wanted the collector over the heater to minimize the amount of space the system would take up, as well as to minimize the amount of plumbing needed. We also decided we would prop the top of the collector up on the vegetable wash station roof to take up less space and use less lumber.

Together the three of us drew out our design for the rack and determined the heights each part needed to be. We looked over how the previous rack was built for inspiration and went from there. We knew we wanted the collector to be at approximately a thirty degree angle for maximum time in the sun throughout the day. We took this into account during construction.

We first dug two, two feet deep holes for the 4 by 4 posts that would hold up the bottom of the rack. We used six foot 4 by 4s so that two feet would be underground and four feet above ground. We put the posts into the ground with concrete. After the concrete had set, we put a 2 by 4 across the two posts to hold up the rack and provide support. We drilled in two shorter 2 by 4s to hold the collector into exact position. Then, we drilled into the top of the outside wall to put in a wooden support rack, raised slightly above the roof. After all these components were complete, we put the collector into place and tested its sturdiness.

Materials used were donated by Almquist Lumber Company. We used pressure treated wood so the rack would have a long lifespan outdoors and we painted it the same color as the vegetable washing station. The paint was also needed as a precaution to seal in the copper the wood was treated with. We also used three inch long deck screws donated by Almquist.

Step 3[edit]

Collector intake and outlet

Once we got the solar hot water heater positioned at a 30-degree angle, and mounted securely, we began connecting components together using copper piping. We had left over copper from the previous installation used to connect the solar collector to the storage tank, however, the angles they previously soldered at would not suffice. Luckily, we were able to heat the joints up with a propane torch and separate the once soldered together joints which allowed us to make use of the valuable copper. We used the existing ¾ “ copper piping and purchased additional pipe and joints to create the water circuit loop from the tank to the storage collector, using lead free soldering. Once the circuit was completed we filled up the tank with water and were then able to test the pump by connecting it to a battery, and began circulating water through the collector, warming the storage tank.

Fixing Pipe

Step 4[edit]

Our next step was to connect the cold intake water to the tank and from the tank, to the sink. We drilled a small hole through the wall and used braided steel piping to connect the pressurized water from the pvc pipe to the tank heat exchange. This involved more soldering to create proper fittings between the copper and the braided steel. From there we were able to complete the heat exchange pressurized circuit by connecting back to the hot water side of the sink faucet. To do so, we needed to reduce the ¾“ copper piping to ½”.


Step 5[edit]

The PV panels on the farm are very old, but they work well for this operation. They are hooked up to a 12 volt battery, which remains charged because the pump does not run all the time. The system has an Eagle D2 Sun Controller, this controller uses thermistors to read temperatures of the water in the tank and, and in the solar collector. It then uses difference in temperature, and high and low readings to determine run time. Turning the pump on whenever it can heat the water in the tank. We hooked up the thermistors and the pump from the controller to the water heater. For the water in the tank, we hooked the thermistor to the heat exchanger pipe right where it comes out from the tank. For the solar collector, we connected the thermistor to the copper pipe as it just exits the panel. From that point all we needed to do was to check in on it and make sure it is operating properly. The day after we finished, the high temp in Arcata was over 80 degrees, the water in the tank got to 110 by the end of the day. The following weeks the water temperature in the tank would fluctuate between 88 and 105 degrees, hitting high temps on sunny calm days, while never dropping below 85 on cloudy days. The water remains warm because water has a great thermal mass, our tank is very large with good insulation, and the outside temperature rarely drops below 50 degrees.

Awesomeness!

Costs[edit]

Listed below are the parts required for completion of the solar hot water heater along with their costs. We received all parts locally and some of them were donated.

Quantity Material Source Total ($) Donations ($)
28 PVC pipes and sink parts Hensel's Ace Hardware 75 0
7 Copper pipe, fittings, nails Sunnybrae Ace Hardware 22 1
12 Lumber, concrete, and screws Almquist Lumber Co. 0 97
Total Cost: $97 Total Donations: $98

Timeline[edit]

This project was done in the spring of 2014.

On Tasks completed
2/8 Tested collector for leaks, moved components into general area, tested pump.
2/16 Cut broken PVC pipe and measured for new ones.
2/23 Placed bark under tank, removed faucet for replacement. Designed frame for solar collector.
3/8 Replaced broken plumbing with new PVC pipe, began frame, tested photovoltaics.
3/20 Picked up lumber from Almquist, put main support posts for rack into the ground, measured angle for collector, built main rack componenets.
4/6 Continued work on rack, saudered copper solar intake and return plumbing, tested collector intake and return.
4/12 Finished rack, painted rack, wrapped copper pipes with insulation.
4/20 Saudered plumbing for cold water intake and hot water output, fixed sink knob.
4/30 Wired solar panels to control box, battery, and pump.
5/4 Tested entire system and put on finishing touches.

Operation[edit]

The system should operate automatically, should it not be starting and stopping automatically, check troubleshooting table below.

Explanatory Video[edit]

Maintenance[edit]

This system requires very little maintenance. The maintenance required involves keeping the collector and solar panels in full sun (trimming back any trees/plants that may get in the way) and replacing any parts (PVC pipe, the battery, etc.) that may break in the future. We do not foresee any parts needing to be replaced in the near future and believe our project will remain standing for quite some time.

Conclusion[edit]

Testing results[edit]

After setting up the system, we ran multiple tests to make sure the heater was working well.

We went out to the farm multiple times in the week after completion to check tank thermometers to make sure the water was rising to a warm enough temperature. We also tested to make sure the pump was starting and stopping at the correct times. This was done by altering the temperature difference on the solar control and making sure the pump started when the collector temperature raised 8 or more degrees higher than the tank temperature. When the temperature difference was lower than 8 degrees, the pump would shut off again.

We found that the water was typically around 90 - 100 degrees Fahrenheit each day, even if it was partially cloudy. So, that test was successful. The test of temperature control also proved successful. The pump started and stopped automatically based on temperature.

Discussion[edit]

After testing, we were surprised that the water stayed around 90 - 100 degrees even on cloudy days. The hot water tank seemed to have a higher thermal mass than we thought and provided warm water for a longer time period than expected (it could run for about 10 minutes or longer before decreasing in temperature).

The pump control for temperature was initially complicated to figure out. We weren't positive if the pump was starting when the temperature of the collector was hotter than the tank and had to create scenarios where we manually changed the collector temperature. We also had to test where the best places for the "thermisters" (copper pieces which measure water temperature for the solar control) were on the copper piping.

Lessons learned[edit]

We learned that the pump did indeed start when the collector was at a greater temperature. Another lesson learned was that the best spots for the thermistors were: on the top of the collector and on the copper pipe that feeds out of the hot water tank before it mixes with cool water and moves to the sink.

Troubleshooting[edit]

Problem Solution
Water is not warm on a sunny day Check to see if pump is starting automatically, turn on manually, make sure temperature difference on solar control is at lowest temperature
Pipes leaking If it is PVC: find replacement part, if it is copper: call someone who can "re-sauder" the joint
Pump does not turn on (manually/automatically) Check that the solar panels are in full sun, test battery for voltage, check all wiring
System leaking Call Six Rivers Solar or another professional to find tank leak, turn ball valve to hot water heater off as to prevent further leaking

OCTOBER 2014 UPDATE[edit]

After a thorough examination of the plumbing system, electrical grid, heating panels, pv panel array, and reservoir, we determined that the system is still in perfect working condition after 6 months of use. The most worn part of the system seems to be the PV panel array, which exhibits some dust or residue build up on the surface of the array, as well as some minor rusting of the array itself. There is a small amount of foliage that is covering a very small portion of some of the panels that could be trimmed back. Some of the duct tape that was used to secure the insulation around some of the plumbing has dried and peeled, and could be replaced. The heating panels, wooden framing, pump, electrical wiring, and internal plumbing seemed to be in the same condition that they were when they were installed, and there is no visible leaks. After testing the temperature of the heated water by hand, it seemed to heat relatively quickly and was significantly warmer than the cold water. This proves that the system can reasonably withstand the environmental conditions of Arcata, and can hold up to its current demand.

Hotwaterpv.jpg

The pump was running when we came to examine the installation, and over the period of examination the water temperature of the reservoir went up several degrees, indicating that the system was operational and effective. Some thoughts about how we might change or update the system included removing the heat exchanging system being utilized currently, and instead using a central heated reservoir that we draw hot water from directly. As well, we could change the location of the thermistors in our temperature sensing circuit so that that the "Sun Controller" is being used more effectively and efficiently.

Suncontrol.jpg

October 2016 Update[edit]

The solar hot water system is currently out of service due to a broken water pump. The pump stopped working in spring 2016, but Bayside is currently in the process of getting it fixed or replaced. At the beginning of October 2016, the solar panel was moved to the other side of the hot water system due to the fig tree’s growth in its original location. Bayside also has plans to move the battery closer to the solar panel’s new location.

IMG 1034.JPG

Special Thanks[edit]

Thank you to Jayme and everyone else at the Bayside Park Farm for giving us this opportunity and feeding us! Thank you to Almquist Lumber Co. in Arcata for donating all the lumber we needed for this project. Thank you to all those who let us borrow their tools. Thank you to Norm at Six Rivers Solar for giving us guidance and being receptive to our questions. Thank you to everyone who supported us and our project.

Solar hot water heater geese.jpg

References[edit]

  1. Bayside Park Farm solar hot water/Previous version
  2. "What is Solar Water Heating?." Solar Water Heating System Basics. http://www.homepower.com/articles/solar-water-heating/basics/what-solar-water-heating (accessed February 8, 2014).
  3. Layton, Julia. "How Solar Water Heaters Work." HowStuffWorks. http://science.howstuffworks.com/environmental/green-tech/sustainable/solar-water-heater1.htm (accessed February 8, 2014).
  4. Jennifer Runyon "What Is Holding Back Solar Hot Water in the US?" Renewable Energy World. http://www.renewableenergyworld.com/rea/blog/post/2012/05/what-is-holding-back-solar-hot-water-in-the-us. (accessed february 9, 2014)
  5. 5.0 5.1 5.2 US Department of Energy 2012. "Solar Water Heaters." Energy.gov. Accessed February, 8th. http://energy.gov/energysaver/articles/solar-water-heaters
  6. 6.0 6.1 Ewing, Rex. 2011. "Two Solar Hot Water Heaters You Can (Probably) Do By Yourself." Country Side and Small Stock Journal 56-8
  7. Davidson, Jane and Wood, Byard 1996. "Solar Hot Water for the Home." Mechanical Engineering 118,8:60-3
  8. Laughton, Chris 2010. Solar Domestic Water Heating. Earthscan.