Nicholas School Internship Blogs

Pulling together a Solar Hot Water System for Small Hope
by -- July 12th, 2013

Working with Small Hope Bay Lodge has been an incredible experience and opportunity to see a project go from vision to completion. The main objectives for the project is to design a working solar hot water system for the resort that would produce positive economic returns, a  reliable source of hot water, and decrease Small Hope’s use of diesel generated electricity (the sole source of energy provided by the local electricity utility, Bahamas Electricity Company). Solar hot water just makes sense here because of the high economic ($.45 per kwh) and environmental costs of diesel generated power, but the immense upfront capital costs still remain a barrier to adoption. Additionally, BEC does not offer an option to sell electricity back to the grid.

The first few weeks of the project had been focused on framing the project, defining the scope, and achieving internal consensus over the type of system that is best for Small Hope. It was challenging to frame and narrow the focus due to the divergent visions held by the Small Hope staff involved in the project. Beyond just providing reliable hot water and cost savings to the resort, Jeff, the owner of Small Hope, also wants to use this project as an opportunity to help spread environmental awareness and empower the local community.

In order to reconcile all of our objectives and priorities, we separated the solar project into two phases; the first phase is focused on providing the best fit system for Small Hope and the second is to create a home design for Jeff’s house that can be easily replicated by community. I believe homemade solar hot water systems can make a significant impact in this community if the knowledge is properly disseminated. In my short time on the island, I have already met several business owners forced to close due to the crippling energy costs and surprisingly high cost of living.

Small Hope Group

The Team!

The Design:

Solar hot water systems can be generally divided into passive and active systems. Passive systems circulate using gravity and natural forces like convection. Active systems use pumps. Within active solar hot water systems, you can have direct or indirect systems. Direct systems heat the water that is being sent to the end user. Indirect systems have a closed circuit of heat transfer fluid which is used to heat the water going to the end user through a heat exchanger.

Blog System Redesign

For our final design (pictured) we settled on creating an active system with both a closed distilled water loop (loop A) and an open indirect loop (loop B). We eliminated the use of a passive system and choose to go with an active system in order to create the reliability needed for a resort. Small Hope’s large scale water usage and guests’ instantaneous expectation for hot water simply cannot be achieved with passive systems. Another major problem we had to design around is the hard water here. The salt water here speeds up corrosion, while the dissolved calcium in the water can easily block piping. In order to avoid the corrosion from the hard water, we decided to create this two loop system and isolate direct contact with the hard water to more easily replaced parts.

Distilled water is used in loop A and will be heated by the flat panel collectors before then being sent to the heat exchanger to dump heat into loop B, which runs through the entire resort so there is less lag when delivering the hot water to its final destination. The distilled water is then cycled through the collectors again. The water for loop B enters the 4 water tanks through an H shaped manifold at the top of each water tank. The water tanks will be placed in a 2×2 formation instead of the inline formation shown in the diagram in order for the water to enter all four tanks simultaneously and at the same pressure/flow rate. Each tank will be connected to a total of 3 manifolds, one at the top for cold water, one in the middle for hot water to be sent out to loop B, and another at the bottom of the tank for the recirculation of hot water in loop B. The water is then passed through the tank where it will mix with the hot water and is then sent out through the middle manifold through loop B. The water in loop B will be continuously circulating and will aggregate more heat each times it passes through.

Progress

Although the concepts behind solar hot water are very simple, the challenge is in the details. Customizing the system for Small Hope and managing the logistics of the project has been an interesting learning experience for me. I have never spent so much time thinking about the arduous journey goods go through to reach its destination. Shipping one small part to the island of Andros requires an extensive amount of planning, organizing, and coordinating between factories, distributors, trucking companies, freight shippers, and customs officials. The past few weeks have been dominated by emails and calls to theses various parties. But the efforts are all starting to come together! The parts are finally starting to get here. The solar panels, concrete and wood arrived late last week. Our pumps, relief valves, and piping should be following shortly. We also started digging the foundation for our solar panels. I’m eager to start getting my hands dirty (I just might regret this phrasing as we manually mix concrete next week).

The Big Dig with Esi Waters (Duke MEM 13) and Jake Vestal (Duke Engineering Management 13)

The Big Dig with Esi Waters (Duke MEM 13) and Jake Vestal (Duke Engineering Management 13)

3 Comments

  1. Frank Spears
    Jul 27, 2013

    Wow. We met you at the end of May and had no idea the scope of the project. Looking good.

    • Michelle Yuan
      Michelle Yuan
      Aug 3, 2013

      Thanks Frank! Hope you had a great time at Small Hope! I’m excited to see what we can do for Jeff and whether or not we can spur some interest in the community! The energy costs here are through the roof! $200 electricity bills for an apartment or small house is considered normal…

      • frank spears
        Aug 4, 2013

        Michelle,

        One more thing…. did you ever get used to the bug bits???

        Frank

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