Comparative Solar Hot Water System

In November of 2011 two solar hot water panels intended to provide heated water to Mod unit 303 were installed. The idea for this innovative and educational project came from Andy Sontag, a former Evergreen student, while implementation has been through the collaborative design and construction by RAD Services and the independent contractor Global Green Energy Corporation (GGEC). The Clean Energy Committee demonstrated their support and faith in RAD by providing a grant in the amount of $15,000 to fund this project. The Comparative Solar Project involves the installation and subsequent comparison of two different solar powered water heating systems. In addition to bringing this housing unit closer to energy independence, this will provide valuable feedback regarding the comparative efficiency of the two solar powered water heating systems.

How Does Solar Hot Water Work?

The systems, Apricus evacuated tubes and Caleffi flat plates, have been positioned on an elevated platform in front of Mod 303, and will use methods of heating water that are variations on the same concept. That is, using the sun’s energy to heat a non-toxic glycerin based heat transfer fluid (HTF) which will then travel through a heat exchanger within a solar water heating tank. While in the heat exchanger, the heat from the HTF will be transferred to the water within the tank.

Apricus Evacuated Tubes

Apricus evacuated tubes do this through the absorption of sunlight, which is trapped as heat by the glass evacuated tube. A copper heat pipe within the evacuated tube contains a small amount of fluid, which will boil when the tube reaches 30° C (86° F), as the evacuated tube is in a vacuum state, which lowers the pressure within the tube below the atmospheric pressure. This causes the boiling temperature of the water to decrease. The resulting vapor rises to the top of the copper heat pipe, heating the HTF that is circulating through the header pipe. This heated fluid travels to the solar water heating tank, where the heat is transferred.

Caleffi Falt Plates

Similarly, Caleffi flat plates absorb the sun’s heat into the flat panels, which heat the HTF circulated through them. Once the temperature of the HTF exceeds that of the water in the tank by 12° F the controller is activated which pumps the heated fluid to the storage tank, where the heat is transferred to the water within the tank.

What's The Benefit?

Each solar power system is capable of producing up to 42,000 BTUs per day, which is the amount necessary to power about five 100 watt light bulbs for 24 hours. The hot water generated from this will be used to provide hot water to Mod 303 as well as heating through a, in-floor radiant heating system, which transfers heat from the water into the unit by circulating the hot water through pipes in the floor.

It has been estimated that the average individual in the U.S. uses approximately 20 gallons of hot water per day, and since modular 303 will house 6 people, this will offset the power needs for hot water usage alone by 120 gallons per day. The radiant heating system will add significant savings in power usage as well, especially during the colder months.

As cloud cover is a regular feature in Washington State, a Takagi supplemental heater will be installed, as well as baseboard heating in order to provide heat in the darker, winter months. These systems will use grid power and will be regulated so that they are only used when insufficient solar energy is available for use.

With a clear focus on the vision of RAD services and the CEC, this project, in collaboration with other sustainability measures, is a significant step toward a fully energy independent housing unit. In addition to this remarkable benefit, this project will provide useful information regarding solar collection efficiency, as well as the benefit of visually announcing TESC’s dedication to sustainability and providing a financially reasonable option for individuals seeking methods through which they may be able to reduce their own carbon footprint.