Capstone project

Solar water heating system

In this system, a solar water heater includes a solar collection array that absorbs solar radiation and converts it to heat. The heat is then absorbed by a heat transfer fluid in which water will be used and passed through the collector. The heat transfer fluid can be either stored or used directly. The system will start from the storage tank where it contains water. A pump will be used to force the fluid to the collector. Heat will be absorbed by the water as it passes through the collector and then it goes back to the storage tank. In solar water heating system, water is heated either directly or indirectly. In the direct water heating system, v.ie designed hot water needs directly in the collector. In an indirect water heating system, the heat transfer fluid is heated in the collector and then sent to the storage tank where it flows through a heat exchanger. The heat is then transferred to the domestic or service tank. In transporting the fluid through the system, there are two ways of doing it. It is either by natural (passive system) or forced circulation (active system). Since v.ie are using a pump to circulate the fluid, this is an active system. Natural circulation occurs by natural connection (therrrosiphoning which needs no control). They are applicable in climates where freezing is infrequent or doesn't exist at all. Malaysia, for example, is a good country to apply this type of system. In domestic solar water heating, the flat plate collector is frequently used. There are various types of flat plate collectors applicable.However, the one we are using is the tubes-in-plate configuration with single glass cover. There are two collectors in the system which is connected in parallel. There are six types of solar systems used to heat domestic and service hot water: Thermosiphon, recirculating, drain dowvn, drain back, indirect water heating and air. The system that we are using is the drain down system. The reason we chose a drain down system is to protect the collector and outdoor pipings against freezing during cold seasons. The drain down valve is interposed between the inlet and outlet of the collector. A standard spool drain down valve is actuated through the differential temperature controller. The drain down valve is mounted belo,; the collectors. The spool valve is energized when a preset low temperature is reached. The recorrmended preset temperature is 40°F to ensure a safe condition. In our system the preset temperature is 60°F. The pump that we installed between the storage tank and the collectors is a photovoltaic centrifugal type. The power requirement for the pump (40 W, 12 V D.C.) and the controller is coming from the photovoltaic cell (installed between collectors).

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