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NORA Oilheat Technicians Manual

Chapter 13 Heating Systems Figure 13-25: External plate heat exchangers Figure 13-26: Tankless coil with a storage tank stainless steel. The temperature in the tank is controlled by an aquastat installed in the tank. See Figure 13-26. Indirect-storage type water heaters The Indirect-Storage type heater also called a “coil-tank” or “indirect fired unit” is a storage tank with a coil of copper inside. The domestic water surrounds the coil and is heated by the boiler water that is circulated through the coil. They are piped and controlled the same as an additional zone to the heating system and may be used on both hot water and steam systems. Since boiler water is circulated, a standard circulator can be used rather than a more expensive non-corrosive one. The domestic water temperature is controlled by an aquastat that turns the circulator and burner on and off. Although these units are more expensive than tankless coils, their 13-20 Heating Systems excellent warranties, improved efficiency, and high recovery rates make them very popular. Figure 13-27 shows an indirect storage type water heater. Water heater components A water heater is a closed vessel, filled with water, normally under city water pressure. When the tank is heated, the tank must contain and store two forms of energy: heat and pressure. If the city water pressure is lost, the tank must also be protected against excess vacuum. If adequate protection is not provided then the homeowner has a bomb sitting in the basement. Relief valves: All water heaters with storage capability should have a temperature/ pressure (T&P) relief valve that is spring loaded, which will discharge water (relief) if the temperature and/or pressure in the tank become too high. The valve must be installed into the tank water directly so it will adequately sense the temperature in the tank. There should never be any type of shut-off devices installed on either the inlet or outlet side of the valve to prevent erroneous shut-off and loss of protection. There should also be a drain line installed on the outlet side of all pressure type valves to direct the hot water to a safe location, in the case of discharge, to avoid damage or injury to any one nearby. On tankless coil applications where no volume of water is being stored in a tank, a pressure only relief valve is used to protect the coil and piping from excessive pressure Vacuum relief valves: Protection Aquastat Control Domestic Water Outlet Storage Tank Domestic Water Pump Inlet Boiler Tanless Coil


NORA Oilheat Technicians Manual
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