Chapter 5 Domestic Hot Water In this section, we’ll examine various ways in which Oilheat systems generate domestic hot water; sizing water heaters; piping and maintenance recommendations; safety concerns; and energy conservation strategies. There are two basic types of water heaters: direct-fired and indirect. Direct-fired water heaters are basically dry base vertical tube boilers; they utilize an oil burner that creates hot combustion gases that heat the water inside the tank. The gases and the water being heated are separated by the wall of the tank. Indirect water heating uses boiler water to heat domestic water. This type features a heat exchanger that draws heat from the heating system water into the domestic water. For many years, the only indirect water heater available was the tankless coil, today there are additional options, including a separate “Indirect Water Heater” consisting of a storage tank, circulator, control and related accessories Direct-fired water heaters Oil-fired water heaters are typically available for residential use in sizes that range from 20 gallons to over 100 gallons. They are available in two configurations, (Figure 1), based on the path of the flue gases: • Center flue heaters feature a path for the flue gases to travel through the inside of the tank. • Rear flue heaters have a path for the flue gases to travel around the outside of the tank. Direct-fired heaters are operated by an aquastat which turns the oil burner on and off to maintain water temperature. 36 National Oilheat Research Alliance Figure 1 Most direct-fired water heaters feature an insulated glass-lined tank. The inside of the steel tank is coated with ceramic lining material that protects the tank from rusting and corrosion. The material is not totally impervious to water, and thus the tank can rust. Manufacturers provide protection for the steel casing by installing replaceable sacrificial anode rods in the tank. These rods should be checked during tune ups and replaced when necessary. Indirect Water Heating Indirect water heating involves the use of a heat exchanger to transfer heat from the boiler water to the domestic water. Tankless coils—there are two types of tankless coils: internal and external. The biggest disadvantage of tankless coils is that a household can easily outrun their ability to generate domestic hot water. Depending on the temperature in the boiler, and the size of the coils in the unit, a busy household may not have sufficient hot water for peak usage.
NORA Advanced Hydronics
To see the actual publication please follow the link above