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Cold Water The temperature of water available in the water supply system will vary. Water from shallow (just below frost line) under ground water service lines enters the building at a temperature that fluctuates with climate, season, and location of the water service line. In a moderate climate, it may range from 35°F (2°C) in midwinter to 70°F (21°C) or more in midsummer. In hot climate regions, water service temperature can reach temperatures above 90°F (32°C) or more in the summer. In harsh desert climates, water must actually be chilled for drinking. Water pumped from deep wells is generally at a fairly constant temperature of 50° to 55°F (10° to 13°C) year-round. Water that remains standing in an underground storage pipe or in an interior water supply line for a long period of time will equilibrate to the temperature of the surrounding space (e.g., room or crawl space temperature). Chilled Water The varying temperature of water extracted from cold water supply lines is normally acceptable. In some instances chilled water is desired, such as from a drinking fountain. In this case, a chiller is used to cool water to a temperature of about 50°F (10°C) before it’s used. A chiller is a vapor compression refrigeration system that cools water much like a refrigerator. Tbl. **12 TYPICAL TEMPERATURES OF HEATED WATER IN BUILDINGS. COMPILED FROM VARIOUS GOVERNMENTAL STANDARDS. Type | Typical Temperatures Lavatory (hand washing, shaving) 105°F 41°C General Bathing (showering and bathing) 115°F 46°C Residential dishwashing and laundry (hot) 140°F 60°C Commercial/institutional laundry 160°F 71°C Commercial/institutional dishwashing-final rinse 180°F 82°C Sanitizing of nursing utensils 180°F 82°C Tbl. **13 LENGTH OF TIME FOR HOT WATER TO CAUSE SCALDING. Temperature of Water: , °F °C Time to Cause Scalding Injury to Skin Heated Water In modern buildings, hot water is desired for bathing, cleaning, washing, and other associated purposes. By definition, hot water is potable water that is heated to at least 120°F. Heated water below 120°F (49°C) is typically called tempered water. Hot water used for household functions such as bathing, dish washing, and clothes washing is referred to as domestic hot water (DHW). In commercial installations, hot water used in nondomestic applications is referred to as building service hot water (BSHW). The temperature of heated water available in the water supply system will vary depending upon need. Typical temperatures of heated water in buildings are provided in Tbl.12. Generally, a lower hot water temperature is more energy efficient and safer (less likely to scald). A higher water temperature (180°F [82°C]) achieves sanitation that is required in commercial (e.g., restaurants) and institutional (e.g., hospital and health center) dishwashing final rinse and laundering operations. The hot water distribution temperature must be higher than 120°F (49°C) because of the concern over Legionella pneumophila (Legionnaires' disease). This bacterium, which can cause serious illness when inhaled, can grow in domestic hot water systems at temperatures of 115°F (46°C) or less. Bacteria colonies have been found in system components, such as showerheads and faucet aerators, and in uncirculated sections of storage-type water heaters. A water temperature of approximately 140°F is suggested to reduce the potential of growth of this bacterium. This higher temperature, however, increases the possibility of scalding. Periodic supervised flushing of fixture heads with 170°F water is recommended in hospitals and health care facilities because the already weakened patients are generally more susceptible to infection. Water temperatures above 110°F (45°C) can be painfully hot to the touch. Exposure to water temperatures of 120°F (49°C) and above will cause scalding (burning) of the skin. See Tbl.** The elderly, young children, and incapacitated individuals are most susceptible to scalding because their reaction time is impeded. In institutional applications (e.g., hospitals and long-term health care centers), hot water available at lavatories, baths, and showers is limited by health regulations to temperatures of about 105°F (41°C). As a result of an unfortunate scalding accident that resulted in a several million-dollar settlement in the early 1990s, water heater manufacturers have lowered the preset temperature on storage tank water heaters from 140°F (60°C) to about 120°F (49°C). Tempered Water Tempered water is a blend of hot and cold water that is mixed at a thermostatic (mixing) valve. It’s used in applications requiring low-temperature hot water. Typical applications include shower rooms and group showers, domestic water for small buildings, and tempered water for light industrial processes (e.g., photographic laboratories). The temperature requirement for tempered water typically ranges from 90° to 110°F (32° to 43°C). Usually the mixing valve is set at the desired temperature and delivers water within _3°F (_1.7°C) that temperature setting. An anti-scald shower valve is a type of thermostatic valve required in residential showers. This valve can be preset to any temperature between 60° and 120°F (15.5° and 49°C) with flow rates between 0.5 gpm and 10 gpm. It compensates for both temperature and pressure changes in the supply lines and protects against water supply failure. Under minor temperature and pressure variations, the delivery temperature of an anti-scald shower valve will hold within _3°F (_1.7°C). If temperature conditions vary greatly (a change of _25°F [_14°C]), delivery temperature will vary. Tbl. **14 TYPICAL HOT WATER USE IN A U.S. HOUSEHOLD BY PERCENTAGE. UNITED STATES DEPARTMENT OF ENERGY. Use | Percentage
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