Paper 4: Controls for Low-Pressure Hot-Water Heating

1967 ◽  
Vol 182 (5) ◽  
pp. 122-128
Author(s):  
F. Porges
Keyword(s):  
High Temperature ◽  
Water Temperature ◽  
Heat Balance ◽  
Low Pressure ◽  
Water Systems ◽  
Hot Water ◽  
Safety Devices ◽  
Advantages And Disadvantages ◽  
Use Of Time ◽  
Protection Devices

The paper describes modulating control for low-pressure hot-water systems. Compensators and mixing valves are described, and their advantages and disadvantages discussed. The use of time switches is described and typical programmes given. Frost-protection devices for overriding time switches are reviewed, and a strong plea is made for greater simplicity. Difficulties which can arise from faulty positioning of thermostats are discussed. Thermostats detecting lower temperatures than they are intended to can cause safety devices to shut the plant down unnecessarily, and examples are given of such occurrences. Heat retained in the boiler refractories can cause the water temperature to go on rising after the burner has shut off. A heat balance is drawn up and suggestions made for preventing this phenomenon from operating high-temperature safety devices. The difficulties of sequence control of two or more boilers in parallel are discussed. It is difficult to find a method of detecting part load which does not make the boilers hunt; this problem is discussed and a solution for one particular case is offered.

Effect of heat flushing on the concentrations of Legionella pneumophila and other heterotrophic microbes in hot water systems of apartment buildings

1996 ◽  
Vol 42 (8) ◽  
pp. 811-818 ◽  
Author(s):  
Outi M. Zacheus ◽  
Pertti J. Martikainen
Keyword(s):  
Water Temperature ◽  
Legionella Pneumophila ◽  
Heterotrophic Bacteria ◽  
Water System ◽  
Water Systems ◽  
Hot Water ◽  
Circulating Water ◽  
Heterotrophic Microbes ◽  
Before And After ◽  
Circulating Water System

The decontamination of Legionella pneumophila and other heterotrophic microbes by heat flushing in four legionellae-positive hot water systems was studied. Before the decontamination procedure, the concentration of legionellae varied from 3.0 × 10−3 to 3.5 × 10−5 cfu/L and the hot water temperature from 43.6 to 51.5 °C. During the contamination the temperature was raised to 60–70 °C. All taps and showers were cleaned from sediments and flushed with hot water twice a day for several minutes. The decontamination lasted for 2–4 weeks. In a few weeks the heat-flushing method reduced the concentration of legionellae below the detection limit (50 cfu/L) in the hot circulating water system just before and after the heat exchanger. The high hot water temperature also decreased the viable counts of heterotrophic bacteria, fungi, and total microbial cells determined by the epifluorescent microscopy. However, the eradication of legionellae failed in a water system where the water temperature remained below 60 °C in some parts of the system. After the decontamination, the temperature of hot water was lowered to 55 °C. Thereafter, all the studied hot water systems were recolonized by legionellae within a few months, showing that the decontamination by heat flushing was temporary. Also, the contamination of other bacteria increased in a few months to the level before decontamination.Key words: legionellae, hot water system, decontamination, water temperature, heterotrophic bacteria.

Occurrence of legionellae in hot water distribution systems of Finnish apartment buildings

1994 ◽  
Vol 40 (12) ◽  
pp. 993-999 ◽  
Author(s):  
Outi M. Zacheus ◽  
Pertti J. Martikainen
Keyword(s):  
Surface Water ◽  
Ground Water ◽  
Water Temperature ◽  
Distribution Systems ◽  
Water Distribution ◽  
Water Distribution Systems ◽  
Water Systems ◽  
Hot Water ◽  
Apartment Buildings ◽  
Water Plants

The occurrence of legionellae in the hot water distribution systems of 67 buildings located in different parts of Finland was studied. Most of the buildings were apartment buildings. They had different hot water temperatures, and some received their cold potable water from surface water plants and some from ground water plants. Hot water samples were taken from taps, showers, and water mains just before and after the heat exchanger. Legionella pneumophila was isolated from 30% of the distribution systems. In the legionella-positive samples the legionella concentration varied from < 50 to 3.2 × 105 colony-forming units (cfu)/L (mean 2.7 × 103 cfu/L). The highest concentration of legionellae was found in the shower water. Legionellae appeared more often and with higher concentrations in hot water systems using cold water processed in surface water plants than in hot water systems associated with ground water plants. A high organic matter content in surface waters might favor the occurrence of legionellae and also the growth of other heterotrophic microbes. Mean water temperature just after heating was slightly higher in the legionella-negative systems than in the legionella-positive systems (53.5 vs. 51.5 °C).Key words: Legionella, organic carbon, hot water distribution system, water temperature.

Low-Pressure, High-Temperature Oxidation of Tungsten

JOM ◽  
1961 ◽  
Vol 13 (7) ◽  
pp. 490-493 ◽  
Author(s):  
R. A. Perkins ◽  
D. D. Crooks
Keyword(s):  
High Temperature ◽  
High Temperature Oxidation ◽  
Low Pressure ◽  
Temperature Oxidation
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