ASHRAE Journal - September 2009 - 70

ASHRAE 19 50 59–2009 YE A R S JOURNAL SummAry this brief primer on steam systems has described simple low pressure steam heating systems. it has traced the development of some of the design ideas, installation practices and components that were devised to solve problems and make the systems operate better. it has also discussed, in general terms, some of the characteristics that make low pressure steam an excellent heat transfer medium. controlling water level in a steam boiler is very important because a flooded boiler has no volume to generate steam, while a low water level may ruin the boiler through overheating. many factors can influence the level in the boiler, and a lot of the piping design and components of the system are directly related to solving this problem. Boiler pressure is essential to distribute steam through the system at a temperature high enough to do the heating job, but it must be controlled to avoid over-stressing the system’s pressure components, and to avoid a dangerous overpressure in the boiler. Venting is important in any steam system because air or other gasses can accumulate to block the flow of steam. Early systems used vents at the radiators and end-of-main, but as systems grew larger and added pumping equipment, most system venting was accomplished at the pump receiver vent. a boiler replacement rather than a change in pumps. As described earlier, a new high efficiency boiler can have the same output rating as an older, larger volume boiler. When one of these smaller boilers replaces a larger one, the result can be boiler flooding because the amount of water in the boiler is no longer great enough to fill the system and start the pump before the feeder is activated. Another pump and receiver combination is needed to make up for the system volume lost as boilers get smaller and more efficient. This is a boiler feed unit and the pump is a boiler feed pump. It differs from a condensate transfer unit in three significant ways: • The boiler feed pump is controlled by a pump control mounted on the boiler, rather than a float switch mounted in the receiver; • The make-up water feeder is attached to the boiler feed unit receiver rather than the boiler so that the feed pump is protected against running dry; and 70 ASHRAE Journal Even though most systems use pumps for handling condensate, gravity drainage is still fundamental to the proper operation of many steam heat exchangers, including the simple cast iron radiators, baseboard units, convectors and air handling coils used in these systems. Steam releases a large amount of latent heat as it condenses, but liquid water contains no latent heat, so waterlogging of any steam device will greatly reduce its heat transfer rate. piping pitch or static head is required to make condensate flow. parallel flow of steam and condensate can limit the possibility of noise and water hammer, while reducing the pipe size required for a given job. Separate piping networks for steam supply and condensate return have become standard, but heat loss from the supply piping makes it necessary to drain the smaller condensate running load from the supply pipes, too. Specialized pumping equipment can be used to collect and return condensate, draw a vacuum on the system, or ensure that the boiler level is properly maintained. Numerous different types of pumps may be required in a given system. finally, remember that all steam systems and installations must conform to local code requirements. this article is not intended to substitute for researching and meeting those requirements. • The receiver is large enough to act as a system reservoir to supply feedwater as the system warms up without cutting off the burner due to low water and, along with the boiler, to store system water during shutdown periods without flooding the boiler or dumping the excess. References 1. Keenan, J., Keyes, F. 1936. Thermodynamic Properties of Steam. New York, New York: John Wiley & Sons Inc. Bibliography ASHRAE. 1992. “Steam systems.” ASHRAE Handbook—HVAC Systems and Equipment. Atlanta, Georgia. Chapter 10. ITT. 1975. Steam Heating Application Manual. Training Manual TES 375. Morton Grove, Illinois: ITT Fluid Handling Division. March. ITT. 1981. Hoffman Steam Heating Systems Design Manual and Engineering Data. Training Manual 181. Morton Grove, Illinois: ITT Fluid Handling Division. January. ITT. 1978. Basic Controls for Low Pressure Steam Boilers. Bulletin SL-BCS. Chicago, Illinois: ITT McDonnell & Miller. a s h r a e. o rg September 2009

ASHRAE Journal - September 2009

Table of Contents for the Digital Edition of ASHRAE Journal - September 2009

ASHRAE Journal - September 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
Getting to Net Zero
Feature Articles
How High Can You Go? Building Height and Net Zero
Lab for Learning
Solar Hot-Water Heating System: Lessons Learned
50th Anniversary—Low Pressure Steam Heating Systems
Building Sciences
Products
Emerging Technologies
People
Classified Advertising
Advertisers Index
ASHRAE Journal - September 2009 - ASHRAE Journal - September 2009
ASHRAE Journal - September 2009 - Cover2
ASHRAE Journal - September 2009 - 1
ASHRAE Journal - September 2009 - 2
ASHRAE Journal - September 2009 - Contents
ASHRAE Journal - September 2009 - 4
ASHRAE Journal - September 2009 - Commentary
ASHRAE Journal - September 2009 - Industry News
ASHRAE Journal - September 2009 - 7
ASHRAE Journal - September 2009 - 8
ASHRAE Journal - September 2009 - 9
ASHRAE Journal - September 2009 - Letters
ASHRAE Journal - September 2009 - 11
ASHRAE Journal - September 2009 - 12
ASHRAE Journal - September 2009 - 13
ASHRAE Journal - September 2009 - 14
ASHRAE Journal - September 2009 - 15
ASHRAE Journal - September 2009 - Meetings and Shows
ASHRAE Journal - September 2009 - 17
ASHRAE Journal - September 2009 - Feature Articles
ASHRAE Journal - September 2009 - 19
ASHRAE Journal - September 2009 - 20
ASHRAE Journal - September 2009 - 21
ASHRAE Journal - September 2009 - 22
ASHRAE Journal - September 2009 - 23
ASHRAE Journal - September 2009 - 24
ASHRAE Journal - September 2009 - 25
ASHRAE Journal - September 2009 - How High Can You Go? Building Height and Net Zero
ASHRAE Journal - September 2009 - 27
ASHRAE Journal - September 2009 - 28
ASHRAE Journal - September 2009 - 29
ASHRAE Journal - September 2009 - 30
ASHRAE Journal - September 2009 - 31
ASHRAE Journal - September 2009 - 32
ASHRAE Journal - September 2009 - 32a
ASHRAE Journal - September 2009 - 32b
ASHRAE Journal - September 2009 - 33
ASHRAE Journal - September 2009 - 34
ASHRAE Journal - September 2009 - 35
ASHRAE Journal - September 2009 - 36
ASHRAE Journal - September 2009 - 37
ASHRAE Journal - September 2009 - Lab for Learning
ASHRAE Journal - September 2009 - 39
ASHRAE Journal - September 2009 - 40
ASHRAE Journal - September 2009 - 41
ASHRAE Journal - September 2009 - 42
ASHRAE Journal - September 2009 - 43
ASHRAE Journal - September 2009 - Solar Hot-Water Heating System: Lessons Learned
ASHRAE Journal - September 2009 - 45
ASHRAE Journal - September 2009 - 46
ASHRAE Journal - September 2009 - 47
ASHRAE Journal - September 2009 - 48
ASHRAE Journal - September 2009 - 49
ASHRAE Journal - September 2009 - 50
ASHRAE Journal - September 2009 - 51
ASHRAE Journal - September 2009 - 52
ASHRAE Journal - September 2009 - 53
ASHRAE Journal - September 2009 - 50th Anniversary—Low Pressure Steam Heating Systems
ASHRAE Journal - September 2009 - 55
ASHRAE Journal - September 2009 - 56
ASHRAE Journal - September 2009 - 57
ASHRAE Journal - September 2009 - 58
ASHRAE Journal - September 2009 - 59
ASHRAE Journal - September 2009 - 60
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ASHRAE Journal - September 2009 - 69
ASHRAE Journal - September 2009 - 70
ASHRAE Journal - September 2009 - 71
ASHRAE Journal - September 2009 - Building Sciences
ASHRAE Journal - September 2009 - 73
ASHRAE Journal - September 2009 - 74
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ASHRAE Journal - September 2009 - 76
ASHRAE Journal - September 2009 - 77
ASHRAE Journal - September 2009 - 78
ASHRAE Journal - September 2009 - 79
ASHRAE Journal - September 2009 - 80
ASHRAE Journal - September 2009 - 81
ASHRAE Journal - September 2009 - Products
ASHRAE Journal - September 2009 - 83
ASHRAE Journal - September 2009 - Emerging Technologies
ASHRAE Journal - September 2009 - 85
ASHRAE Journal - September 2009 - 86
ASHRAE Journal - September 2009 - 87
ASHRAE Journal - September 2009 - 88
ASHRAE Journal - September 2009 - 89
ASHRAE Journal - September 2009 - People
ASHRAE Journal - September 2009 - 91
ASHRAE Journal - September 2009 - 92
ASHRAE Journal - September 2009 - Classified Advertising
ASHRAE Journal - September 2009 - 94
ASHRAE Journal - September 2009 - 95
ASHRAE Journal - September 2009 - Advertisers Index
ASHRAE Journal - September 2009 - Cover3
ASHRAE Journal - September 2009 - Cover4
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