ASHRAE Journal - July 2010 - 37
Figure 1: Schematics of the central chilling system.
heat exchangers. Zones 3 and 4 are supplied with the secondary chilled water through the first stage heat exchangers (HX-42) located on the 42nd floor. Some of the chilled water after the first stage heat exchangers is delivered to Zone 3, and some is delivered to the second stage heat exchangers (HX-78) located on the 78th floor. The design chilled water supply is 6.3°C (43.3°F), and the return temperature is 11.3°C (52.3°F) at the secondary sides of the heat exchangers in Zone 1, and the first stage heat exchangers in Zones 3 and 4. Both design supply and return temperatures at the secondary sides of the second stage heat exchangers in Zone 4 are 7.1°C (44.8°F) and 12.1°C (53.8°F), respectively. All pumps in the secondary water system are equipped with variable-frequency drives (VFDs) except the primary chilled water pumps dedicated to the heat exchangers in Zones 3 and 4, which are constant speed pumps. An alternative design configuration for these heat exchangers without using the dedicated primary chilled water pumps is proposed in a previous ASHRAE Journal article.1 All variable speed pumps in the secondary system can be categorized into two groups: the pumps distributing water to terminal units and the pumps distributing water to heat exchangers. This article focuses on the speed control of variable
July 2010
speed pumps distributing water to heat exchangers. The speed control of variable speed pumps distributing water to terminal units has been extensively studied elsewhere.2–6
Original Control Strategy
Figure 2 shows the original control strategy used in this building for controlling the operating speed of variable speed pumps distributing water to heat exchangers. In this strategy, the measured temperatures at the secondary side and the measured differential pressure at the primary side of heat exchangers are used. The operating speed of the pump in the primary side is controlled by maintaining the differential pressure at the primary side at a predetermined constant value (Figure 2). To maintain the supply water temperature at the secondary side, a modulating valve is installed at the primary side of each heat exchanger loop. The opening of the modulating valve is controlled to maintain the supply water temperature at the secondary side at its setpoint. When the load of the terminal units changes, the opening of the modulating valves is adjusted to meet the preset chilled water temperature setpoint and, therefore, meet the load change of the terminal units. The speed of the pumps at the primary side is modulated to maintain a constant differential pressure at the primary side. The control algorithm used in this method is similar to the
ASHRAE Journal 37
ASHRAE Journal - July 2010
Table of Contents for the Digital Edition of ASHRAE Journal - July 2010
ASHRAE Journal - July 2010
Table of Contents
Commentary
Industry News
Letters
Meetings and Shows
Sizing Calculation Spreadsheet: Vertical Geothermal Borefields
HVAC for Prisons
Control Strategies for Variable Speed Pumps In Super High-Rise Building
Maintaining Green
Sustainable Products Capabilities
Emerging Technologies
Technical Topics
Special Products
People
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - July 2010 - Intro
ASHRAE Journal - July 2010 - ASHRAE Journal - July 2010
ASHRAE Journal - July 2010 - Cover2
ASHRAE Journal - July 2010 - 1
ASHRAE Journal - July 2010 - 2
ASHRAE Journal - July 2010 - Table of Contents
ASHRAE Journal - July 2010 - Commentary
ASHRAE Journal - July 2010 - 5
ASHRAE Journal - July 2010 - Industry News
ASHRAE Journal - July 2010 - 7
ASHRAE Journal - July 2010 - 8
ASHRAE Journal - July 2010 - 9
ASHRAE Journal - July 2010 - 10
ASHRAE Journal - July 2010 - 11
ASHRAE Journal - July 2010 - Letters
ASHRAE Journal - July 2010 - 13
ASHRAE Journal - July 2010 - 14
ASHRAE Journal - July 2010 - 15
ASHRAE Journal - July 2010 - 16
ASHRAE Journal - July 2010 - 17
ASHRAE Journal - July 2010 - Meetings and Shows
ASHRAE Journal - July 2010 - 19
ASHRAE Journal - July 2010 - Sizing Calculation Spreadsheet: Vertical Geothermal Borefields
ASHRAE Journal - July 2010 - 21
ASHRAE Journal - July 2010 - 22
ASHRAE Journal - July 2010 - 23
ASHRAE Journal - July 2010 - 24
ASHRAE Journal - July 2010 - 25
ASHRAE Journal - July 2010 - 26
ASHRAE Journal - July 2010 - 27
ASHRAE Journal - July 2010 - 28
ASHRAE Journal - July 2010 - 29
ASHRAE Journal - July 2010 - HVAC for Prisons
ASHRAE Journal - July 2010 - 31
ASHRAE Journal - July 2010 - 32
ASHRAE Journal - July 2010 - InsertA
ASHRAE Journal - July 2010 - InsertB
ASHRAE Journal - July 2010 - 33
ASHRAE Journal - July 2010 - 34
ASHRAE Journal - July 2010 - 35
ASHRAE Journal - July 2010 - Control Strategies for Variable Speed Pumps In Super High-Rise Building
ASHRAE Journal - July 2010 - 37
ASHRAE Journal - July 2010 - 38
ASHRAE Journal - July 2010 - 39
ASHRAE Journal - July 2010 - 40
ASHRAE Journal - July 2010 - 41
ASHRAE Journal - July 2010 - 42
ASHRAE Journal - July 2010 - 43
ASHRAE Journal - July 2010 - Maintaining Green
ASHRAE Journal - July 2010 - 45
ASHRAE Journal - July 2010 - 46
ASHRAE Journal - July 2010 - 47
ASHRAE Journal - July 2010 - 48
ASHRAE Journal - July 2010 - 49
ASHRAE Journal - July 2010 - 50
ASHRAE Journal - July 2010 - Sustainable Products Capabilities
ASHRAE Journal - July 2010 - 52
ASHRAE Journal - July 2010 - 53
ASHRAE Journal - July 2010 - 54
ASHRAE Journal - July 2010 - 55
ASHRAE Journal - July 2010 - 56
ASHRAE Journal - July 2010 - 57
ASHRAE Journal - July 2010 - 58
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ASHRAE Journal - July 2010 - 69
ASHRAE Journal - July 2010 - 70
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ASHRAE Journal - July 2010 - 73
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ASHRAE Journal - July 2010 - 85
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ASHRAE Journal - July 2010 - 91
ASHRAE Journal - July 2010 - 92
ASHRAE Journal - July 2010 - 93
ASHRAE Journal - July 2010 - 94
ASHRAE Journal - July 2010 - 95
ASHRAE Journal - July 2010 - Emerging Technologies
ASHRAE Journal - July 2010 - 97
ASHRAE Journal - July 2010 - 98
ASHRAE Journal - July 2010 - 99
ASHRAE Journal - July 2010 - Technical Topics
ASHRAE Journal - July 2010 - 101
ASHRAE Journal - July 2010 - 102
ASHRAE Journal - July 2010 - 103
ASHRAE Journal - July 2010 - Special Products
ASHRAE Journal - July 2010 - 105
ASHRAE Journal - July 2010 - 106
ASHRAE Journal - July 2010 - 107
ASHRAE Journal - July 2010 - People
ASHRAE Journal - July 2010 - Products
ASHRAE Journal - July 2010 - Classified Advertising
ASHRAE Journal - July 2010 - 111
ASHRAE Journal - July 2010 - Advertisers Index
ASHRAE Journal - July 2010 - Cover3
ASHRAE Journal - July 2010 - Cover4
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