ASHRAE Journal - November 2009 - 65

Technical Topics Horizontal Unit Above Hall 1" U-Tubes for Bore Depths to 300' 1.25" U-Tubes for Bore Depths to 500' 2" Circuit Headers for Flows Up to 30 gpm, 3" for 30 to 100 gpm. Insulated Cabinet Unit With Low Speed, Soft Start Fan 2" 1" 1.25" Reducers 2" 1" 1.25" Reverse-Return Reducing Headers Main Headers to Building 20' 1.50" 1.50" Vertical UpFlow Unit in Closet (Necessary to Promote Effective Purging) Small, Local Units Reduce Duct Cost, Minimize Fan Energy, and Require Minimal Maintenance Purge Valves Buried Valve Vault – 20 Circuits Figure 1: Options for heat pump location for simple GSHP. Figure 2: Exterior piping configuration for not-so-simple GSHP. GSHPs: Simple Is Better By Steve Kavanaugh, Ph.D., Fellow ASHRAE needed relief for an overextended workforce. Lawson turned to ground source heat pumps (GSHPs) in the mid-1980s when they were primarily a residential application. His priority was a simple, low-maintenance system that could easily replace failing conventional classroom units. He convinced a nearby manufacturer to produce water-to-air heat pump console units large enough for classroom loads with a sloped top so that books could not be stacked on the supply air vents. Two or three vertical ground loops located just outside the building walls were linked to the unit with a small wet-rotor pump. Today, AISD and several nearby school districts have more than 125 schools that continue to use Lawson’s simple one heat pump–one ground loop–one pump GSHP system. Mike Green, a mechanical engineer in Texas, had several interesting experiences during the early days of GSHPs in Austin; including the time U-tubes were inserted at the end of the day into what was thought to be dry holes. The following morning the job site resembled a bowl of black spaghetti since the holes, which had been dried during the air drilling process, were filled with water. In spite of this and other challenges, he was sold on the technology since no one called to complain after the project had been completed. Green continues to design GSHPs for new schools in districts surrounding Austin using the same simple loop designs. An important November 2009 s with many maintenance supervisors, Bob Lawson of the Austin (Texas) Independent School District (AISD) lesson learned was to increase the separation distance between vertical bores to at least 20 ft (6 m). The heat pumps are ducted and located in mezzanines above hallways (Figure 1). Although there are challenges to his allegiance to simplicity, the success of his approach is supported by school officials including those at Leander ISD. The district recently began applying for ENERGY STAR ratings and owns 19% of the rated schools in Texas.1 Simplicity in Illinois Kirk Mescher, P.E., Member ASHRAE, Columbia, Mo., has his own twist on simplicity for retrofitting older schools in central Illinois. Mescher links several heat pumps to a one-pipe building loop and a central ground loop without costly exterior valve vaults.2 The heat pumps are typically a variation of Lawson’s approach of classroom units with on-off circulator pumps. However, these larger units are quiet and much more efficient and serviceable than those available in 1985. Mescher’s success is also verified by ENERGY STAR rating, with almost all of his projects rating above 90 and many of them without the benefit of building lighting or envelope upgrades. He is able to keep total HVAC system costs between $13 and $18/ft2 ($140 and $190/m2) to ensure that success is achieved without the elevated price tags of more elaborate GSHP designs. One of Mescher’s clients is the McLean County Unit District No. 5, which owns 28% of the ENERGY STAR rated schools in Illinois,1 and it is equally pleased with the lower maintenance of simple GSHPs.3 Simplicity Not Standard Practice A more common approach to school GSHP design is to link a large central ground loop to an interior piping network connecting heat pumps throughout the building in a manner similar to conventional chilled water piping. The ground loop is a matrix of vertical U-tube ground heat exchangers that are arranged in subcircuits of six to 20 loops each. Typically, a network of valves is used ASHRAE Journal 65

ASHRAE Journal - November 2009

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

ASHRAE Journal - November 2009
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Upgrading Chilled-Water Systems
50th Anniversary Feature: Energy Savings from Pump Impeller Trimming
Building Sciences
InfoCenter
Special Supplement: BACnet® Today
BACnet Table of Contents
BACnet and the Smart Grid
An Untangled Web: How BACnet is Connecting at ASHRAE’s Headquarters
Visualizing BACnet
BACnet & Trigeneration
BACnet Gets Smaller
Technical Topics
Washington Report
Special Products
Emerging Technologies
People
Research Topics
Products
Classified Advertising
Advertisers Index
ASHRAE Journal - November 2009 - ASHRAE Journal - November 2009
ASHRAE Journal - November 2009 - Cover2
ASHRAE Journal - November 2009 - 1
ASHRAE Journal - November 2009 - 2
ASHRAE Journal - November 2009 - Contents
ASHRAE Journal - November 2009 - 4
ASHRAE Journal - November 2009 - Commentary
ASHRAE Journal - November 2009 - Industry News
ASHRAE Journal - November 2009 - 7
ASHRAE Journal - November 2009 - Letters
ASHRAE Journal - November 2009 - 9
ASHRAE Journal - November 2009 - 10
ASHRAE Journal - November 2009 - 11
ASHRAE Journal - November 2009 - 12
ASHRAE Journal - November 2009 - 13
ASHRAE Journal - November 2009 - Meetings and Shows
ASHRAE Journal - November 2009 - 15
ASHRAE Journal - November 2009 - Upgrading Chilled-Water Systems
ASHRAE Journal - November 2009 - 17
ASHRAE Journal - November 2009 - 18
ASHRAE Journal - November 2009 - 19
ASHRAE Journal - November 2009 - 20
ASHRAE Journal - November 2009 - 21
ASHRAE Journal - November 2009 - 22
ASHRAE Journal - November 2009 - 23
ASHRAE Journal - November 2009 - 24
ASHRAE Journal - November 2009 - 25
ASHRAE Journal - November 2009 - 26
ASHRAE Journal - November 2009 - 27
ASHRAE Journal - November 2009 - 28
ASHRAE Journal - November 2009 - 29
ASHRAE Journal - November 2009 - 30
ASHRAE Journal - November 2009 - 31
ASHRAE Journal - November 2009 - 32
ASHRAE Journal - November 2009 - 33
ASHRAE Journal - November 2009 - 33A
ASHRAE Journal - November 2009 - 33B
ASHRAE Journal - November 2009 - 50th Anniversary Feature: Energy Savings from Pump Impeller Trimming
ASHRAE Journal - November 2009 - 35
ASHRAE Journal - November 2009 - 36
ASHRAE Journal - November 2009 - 37
ASHRAE Journal - November 2009 - 38
ASHRAE Journal - November 2009 - 39
ASHRAE Journal - November 2009 - 40
ASHRAE Journal - November 2009 - 41
ASHRAE Journal - November 2009 - 42
ASHRAE Journal - November 2009 - 43
ASHRAE Journal - November 2009 - 44
ASHRAE Journal - November 2009 - 45
ASHRAE Journal - November 2009 - Building Sciences
ASHRAE Journal - November 2009 - 47
ASHRAE Journal - November 2009 - 48
ASHRAE Journal - November 2009 - 49
ASHRAE Journal - November 2009 - 50
ASHRAE Journal - November 2009 - 51
ASHRAE Journal - November 2009 - 52
ASHRAE Journal - November 2009 - 53
ASHRAE Journal - November 2009 - InfoCenter
ASHRAE Journal - November 2009 - 55
ASHRAE Journal - November 2009 - 56
ASHRAE Journal - November 2009 - 57
ASHRAE Journal - November 2009 - 58
ASHRAE Journal - November 2009 - 59
ASHRAE Journal - November 2009 - 60
ASHRAE Journal - November 2009 - 61
ASHRAE Journal - November 2009 - 62
ASHRAE Journal - November 2009 - 63
ASHRAE Journal - November 2009 - 64
ASHRAE Journal - November 2009 - Special Supplement: BACnet® Today
ASHRAE Journal - November 2009 - B2
ASHRAE Journal - November 2009 - B3
ASHRAE Journal - November 2009 - BACnet Table of Contents
ASHRAE Journal - November 2009 - B5
ASHRAE Journal - November 2009 - B6
ASHRAE Journal - November 2009 - B7
ASHRAE Journal - November 2009 - BACnet and the Smart Grid
ASHRAE Journal - November 2009 - B9
ASHRAE Journal - November 2009 - B10
ASHRAE Journal - November 2009 - B11
ASHRAE Journal - November 2009 - B12
ASHRAE Journal - November 2009 - B13
ASHRAE Journal - November 2009 - An Untangled Web: How BACnet is Connecting at ASHRAE’s Headquarters
ASHRAE Journal - November 2009 - B15
ASHRAE Journal - November 2009 - B16
ASHRAE Journal - November 2009 - B17
ASHRAE Journal - November 2009 - B18
ASHRAE Journal - November 2009 - Visualizing BACnet
ASHRAE Journal - November 2009 - B20
ASHRAE Journal - November 2009 - B21
ASHRAE Journal - November 2009 - B22
ASHRAE Journal - November 2009 - B23
ASHRAE Journal - November 2009 - BACnet & Trigeneration
ASHRAE Journal - November 2009 - B25
ASHRAE Journal - November 2009 - B26
ASHRAE Journal - November 2009 - B27
ASHRAE Journal - November 2009 - BACnet Gets Smaller
ASHRAE Journal - November 2009 - B29
ASHRAE Journal - November 2009 - B30
ASHRAE Journal - November 2009 - B31
ASHRAE Journal - November 2009 - B32
ASHRAE Journal - November 2009 - Technical Topics
ASHRAE Journal - November 2009 - Washington Report
ASHRAE Journal - November 2009 - 67
ASHRAE Journal - November 2009 - Special Products
ASHRAE Journal - November 2009 - 69
ASHRAE Journal - November 2009 - Emerging Technologies
ASHRAE Journal - November 2009 - 71
ASHRAE Journal - November 2009 - People
ASHRAE Journal - November 2009 - 73
ASHRAE Journal - November 2009 - Research Topics
ASHRAE Journal - November 2009 - Products
ASHRAE Journal - November 2009 - Classified Advertising
ASHRAE Journal - November 2009 - 77
ASHRAE Journal - November 2009 - 78
ASHRAE Journal - November 2009 - 79
ASHRAE Journal - November 2009 - Advertisers Index
ASHRAE Journal - November 2009 - Cover3
ASHRAE Journal - November 2009 - Cover4
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