ASHRAE Journal - May 2011 - 54

Optimizing Geothermal Cost

Typically, Quebec’s average winter temperature is 14°F (–10°C). Sporadically, temperatures can drop as low as –30°F (–35°C). During summer, temperatures can rise to more than 95°F (35°C). This means that designers must install powerful equipment that rarely works at full capacity. The average heating or cooling part load for a building in Quebec is generally under 50% of its peak load. The engineering team wanted to design systems that could offer good efficiency throughout the year. Knowing that heat pump efficiency is reduced considerably when used at part load and that geothermal system excavation and materials are quite costly, designers decided to evaluate a cheaper auxiliary heating system (electric boiler) to supply extra heat during periods of intense cold. Energy simulation models helped pin down the percentage of the maximum capacity that should be ensured by the geothermal system. This optimal combination of systems made it possible to reduce the size of the geothermal exchanger to 70% of the design’s peak load, consequently keeping excavation

and material costs to a minimum. Three boreholes with a depth of 500 ft (152 m) each were drilled and connected to a 14 ton (49 kW) water-to-water heat pump. Heat pump source side fluid is a mixture of water and methanol arriving from the geothermal boreholes with an inlet minimum temperature of 30°F (–1°C) while heat pump load side fluid is a mixture of water and glycol with an inlet temperature around 75°F (24°C) and a flow rate of 35 gpm (2 L/s). The heat pump can provide heating with a COP of 3.2 and cooling with an EER of 11.3. Furthermore, by reducing the size of the heat pump by 30% under peak load, designers ensured that the equipment would work more hours at full capacity, therefore maximizing heat pump efficiency.
Radiant Floor Heating

Building at a Glance
Name: St. Johns School Location: Saint-Jean-sur-Richelieu, Québec, Canada Owner: Riverside School Board Principal Use: School Includes: science rooms with laboratories and a library Employees/Occupants: 120 Gross Square Footage: 9,000 ft2 Conditioned Space: 9,000 ft2 Substantial Completion/Occupancy (date): June 2006 Occupancy: 100%

The geothermal loop is used to treat fresh air and supply an hydronic radiant floor heating system (Figure 1), installed into the concrete floor slabs of the classrooms and library. By signif icantly reducing stratif ication effects, radiant floor heating provides even, comfortable warmth because the

heated concrete floor acts as a thermal mass. Temperature sensors, located in the rooms and floor slabs, satisfy occupant demand. The radiant floor heating is comfortable and silent, and provides roomier and more aesthetically pleasing spaces since there is no apparent equipment, which was appreciated by the client.

Filter

Exhaust Solar Wall

Main Exhaust

Enthalpy Wheel Heating/Cooling Coil SCR Fresh Air Supply To Other Rooms Filter

Fresh Air

Fresh Air Bypass Water-toWater Heat Pump Fresh Air Supply

Geothermal Boreholes

To Radiant Floor Heating in Other Rooms

Electric Boiler

Radiant Floor Heating Room

Figure 1: Geothermal loop treats fresh air and supplies a hydronic radiant floor heating system.
54 ASHRAE Journal ashrae.org May 2011



ASHRAE Journal - May 2011

Table of Contents for the Digital Edition of ASHRAE Journal - May 2011

ASHRAE Journal - May 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Seismic Restraint
Plug Load Design Factors
Technology Award Case Studies:
State-of-Art School
Green School Lab
Eco-Friendly, Affordable, School
Building Sciences
Special Section
InfoCenter
Solar NZEB Project
Emerging Technologies
IAQ Applications
Washington Report
International Column
Products
People
Classified Advertising
Advertisers Index
ASHRAE Journal - May 2011 - Intro
ASHRAE Journal - May 2011 - ASHRAE Journal - May 2011
ASHRAE Journal - May 2011 - Cover2
ASHRAE Journal - May 2011 - 1
ASHRAE Journal - May 2011 - 2
ASHRAE Journal - May 2011 - Contents
ASHRAE Journal - May 2011 - Commentary
ASHRAE Journal - May 2011 - 5
ASHRAE Journal - May 2011 - Industry News
ASHRAE Journal - May 2011 - 7
ASHRAE Journal - May 2011 - 8
ASHRAE Journal - May 2011 - 9
ASHRAE Journal - May 2011 - 10
ASHRAE Journal - May 2011 - 11
ASHRAE Journal - May 2011 - 12
ASHRAE Journal - May 2011 - 13
ASHRAE Journal - May 2011 - Letters
ASHRAE Journal - May 2011 - 15
ASHRAE Journal - May 2011 - 16
ASHRAE Journal - May 2011 - 16a
ASHRAE Journal - May 2011 - 16b
ASHRAE Journal - May 2011 - 17
ASHRAE Journal - May 2011 - Meetings and Shows
ASHRAE Journal - May 2011 - 19
ASHRAE Journal - May 2011 - Seismic Restraint
ASHRAE Journal - May 2011 - 21
ASHRAE Journal - May 2011 - 22
ASHRAE Journal - May 2011 - 23
ASHRAE Journal - May 2011 - 24
ASHRAE Journal - May 2011 - 25
ASHRAE Journal - May 2011 - 26
ASHRAE Journal - May 2011 - 27
ASHRAE Journal - May 2011 - 28
ASHRAE Journal - May 2011 - 29
ASHRAE Journal - May 2011 - Plug Load Design Factors
ASHRAE Journal - May 2011 - 31
ASHRAE Journal - May 2011 - 32
ASHRAE Journal - May 2011 - 33
ASHRAE Journal - May 2011 - 34
ASHRAE Journal - May 2011 - 35
ASHRAE Journal - May 2011 - State-of-Art School
ASHRAE Journal - May 2011 - 37
ASHRAE Journal - May 2011 - 38
ASHRAE Journal - May 2011 - 39
ASHRAE Journal - May 2011 - 40
ASHRAE Journal - May 2011 - 41
ASHRAE Journal - May 2011 - 42
ASHRAE Journal - May 2011 - 43
ASHRAE Journal - May 2011 - Green School Lab
ASHRAE Journal - May 2011 - 45
ASHRAE Journal - May 2011 - 46
ASHRAE Journal - May 2011 - 47
ASHRAE Journal - May 2011 - 48
ASHRAE Journal - May 2011 - 49
ASHRAE Journal - May 2011 - 50
ASHRAE Journal - May 2011 - 51
ASHRAE Journal - May 2011 - Eco-Friendly, Affordable, School
ASHRAE Journal - May 2011 - 53
ASHRAE Journal - May 2011 - 54
ASHRAE Journal - May 2011 - 55
ASHRAE Journal - May 2011 - 56
ASHRAE Journal - May 2011 - 57
ASHRAE Journal - May 2011 - Building Sciences
ASHRAE Journal - May 2011 - 59
ASHRAE Journal - May 2011 - 60
ASHRAE Journal - May 2011 - 61
ASHRAE Journal - May 2011 - 62
ASHRAE Journal - May 2011 - 63
ASHRAE Journal - May 2011 - 64
ASHRAE Journal - May 2011 - 65
ASHRAE Journal - May 2011 - 66
ASHRAE Journal - May 2011 - 67
ASHRAE Journal - May 2011 - InfoCenter
ASHRAE Journal - May 2011 - 69
ASHRAE Journal - May 2011 - 70
ASHRAE Journal - May 2011 - 71
ASHRAE Journal - May 2011 - 72
ASHRAE Journal - May 2011 - 73
ASHRAE Journal - May 2011 - 74
ASHRAE Journal - May 2011 - 75
ASHRAE Journal - May 2011 - 76
ASHRAE Journal - May 2011 - 77
ASHRAE Journal - May 2011 - Solar NZEB Project
ASHRAE Journal - May 2011 - 79
ASHRAE Journal - May 2011 - 80
ASHRAE Journal - May 2011 - 81
ASHRAE Journal - May 2011 - 82
ASHRAE Journal - May 2011 - 83
ASHRAE Journal - May 2011 - 84
ASHRAE Journal - May 2011 - 85
ASHRAE Journal - May 2011 - 86
ASHRAE Journal - May 2011 - 87
ASHRAE Journal - May 2011 - 88
ASHRAE Journal - May 2011 - 89
ASHRAE Journal - May 2011 - Emerging Technologies
ASHRAE Journal - May 2011 - 91
ASHRAE Journal - May 2011 - 92
ASHRAE Journal - May 2011 - 93
ASHRAE Journal - May 2011 - 94
ASHRAE Journal - May 2011 - 95
ASHRAE Journal - May 2011 - IAQ Applications
ASHRAE Journal - May 2011 - 97
ASHRAE Journal - May 2011 - 98
ASHRAE Journal - May 2011 - 99
ASHRAE Journal - May 2011 - 100
ASHRAE Journal - May 2011 - 101
ASHRAE Journal - May 2011 - Washington Report
ASHRAE Journal - May 2011 - 103
ASHRAE Journal - May 2011 - International Column
ASHRAE Journal - May 2011 - 105
ASHRAE Journal - May 2011 - 106
ASHRAE Journal - May 2011 - Products
ASHRAE Journal - May 2011 - 108
ASHRAE Journal - May 2011 - People
ASHRAE Journal - May 2011 - Classified Advertising
ASHRAE Journal - May 2011 - 111
ASHRAE Journal - May 2011 - Advertisers Index
ASHRAE Journal - May 2011 - Cover3
ASHRAE Journal - May 2011 - Cover4
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