ASHRAE Journal - May 2011 - 56

Recovering Energy from Exhaust Air

With Quebec’s climate, a lot of energy is needed to treat 100 5,000 Average Solar Radiation incoming fresh air. Designers took advantage of the energy Average Temperature available in the fresh air/exhaust air process, by installing an Average Minimum Temperature 80 4,000 enthalpy wheel that recovers wasted latent and sensible energy from exhaust air, with an efficiency of 76%. To enhance the heat exchange process, the wheel was sized to allow low velocities 60 3,000 (around 400 fpm [2 m/s]). Even with the enthalpy wheel, incoming fresh air at a flow rate of 3,000 cfm (1416 L/s) still needed significant amounts of 40 2,000 energy. The designers looked into other “off the grid” solutions. The Montreal region may be cold, but it’s relatively sunny even during winter. This makes for ideal conditions, particularly 20 1,000 during the end of winter and beginning of spring when available solar radiation is higher but outside temperatures are still low (Figure 2). 0 Jan. Feb. Mar. Apr. May Jun. Jul. Aug. Sep. Oct. Nov. Dec. Designers assessed an interesting way of taking advantage of the available passive solar energy using a solar wall system. The installation of a 316 ft2 (29 m2) metal-clad solar Figure 2: Montreal average temperature and solar radiation. radiation collector on the southbound wall of the school provides 14.5 MWh of solar energy annually, close to 10% For example, the BMS automatically selects the most efficient of the energy needed to heat outdoor air. In addition to pro- combination of the solar wall and enthalpy wheel, depending on viding renewable energy, heat loss from the wall covered by available energy and the building’s needs. Programmable lightthe solar panel is recovered and used to ing schedules help to ensure that lighting preheat the air, doubling the R-value of devices (1.2 W/ft2 [13 W/m2]) are off after 168,582 the wall to about R-50. Also, the solar operating hours. Moreover, by ensuring 193,036 wall diminishes the particulate levels in appropriate control of the building’s in58,306 188,634 the air drawn through it, which reduces ternal environment, the BMS allows the filter maintenance. school’s technical staff to quickly respond 416,957 The three-step fresh air heating system to HVAC-related complaints. (solar wall, enthalpy wheel and geotherEnergy simulation models helped demal loop) was so effective that it was signers predict energy savings of about Standard Construction decided to boost the ventilation system 590 million Btu (173,000 kWh) a year, 1,085,000 kBtu to add fresh air to parts of the existing an energy reduction of 55% compared building that needed it. to an equivalent building with standard Since the project’s HVAC design was HVAC systems. These results were later 178,680 104,969 more sophisticated than a conventional compared and confirmed with actual rooftop/boiler design, it was essential to building consumption. By running 55,517 103,333 link the HVAC systems into a building mostly on clean renewable energy (solar 50,947 management system (BMS) to simplify and geothermal) the new school building operation and maintenance activities. reduces greenhouse gas emissions by A newly released BMS was selected 45 metric tons/year. St. Johns School (Uses 55% Less Energy) because it offered better flexibility and Figure 3 shows the annual energy break495,000 KBtu a more user-friendly graphical interface down for a school with standard HVAC Heating Cooling Lights Equipment than the other systems on the market. Of systems (121 kBtu/ft2·yr [1 368 392 kJ/ Domestic Hot Water course, this also meant that it was more m2·yr]) compared to St. Johns School’s Figure 3: Energy breakdown (kBtu). expensive. efficient design (55 kBtu/ft2·yr [624 289 Fortunately, installation costs were kJ/m2·yr]). Energy used for heating is, by reduced because the manufacturer was interested in partici- far, the most affected with a decrease of 87%. The combination pating in a sustainable design project. The BMS controls of heat recovery, efficient equipment and renewable energy reand monitors all mechanical HVAC equipment, allowing duce heating energy consumption by more than 85%. Financial temperature setback during unoccupied periods, equipment savings on energy bills confirmed that the initial overrun cost operation schedules and effective monitoring and targeting for efficient equipment was a sensible investment. With the help of energy consumption. of government subsidies the payback period was three years.
56 ASHRAE Journal ashrae.org May 2011
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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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