Consulting-Specifying Engineer - November 2008 - (Page 24)

Sensitivity to hand motion Wallmounted ultrasonic sensor Sensitivity to arm and upper torso motion 10 ft Sensitivity to full-body motion 20 ft 30 ft 40 ft Figure 2 Many manufacturers offer application guides for wall-mounted sensors. Source: Wattstopper are controlled. As architectural finishes are installed, multiple construction site visits may reveal errors in OS locations and save the project time and money. Verifying the location prior to and immediately following installation is a good goal. The OS manufacturer’s literature will clearly indicate the optimum placement and sensitivity options and provide opportunity for owner training. The setpoints, sensitivity, and delay are recorded by the installing the contractor’s start-up records. Typically, setpoints for sensitivity and time limit are not in the project documents. The commissioning authority must, therefore, be familiar with the equipment and request setpoints and expectations for the operation of the equipment. If nowhere else, this should be documented in the owner’s project requirements, pre-functional test document, or functional test document. The affordability and reliability of occupancy sensors have led to their integration into HVAC equipment. Engineers tasked to maximize energy savings using off-the-shelf technology are employing occupancy sensors to communicate with variable air volume boxes and even thermostatically controlled rooftop units. A single or bank of occupancy sensors may be used to turn down ventilation rates when spaces are not fully occupied or to allow the space temperature setpoint to creep up or down a few degrees when spaces are totally unoccupied. Figure 3 shows a typical commercial thermostat indicating relays for a time clock. Integrate an occupancy sensor into the contacts of the thermostat and you get a rooftop unit that can be scheduled to switch to unoccupied mode immediately at the end of the workday. It is worth mentioning that roughly half of all U.S. commercial floor space is fully or partially cooled through packaged rooftop equipment and controlled by a commercial thermostat (EIA 1998). Although a very elegant detail in the drawings, this application requires atypical wiring, OS sensor tuning, and owner training: a very good casework on the benefits of commissioning. Daylight responsive lighting controls typically require daylight sensors, such as photocells, mounted near the skylight or window. As with OS, these should be clearly indicated on the drawings, indicating the controlled fixtures, and aligned with the recommended placement. For photocells, placement in close proximity to glazing is of special concern and must be carefully coordinated for proper operation. In addition, highly reflective architectural finishes can affect operation. As with an OS, verifying the location prior to and immediately following installation is a good goal and will help catch unseen obstructions from architectural finishes and furniture. The controlled fixtures will be located within the daylit zone. The California Energy Commission 1 and the Oregon Dept. of Energy 2 both provide practical design guidance for selecting the daylit zone. 12 W2 MISC1 RS2 MISC3 RS+5 RS1 RSGND W1/O/B Y1 G MISC2 CK1 CKGND R C Figure 3 This generic thermostat shows generic Y1, Y2, W1, W2, etc. contactors. These don’t change from manufacturer to manufacturer. 24 Consulting-Specifying Engineer • NOVEMBER 2008

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Consulting-Specifying Engineer - November 2008 Contents Viewpoint News M/E Roundtable Comissioning Lighting Controls Prevent Plugholing: Smoke Control Done Right Commercial Geothermal Heating and Cooling System Design Codes &�Standards Case Study New Products Equipment Lifecycles Advertiser Index Green Space

Consulting-Specifying Engineer - November 2008

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