Understanding Lamp Operating Factors and Light Efficacy

1. Lamp operating factor • Published lumen output is based on laboratory conditions • Voltage • Rated at line voltage of 115V • Standard reactor ballast • Electromagnetic (ballast factor =< 1) • Electronic (ballast factor =<> 1) • Vertical lamp burning position for high intensity discharge lamps

2. Luminous efficacy is the light output per unit of electrical power [W] input, or lumen/Watt [lpw]. • Theoretically • 1 W  683 lm monochromic green light • 1 W  200 lm white light • Realistically • incandescent lamps: 10 to 25 lpw efficacy • Fluorescent lamps: 50 to 95 lpw • Interior spaces in large office buildings • Heat from lights, appliances, people  need year-round cooling

3. Energy distribution of typical 40W cool white fluorescent lamp[Figure 15-8 in Tao & Janis 2001]

4. Fluorescent lamps have negative electrical resistance. Once arc is struck, ionized mercury vapor becomes increasingly more conductive • A ballast is therefore used to (1) boost the voltage at the lamp terminals to start and (2) limit the maximum flow of current. • Ballast factor [-] is the ratio of the light output [lm] produced by lamps operating on a commercial ballast to the light output [lm] of the same lamp operating on a standard reference ballast in the laboratory. • Values range from 0.8 to 1.2

5. Ex. 2-2 Cooling Space heat gain = 69,551 Btu/hr CFM supply = 69,551 Btu/hr (1.1 * [78°F-55°F]) = 2,750 cfm Ex. 2-3 Cooling + Plenum Space heat gain = 43,684 Btu/hr CFM supply = 43,684 Btu/hr (1.1 * [78°F-55°F]) = 1,727 cfm Q = 1.1 * CFM * (Tspace - T supply)and assume Tsupply air = 55°F

6. HVAC Delivery Systems • Produce heating & cooling – head-end devices • Furnaces and boilers • Refrigeration devices • Move heat transfer fluids • Air handling equipment • Ducts, grilles, and diffusers • Pipe and pumps • Control delivery • Ability to maintain space conditions • Complexity of operations and maintenance • Energy consumption

7. Methods of Control • Vary T of supply air + hold flow = cte • Vary flow of warm and cold air + hold T = cte • Vary T and vary flow of supply air • ZONE is an area for which temperature (humidity) is controlled by a single thermostat.

8. Basic Control Devices • Sensor: measures the monitored or controlled variable • Controller: processes the sensor signal and decides to send signal to monitoring station or to actuator. • Two-position or proportional signal • Direct- or reverse acting • Actuator: manipulates equipment (e.g., damper or valve) to meet desired point of the controlled variable.

9. Sensors • Thermostat senses and controls temperature • may have mode switch for heating and cooling • Humidistat is a device that senses and responds to humidity, relative or absolute

10. Other sensors • Pressure switches and transmitters • Flow switches and transmitters • Speed switches and transmitters, which respond to flow, pressure, or a program • Position switches, which respond to signals to open, close, and modulate dampers, valves, etc.

11. Life Safety System • Sandwich system • Negative pressure on fire floor • Positive pressure on floors immediately above and below • allow occupants to evacuate the fire floor • minimize opportunity for smoke to migrate to surrounding floors • Smoke exhaust fan • Stair pressurization fan • Equipment shutdown

12. San Francisco Civic Center • Project organization • Floor by floor system = sandwich construction (drawing Ozger) • Placement of air terminals, VAV system • Hierarchical control system

13. Passive cooling design strategies by climate [Fig. 2.13 in Stein and Reynolds]

14. Dual control system -- GAP • Mixed air (see paper)