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Unformatted text preview: Handbook of Fundamentals SI 2009 (Chapter 9) Some example requirements from: “ASHRAE 62.1-2010: Ventilation for Acceptable Indoor Air Quality” From Table 6-1: Minimum Ventilation Rates in Breathing Zone Occupants L/s/person Floor Area L/s/m2 Offices 2.5 0.3 Lecture Classroom 3.8 0.3 Manufacturing 5.0 0.9 Space Type Houses are often ventilated primarily by “leakage”, although most have some exhaust fans (e.g. bathroom). Some newer houses may have mechanical ventilation. Commercial Air-Handling System – Components? Mixed Air Filter Cooling Heating Humidifier Coil Coil Supply Fan Supply Air Outside Air To Other Zones Supply Duct Recirculated Air Motor Condensate (to drain) Exhaust Air Exhaust Fan Exhaust Air Ceiling Space (Plenum) Return Fan Return Air Grille “Terminal Unit” Heating/Cooling Heating/Cooling Distribution System Diffuser ZONE T Thermostat Condensate (to drain) Grille A particular home heating and cooling system: Thermostat A/C Condenser Natural Gas Furnace & Cooling Coil cooling coil heat exchanger section burner section filter induced draft fan and motor indoor fan and motor return air condensate pump furnace nameplate rated input: 80,000 btu/hr rated output: 74,000 btu/hr Recall: Preliminary Energy Audit Data… Monthly Natural Gas Use vs Average Monthly Outdoor Air Temperature 20 2007 18 2008 16 2009 14 Monthly Natural Gas Use, m3/day 2011 12 2012 10 8 6 4 2 0 -15 -10 -5 0 5 10 15 Monthly Average Outdoor Air Temperature, °C 20 25 Home Energy Audit: First Estimate of Natural-Gas Uses… 2,505 m3 Natural Gas Meter 365 m3 Water Heater 2104 m3 Furnace Note: Approximate “Higher Heating Value” of Natural Gas 1 m3 ≈ 37-38 MJ ≈ 35,000-36,000 btu Home Energy Audit: First Break-out of Electricity Uses… Component Estimated Annual Consumption Total Electricity 6,100 kWh (100%) Refrigerator 518 kWh (8.5%) Chest Freezer 336 kWh (5.5%) Other Electricity (?) 5,246 kWh (86%) Commercial Equipment -- “Packaged Rooftop Units” • The most common type of HVAC system used in commercial buildings in North America. • Self-contained electric cooling section (“DX”) • Supply fan (indoor fan) is usually constant volume. • In Canada, the heating section is usually a natural gas fired furnace. Packaged Roof-Top Unit (RTU) Condenser Indoor Fan, Fan + Motor Belt Drive, Motor Condenser Coil Evaporator Coil Filter Air Intake Furnace Roof Compressor + Motor Supply Air Supply Duct Return Air Diagram adapted from “HVAC Simplified” (Kavanaugh/ASHRAE, 2009) Schematic Representation of a Mixed-Air, Single-Zone, Air-Handling System (“All-Air”, Variable-Temperature, Constant-Volume System) Outside Air Outside Air Damper Cooling Mixed Air Heating Supply Fan Recirc Air Economizer Control Return Air Damper T Exhaust Air Exhaust (Relief) Damper Return Fan ZONE Supply fan flow is usually constant-volume (fixed-speed). The zone thermostat controls the Supply Air Temperature (i.e. heating/cooling coil operation). ASIDE: Schematic Representation of a Mixed-Air, Multiple-Zone, Air-Handling System (Variable-Air-Volume (VAV) System) O/A Damper Mixed Air Cooling Heating Variable Volume Supply Fan SAT To Other Zones Economizer R/A Damper VAV box VAV box T ZONE 1 R/F heater T ZONE 2 heater Supply Air Temperature (SAT) is usually cool relative to room temperature. SAT may be held constant (e.g. 13°C/55°F), or increased during periods when cooling load is lower (e.g. based on outside air temperature or zone loads). ASIDE: Schematic Representation of a Zonal System HVAC System (2-Pipe Fan-Coil System) Heating Unit Seasonal switch-over valves To Other Zones Cooling Unit ZONE 1 ZONE 2 T T Pump Heating Outside Air Cooling “Make-Up Air Unit” Fan SAT To Other Zones Make-Up Air Unit typically delivers “tempered” ventilation air to the zones (e.g. the supply air is conditioned to near “room temperature” for delivery). ASIDE: Schematic Representation of a Zonal System HVAC System (Water-Loop Heat-Pump System) cooling tower return pipe supply pipe boiler ZONE 1 ZONE 2 Zones terminal units, e.g. water-to-air heat pumps Outside Air Exhaust Air Cooling Heating Supply Fan Exhaust Fan Make-Up Air Unit typically delivers “tempered” ventilation air to the zones (e.g. the supply air is conditioned to near “room temperature” for delivery). Simplified Schematic of a Hydronic Heating System heat radiator Pump electricity Motor ZONE 2 heat radiator T flue T Flame Pump BOILER ZONE 3 T Motor electricity heat radiator fuel air ZONE 1 T Some Definitions of Equipment Efficiency Fuel-Fired Heater η= efficiency OUTPUT INPUT steady-state energy balance: e.g. “boiler” = + losses energy flow-rates input fuel Boiler ηB output useful heat delivered steady-state efficiency: = Annual Efficiency (Seasonal Efficiency) , = , losses , Boiler , Electric Motor input + output Motor electric power mechanical power losses Torque × Rotational Speed (N·m) (rads/sec) η= OUTPUT INPUT = mechanical power out electric power in Airflow Fan? “fluid power” out η fan = Δ × Fan Airflow mechanic...
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This note was uploaded on 10/04/2012 for the course ME 760 taught by Professor Davidmather during the Spring '12 term at Waterloo.

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