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belt drive airflow fan belt drive electric motor

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Unformatted text preview: al power in η= OUTPUT INPUT = pressure increase fluid volumetric flowrate “fluid power” delivered mechanical power in Fan Motor Δ “fluid power” out: Note: A pump is similar. = Δ × Belt Drive?? Airflow η fan Belt Drive + - Electric Motor η motor η drive Fan Airflow Thermostat Controlling Furnace with “On-Off” Burner Indoor Air Temperature (as detected by thermostat) 20.5℃ 20.0℃ “throttling” 19.5℃ time ON OFF ON OFF burner turns off burner turns on heat gains heat from furnace T heat losses Load Duration Curve - Calculation Example Hourly Heating Loads from Energy Simulation for a Particular Building 500 450 400 350 Heating Load (MBH) 300 250 200 150 100 Summer heating system shutdown 50 0 1 1001 2001 3001 4001 Hour 5001 6001 7001 8001 Heating Load Duration Curve: 500 450 400 peak 350 Heating Load (MBH) 300 250 200 150 100 50 0 1 1001 2001 3001 4001 5001 6001 7001 8001 Hour Number (End of Aside.) Simplified Schematic: Two Boilers connected to hydronic heating loop pump Capacity 200 MBH BOILER 2 pump Capacity 200 MBH BOILER 1 pump HEATING LOAD LOAD DURATION CURVE MBH peak = 393 MBH 400 350 300 HEATING LOAD 250 total annual load = 443 million btu’s (area under curve) 200 150 BOILER 2 100 50 BOILER 1 0 0 1 1001 2001 2500 Hours 3001 4001 5000 5001 Say design is to be: 2 Boilers (each 200 MBH) Available Boiler Options: Type Output Capacity Annual Efficiency Capital Cost Model A 200 MBH 80% $5,000 Model B 200 MBH 90% $8,000 fuel cost = $12 / million btu Is it better to select Model A or Model B? MBH Each boiler operating alone can meet loads up to 200 MBH. 400 350 two boilers firing When load is more than 200 MBH, both boilers must fire. 300 250 200 150 one boiler firing 100 50 0 0 1 1001 2001 2500 Hours 3001 4001 5000 5001 MBH 400 LEAD - LAG Boiler Operation 350 LAG BOILER 300 fires when Lead can’t meet load on its own fires first 250 200 150 LEAD BOILER 100 50 0 0 1 1001 2001 2500 Hours 3001 4001 5000 5001 MBH Total Annual Load = 443 million btu 400 350 LAG BOILER Portion of load to be met by “Lag” boiler = 16 million btu (4%) 300 250 200 Portion of load that can be met by “Lead” boiler = 427 million btu (96%) 150 LEAD BOILER 100 LEAD BOILER 50 0 0 1 1001 2001 2500 Hours 3001 4001 5000 5001 COST-BENEFIT ANALYSIS Simple P ayback P eriod (years) Capital Cost Annual Fuel Cost Incremental Capital Cost A 80% $5,000 $6,408 - - - Lag A 80% $5,000 $240 - - - - - $10,000 $6,648 - - - B 90% $8,000 $5,688 $3,000 $720 4.2 Lag B 90% $8,000 $214 $3,000 $26 115 Total - - $16,000 $5,902 $6,000 $746 8.0 Lead 3 Eff Lead 2 Model Total 1 Boiler Lead Design Option Annual Fuel Cost Savings B 90% $8,000 $5,688 $3,000 $720 4.2 Lag A 80% $5,000 $240 - - - Total - - $13,000 $5,928 $3,000 $720 4.2 BOILER 2 Capacity 200 MBH BOILER 1 Capacity 200 MBH HEATING LOADS Building Energy Performance – Spring 2012 - Topic 13 - Aspects of Electric Motors for HVAC Equipment Electric Motors Many HVAC devices are driven by electric motors, including: • fans • pumps • compressors Motor + electricity - mechanical power Motor sizes encountered in HVAC applications can vary greatly. For example: • 1/20 hp motor driving a small fan • 75 hp motor driving a pump in a large chilled water distribution system Note: 1 horsepower = 1 hp ≈ 746 Watts = 0.746 kW TERMINOLOGY rotor stator Electrical Power Input + Mechanical Power Output: “Shaft Power” or “Brake Power” Motor losses (heat) Output (Watts) = Mechanical power delivered by rotor = Torque × Rotational Speed (N∙m) (rads/sec) I-P Units for: Brake Power (Shaft Power) • Much industry information is in Inch-Pound units… Torque: ft∙lbf Rotational Speed: rpm Mechanical Power: hp 2 × ( ∙ ) × 2 × × = = 33000 ( ∙ / ∙ ) 33000 ( ∙ ) × × = = 5252 ( ∙ / ∙ ) 5252 “Rated Power” / “Motor hp” / “Motor kW” = Nominal maximum output power that the motor can produce (“size of the motor”; capacity) Mechanical Output Power + Motor - e.g. A “10 hp” motor is rated to deliver up to ≈ 10 hp (7.46 kW) of mechanical output power Motor Efficiency + Motor - losses !""# = Output = Input Watts Watts I-P Units: output power = “brake horsepower” (bhp) bhp × 746 = “brake watts” watts/hp !""# = bhp × 746 Calculating Electrical Input Power: × 746 = = $!""# $!""# input output losses “Rated Motor Efficiency” • Typically refers to the efficiency when the motor is operating at full-load For example: For a “10 hp” motor with rated efficiency of 90%... At full-load, = 10 hp = 7460 W (output power) = 7460 W 0.90 = 8289 W (input power) “Rated Speed” • Typically refers to the rotor’s rotational speed (e.g. rpm) when operating at full-load For example: Rated Speed = 1750 rpm at 10 hp output Note: 1750 rev/min × 2π rads/rev × 1 min/60 sec = 183.3 rads/sec Types of Electric Motors typically found in HVAC Systems: AC / 3-phase (“Polyphase Induction Motors”) • “Squirrel Cage” Most common type for HVAC fans and pumps 1 hp and larger AC / 1-phase (“Single-phase Induction Motors”) • Capacitor R...
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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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