Transcription
HVACPart 2: the details
HVAC Heating, Ventilation and AirConditioning Provides comfort for people Allows humans to existunder adverse conditions.
Load Calculations Heating and CoolingAccuracy important!Design conditionsBuilding shell loadR, U valueInternal loadVentilation loadInfiltrationOccupancy schedules
Heat Transfer Conduction Convection Radiation Resistance (R-Value) U 1/R Gheat U x A x ΔTU-Value is the rate ofheat flow in Btu/hthrough a one ft2 areawhen one side is 1oFwarmer
Solar Heat Gain Coefficient§ Theamount of solarheat energy allowed topass through a window§ Example:SHGC 0.40Allows 40% through andturns 60% away
Psychrometrics Dry bulb temp.Wet bulb temp.HumidityDew pointMoisture ric Chart
Basic Refrigeration CycleCondenserCompressorExpansionValveEvaporator
Basic HVAC Equipment Fans / BlowersFurnace / Heating unitFiltersCompressorCondensing unitsEvaporator (cooling coil)Control SystemAir Distribution System
System Types and Common Terms Packaged RooftopUnit Split System Heat Pump Geothermal Air to Air Hydronic (water) PTAC / PTHP""""Constant VolumeVariable VolumeIndoor Air QualityDirect Expansion
Packaged Rooftop Units
Split SystemDuctworkHeatingand CoolingEquipmentFURNACEA/C UNITTemperature &Humidity Controls
Heat Pump Operate on simplerefrigeration cycle Reversing the cycleprovides heating Temperaturelimitations Air to air Water source Geothermal Lake coupled
Variable Air VolumeSupply DuctsVAV BoxHeat Coil w/TempResetCool Coil w/Temp ResetFiltersReturn AirVariable SpeedSupply FanReheat CoilTTZone ThermostatVariable SpeedReturn FanReturn DuctsHVAC-14
Terminal UnitsVariable volume:ParallelConstant volume:Series
Hydronic systems Pumps Piping Valves
Control Devices Thermostats– Manual– Programmable Optimum Start DDC Systems Variable Speed Drives Automatic Valves and Dampers Outdoor Sensors
Major Equipment Chillers Boilers Cooling Towers
EconomizersFree cooling source: When available, use cool outdoor airinstead of mechanically cooled air.Minimum supplyof outside air55 oF80 oFNormal OperationOutside air dampers arepositioned to provide theminimum outside air55 oF andup85%outsideair85%exhaust80 oFEconomizer OperationOutside air dampers are fullyopen. Maximum outside air isprovided
EconomizersAir SideWater Side
Zoning and Economizers Economizers provide “free cooling”when outdoor conditions are optimal Proper orientation & zoning yieldscomfort & efficiencyNWCoreSE
Air Distribution Ductwork– Metal– Flexible– Ductboard Grilles, Louvers,& Registers Dampers– Shut off– Fire– Smoke Sealants Supports
Additional Equipment Energy Recovery Units Desiccant Systems
Additional Equipment Heat ExchangersHumidifiersSilencers
Mechanical Dehumidification Return air is mixed with ventilation air Cold coil condenses moistureFilter Heat is added back (electric or gas) so thatroom air is not over cooled- Reheat
Historical Minimum VentilationRates (cfm/person)70Smoking Smoking SHRAE 62-810
Improved Ventilation Effectiveness Effective mixing of ventilation airwithin space Vary ventilation based on thenumber of occupants and processloads - changes in occupancy canbe measured by CO2 sensors Consider designs that separateventilation and space conditioning Utilize heat recovery systems toreduce system size energy costs Avoid: loading docks, exhaustvents, plumbing stacks, wastecollection & stagnant water
HVAC Heating, Ventilation and Air Conditioning Provides comfort for people Allows humans to exist under adverse conditions. Load Calculations Heating and Cooling Accuracy important! Design conditions Building shell load R, U value .
