HVAC/Psychometrics Flashcards
(12 cards)
Purpose of HVAC system
Heat, Ventilation, Air Conditioning
How is the 1st law of thermodynamics applied to HVAC?
Conservation of energy - we can use heat to do work and vice versa
How does the 2nd law of thermodynamics apply to HVAC?
Heat moves to cooler areas, need HVAC to overcome gains and losses
What are heat gains and losses in a building?
Gains: people, equip,emit, lighting, solar
Losses: envelope losses,slabs, infiltration, ventilation
What is the basic refrigeration cycle?
Used work (electric energy) to move heat (thermal energy) from cold to hot
What are the key equipment pieces in the refrigeration cycle?
Condenser - refrigerant condenses
Compressor - Refrigerant compresses
Evaporator - refrigerant evaporates
Expansion valve - refrigerant expands
How is refrigeration cycle efficiency calculated?
Coefficient of Performance is used for all systems
EER - heat pumps
kW/ton - chillers
What are the components of a heat pump and what do they do?
Evaporator: absorbs heat (outside for heating, indoors for cooling)
Condenser: rejects heat (inside for heating, outdoors for cooling)
Reverse valve: switches condenser and evaporator and changes direction of fluid
What are common air system components?
Mixing box, air filter, heating coil, cooling coil, fan
What are common water system components?
Pipes
Valves
Pumps
Chillers
Cooler
Boiler
Differences between Constant Air Volume and Variable Air Volume?
CAV - large open areas, zone thermostat controls TSA; CFMSA changes with load
VAV - Larger facilities, TSA is constant; Zone thermostat controls CFMSA
What is the difference between decentralized and centralized units?
Centralized - HVAC serves multiple zones
Decentralized - HVAC has one system/zone
