Quiz 1 Flashcards
Define Single Zone Unit
Constant volume system that serves ONE zone, which may consist of one to several rooms but ONE thermostat controlling the temperature of the zone
Define Multi Zone Unit
-Constant volume system that serves MULTIPLE zones via separate ducts.
-Each zone has a temp sensor
-Has a “hot” deck and a “cold” deck and mixes SA for the zone at air handler to provide temp needed by individual zone
Define Variable Air Volume (VAV) Unit
-A unit that provides constant temp but a variable volume of air to a series of VAV boxes which serve multiple spaces.
-VAV Boxes open and close to admit more or less of the constant temp air to regulate temp of each space based on the individual space temp sensor
Define Chiller
The equipment in a chilled water system that cools the water which is circulated through the air handler cooling coil to provide cool air to the space.
Define Hot Water Boiler
The equipment in a hot water heating system that heats the water which is pumped through the air handler heating coil to provide warm air to the space.
Define Direct Expansion (DX) Cooling
-Stand-alone system
-Heat from the space is absorbed directly by a refrigerant circulating in the air handler cooling coil.
-The space heat is rejected to the outside air by the condensing unit.
Define Chilled Water Cooling
-Heat from the space is absorbed by chilled water pumped through the air handler cooling coil.
-The space heat is rejected to the outside by a cooling tower or condensing unit.
Define Hot Water Heating
-Hot water from a boiler is pumped through the air handler hot water coil.
-The cold space air absorbs the heat from the hot water to provide warm air to the space.
Define Gas Heating
-Room air is drawn across heat exchanges which are heated by burnging natural gas within the sealed and vented heat exchanges.
-The air handler fan then circulates the warm air through the room raising the space temperature.
-Cheaper than electric heat - only 80% efficient; not charged for demand
Define Electric Heating
-Electricity flows through an electric coil in an air handler causing the coil to become hot. Room air is blown across the coil warming the air and sending it back to the space for heating.
-More expensive than gas - 100% efficient at the unit, however, the price per BTU is higher because of power loss at the site of production and transportation.
-Measured in KW creating demand charges
Define Split System
A DX AC system with the air handler and evaporator coil inside the building and the condensing unit outside (split).
Define Variable Air Volume (VAV) Box
Regulates the volume of constant temperature air flowing into the space to maintain the desired room temp.
Define Pump
-Used in chilled water cooling or hot water heating
-Creates the circulation of water through insulated water piping to the air handler coils and back
Define Compressor
-Component of refrigerant cycle in a DX cooling system
-Generally found in the outside condensing unit
-Raises the temperature and pressure of the refrigerant vapor so that outside air may be used to cool the vapor in the condenser coil, causing it to condense to a liquid which rejects space heat to the outside air.
Define Expansion Valve
-Separates the high pressure liquid refrigerant from the low pressure evaporator coil in the refrigerant cycle.
-As the liquid refrigerant passes through the expansion valve and the pressure and boiling point is decreased, the refirgerant can now boil or “evaporate” as it passes through the evaporator coil.
Define Condensor
-Coil on the outside condensing unit that cools the compressed refrigerant vapor when outside air is drawn through the coil fins by the condenser fan.
-Cooling the vapor and condensing it to a liquid releases the indoor heat to the outside air.
Define Evaporator
-Cooling coil in a DX system air handler that is cooled directly by the evaporation of refrigerant as a part of the refrigerant cycle.
Define Tons of Refrigeration
-Removing 12,000 BTUs of heat from a space in one hour equals one ton of refrigeration.
Define British Thermal Unit (BTU)
-Amount of thermal energy necessary to raise the temperature of one pound of pure liquid water by one degree Fahrenheit at the temperature at which water has its greatest density (39°F)
Define Rooftop Unit
-Either packaged (all components of refrigeration cycle in one enclosure) or get cooling from another location such as a chiller.
-Supply and return air ducts attach at the bottom and go through the roof. Can be DX or CHW (DX is usually packaged)
Standard occupied cooling set point
72°
Standard occupied heating set point
68°
Standard unoccupied cooling set point
95°
Standard unoccoupied heating set point
50°
Standard Dead Band
4° Minimum
