study guide exam 2

Electric boilers are available up to _____________________ kW for generation of steam and hot water.

12,000

At altitudes up to _____________________________ feet about sea level, air density does not vary sufficiently to create heat transfer problems.

2,000

The most common type of central air conditioner is a split system

A split system has the condensing unit (containing the compressor, condensing coil and fan, and expansion valve) located outside and a cooling coil (an evaporator in an air-handling unit or in the ductwork near the furnace) located inside

mechanical rooms

About 4 to 6% of a building's gross floor area should be available at each floor for air-handling equipment In commercial buildings, usually about 1 to 2% of the building's gross floor area is needed for the mechanical room for the central heating and cooling plant In large buildings, main mechanical equipment rooms generally shall have clear ceiling heights of not less than 12 ft (3.6 m). Where maintenance requires the lifting of heavy parts [100 pounds (45 kg) or more], hoists and hatchways should be installed.

air humidification

Air is mixed with water vapor, in proportions that vary with climate, season, and daily weather conditions There are three methods of air humidification. Atomization Vaporization Evaporation

Which of these is not one of the basic types of fans used HVAC applications, classified according to the direction of the airflow through the impellor.

All of these answers are correct. Centrifigal RECIPROCATING Axial

multiple small boilers

An installation of multiple small boilers is typically more efficient and effective than an installation of a single large boiler A small boiler is normally more efficient than a comparable large boiler A boiler is most efficient when it operates at or near its rated capacity.

As with estimation of heating energy consumption and operating costs, calculations can be done using one of three basic methods. Which of the answers is not one of the three methods:

COOLING LOAD ESTIMATION ANALYSIS hour-by-hour simulation Bin energy estimation Degree-day energy estimation

Which of the following is not a type of mechanical vapor-compression refrigeration chiller?

DIAPHRAGM CHILLER Centrifugal Chillers Screw Chillers Scroll Chillers Reciprocating Chillers

As with estimation of heating energy consumption and operating costs, calculations can be done using one of three basic methods:

Degree-day energy estimation Bin energy estimation Hour-by-hour simulation

There are a number of accepted methods used in duct design. Which of the answers listed is not one of them?

Ductile reduction

Dampers are normally fitted with the ducts themselves and must be manual.

False

Air Flow

Flow of air is caused by a pressure difference (ΔP). Flow will originate from a region of high pressure and proceed to an area of lower pressure Airflow can be turbulent or laminar: Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. Turbulent flow occurs when there is a disruption between the laminar layers within the airflow from the formation of eddies and chaotic motion.

The use of refrigeration to provide both heating and cooling for a space is accomplished with a device called a _____________________.

Heat pump

Air Conditioning is a process that involves all of the following except:

Heating air Cooling air Humidifying air Dehumidifying air Cleaning air PASTEURIZING AIR

Which of the following is not a type of duct layout?

Pinwheel arrangement

_______________________________ is the amount of total pressure required to move air through the diffuser.

Pressure loss

humidifiers

Residential humidifiers are the evaporation or atomization type They rely upon heated air flowing across a water surface, air circulating over or through a wetted media, or small particles of water introduced into the airstream The fan drives air on a furnace Types of residential humidifiers include the following Pan-Type Humidifiers Wetted Media Humidifiers Atomizing Humidifiers Portable Humidifiers commercial systems tend to be more complex

designing a duct system

The main goal in designing HVAC ductwork is to select the smallest (and lowest cost) duct sizes that can be used without producing a large total pressure loss necessitating a powerful (and noisy) fan and without generating excessive noise from high velocities. Additionally, the duct system should be routed to minimize the individual lengths of the various duct runs

All boiler systems require water treatment

True

Oversizing a cooling system adversely influences efficiency and performance.

True

building commissioning

a new building project or retrofit to an existing building with highly sophisticated or innovative systems generally requires additional attention to be sure that it operates as designed ensure that all systems are built and function as intended

mechanical code

a set of standards adopted into law by local government entities to regulate mechanical systems and equipment including HVAC, exhaust systems, chimneys, and vents, ducts, appliances, boilers, water heaters, refrigeration, hydronic piping, and solar systems

cooling load calculations

are made to size an HVAC cooling system and its components based upon the effects of heat gains and building performance at extreme conditions, usually midday during the summer

Summer design conditions

are used by the designer to determine the peak operating conditions under which HVAC systems and equipment (e.g., equipment for cooling, ventilating, dehumidifying, condensing) must operate during the summer.

Which of these are not one of the types of commercially available air cleaners?

compression filters

Infrared heaters

consist of a hot surface that radiates heat energy in a specific direction. In large space heating designs, adjustable reflectors that are part of the heating unit control distribution patterns Radiated energy warms floors and other objects in the space Little energy is lost because air is a poor absorber Heat is released from these objects by convection

dampers

damper- is an airflow control device used in ductwork to vary the volume of air passing through an air outlet, air inlet, or duct A damper opens and closes to control airflow Air dampers are placed in ductwork and allow the quantity of air in different parts of the ventilation ductwork to be adjusted The door-like mechanism of a damper manually or automatically opens and closes, thereby controlling flow of air

ductwork

duct- is a hollow pipe or conduit that conveys and transfers air in a heating, ventilating, and cooling system fitting- fitting is a coupling, tee, elbow, or similar duct section that changes the direction of airflow or changes the size or shape of the duct (called a transition) ductwork- is a network of ducts that confines and channels air and serves as the distribution system in a heating, ventilating, and cooling air system ducts and duct fittings are made of rigid steel and aluminum sheets of metal, a fiberglass composite, or thermoplastics

residential cooling load computations

heat gain from infiltrated air is included with the heat gain from outdoor ventilation air mainly because there are no code requirements for ventilating residences and because the load associated with ventilation air is comparatively small in comparison to ventilation requirements from commercial buildings

how does heat in a building affect cooling load?

heat that enters a building interior can affect the cooling load instantly or may be temporarily stored in materials or furnishings and released to affect the cooling load at a later time convective and latent heat flows are instantaneous radiant heat gains tend to be stored in building materials and released at a later time

heat balance (HB) method

indicates the balance of all heat transfer in a room to determine the cooling load

Proper sealing of plenums, air-handling units, and ducts is _________________________ in eliminating leaks in a duct system.

indispensable

An ________________________ is a type of fan-coil unit that receives primary air from a central air-handling unit, which includes ventilation (outdoor) air.

induction unit

central air conditioner

is a DX refrigeration cooling system. It has four basic parts: a condensing unit (containing the compressor, condenser, and expansion valve), a cooling coil (an evaporator in the air-handling unit or ductwork near the furnace), ductwork (to distribute the cooled air), and a control mechanism such as a thermostat

fans

is a machine for moving air by means of a rotating impeller using centrifugal or propeller action Two basic types of fans are used in HVAC applications: Axial Centrifugal

Transitional flow

is a mixture of laminar and turbulent flow, with turbulence in the center of the duct, and laminar flow near the edges.

refrigerants

is a substance that produces a refrigerating effect while expanding or vaporizing as it circulates as a gas or liquid through a closed vapor-compression refrigeration system.

Cooling load hours

is a time quantity developed by the HVAC industry to specify the number of hours that a cooling system would typically operate at a specific geographical location.

supply outlet

is an opening through which air is introduced into the space The proper selection of diffusers, grilles, and registers is necessary to ensure that both occupant comfort and adequate ventilation mixing are provided

standard air

is defined as dry air at standard atmospheric pressure (14.696 lb/in2, 101 325 Pa, 29.92 inches of mercury) and room temperature (70°F, 21.1°C); its mass density is normally 0.075 lb/ft3 (1.189 kg/m3) As air temperature increases, its density decreases; air becomes lighter when it is heated and heavier when it becomes colder

Aspect ratio

is the relationship between the width (w) and height (h) of a duct, expressed as a ratio: w/h.

quantity of heat gain

is universally expressed in Btu or W-hr and rate of heat gain in Btu/hr or W

2 types of dampers

manual damper-ndamper generally consists of a sheet metal (or similar material) flap, shaped to fit the inside of a round or rectangular duct motorized damper- nis generally used in a zoned system (see Thermal Zoning section) to automatically deliver conditioned air to specific rooms or zones.

rule-of thumb method

most basic and least accurate method 400 to 600 ft^2 of floor area per ton of cooling required based upon geographic location)

In performing cooling load calculations for commercial buildings, the spaces need to be divided into zones that have _____________________ load parameters.

similar

heat gain

the amount of heat that a building or building space accumulates from external sources (high outside temperature and solar radiation) and internal sources (occupants, lights, equipment, and appliances)

cooling load

the heat the HVAC equipment must remove to maintain the building interior at inside design conditions

static pressure

the pressure exerted against the side walls of the duct no differently than atmospheric pressure presses against a body's surface

radiant time series (RTS) method

uses an array of repetitive equations to produce accurate results and is less dependent on approximated data