HVAC Flashcards

Question

Energy transfer wheel A. temper incoming air with exhaust air B. use ground temperature for heating or cooling C. capture the heat of flue-gases to warm cold water D. exchange heat from solar panels to an airstream

Answer 1

A. temper incoming air with exhaust air AN energy transfer wheel transfers heat between two airstreams (incoming air and exhaust air) using a lithium chlooride-impregnated heat exchanger. Option B decribes a ground source heat pump. This type of system uses the constant temperature of the ground to heat or cool a building. Option C describea boiler fuel economizer. Option D describes a standard heat exchanger

Answer 2

A. electricity In the NW part of the USA, electrical generating facilities are plentiful and provide a relatively low cost way to heat buildings Natural gas is popular in the Midwest, while oil is commonly used in the northeastern USA. Steam is not economical unless it is produced in a central facility for use in an urban area or is a by -product of other types.

Answer 3

C. I, II, III, iV Humidity does not affect heat gain.

Answer 4

B. design cooling factor The desgin cooling factor and the area of glass must both be known to calculate solar heat gain. Equivalent temperature difference is used to calculate heat gain through the building envelope, such as walls and roofs.

Answer 5

A. relative humidity is the best measure of thermal comfort Although relative humidity affects the way a person feels in a space, it is not the primary measure of thermal comfort. Effective temperature (ET) is a better indicator of comfort because because it takes all the variables into account. For example, even at a high humidity of 75%, if the temperature is cool enough or there is enough of a breeze, most people will feel comfortable.

Answer 6

D. II, III, IV The climatic zone, scale of the building, and cost and efficiency of the HVAC system would drive the specification. The shopping mall would be planned for relatively fixed sizes of rental spaces, so flexibility would not be one of the most important considerations. Because the tenant mix would probably not be completely known at the time of design, the tenant's preference could not be solicited even if it were appropriate.

Answer 7

wet buld temperature

Answer 8

C. determine optimum ventilation rates ## Footnote The psychrometric chart is a graphical representation of air, heat, and moisture. It does not indicate or take into account the effects of air movement or ventilation rates on human comfort.

Answer 9

D. water-loop heat pumps Water-loop heat pumps use a continuous flow of temperate water to extract heat from areas that need to be cooled and add heat to other areas requiring heating using very little, if any, additional energy input. Heat pipes are not appropriate because they would simply prewarm cool outdoor air. A recuperative fuel economizer is another type of system that simply uses hot exhaust gas to preheat incoming air or water. This type of equipment would save energy by increasing the efficiency of teh heating plant.

Answer 10

In climates wehere the difference between indoor and outdoor air temperature is high.

Answer 11

7600 sq ft For most midsize buildings, an all air or air water system needs about 3% to 9% of teh gross area for HVAC system mechanical space. Office buildings fall somewhere near the midpoint of the range, so use 6% for this question. ^% of the estimated 126,000 sq ft gross area is 7560 sq ft. rounded up to 7600 sq ft.

Answer 12

C. natural gas has a higher heating value than does propane ## Footnote

Answer 13

D. round A round duct is the most efficient choiec and offers the smallest possible perimeter for the same cross-sectional area, thus minmizing friction and pressure loss. A square duct is the next most efficient shape, being closest to a circle. A square shape would use the available space most efficiently, but it is not as efficient overall as a round duct. As ducts become more rectangular, they become less efficient and increased friction loss. A rectangular duct with the long dimension horizontal would only be used if space was a problem.

Answer 14

3413 Btu/kWh

Answer 15

- easy to install and control - simple operation - flexible zoning - little space required

Answer 16

most expensive type, especially for high heating loads

Answer 17

2500 Btu/kWh

Answer 18

portable and good for remote areas

Answer 19

not as clean burning as natural gas

Answer 20

1050 Btu/kWh

Answer 21

Most efficient fossil fuel, clean burning

Answer 22

can't be used in remote areas

Answer 23

137,000-141,000 btu/gal

Answer 24

portable and storable

Answer 25

- wide price flucuation - burning equipment needs lots of maintenance - must be stored securely

Answer 26

B. a damper A standard gas furnace does not have a damper. Only a special energy-saving furnace would sometimes have a damper that automatically closes when the furnace is off.

Answer 27

B. uses outdoor air to cool a building An economizer cycle introduces outdoor air when the ambient temperature is low enough to assist in cooling

Answer 28

B. latent heat only

Answer 29

D. vapor pressure Wind pressure, stack pressure, and HVAC fan pressure can all influence infiltration and exfiltration rates. Vapor pressure does not cause air movement; rather, vapor pressure is a movement of moisture.

Answer 30

C. Provide an active noise-canceling system emitting out-of-phase noise An active noise-canceling system would help to reduce the noise in a duct system without reducing airflow. This type of system analyzes the noise from the blowers and other system components and synthesizes a noise that is exactly out of phase with the mechanical noise. The two sounds cancel each other and the result is perceived silence.

Answer 31

They achive heat transfer by passing the hot gases in a boiler's stack through a heat exchanger, thus preheating the incoming boiler water.

Answer 32

They can be used for heat transfer between intake and exhaust air ducts when these two airstreams are rather far apart. This circulating heat-transfer fluid usually contains anti-freeze; it provides simple sensible heat transfer with no restrictions on exhaust and intake location

Answer 33

Buildings with high internal gains because they need cooling even when the outdoor temperature is chilly.

Answer 34

Low rise buildings

Answer 35

Long runs of pipes are required for the system

Answer 36

The process of inspecting, testing, starting up, and adjusting building systems and then verifying and documenting that they are operating as intended and meet the design criteria of the contract documents

Answer 37

When building heat is not needed a heat rejection condenser sends heat to the cooling towers. When heat is needed a separate heat recovery condenser sends excess heat to fan coil units or other devices

Answer 38

Heats water by passing hot gasses directly through water

Answer 39

Where there is a continuous demand for hot water (food processing, laundries, industrial purposes)

Answer 40

Device that recovers the sensible and latent heat from the high heat of exhaust flue gases that would normally be discharged to the atmosphere.

Answer 41

Air distribution system that supplies air at floor level, air rises as it heat and it enters the return ducts through grilles in the ceiling

Answer 42

Compose a heating a cooling system that uses a series of heat pumps for different zones of a building which are all connected to the same piping system of circulating water. Zones that are cooling, dump heat into the system, other zones need heating and extract heat from the system.

Answer 43

Between 60-90 deg F

Answer 44

Uses water, ice, or rock beds to store excess heat or coolth for use at a later time

Answer 45

Devices that reclaim waste energy from the exhaust air stream and uses it to condition incoming fresh air

Answer 46

Flat pipe recovery units, energy transfer wheels, heat pipes

Answer 47

1) the fresh air intake must be kept as far away from the exhaust outlet as possible; 2) exhaust air that contains excessive moisture, grease, or other contaminants should be separated from the heat exchanger; 3) in cold winter conditions, a defroster in the device may be needed to prevents the condensate in the exhaust air from freezing

Answer 48

Transfer heat between two air streams through the use of a heat exchanger wheel consisting of small openings through which the air passes. They are also called enthalpy heat exchangers

Answer 49

Comercial buildings and hospitals

Answer 50

They transfer latent heat as well as sensible heat

Answer 51

A self contained device that transfers sensible heat energy from hot exhaust air to cool outdoor air

Answer 52

Incoming and outgoing air streams must be adjacent

Answer 53

Devices that use water or other liquid agent to exchange heat. In winter the system pumps heat exchanger over hot exhaust air and uses that heat to preheat incoming cool out door air

Answer 54

A window that uses a double pained insulated glass unit over which another pane of glass is placed on the inside of the building. Air is drawn up between the inside pane and the main window unit and is extracted into the return air system

Answer 55

Easily controlled, efficient heat transfer

Answer 56

Return air is supplied at the bottom of the unit and heated air is delivered to the bonnet above the furnace where it is distributed

Answer 57

Works opposite of upflow furnace; used where duct work is located in a basement or crawlspace

Answer 58

Direct Expansion (DX) also known as incremental unit

Answer 59

Take the difference between an indoor temp of 65 deg F and the average outside temp for a 24 ho period. The values for each day of the year are added to get the total number of degree days

Answer 60

Amount of heat need to raise a gallon of water 1 deg F

Answer 61

Compression

Answer 62

A chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. This liquid can then be circulated through a heat exchanger to cool air or equipment as required.

Answer 63

If the reheating equipment is located near the conditioned space

Answer 64

For large buildings and institutions, where temperature regulation is required, humidity control is needed, and energy conservation is a concern; efficient for internally loaded buildings

Answer 65

Limited in ability to compensate for extremes in simultaneous heating an cooling demands

Answer 66

- When more flexibility is required - Can respond to varying requirements

Answer 67

- inefficient because hot and cool air have to be supplied winter or summer - previously cooled air may need to be heated and vice versa - system requires larger powerful fans therefore more energy - noise problems in ductwork - more ductworks means more expensive

Answer 68

If reheating coils are located in ductwork to serve an entire zone

Answer 69

- Humidity and temperature can be carefully controlled - low supply temperature equates to smaller duct sizes and lower fan horsepower

Answer 70

Simultaneous heating and cooling in building

Answer 71

Medium sized buildings or where a central mixing unit is located on each floor

Answer 72

relative humidity

Answer 73

....melt a solid

Answer 74

change a liquid into a gas

Answer 75

transmittance- the situation in which the radiation passes through the material absoptance-the situation in which the radiation is converted into sensible heat within the material reflectance-the situation in which the radiation is reflected off the surface emittance- the situation in which the radiation is given off by the surface, therby reducing the sensible heat content of the object

Answer 76

They neither absorb not emit radiation readily

Answer 77

Heat capacity is the amount of heat per unit mass required to raise the temperature by one degree F.

Answer 78

1. Air temperature: determines the rate at which heat is lost to the air by convection. Above 98.6 deg F, heat flow reverses and the body will gain heat. 2. Relative humidity: the higher the relative humidty, the harder it is to achieve cooling through evporation 3. Air velocity: air movement affects heat loss rate by both convection and evaporation. 4. Mean radiant temperature: example-when you in front of a south facing window in the winter, you may actually feel too warm even though the air temperature is at a comfortable 75 deg F.

Answer 79

the maximum output potential of a heating/cooling system in one hour and is used to size HVAC equipment

Answer 80

the amount of heat lost at design outdoor and indoor conditions which must be made up by the HVAC system to maintain occupant comfort

Answer 81

an HVAC energy rating

Answer 82

retard the flow of heat

Answer 83

encourage heat flow

Answer 84

used for calculating heat gain through a building envelope, and takes into account air temperature differences, effects of sun, thermal mass storage effects of material, color of finishes, etc.

Answer 85

used for calculating heat gain through glazing, takes int account glazing type, interior shading, and outdoor temperature

Answer 86

an equivalent temperature difference used for calculating the instantaneous external cooling load across a wall or roof

Answer 87

how much radiant energy that is reflected by a surface where 0 is a flat black surface which absorbs all heat and 1 is a mirror (rate is listed as a fraction or percent).

Answer 88

the speed with which heat passes through a material. Metals are high, and soils/sand are low.

Answer 89

equipment that permits the use of outdoor air instead of refrigeration units for building cooling when conditions are right

Answer 90

evaluates both temperature and humidity, mixes appropriate outdoor/indoor air to achieve comfortable conditions without cooling

Answer 91

gravity heating systems used by the romans to heat public baths and private houses

Answer 92

amount of cooling required to convert a ton of water to ice in a 24 hour period, equal to 12,000 BTUH

Answer 93

comfort issues, cold drafts, and noxious doers that rush in through cracks and Outside doors may difficult to adjust and open and dangerous to close • Flues intended to discharge combustion products may backdraft

Answer 94

ASHRAE Standard 62.1-2001

Answer 95

tool used to identify drafts and air leaks, pull on the trigger and see how smoke moves to show air movement

Answer 96

the highest efficiency option, typically found in special air cleanser for unusually polluted or IAQ demanding environments like hospitals

Answer 97

very common • Fibrous Panel Filters: furnished with HVAC equipment and function mainly to protect fans from large particles of lint or dust • The least effective in cleaning air • Media Filters: more fine and use filter paper in please within a frame, working by straining and impaction (90% efficient)

Answer 98

more money, but produce less air movement as two sets of chard plates attract dust. Are cleaned by washing off.

Answer 99

for gaseous removal and vary depending on pollutant Activated charcoal filters: more common, absorb materials with high molecular weights and allow low weights to pass

Answer 100

sometime used to control bacteria growth and control humidity

Answer 101

can pose a threat due to ozone production, but demand less maintenance

Answer 102

equipment that creates warm or cool water or air, typically in a mechanical room

Answer 103

typically the space above a suspended ceiling used to convey return air

Answer 104

a heat rejection device which extracts waste heat to the atmosphere through the cooling of a water stream to a lower temperature. Often found on the roof.

Answer 105

used in hot climate with high cooling demands

Answer 106

a ventilation system that consists of air intakes, filters, fans, electric heating coils, connected ductwork/components, fire/control dampers, electric reheat boxes, air boards, and control systems. Can also include DX or chilled water cooling coil, refrigerant storage and pump systems

Answer 107

a unitless number that is a rating of the efficiency of heating or cooling equipment

Answer 108

single number figure of merit based on part load EER or COP expressing part load efficiency for air condition and heat pump equipment

Answer 109

standardized system for rating the energy efficiency of residential buildings. Score is between 0 - 100 and indicates the relative energy efficiency compared to a HERS efficient home.

Answer 110

ration of net cooling capacity in BTUH to the total rate of electrical input in watts, under designated operating conditions

Answer 111

an appliance fired by gas or oil to heat air and then distribute it throughout a building in a heating system • 80% efficiency • Upflow Furnace: return air is supplied at the bottom of the unit and heated air is expelled at the top of the furnace and distributed through ductwork • Downflow Furnace: the opposite of upflow, used where ductwork is located in the basement and furnace is on the first floor • Horizontal (Lowboy) Furnace: used where headroom is limited

Answer 112

a closed vessel in which water or other fluid is heated by gas or oil, but does not necessarily boil. The heated/vaporized fluid exits the boiler for use in various heating systems • 80% efficiency • Typically has tubes containing water to be heated that are situated within a combustion chamber where heat exchange takes place • Gasses and other combustible products are carried away through breeching into a flue • It’s the most basic system • Life cycle cost can be high • Types of Boilers: • Fire Tube Boiler: water paternally fills a barrel with a small volume left above to accommodate steam, used in early all steam locomotives, a low rate of steam production but high steam storage capacity. Mostly burn solid fuels and but can burn liquid or gas • Water Tube Boiler: water tubes are arranged inside a furnace. Gives high steam production rates but less storage capacity. Generally preferred in high pressure application since high pressure water/steam is contained within small diameter pipes • Modular: packaged boiler system that operate in parallel or series to provide varying amounts of steam. Typically most efficient when run at full capacity. • Packaged Type: comes in a compel package, requires only the steam, water pie work, fuel supply and electrical connection. • Electric: steam is generated using electricity rather than the combustion of a fuel. More expensive than gas run boilers but are simple and easy to use.

Answer 113

• Fluorocarbons, especially chlorofluorocarbons, are being phased out because they deplete the ozone layer • Ammonia • Sulfur Dioxide • Non-halogenated Hydrocarbons (e.g.: propane) work, but are flamable • Non-CFC refrigerants may be less effective and involve a higher energy cost

Answer 114

Based on the transfer of heat during the liquefaction and evaporation of a refrigerant. Latent heat is released as refrigerant changes form • Compressor: takes refrigerant in gas form and compresses into a liquid • Condenser: refrigerant passes through and latent heat is released, usually on the outside of the building • Evaporator: expands refrigerant, vaporizes back to gas absorbing surrounding heat

Answer 115

produces chilled water and is accomplished by the loss of heat when water evaporates. • Produced in a closed loop system by a salt solution (brine) that draws vapor from the evaporator. • Less efficient than compressive systems • Needs about 2 times the heat rejection capacity of the compressive cycle

Answer 116

water is dropped over pads or tubes that circulate outdoor air or water. • Free water evaporates to vapor and the heat is drawn from circulating air or water to disturb to indoor spaces • Works well in hot-arid climates with low humidity • Simple to construct • Requires no refrigerant line • Even though a change in total heat occurs, evaporative cooling is accompanied by an increase in relative humidity.

Answer 117

• Lower cost • Less ductwork • Returns can be ducted or open in the space between the ceiling and floor/ roof above, called a plenum • Easy to operate • Good for controlling IAQ

Answer 118

* Can only heat or cool * Only works when loads are similar through a building * Bad for perimeter zones in cold climates * Thick distribution trees * Can be noisy

Answer 119

* Typical residential system * Common in buildings with large open spaces, few windows, uniform loads, like theaters, department stores, exhibition halls

Answer 120

* A single supply duct runs to all rooms with a constant air flow * Rate of air flow is controlled by a damper at each diffuser * Controlled by one thermostat

Answer 121

* Combination of two single duct systems, one for hot air, and one for cold air * Two streams are joined at a mixing box controlled by a thermostat in the zone

Answer 122

• Can heat and cool at the same time • Constant airflow volume • Good for perimeter zones • Easy to install • Good for linear buildings

Answer 123

* Twice as much ductwork (one to heat, one to cool) * Both boiler and chiller have to run all the time * The most energy is consumed with this system large fans) * noisy distribution

Answer 124

* Hot and cold air produced * Each room has a thermostat which mixes air in box before entering room * Common in hospitals * Mostly replaced by VAV systems

Answer 125

* Like a Double Duct system, but the mixing box is in the mechanical room * Premixed air is sent to each zone

Answer 126

* Efficient with a few zones * Separate duct runs, nothing is shared * Easy to sub monitor

Answer 127

* Lots of ductwork is required * Not efficient with many zones or non-square building

Answer 128

* Good for mall spaces where each tenant has control * Good for square building plans with few zones * Used in medium sized buildings

Answer 129

Variable Air Volume * Air is heated or cooled at a central location and distributed through a single duct. * Thermostat controls a damper at each zone to control the volume of conditioned air into that space.

Answer 130

* Can heat and cool different zones at the same time * Most common and efficient system * Saves energy because it doesn’t have to run peak all the time

Answer 131

* Can’t heat and cool different rooms in the same zone at the same time * A maintenance nightmare! * Requires a lot of interstitial space

Answer 132

* Can be single or multiple single duct systems * A zone can be one or many rooms * System is set to handle hottest or coldest room and rest adjust * Used in large buildings where temp regulation is required

Answer 133

• A self contained unit where air comes directly in from the outside, conditioned and sent into the space

Answer 134

• Use when ducts are impracticable to run • Each unit can have it’s own utility bill

Answer 135

• One unit is required for each zone

Answer 136

* Can run on just electric, but can also connect to hot/cold piping * They’re the units you see in big box stores

Answer 137

* Return air and fresh outside air are combined and cooled and dehumidified * Distributed in constant volume at a low temperature

Answer 138

* Humidity and temperature can be controlled * Ducts are smaller * Fan horsepower is lower

Answer 139

• Uses more energy because primary air volume needs to be cooled most of the time and reheated

Answer 140

* Terminal: equip. located near conditioned space * Zone: coils are located in ducts to serve an entire zone * Economizer Cycle: outside air can be used when temps are low enough

Answer 141

* Air is supplied to a building under high pressure/ velocity to each induction unit * Outside air is mixed with recirculated conditioned air

Answer 142

• Ducts are smaller

Answer 143

* Workbestin perimeter rooms of multi story multi room buildings * Need extra distribution for water

Answer 144

• Perimeter zoned areas: schools, offices, labs

Answer 145

* single supply and return pipe * hot water is circulated through each register and back to the pipe

Answer 146

* Low initial cost • Simple * Can be combined with a forced air system, or stand alone

Answer 147

• Can’t go very far because water temp drops • Can only heat or cool at one time • first register will be hot, the next a little cooler, etc

Answer 148

• Like a Single Pipe System, but separate supply and return pies are used

Answer 149

* Doesn’t put used water (that’s cooler) into the supply line for the next register * Can be combined with forced air system, or stand alone

Answer 150

• Can only heat or cool at one time

Answer 151

• Like a 2 Pipe system, but both hot and cold water are mixed in a common return pipe

Answer 152

* Can heat and cool at the same time * Can be combined with forced air system, or stand alone

Answer 153

* Mixes cold and warm water in return pipe * Less efficient than a two/four pipe system

Answer 154

• Like (2) two pipe systems, but there’s one for hot and one for cold

Answer 155

* Can heat and cool at the same time * Can be combined with forced air system, or stand alone

Answer 156

more expsensive due to piping

Answer 157

* Combination Hydronic Four Pipe system and constant air volume that can heat and cool at the same time * A boiler and chiller each attached to a two-pipe system AND ductwork for the supply air

Answer 158

* One of the most efficient systems * Versatile because it can provide heating and cooling simultaneously * Sends clean conditioned air through a single duct * A fan blows air over a hot or cool coil in each room * Can be just used for ventilation without heating/ cooling activated

Answer 159

• High initial cost • Highest installation cost because there’s ductwork and plumbing involved

Answer 160

• Water is circulated through the building, each zone has a heat pump and fan and short ducts that recalculates air within that zone * Each zone has its own heat pump and fan * Pump either removes heat from water and blows it into a room or removes heat from a room and into the water

Answer 161

• Good efficiency • Reduces extensive ductwork • Returns over 200% its electrical input when outdoor temp is above freezing

Answer 162

• High initial cost • May need chiller to cool water if all zones are cooling simultaneously • May need a boiler to reheat up water

Answer 163

outdoor air is used when it’s cool enough (about 60oF), reducing the energy required for refrigeration • It’s a mechanical substitution for an open window • Still better than nothing...and filtered air improves indoor air quality • As temperature drops outside, less fresh air is introduced because it has to be heated

Answer 164

use two condensers that operate based on the heating or cooling needs of the building • Efficiency is having varying sized chillers and operating the best sided chiller for the load

Answer 165

commonly powered by gas, higher initial cost, but can be more efficient for buildings in areas where electricity costs are high and low cost heat sources like steam are available

Answer 166

more efficient absorption chiller powered by hot water from standard flat plate solar collectors • Water sully can be from 175oF - 195oF • operation costs can be less than compressive type chillers

Answer 167

heat water by passing hot gases (by way of flue gases containing sensible and latent heat) through water • Heat exchanger on the combustion chamber reclaims any heat lost in chamber. • Good for applications where hot water is needed constantly

Answer 168

recovers sensible and latent heat that preheats the cold water entering the boiler • This heat would typically be discharged to the atmosphere • Flue gases are also cooled enough to achieve condensation

Answer 169

air distribution systems where supply air originates at the floor and rises to return in grilles int eh ceiling • Improves indoor air quality and energy savings • Most systems use an access floor system for duct work

Answer 170

heating and cooling systems that uses a series of heat pumps for different zones in the building • Water loop is maintained at a temperature range of 60o - 90oF and can simultaneously heat or cool zones with no additional energy • Reduces piping costs for 2 and 4 pipe systems

Answer 171

uses water, ice, or rock beds to store excess heat or coolness for use in the future • Takes advantage of temperature swings and off-peak energy consumption to manage buildings energy needs

Answer 172

must have two separate ducts for incoming air and exhaust air separated by a thin heat transfer wall

Answer 173

transfer heat through a heat exchanger wheel with small opening where air passes through. Latent and sensible heat is transferred

Answer 174

hot exhaust air passes over the heat pipe and vaporizes a refrigerant inside the pipe, which passes to the area of cool incoming air. • As the refrigerant condenses, it gives off heat, warming the incoming air. • Outgoing and incoming streams must be adjacent to each other

Answer 175

use water or other liquid to exchange heat • Advantage is incoming/exhaust air streams don’t need to be adjacent to each other • Energy ranges from 50 - 70%

Answer 176

used a double paned glass over another pane of glass on the interior where air is drawn up between the inside pane and main window unit and is extracted into the return air system • Eliminates the need for a perimeter heating system

Answer 177

heat or cool air by circulating it in pipes buried in the ground • Can only be used for low-rise buildings and becomes inefficient if long runs are involved.

Answer 178

cooling tower

Answer 179

condenser pump

Answer 180

humidifier

Answer 181

evaporative chiller

Answer 182

compressor

Answer 183

air handling unit

Answer 184

compressive refrigeration unit

Answer 185

modulating dampers

Answer 186

air filter

Answer 187

pre heater

Answer 188

finned cooling coil

Answer 189

turning vanes: reduces friction at corners

Answer 190

converntional turns: reduces friction at corners

Answer 191

splitter vanes: use where duct branches off for flow control

Answer 192

The American Society of Heating, Refrigerating, and Air Conditioning Engineers

HVAC Flashcards

(223 cards)