HVAC Flashcards
stWhat is this and what does it do?
opposed-blade/ balancing. It regulates flow of air
What boiler component is the arrow pointing to?
Burner
What boiler component is the arrow pointing to?
Access door
What is the arrow pointing to?
Breeching connect to chimney allows hot gases to pass through to the outside of the building
What is the arrow pointing to?
Firebrick or other fire resistant material
What is the arrow pointing to?
Combustion Chamber
What are the arrows pointing to?
A. steam or hot water
B. cast iron boiler section
A small one-story building in a temperate climate has been design with its long side oriented south. If a southern view is not a concern, the best passive solar heating method would be A. direct gain space B. Trombe wall C. greenhouse D. convection loop
B. Trombe wall If view is a consideration, a direct gain space, greenhouse, pr convective loop using mass in teh flooring and wall materials would be a better choice.
The stored heat in a Trombe wall is circulated by what means?
convection
What is the primary disadvantage of a Trombe wall?
Trombe wall are most effective when oriented south and situated behind glass. however, they block potential views and block glazing that could be a window.
True or False: Hydronic systems can be combined with forced air systems
True
COP Stands for: a. Creative Office Plan b. Coefficient Of Photovoltaic’s c. Coefficient of Performance d. Commissioning is an Organized Process
c. Coefficient of Performance
True of False: An evaporative chiller and a cooling tower are not the same thing.
False
Duct sizes are given in: a. Square feet of cross sectional area b. Square yards of cross sectional area c. Square inches of cross sectional area d. Square cubits of cross sectional area
c. Square inches of cross sectional area
In duct sizing, the friction loss is expressed in_____ this is also known as Static Head. a. Inches of Freon per 100 feet b. Inches of water per 10 feet c. Inches of water per 100 feet d. Inches of cool-aid per 1000 feet
c. Inches of water per 100 feet
What system automatically adjusts heating or cooling output and distributes the air between various zones as required? a. Multi-zone system b. Dual duct system c. Automatic thermal control system d. 4 pipe system
c. Automatic thermal control system
A centrifugal fan is also called a: a. Circular fan b. Squirrel cage blower c. Centripetal fan
b. Squirrel cage blower
Gray water is NOT derived from which of the following? a. Lavatories b. Roof drains c. Effluent d. Swales
c. Effluent
What does a pressure relief valve do for a boiler?
Relieves excess system pressure. Usually set at 30 psi
Melting ice consumes A. enthalpy B. sensible heat C. dew point temperature D. latent heat
D. latent heat The addition of sensible heat is what raises the temperature, but at 32 deg F the addition of more heat no longer immediately raises the temperature more. Instead, the added heat serves to melt the ice, and the temperature doesn’t rise again until the ice is melted.
Which HVAC system would be the most appropriate choice for a hospital? A. multizone B. high velocity dual duct C. variable air volume D. fan coil with supplementary air
A. fan coil with supplementary air A system that exhausts all return air would be the best choice. A fain coil with supplementary air would satisfy this requirement. All other systems listed return room air to the main AHU where some if it is reused.
Which of the following contributions to indoor air quality can be controlled by the HVAC system? (choose 4) A. outgassing B. air change effective ness C. VOC content of building materials D. carbon dioxide levels E. humidity F. mold growth
BDEF
1 ton of air conditioning = ____Btu/hr?
12,000
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
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
Which of the following energy sources would be the most economical option for heating a small reatil building in Washington state?
A. electricity
B. natural gas
C. oil
D. steam
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.
Which of the following have a significant effect on heat gain?
I. motors
II. sunlight
III. people
IV. flourescent lighting
V. humidity
A. II, III only
B. II, III, V
C. I, II, III, iV
D. I, II, III, IV, V
C. I, II, III, iV
Humidity does not affect heat gain.
In calculating solar heat gain, what value must be known in adition tot eh area of the glass?
A. mean radiant temperature
B. design cooling factor
C. equivalent temperature difference
D. coefficient of heat transfer
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.
Select the INCORRECT statement.
A. relative humidity is the best measure of thermal comfort
B. People feel more comfortable in the winter if the MRT is high
C. There are differences in comfort level among different cultural groups
D. The range of comfortable dry-bulb temperatures is depndent on air movement
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.
A developer in a midsize Arizona city is planning to build a small shopping mall for resale. The one story mass will consist of 40,000 sq ft of rentable area surrounding a small enclosed courtyard. Existing utilities adjacent to the sire include water, sanitary sewer, storm sewer, natural gas, and electricity. Which three of the following factors would be the most important in the selection of an HVAC system for this project?
I. flexibility
II. climatic zone
III. economics
IV. the tenant’s preference
V. building scale
A. I, II, V
B. I, III, IV
C. II, III, IV
D. II, III, IV
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.
A sling psychrometer is primarily used to measure what?
wet buld temperature
The psychrometric chart CANNOT be used to
A. plot the comfort zone
B. design HVAC
C. determine optimum ventilation rates
D. determine the point of water condensation
C. determine optimum ventilation rates
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.
A building in a temperate climate will have some areas that require cooing and others that require heating at the same time. To minimize energy use, the best devices to employ are
A. energy recovery ventilators
B. heat pipes
C. recuperative fuel economizers
D. water-loop heat pumps
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.
In what situations do energy recovery ventilators work best?
In climates wehere the difference between indoor and outdoor air temperature is high.
A seven story office building is to have a variable air volume system. The building will have 105, 00 sq ft of net space and an estimated 126, 00 sq ft of gross area. About how much space should be allowed for HVAC systems?
A. 2500 sq ft
B. 3800 sq ft
C. 6300 sq ft
D. 7600 sq ft
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.
Select the incorrect statement
A. A health center would probably use no. 4 or no. 5 fuel oil
B. Heat pumps rely on solar energy more than on electricity
C. natural gas has a higher heating value than does propane
D. electricity is not a good choice for poewring boilers in remote areas
C. natural gas has a higher heating value than does propane
A main trunk duct is to be placed in the interstitial space above a suspended ceiling and below the structural framing. The space is not constricted. Assuming equal capacities, which of the following shapes of ducts would be best used?
A. rectangular, with the long dimension horizontal
B. rectangular, with the long dimension vertical
C. square
D. round
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.
A
3413 Btu/kWh
B
- easy to install and control
- simple operation
- flexible zoning
- little space required
C
most expensive type, especially for high heating loads
D
2500 Btu/kWh
E
portable and good for remote areas
F
not as clean burning as natural gas
G
1050 Btu/kWh
H
Most efficient fossil fuel, clean burning
I
can’t be used in remote areas
J
137,000-141,000 btu/gal
K
portable and storable
L
- wide price flucuation
- burning equipment needs lots of maintenance
- must be stored securely
A standard gas furnace has all the following EXCEPT
A. a flue
B. a damper
C. a combustion chamber
D. filters
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.
An ecomomizer cycle
A. only cools as much chilled water as required by the demand load
B. uses outdoor air to cool a building
C. automatically reduces the amount of time the compressor runs
D. uses air and water to cool the condenser coils
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
Which of the following can produce a change in state?
A. sensible heat only
B. latent heat only
C. sensible and latent heat
D. none of the above
B. latent heat only
Air barriers are designed to stop infiltration and exfiltration caused by all of the following EXCEPT
A. wind pressure
B. stack pressure
C. HVAC pressure
D. vapor pressure
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.
Which of the following strategies would effectively reduce the noise caused by a duct system without reducing airflow?
A. Specify duct liners for all supply and return ducts
B. Specify 90 bends in short duct runs
C. Provide an active noise-canceling system emitting out-of-phase noise
D. Specify fiberglass baffles
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.
What are boiler flue conomizers?
They achive heat transfer by passing the hot gases in a boiler’s stack through a heat exchanger, thus preheating the incoming boiler water.
What are runaround coils?
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
In what types of buildings are economizers cycle very effective?
Buildings with high internal gains because they need cooling even when the outdoor temperature is chilly.
A ______ mixes both the hot and cold in a common return pipe.
3 pipe
Where are ground coupled heat exchangers used?
Low rise buildings
What are the disadvantages of ground coupled heat exchangers?
Long runs of pipes are required for the system
What is building commissioning?
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
What is the ideal temperature of outdoor air, to be used for economizer?
60 deg F
What is the dual condenser chiller method?
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
What is a direct contact water heater?
Heats water by passing hot gasses directly through water
Where is a direct contact water heater ideally used?
Where there is a continuous demand for hot water (food processing, laundries, industrial purposes)
What is a recuperative boiler
Device that recovers the sensible and latent heat from the high heat of exhaust flue gases that would normally be discharged to the atmosphere.
What is displacement ventilation?
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
What is a water loop heat pump?
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.
At what temperature is a water loop heat pump maintained?
Between 60-90 deg F
What is thermal heat storage?
Uses water, ice, or rock beds to store excess heat or coolth for use at a later time
What are energy recovery ventilators, also called air-to-air heat exchangers
Devices that reclaim waste energy from the exhaust air stream and uses it to condition incoming fresh air
What are the 3 devices used to make air-to-air heat exchange?
Flat pipe recovery units, energy transfer wheels, heat pipes
What are the 3 conidtions that should be met when using energy recovery ventilators
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
What are energy transfer wheels? What other name do they have?
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
Where are energy transfer wheels usually used?
Comercial buildings and hospitals
What are the advantages of energy transfer wheels?
They transfer latent heat as well as sensible heat
What is a heat pipe?
A self contained device that transfers sensible heat energy from hot exhaust air to cool outdoor air
What is the primary requirement for heat pipes to work?
Incoming and outgoing air streams must be adjacent
What are water to water heat exchangers?
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
What is an extract air window?
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
What are the advantages of all-water HVAC?
Easily controlled, efficient heat transfer
What is an upflow furnace?
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
What is a downflow furnace?
Works opposite of upflow furnace; used where duct work is located in a basement or crawlspace
What is simplest type of HVAC system?
Direct Expansion (DX) also known as incremental unit
How do you find the number of degree days?
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
What is a BTU?
Amount of heat need to raise a gallon of water 1 deg F
Which method of refirgeration more efficient aborption or compression?
Compression
What is a chiller?
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.
What is a terminal reheat system?
If the reheating equipment is located near the conditioned space
When is a variable air volume system used?
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
What are disadvantages of VAV?
Limited in ability to compensate for extremes in simultaneous heating an cooling demands
When is dual duct used? What are advantages?
- When more flexibility is required
- Can respond to varying requirements
What are disadvantages of dual duct HVAC?
- 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
What is a zone reheat system?
If reheating coils are located in ductwork to serve an entire zone
What are the advantages of a reheat system?
- Humidity and temperature can be carefully controlled
- low supply temperature equates to smaller duct sizes and lower fan horsepower
What are the advantages of a multi zone system?
Simultaneous heating and cooling in building
When is a multi zone system used?
Medium sized buildings or where a central mixing unit is located on each floor
What do these lines indicate on the psychrometric chart?
dew point
What do these lines indicate on the psychrometric chart?
dry bulb
What do these lines indicate on the psychrometric chart?
relative humidity
What do these lines indicate on the psychrometric chart?
wet bulb
“heat of fusion” is required to ……
….melt a solid
“heat of vaporization” is required to …
change a liquid into a gas
What are the 4 possible interations of radiadation? describe them?
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
Why are polished metal surfaces, such as shiny aluminum, used as radiant insulators?
They neither absorb not emit radiation readily
What is heat capacity?
Heat capacity is the amount of heat per unit mass required to raise the temperature by one degree F.
What are the four environmental conditions that allow heat to be lost? Describe them.
- 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.
- Relative humidity: the higher the relative humidty, the harder it is to achieve cooling through evporation
- Air velocity: air movement affects heat loss rate by both convection and evaporation.
- 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.
Full Load Hours:
the maximum output potential of a heating/cooling system in one hour
and is used to size HVAC equipment
Peak Heat Loss:
the amount of heat lost at design outdoor and indoor conditions which
must be made up by the HVAC system to maintain occupant comfort
Service Energy Efficiency Rating (SEER):
an HVAC energy rating
Insulators:
retard the flow of heat
Conductors:
encourage heat flow
Design Equivalent Temperature Difference (DETD):
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.
Design Cooling Load Factor (DCLF):
used for calculating heat gain through glazing,
takes int account glazing type, interior shading, and outdoor temperature
Cooling Load Temperature Difference (CLTD):
an equivalent temperature difference
used for calculating the instantaneous external cooling load across a wall or roof
Albedo:
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).
Conductivity:
the speed with which heat passes through a material. Metals are high, and soils/sand are low.
Economizer:
equipment that permits the use of outdoor air instead of refrigeration units for building cooling when conditions are right
Enthalpy Economizer:
evaluates both temperature and humidity, mixes appropriate outdoor/indoor air to achieve comfortable conditions without cooling
Hypocausts:
gravity heating systems used by the romans to heat public baths and private houses
Ton:
amount of cooling required to convert a ton of water to ice in a 24 hour period, equal to 12,000 BTUH
Negative pressure problems include:
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
The national consensus standard for outside air ventilation is
ASHRAE Standard 62.1-2001
Smoke Pencil:
tool used to identify drafts and air leaks, pull on the trigger and see how
smoke moves to show air movement
High Efficiency Particulate Arrestance (HEPA):
the highest efficiency option, typically found in special air cleanser for unusually polluted or IAQ demanding environments like hospitals
Particulate filters:
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)
Electrostatic Filters:
more money, but produce less air movement as two sets of chard plates attract dust. Are cleaned by washing off.
Absorption filters:
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
Air Washers:
sometime used to control bacteria growth and control humidity
Electronic air cleaners:
can pose a threat due to ozone production, but demand
less maintenance
Plant:
equipment that creates warm or cool water or air, typically in a mechanical room
Plenum:
typically the space above a suspended ceiling used to convey return air
Cooling Tower:
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.
Chiller:
used in hot climate with high cooling demands
Air Handling Unit (AHU):
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
Coefficient of Performance (COP):
a unitless number that is a rating of the efficiency of heating or cooling equipment
Integrated Part Load Value (IPLV):
single number figure of merit based on part load EER or COP expressing part load efficiency for air condition and heat pump equipment
Home Energy Rating System (HERS):
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.
Energy Efficiency Ratio (EER):
ration of net cooling capacity in BTUH to the total rate of electrical input in watts, under designated operating conditions
Furnace:
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
Boiler:
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.
Refrigerant types:
• 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
Compressive Refrigeration:
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
Refrigeration by Absorption:
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
Evaporative Cooling (Swamp Cooler):
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.
Single Duct System Advantages
• 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
Single Duct System Disadvantages
- 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
Single Duct System, where is it typically used?
- Typical residential system
- Common in buildings with large open spaces, few windows, uniform loads, like theaters, department stores, exhibition halls
What is a single duct system?
- 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
What is a double duct system?
- 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
Double Duct advantages
• Can heat and cool at the same time
• Constant airflow volume
• Good for perimeter zones
• Easy to install
• Good for linear
buildings
Double Duct disadvantages
- 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
Double Duct, where is it used?
- 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
What is a multizone system?
- Like a Double Duct system, but the mixing box is in the mechanical room
- Premixed air is sent to each zone
Multizone advantages
- Efficient with a few zones
- Separate duct runs, nothing is shared
- Easy to sub monitor
Multizone disadvantages
- Lots of ductwork is required
- Not efficient with many zones or non-square building
Mulitzone, where is it used?
- Good for mall spaces where each tenant has control
- Good for square building plans with few zones
- Used in medium sized buildings
What is a VAV system?
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.
Advantages of a VAV system?
- 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
disadvantages of a VAV system?
- Can’t heat and cool different rooms in the same zone at the same time
- A maintenance nightmare!
- Requires a lot of interstitial space
VAV System, where is it used?
- 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
What is a unitary HVAC system?
• A self contained unit where air comes directly in from the outside, conditioned and sent into the space
Advantages of unitary system
• Use when ducts are
impracticable to
run
• Each unit can
have it’s own utility bill
Disadvantages of unitary system
• One unit is required for each zone
Unitary system, where is it used
- Can run on just electric, but can also connect to hot/cold piping
- They’re the units you see in big box stores
What is a Reheat (Constant Volume) System
- Return air and fresh outside air are combined and cooled and dehumidified
- Distributed in constant volume at a low temperature
Advantages of Reheat (Constant Volume)
- Humidity and temperature can be controlled
- Ducts are smaller
- Fan horsepower is lower
Disadvantages of Reheat (Constant Volume)
• Uses more energy because primary air volume needs to be cooled most of the time and reheated
Types of Reheat systems (constant volume)
- 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
What is an induction system?
- Air is supplied to a building under high pressure/ velocity to each induction unit
- Outside air is mixed with recirculated conditioned air
Advantages of induction system?
• Ducts are smaller
Disadvantages of induction system
- Workbestin perimeter rooms of multi story multi room buildings
- Need extra distribution for water
Induction system, where is it used?
• Perimeter zoned areas: schools, offices, labs
What is a Hydronic Single Pipe?
- single supply and return pipe
- hot water is circulated through each register and back to the pipe
Advantages of single pipe hydronic
- Low initial cost • Simple
- Can be combined with a forced air system, or stand alone
Disadvantages of single pipe hydronic
• 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
What is Hydronic Two Pipe?
• Like a Single Pipe System, but separate supply and return pies are used
Advantages of hydronic 2 pipe
- 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
disadvantages of hydrinic 2 pipe
• Can only heat or cool at one time
What is Hydronic Three Pipe
• Like a 2 Pipe system, but both hot and cold water are mixed in a common return pipe
Advantages of hydonic 3 pipe
- Can heat and cool at the same time
- Can be combined with forced air system, or stand alone
Disadvantages of hydronic 3 pipe
- Mixes cold and warm water in return pipe
- Less efficient than a two/four pipe system
What is hydronic 4 pipe
• Like (2) two pipe systems, but there’s one for hot and one for cold
Advantages of hydronic 4 pipe
- Can heat and cool at the same time
- Can be combined with forced air system, or stand alone
Disadvantages of hydronic 4 pipe
more expsensive due to piping
What is a fan coil?
- 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
Advantages of a fan coil
- 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
Disadvantages of fan coil
• High initial cost
• Highest
installation cost because there’s ductwork and plumbing involved
Decribe a heat pump
• 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
Advantages of heat pump
• Good efficiency
• Reduces
extensive
ductwork
• Returns over
200% its electrical input when outdoor temp is above freezing
Disadvantages of heat pump
• High initial cost
• May need chiller
to cool water if all zones are cooling simultaneously
• May need a boiler to reheat up water
Economizer Cycle:
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
Dual Condenser Chillers:
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
Gas Fired Absorption Chillers:
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
Solar Powered Absorption Cooling:
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
Direct Contact Water Heaters:
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
Recuperative Gas Boilers:
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
Displacement Ventilation:
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
Water Loop Heat Pumps:
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
Thermal Energy Storage:
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
Flat-Plate Heat Recovery Units:
must have two separate ducts for incoming air and exhaust air separated by a thin heat transfer wall
Energy transfer wheels (enthalpy heat exchanger):
transfer heat through a heat exchanger wheel with small opening where air passes through. Latent and sensible heat is transferred
Heat Pipes:
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
Water to Water Heat Exchangers:
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%
Extract Air Windows:
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
Ground coupled heat exchangers:
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.
cooling tower
condenser pump
humidifier
evaporative chiller
compressor
air handling unit
compressive refrigeration unit
modulating dampers
air filter
pre heater
finned cooling coil
boiler
turning vanes: reduces friction at corners
converntional turns: reduces friction at corners
splitter vanes: use where duct branches off for flow control
What to arrows indicate on psychometric chart?
ASHRAE stand for what?
The American Society of Heating, Refrigerating, and Air Conditioning Engineers
