Term
|
Definition
occurs when the body is able to dissipate the heat and moisture it
produces naturally, and maintains normal body temperature.
Thermal balance must exist between body and environment. |
|
|
Term
|
Definition
the physical property that determines the direction of heat flow
between two objects placed in thermal contact |
|
|
Term
|
Definition
| a form of energy, movement at molecular or atomic level. manifested in materials by a rise of temperature, fusion, expansion, or evaporation. |
|
|
Term
| Thermal Comfort Variables |
|
Definition
Comfort is controlled by four variables: (dry-bulb) air temperature, (relative)
humidity, radiant temperature, and air speed. |
|
|
Term
|
Definition
a temperature representing the combined effect of ambient
temperature, relative humidity, and air movement on the sensation of warmth or
cold felt by the human body, equivalent to the dry bulb temperature of still air at 50%
relative humidity which induces an identical sensation. |
|
|
Term
| Psychrometric chart VARIABLES (7) |
|
Definition
Dry-bulb Temperature
% relative humidity
wet-bulb termperature
dew point
water vapor content
enthalpy
specific volume |
|
|
Term
| Psychrometric Chart VARIABLES - Dry-bulb temperature |
|
Definition
| the air temperature (ºF) indicated by a standard thermometer |
|
|
Term
| Psychrometric Chart VARIABLES - % relative humidity |
|
Definition
the amount of water vapor held in the air as a percent of the maximum amount of water vapor the air
can hold at a specific temperature (warmer air can hold more water vapor). Air simply acts as a transporter of water
vapor, not a holder of it. In fact, water vapor can be present in an airless volume and therefore the relative humidity of
this volume can be readily calculated. The misconception that air holds water is likely the result of the use of the
word saturation which is often misused in descriptions of relative humidity. In the present context the word saturation
refers to the state of water vapor, not the solubility of one material in another |
|
|
Term
| Psychrometric Chart VARIABLES - Wet-bulb temperature |
|
Definition
the temperature (ºF) indicated by a thermometer with a wet wick attached to its bulb; the wick is
located in a moving air stream to encourage evaporation. The wet-bulb temperature is the minimum temperature which
may be achieved by purely evaporative cooling of a water-wetted ventilated surface. For a given parcel air at a known
pressure and dry-bulb temperature, wet-bulb temperature corresponds to unique values of relative humidity, dew point
temperature, and other properties. For air that is less than saturated (100 percent relative humidity), the wet-bulb
temperature is lower than the dry-bulb temperature; and the dew point temperature is less than the wet-bulb
temperature.
Cooling of the human body through perspiration is inhibited as the wet-bulb temperature (and relative humidity) of the
surrounding air increases in summer. Other mechanisms may be at work in winter if there is validity to the notion of a
"humid cold."
Lower wet-bulb temperatures in summer can translate to energy savings in air-conditioned buildings due to:
Reduced dehumidification load for ventilation air
Increased efficiency of cooling towers |
|
|
Term
| Psychrometric Chart VARIABLES - Dew point |
|
Definition
the air temperature at which condensation begins. (DPT) is that temperature at which a moist air sample at the
same pressure would reach water vapor saturation. At this saturation point, water vapor would begin to condense into
liquid water fog or if below freezing, solid frost, as heat is removed. The dew point temperature is measured easily and
provides useful information, but is normally not considered an independent property. It duplicates information available
via other humidity properties and the saturation curve. |
|
|
Term
| Psychrometric Chart VARIABLES - Enthalpy |
|
Definition
the total heat contained in an air/water vapor mixture (BTU per pound of air). Enthalpy is the sum of sensible plus
latent heat: heat content per unit mass. Lines of enthalpy are parallel to lines of constant wet bulb temperature. |
|
|
Term
| Psychrometric Chart VARIABLES - Specific volume |
|
Definition
the number of cubic feet that 1 pound of air occupies (at 70 °F & 14.7 psi). It is also called Inverse
Density, is the volume per unit mass of the air sample. The units are cubic feet per pound of dry air. |
|
|
Term
| Psychrometric Chart VARIABLES - Water vapor content |
|
Definition
he weight of water vapor held in 1 pound of air (weight is measured in grains, 1 grain = 1/7,000 of a
pound) |
|
|
Term
| Study finding characteristics of air/water vapor using psychometric chart (MEEB 282-283) |
|
Definition
|
|
Term
|
Definition
| a subjective experience, lack of heat |
|
|
Term
|
Definition
energy is transmitted between two bodies by a third medium:
circulation of a fluid. Primarily dependent on air motion, air temperature, humidity. |
|
|
Term
|
Definition
energy is transmitted between two bodies by direct contact. Primarily
dependent on surface temperature. |
|
|
Term
|
Definition
energy is transmitted between two bodies by energy waves. Primarily
dependent on orientation of the body, surface temperature. Radiation uses photons
to transmit electromagnetic waves through a vacuum, or translucent medium. |
|
|
Term
|
Definition
energy is transmitted between two bodies by vapor. Primarily
dependent on humidity, air motion, air temperature. |
|
|
Term
|
Definition
time rate of heat flow through a unit area of a given material
of unit thickness when the temperature difference across the thickness is one unit of
temperature. |
|
|
Term
|
Definition
| time rate of heat flow through a unit area of a given material of a given thickness when the temperature difference across the thickness is one unit of temperature. |
|
|
Term
|
Definition
reciprocal of thermal conductance, expressed as the
temperature difference required to cause heat to flow through a unit area of material
of a given thickness at the rate of one heat unit at a time. |
|
|
Term
|
Definition
R-value: a measure of the thermal resistance of a given material, used to specify
the performance of thermal insulation.
U-value: measure of the thermal transmittance of a building component or
assembly, equal to the reciprocal of the total R-value of the component or assembly. |
|
|
Term
| Thermal transmittance or Coefficient of heat transfer |
|
Definition
Time rate of heat flow
through a unit area of building component or assembly when the difference
between the air temperatures on the two sides is one unit of temperature. |
|
|
Term
|
Definition
Batt insulation, rigid board insulation, foamed in-place, loose-fill, reflective
insulation, dead air space. |
|
|
Term
|
Definition
How much heat can be absorbed or store in a material , compared to
the storage capacity of water.
More heat energy is required to increase the temperature of a substance with high
specific heat capacity than one with low specific heat capacity. For instance, eight
times the heat energy is required to increase the temperature of an ingot of
magnesium as is required for a lead ingot of the same mass. The specific heat of
virtually any substance can be measured, including chemical elements, compounds,
alloys, solutions, and composites. |
|
|
Term
|
Definition
British Thermal Unit
Amount of heat needed to raise the temperature in a pound of water by one degree
ºF. |
|
|
Term
| Specific Heat of brick, soft wood and trombe wall |
|
Definition
Brick 0.22
Soft wood 0.39
Trombe wall |
|
|
Term
|
Definition
| the ability of a surface to emit heat by radiation |
|
|
Term
|
Definition
| the extent to which it diffusely reflects light from the sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation. It is a unit-less measure indicative of a surface's or body's diffuse reflectivity |
|
|
Term
| Know how to calculate U-Value |
|
Definition
Kaplan 49-53
MEEB: 185-187. Sdd R-value of all materials and then set the sum under 1. Eg. Total R-value = 18.3 (sum of material r-values): U-value = 1/18.3 |
|
|
Term
|
Definition
|
|
Term
| R-value of dry earth, 8" concrete block, Polyurethane insulation, and air spaceAluminum foil facing air space |
|
Definition
dry earth - 0.2,
8" concrete block - 2.0,
Polyurethane insulation - 6.0,
air space where Aluminum foil facing air space - 3.0 |
|
|
Term
| Outdoor air - code and cost |
|
Definition
Outdoor air must be provided in buildings for health reasons as mandated by code.
Outdoor air is expensive because it costs a lot to heat it in winter and cool it in summer. |
|
|
Term
|
Definition
air brought into a building by fans or openings. In large buildings with few
operable windows, ventilation is necessary to assure healthy and odor free conditions. The quantity
of ventilation air brought into a building is determined by building codes according to the number of
occupants and their activities. |
|
|
Term
|
Definition
flow of air from outside to inside via cracks or openings in the building envelope.
Kaplan: 54-55
Because it's expensive to heat or cool outdoor air, efficient buildings conserve energy by:
Careful control of fresh/outdoor air quantities. Using heat exchangers to temper outdoor air. Using an
economizer, instead of refrigeration equipment. |
|
|
Term
|
Definition
equipment that permits the use of outdoor air instead of
refrigeration units for building cooling when outdoor temperature conditions are right. Even better is
an enthalpy controlled economizer which evaluates both outdoor temperature and humidity, and then
mixes appropriate quantities of outdoor and indoor air to achieve comfortable conditions without
cooling. |
|
|
Term
|
Definition
ransfer heat from exhaust air to incoming outdoor air.
Heat exchangers permit building operators to use outdoor air for odor control without paying the full
price of heating or cooling it. |
|
|
Term
| Infiltration - value and calculation |
|
Definition
Residences and small buildings often rely on infiltration to provide all
necessary outdoor air; unusual requirements like smelly cooking are taken care of by opening doors
15
and windows. Quantifying building infiltration is difficult because of the many variables involved. |
|
|
Term
| Heat direction - when cold |
|
Definition
When the weather is cold, heat travels
from inside (high) to outside (low). |
|
|
Term
|
Definition
calculated to determine the size of heating
equipment. Heat leaves a building by only two routes: the building's skin conducts
heat to colder outdoor surroundings, and cold outdoor air replaces heated building
air. |
|
|
Term
|
Definition
All parts of a building's skin lose heat to colder surroundings, and the rate of heat loss is determined by the U value of the skin. U is the number of STUH conducted through 1 sqft. of a construction when a 1°F temperature difference drives heat flow. Conducted heat losses are given by the formula:
q\c/ = UA x delta T
U= Conductance value in BTUh/sqft./°F
A= Area in sqft.
ΔT= Temperature Difference indoor-outdoor
Results in = Rate of heat flow, BTU per Hour.
16
Since peak heat loss is used to size heating equipment the outdoor temperature is selected for a typical cold winter day. |
|
|
Term
A roof covers an area 40 ft wide and 80 fl long. With heavy insulation, the resistance has been
l l t d 38 ft2 calculated as ft2-hr-OFlBtu and the design equivalent temperature difference is 44°F. The design
temperature is - 5°F and it is desired to maintain a 70 aF indoor temperature. The heal loss through
the roof is most nearly |
|
Definition
Solution The design equivalent temperature difference has no bearing on the solution to this problem.
First, calculate the U value, which is the reciprocal of the R-value.
U= 1/38 ft2-hr- ºF /Btu= 0.026 Btu/ft2-hr- ºF
Temperature difference:
ΔT=T indoor-Tdesign=70-(-5)= 75 ºF
Roof area: 40x80=3,200 f2
Heat loss:
q=U A ΔT= (0.026 Btu/ft2-hr- ºF)(3,200 ft2) (75 ºF)=6,240 Btu/hr. |
|
|
Term
|
Definition
a day whose mean temperature is one degree below a reference
temperature of 65°F. Two degree days may be a single day with a mean
temperature of 63° (two degrees below 65°) or two days at 64°. |
|
|
Term
|
Definition
a day colder than 98% of the days experienced in the area. Is another
way to size equipment |
|
|
Term
| energy flow rate over a period of time formula |
|
Definition
qc = U (A)24 (DD)
This formula allows us to compare alternatives over a period of time
MEEB: 254-258
Kaplan: 53-54 |
|
|
Term
| three added factors to heat gain |
|
Definition
| sun, internal loads, and latent heat |
|
|
Term
|
Definition
can radiate up to 350 BUTH on each square foot it reaches
radiant energy passes easily through glass
a specific time must be used to estimate solar gain |
|
|
Term
| Solar Heat gain through roofs and walls |
|
Definition
can also increase the temperature of roofs
and walls above ambient air temperature, and heat flow into the conditioned space is
increased as a result. |
|
|
Term
| Heat gain - Internal Loads |
|
Definition
people, lights, appliances, motors, and food preparation
People and cooking can add both sensible (dry) and latent (wet) heat
motors and lights add only sensible heat
HVAC equipment must remove internally
generated heat to maintain comfortable interior conditions |
|
|
Term
|
Definition
exists in the water vapor carried by air
as air temperature increases
its ability to carry water vapor increases
Significant air conditioning capacity is required to
dehumidify moist outdoor air but cool dry air is necessary for comfort
A ton of air conditioning is equivalent to 12,000 Btu/hr. This is the amount of refrigeration
needed to make one ton of ice per day from 32°F water |
|
|
Term
|
Definition
| tilt of the earth's axis, |
|
|
Term
| Passive Solar Heating - Critical factors |
|
Definition
site and location of the building, climate, design and construction,
solar orientation, fenestration and shading elements, and the use of heat sinks.
Key word: integration of these principles. |
|
|
Term
|
Definition
| a line joining an object and the sun; it becomes the direct normal intensity when it is perpendicular to the object and achieves maximum intensity. |
|
|
Term
|
Definition
radiant heat gain
The main source of heat gain into a building
Roofs receive the majority of the solar radiation |
|
|
Term
|
Definition
sheets separated by a sealed air/gas space (fused edges or
spacer edged) |
|
|
Term
|
Definition
insulating glass that has coatings in one or various sheets of glass and the coating
reflects radiation while light can penetrate
Coating a glass surface with a low-emittance material reflects a significant amount of the
radiant heat, thus lowering the total heat flow through the window. Low-E coatings are
transparent to visible light, and opaque to infrared radiation. Different types of Low-E
ti coatings have been designed to allow different levels of protection against solar gain. |
|
|
Term
Low-e side for To keep the sun's heat out of the house (for hot climates, east and west-facing windows,
and unshaded south-facing windows), |
|
Definition
low-E coating should be applied to the outside
pane of glass |
|
|
Term
low-e side if windows are designed to provide heat energy in the winter and keep
heat inside the house (typical of cold climates) |
|
Definition
the Low-E coating should be applied to the
inside pane of glass |
|
|
Term
| borosilicate glass propserties |
|
Definition
|
|
Term
The heat gain for a building has been calculated at
144,000 Btu/hr What size compressive refrigeration machine |
|
Definition
Size = 144000/12000 = 12 tons.
A ton of air conditioning is equivalent to 12,000 Btu/hr
This is the amount of cooling capacity needed for the facility, and shows the direct application of
heat gain calculations. |
|
|
Term
|
Definition
significant contaminant that affects indoor air quality
Radon gas from
natural sources can accumulate in buildings, especially in confined areas such as
the basement
can be found in some spring waters and hot springs.
Depending on how houses are built and ventilated, radon may accumulate in
basements and dwellings |
|
|
Term
|
Definition
Minimum Efficiency Reporting Value: a
measurement scale designed in 1987 by ASHRAE to rate the effectiveness of air
filters.
The scale is designed to represent the worst case performance of a filter when
dealing with particles in the range of 0.3 to 10 microns. The MERV rating is from 1
to 16. Higher MERV ratings correspond to a greater percentage of particles
captured on each pass |
|
|
Term
| Combustion heating - generates: |
|
Definition
carbon monoxide, breathable particulates, at times, nitrogen
dioxide |
|
|
Term
| Fireplaces v. wood stoves |
|
Definition
Fireplaces = terrible for heating because of heat loss through the chimney
Wood stoves are better, but air control is the key factor. Best ones: air comes only
from a controlled damper; door is gasketed.
Mainly work through radiant heat: Masonry/concrete as heat sinks.
Circulating stoves allow convection.
Placement in building is critical!
Wood storage is a major concern. |
|
|
Term
|
Definition
heats air. A fan is necessary to propel it. (Historic
buildings had gravity air heating.) Ductwork is used to guide its path.
It uses similar components than HVAC systems, so it is usually combined.
Requires;
Auto firing of oil/gas
Operational / safety controls
Blower / fan
Filter
Dampers and registers
Exhaust. |
|
|
Term
|
Definition
heats water. Water is circulated, and it is used to heat the served
spaces: it can be done via convection or radiation. |
|
|
Term
|
Definition
gravity air heating systems used by the Romans at public baths and
private houses. Spaces were built under the habitable areas supported by short
columns or pillars, to house furnaces, and allow hot air to circulate. Chases built in
the walls allowing hot air and combustion by-products from furnaces to also heat the
walls and escape out of flues in the roof Radiant heating and convection would
walls, roof. heat the spaces, without having combustion gases in the spaces. |
|
|
Term
hourly fuel consumption:
coal
electricity
natural gas
#2 fuel oil
wood |
|
Definition
coal: 14,600 BTU/lb
electricity: 3413 kW/h
natural gas: 1050 BTU/cu ft
#2 fuel oil: 141,000 BTU/gal
wood: 7,000 BTU/lb
fuel (gal or lb) h = qc (heat loss -BTU/h)/(BTU per gal or lb) (efficiency)
MEEB: 225 |
|
|
Term
heating means:
boiler -
convection -
radiation -
furnace - |
|
Definition
boiler - hydronic
convection - radiators, baseboards
radiation - floor/wall pipes
furnace - ducted air |
|
|
Term
|
Definition
Hot water is circulated to fin tube convectors or radiators. These allow cold air to be
heated.
Typically used in buildings where cooling is not needed, and ventilation can be
accomplished through windows or other means. They can be used to supplement
other systems.
Economical and simple to install and operate. Good comfort during heating season.
Space efficient, convectors are available in many shapes. Dampers, thermostatic
valves, zone pumps, and valves are some of the means to control the system. Low
tech! |
|
|
Term
|
Definition
| Water at station 5 will be cooler that 1. |
|
|
Term
| central loop with diverts/ branches |
|
Definition
valves can be used at each one to reduce
heat or to shut off heating to an area. Water at station 5 will be cooler that 1, but
less so, because water is not circulating through the convectors, but accepts water
from them |
|
|
Term
|
Definition
It provides the same water temperature to each
convector. Equal friction / equal flow is achieved by reversing the return, so each
convector has the same pipe run. Uses more pipe than series perimeter loop or central loop with diverts/ branches |
|
|
Term
| aqueduct second use and other Roman passive techniques |
|
Definition
Romans circulated aqueduct water through walls to cool their houses. Evaporative cooling was an
extended practice around the Mediterranean Sea |
|
|
Term
manually powered
rotary fan inventor |
|
Definition
| 2nd century Chinese inventor Ding Huan of the Han Dynasty |
|
|
Term
|
Definition
In 747, Emperor Xuanzong of the Tang Dynasty built the Cool Hall with water-powered fan wheels for
air conditioning as well as rising jet streams of water from fountains. |
|
|
Term
|
Definition
| used cisterns and wind towers to cool buildings during the hot season |
|
|
Term
|
Definition
In the 1600s Cornelius Drebbel demonstrated "turning Summer into Winter" for James I of England
by adding salt to water |
|
|
Term
| Benjamin Franklin and John Hadley |
|
Definition
In 1758, Benjamin Franklin and John Hadley confirmed that evaporation of highly volatile liquids such
as alcohol and ether could be used to lower the temperature of an object past the freezing point of
water. |
|
|
Term
|
Definition
In 1820 Michael Faraday discovered that compressing and liquefying ammonia could chill air when
the liquefied ammonia was allowed to evaporate. |
|
|
Term
|
Definition
| In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida |
|
|
Term
| commercial applications of air conditioning |
|
Definition
manufactured to cool air for industrial
processing rather than personal comfort. |
|
|
Term
| first modern electrical air conditioning |
|
Definition
In 1902 the first modern electrical air conditioning was
invented by Willis Haviland Carrier in Syracuse, NY.
controlled not only temperature but also humidity |
|
|
Term
| Larkin Company administration building |
|
Definition
1904 - first entirely air-conditioned modern office building on
record.... |
|
|
Term
|
Definition
In 1906, Stuart W. Cramer of Charlotte, NC was exploring ways to add moisture to the air in his
textile mill. Cramer coined the term "air conditioning." Willis Carrier adopted the term. |
|
|
Term
|
Definition
| created the first chlorofluorocarbon gas, Freon, in 1928 |
|
|
Term
| Compressive refrigeration |
|
Definition
based on the change of a gas to a liquid by mechanical
method. It is condensed.
The gas releases latent heat as it is compressed. This part of the system gets
hot.
As the liquid expands and vaporizes to a gas, it absorbs latent heat. That part of
the system gets cold. |
|
|
Term
| Four components of Compressive refrigeration |
|
Definition
| valve, evaporator coil, compressor, and condenser coil |
|
|
Term
|
Definition
direct expansion (DX) system, where the
evaporator is in direct contact with the air stream, so the cooling coil of the airside
loop is also the evaporator of the refrigeration loop. The term “direct” refers to the
position of the evaporator with respect to the cooling coil. |
|
|
Term
|
Definition
system that uses reversible refrigeration cycle to heat and cool a
facility. It “pumps” heat out in summer, and “pumps” heat in during winter. It uses
temperature differentials to gain energy savings. The heat pump is a normal
compressive cooling mechanism that can be reversed to provide heating.
For cooling, the interior heat is moved outdoors. Heating uses higher temperatures,
also outdoors, and using the inverse path, transfer that energy inside.
Note that the condenser and the evaporator switch roles, and the valve and the
compressor work in the opposite direction.
Heat pumps are efficient in moderate temperatures, or when there is access to a
medium that has a stable temperature or a differential.
(Single package, or split, air-to-air, water-air, ground-air) |
|
|
Term
|
Definition
Absorption refrigeration uses the physical property of certain saline solutions to
“suck” water vapor or moisture.
Creating vapor (evaporation) results in cooling.
Remember rubbing alcohol in your arms, and how its evaporation results in a
cooling sensation?
Salt used: Lithium Bromide.
Heat is used to re-generate the saline solution. |
|
|
Term
|
Definition
Vapor is pulled from the evaporator by the “dry saline” (unsaturated) which
becomes saturated.
The evaporation lowers the temperature which can be used to extract heat from a
space.
Water is circulated from the system allowing the removal of heat and its release to
the exterior.
Heat sources can be the sun, gas, or waste heat.
Double effect, and triple effect units add other evaporators/ condensers to increase
the temperature drop, and increase the efficiency.
Not as efficient as a compression unit. Chillers require a lot more space.
Three LOOPS or circuits: purple, grey, and red/blue. |
|
|
Term
| Local HVAC systems advantages |
|
Definition
Attractive when differences in schedule, function, and placement in the building are
significant.
Minimizes distribution (water or air)
Greatly simplifies controls.
Breakdowns only affect part of the building |
|
|
Term
| Local HVAC systems disadvantages |
|
Definition
| Energy, maintenance, air quality, noise |
|
|
Term
| Local HVAC systems definition and types |
|
Definition
Independent, self-contained pieces of equipment are located in different places of
the building.
wall units
roof top/single-package
split unit |
|
|
Term
| Central systems advantages |
|
Definition
Attractive when similarities in schedule, function, and placement in the building are
significant.
Saves energy, as the system is more efficient.
Ease of centralized maintenance
Air quality is easier to control
Noise is easier to control
Distribution is very important. (Water or air) Large trees. |
|
|
Term
| Central systems disadvantages |
|
Definition
Conditioning is provided by large equipment situated in one or more mechanical
spaces. |
|
|
Term
| Central systems definition and types |
|
Definition
Room / space, complex controls, breakdowns affect part of the building
all-air single duct, constant air volume
all-air multi-duct, constant air volume (multi-zone)
all-air, single duct, variable air volume
air and water induction system
all-water, fan coil terminals
all water, closed loop heat pumps |
|
|
Term
|
Definition
Air occupies a larger volume of space, holds much less heat per unit of volume than
water; at high velocities, noise can result.
Water uses less space, so the refrigeration components can be separated from the spaces. |
|
|
Term
|
Definition
Q = AV
Q - air volume in cfm
A - area (section) of duct
V - velocity
factor: friction loss |
|
|
Term
|
Definition
| Air moves because of a pressure differential. Air is a gas, so it is compressible |
|
|
Term
|
Definition
from 300 to 200 feet per minute Water is moved by pumps that also create
a pressure delta. Water systems require the use of heat exchangers or coils. |
|
|
Term
|
Definition
| inefficiency due to turns, and contact with duct walls |
|
|
Term
| all-air, single duct, CAV |
|
Definition
Air is treated (heated or cooled, mixed with fresh air, filtered, de-humidified) at a
central source.
Supply and return are a simple circuit.
A master (single!) thermostat controls the system for all the building. |
|
|
Term
| all-air, single duct, CAV applications |
|
Definition
Buildings with large open spaces, uniform loads, few windows, uniform scheduling:
theaters, department stores, exhibition halls. |
|
|
Term
| all-air, single duct, CAV components |
|
Definition
| A packaged system (central or split) could provide all parts, joining boiler, chiller, and air handler. |
|
|
Term
|
Definition
Each zone has a centrally conditioned, different temperature air supply, and
these are separated.
Chiller and boiler work at the same time, and hot and cool air are mixed before
traveling to each zone, or re-heat coils at the fan room (air handler) regulate the
temperature to accommodate independent needs. Single return system.
Require larger space, specially for ductwork. |
|
|
Term
| multi-duct system applications |
|
Definition
Medium sized buildings, or large buidlings with separate mechanical rooms for
segments of the facility. |
|
|
Term
| single duct, variable air volume |
|
Definition
Similar to single/constant, but with significant differences:
Air is treated (heated or cooled, mixed with fresh air, filtered, de-humidified) at a
central source. Air volume flow is controlled, instead of air temperature.)
Supply and return are a simple circuit, but the building is separated in zones. Each
zone has separate controls. |
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Term
| single duct, variable air volume - applications |
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Definition
great system, widely used, and found in all type of buildings.
Versatile! |
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Term
| single duct, variable air volume - Disadvantages |
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Definition
| limited range of temperatures (heating and cooling simultaneously), scheduling. |
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Term
| single duct, variable air volume - Variations |
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Definition
Combined with a secondary system to provide perimeter supplement, to deal with
large differences of temperature. |
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Term
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Definition
pipe coil or electrical resistance that rises temperature before the
air is circulated to the zones, as needed. Allows a wider range of temperatures. |
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Term
| Secondary induction system |
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Definition
smaller high velocity ducts allow treated air to be
mixed with existing air at each zone, to reduce the size of the ductwork. |
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Term
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Definition
| heated and cooled air run parallel, and are mixed at each zone |
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Term
| air-water induction system |
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Definition
A high velocity, constant volume fresh air supply is brought to each terminal, where
it is forced to circulate through an opening in such a way that the air in the space is
induced (forced) to mix with the new flow. Temperature is obtained by the contact of
air with hot or cold water in the induction unit. An equivalent amount is exhausted
without returning to the air handler. Good circulation results, with only a small
amount of treated air. Control is obtained via the water temperature or the
circulation of air. |
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Term
| air-water induction system - applications |
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Definition
It is used in spaces next to the exterior, with wide range of loads, and control of
humidity is not critical. |
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Term
| air-water induction system - disadvantages |
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Definition
| Complicated, noisy, energy in-efficient, humidity control is not possible. |
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Term
| air-water induction system - components |
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Definition
Chiller, boiler, double water tree, induction units, ductwork, exhaust
system. |
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Term
| Fan coil system with supplementary air |
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Definition
Fan coil units are familiar units located below windows. At each terminal, a fan
mixes existing air with an exterior supply. It goes through a filter, and by water coils
that heat or chill the air. A thermostat controls the water supply to the unit. |
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Term
| Fan coil system with supplementary air - applications |
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Definition
Buildings with many zones, with varied schedules, and spaces along perimeter.
Hotels, motels, schools, apartments, offices. |
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Term
| Fan coil system with supplementary air - advantages |
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Definition
| No fan room or ductwork inside the building. Temperature is individually controlled. |
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Term
| Fan coil system with supplementary air - disadvantages |
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Definition
| Maintenance in occupied spaces, humidity control, condensate piping. |
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Term
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Definition
Heat pumps draw heat from the loop or discharge heat to it, heating or cooling. In
large buildings in cold weather, it is possible to obtain heat from the internal parts to
heat the perimeter. In hot weather, a cooling tower might be used to discharge
excessive heat. This can be considered an all water system. |
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Term
| closed loop heat pump - locations |
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Definition
This can be an efficient system that does not occupy a lot of room. It allows for
varied scheduling. |
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Term
| closed loop heat pump - advantages |
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Definition
| above ceilings, perimeter, or under windows. |
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Term
| closed loop heat pump - disadvantages |
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Definition
It can be an expensive system to install, and requires maintenance in occupied
areas. Requires temperate/ stable conditions, or warm water in winter and cool
water in summer. |
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Term
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Definition
Building use
Architecture and lay-out
Cycles / Diversity of occupancy
Control requirements
Building scale
Energy sources
Climatic zone
Initial cost
Long term/ lifetime costs |
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Term
| air handler, chiller, boiler, and cooling tower - exchange loops |
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Definition
Two heat exchange loops, one refrigeration loop:
1. Air/water to refrigerant (gas)
2. Refrigerant compression cycle.
3. Refrigerant to water-air. |
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Term
| air handler, chiller, boiler, and cooling tower - location of the refrigeration loop |
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Definition
| Having it compact and installed inside the chiller minimizes maintenance, but more important, reduces the potential for refrigerant leaks, simplifies refrigerant handling practices, and typically makes it easier to contain a leak if one occurs. |
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Term
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Definition
An air handler, or air handling unit (AHU), is a device used to condition and circulate
air. Usually, an air handler is a large metal box containing a blower, heating and/or
cooling elements, filter racks or chambers, sound attenuators, and dampers. Air
handlers connect to ductwork that distributes the conditioned air through the
building, and returns it to the AHU. Can mix fresh and return air. The cooling coils in
the air handler transfer sensible heat and latent heat from the air to the chilled
water, thus cooling and usually dehumidifying the air stream. |
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Term
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Definition
complex refrigeration machine, and a heat exchanger. It removes
heat from a liquid using compression or absorption. The water that is chilled may
also contain 20% glycol and corrosion inhibitors.
The chilled water is used to cool and dehumidify air in the air handler units or
equivalent. The heat is extracted via a water loop and a cooling tower, or heat from
the water is cooled using air. Most chillers are designed for indoor operation, but
some are weather-resistant. Chillers are precision machines that are very expensive
to purchase and operate.
There are air chillers that do not require a cooling tower. These eliminate the third
loop, releasing heat from the refrigerant directly to the air, using a fan. |
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Term
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Definition
Cooling towers are heat removal devices used to transfer process waste heat to the
exterior air. Cooling towers may either use the evaporation of water to remove heat
and cool the working fluid to near the wet-bulb air temperature or rely solely on air
to cool the working fluid to near the dry-bulb air temperature.
Water cascades inside a louvered box that uses a fan to increase air movement and
maximize contact of the water with it.
There are vertical ones, and cross-flow ones. |
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Term
| Cooling towers - disadvantages |
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Definition
Create a microclimate and are noisy. Fog can occur in cold weather. Corrosion and
biological problems are issues.
Water needs to be replaced on a regular basis, as it escapes via evaporation. |
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Term
| Closed circuit evaporative cooler |
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Definition
no water, direct refrigerant, enclosed cooling
water box. |
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Term
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Definition
VAV box, is control device that manages flow at
the zone-level. It is a calibrated air damper with an automatic actuator. The VAV
terminal unit is connected to either a local or a central control system. Historically,
pneumatic control was commonplace, but electronic direct digital control systems
are popular especially for mid-to-large size applications. Hybrid control, for example
having pneumatic actuators with digital data collection, is popular as well.
Control of the system's fan capacity (VARIABLE FAN SPEED) is critical in VAV
t With systems. Without proper and rapid flow rate control, the system's ductwork, or its
sealing, can easily be damaged by over-pressurization. However, the fan capacity
control is the primary advantage of VAV systems, especially with modern electronic
variable speed drives, because the energy consumed by fans is a substantial part of
the total cooling energy requirements of a building |
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