HVAC

heat transfer methods

Based on the concept of the heat exchange from a source where heat (or coolness) is not wanted to a place where it is desired

compressive refrigeration

Based on the transfer of heat during the liquefaction and evaporation of a refrigerant. Latent heat is released as refrigerant changes form

cooling system

Chilled air or water produced by compressive refrigeration, absorption, or evaporative cooling

infiltration

The unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope, and through the use of doors for passage Sometime called air leakage

barometric damper (draft regulator)

a balanced air valve positioned to admit air to the flue or stack of a furnace in order to maintain a constant amount of draft.

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

turning vane

a curved fin that fits inside a duct to direct the flow of air to another direction without adding noise to the system

flue

a duct for smoke and waste gases produced by a fire, gas heater, power station or other fuel burning installation

freon

a family of several CFC gasses used in the refrigeration cycle

draft

a flow of air through a flue or chimney

condenser

a heat exchanger in which refrigerant vapor is condensed (liquified) releasing heat to an external medium

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.

convector

a heating device arranged to deliver heat to the air primarily by convection

splitter damper

a single blade damper that is hinged at one end and installed to divert air from a main duct into a branch duct

induction

a small amount of supply air at a very high velocity is delivered to a box and mixed with air brought in from the room inducing a greater airflow

coefficient of performance (COP)

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

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

overall thermal transmission value (OTTV)

a weighted average U-value for all the exterior surfaces of the building.

reheat

adding of sensible heat to a supply air stream which has been previously cooled

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

DX (direct expansion)

alternative to chilled water system in HVAC used to cool air containing water vapor. A refrigerant is used to remove sensible/latent heat from air

ton

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

service energy efficiency rating (SEER)

an HVAC energy rating

furnace

an appliance fired by gas or oil to heat air and then distribute it throughout a building in a heating system

cooling load temperature difference (CLTD)

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

heat exchanger

any device used for transferring heat from one fluid to another, where the fluids are physically separated

exhaust air

any foul or unwanted air removed from a space by mechanical means

electronic air cleaners

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

packaged boiler

comes in a complete package, requires only the steam, water pie work, fuel supply and electrical connection.

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

building automation system (BAS)

computer based integrated system used to monitor and control building systems

solar air conditioning

cooling system that provides refrigerated air using solar radiation as the prime source of energy

distribution system

delivers the heated or cooled air or water to the necessary areas in a building called zones

mixing box

enclosure in which two air streams are mixed, commonly used in a dual duct system

conductors

encourage heat flow

plant

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

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

absorption filters

for gaseous removal and vary depending on pollutant

hypocausts

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

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.

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

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

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

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)

activated charcoal filters

more common, absorb materials with high molecular weights and allow low weights to pass

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

electrostatic filters

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

media filters

more fine and use filter paper in please within a frame, working by straining and impaction (90% efficient)

forced convection

movement of a fluid by a fan or pump in order to force heat exchange

flat plate heat recovery units

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

flue

noncombustible and heat resistant passage in a chimney used to convey products of combustion from a furnace, fireplace, or boiler to the atmosphere...sometime just the chimney itself

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

modular boiler

packaged boiler system that operate in parallel or series to provide varying amounts of steam. Typically most efficient when run at full capacity.

building commissioning

process of inspecting, testing, starting up, and adjusting building systems to verify that they're working in accordance with the contract documents

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

energy efficiency ratio (EER)

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

energy recovery ventilators (air to air heat exchangers)

reclaim waste energy from the exhaust air stream and use it to condition the incoming fresh air • Energy can be reduced from 60% - 70% • Efficient in climates where indoor-outdoor temperature differentials are high • Fresh air intake must be from the exhaust outlet, exhaust air containing excessive moisture, or contaminates should be separate from heat exchanger air

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

insulators

retard the flow of heat

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

air washers

sometime used to control bacteria growth and control humidity

prescriptive code

specifies how to build a building

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.

performance code

states the final result and how it will be measured, but doesn't say how to actually achieve the result

electric boiler

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

substance used in a heat cycle usually including a reversible phase transition from a liquid to a gas

ventilation

supplying or removing of air by mechanical or natural mans to or from a given space

indoor air quality (IAQ)

the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants

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

infiltration load

the amount of heat required to bring outside air that has leaked inside a building up to the desired indoor temperature.

high efficiency particulate arrestance (HEPA filter)

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

full load hours

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

distribution trees

the means for delivering heating and cooling

evaporator

the part of a refrigeration system in which the refrigerant evaporates and absorbs heat from the medium to be cooled

conductivity

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

air movement

the velocity of air in an enclosed space measured in feet per minute

smoke pencil

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

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

air conditioning

treating of air in an occupied space to control tis temperature, humidity, and cleanliness

plenum

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

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

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

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

chiller

used in hot climate with high cooling demands

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

steam trap

valve which permits passage of air or water, but not steam...often used with steam radiators

zones

vary depending on the type and use of a building. (e.g.: each story, offices vs. apartments, commercial vs. recreational spaces). It's design specific.

blowdown

water intentionally wasted from a boiler to avoid concentration of impurities during evaporation of steam

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.

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

forced air system

• Cool or heat by conditioned air alone • Move air through a coil to heat space via ductwork • Supply air, return air and other stuff that comes back with it • The coil is a direct fire gas coil, or electrical resistance. If you see a "DX" air coil don't use it...it's cheap and lousy.

types of refrigerants

• 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 cos

hydronic (HVAC distribution system)

• Hot water or steam circulates through registers/pipes which radiate heat into space • Many hydronic systems are also radiant and can be combined with forced air systems

electrical (HVAC distribution system)

• Simplest and lowest in first costs, but most expensive in life cycle costs, and really only justified in very mild climates • Radiant Systems: radiant panels or wires embedded in ceiling or floor • Baseboard Heaters: Convective Air

direct expansion (DX) system

• Simplest type of system • A self contained unit that passes non-ducted air to be cooled over the evaporator and back into the room • Condenser uses outdoor air directly • Typically placed on exterior walls, or roof mounted

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