Building Systems_Work

Heat pumps are better at turning energy into heat by about how many times compared to electric

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Forced Air 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. 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 Can't heat and cool different rooms in the same zone at the same time • A maintenance nightmare, Requires a lot of interstitial space 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

Sprayed Foam and Foamed in Place

Cementitious, Phenolic, Polyisocyanurate, Polyurethane • Use in enclosed existing wall, new walls, unfitted attic floors • Good for adding insulation

Cooling Systems

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

Worst type of heating

Electric resistance

Energy used by HVAC accounts for

Energy used by HVAC accounts for 40%-60% of overall consumption in the building (type, climate, design, etc, can vary that number).

Evaporation and Condensation pressures

Evaporation occurs at low temperature and low pressure • Condensation occurs at high temperature and high pressure

Typical Refrigeration Process Cycle

Evaporator, Compressor, Condenser, Expansion Valve

Class I vapor retarder (less than 1 perm)

Glass Sheet Metal Polyethylene Sheet Rubber Membrane

HVAC: Hydronic Systems:

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

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

Fans

There are many types of fans, bladed fan is the most common • Centrifugal fan is used for moving large amounts of air (it's sometimes called a squirrel cage)

Dampers

Valve or plate that stops or regulates the flow of air inside a duct, chimney, variable air volume box, other HVAC equipment • Balances the system and allows for adjustments based on the occupants needs • Can be used to cut off or regulate air to a room • Controlled by a thermostat or automation system

Perm

unit of permeability for a given material, expressing the resistance of the material to the penetration of moisture. One perm = flow of one grain of water vapor through one square foot of surface per hour with a pressure difference of one inch of mercury.

Efficient HVAC: 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

Heat Transfer Methods 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%

Heat Transfer Methods: 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

Efficient HVAC: 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

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.

Which is more efficient medium to carry heat?

water over air

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

Feedwater

water used to supply a boiler to generate steam or hot water

Forced Air System: Single Duct

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

Ductwork Distribution and Sizing:

• Allow 3 sq.ft. - 6 sq.ft. for every 1,000 sq.ft. of floor space for horizontal and vertical duct runs. • Loss of pressure is due to friction of the air moving through the ducts, fittings, registers, and other components • Appropriate velocities range from 300 fpm (quiet) to 2,000 fpm.

Loose Fill and Blow in Insulation

• Cellulose, Fiberglass, Mineral Wool • Enclosed existing wall or new wall cavity, unfinished attic floors, hard to reach places • Good for adding extra insulation

HVAC: Forced Air Systems

• 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.

Blanket (Batts and Rolls) Insulation

• Fiberglass, Mineral Wool, Plastic Fibers, Natural Fibers • Used in unfinished walls, foundations walls, floors, ceilings • Fitted between studs, joints, and beams • Suited for standard stud spacing

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

• Structurally Insulated Panels (SIPs)

• Foam board or liquid foam insulation, straw core insulation • Unfinished walls, ceilings, floor, and roofs • Provide superior and uniform insulation

Sizing HVAC Systems

• System capacity: determine the primary determinants in sizing equipment...the total heat losses and gains a building will experience in the most extreme conditions • Design heat loss can be best described as an estimation of the worst likely hourly heat flow from a building to the surrounding environment based upon a chosen outside temp • Locating a heat source below a window evens out the temperature in a room, but increases the heat loss through the window.

Phase Change Equipment

• Using electrical energy to "pump" heat from one area to another • Typical Coefficient of Performance (COP) for a heat pump in heating mode is 1.25 - 3.0 (watt/watt or BTU/BTU) • Coefficient of Performance is a unitless measure of BTU/BTU or watt/watt that measures how much you put in compared to how much you get out • you get at least 1.5 BTU of energy for every BTU u put in • But remember, it's electrical energy • COP and overall efficiency • COP depends on outdoor temperature if you have a typical heat pump • The COP drops when the temperature drops (which is why heat pumps don't work so well in extreme cold climates) • extreme climates, GAS is the best cuz it's not affected by climate • Ground source heat pumps don't react to outdoor conditions, just the ground temp • Have a COP of about 5.0HUGE and 5x better than electrical heat

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

Vapor Diffusion Retarder

a material that reduce the rate at which water vapor can move through material.

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

Overall Thermal Transmission Value (OTTV)

a weighted average U-value for all the exterior surfaces of the building. • An example is a combination of prescribe and performance codes

Mixing Box

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

Heat Transfer Methods: 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

Efficient HVAC: 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

Efficient HVAC: 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 Transfer Methods: Energy Recovery Ventilators (Air to Air Heat Exchangers) : 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

Efficient HVAC: 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

Fiberglass Lined Ducts

lined with an external or internal fiberglass duct liner, used to insulate dry ducts from heat loss, to avoid condensation, and or to reduce the sound of the system

Air Barrier

membrane that controls air leakages into and out of the building envelope • 25 - 40% of heating energy is lost due to infiltration • Air Barriers provide a continuous pain of air tightest with all moving joints made flexible while still being sealed Some air barriers can las be water vapor permeable, while others can perform the function of a vapor barrier too • Air permeability is ≤ 0.004 cfm/ft2 under a pressure of 0.3" of water

Efficient HVAC: 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

Sheet Metal Ducts

most common and made of galvanized steel or aluminum, most durable and least likely to have mold/bacteria growth

Heat Transfer Methods: Energy Recovery Ventilators (Air to Air Heat Exchangers) : 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

Modular

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

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

Heat Transfer Methods: 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 • A defroster may be needed to avoid condense in the exhaust air from freezing Common Devices: Flat Plate Heat Recovery Unit, Energy Transfer Wheels (enthalpy heat exchangers), heat pipes

Efficient HVAC: 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

Typical Refrigeration Process Cycle: Compressor (2)

refrigerant vapor comes in from the low pressure side of the circuit and discharges it at a much higher pressure into the high pressure side of the circuit • The compressor is the heart of the system; it keeps the refrigerant flowing through the system at specific rates of flow, and at specific pressures. • The rate of flow thru the system will depend on the size of the unit • The operating pressures will depend on the refrigerant being used and the desired evaporator temperature.

Hydronic Systems: Hydronic Single Pipe

single supply and return pipe • hot water is circulated through each register and back to the pipe • Low initial cost, Simple • 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 • Can be combined with a forced air system, or stand alone

Energy Code: Prescriptive Code

specifies how to build a building • ASHRAE 90-xx series covers the exterior envelope, HVAC equipment, water heating equipment, and electrical distribution

Energy Code: Performance Code

states the final result and how it will be measured, but doesn't say how to actually achieve the result • Building Energy Performance Standards (BEPS) specifies an energy budget per square foot for various building functions

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.

Typical Refrigeration Process Cycle: Expansion Valve (4)

the dividing point between the high pressure and low pressure sides of the system and is designed to maintain a specific rate of flow of refrigerant into the low side of the system. • When the high pressure liquid refrigerant passes through the metering device, its pressure will drop to a low pressure that will be equivalent to about 10° to 15° below the design temperature of the evaporator. • It starts evaporating immediately and shoots out into the evaporator foaming, bubbling, and boiling • Think of it like a warm soda when you shake the bottle and pop the top off....it goes everywhere.

Distribution Trees

the means for delivering heating and cooling Roots: the machines that provide heat and cold • Trunk: the main duct or pipe from the mechanical equipment to the zone to be served • Branches: the many smaller ducts or pipes that lead to individual spaces • A building can have one giant distribution tree, or multiple smaller tress • Air distribution trees are bulky and likely to have a major visual impact unless they're hidden above ceilings, below floors, in chases. • Integrating vertical distribution trees with a structure saves on floor place • A distribution tree that flows from a rooftop central AHU reduces duct size on lower building floors • Single duct HVAC systems have the small tree in the all air system class

Air Sealing

the process of sealing ducts, openings, and cracks to prevent air leakage

Heat Transfer Methods: Energy Recovery Ventilators (Air to Air Heat Exchangers) : 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

Friction loss in a circular duct (∆p)

(0.109136 CFM1.9) / (Equivalent duct diameter5.02)

Vapor Diffusion Retarders

(often referred to as vapor barriers) • Prevent movement of water vapor out of building in cold climates and into buildings in hot climates. • Should go on the "warm side of the insulation" • In the Northwest that means it's located between the insulation and inside space • In the Southwest it's located between the insulation and the outside space • The ability of a material to retard water vapor is measured in perms • Control moisture in walls, slabs on grade, floors, crawlspaces, ceilings, etc • Only retard moisture due to diffusion, most moisture actually gets in via capillary action or through air leaks

Cross section area of duct (A)

144 x (the flow rate in cubic ft. Per min, Qcfm) / Velocity measured in feet per minute (V)

Forced Air System: Unitary

A self contained unit where air comes directly in from the outside, conditioned and sent into the space Use when ducts are impracticable to run • Each unit can have it's own utility bill One unit is required for each zone Can run on just electric, but can also connect to hot/cold piping • They're the units you see in big box stores

Forced Air System: Induction

Air is supplied to a building under high pressure/velocity to each induction unit • Outside air is mixed with recirculated conditioned air • Ducts are smaller • Work best in perimeter rooms of multi story multi room buildings • Need extra distribution for water • Perimeter zoned areas: schools, offices, labs

HVAC Distribution Systems, or how spaces are served by the plant, can be

All Water System (only pipes) • All Air System (only ducts) • Combined Water and Air (pipes and ducts...expensive!)

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. Components: • 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

Hydronic System: 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 • One of the most efficient systems • Versatile because it provide heating and cooling simultaneously • High initial cost • Highest installation cost cuz there's ductwork & plumbing involved • 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

Forced Air System: Double Duct aka "Dual Duct" aka "High Velocity"

Combination of two single duct systems, 1 for hot air, and 1 for cold • 2 streams are join@ a mixing box controlled by thermostat in zone Can heat and cool at the same time, Constant airflow volume • Good for perimeter zone, Easy to install • Good for linear buildings 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 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 syste

Concrete Block and Insulated Concrete Blocks

Concrete Block and Insulated Concrete Blocks: • Foam Board placed on the outside for new construction and inside for existing • Used in unfinished walls, foundation walls, walls • Insulating cores increase wall R-Value

Diffusers

Control the way the air enters a space from ductwork • Slow the velocity and enhancing mixing into the surroundings • Used on both all air and air water HVAC systems • Deliver conditioned and ventilation air • Evenly distribute flow of air as desired • Create low velocity air movement int he occupied portion of the room • Do it all as quietly as possible • Can be round, rectangles, linear slot diffusers

Ducts

Ductwork efficiency depends on having the least possible perimeter distance, allowing for less retsina and friction for air to move • Usually rectangular or round, though now spiral ovals are becoming more common • Circular cross section is best, especially high velocity system • Increase air friction often causes problems in higher velocity ducts • Higher duct velocities result in higher duct system resistance, which results in increased fan horsepower.

Rigid Fibrous or Fiber Insulation

Fiberglass, Mineral Wool • Ducts in unconditioned spaces, high temp spaces

Insulating Concrete Forms Insulation

Foam boards or blocks: • Used in unfinished walls, foundation walls • Part of the building structure - the insulation is literally built in

Reflective Systems Insulation

Foil Faced Kraft Paper, paper film, polyethylene bubbles, cardboard • Unfinished walls, ceilings, and floors • Foil, films or paper fitted between wood frame studs, joists, rafters, beams

Hydronic System: Hydronic Four Pipe

Like (2) two pipe systems, but there's one for hot and one for cold • Can heat and cool at the same time • More expensive due to piping • Can be combined with forced air system, or stand alone

Hydronic Systems: Hydronic Three Pipe

Like a 2 Pipe system, but both hot and cold water are mixed in a common return pipe • Can heat and cool at the same time • Mixes cold and warm water in return pipe • Less efficient than a two/fourpipe system • Can be combined with forced air system, or stand alone

Forced Air System: Multi Zone

Like a Double Duct system, but the mixing box is in the mechanical room • Premixed air is sent to each zone Efficient with a few zones • Separate duct runs, nothing is shared • Easy to sub monitor Lots of ductwork is required • Not efficient with many zones or non-square building • Good for mall spaces where each tenant has control • Good for square building plans with few zones Used in medium sized buildings

Hydronic Systems: Hydronic Two Pipe

Like a Single Pipe System, but separate supply and return pies are used • Doesn't put used water (that's cooler) into the supply line for the next register • Can only heat or cool at one time • Can be combined with forced air system, or stand alone

Duct Speeds

Low Velocity =1,000 - 2,200 fpm Medium Velocity = 2,200 - 2,500 fpm High Velocity =+ 2,500 fpm

Types of air barriers:

Mechanically attached:(e.g.: Tyvek, which is moisture and air barrier) • Self-Adhered: typically water resistant and vapor barrier • Fluid Applied: heavy bodied paints or coatings including polymeric based • Closed Cell: density spray applied polyurethane foam which provides insulation too • Boardstock: (e.g.: 12 mm plywood or OSB, or 25 mm extruded polystyrene)

Types of Vapor Diffusion Retarders:

Membrane: thin and flexible like paper-faced fiberglass roll insulation or foil backed wall board. Can also be rigid and thick like rigid foam insulation, aluminum, stainless steel, which are fastened and sealed a joints • Coatings: paint-like system applied as a liquid

Types of Dampers

Opposed Blade/Balancing: regulates the flow of air • Splitter Vanes: used where duct branches off for flow control • Conventional Turns: reduces friction at the corners • Turning Vanes: reduces friction at the corners

Foam Board or Rigid Foam Insulation

Polystyrene, Polyisocyanurate, Polyurethane • Used in unfinished walls, foundation walls, floors, ceilings, unneeded low slope roofs • Interior application must be covered with gyp board for fire safety • Exterior application must be covered with weatherproof facing

increases the heat loss through the window. • Mechanical Room Space Requirements:

Preliminary sizing for medium to large buildings should be 3% - 9% of gross building area for air or air/water systems • Allow 1% - 3% for water systems • Area will accommodate all equipment (e.g.: boilers, chillers, fans, pumps, piping) • Space needs to be twice the length of the major equipment (e.g.: boiler or chiller) and 12'-0" - 18'-0" tall

Type of Distribution System: Electric

Radiant heat is run through panels or wires to rooms Low initial cost • Simple system • Can turn on only in occupied room Expensive life cycle cost • Wasteful Baseboard heat uses convection to heat spaces

Insulated Ductwork:

Reduces heat loss/heat gain of air during delivery • Isolates air nosies in duct from spaces • Prevents condensation on outside for cool-air ducts

Typical Refrigeration Process Cycle: Evaporator (1)

Relatively warm air (or water, if the unit is an ice machine) flows over the evaporator coil • The system is designed so that the heat in the relatively warm air, water or ice cream mix flowing over the evaporator will move into the cold evaporating refrigerant. This process will continue to cool the air, water, or ice cream mix that's flowing over the evaporator until it reaches the design set point or thermostat setting. • So, when you turn on the refrigerator, freezer, ice machine or ice cream machine, the system is designed so that the evaporator will stay colder than whatever it's cooling, and will continuously remove heat from it and cool it.

Forced Air System: Reheat (Constant Volume)

Return air and fresh outside air are combined and cooled and dehumidified • Distributed in constant volume at a low temperature • Humidity and temperature can be controlled • Ducts are smaller, Fan horsepower is lower • Uses more energy because primary air volume needs to be cooled most of the time and reheated • 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

HVAC: Electrical Systems

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

HVAC: 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

Chimney

The height of a wood burning chimney depends on the roof it is sticking out from • It must meet safety (distance from the roof and combustibles) and draft capabilities requirements • The highest point in which the chimney passes through the roof must be at least 3'-0" below the top of the chimney (aka: it must be at least 3'-0" tall, measured from the tallest side) • The top of the flue must be 2'-0" higher than any part within 10'-0" horizontal of the flue

Hydronic System: 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 • Good efficiency, Reduces extensive ductwork • Returns over 200% its electrical input when outdoor temp is above freezing • High initial cost, May need chiller to cool water if all zones are cooling simultaneously • May need a boiler to reheat up water • 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

Packaged Type

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

Efficient HVAC: 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

Typical Refrigeration Process Cycle: Condenser (3)

hot refrigerant vapor discharged from the compressor travels through the condenser, the cool air or water flowing through the condenser coil absorbs enough heat from the vapor to cause it to condense. • Most air cooled refrigeration systems are designed so that the refrigerant will condense at a temperature about 25 - 30˚ above the ambient air temperature around the condenser. • Condensing is good because it allow the heat energy in the vapor to move into that relatively cold air or water and cause the refrigerant to condense. • High pressure liquid refrigerant will flow down the liquid line, through a filter drier that is designed to prevent contaminants from flowing through the system, and on to the metering device.

Infiltration Load

is the amount of heat required to bring outside air that has leaked inside a building up to the desired indoor temperature. • The highest rate of heat gain/loss in a building is usually a result of outside air infiltration