Chp 5 Cooling load computations

the latent cooling load of a residence is computed as ---- or less of the total sensible load.

30%

the typical inside design temp range for cooling in most US home is usually from --- to ----.

74 to 78 F

Before the recent technological advancements that led to high-performance glazings (i.e., use of tints, films, and coatings), a typical window with one or two layers of glass allowed about ___to _____ of the solar energy to enter a building.

75%/85%

air exchange rate (ACH)

Sensible heat gain resulting from infiltration is typically determined with the air-change technique using a volume of air equivalent to the number of air exchanges in the structure or room per hour,

Oversizing a cooling system adversely influences efficiency and performance. true/false

True

admittance method

allows calculation of overheating temperature of the room, or peak cooling load calculation for a constant environmental temperature

Transmission

are the result of heat passing through a material in the building envelope or through an assembly of materials.

inside design conditions

are the target indoor envior'l conditions intended to achieve thermal comfort

Ventilation heat gains

are tied to the energy required to condition outside air that is mechanically introduced into the building to maintain occupant comfort and avoid adverse health effects.

ACCA'S Manual N- commercial load calcualtion

can be used to estimate heating and cooling loads for small- and mid-sized commercial structures

cooling load temperature difference/ solar cooling load factor/ cooling load factor (CLTD/SCLF/CLF)

derived from the transfer function method and uses tabulated data to to simplify the calculation process

In cooling load computations, sensible heating loads are associated with: Heat transmission through opaque _____ assemblies. ex: roofs walls floor ceilings ----- heat gain through transparent or translucent envelope assemblies leakage of outside air thru the bldng envelope (------) air introduced for ----- Occupants lights equip and appliance

envelope/ Solar/ infiltration/ ventilation

convective and latent heat flows are instantaneous; gain _____ loads

equal

quantity of heat gaines

expressed in btu or w-hr

For large building floor areas, a minimum of ---- per floor (one zone for each exposure: north, south, east, west, and an interior zone) is recommended.

five zones

Sensible and Latent heat gains make the total ------ of a building

heat gain

What are three basic methods that are used to estimate heating energy consumption and operating costs?

hour-by-hour simulation degree-day energy estimation Bin energy estimation

A higher number of cooling load hours indicates that the cooling system will operate longer, resulting

in higher energy consumption

heat balance method

indicates the balance of all heat transfer in a room to determine the cooling load

In residential cooling load computations, the heat gain from---- is included with the heat gain from ------mainly because there are no code requirements for ventilating residences and because the load associated with ventilation air is comparatively small in comparison to ventilation requirements for ------ buildings.

infiltrated air/outdoor ventilation air/ commercial

transfer function method

is a derivative of the heat balance method

Cooling load hours

is a time quantity developed by the HVAC industry to specify the number of hours that a cooling system would typically operate at a specific geographical location.

air change (ACH = 1.0)

is equal to the volume of the room or space under consideration being exchanged in one hour.

Sensible heat

is heat that is associated with a change in temperature of a substance. It is a heat that a substance absorbs, and while its temp goes up, the substance does not change its state.

Design methodology results in equipment already sized for peak conditions, so equipment

is oversized when operating at nonpeak, part-load duty the majority of the time.

latent heat gains

is the energy required to change the state of a substance from solid to liquid (latent heat of fusion) or a liquid to gas (latent heat vaporization), without a change in temperature

Solar radiation

is the energy that a building absorbs from solar energy striking its exterior and conducting to the interior or energy transmitted through windows and being absorbed by materials in the building interior.

The cooling load

is the heat the HVAC equip must remove to maintain the building interior at inside design conditions

ASHRAE, in its residential heating load computation technique, suggests a slightly more complex approach that involves computation of the

latent load (LF) multiplier.

A small part of this sensible heat gain is stored in the ____ of the structure as an increase in _____ and then-----after the occupants leave

mass/temperature/released

in cooling load computations, latent heating loads are related to: ------ outside air from infiltration and ------- Occupant ------ and activities ( bathing and cleaning) moisture from equipment and appliances

moisture-laden/ ventilation/ respiration

Time-delay effects of radiation, and thermal mass and thermal lag, a buildings heat gain and cooling load are ------

not equal

Internal Heat

occupants, lights, equipment, computers, and appliances reject heat into the occupied space

Infiltration heat gains

relate to the energy required to cool and dehumidify unconditioned air that has leaked into the building space through the building envelope.

In small buildings with a single zone, load calculations should be made on a ------- or ------ basis bc a HVAC system must properly deliver heating/cooling to the specific rooms or spaces.

room-by-room or zone-by-zone

what is the most basic and least accurate method in computing the cooling load of a building?

rule of thumb method

The total cooling load is the sum of the

sensible loads and the latent loads:

Occupants release both ---- heat and _____heat into an occupied conditioned space. The sensible heat production of an occupant will vary based on ----and----

sensible/latent. activity level/body type

The peak load of an HVAC system will occur when the --- of the loads in the individual rooms or zones being served is the ---, which is typically --- than the sum of the peak loads in the individual rooms or zones being served.

sum/ greatest/ less

Heat gain

the amount of heat that a building space accumulates from external sources (high outside temp and solar radiation) and internal sources ( occupants, lights, appliances)

sensible heat ratio SHR

the ratio btw the sensible heating load and the total heat load

summer design conditions

used by the designer to determine the peak operating conditions under the HvAc systems and equipment must operate during the summer

radiant time series

uses an array of repetitive equations to reproduce accurate results and is less dependent on approximated data

total equivalent differential/ time averaging

was the preferred method for hand or simple spreed sheet calculation b4 the introduction of the CLTD/SLF/CLF method

The cooling load resulting from heat transmission through opaque (non-translucent) components of above-grade exterior envelope assemblies (e.g., walls, roofs, ceilings, floors, and doors) occur.....

when heat from the outside flows through the external building envelope

In performing cooling load calculations for commercial buildings, the spaces need to be divided into ____ that have _____ load parameters

zones/similar