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Lecture 11Mechanical System Space

RequirementsMechanical System Exchange Loops

HVAC Systems

Lecture 11Mechanical System Space

RequirementsMechanical System Exchange Loops

HVAC Systems

Mechanical Room SizingMechanical Room Sizing Mechanical Room SizingMechanical Room Sizing

Mechanical RoomMechanical RoomContains primary equipment (boiler, chiller,

etc.)

Usually adjacent to other service areas (loading docks, electrical substation, transformer vault, etc.)

Generally away from public entry

Include space for service/maintenance

S: p. 406, F.10.18

Mechanical Mechanical Room SizingRoom Sizing

Generally sized based on total floor area in building served

S: p.399, T.10.3

Mechanical Mechanical Room SizingRoom Sizing

Size mechanical room space

ApplicationSquare Footage

S: p.399, T.10.3

Mechanical Mechanical Room SizingRoom Sizing

Sizing Example

150,000 SF Department Store

Mechanical Room: 3,200 sf

S: p. 399, T.10.3

Fan Room SizingFan Room Sizing Fan Room SizingFan Room Sizing

Fan RoomsFan Rooms

Contain secondary equipment (air handlers, heat exchanger, etc.)

Usually adjacent to or within area served

Include space for service/maintenance

S: p. 426, F.10.42

Fan RoomsFan Rooms

Require connection/ access to fresh air

Require means of discharging return air/ exhaust air

Minimum 25’ distance of fresh air inlet away from contaminant source

University of Michigan Hospital, Ann Arbor, MI

Fan Room Fan Room SizingSizing

Generally sized based on total floor area of the thermal zone in building served

S: p. 400, T.10.4

Fan Room Fan Room SizingSizing

Size fan room

ApplicationSquare Footage

S: p. 400, T.10.4

Fan Room Fan Room SizingSizing

Sizing Example

150,000 SF Department Store

Supply/Return Mains: 120 sf for each

Fan Room: 5,200 sfFresh Air Inlet: 500 sfExhaust Air Outlet: 400 sf

S: p. 400, T.10.4

Fresh Air InletsFresh Air Inlets

Avoid contamination sources (25’ minimum) Loading docks Smoking areas Cooling Towers Exhaust air outlets Plumbing vents Others…

Mechanical System Mechanical System Exchange Loops Exchange Loops Mechanical System Mechanical System Exchange Loops Exchange Loops

Mechanical System Exchange Mechanical System Exchange LoopsLoops

Heat is removed/ added via heat exchange loops.

S: p. 402, F.10.15

Mechanical System Exchange Mechanical System Exchange LoopsLoops

Cooling Mode

S: p. 402, F.10.15

Mechanical System Exchange Mechanical System Exchange LoopsLoops

Heating Mode

S: p. 402, F.10.15

Cooling TowerCooling Tower Cooling TowerCooling Tower

Cooling TowerCooling Tower

Divided into a series of cells for redundancy/ serviceability

Significant structural load:Rooftop vs At-grade

Potential air contamination

Locate based on prevailing wind direction

S: p.415, F. 10.30

Cooling TowerCooling Tower

Service access needed for water treatment/debris removal

Biocides can cause etching on glass and other surfaces

Minimum 25’ distance away fresh air inlet or fenestration

University of Michigan Hospital, Ann Arbor, MI

Cooling TowerCooling TowerSizingSizing

Sizing Example

150,000 SF Department Store

Cooling Tower: 560 sf

S: p.399, T.10.3

HVAC SystemsHVAC Systems HVAC SystemsHVAC Systems

System TypesSystem Types

All-AirAir-WaterAll-WaterUnitary Refrigerant System

Selection CriteriaSelection Criteria

Control capability and flexibility required

Environmental requirements

Cost of construction Energy consumption System effficiency

All-Air SystemsAll-Air Systems

Heating/cooling media delivered via air only

Advantages: Humidification & Heat recovery Complex zoning Close humidity & temperature control (exc. VAV) Can use outside air for economizer cycle

Disadvantages: Special care for maintenance access Supplemental perimeter radiation may be needed Higher volume of space needed

All-Air SystemsAll-Air Systems

Single zoneTerminal reheat Multizone Dual duct Variable air volume (VAV)

Single ZoneSingle Zone

One thermostat controls several rooms in a single thermal zone

Applications requiring air filtration and humidity control

Uneven comfort for multiple rooms

Terminal ReheatTerminal Reheat

One thermostat controls one room as a single thermal zone with a reheat coil control discharge air temperature

Poor energy efficiency

MultizoneMultizone

One thermostat controls discharge dampers to adjust air temperature to each room

Small buildings with limited distances for duct runs

Simultaneous heating and cooling

Dual DuctDual Duct

One thermostat controls mixing box for each room

Applications requiring precise control of temperature and humidity

Energy inefficientHigh maintenanceExpensive to build

Variable Air VolumeVariable Air Volume

One thermostat controls VAV valve for each room and reduces airflow under lower load

Applications where loads vary significantly (offices, schools)

Poor humidity controlSubcooling

Distribution PathsDistribution Paths

Air may be distributed from the ceiling or the floor

Distribution Paths—Ceiling Distribution Paths—Ceiling

Conventional distribution is from the ceiling

Air discharge: 55ºFVelocity is 100-500 fpm

S: p.439 F.10.54

Distribution Paths—Floor Distribution Paths—Floor

Also known as displacement cooling

Air discharge: 60+ºFVelocity is slower than ceiling discharge

Higher ceilings

S: p. 394, F.10.12

S: p. 433, F.10.48

Air-Water SystemsAir-Water SystemsHeating/cooling media delivered via air and water

Advantages: Flexible placement Centralized humidity and filtration Space heating

Disadvantages: Condensation Noise

Induction

Fan Coil Unit

S: p. 396, F.10.13

All-Water SystemsAll-Water Systems

Heating/cooling media delivered via water only

Advantages: Flexible placement Space heating

Disadvantages: Condensation Noise

Fan Coil UnitFan Coil UnitFan draws air from room across coils

FlexibleLess spaceLow cost

NoisePoor ventilation/humidityMaintenanceCondensation controlSimultaneous heating and cooling

S: p. 398, F.10.14

Unitary Refrigerant SystemUnitary Refrigerant SystemHeating/cooling media delivered via local equipment

Advantages: Individual room control Independent heating and cooling Single zone affected by malfunction Low initial cost Reliability

Disadvantages: Short life Noise Humidity control Air filtration Ventilation

Through the wall air-conditioning

Heat pumps