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HVAC System DesignSimplified Method for Early DesignEnvironmental

Technology 1

Part

Classroom 1 Classroom 2 Classroom 3 Classroom 4

Corridor

Air Delivery sideReturn ducts and diffusers

Mechanical Room

Air Handling Unit(Air-conditioning)

VAV Box VAV Box VAV Box VAV Box

Supply ducts and diffusers

Fresh outside air

ETone

! Estimate the space cooling requirement

! Estimate ventilation requirement

! Determine supply air quantiy for eachzone and AHU

! Estimate equipment sizes - space sizes

! Revise system layout

Introduction

HVAC Design Procedures

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Residential 1cfm/sfOffice 1.2 cfm/sfSchool 1.5 cfm/sfAud. / theater 2.5 cfm/sfventilation load not included

Estimate Space Cooling Load

Simplified method for determining the spacecooling load

Floor area x cooling load factor = required cfm

Cooling load factor

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Classroom 1 Classroom 2 Classroom 3 MechanicalClassroom 425'X30' 25'X30' 25'X30' 25'X30'750 sf 750 sf 750 sf 750 sf

1,125 cfm 1,125 cfm 1,125 cfm 1,125 cfm

Estimate Space Cooling Load Example

Calculate floor area

Determine CFM required(Floor area) x (1.5 cfm - school)

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Residential 10 cfm/personOffice 20 cfm/personSchool 15 cfm/personAud. / theater 15 cfm/personadds to the space cooling load

Estimate Ventilation Load

Ventilation Requirements

# of people x ventilation factor = required cfm

Ventilation factor

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Classroom 1 Classroom 2 Classroom 3 MechanicalClassroom 430 people15 cfm/prn

450 cfm

30 people15 cfm/prn

450 cfm

30 people15 cfm/prn

450 cfm

30 people15 cfm/prn

450 cfm

Estimate Ventilation Load Example

Calculate ventilation requirement15 cfm per person

Use MEEB table 5-8 (page 226) to estimate occupancy count.

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Classroom 1 Classroom 2 Classroom 3 MechanicalClassroom 4

450 cfm 450 cfm 450 cfm 450 cfm

1,575 cfm

1,800 (vent) + 4,500 (cool) = 6,300 cfm

AHU1,125 cfm 1,125 cfm 1,125 cfm 1,125 cfm

1,575 cfm 1,575 cfm 1,575 cfm

Estimate Total Supply Air

Determine total supply air to spaceVentilation + cooling = total supply air

Determine AHU Supply air totalSum of supply air to all zones served

Example

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1,575 cfmtotal airrequired

Table reprinted from Architectureal Graphic Standards

Estimate Equipment Sizes

VAV box sizesrequired at each zone for temperature controlSee course handout

•

Example

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6,300 cfmrequired

Estimate Equipment SizesAir Handler Unit SizesSupply air to multiple zonesSee course handout

Example

•

Room dimensions: 18' -6" wide22' - 3" long 9' - 6" tall

Table reprinted from Architectureal Graphic Standards

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4,500 cfm per AHU

6,300 CFM per AHU

Estimate Equipment SizesCalculating the refrigeration requiredConverting air flow quantities to tons of cooling required

Cooling CFM (estimate based on internal air conditions)

Ventilation CFM (based on external air conditions)

1,800 cfm per AHU

Total CFM

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Estimate Ventilation LoadVentilation Sensiblebased on the )t between cooling coil and outside temp

1,800 cfm per AHUDesignCondition95 EF80 % rh

Qsensible = 1.08 x CFM x )t

Qsensible = 1.08 x 1,800 cfm x 40EF

Qsensible = 77,760 btu’s hr

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Estimate Ventilation LoadVentilation Latentbased on the )w between cooling coil and outside temp

1,800 cfm per AHUDesignCondition95 EF80 % rh

Qlatent = 4,840 x CFM x )w

Qlatent = 4,840 x 1,800 cfm x .o2 lb

QLatent = 174,240 btu’s/hr

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Estimate Ventilation LoadVentilation Total Load

DesignCondition95 EF80 % rh

Qlatent = 4,840 x CFM x )w

Qventilation = 174,240 btu/hr + 77,760 btu/hr

Qsensible = 1.08 x CFM x )t

Qtotal ventilation

Qventilation = 252,000 btu/hr

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4,500 cfm per AHU (1 of 15 units)

15 AHU’s in school x 4,500 = 67,500 cfmTotal for school

67,500 cfm ÷ 400cfm/ton = 169 tons of cooling

Estimate Equipment Sizes

Refrigeration Equipment Sizesbased on the tons of cooling required

1 ton of cooling . 400 cfm1 ton of cooling . 12,000 Btu/hr

Example

Conversion from cfm to tons(cooling load)

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252,000 Btu/hr per AHU (1 of 15 units)

15 AHU’s in school x 252,000 = 3,780,000Btu Total for school

3,780,000 ÷ 12,000 btu/ton = 315 tons of cooling

Estimate Equipment Sizes

Refrigeration Equipment Sizesbased on the tons of cooling required

1 ton of cooling . 400 cfm1 ton of cooling . 12,000 Btu/hr

Example

Conversion from cfm to tons(Ventilation load)

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Estimate Equipment Sizes

Refrigeration Equipment Sizesbased on the tons of cooling required

1 ton of cooling . 400 cfm1 ton of cooling . 12,000 Btu/hr

Example

Total Cooling Required - 484 tons

Space Cooling Load - 169 tons

Space Ventilation Load - 315 tons

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484 tonsof coolingrequired

Estimate Equipment Sizes Example

Chiller SizeTwo chillers are required

• reduced off-season loads• repair and maintenance

•

2 - 250 ton chillers

Table reprinted from Architectureal Graphic Standards

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484 tonsof coolingrequired

Estimate Equipment Sizes Example

Chiller Room• Dimensions from previous table• Room layout with pumpe

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Estimate Equipment Sizes484 tonsof coolingrequired

Example

Cooling Tower SizeBased on tons of cooling required

•

3+ - 150 ton cooling towers

Table reprinted from Architectureal Graphic Standards

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Classroom 1 Classroom 2 Classroom 3 Classroom 4

Corridor

Air Delivery sideReturn ducts and diffusers

Mechanical Room

Air Handling Unit(Air-conditioning)

VAV Box VAV Box VAV Box VAV Box

Supply ducts and diffusers

Fresh outside air

System Design

Revise basic layout adding equipment sizes

ETone

! Estimate the space cooling requirement

! Estimate ventilation requirement

! Determine supply air quantiy for eachzone and AHU

! Estimate equipment sizes - space sizes

! Revise system layout

Review

HVAC Design Procedures

ETone

HVAC System DesignSimplified Method for Early DesignEnvironmental

Technology 1

Part

Classroom 1 Classroom 2 Classroom 3 Classroom 4

Corridor

Air Delivery sideReturn ducts and diffusers

Mechanical Room

Air Handling Unit(Air-conditioning)

VAV Box VAV Box VAV Box VAV Box

Supply ducts and diffusers

Fresh outside air