hvac design 1
TRANSCRIPT
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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
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! 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
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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
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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