HVAC System Design Simplified Simplifi ed Method for Early Design Part
Air Delivery side Return ducts and diffusers
Classroom 1
Classroom 2
Classroom 3
Classroom 4
VAV Box
VAV Box
VAV Box
VAV Box
Mechanical Room Fresh outside air
Air Handling Unit
Environmental Technology 1
Introduction HVAC Design Procedures !
Estimate the space cooling requirement
!
Estimate ventilation requirement
!
Determine supply air quantiy for each zone and AHU
!
Estimate equipment sizes - space sizes
!
Revise system layout
Estimate Space Cooling Load Simplified method for determining the space cooling load Cooling load factor
Residential
1cfm/sf
Office
1.2 cfm/sf
School
1.5 cfm/sf
Aud. / theater
2.5 cfm/sf
ventilation load not included
Floor area x cooling load factor = required cfm
Estimate Space Cooling Load
Example
Calculate floor area Determine CFM required (Floor area) x (1.5 cfm - school)
Classroom 1
Classroom 2
Classroom 3
25'X30' 750 sf
25'X30' 750 sf
25'X30' 750 sf
1,125 cfm
1,125 cfm
1,125 cfm
Classroom 4 25'X30' 750 sf
1,125 cfm
Mechanical
Estimate Ventilation Load Ventilation Requirements Ventilation factor
Residential
10 cfm/person
Office
20 cfm/person
School
15 cfm/person
Aud. / theater
15 cfm/person
adds to the space cooling load
# of people x ventilation factor = required cfm
Estimate Ventilation Load
Example
Calculate ventilation requirement 15 cfm per person Use MEEB table 5-8 (page 226) to estimate occupancy count.
Classroom 1
Classroom 2
Classroom 3
Classroom 4
30 people 15 cfm/prn
30 people 15 cfm/prn
30 people 15 cfm/prn
30 people 15 cfm/prn
450 cfm
450 cfm
450 cfm
450 cfm
Mechanical
Estimate otal Supply Air
Example
Determine total supply air to air to space Ventilation + cooling = total supply air
Determine AHU Supply air total Sum of supply air to all zones served
Classroom 1
Classroom 2
Classroom 3
450 cfm 1,125 cfm
450 cfm 1,125 cfm
450 cfm 1,125 cfm
450 cfm 1,125 cfm
1,575 cfm
1,575 cfm
1,575 cfm
1,575 cfm
Classroom 4
1,800 (vent) + 4,500 (cool) = 6,300 cfm
Mechanical AHU
Estimate Equipment Sizes VAV box sizes required at each zone for temperature control See course handout
•
Example
1,575 cfm total air required
Estimate Equipment Sizes Air Handler Unit Sizes Supply air to multiple zones See course handout
• Table reprinted from Architectureal Graphic Standards
Room dimensions: 18' -6" wide 22' - 3" long 9' - 6" tall
Example
6,300 cfm required
Estimate Equipment Sizes Calculating the refrigeration required Converting air flow quantities to tons of cooling required
Cooling CFM (estimate based on internal air conditions) 4,500 cfm per AHU Ventilation CFM
(based on external air conditions)
1,800 cfm per AHU
Total CFM 6,300 CFM per AHU
Estimate Ventilation Load Ventilation Sensible based on the
)t
between cooling coil and outside temp
1,800 cfm per AHU
Qsensible = 1.08 x CFM x ) t Qsensible = 1.08 x 1,800 cfm x 40EF Qsensible = 77,760 btu’s hr
Design Condition 95 EF 80 % rh
Estimate Ventilation Load Ventilation Latent based on the
)w
between cooling coil and outside temp
1,800 cfm per AHU
Qlatent = 4,840 x CFM x )w Qlatent = 4,840 x 1,800 cfm x .o2 lb QLatent = 174,240 btu’s/hr
Design Condition 95 EF 80 % rh
Estimate Ventilation Load Ventilation Total Load Qventilation = 174,240 btu/hr + 77,760 btu/hr Qventilation = 252,000 btu/hr
Qsensible = 1.08 x CFM x ) t
Qlatent = 4,840 x CFM x )w Q total ventilation
Design Condition 95 EF 80 % rh
Estimate Equipment Sizes
Example
Refrigeration Equipment Sizes based on the tons of cooling required 1 ton of cooling 1 ton of cooling
400 cfm . 12,000 Btu/hr .
Conversion from cfm to tons (cooling load) 4,500 cfm per AHU (1 of 15 units) 15 AHU’s in school x 4,500 = 67,500 cfm Total for school 67,500 cfm ÷ 400cfm/ton = 169 tons of cooling
Estimate Equipment Sizes
Example
Refrigeration Equipment Sizes based on the tons of cooling required 1 ton of cooling 1 ton of cooling
400 cfm . 12,000 Btu/hr .
Conversion from cfm to tons (Ventilation load) 252,000 Btu/hr per AHU (1 of 15 units) 15 AHU’s in school x 252,000 = 3,780,000 Btu Total for school 3,780,000 ÷ 12,000 btu/ton = 315 tons of cooling
Estimate Equipment Sizes Refrigeration Equipment Sizes based on the tons of cooling required 1 ton of cooling 1 ton of cooling
400 cfm . 12,000 Btu/hr .
Total Cooling Required - 484 tons Space Cooling Load - 169 tons Space Ventilation Load - 315 tons
Example
Estimate Equipment Sizes Chiller Size Two chillers are required
• reduced off-season loads • repair and maintenance
Example
484 tons of cooling required
•
Table reprinted from Architectureal Graphic Standards
Estimate Equipment Sizes Chiller Room • Dimensions from previous table • Room layout with pumpe
Example
484 tons of cooling required
Estimate Equipment Sizes Cooling Tower Size Based on tons of cooling required
• Table reprinted from Architectureal Graphic Standards
3+ - 150 ton cooling towers
Example
484 tons of cooling required
System Design Revise basic layout adding equipment sizes
Air Delivery side Return ducts and diffusers
Classroom 1
Classroom 2
Classroom 3
Classroom 4
VAV Box
VAV Box
VAV Box
VAV Box
Supply ducts and diffusers
Corridor
Mechanical Room Fresh outside air
Air Handling Unit (Air-conditioning)
Review HVAC Design Procedures !
Estimate the space cooling requirement
!
Estimate ventilation requirement
!
Determine supply air quantiy for each zone and AHU
!
Estimate equipment sizes - space sizes
!
Revise system layout
HVAC System Design Simplified Method for Early Design Part
Air Delivery side Return ducts and diffusers
Classroom 1
Classroom 2
Classroom 3
Classroom 4
VAV Box
VAV Box
VAV Box
VAV Box
Mechanical Room Fresh outside air
Air Handling Unit
Environmental Technology 1
