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ASHRAE 62.1

The Importance of DOAS
by

Matt Zblewski

on 5 May 2014

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Transcript of ASHRAE 62.1

ASHRAE 62.1
&
The Advantages of DOAS
Matt Zblewski
B.S. in Mechanical Engineering
Michigan Technological University
Regional Sales Manager
Modine Manufacturing Co.
Demand Control Ventilation
Determine ventilation rate from selective occupant evaluation
Irritation of eyes, nose and upper respiratory
Odors
Generally need 80% to deem air not objectionable
Typically increases in outdoor airflow rates increase acceptability
Subjective Evaluation (6.3.4.2)
Steady State or Dynamic mass-balance analysis
Determine minimum outdoor air required to achieve concentration limits for each contaminant
Mass Balance Analysis (6.3.4.1)
Contaminant Sources
Both Indoor/Outdoor sources identified
Emission rate for each determined
Contaminant Concentration
Concentration limit/Corresponding exposure period
Appropriate reference to a cognizant authority
Perceived indoor air quality
Specified in percentage of occupants expressing satisfaction with perceived IAQ
Outdoor airflow rate must be the larger of those determined in accordance with Section 6.3.4.1 and either 6.3.4.2 or 6.3.4.3
IAQ Procedure
Outdoor airflow rate must not be less than found in similar zone
Contaminants of concern
Concentration limits
Air cleaning efficiency
Acceptability limits
Similar zone must be in accordance with 6.3.4.2
Similar Zone (6.3.4.3)
ASHRAE 62.1-2010
&
The Advantage of DOAS

How do we determine the rate?
Ventilation Rate Procedure
IAQ Procedure
Natural Ventilation Procedure
Ventilation Rate Procedure
Vbz = Rp*Pz +Ra*Az

Vbz = Ventilation Breathing Zone
Rp = Ventilation rate per person
Pz = Population of zone
Ra = Ventilation rate per zone area
Az = Area of zone
Vbz = 5*50 + 0.06*1000
Vbz = 310 cfm
Other Factors
Demand Control Ventilation
Three Procedures
Space Type/Application
Occupational Rate
Floor Area
Three Different Procedures
Why Dedicated Outside Air Systems?
Typically from occupants
Office example
185 btu/hr per person
17 cfm ventilation per person
Offset Space Latent
Comply with ASHRAE 62.1
It is almost impossible to defend ventilation amount in all air VAV systems
Ventilation distribution is uneven
Product of too many variables
Minimum ventilation settings
Space sensible load
Exhaust and exfiltration
100% OA systems place proper ventilation air quantities in every space
Proper Ventilation
Offset Space Latent
From this example, it can be shown that the supply air dew point must be 16 grains lower than the space dew point to offset the space latent.

Let’s check this out on the psychrometric chart
Offset Space Latent
16 gr/lb
Target Space Conditions
DB = 75°
RH = 50%
DP = 55°
Supply Conditions
DB = DP = 47°
Improve Indoor Air Quality
Local units only see space sensible load
Little or no moisture on cooling coils
No clogged/overflowed drain pans
No chance to grow bacteria
Improve IAQ
Demand Control Ventilation
Other Factors
Q = CFM*ΔGr*0.68

185 = 17*ΔGr*0.68

185/(17*0.68) = ΔGr

16 = ΔGr
(Table 6-2)
Full transcript