 2011 Addison
100% Outside Air and
Dehumidification
Management
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air - What is it ?
• Referred to as “Make-up Air”
– Unit operates continually during occupied
mode
– Replaces exhausted air
– No mixture with return air
– Totally changing load
• Summer design (High temperature and high
humidity)
• Winter design (Cold temperature)
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Why 100% Outside Air?
• Ventilation standards indicating recommended air changes for a
variety of space usages and occupancy have been established by
ASHRAE. The ventilation requirements for a given structure or
space are based either on desired number of air changes or the
number of occupants.
• The amount of outside air fresh air required for each change per
hour equals the amount of inside air that must be removed from the
space during the same time span.
• CFM= Area of space / Minutes of air changes
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Ventilation Requirements
(continued)
•
•
•
•
•
•
College classroom 8 air changes
Hospitals
9-17 air changes
Kitchens
10-20 air changes
Schools
8-12 air changes
Theaters
5-10 air changes
Factory Buildings 10-15 air changes
20-30 cfm/person
40-50 cfm/person
40-50 cfm/person
30-35 cfm/person
10-15 cfm/person
25-30 cfm/person
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Applications of Make-Up Air
•Return Air Ducts
–Typically will not affect space conditions
– May not require Reheat
– Control is not as critical
•Direct to Space
–Usually applied to large areas
•(Auditoriums, Kitchens, Corridors)
– More precise control is necessary
– Reheat is required for control
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air “Supply Air
Properties”
• Unit discharge air properties
– Main purpose – positively impact building
humidity
• Lowest dew point possible
– Ideally close to room (neutral) conditions
• Typically between 68 -72 degrees
• Not to overcool or overheat space
– Below 70% RH per ASHRAE standards
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Dew Point Comparison
Reheating to Neutral Air
DRY BULB TEMPERATURE - °F
70°F
DEW POINT
72°F
75°F
RELATIVE HUMIDITY – RH %
45°F
40.6
37.9
34.3
50°F
49
45.8
41.4
55°F
58.9
55.1
49.8
60°F
70.6
65.9
59.6
65°F
84.2
78.6
71.1
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Air Control
• Leaving Air Control
– Hot Gas Reheat
• Cycling Control
• Modulating Control
• Room Control
– Hot Gas Reheat
• Cycling in conjunction with a reheat thermostat
• Modulating in conjunction with a reheat sensor
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100 % Outside Air - Room
Reheat Control
T
T
Reheat Control - room
thermostat in series with
discharge thermostat
(neutral or cold air)
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Compressors Usage
• Single Compressor -- Single Circuit
– Used when low dew point in required
– Dehumidifies all the air all of the time
• Dual Circuits – Single Compress each circuit
– Used when leaving air conditions are not critical
– Air will bypass lag circuit and then mix with lead circuit
• Dual Circuits – Two compressors (Tandem) each circuit)
– Lag compressor cycles based on suction pressure.
– Four (4) stage operation
– Large Tonnage
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
“Refrigeration” Control
• Hot Gas Bypass
– Modulates to match the evaporator load
– Evaporator freeze protection
– Suction pressure activated
• Hot Gas Reheat
– Raises leaving air temperature to room neutral conditions
– Cycling with discharge air thermostat
– Modulating with sensor.
• Liquid Subcool Coil
– Raises leaving air temperature
– Subcools liquid
– Two (2) degrees of subcool equals one (1) percent increase
in evaporator capacity
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Standard Cycling Hot Gas
Reheat
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Hot Gas Reheat Plus Sub-Cooling
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Hot Gas Reheat Using Digital Scroll
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air Example
•
•
Summer design
– 1800 cfm
– 92/75 ambient
– Leaving air
• 55 deg Dew Point
• 65 deg leaving air temperature
Winter design
– 0 degree ambient
– Leaving air (minimum 70 deg)
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Summer Design w/Reheat
Supply Temp.
55.0/55.0
Ambient
92/75
Leaving Air
79.7/64.1
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air Summer
Design w/Reheat Plus
Liq. Sub-cool
66.1/59.4
Supply Temp.
52.2 D.P.
Ambient
92/75
Leaving Air
90.5/67.7
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Summer Part Load w/Reheat
Supply Temp.
53.9 D.P.
Ambient
75/75
Leaving Air
86.1/64.3
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Part Load w/Reheat Plus
Liq. Sub-cool
65.7/58.8
Supply Temp.
50.8 D.P.
Ambient
75/75
Leaving Air
94.0/67.1
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Summer Part Load w/Reheat
Supply Temp.
48.8/48.8
Ambient
70/70
Leaving Air
79.5/61.2
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Part Load w/Reheat Plus
Liq. Sub-cool
59.9/54.3
Supply Temp.
48.1 D.P.
Ambient
70/70
Leaving Air
83.1/64.3
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Summer Part Load w/Reheat
Supply Temp.
46.8/46.8
Ambient
65/65
Leaving Air
73.7/63.8
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Part Load w/Reheat Plus
Liq. Sub-cool
55.8/51.5
Supply
Temp.
47.0 D.P.
Ambien
t
65/65
Leaving Air
79.4/61.0
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Summer Part Load w/Reheat
Supply Temp.
51.4/51.4
Ambient
60/60
Leaving Air
64.3/56.2
10 ton
1800cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Part Load w/Reheat Plus
Liq. Sub-cool
55.2/52.1
Supply Temp.
50.4 D.P.
Ambient
60/60
Leaving Air
72.6/57.4
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
100% Outside Air
Winter Design Conditions
175,000 BTUH
Furnace
Ambient
0
Leaving Air
72
10 ton
1800 cfm
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Recap
•
Do No Harm
– Dehumidify to 55 0 Dew Point or less.
– Reheat to Room Neutral.
– Temper to Room Neutral
– Possible humidify when ambient
temperatures are below 35 0
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Energy Conservation Wheel
Applications
• Require exhaust air from the building
• Require defrost in most areas
• Total Unit EER can exceed 25 on some
water source heat pump applications
This document is intended to assist licensed professionals in the exercise of their professional judgment.
 2011 Addison
Dedicated Outdoor Air
Load Reduction
Example:
ASHRAE Design Conditions
for Atlanta, GA
Cooling Mode
100% OA w/ Energy
Conservation Wheel
Cooling
Dehum.
Cooling
Dehum.
Evaporator
Discharge Air
(enthalpy)
(db / wb)
(enthalpy)
93.9 / 74.8
38.22
----52.0 / 52.0
21.43
82.0 / 76.4
39.91
----52.0 / 52.0
21.43
Total Capacity
MBH
327.62
360.63
Sensible Capacity
MBH
199.26
142.67
Latent Capacity
MBH
128.36
217.96
93.9 / 74.8
38.22
80.7 / 67.0
31.50
52.0 / 52.0
21.43
196.58
-40.0%
136.49
-31.5%
60.09
-53.2%
82.0 / 76.4
39.91
77.1 / 67.6
32.02
52.0 / 52.0
21.43
206.61
-42.7%
119.37
-16.3%
87.24
-60.0%
Outdoor Air
ECW Supply Air
Loads based on:
• 4250 cfm supply and exhaust
airflow
• 48” Energy Conservation
Wheel
• 75F/ 50%RH summer exhaust
air
• 70F / 30%RH winter exhaust
100% OA
(db / wb)
(enthalpy)
(db / wb)
Heating Mode
Outdoor Air
ECW Supply Air
Unit Supply Air
(db)
(db)
(db)
0
--70
Heating Capacity
MBH
321.30
•Source: www.novelaire.com
(graphic)
This document is intended to assist licensed professionals in the exercise of their professional judgment.
0
48.8
70
97.31
-69.7%
 2011 Addison
for your attention
This document is intended to assist licensed professionals in the exercise of their professional judgment.