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  4. 3.7 HVAC Secondary Systems

3.7.7 Humidity Controls and Devices

General

Humidifier Type
Applicability Optional humidifier
Definition The type of humidifier employed. Choices include:
  • Hot-Water
  • Steam
  • Electric
  • Evaporative Humidification
Units List (see above)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Humidistat Maximum Setting
Applicability Systems with humidity control
Definition The control setpoint for dehumidification
Units Percent (%)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Humidistat Minimum Setting
Applicability Systems with humidity control
Definition The control setpoint for humidification
Units Percent (%)
Input Restrictions As designed
Baseline Rules Same as proposed design

Desiccant

Desiccant Type
Applicability Systems with desiccant dehumidification
Definition Describes the configuration of desiccant cooling equipment
The following configurations for desiccant systems are allowed:
  • LIQ-VENT-AIR1 – a liquid desiccant dehumidifying unit
  • LIQ-VENT-AIR2 – a liquid desiccant dehumidifying unit combined with a gas-fired absorption chiller
  • SOL-VENT-AIR1 – a solid desiccant dehumidifying unit
  • NO-DESICCANT – the default, which indicates that no desiccant system is present
Units List (see above)
Input Restrictions As designed
Baseline Rules Not applicable
Desiccant Control Mode
Applicability Systems with desiccant dehumidification
Definition The method of controlling the operation of the desiccant unit. For liquid-based systems this can be either:
  • Dry-bulb – the desiccant unit is turned on whenever the outside air dry-bulb exceeds a set limit.
  • Evaporative cooling– cycles the desiccant unit on when an evaporative cooler is on to maintain a dewpoint setpoint.
  • Dewpoint – cycles the desiccant unit on and off to maintain the dewpoint temperature of the supply air.
For solid-based systems the following configurations are possible:
  • Dehumidification only – the desiccant unit cycles on and off to maintain indoor humidity levels
  • Sensible heat exchanger plus regeneration – the desiccant unit includes a sensible heat exchanger to precool the hot, dry air leaving the desiccant unit. The air leaving the exhaust side of the heat exchanger is directed to the desiccant unit
  • Sensible heat exchanger – the desiccant unit includes a heat exchanger, but the air leaving the exhaust side of the heat exchanger is exhausted to the outdoors
Units List (see above)
Input Restrictions As designed
Baseline Rules Not applicable
Desiccant Air Fraction
Applicability Systems with desiccant dehumidification
Definition The fraction of the supply air that passes through the desiccant unit. Typically either the minimum outside air fraction or all of the air passes through the desiccant system.
Units Ratio
Input Restrictions As designed
Baseline Rules Not applicable
Desiccant Heat Source
Applicability Systems with desiccant dehumidification
Definition The source of heat that is used to dry out the desiccant. This can be either:
  • Gas – Hydronic – the regeneration heat load is met with a gas-fired heater
  • Hot water – the heat load is met with hot water from the plant
Units List (see above)
Input Restrictions As designed
Baseline Rules Not applicable
Liquid Desiccant Performance Curves
Applicability Systems with liquid-based desiccant dehumidification
Definition

A set of performance curves that apply to liquid desiccant systems.

(6.7.7-1)

$$ D\!ESC\!\!-\!\!T\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-2)

$$ D\!ESC\!\!-\!\!W\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-3)

$$ D\!ESC\!\!-\!\!Gas\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-4)

$$ D\!ESC\!\!-\!\!kW\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

where

DESC-T-FTW temperature leaving desiccant unit
DESC-W-FTW humidity ratio leaving desiccant unit
DESC-Gas-FTW Gas usage of desiccant unit
DESC-kW-FTW Electric usage of desiccant unit
T entering air temperature
w entering humidity ratio

[table title="Liquid Desiccant Unit Performance Curves" id="liquid-desiccant-unit-performance-curves"]

Coefficient DESC-T-FTW DESC-W-FTW DESC-Gas-FTW DESC-kW-FTW
a 11.5334997 11.8993998  58745.8007813 3.5179000
b 0.6586730  -0.2695580  -1134.4899902 -0.0059317
c -0.0010280  0.0044549  -3.6676099 0.0000000
d 0.2950410  0.0830525  3874.5900879 0.0040401
e -0.0001700 0.0006974 -1.6962700 0.0000000
f -0.0008724 0.0015879 -13.0732002 0.0000000
Units Data structure
Input Restrictions As designed, default to values in [bookref id="liquid-desiccant-unit-performance-curves"]
Baseline Rules Not applicable
Desiccant Dewpoint Temperature Setpoint
Applicability Systems with desiccant dehumidification
Definition The setpoint dewpoint temperature of the air leaving the desiccant system
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 50°F.
Baseline Rules Not applicable
Desiccant Heat Exchanger Effectiveness
Applicability Systems with desiccant dehumidification
Definition The effectiveness of a sensible heat exchanger used with a desiccant system
Units Ratio
Input Restrictions As designed
Baseline Rules Not applicable
Desiccant Heat Exchanger Pressure Drop
Applicability Systems with desiccant dehumidification
Definition The pressure drop across a sensible heat exchanger used with a desiccant system
Units in. H2O
Input Restrictions As designed. Defaults to 1.0 in. H2O
Baseline Rules Not applicable

Minimum volume setpoint shall be 50% of the maximum design airflow rate, the minimum ventilation outdoor airflow rate, or the airflow rate required to comply with applicable codes or accreditation standards, whichever is larger. Fan volume shall be reset from 100% airflow at 100% cooling load to minimum airflow at 50% cooling load. Supply air temperature setpoint shall be reset from minimum supply air temperature at 50% cooling load and above to space temperature at 0% cooling load. In heating mode supply air temperature shall be modulated to maintain space temperature, and fan volume shall be fixed at the minimum airflow.

General

Humidifier Type

Applicability

Optional humidifier

Definition

The type of humidifier employed. Choices include1 :

  • Isothermal Humidification. the water vapor is dispersed in the air after having been created by boiling water.  Isothermal humidification requires an external source of energy to change the state of the water.  In the commercial HVAC world Isothermal Humidification has been used for years in nearly all applications. Types include:
  • Direct Steam Injection
  • Steam-To-Steam
  • Gas-To-Steam
  • Electric Steam
  • Infra-Red
  • Adiabatic Humidification. finely atomized water is introduced into the air.  The adiabatic process does not involve the contribution of thermal energy from an external source.  There is no heat added. Types include:
    • High Pressure Atomizing
    • Air/Water Atomizing
    • Ultrasonic
    • Wetted Media Evaporative

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

The baseline building shall have humidification if the proposed design does, but the system shall be non-adiabatic. For systems serving computer rooms, the baseline shall nt have reheat for the purpose of humidification.

 

Humidistat Maximum Setting

Applicability

Systems with humidity control

Definition

The control setpoint for dehumidification

Units

Percent (%)

Input Restrictions

As designed

Baseline Rules

Same as the proposed design

 

Humidistat Minimum Setting

Applicability

Systems with humidity control

Definition

The control setpoint for humidification

Units

Percent (%)

Input Restrictions

As designed

Baseline Rules

Same as proposed design

Desiccant

Desiccant Type

Applicability

Systems with desiccant dehumidification

Definition

Describes the configuration of desiccant cooling equipment
The following configurations for desiccant systems are allowed:

  • LIQ-VENT-AIR1 – a liquid desiccant dehumidifying unit
  • LIQ-VENT-AIR2 – a liquid desiccant dehumidifying unit combined with a gas-fired absorption chiller
  • SOL-VENT-AIR1 – a solid desiccant dehumidifying unit
  • NO-DESICCANT – the default, which indicates that no desiccant system is present

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Desiccant Control Mode

Applicability

Systems with desiccant dehumidification

Definition

The method of controlling the operation of the desiccant unit. For liquid-based systems this can be either:

  • Dry-bulb – the desiccant unit is turned on whenever the outside air dry-bulb exceeds a set limit.
  • Evaporative cooling– cycles the desiccant unit on when an evaporative cooler is on to maintain a dewpoint setpoint.
  • Dewpoint – cycles the desiccant unit on and off to maintain the dew point temperature of the supply air.

For solid-based systems the following configurations are possible:

  • Dehumidification only – the desiccant unit cycles on and off to maintain indoor humidity levels
  • Sensible heat exchanger plus regeneration – the desiccant unit includes a sensible heat exchanger to precool the hot, dry air leaving the desiccant unit. The air leaving the exhaust side of the heat exchanger is directed to the desiccant unit
  • Sensible heat exchanger – the desiccant unit includes a heat exchanger, but the air leaving the exhaust side of the heat exchanger is exhausted to the outdoors

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Desiccant Air Fraction

Applicability

Systems with desiccant dehumidification

Definition

The fraction of the supply air that passes through the desiccant unit. Typically either the minimum outside air fraction or all of the air passes through the desiccant system.

Units

Ratio

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Desiccant Heat Source

Applicability

Systems with desiccant dehumidification

Definition

The source of heat that is used to dry out the desiccant. This can be either:

  • Gas – Hydronic – the regeneration heat load is met with a gas-fired heater
  • Hot water – the heat load is met with hot water from the plant

Units

List (see above)

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Liquid Desiccant Performance Curves

Applicability

Systems with liquid-based desiccant dehumidification

Definition

A set of performance curves that apply to liquid desiccant systems.

(Equation 3.7.7-1)

$$DESC\_T\_FTW = a + b \cdot T + c \cdot T^{2} + d \cdot w + e \cdot w^{2} + f \cdot T \cdot w$$

(Equation 3.7.7-2)

$$DESC\_W\_FTW = a + b \cdot T + c \cdot T^{2} + d \cdot w + e \cdot w^{2} + f \cdot T \cdot w$$

(Equation 3.7.7-3)

$$DESC\_Gas\_FTW = a + b \cdot T + c \cdot T^{2} + d \cdot w + e \cdot w^{2} + f \cdot T \cdot w$$

(Equation 3.7.7-4)

$$DESC\_kW\_FTW = a + b \cdot T + c \cdot T^{2} + d \cdot w + e \cdot w^{2} + f \cdot T \cdot w$$

where

DESC-T-FTW

temperature leaving desiccant unit

DESC-W-FTW

humidity ratio leaving desiccant unit

DESC-Gas-FTW

Gas usage of desiccant unit

DESC-kW-FTW

Electric usage of desiccant unit

T

entering air temperature

w

entering humidity ratio

a, b, c, d, e, f

Coefficients taken from Appendix H

Units

Data structure

Input Restrictions

As designed, default to values in Appendix H

Baseline Rules

Not applicable

 

Desiccant Dewpoint Temperature Setpoint

Applicability

Systems with desiccant dehumidification

Definition

The setpoint dewpoint temperature of the air leaving the desiccant system

Units

Degrees Fahrenheit (°F)

Input Restrictions

As designed. Defaults to 50°F.

Baseline Rules

Not applicable

 

Desiccant Heat Exchanger Effectiveness

Applicability

Systems with desiccant dehumidification

Definition

The effectiveness of a sensible heat exchanger used with a desiccant system

Units

Ratio

Input Restrictions

As designed

Baseline Rules

Not applicable

 

Desiccant Heat Exchanger Pressure Drop

Applicability

Systems with desiccant dehumidification

Definition

The pressure drop across a sensible heat exchanger used with a desiccant system

Units

in. H2O 

Input Restrictions

As designed. Defaults to 1.0 in. H2O

Baseline Rules

Not applicable
 

 

  • 1This information is taken from http://www.dac-hvac.com/ask-rick-what-is-adiabatic-humidification/. The biggest advantages of Adiabatic Humidifiers are: energy savings, precise humidity control, simple technology. The disadvantages are  longer absorption distances (more length need in an air handling unit), requires preheat of supply air, typically requires RO water, compressed air required on air/water systems.
90.1-2019

This section addresses:

General

Humidifier Type
Applicability Optional humidifier
Definition The type of humidifier employed. Choices include:
  • Hot-Water
  • Steam
  • Electric
  • Evaporative Humidification
Units List (see above)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Humidistat Maximum Setting
Applicability Systems with humidity control
Definition The control setpoint for dehumidification
Units Percent (%)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Humidistat Minimum Setting
Applicability Systems with humidity control
Definition The control setpoint for humidification
Units Percent (%)
Input Restrictions As designed
Baseline Rules Same as proposed design

Desiccant

Desiccant Type
Applicability Systems with desiccant dehumidification
Definition Describes the configuration of desiccant cooling equipment
The following configurations for desiccant systems are allowed:
  • LIQ-VENT-AIR1 – a liquid desiccant dehumidifying unit
  • LIQ-VENT-AIR2 – a liquid desiccant dehumidifying unit combined with a gas-fired absorption chiller
  • SOL-VENT-AIR1 – a solid desiccant dehumidifying unit
  • NO-DESICCANT – the default, which indicates that no desiccant system is present
Units List (see above)
Input Restrictions As designed
Desiccant Control Mode
Applicability Systems with desiccant dehumidification
Definition The method of controlling the operation of the desiccant unit. For liquid-based systems this can be either:
  • Dry-bulb – the desiccant unit is turned on whenever the outside air dry-bulb exceeds a set limit.
  • Evaporative cooling– cycles the desiccant unit on when an evaporative cooler is on to maintain a dewpoint setpoint.
  • Dewpoint – cycles the desiccant unit on and off to maintain the dewpoint temperature of the supply air.
For solid-based systems the following configurations are possible:
  • Dehumidification only – the desiccant unit cycles on and off to maintain indoor humidity levels
  • Sensible heat exchanger plus regeneration – the desiccant unit includes a sensible heat exchanger to precool the hot, dry air leaving the desiccant unit. The air leaving the exhaust side of the heat exchanger is directed to the desiccant unit
  • Sensible heat exchanger – the desiccant unit includes a heat exchanger, but the air leaving the exhaust side of the heat exchanger is exhausted to the outdoors
Units List (see above)
Input Restrictions As designed
Desiccant Air Fraction
Applicability Systems with desiccant dehumidification
Definition The fraction of the supply air that passes through the desiccant unit. Typically either the minimum outside air fraction or all of the air passes through the desiccant system.
Units Ratio
Input Restrictions As designed
Desiccant Heat Source
Applicability Systems with desiccant dehumidification
Definition The source of heat that is used to dry out the desiccant. This can be either:
  • Gas – Hydronic – the regeneration heat load is met with a gas-fired heater
  • Hot water – the heat load is met with hot water from the plant
Units List (see above)
Input Restrictions As designed
Liquid Desiccant Performance Curves
Applicability Systems with liquid-based desiccant dehumidification
Definition

A set of performance curves that apply to liquid desiccant systems.

(6.7.7-1)

$$ D\!ESC\!\!-\!\!T\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-2)

$$ D\!ESC\!\!-\!\!W\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-3)

$$ D\!ESC\!\!-\!\!Gas\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-4)

$$ D\!ESC\!\!-\!\!kW\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

where

DESC-T-FTW temperature leaving desiccant unit
DESC-W-FTW humidity ratio leaving desiccant unit
DESC-Gas-FTW Gas usage of desiccant unit
DESC-kW-FTW Electric usage of desiccant unit
T entering air temperature
w entering humidity ratio

[table title="Liquid Desiccant Unit Performance Curves" id="liquid-desiccant-unit-performance-curves"]

Coefficient DESC-T-FTW DESC-W-FTW DESC-Gas-FTW DESC-kW-FTW
a 11.5334997 11.8993998  58745.8007813 3.5179000
b 0.6586730  -0.2695580  -1134.4899902 -0.0059317
c -0.0010280  0.0044549  -3.6676099 0.0000000
d 0.2950410  0.0830525  3874.5900879 0.0040401
e -0.0001700 0.0006974 -1.6962700 0.0000000
f -0.0008724 0.0015879 -13.0732002 0.0000000
Units Data structure
Input Restrictions As designed, default to values in [bookref id="liquid-desiccant-unit-performance-curves"]
Desiccant Dewpoint Temperature Setpoint
Applicability Systems with desiccant dehumidification
Definition The setpoint dewpoint temperature of the air leaving the desiccant system
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 50°F.
Desiccant Heat Exchanger Effectiveness
Applicability Systems with desiccant dehumidification
Definition The effectiveness of a sensible heat exchanger used with a desiccant system
Units Ratio
Input Restrictions As designed
Desiccant Heat Exchanger Pressure Drop
Applicability Systems with desiccant dehumidification
Definition The pressure drop across a sensible heat exchanger used with a desiccant system
Units in. H2O
Input Restrictions As designed. Defaults to 1.0 in. H2O

General

Humidifier Type
Applicability Optional humidifier
Definition The type of humidifier employed. Choices include:
  • Hot-Water
  • Steam
  • Electric
  • Evaporative Humidification
Units List (see above)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Humidistat Maximum Setting
Applicability Systems with humidity control
Definition The control setpoint for dehumidification
Units Percent (%)
Input Restrictions As designed
Baseline Rules Same as the proposed design
Humidistat Minimum Setting
Applicability Systems with humidity control
Definition The control setpoint for humidification
Units Percent (%)
Input Restrictions As designed
Baseline Rules Same as proposed design

Desiccant

Desiccant Type
Applicability Systems with desiccant dehumidification
Definition Describes the configuration of desiccant cooling equipment
The following configurations for desiccant systems are allowed:
  • LIQ-VENT-AIR1 – a liquid desiccant dehumidifying unit
  • LIQ-VENT-AIR2 – a liquid desiccant dehumidifying unit combined with a gas-fired absorption chiller
  • SOL-VENT-AIR1 – a solid desiccant dehumidifying unit
  • NO-DESICCANT – the default, which indicates that no desiccant system is present
Units List (see above)
Input Restrictions As designed
Desiccant Control Mode
Applicability Systems with desiccant dehumidification
Definition The method of controlling the operation of the desiccant unit. For liquid-based systems this can be either:
  • Dry-bulb – the desiccant unit is turned on whenever the outside air dry-bulb exceeds a set limit.
  • Evaporative cooling– cycles the desiccant unit on when an evaporative cooler is on to maintain a dewpoint setpoint.
  • Dewpoint – cycles the desiccant unit on and off to maintain the dewpoint temperature of the supply air.
For solid-based systems the following configurations are possible:
  • Dehumidification only – the desiccant unit cycles on and off to maintain indoor humidity levels
  • Sensible heat exchanger plus regeneration – the desiccant unit includes a sensible heat exchanger to precool the hot, dry air leaving the desiccant unit. The air leaving the exhaust side of the heat exchanger is directed to the desiccant unit
  • Sensible heat exchanger – the desiccant unit includes a heat exchanger, but the air leaving the exhaust side of the heat exchanger is exhausted to the outdoors
Units List (see above)
Input Restrictions As designed
Desiccant Air Fraction
Applicability Systems with desiccant dehumidification
Definition The fraction of the supply air that passes through the desiccant unit. Typically either the minimum outside air fraction or all of the air passes through the desiccant system.
Units Ratio
Input Restrictions As designed
Desiccant Heat Source
Applicability Systems with desiccant dehumidification
Definition The source of heat that is used to dry out the desiccant. This can be either:
  • Gas – Hydronic – the regeneration heat load is met with a gas-fired heater
  • Hot water – the heat load is met with hot water from the plant
Units List (see above)
Input Restrictions As designed
Liquid Desiccant Performance Curves
Applicability Systems with liquid-based desiccant dehumidification
Definition

A set of performance curves that apply to liquid desiccant systems.

(6.7.7-1)

$$ D\!ESC\!\!-\!\!T\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-2)

$$ D\!ESC\!\!-\!\!W\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-3)

$$ D\!ESC\!\!-\!\!Gas\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

(6.7.7-4)

$$ D\!ESC\!\!-\!\!kW\!\!-\!\!FTW = a + b \times T + c \times T^2 + d \times w + e \times w^2 + f \times T \times w$$

where

DESC-T-FTW temperature leaving desiccant unit
DESC-W-FTW humidity ratio leaving desiccant unit
DESC-Gas-FTW Gas usage of desiccant unit
DESC-kW-FTW Electric usage of desiccant unit
T entering air temperature
w entering humidity ratio

[table title="Liquid Desiccant Unit Performance Curves" id="liquid-desiccant-unit-performance-curves"]

Coefficient DESC-T-FTW DESC-W-FTW DESC-Gas-FTW DESC-kW-FTW
a 11.5334997 11.8993998  58745.8007813 3.5179000
b 0.6586730  -0.2695580  -1134.4899902 -0.0059317
c -0.0010280  0.0044549  -3.6676099 0.0000000
d 0.2950410  0.0830525  3874.5900879 0.0040401
e -0.0001700 0.0006974 -1.6962700 0.0000000
f -0.0008724 0.0015879 -13.0732002 0.0000000
Units Data structure
Input Restrictions As designed, default to values in [bookref id="liquid-desiccant-unit-performance-curves"]
Desiccant Dewpoint Temperature Setpoint
Applicability Systems with desiccant dehumidification
Definition The setpoint dewpoint temperature of the air leaving the desiccant system
Units Degrees Fahrenheit (°F)
Input Restrictions As designed. Defaults to 50°F.
Desiccant Heat Exchanger Effectiveness
Applicability Systems with desiccant dehumidification
Definition The effectiveness of a sensible heat exchanger used with a desiccant system
Units Ratio
Input Restrictions As designed
Desiccant Heat Exchanger Pressure Drop
Applicability Systems with desiccant dehumidification
Definition The pressure drop across a sensible heat exchanger used with a desiccant system
Units in. H2O
Input Restrictions As designed. Defaults to 1.0 in. H2O