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6.7.7 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 6.7.7-1: "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 Table 6.7.7-1
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