Humidity Control with AC Equipment

Heat from the sun warming building

components, along with indoor heat

from lighting and appliances are normal

Heat Load Sources that raise the indoor

air temperature above the T-Stat setpoint

initiating a cooling cycle.

 

The air conditioning system removes

airborne moisture as it lowers the air

temperature. Any time the air conditioner

is running moisture is being removed

and the indoor air temperature is

dropping simultaneously.

 

Coincidental Humidity Control

Humidity Control using conventional

AC equipment is the coincidental result

of a continuous heat load source

creating an AC demand to run a cooling

cycle and lower the indoor air

temperature. Heat is required to use air

conditioning. If no heat is present the

thermostat will not operate

a cooling cycle.

 

Stand-Alone Dehumidifiers

Simple dehumidifiers can be used to

control relative humidity in conditioned

spaces. A humidistat commands DH

operation according to indoor relative

humidity level regardless of indoor

Temperature.  Dehumidifiers do not cool

the space like air conditioning systems.

Dehumidifiers have a cooling coil to chill

air below its dewpoint condensing

water vapor. A second "Reheat" coil

warms the air leaving the cooling coil

before it discharges into the space.

It can continue operating continuously

without ever overcooling the space.

Stand-Alone Dehumidifier substituting

for AC operation Simple dehumidifiers

located in the same space served by a

central AC system can substitute for

AC operation during unoccupied

periods when used to control

humidity without the need to

keep indoor temperature levels low as

well. The air conditioning system

is left in the "Off" mode while the

indoor humidity is being controlled

directly by the humidistat.

Advanced Thermostat / Humidity

Integrated  Control Systems

Advanced Digital Controls can operate

air conditioning and dehumidification

equipment  in concert with each other.

From a single wall mounted digital

interface screen, the user can select

both indoor temperature and

the relative humidity. The user specified

temperature is satisfied by shutting off

the dehumidifier while the AC is running,

and enabling dehumidifier operation

only after the desired indoor temperature

is achieved. Once the indoor temperature

setting is satisfied, the dehumidifier will

come on and run if the relative humidity

is still higher than specified after cooling.

This is the only configuration that offers

precise temperature and relative

humidity control regardless

of heat load.

 

AC Operation Requires Heat

The conditioned space will not have

sufficient moisture removal if the result

of air conditioning system operation is

not frequent enough or for long enough

durations to control moisture,

coincidental to indoor air temperature

control. If there is no heat load and an

air conditioning system is forced to run

anyway ; temperatures will drop

continuously until freeze-up occurs or

on some systems until shut down

occurs on systems with integral

freeze-up safety controls.

Over Cooling with Air Conditioning

Attempting to improve humidity control

by over-cooling a building can cause

additional indoor moisture problems.

Moisture migrates more rapidly through

building materials toward lower

temperatures wetting the materials

faster. Condensation occurs on

airhandler cabinets, ductwork other

components that are over-chilled by

the air inside them. The cold damp

indoor environment created

encourages microbial growth

in the air and on

indoor surfaces.

 

Humidity Control Using Air Conditioning System

 

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