Honeywell AUTOMATIC CONTROL User Manual

PSYCHROMETRIC CHART FUNDAMENTALS
53
ENGINEERING MANUAL OF AUTOMATIC CONTROL
COOLING
COIL
HEATING
COIL
SUPPLY FAN
90°F DB
71.3°F WB
40% RH
48°F DB
46°F WB
85% RH
60°F DB
51.2°F WB
56% RH
V
H
C2600
V
T
Fig. 29. Fan System with Dehumidification and Reheat.
Figure 30 illustrates cooling and dehumidification with reheat
for maintaining constant relative humidity. Air enters the coils
at Point A, is cooled and dehumidified to Point B, is reheated
to Point C, and is then delivered to the controlled space. A space
humidistat controls the cooling coil valve to maintain the space
relative humidity. A space thermostat controls the reheat coil
to maintain the proper dry-bulb temperature.
B
C
A
48°F DB
46°F WB
85% RH
60°F DB
51.2°F WB
56% RH
90°F DB
71.3°F WB
40% RH
C1850
Fig. 30.
PROCESS SUMMARY
Figures 31 and 32 summarize some principles of the air
conditioning process as illustrated by psychrometric charts.
— Sensible heating or cooling is always along a constant
moisture line.
—When latent heat is added or removed, a process line
always crosses the constant moisture lines.
LATENT HEAT CHANGE
SENSIBLE HEAT CHANGE
C1851
Fig. 31.
A
C
B
D
E
F
G
H
SUMMARY OF ALL PROCESSES CHARTABLE.
PROCESS MOVEMENT IN THE DIRECTION OF:
— A, HEATING ONLY - STEAM, HOT WATER OR ELECTRIC HEAT COIL
— B, HEATING AND HUMIDIFYING - STEAM HUMIDIFIER
OR RECIRCULATED HOT WATER SPRAY
— C, HUMIDIFYING ONLY - AIR WASHER WITH HEATED WATER
— D, COOLING AND HUMIDIFYING - WASHER
— E, COOLING ONLY - COOLING COIL OR WASHER AT
DEWPOINT TEMPERATURE
— F, COOLING AND DEHUMIDIFYING - CHILLED WATER WASHER
— G, DEHUMIDIFYING ONLY - NOT PRACTICAL
— H, DEHUMIDIFYING AND HEATING - CHEMICAL DEHUMIDIFIER
C1852
Fig. 32.
— Enthalpy and humidity ratio, or moisture content, are
based on a pound of dry air. Zero moisture is the bottom
line of the chart.
—To find the sensible heat content of any air in Btu, follow
the dry-bulb line to the bottom of the chart and read the
enthalpy there, or project along the enthalpy line, and
read the Btu per pound of dry air on the enthalpy scale.
ASHRAE PSYCHROMETRIC CHARTS
The following two pages illustrate ASHRAE Psychrometric Charts No. 1 and No. 2.

Honeywell AUTOMATIC CONTROL Specifications

General

Brand	Honeywell
Model	AUTOMATIC CONTROL
Category	Controller
Language	English