Heating Equipment - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

CONTROL FUNDAMENTALS
Infiltration is the process by which outdoor air enters a
building through walls, cracks around doors and windows, and
open doors due to the difference between indoor and outdoor
air pressures. The pressure differential is the result of
temperature difference and air intake or exhaust caused by fan
operation. Heat loss due to infiltration is a function of
temperature difference and volume of air moved. Exfiltration
is the process by which air leaves a building (e.g., through walls
and cracks around doors and windows) and carries heat with it.
Infiltration and exfiltration can occur at the same time.
Ventilation brings in fresh outdoor air that may require
heating. As with heat loss from infiltration and exfiltration, heat
loss from ventilation is a function of the temperature difference
and the volume of air brought into the building or exhausted.

HEATING EQUIPMENT

Selecting the proper heating equipment depends on many
factors, including cost and availability of fuels, building size
and use, climate, and initial and operating cost trade-offs.
Primary sources of heat include gas, oil, wood, coal, electrical,
and solar energy. Sometimes a combination of sources is most
economical. Boilers are typically fueled by gas and may have
the option of switching to oil during periods of high demand.
Solar heat can be used as an alternate or supplementary source
with any type of fuel.
Figure 4 shows an air handling system with a hot water coil.
A similar control scheme would apply to a steam coil. If steam
or hot water is chosen to distribute the heat energy, high-
efficiency boilers may be used to reduce life-cycle cost. Water
generally is used more often than steam to transmit heat energy
from the boiler to the coils or terminal units, because water
requires fewer safety measures and is typically more efficient,
especially in mild climates.
THERMOSTAT
HOT WATER
SUPPLY
FAN
HOT WATER
RETURN
Fig. 4. System Using Heating Coil.
An air handling system provides heat by moving an air stream
across a coil containing a heating medium, across an electric
heating coil, or through a furnace. Unit heaters (Fig. 5) are
typically used in shops, storage areas, stairwells, and docks.
Panel heaters (Fig. 6) are typically used for heating floors and
are usually installed in a slab or floor structure, but may be
installed in a wall or ceiling.
VALVE
DISCHARGE
AIR
C2702
FAN
COIL
UNIT HEATER
Fig. 5. Typical Unit Heater.
GRID PANEL
SERPENTINE PANEL
Fig. 6. Panel Heaters.
Unit ventilators (Fig. 7) are used in classrooms and may
include both a heating and a cooling coil. Convection heaters
(Fig. 8) are used for perimeter heating and in entries and
corridors. Infrared heaters (Fig. 9) are typically used for spot
heating in large areas (e.g., aircraft hangers, stadiums).
WALL
HEATING
COIL
OUTDOOR
AIR
Fig. 7. Unit Ventilator.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
10
STEAM OR
HOT WATER
SUPPLY
CONDENSATE
OR HOT WATER
RETURN
STEAM TRAP
(IF STEAM SUPPLY)
C2703
HOT WATER
SUPPLY
HOT WATER
RETURN
HOT WATER
SUPPLY
HOT WATER
RETURN
C2704
DISCHARGE
AIR
FAN
COOLING
COIL
DRAIN PAN
MIXING
DAMPERS
RETURN
AIR
C3035