Environmental Engineering Reference
In-Depth Information
Indoor Air Quality Standard of Performance
Central Air-Handling Unit (AHU-1)
GENERAL INFORMATION
System type
: Variable air volume (VAV) built-up air handling unit with chilled
water cooling, hot water heating, and an economizer cycle. Conditioned and
ventilation air is supplied to the space through VAV terminal diffusers. Supple-
mental heat is provided by a perimeter baseboard hot water radiation system.
Area served:
This two-story building is served by AHU-1, 2, 3 (all identical). Each
room has individual control, and each floor is divided into two primary suites
for the purpose of minimum air control.
Description:
AHU-1, 2, and 3 are equipped with a chilled water coil (440 Mbh,
88 gpm, 45°F entering, 55°F leaving), a hot water coil (500 Mbh, 33 gpm, 120°F
entering, 90°F leaving), an economizer section, filters and a supply fan (20,000
cfm), and return (18,000 cfm) fan. Each air handler provides a variable volume
of air to maintain a constant static pressure (0.4”w.g.) in the ductwork, based on
a static pressure sensor located in the supply ductwork above room 125, 225,
and 280, respectively. Individual zone VAV terminal units vary the air to maintain
the space setpoint based on integral thermostats.
The supply air temperature is reset based on the return air temperature. At a
return air temperature of 76°F, 50°F supply air is provided, and at a return air
temperature of 72°F, 58°F supply air is provided. A central direct digital control
(DDC) system maintains the discharge air temperature by varying the position of
the chilled and hot water coil valves. The controls also operate the economizer
when the outdoor air temperature is below 65°F. When the outdoor air is above
63°F, the outdoor air dampers go to their minimum position. The minimum
position is reset based on the total supply airflow to maintain 4000 cfm of outdoor
air. At full system flow the outside air dampers are set to 20% flow and at
minimum system flow (5000 cfm), the dampers are set to 80% of flow (4000 cfm).
Cooling is disabled below an outdoor air temperature of 55°F, and Heating is
disabled above an outdoor air temperature of 53°F.
Figure 13.3
Model standard of performance for a central air handling unit. (From
Dorgan, C.E. and Dorgan, C.B.,
Proc. 8th Internatl. Conf. Indoor Air Quality & Climate
,
Edinburgh, 4, 218, 1999.)
devices, outdoor air dampers, humidifiers, dehumidification coils, drain
pans, outdoor air intakes, sensors, cooling towers, and floor drains. Main-
tenance activities beyond these core requirements would be included in a
guidance document.
2.
Lead
The 1995 HUD
Guidelines for the Evaluation and Control of Lead-Based Paint
Hazards in Housing
describe good practice procedures to use when conducting:
building inspections for lead, risk assessments, and lead abatements employ-
