M. Kintner-Meyer, A.F. Emery / Energy and Buildings 23 (1995) 19-31
21
Condenser Loop
Direct Chiller
Cooling Tower
Storage Chiller Storage
Fig. 1. Schematic of air-conditioning system and building.
Chilled Water Loop
Air handler
storage discharging loop is added to the chilled water
main at the same water temperature.
The ice-storage tank is of a commonly used ice-on-
coil design where plastic tubing submerged in water
serves as a heat exchanger. A water/glycol solution
circulates inside the supply tubing at a temperature of
-4 °C and extracts heat from the water to create ice
on the outside of the tubing.
Both chillers are of a hermetic centrifugal type. The
heat extracted from the chilled water loop is released
into the condenser water loop and finally transferred
to the ambient air in the cooling tower. Fans at the
top of the cooling tower are used to maintain a sufficient
air mass flow rate to enable the mass and heat transfer
from the warmer water to the colder air.
The conditioned air is delivered by a variable air
volume system. The air entering the air handling unit
is generally a mixture of filtered recirculated and fresh
air. The fresh air fraction can be controlled but may
never he reduced to values below that needed to meet
the indoor air qualit3' standards.
4. Description and operation of building
The building is a s:imulated high-rise office building
with an approximate floor area of 33 600 m 2. Fig. 2
shows the dimensions for one floor. The building is
occupied from 7:00AM to 6:00PM. Three building types
are discussed in this analysis: (1) a thermally heavy
Table 1
Building specifics for the iheavy, light and ultra-light building
building with relatively thick interior and exterior walls,
(2) a thermally light building with approximately half
the wall thickness of the heavy building, (3) a thermally
ultra-light building with the same wall thickness as the
light, however, the thermal capacitance of all exterior
walls are assumed zero. The ultra-light building type
was chosen to simulate a typical light shell building
type with relatively little thermal capacitance in the
exterior wails. Table 1 lists the wall compositions for
each building type.
The number of occupants is assumed to be 3600 and
remains constant throughout the 7:00AM to 6:00PM
work period. With a total floor area of 33 600 m 2, the
occupant density amounts to about 10 m2/person. A
total heat gain from occupants of 160 kW was used
which corresponds to ASHRAE's published data for
office work [15]. With additional heat gain from office
equipment the total internal heat gain amounted to 38
W/m 2, which lies within the typical range for office
buildings of 20-50 W/m 2.
The estimation for the human moisture release into
the building was based on ASHRAE's respiratory rate
estimates [15]. A value of 1.333 10 -5 kg/s/person of
water was employed in this analysis.
The optimization is conducted first using Seattle
weather data and the electric rates of the local power
utility, Seattle City Light [16]. In Section 6.5, a regional
comparison of savings potentials is presented which
compares the optimal building control results for the
locations Phoenix, AZ; San Diego, CA; and the island
of Hawaii.
Wall name Heavy Light Ultra-light
Exterior walls
Floor
Ceiling
North, south windows
2 cm marble siding, 20 cm concrete 2 cm marble siding, 10 cm concrete 2 cm marble siding, 10 cm concrete
wall wall wall (zero capacitance)
21) cm concrete wall with lightweight 10 cm concrete wall with lightweight same as light
1.5 cm carpeting 1.5 cm carpeting
21) cm concrete wall 10 cm concrete wall same as light
tiiple glazing triple glazing same as light