A commercial office building, comprising 803,529 square
feet total, 25 story office floors each covering 20,000
square feet. LaSalle occupancy is near 100%. Energy
costs had risen from $1.44 per sq. ft. in 1994, ($1,156,336.00
total building energy costs) to $1.85 ($1,489,229.00
total building energy costs) in 1995 primarily as
a result of an increase in tenant occupancy to the
present levels. BTU’s per square foot had similarly
risen from 89,198 to 118,305, an increase of 32.63%,
while heating degree days increased 3.16% and cooling
degree days increased 43.76%.
overall energy costs, primarily steam consumption,
without negatively affecting tenant comfort or adversely
affecting IAQ. Steam consumption accounts for 16%
of the total utility costs while chilled water & electricity
each accounts for 42% of the remaining energy costs
one CO2 duct mounted sensor per AHU, (one AHU per
floor), revise EMS control program to accomplish CO2
Demand Controlled Ventilation and revise control of
minimum outside air dampers to incorporate full modulation
vs. Fixed minimum setting.
VFD’s on all vane axial fan motors to take advantage
of the reduced air flow requirements using CO2 Demand
Controlled Ventilation strategy. Install VFD’s on
the remaining tower floor AHU’s (approx. 12) to coincide
with the reduced volume of air supplied and exhausted
to each floor.
VFD’s on 2-30HP & 2-50HP chilled water pumps with
pressure transmitters for accurate control of chilled
water to all tower AHU’s to take advantage of the
reduced chilled water demand occurring from reduced
air volumes requiring conditioning.
Revise control sequence for all of the systems above
to accommodate VFD control.
Each floor AHU is limited to providing approximately
6000 CFM outside air, sufficient to meet ASHRAE design
conditions for the expected occupancy levels. Each
floor AHU is powered by one 20 HP motor.
Outside air is delivered to the floor AHU’s by means
of a central vertical duct system capable of providing
approximately 175,000 CFM. The OA fan system is comprised
of twin fans located in the sub basement and penthouse.
The sub basement fan system is made up of 1-20HP &
1-60HP vane axial fans. The penthouse fan system is
made up of twin 40HP vane axial fans. Each system
has steam coils to precondition the outside air to
near discharge conditions of 55°F. The sub basement
fan has a heat recovery coil to capture wasted heat
from the building exhaust fan system.
High pressure steam and chilled water is provided
by the Minneapolis Energy Center: Steam costs are
$.00001096 per purchased BTU. Chilled water costs
are $.00002278 per purchased BTU.
at approximately $500 per AHU annually were
on the basis of 50 MMBTU per 1000 CFM of air
at approximately $3000 per AHU annually on the
basis of 150 MMBTU per 1000 CFM of air saved*.
annual of $87,500 were projected netting an
expected simple Return On Investment of less
than six (6) months for the CO2 control portion
of the project.
savings from the proposed installation of VFD’s
and essential EMS changes on all systems is
expected to yield an ROI of approximately two
(2) years. The
original estimated energy savings represents
an approximate reduction of 6% from the 1995
total energy costs.
March 10, 1997:
chilled water and steam consumption have been reduced
substantially. When compared to February of the previous
year (1996) steam consumption has been reduced by
approximately 35%, chilled water has been reduced
by approximately 55% as a result of changes to the
chilled water pump control sequence and early results
of the CO2 Demand Controlled Ventilation strategy.
CO2 levels on the controlled and monitored tower floors
have typically not exceeded approximately 700PPM,
allowing the significant reduction of outside air
required to meet conditions for acceptable IAQ. Outside
air levels are currently calculated to meet the general
and bathroom exhaust fan CFM’s to maintain a slight
positive pressure relative to the outside.
Comparison of the actual CO2 results against the Telaire
model indicate that the modeled profile is slightly
more conservative in predicting expected maximum CO2
levels, thus it is expected that incrementally greater
CFM reductions are likely.
August 31, 1997:
Chilled Ton Hours have been reduced by 181,900, or
Total Steam in 1,000 pounds have been reduced by 5,809
Total Electric KWH have been reduced by 549,200 or