The facility is a 54-bed heart hospital with
four operating theaters; Cath and diagnostic labs, ICU, CCU,
and an around the clock emergency room serviced by air and ground
transportation. The facility is approximately 160,000 square
feet multi-story (basement and two floors above grade) building.
The heating, ventilating and air conditioning (HVAC) system
- Constant flow chilled water/hot water systems including
2 parallel piped water cooled water chillers, approximately
320 tons each.
- 8 central station air-handling units, all of which equipped
for variable volume (VAV) using either variable frequency
drives or inlet guide vanes, all having both supply and return
fans and 100% outside air economizer capabilities.
- Approximately 240 constant and variable volume boxes, most
with reheat coils.
- Complete direct digitally controlled Energy Management System
- Inability to satisfy all of the facility’s temperature,
humidity requirements, including ICU areas due to original
HVAC system design and installation
- Space pressure problems, i.e. pressures between sterile
areas inverse from required
- Questionable design practices
- Risk management and regulatory agency compliance issues
due to the above
- Excessive utility costs
provided a detailed study and report of the HVAC System’s existing
conditions and operations including design and DDC system deficiencies,
potential energy conservation opportunities with budgeted project
costs and economic analysis, and maintenance related operational
and efficiency analysis. The result of this study became an
approximately $1,800,000 HVAC system redesign and modifications
for the facility, including construction document preparation,
commissioning and OptimissioningSM
of the entire facility.
The modifications included replacement of
numerous in-duct fire/smoke dampers (FSD) and air handling unit
supply air discharge ducts to reduce the air distribution system’s
total pressure drop. The analysis determined that the total
system pressure drop was significantly higher than the design
intent, and as a result the air handling units did not have
the capability to provide the airflow required to all zones,
especially those distant from the air handling units. The higher
than design system pressures were also causing serious duct
leakage, up to 25% on some systems, exacerbating the comfort
issues. The following graph illustrates the design and calculated
This lack of capacity, even at 100% fan speeds,
resulted in an inability to maintain temperature/humidity requirements
as well as poor ventilation control and indoor air quality.
Also, with these conditions there was no way to capitalize on
the energy management capabilities (VAV) of the air handling
units. To complicate matters, large space pressure differences
were existing between sterile areas due to return air fan control
schemes and the original outside air system design criteria.
The original design for outside air included a large, passive
(not forced air) outside air “plenum” to which individual outside
air ducts attached to all air handling units. Preliminary testing
showed that this “sharing” of the main outside air duct was
resulting in some air handling units actually introducing return
air from other air handling units via the outside air system.
In other words, among other noted problems, sterile (surgery,
etc.) areas were introducing air from less sterile areas. The
entire outside air deliver system was egregiously deficient.
Part of the HVAC system redesign required
that the outside air ducts to each air handling unit be replaced
with smaller ducts and were equipped with outside air flow measuring
stations. The smaller sizes provided the minimum velocities
necessary to make the stations work correctly and to permit
outside air control and monitoring. Also, Energy-Environment-Economics
designed and implemented innovative outside air/return air/mixed
air damper control algorithms, combined with a revised supply
air fan/return air fan tracking algorithm, that solved the outside
air delivery issues.
Through exhaustive field work, the engineering study also identified
select areas where space was available to increase the size
and lower the subsequent pressure drops of the FSD’s that had
especially high pressure drops and would have the most effect
on shifting the system curve back to design as shown above.
Affected areas were systematically taken off-line during low
census and off-hour times, and these FSD’s were replaced and
the system brought back on-line in the morning. Accurate construction
documents were mandatory, as was scheduling of all related shutdown
activities. During this process, the ductwork was also re-sealed
to minimize the extreme leakage.
System testing during analysis also revealed large pressure
drops at the supply air discharge ducts at each air handling
unit, caused by system effect pressure losses due to duct configurations.
New designs were developed, and these changes were made simultaneously
during the system shutdowns. Finally, to maximize the system
shift, existing inlet guide vanes were removed and replaced
with variable frequency drives. The net result of the air distribution
system modifications was to shift the system curve within design,
allowing sufficient air at required temperatures to be supplied
to all zones. The outside air delivery system corrections, combined
with the modifications to the EMS, solved the IAQ and space
pressure control issues. All corrections to the air distribution
system collectively solved the very serious problems, and were
also very successful in reducing the energy consumption of the
System performance and efficiency was vastly improved through
the proper application of variable air technologies and converting
the constant volume chilled water system to variable primary.
Inefficient equipment such as 3-way control valves and fan inlet
guide vanes were replaced with pressure-independent 2-way control
valves and variable frequency drives respectively. The installation
of properly sized cooling towers and plate frame heat exchanger
provided non-existent redundancy and reduced operating costs.
All new devices - variable frequency drives, outside air flow
measuring and control devices, et. al. – were integrated into
the Energy Management System (EMS) sequences of operations.
The sequences of operations were completely rewritten for maximum
performance and efficiency during the OptimissioningSM process,
including reset schedules for the air handling units. EMS communication
with the chillers was established, enabling reset schedules
to be established and more reliable control over central plant
operations. Space pressure sensors and control algorithms were
incorporated, as were air handling unit outside air control
algorithms. Differential pressure sensors were installed into
the revised chilled water system, and all facets of the new
system’s controls requirements were designed, implemented and
optimized. All critical EMS setpoints, including economizer
changeover, chilled water supply, supply air temperature, and
air handling unit static were painstakingly established for
maximum energy efficiency. All VAV/FPVAV boxes were calibrated
during the HVAC system wide Test & Balance process.
These system improvements were completed with
no interruption in services, as affected areas were systematically
taken off-line during low census periods and returned to operation
the following morning(s). the new control algorithms for the
entire system(s), coupled with the installation of new and/or
relocated controls devices, allowed us to properly monitor,
control and most importantly satisfy all space temperature and
pressure and outside air flow requirements throughout the entire
facility at all times and any conditions. The project resulted
in eliminating all deficiencies associated with the HVAC system
and reduced energy costs by approximately $100,000/year, but
most importantly all compliance and risk management issues were
addressed and corrected.
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