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Ultra-Sorb Improves Absorption and Reduces Operating and Maintenance Costs
West Atrium, Walter Mackenzie Health Sciences Center
The Walter MacKenzie Center of the University of
Alberta Hospitals is the primary teaching and research
institution in the Province of Alberta. With 950 beds
for patients, research laboratories and the Provincial
Laboratory of Public Health, this is a very large building
by any standard.
Twenty-six air systems serve this facility of which 21
had been utilizing capillary air wash technology for
humidifi cation since the completion of the second phase
of the hospital in 1982. The remaining units used
horizontal steam grid technology for humidifi cation. The
steam grid units served operating suites and a recent
pharmacy addition.
AIR WASHERS REPLACED
Reid Crowther and Partners Ltd. were engaged in 1994
to design the conversion of capillary air wash systems to
steam grid humidifiers. Working with Mr. Jim Thompson
and Mr. Mike Prasek of the Hospital Physical Plant it
was determined that the hospital desired replacing the
capillary air wash systems for a number of reasons.
The first and foremost reason was the operating cost
of producing and delivering demineralized water
for the air wash system estimated at $200,000 per
year. The yearly replacement of the air wash cells at
approximately $23,000 per unit also contributed to the
financial component of the replacement. Odors from the
air wash cells and the cooling effect provided from the
air wash system in winter conditions also contributed to
the case for replacing the air wash systems.
Ultra-Sorb LV Steam Dispersion Tube
Panel Installed At Walter Mackenzie
Health Sciences Center
LARGE AIR HANDLERS REQUIRED SPECIAL NEEDS
The configuration of the air handling units caused a great deal of
concern for this humidification project as can be seen in Figure 3-1 on
the next page. These units move on average 60,000 CFM of air each.
In some cases close to 100% outdoor air is moved resulting in enormous
humidification requirements in winter when ambient temperatures drop
to -40° F. The proposed steam grid was to be located upstream of the
system cooling coils and supply air fan in the same location as the
capillary air wash system. This was the only available location to install
the units since downstream of the cooling coils sufficient space was not
available prior to the final filters, and downstream of the final filters the
distribution ductwork decreased in size to deliver air at high velocity to
the building.
The design conditions of the new steam humidification system dictated
that up to 1200 lbs/hr of steam would be required for some units during
winter ambient design conditions or the free cooling conditions of spring
and fall. Each unit differs in the season for peak steam use since the
amount of outdoor air used for ventilation varies for each unit and could
be changed at any time to suit renovation within the hospital.
STEAM ABSORPTION WAS CRITICAL
Another critical design criteria based on the proposed location for the
new steam grid system was the short absorption non-wetting distance
available prior to the moisture eliminators. Obviously it is desirable
to have steam absorption prior to the eliminators since the object of
humidification is to add moisture to the airstream. Non-wetting distances
greater than 4 feet would result in ineffi cient humidification and moisture
carry over into the supply fan cabinet.
SEVERAL OPTIONS WERE CONSIDERED
A number of steam humidification systems were investigated to meet the
design criteria for this project based on a desire to keep the per unit cost
of the new grid to below $10,000, the value at which it was determined
the feasibility of the new installation compared against operating cost
was acceptable. A traditional horizontal grid system was investigated
but non-wetting distances of up to 16 feet were calculated. An atomizing
system was reviewed but resulted in uneven fog distribution across the
cross section of the unit. Finally the DriSteem Ultra-sorb® system was
investigated.
ULTRA-SORB PROVIDED THE SOLUTION
The Ultra-sorb system offered many advantages to this installation. The 12 feet
high and 9 feet wide unit was expected to provide even steam distribution.
Comparing a different number of tubes and center to center dimensions
resulted in an optimized steam distribution manifold for this application.
Absorption distances of as little as 15 inches were possible with the 6 inch
center to center tube spacing. The system required only a modulating steam
control valve. Steam pots or separators were not required which simplified
and reduced long term maintenance. It is remarkable that the capital cost of
each grid was approximately $7,000 — the lowest priced option studied. The
installation is shown in Figure 3-2 below.
Job Summary
Concerns
• Operating cost of $200,000/yr for DI
water.
• Replacement air wash cell cost of
$12,000/yr.
• Complaints of odors from the wash cells.
• Excessive unwanted “free cooling”
increasing the preheat coil load.
• Maintain new per unit replacement cost
under $10,000.
Solution
• Install Ultra-sorb LV dispersion tube panels
in the same sectional space as the previous
air wash cells.
Operational results
• Minimized odor complaints from building
occupants.
• Eliminated the evaporative cooling effect
and greatly lowered the preheat coil load.
• Improved control of the air handling system
and increased occupant satisfaction.
Financial results
• Elimination of the excessive yearly cost of
$12,000 for replacement air wash cells.
• No net increase in the cost of steam since
the reduction in preheat load matches the
consumption used for humidification.
Payback: Less than ½ year
Increase in operating cost: None
Other features of the vertical Ultra-sorb system which were considered
beneficial included:
- The ability to positively shut off steam to the grid when steam was not
required thereby eliminating standby steam normally required to maintain
the jacket temperature of steam jacketed dispersion tubes (horizontal
grids).
- The ability to characterize tubelets in the vertical tube to provide even
steam distribution across the unit cross section.
- The ability to guarantee drip-free operation because of the tubelets’
insertion distance into the steam supply tubes. Condensate travels along
the walls of the supply tubes and never reaches the distribution tubelet
orifice.
Operational tests on the units have shown dramatic results. First, the quality
of the humidification improved, with less odor complaints from building
occupants. Operationally, removal of the air wash system and installation
of the steam humidification system has resulted in little increase in steam
use by the hospital. Steam is used for the preheat coils of the system, less
preheat is now required to counteract the air wash cooling effect. In fact,
the amount of steam used by the new steam humidifi cation system is almost
identical to the amount of steam used to generate the extra preheat previously
required. Controllability of the air handling system is also improved with more
predictable characteristics resulting from the steam humidification system.
This project has been a great success due to the efforts of the entire team
including the Physical Plant department of the hospital and by DriSteem
through our local representatives Bart Bartlett and Darren McPherson of Kehoe
Equipment in Edmonton.