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National Institutes of Health Building 37 Modernization
Bethesda, Maryland
Katie L. McGimpsey
Mechanical Option
11
MECHANICAL DEPTH – EXISTING MECHANICAL SYSTEM ____________ ___________
The need to maintain occupancy during the renovation and the strict NIH
Design Guidelines were the main driving forces behind the design. The
mechanical engineering group, Affiliated Engineers, Inc., worked closely with
NIH beginning with schematic design and continuing through construction to
develop the following design objectives and requirements, ensuring NIH Design
Guidelines were followed.
Design Objectives & Requirements
The driving design objectives and requirements needed to ensure operability a
state-of-the-art laboratory facility include:
1) Provide the facility with sufficient indoor conditions (thermal
comfort, indoor air quality – IAQ and safety) so to maximize
efficiency and productivity of the NIH-NCI employees.
2) Provide the facility with a system that integrates and successfully
phases out the existing mechanical system with the new design in
conjunction with the district heating and cooling systems.
3) Provide the facility with a system that strictly adheres to the NIH
Design Guidelines.
Outdoor and Indoor Design Conditions
NIH Building 37 is located on the Bethesda,
Maryland campus, which is not listed in ASHRAE
Fundamentals Climatic Design Information
chapter, so the design conditions for Camp
Springs, Maryland Andrews AFB were used. The
cooling load for NIH Building 37 was calculated
Table 1
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Mechanical Option
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using outdoor design conditions of 35ºC dry-bulb temperature and 26ºC wet-
bulb temperature, corresponding to ASHRAE 0.4% design conditions. Similarly,
the heating load was calculated using outdoor design conditions of -23ºC, which
is well below ASHRAE design conditions for the area. Based on design
documents, indoor design conditions are set at 23ºC and 50% relative humidity.
The outdoor design conditions are summarized in Table 1. The requirements
for laboratory spaces and perimeter research offices do not differ from one
another.
Design Heating and Cooling Loads
All of the heating and cooling in the building is being supplied by central plants
on the NIH campus. The total heating load = 1020.6 MBH and the total cooling
load = 1393.8 tons. There is also a cogeneration plant servicing the building
through a turbine powered by natural gas that is coupled to an electric
generator. The exhaust from the turbine flows through a boiler and produces
steam at 100,000 lbs/hr which services all the buildings on the NIH campus.
Mechanical System - Airside
The airside mechanical system for NIH Building 37 Modernization consists of
eight packaged air-handling units supplying “once-through” 100% outdoor air
through a zoned variable-air-volume system, to the occupied spaces at 23ºC.
The eight AHUs range anywhere from 28,314 L/s to 29,258 L/s and are located
in the mechanical penthouse, directly above the sixth floor. In the basement,
where existing mechanical equipment is located, there are two packaged air-
handling units; one supplying variable outdoor air with an economizer and one
supplying constant volume variable outdoor air for cooling only to the
transformer room. Variable-air-volume (VAV) boxes with heating coils
distribute air from the air-handling units to all of the occupied zones. Factory
National Institutes of Health Building 37 Modernization
Bethesda, Maryland
Katie L. McGimpsey
Mechanical Option
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assembled, horizontal, draw-through type fan coil units were used in some
zones not being supplied to by the air-handling system. There are eight fume
exhaust fans installed in parallel, all connected to a common fume exhaust
plenum. Each fan has a capacity of 32,089 L/s and a schematic of the central
fume exhaust flow can be viewed in Technical Assignment #3. In the analysis
of the airside mechanical system, only the eight AHUs in the mechanical
penthouse will be considered.
Mechanical Systems – Waterside
Chilled water is provided by the NIH central chilled-water distribution system,
and is supplied to the building at 6ºC and leaves at 16ºC. Roughly 2500 tons of
water is distributed to Building 37 by three (constant speed) tertiary pumps.
All three pumps are sized at 50% capacity and are piped in parallel, with two
pumps operating at any one time and the third acts as standby. Chilled water
serves fan coil units, as well as cools process equipment located throughout the
building. Steam is provided by large boilers at 165 psi, and then flows from the
NIH central heating plant in Building 11 to various buildings on the campus.
Approximately 20,000 lbs/hr of steam enters Building 37 to serve the heating
coils in the AHUs. An underground tunnel system provides piping from the
central plants to the various buildings on the NIH campus.
National Institutes of Health Building 37 Modernization
Bethesda, Maryland
Katie L. McGimpsey
Mechanical Option
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MECHANICAL DEPTH - MECHANICAL SYSTEM REDESIGN PROPOSAL & JUSTIFICATION __________ Critique of Mechanical System
After performing analyses, calculations and finally making assessments based
on ASHRAE Standard 62-2001 Addendum n and ASHRAE Standard 90.1-2001 in
Technical Assignments #1, #2 and #3, key features of the design and features
not addressed in the design showed possible areas of improvement.
Careful considerations and precautions were made during the design of the
modernization of Building 37 to follow the strict design guidelines set forth by
NIH. Laboratory/research facilities are inherent consumers of natural
resources, with little or no heat/energy recovery, as is with Building 37. Based
on Technical Assignment #2, it was estimated that the HVAC energy usage per
year for Building 37 = 75,673,173.57 kWh. Because of the high energy usage
per year, the main goal in mind was to implement a low-energy design.
Since this facility was designed for 100% OA with a minimum of six air changes
per hour (ACH), the large volume of ventilation air required poses the
opportunity to reduce the amount of energy required to condition ventilation
air. The engineers for Building 37 did just this, as they designed for variable-
air-volume (VAV) fume hoods, VAV supply with terminal reheat devices and
hood exhaust systems. Also, in regards to the building envelope and its
influence on the energy efficiency, existing windows were replaced with
inoperable, low-emissive (low-E) insulating glass, so not to compromise the
mechanical system design. Occupancy controls are utilized in individual
research offices, public areas where feasible, such as service corridors, large
rooms and lavatories, using ultrasonic-type dual technology with passive
infrared sensors.
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Bethesda, Maryland
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Mechanical Option
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Since Building 37 also supports other spaces such as conference rooms and
office suites, which require significantly less stringent HVAC requirements, as
well as laboratory spaces, the integration of these dissimilar types of
occupancies increases the potential for wasted energy. While the engineers
and designers of Building 37 have implemented several design features to
improve building energy performance, the modernization of Building 37 did not
include any design for heat/energy recovery. With 100% OA being supplied,
heat/energy recovery from exhaust air looks to be a viable option.
Information on the waterside mechanical system of NIH Building 37 is
unavailable. The National Institutes of Health will not disclose any information
concerning the central chiller, central steam and cogeneration plants servicing
the buildings on the NIH campus.
Alternatives Considered
Any proposal to redesign components of the central chiller, central steam or
cogeneration plants were disregarded due to the inability to gain access to vital
information. NIH has disclosed this sensitive information due to security issues.
Other than any redesign ideas for the central plants, the only design
alternatives that could be considered involved just the airside mechanical
system in Building 37. Focus was turned to investigating several different
energy recovery alternatives. The different alternative considered include a
heat pipe, run-around coils and a total enthalpy wheel (taking into account
both sensible and latent loads). The options are briefly outlined below.
National Institutes of Health Building 37 Modernization
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Mechanical Option
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Heat Pipe
In a heat pipe system, supply and exhaust airstreams should be located next to
each other to ensure proper operation. The basic mechanics of the heat pipe
system uses the movement of boiling and condensing refrigerant inside a sealed
pipe to act as the heat transfer medium. There is no mixing of the airstreams,
and no power source is needed to drive the heat transfer process. According to
ASHRAE Laboratory Design Guide, the efficiency of sensible heat transfer
ranges between 45% and 65%.
Run-around coils
A run-around coil heat recovery system consists of a matched pair of coil heat
exchangers, in which the two coils are piped together in a continuous loop for
the heat transfer medium to flow. Since the unit is self-contained, there is no
mixing of the airstreams
Total enthalpy wheel – Passive Desiccant Dehumidification Wheel
In a desiccant dehumidification unit, it is necessary for the supply air and
exhaust air streams to be located next to each other to ensure proper
operation of the system. This close proximity to contaminated exhaust air
raises serious questions of cross-
contamination in laboratory
facilities. In response to this concern, SEMCO manufactures a wheel (EXCLU-
SIEVE) with a sieve of 3 angstroms (Å), prohibiting anything larger than this to
absorb/transfer from the wheel. To gain a perspective on size, refer to Table
2. The EXCLU-SIEVE wheel utilizes a 3Å molecular sieve desiccant coating to
limit the risk of desiccant cross-contamination between the exhaust air stream
and outdoor air stream. Molecular sieves are structurally stable, chemically
inert and have a strong
smallest virus 1000 angstroms > 3 angrstrom sieve
water molecule 265 angstroms < 3 angstrom sieve
Table 2
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Mechanical Option
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affinity for water vapor and it is this strong affinity for water vapor which
produces the high rate of adsorption resulting in superior latent transfer
performance. In this type of system, typical heat transfer efficiency ranges
between 50% and 85%, according to the AHSRAE Laboratory Design Guide.
Redesign Proposal & Justification
The driving factors behind the final redesign proposal for NIH Building 37
Modernization were finding a cost effective solution to the issue of heat
recovery for the airside mechanical system. After contemplating the pros and
cons of the other design alternatives, the final solution will incorporate a
passive desiccant dehumidification system in the airside mechanical system to
account for heat recovery. Due to the humid climate during the summer
months of the facility, the need to dehumidify is necessary in any redesign
proposal. The two primary loads in conventional “air-conditioning” are
sensible and latent loads – the sensible load taking into consideration the
temperature component and the humidity portion being taken care of by the
latent load. The only energy used by the desiccant dehumidification units is
the fan energy required to move the air. Desiccant dehumidification is
beneficial in all types of buildings by improving indoor air quality (IAQ),
reducing the latent portion of the cooling load, reducing odor and decreasing
operational costs of facilities. The process involves the removal of moisture
from humid air with the aid of a desiccant material that absorbs the water
vapor as opposed to condensing it. Although the desiccant system’s first cost
cannot compete with conventional air-conditioning, the conventional system
can be reduced in size when configured to work with desiccant
dehumidification units.
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Bethesda, Maryland
Katie L. McGimpsey
Mechanical Option
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MECHANICAL DEPTH – PASSIVE DESICCANT DEHUMIDIFICATION __________
Redesign Introduction
The existing mechanical system in NIH Building 37 does not account for any
heat or energy recovery. In research and laboratory facilities, where fume
hoods are in place, the concern of cross contamination in air-to-air heat
recovery is heightened. In NIH Building 37, the exhaust airstream ducts are
located relatively close to the outdoor airstreams, so the proximity of the
airstreams is not an issue for the redesign. This section goes into the
calculations and simulation results from applying a passive desiccant
dehumidification system to the existing mechanical system for NIH Building 37.
Existing Loads
Through Carrier’s Hourly Analysis
Program (HAP) it was found that the
total cooling coil load = 1393.8 tons
and the total heating load = 1020.6
MBH. The loads contributed to each
air-handling unit are summarized in
Table 3. The annual cost to operate
Building 37 is $858,756/year.
Appendix I includes a complete printout of the HAP output from the simulation.
SEMCO Model
The SEMCO Energy Recovery Wheel Technical Guide and SEMCO TE Wheel
Modeling Program were used to size and select an appropriate passive
desiccant wheel. Both references were supplied by SEMCO Representative,
Rick Caldwell. The design guide presents the SEMCO EXCLU-SIEVE® total energy
(TE3) recovery wheel. The selection procedure in the technical guide was
Total Cooling Coil Load
(tons)
Total Heating Load
(MBH)
AHU−1 178.6 415.7
AHU−2 204 105.8
AHU−3 175 104.1
AHU−4 168.2 87.1
AHU−5 167.8 80.3
AHU−6 167.1 72.4
AHU−7 167.4 74.3
AHU−8 165.7 80.9
Total 1393.8 1020.6
Table 3
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Mechanical Option
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followed to select the appropriate total energy recovery wheel, and then the
modeling program was used to calculate an energy analysis and cost analysis.
SEMCO ELCLU-SIEVE® 3Ǻ Molecular Sieve
SEMCO’s EXCLU-SIEVE® total energy recovery wheel provides features that
optimize the sensible (temperature) recovery of performance, and also
provides latent (moisture) recovery efficiencies that match the improved
sensible values. This is accomplished through EXCLU-SIEVE’s 3Ǻ molecular
sieve desiccant coating. The high rate of absorption allows for effective
moisture transfer between the outdoor and exhaust airstreams.
Molecular sieves are crystalline metal alumino-silicates, and a close up view
can be seen in Picture 3. When it is combined with oxygen atoms, the three-
dimensional interconnecting network expands its internal surface area where
passing liquids and gases in the airstreams are adsorbed. The 3Ǻ molecular
sieve has the unique capability of limiting adsorption to materials that are
smaller than approximately 3 angstroms.
Picture 3
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Bethesda, Maryland
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Mechanical Option
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SEMCO Technical Guide Calculations
An excel worksheet was created following the design procedure. The complete
printout of calculations for the unit selection can be found in Appendix II.
The first step involved was selecting the wheel, based on airflow. Using Figure
2, EXCLU-SIEVE TE3-70 model was determined to be suitable given all the
airflows. Step 2 involved determining the unit effectiveness and the following
equations were used.
Step 3 involved the calculations
of unit performance and these
calculations can be found in
Appendix II.
( )( )
( )( )
( )
( )31
min
34
31min
12
31min
4
31min
21
XXV
VXX
XXV
VXX
XXV
XXV
XXV
XXV
r
s
s
s
r
r
ss
−+=
−−=
−
−=
−
−=
ε
ε
ε
ε
Figure 2
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Mechanical Option
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The purge volume was calculated in step 4 of the design procedure. A purge
section is utilized to avoid carry-over of exhaust air into the supply air-stream.
or all AHUs, the purge volume = 3800 cfm with a purge index setting = 4. A
schematic for purge operation is shown in Figure 3.
Step 5 calculated the reduction in
required chiller and/or boiler
capacity, and was estimated through
the following equations.
( )
( )000,33
5.4
000,12
5.4
OUTIN
OUTIN
hhscfmcapacityBoiler
hhscfmcapacityChiller
−=
−=
Table 4 summarizes the wheel selection results given the required airflows for
each AHU.
Face Velocity Pressure Loss EffectivenessPurge
Volume
Chiller
Reduction
Capacity
Boiler
Reduction
Capacity
fpm in. wg % Supply Return Supply Return cfm tons boiler hp
800 0.8 83.5 1.73 0.63 1.22 0.51 3800 336.23 147.12
850 0.9 82.5 1.73 0.63 1.22 0.51 3800 347.44 152.03
850 0.9 82.5 1.73 0.63 1.22 0.51 3800 347.44 152.03
800 0.8 83.5 1.73 0.63 1.22 0.51 3800 336.23 147.12
800 0.8 83.5 1.73 0.63 1.22 0.51 3800 336.23 147.12
800 0.8 83.5 1.73 0.63 1.22 0.51 3800 336.23 147.12
850 0.9 82.5 1.73 0.63 1.22 0.51 3800 347.44 152,03
850 0.9 82.5 1.73 0.63 1.22 0.51 3800 347.44 152,04
Unit Effectiveness
Cooling
Unit Effectivenss
Heating
Figure 3
Table 4
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Mechanical Option
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Based on SEMCO Energy Recovery Wheel Technical Guide design procedure,
SEMCO TE3-70 energy recovery wheel was selected, and Table 5 summarizes
the performance data and unit dimensions, which are common for all eight
AHUS. Figure 4 shows the dimensions of the wheel. The TE3-70 wheels add an
additional 37,440 lbs of load in the mechanical penthouse.
SEMCO TE Wheel Modeling Program
This program was used to check the results of the excel worksheet derived
results and also to compute cost analysis information. The complete printout
of results from the simulation can be found in Appendix III. Table 6
summarizes the costs and also compares the cooling and heating loads for the
new input capacities to the existing loads. Each unit is approximately $45,000
with a $22,500 installation cost. The first cost savings range between
approximately $60,000 and $65,000 depending on the AHU. There is an
immediate payback with positive present cash flow values ranging between
$234,000 and $241,000.
Velocity 900 fpm
Wheel Efficiency 76 %
Pressure Drop 0.94 in. wg
Wheel Model Size 70
Airflow Rate 63,360 cfm
A 171.5 in.
B 79.1 in.
C 89.4 in.
D 84.3 in.
W 23.0 in.
Net Wt. 4680 lbs
Flow Area/Side 70.4 ft2
Nominal cfm 56000 cfm
Performance Data for TE3 Wheels
Unit Dimensions
Table 5 Figure 4
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Mechanical Option
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Equipment
First Cost
($)
Installation
Cost
($)
First Cost
Savings
($)
Immediate Payback w/
Positive Present Cash
Value of
Cooling Capacity
Input Required
(tons)
Cooling Load from
Existing System
(tons)
Heating
Capacity
Required
(MBH)
Heating Load
from Existing
System
(MBH)
AHU−1 45,000 22,500 60,362 233,838 161.59 178.6 1165 415.7
AHU−2 45,000 22,500 64,030 241,280 168.02 204 1217 105.8
AHU−3 45,000 22,500 64,030 241,280 168.02 175 1217 104.1
AHU−4 45,000 22,500 60,362 233,838 161.59 168.2 1165 87.1
AHU−5 45,000 22,500 60,362 233,838 161.59 167.8 1165 80.3
AHU−6 45,000 22,500 60,362 233,838 161.59 167.1 1165 72.4
AHU−7 45,000 22,500 64,030 241,280 168.02 167.4 1217 74.3
AHU−8 45,000 22,500 64,030 241,280 168.02 165.7 1217 80.9
Total 360,000 180,000 497,568 1,900,472 1318.44 1393.8 9530 1020.6
Table 6