national institutes of health building 37 modernization ... · national institutes of health...

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


Bethesda, Maryland

Katie L. McGimpsey

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


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

13

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.


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

14

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.


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

15

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.


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

16

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


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

17

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.


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

18

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


Bethesda, Maryland

Katie L. McGimpsey

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


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

20

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


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

21

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


Bethesda, Maryland

Katie L. McGimpsey

Mechanical Option

22

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


Bethesda, Maryland

Katie L. McGimpsey

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

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