Commissioning Humidity Control Systems in Critical ...Commissioning Humidity Control Systems in Critical Environments Roy H Feinzig, PE LEED AP Principal EYP Mission Critical Facilities

Commissioning Humidity Control Systems in Critical EnvironmentsRoy H Feinzig, PE LEED APPrincipalEYP Mission Critical Facilitieswww.eypmcf.com

15th National Conference on Building CommissioningMay 2-4, 2007

Why Control Humidity?

| In a critical environment, humidity control is just as important as temperature control in assuring reliability

| Low humidity can lead to static damage

| High humidity can lead to degradation of electronic equipment and swelling or delamination of printed circuit boards

| The result will be equipment failure and reduced up-time


Normal Conditions

| How Do We Measure Humidity? | Absolute

| Specific

| Relative

| Dew Point

| Baseline typical data center space conditions| 72°F db and 45% RH

| The specific humidity at this condition is 0.077 lb water / lb dry-air

| 54 grains/ lb dry-air

| The dew point at these conditions is 50°F


Normal Conditions

|Relative Humidity vs. Temperature

|@ 54 grains/ lb dry-air

95%52°F65%62°F45%72°F33%82°F24%92°FRH %Temperature db


Consequences of Low Humidity

|Static Electricity| Humidity is low

| Static is high

|How much static electricity is too much?

18,000 Volts1,500 VoltsWork chair padded with urethane foam

20,000 Volts1,200 VoltsCommon poly bag picked up from bench

7,000 Volts600 VoltsVinyl envelopes for work instructions

6,000 Volts100 VoltsWorker at bench

35,000 Volts1500 VoltsWalking Across Carpet

12,000 Volts250 VoltsWalking over vinyl flooring

Static Charge at 10-20% RH

Static Charge at 65-90% RH

Activity


Consequences of Low Humidity

| Today's electronic equipment has a dense geometry, and is composed of thin, easily damaged, materials

| Damage caused by Electro-Static Discharge (ESD)| Catastrophic failure| Low grade damage that makes equipment susceptible to later failure| Cumulative degradation from repeated, low voltage exposures

| Above 40% rh static electricity does not accumulate| Below 30% rh the same materials will accumulate static

electricity| Humidity control is the surest, easiest way to mitigate

the build-up of static electricity


Consequences of High Humidity

| Changes in surface resistivity that alter timing circuits, change the frequency of oscillator circuits, change the current level in a constant current source, result in loss of sensitivity or reduce the input impedance on high impedance amplifiers

| Electrical shorts| Swelling and binding of mechanical moving parts| Localized corrosion| Delamination of printed circuit board (PCB) materials| For facilities with older raised floor tiles where galvanic coatings

were used, high humidity can cause the formation of a zinc solute, which can lead to the growth of zinc whiskers (filamentary growth on metallic materials) on PCBs. Whiskers can grow long enough toshort out circuitry.


Consequences of High Humidity—Zinc Whiskers


How Should We Control Humidity?

| Many engineers, owners and operators have experience with various configurations and systems and have strong opinions for and against.

| Local vs. Remote | Does the facility have a dedicated make-up air/pressurization AHU

with redundant back-up?

| The incremental cost of adding humidification and reheat (for dehumidification) is marginal.

| Run city water piping to only one or two locations as opposed to CRAC units throughout the raised floor.

| Significant cost savings for running smaller power circuits to each CRAC unit (no local humidifier or reheat).


What Type of Humidifier to Use?

MediumMed—HighMediumHighMaintenance

HighLowHighLowOperating

Lo—Med HighLo—Med LowCapital

Relative Costs

HighMediumMediumHighMaintenance Attention

MediumExcellentExcellentMediumSanitation / Corrosion

Fast / Precise

Fast / Precise

SlowSlow / Imprecise

Control Response

ExcellentExcellentExcellentPoorVapor Quality

SmallSmall to large

Small to medium

Medium to large

System Size

Some increase

Substantial drop

Some increase

Substantial drop

Effect on Temperature

InfraredUltrasonicElectric Steam

Spray PadComparison Criteria







|Ultrasonic humidifiers require de-ionized water

|This comes from a reverse osmosis (RO) water treatment system





|This is an example of a newer style of “spray pad”that eliminates some of the problems with older systems

|The basin is still a potential sanitation problem

|Close control requires multi-bank installations with face and bypass dampers

|Slow to start


Safeties

|Critical safeties| High limit cutout

| Air flow proving switch

| Leak detector


Other Design Considerations

| Correct system sizing| Is design condition 100% OA at 55°F on a clear, dry day?

| Is it mixed air condition in the dead of winter?

| Were the cooling effects of evaporative and ultrasonic systems considered?| Humidification system size can be reduced on mixed air units.

| Is the discharge air temperature fixed, or adjusted on a ratio ramp with a rise in humidifier output PID for units that are for pressurization, not cooling? | The air can hold more moisture at higher temperatures.



| Computer Room Air Handling units are sensible coolers

| Rule of Thumb: Supply 25% with humidifiers| This works if there is a vapor barrier

| This doesn’t work if the operators change the temperature and humidity setpoints,

| or lower the chilled water supply temperature,

| and the units do latent cooling and remove too much moisture from the air

| As CxA find out how the operators plan to operate!| It may affect design



|Proper layout|Are the velocity and straight duct run, etc. requirements of the system manufacturer met?

| Ultrasonics, for example, require a uniform 300-600 fpm and 500 fpm is ideal

|This will never work right!|And don’t forget the drains

| Every distributor and generator needs one!


Dehumidification is a Simpler Matter

| Sub-cool the air to remove moisture

| Reheat as required to maintain space temperature

| In a central system provide a reheat coil and program a dehumidification sequence into the control logic

| For a CRAC unit, add a reheat coil, enable the dehumidification cycle, control for absolute humidity

| For a chilled water unit the chilled water temperature must be low enough to allow dehumidification

| Reheat coils are necessary to prevent overcooling the floor, particularly at low load conditions


Vapor Barriers

| As CxA we have the ability and responsibility to connect the HVAC design with the Architecture

| First remember moisture does not follow pressurization| Moisture flows from high humidity spaces to low humidity spaces

| Humidity can migrate from a low air pressure to a high air pressure

| Pressurization cannot take the place of a vapor barrier

| Installation of a vapor barrier is necessary to mitigate moisture migration so the humidity control system can function properly| The vapor barrier must have a permeability rating of 1 or lower

| Aluminum foil (0.0001), 6 mil polyethylene sheet (.06)


Installation Issues

|Electrode steam humidifier

| This graphic illustrates the importance of proper distributor installation, generator location, steam and condensate line locations and trapping

|Bring the IOM on your construction inspection


Installation Issues

|Ultrasonic humidifier installation examples


Installation Issues

|Ultrasonic humidifier installation examples


Functional Testing

| Include safeties and alarms

| Before start-up, document all setpoints and alarm values| Verify with Owner and O&M staff


Functional Testing

| CRAC and CRAH units| Verify humidification is enabled

| Verify dehumidification is enabled and stages are correct on units so equipped

| Control method (absolute or relative) is selected

| Sensitivity or deadband set (typically 3 or 5%)

| Select humidifier pan (large or small for infrared or steam, respectively)

| Set IR fill rate (for infrared humidifiers)

| Test the high and low humidity alarms by alternately setting the alarm values above and below the current setpoint (by more than deadband)


Functional Testing

| CRAC and CRAH units| Change the humidification setpoint to 10% above the current return

air humidity

| Infrared lamps light in 6 seconds and quickly produce steam

| Verify all lamps light and take an amp reading for comparison tocatalog value

| Steam canisters take longer to boil, so take an amp reading when full boil is reached

| Remember that steam cans should be run for 24 hours before testing

| For dehumidification, change the humidity and temperature setpointsto engage the dehumidification cycle and verify one compressor is running (or chilled water valve is open) and that the appropriate stages of heating are energized


Functional Testing

| Electrode Steam Canisters| AHU OFF, drain valve open, make-up valve closed

| AHU ON & Humidifier commanded ON, drain valve closed, make-up valve open

| AHU ON & Humidifier commanded OFF, drain valve open, make-up valve closed

| Force demand to 100%, the tank fills

| While filling trip the air proving switch, filling stops

| Repeat for the limit stat

| Resume filling and record the fill rate

| Allow the tank to fill until it stops and mark level with a Sharpie


Functional Testing

| Electrode Steam Canisters| Verify operation of the manual drain switch

| Record the drain rate

| Simulate a high humidity condition at the humidistat, demand meter goes to zero

| Verify demand meter climbs as humidistat dries out.


Functional Testing

| Testing ultrasonic humidifiers is similar

| System should drain down when not in use (3 days)

| Test the RO system as well| Alarms and cut outs for high conductivity

| Flush and backwash cycles

| Spray pads are also similar with the addition of the pump that runs on a call for humidity| Level control in sump

| Include timed drain cycle


Integrated System Testing

| Include recording of humidity in the critical space during full load testing

| Space temperature rises and falls rapidly during power failure and recovery tests

| Relative humidity will similarly vary

| Specific or absolute humidity should not vary much

| If control is based on relative humidity, as the mechanical plant and space temperatures recover, the relative humidity rises rapidly, perhaps faster than the mechanical plant can accommodate.


Integrated Testing

Humidity

0

10

20

30

40

50

60

70

80

8:15

8:30

8:45

9:00

9:15

9:30

9:45

10:0

010

:15

10:3

010

:45

11:0

011

:15

11:3

011

:45

12:0

012

:15

12:3

012

:45

13:0

013

:15

13:3

013

:45

14:0

014

:15

14:3

014

:45

15:0

015

:15

15:3

015

:45

16:0

016

:15

16:3

016

:45

17:0

017

:15

17:3

017

:45

18:0

018

:15

18:3

018

:45

19:0

019

:15

time

Relative Humidity (%) Dew Point (degF) Absolute Humidity (gm/M3)


Summary

| Control of humidity in a critical environment is as important to assuring reliability as temperature control

| Low humidity can lead to static damage| High humidity can lead to degradation of electronic

equipment and swelling or delamination of printed circuit boards

| Guide the project team on local vs. remote humidification

| Guide the project team on the pros and cons of ultrasonic, spray pad, electrode steam and infrared humidification


Summary

| Bring the IOM to construction inspections and testing

| Include safeties and alarms in functional testing

| Trend humidity as well as temperature during Integrated System Testing.


Thank You

| Questions?| Roy H Feinzig, PE LEED AP

PrincipalEYP Mission Critical [email protected]

© 2007 EYP Mission Critical Facilities®

Documents

Commissioning Humidity Control Systems in Critical ...Commissioning Humidity Control Systems in Critical Environments Roy H Feinzig, PE LEED AP Principal EYP Mission Critical Facilities