Moisture Control in Museums and Archives - Setty · Moisture Control in Museums Data collection within the wall cavity to support the calculated temperature profile. Three battery-powered

Moisture Controlin

Museums

Presented by

Boggarm S. Setty, P.E.Setty & Associates, Ltd.

ASHRAE Winter Meeting, New York, January 2008

Moisture Control in Museums

Hirshhorn Museum,Washington, DC

Case in Point


Issues relate to Excessive Humidity in Existing Areas

Moisture Condensation• In Areas such as Floors and Walls

Moisture Condensation behind Exhibits

Existing HVAC Systems •Do not maintain necessary temperature and humidity conditions

HSMG’s Study determined Solutions to Humidity Issues

Issues


Initiated Thermography of Areas where Condensation is occurring

Thermal Images: Interior Surface Temperatures of Exterior Walls

ThermographyAreas of Thermography


Each color shade = Different Temperature

Thermography


Interior Surface Temp of Exterior Walls

Color Temperature Bars: Yellow-Orange-Red = Warm Temperatures Green-Blue-Dark Blue = Cold Temperatures

Thermography


Determine Existing Envelope Conditions to prevent condensation with insulation options.

Monitor Exterior Wall Dewpoint and Temperature Profiles during winter months.

Determine Building Pressure Characteristics when system is in operation.

Determine HVAC Control System operation.

Recommend proper Envelope Modification, HVAC Improvements and Recommissioning to Prevent Condensation.

Study Issues

Round Envelope: 24-inch thick concrete No Insulation Exterior: Rough Finished Interior Drywall or Plaster Finish Concrete Structure:


Envelope Characteristics

VINYL BASE,

FINISH FLOORBASE

SECURE TO CONCRETECONT. METAL RUNNER

DECK ABOVE

20 GA @ 16" O.C.

BD. @ EACH SIDE1 LAYER OF 5/8" GYP.

3 5/8" METAL STUDSPLAN

TOP

CEILING

SEE SCHEDULE


Exhibit Levels 2 and 3 are served by 4 Air Handling Units

Each unit has a Cooling Coil, Steam Humidifier

Branch Duct has Steam Reheat Coils

Humidity Sensors on Return Air Grilles on Each Floor

Galleries are supplied with Sidewall Registers

Design requires Mixing of Gallery Air

DDC Computer calculates the Return Air Dewpoint and makes changes to Supply Air Dewpoint

Dewpoint reset as necessary

Existing HVAC Control Systems

Existing HVAC System Distribution


AHU 2 New Control Diagram

Existing HVAC Control System


Typical Gallery Air Distribution


Building has High Humidity Levels with occasional Condensation on Cold Walls

More Condensation behind Exhibits

More Condensation on Second Floor

Possible Pressure pushing High Humidity Air, which will condense in the Walls

Evaluation of Existing Conditions


Condensation occurred when Outside Temperature was Low, Approximately 150F

To facilitate Multiple Wall Conditions, “Therm” Program was utilized for Dewpoint Calculations

Graph indicates Temperature Profile at Various Points of the Wall

Temperature and Dewpoint Calculations


Envelope Characteristics


“Therm” program used to calculate temperature profiles for existing and hypothetical modified walls.• Plaster Surface Temperature: 65°F• Concrete Wall Temperature: 53°F• Outside Temperature: 15°F

Condensation can occur with these temperature profiles

Condensation Calculations


Data collection within the wall cavity to support the calculated temperature profile.

Three battery-powered data loggers for temperature and humidity recording placed between the plaster and the reinforced concrete wall.

Fourth recorder was placed in the outdoor intake plenum.

Conditions:

• Outside air temperature: 25°F• Concrete surface temperature: 50°F

Condensation may occur at these temperatures.

Field Measurements


Hourly Constant Temperature 50% to 60% Relative Humidity

Temperature and Humidity Profile

3rd Floor, AHU 5 - January 1 through 31, 2005

0

10

20

30

40

50

60

70

80

90

100

Deg

rees

F o

r %

RH

Temperature Relative Humidity

Reflects Changes in Humidity Ratio


Instruments used:

• Infrared Mini-thermostat• Electronic Digitized Temp/Humidity Instrument

Measurements Conducted for AHU# 5, 6 and 7 Temperature Measurements Nearly Constant Temperature 50% to 60% Relative Humidity Fluctuations in Relative Humidity Observed for

all AHU’s

Temperature Measurements


Return Air Dewpoint - 3rd Floor, AHU 5 - January 1 through 31, 2005

44

46

48

50

52

54

56

Deg

rees

F

Moisture Control in Museums Data shows High Dewpoint Levels Increase in Condensation Control System tries to maintain Dewpoint

Return Air Dewpoint - 3rd Floor, AHU 7 - January 1 through 31

50

51

52

53

54

55

56

57

58

59

60

Deg

rees

F


Return Air Dewpoint - 2nd Floor, AHU 7 - January 1 through 31

47.00

48.00

49.00

50.00

51.00

52.00

53.00

54.00

55.00

56.00

57.00

58.00

Deg

rees

F


»

Return Air Dewpoint - 4th Floor, AHU 6 - January 1 through 31

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

Deg

rees

F

Moisture Control in MuseumsReturn Air Dewpoint - 3rd Floor, AHU 2 - January 1 through 31, 2005

45.00

46.00

47.00

48.00

49.00

50.00

51.00

52.00

53.00

Deg

rees

F

Moisture Control in MuseumsReturn Air Dewpoint - 4th Floor, AHU 5 - January 1 through 31

47.00

48.00

49.00

50.00

51.00

52.00

53.00

54.00

55.00

Deg

ree

F

Moisture Control in Museums Reset during Winter Conditions

Return Air Dewpoint - 3rd Floor, AHU 5 - January 1 through 31, 2005

44

46

48

50

52

54

56

Deg

rees

F

Constant Dewpoint for Summer


Over-pressurization pushes Air into the Wall, causing Condensation

Maintaining Positive Pressure at Building Wall does not guarantee Condensation Prevention

Normal Practice Recommended to Maintain Slight Positive Pressure, approximately 2 Pascal

Neutral Pressure prevents Exfiltration of Air during low Outside Air Temperatures

Pressurization


Option 1: 2-inch Foam Insulation

Insulation Options

Temperature Profile for Interior Polyurethane Insulation


Option 2: Spray Cementitous Insulation on Wall

Temperature Profile for Interior Cementitious Insulation


Option 3: External Foam Insulation

Temperature Profile for External Foam Insulation


Option 4: External Polystyrene Insulation

Temperature Profile for External Polystyrene Insulation


Condensation of interior air against colder surface of the primary wall.

By design, outer perimeter wall is farthest from the air diffusers and receives less warm air.

Controling dewpoint is not feasible. Accuracy of sensor performance is improper. High humidity levels allow condensation on cold walls,

especially behind exhibits. Wall insulation was not possible due to prohibitive cost. Resolved by lowering the dewpoint and maintaining it

constant.

Conclusions


Revise Dewpoint Reset

Maintain Constant Dewpoint Summer Maximum And Winter Reset 45% R.H.(±8%) And 700F (±40F) Seal Walls And Use Vapor Resistant Materials Manage Building Pressure Review Control Sensor Pressure Review Control Sensor Locations Commission Entire Control System Operation

Design Recommendations


Building New Pressurization Diagram

Design Recommendations


Maintain Slightly Positive Pressure -- 2 Pascals

Variable Frequency Drives on all AHU’s and Return Air Fans

Run AHU’s at half-speed during unoccupied hours

Connect all the Existing Fans to the DDC System

Constant Dewpoint Temperature during Summer and Reset during Winter

Commissioning / Building Pressure Control


Questions and Answers

Documents

Moisture Control in Museums and Archives - Setty · Moisture Control in Museums Data collection within the wall cavity to support the calculated temperature profile. Three battery-powered