Application Note

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Application Note

From the Fluke Digital Library @ www.fluke.com/library

Tools featured:

Temperature humidity meter, pipe

clamp prob

e, I

R thermometer, D

Measurements taken:

Relative humidity, wet bulb

temperature, dew point, superheat

Testing

Functions

Case

Study

Investigating residential

humidity complaints

the carpet to the air

. This is

good for the carpet, but

contributes to higher RH in the

occupied space. This is good

ecause it

’s easier to deal w

ith

RH issues than floor moisture

issues

Scenario: Single stage residen-

tial cooling equipment. Home-

owner complains that humidity

is too high at their desired ther-

mostat setting.

Observations: Ranch house.

Air handler and ductwork in

attic. Slab construction.

Carpeted floors. Thermostat

setting 74 °F. System installed

last summer and load calcula-

tions were based on ACCA best

practices for “mixed/humid”

temperature zone.

Actions: You think this is too

easy. Probably a system-related

problem (dirty filter, low charge,

dirty condenser; the usual stuff.)

But you also realize that it’s

been a little cooler than most

summers. You measure the

indoor temperature and relative

humidity and find that it is

74.5 °F, 68 % RH, 66 °F WB,

and 63.3 °F DP.*

You are concerned because

ith a c

ooler than normal

summer, operating times are

less (less moisture removal),

and carpet over c

oncrete slab

can hide moisture problems and

create an environment for

fungal growth. You wonder if

there is a moisture-holding

sand layer between the vapor

barrier and the slab, which

would exacerbate moisture

problems under the carpet.

With your Fluke 6

0 series

infrared thermometer pointed at

the carpeted floor, you measure

68 °F. This is above dew point

and your psychrometric chart

tells you the vapor pressure is

reater in the carpet than in the

air, so moisture w

ill travel from

Indoor ambient (dry bulb) temperature on the

Fluke 971.

Indoor wet bulb temperature.

Indoor dewpoint temperature.

Summary of content (3 pages)

PAGE 1
Investigating residential humidity complaints Application Note Testing Functions Case Study Tools featured: Temperature humidity meter, pipe clamp probe, IR thermometer, DMM Measurements taken: Relative humidity, wet bulb temperature, dew point, superheat Scenario: Single stage residential cooling equipment. Homeowner complains that humidity is too high at their desired thermostat setting. Observations: Ranch house. Air handler and ductwork in attic. Slab construction. Carpeted floors.
PAGE 2
You ask the homeowner if any remodeling changes have occurred to the house. They say, “No. Wait. We had a new roof installed. Does that count?” You ask, “Same composition roof?” They say, “Yes, but we changed the color from dark green to white.” You say, “Thanks. I also noticed that you run your fan continuously. Is there a reason for that?” They say, “We think it keeps the air moving and makes it feel more comfortable.” You think you’ll comment on that later after you have finished gathering data.
PAGE 3
Options 1, 2, and 3 are implemented. Since the equipment is not oversized, you think it will result in the desired effect. Option 4 makes you nervous, so you decide if further improvement is needed later, you can try it then. You don’t want to bring up options 5 and 6 due to the inevitable cost discussion. So now it’s time for your presentation to the homeowner... “The high humidity you have been experiencing indoors is a result of lower outdoor temperatures that result in less operating time.