Psychrometrics - HVAC Excellence

Report
PSYCHROMETRICS TERMINOLOGY &
PROBLEM SOLVING
Presented by: Earl Delatte
psychrometrics
OLD QUOTE
 “I am certain that no air is so unwholesome
as air in a closed room that has been often
breathed an not changed.”
Benjamin Franklin
Mid 1700s
psychrometrics
HUMIDITY VS. TEMPERATURE
Which is important for our comfort.
BOTH
psychrometrics
HUMIDITY CONTROL
High indoor humidity is often difficult to control.
An air conditioners primary function is to heat or
cool the air.
Removing moisture from the air is the end result
of cooling.
It is a standard practice to use an air conditioner
in humid climates to dehumidify as well as cool a
given space.
Remember moisture removal isn’t the air
conditioner’s primary function.
psychrometrics
WE SPEND MOST OF OUR LIVES IN
BUILDINGS
We spend an average of more than 85% of our
time in buildings, much of it inside our home.
EPA studies have shown that indoor air
contains 3 to 5 times more pollutants than
outdoor air.
Maybe this may explains the upsurge of
allergies we have living in tight homes today.
psychrometrics
PSYCHROMETRIC CHART
Organizes the properties of air into a very useable graph
BREAKDOWN OF THE LINES
Enthalpy
BTU / lb
Dew
Point
100%
Saturation
Specific
Volume
Dry
Blub
Relative
Humidity
Grains of
Moisture
Wet
Blub
psychrometrics
SOURCES OF WATER VAPOR
 The following are examples of how water vapor is
introduced inside a home.
 Cooking
 Showers
 Humidifier
 Laundry
 Condensation
 Perspiration
 Firewood
 Wet clothes / shoes
 Refrigerators
 Aquarium Plant Shower
psychrometrics
DEW POINT
 The temperature which moisture starts to
condense out of the air.
 Dew point is also known as saturation
temperature.
 Dew point temperature is determined by moving
from a state point horizontally to the left along
lines of constant humidity ratio until the upper,
curved, saturation temperature boundary is
reached.
psychrometrics
DEW POINT
Temperatures are read at the
Saturation line from a set
point to the left along
humidity ratio lines.
MOISTURE CONTENT (BTU/LBAIR)
Saturation
Line
80°
70°
60°
50°
40°
30°
psychrometrics
HUMIDITY RATIO
GRAINS OF MOISTURE
Grains of water per pound of air at 100 %
humidity, (7007 grains equal 1 pound). This
number is commonly rounded to 7000.
Humidity ratio is represented by lines of
constant humidity running horizontally across
the chart to the right from a set point.
 Grains are represented with the symbol w
psychrometrics
HUMIDITY RATIO
MOISTURE CONTENT SCALE
180
Moisture in grains
are read from a set
point to the right side
of the chart.
170
160
150
130
120
110
100
90
80
70
60
50
40
30
20
10
0
psychrometrics
Grains of MOISTURE
140
HUMIDITY
Humidity a term for water vapor in the air.
Humidity has many sources, evaporation from
oceans, lakes, rivers, and ponds introduces
water into the air.
psychrometrics
DEW POINT
72 DRY BULB 62 WET BULB
psychrometrics
GRAINS OF MOISTURE
psychrometrics
ENTHALPY
72 DRY BULB 62 WET BULB
psychrometrics
PLOT POINT INFORMATION
psychrometrics
INCREASING HUMIDITY
WITHOUT CHANGING DRY BULB
psychrometrics
DATA FOR INCREASING HUMIDITY
psychrometrics
ASHRAE STANDARDS
Specify ideal comfort ranges of 68F to 74F at
40% to 60% relative humidity in the winter
months.
73F to 79F at 40% to 60% relative humidity in
the summer months. (75° & 50% RH)
psychrometrics
ASHRAE 62.2
Spells out the rules contractors must follow to
achieve acceptable Indoor Air Quality.
It also provides the background for equipment
such as ultra quiet fans, efficient heat recovery
ventilators (HRVs), energy recovery ventilators
(ERVs), new control strategies, and integrated
systems.
These are all solutions that combine
ventilation with heating and cooling systems.
psychrometrics
LARGE SOURCE OF MOISTURE
Return air leakage is the largest source of
moisture you’ll often find. Return air leakage
from unconditioned attics is often the worst
source of moisture.
WHY
 A 150 CFM return air leak from a 130F attic
can easily raise the humidity in a home by as
much as 30% in several hours.
psychrometrics
psychrometrics
PSYCHROMETRIC REPORT
psychrometrics
PSYCHROMETRIC REPORT
psychrometrics
CHANGING EQUIPMENT
LATENT CAPACITY
In the attempt to win the efficiency war, some
manufacturers have significantly reduced the
moisture removal capacity of their cooling
equipment.
Just read their rated latent removal capacity
under normal operating conditions from their
engineering data and compare it to older or
less efficient equipment
psychrometrics
EQUIPMENT OVER SIZING
Intensifies this issue as equipment shortcycles and inhibits the evaporator from
reaching its maximum potential for long
periods of brief operation.
psychrometrics
APPLICATION SHR
is largely a function of equipment type,
operation mode, and the latent loads
generated within the building, infiltrated
through the envelope, or introduced as
ventilation requirements.
psychrometrics
APPLICATION SHR
Particularly related to changing application
SHR is the on-going evolution occurring with
building codes and standards.
Two industry standards significantly affecting
application SHRs are ASHRAE Standard 90 (i.e.,
save energy by making buildings tighter)
ASHRAE Standard 62 (i.e., improve indoor IAQ
by bringing in outside ventilation air).
psychrometrics
APPLICATION SHR
These two standards in combination —
tighter, non-breathable envelopes with
introduction of potentially moist outdoor
ventilation air really make for some
challenging design considerations in humid
areas.
psychrometrics
AQUARIUM PLANT SHOWER
However, during the rest of the year, too much
humidity is the problem. This isn’t only a
comfort problem, it’s also a potential health
problem.
Mold is more likely to grow when the relative
humidity level is above 50%. Most molds
really like relative humidity above 70%.
psychrometrics
HEAT LOAD SHR
Just remember, when sizing the equipment,
it’s important to pay as much attention to
latent load as to the sensible load.
psychrometrics
NOW WHAT
When the air conditioner is the only way you
have to control high indoor humidity, there
are several ways you can enhance its
performance.
One of the simplest ways is to adjust airflow.
Most brands of equipment can be run with
350 cfm of airflow per ton of cooling with little
loss of overall performance.
This makes the indoor coil colder than normal,
resulting in better moisture removal.
psychrometrics
ADDITIONAL SOLUTIONS
 The next method is very similar. Install a singlepole, double-throw relay in the indoor unit,
connected to a dehumidistat.
 This requires a multi-speed blower. Connect the
common terminal of the relay to the cooling
speed tap of the blower relay. Connect the
normally open and normally closed terminals of
the relay to two different blower motor speed
taps.
 Set the dehumidistat to the desired relative
humidity
psychrometrics
ADDITIONAL SOLUTIONS
If you install a system with a variable speed
indoor blower, the blower can be set for the
exact airflow you want, as long as the duct
system is capable of supporting that setting.
Most variable speed blowers have enhanced
dehumidification modes. These blowers run at
about 200 cfm/ton for the first few minutes.
Then they ramp up to 80% required airflow for
five to eight minutes more.
psychrometrics
If the thermostat is still not satisfied, they
ramp up to full airflow. This produces very
cold indoor coils when the system has short
run times due to mild weather, but still
supplies full rated airflow during periods of
extremely hot weather.
psychrometrics
DEHUMIDIFICATION
Another way to dehumidify a house is to use a
dehumidifier.
This requires another piece of equipment and
another controller, but it’s more energy
efficient than using reheat.
psychrometrics
ADDING FOAM INSULATION TO
EXISTING HOME
 A home is a system consisting of the envelope,
the insulating barrier, ventilation, occupants and
their lifestyle and a heater and air conditioner.
 Change any of these components will affects
most or all of the others.
 Adding foam insulation to an existing home
without modifying the other components may
decrease utility bills, increase humidity and
increase pollutants in the home. Why?
psychrometrics
DEFINITIONS
Envelope - windows, walls, ceilings, floors
Insulating Barrier - house wrap, foam board,
fiberglass, weather stripping
Ventilation - bathroom vents, kitchen hoods, dryer
vents
Occupants and Lifestyle - size of family,
heating/cooling/humidity preferences
Comfort Control Systems - air conditioner, heater,
humidifier, dehumidifier, filtration and air
purification devices.
psychrometrics
LOWER UTILITIES
Depending on how much of the envelope is
coated with foam, the amount of air
conditioning required to cool the home is
reduced.
Without changing the size of air conditioner,
the system will run less.
You might think that this is a good thing and it
is regarding your utility bill. However....
psychrometrics
HUMIDITY
An air conditioner is a giant dehumidifier.
When it's not running it is not dehumidifying.
Higher humidity in a home can make the
house feel "muggy" and encourage mold
growth.
psychrometrics
INDOOR AIR QUALITY
Homes breathe through vents, cracks around
windows and doors, electrical outlets, attic
doors, etc.
Infiltration of fresh air causes your air
conditioner and heater to work harder but it
flushes out humidity, germs and pollutants.
Anytime you lessen the infiltration of outside
air you increase the amount of pollutants in
the home
psychrometrics
FOAM INSULATION
Foam insulation is in a semi-liquid state before
being sprayed into the attic, walls and anywhere
else that outside air needs to be put in check and
inside that needs to be blocked from escaping.
When sprayed into the area, this foam goes in like
liquid and “melts” into the cracks and holes but
simultaneously it expands to up to 3 times its
original size.
psychrometrics
FOAM INSULATION
As it expands it will adhere and fill in any
“seam” between the other side and this gives
you a 100% seal which is highly efficient.
psychrometrics
CLOSE CELL FOAM
What makes closed cell spray foam superior?
In addition to trapping air,
It also prevents air from flowing through it,
and therefore reduces the heat scavenging.
Effects of wind-washing. It’s like putting a
wind-breaker over a sweater.
psychrometrics
CLOSE CELL FOAM
PERFORMANCE IS GOVERNED BY:
• The number of bubbles or pockets
• The size of the bubbles
• What the bubbles are filled with
psychrometrics
ATTIC INSULATION
Plays a critical role in home energy performance.
In reality, most building scientists agree that the
attic should be the first objective area for
insulation and air-sealing upgrades for energy
saving.
Many homes are built with code required
minimum levels of attic insulation that are
inferior to current sanctions established by the
U.S. Dept. of Energy.
psychrometrics
WHERE TO INSULATE
psychrometrics
ZONE MAP
psychrometrics
EFFECTS OF FOAM INSULATION
ON A/C
When we add foam insulation to an existing
home without adjusting the other components:
What is the outcome?
decrease utility bills
increase humidity
increase pollutants in the home
Why
psychrometrics
LOWER UTILITIES
Depending on how much of the envelope is
coated with foam, the amount of air
conditioning required to cool the home is
reduced.
Without changing the size of air conditioner,
the system will run less. You might think that
this is a good thing and it is regarding your
utility bill.
However....
psychrometrics
HUMIDITY
An air conditioner is a giant dehumidifier.
When it's not running it is not dehumidifying.
Higher humidity in a home can make the
house feel "muggy“ you set the thermostat to
a lower temperature.
Encourage mold growth.
psychrometrics
BASIC ADVERTISMENT
When our bodies cannot dissipate our own
internal heat normally, we feel too hot. Foam
insulated buildings are much more
comfortable since they do not have these
temperature and humidity struggles.
Temperatures remain much more consistent
and lower humidity levels greatly improve the
indoor quality. Utility bills are much smaller
and our skin feels more comfortable.
psychrometrics
DEHUMIDIFICATION
 Our air conditioning and heating systems not only
keep us cool in the summer and warm in the
winter; they also dehumidify our indoor air.
 Lower levels of moisture in the air, greatly
improves comfort levels inside a building.
 You see our skin feels too hot or cold if
temperatures are too high or low and higher
humidity levels will magnify our level of
discomfort.
psychrometrics
POLLUTANTS
Homes breathe through vents, cracks around
windows and doors, electrical outlets, attic
doors, etc.
 This infiltration of fresh air causes your air
conditioner and heater to work harder but it
flushes out humidity, germs and pollutants.
Anytime you lessen the infiltration of outside
air you increase the amount of pollutants in
the home.
psychrometrics
INSTALL TWO-STAGE AIR
CONDITIONING
 Newer high-efficiency air conditioners run at 5070% capacity on low speed and 100% on high.
 When we size air conditioners to cool a home
based on average of the hottest days of the year,
they’re oversized most of the other days.
 By running on low speed most of the time, twostage units use less electricity and have longer
run times. When a system is running, it is
dehumidifying more moisture in the home.
psychrometrics
ADVANCED AIR PURIFICATION
Depending on how tight your envelope is you
will have to add some type of air purification
to the home.
One-inch disposable filters (fiber glass) were
designed to protect your air conditioning
equipment but had very little effect on our
health and comfort.
Innovative purification systems use various
combinations of 4-6" filters, ionization and
ultra-violet to decontaminate air
psychrometrics
CONSIDER DEHUMIDIFICATION
Can't replace your air conditioner at this time?
A whole house dehumidifier can reduce
humidity to acceptable levels.
Some of these units will introduce outside air
and process it before it enters your envelope.
psychrometrics
INFILTRATION
It is estimated that 60% of our energy bills are
caused by air infiltration.
Adding additional R value has no effect on air
infiltration
Running your air conditioner without sealing
your air leaks is like running your refrigerator
with the door open.
psychrometrics
INTRODUCE FRESH AIR
By intentionally introducing a small amount of
filtered fresh air from outside to the return air
of a system, you can create a controlled
version of infiltration.
This will help decrease carbon dioxide and
other pollutants in our home.
psychrometrics
CONCLUSION
Foam is a wonderful product. But, if you wish
to have a completely sealed, energy efficient
foam home, you are responsible for the future
health and comfort of the occupants.
You can plan for it in advance to fix the
problems that foam can created in your home
psychrometrics
HEAT LOADS
Sensible heat and latent load. 75 to 25 or
80 to 20
75 degrees 50% RH normal insulation 4 ton
Two instead of four.80 % RH
psychrometrics
ANY QUESTIONS
psychrometrics
THANK YOU FOR ATTENDING
www.escogroup.org
psychrometrics

similar documents