# Psychrometrics Terminology & Problem Solving

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Psychrometrics Terminology & Problem Solving
Presented by: Earl Delatte

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

HUMIDITY VS. TEMPERATURE
Which is important for our comfort. BOTH

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.

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.

Organizes the properties of air into a very useable graph
Psychrometric chart Organizes the properties of air into a very useable graph

Breakdown of the Lines Dry Blub Relative Humidity Dew Point 100%
Saturation Enthalpy BTU / lb Wet Grains of Moisture Specific Volume

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

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. To remove moisture from the air, an air conditioner evaporator coil must operate below the dew point temperature. Moisture will collect on the cold surface of an evaporator coil and then drain through the condensate line.

dew point Saturation Line
MOISTURE CONTENT (BTU/LBAIR) Temperatures are read at the Saturation line from a set point to the left along humidity ratio lines. 80° 70° 60° 50° 40° 30°

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

Humidity Ratio MOISTURE CONTENT SCALE
Grains of MOISTURE 180 170 160 150 140 130 120 110 100 90 80 Moisture in grains are read from a set point to the right side of the chart. 70 60 50 40 30 20 10 Traveling side to side, moisture content does not change Traveling up, moisture content increases Traveling down, moisture content decreases

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.

DEW POINT 72 Dry Bulb 62 Wet Bulb

GRAINS OF MOISTURE

Enthalpy 72 Dry Bulb 62 Wet Bulb

PLOT POINT INFORMATION

INCREASING HUMIDITY WITHOUT CHANGING DRY BULB

DATA FOR INCREASING HUMIDITY

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)

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.

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.

PSYCHROMETRIC REPORT

PSYCHROMETRIC REPORT

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

EQUIPMENT OVER SIZING Intensifies this issue as equipment short-cycles and inhibits the evaporator from reaching its maximum potential for long periods of brief operation.

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.

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).

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.

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%.

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.

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.

Additional solutions The next method is very similar. Install a single-pole, 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

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.

If the thermostat is still not satisfied, they ramp up to full airflow
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.

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.

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?

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.

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....

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.

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

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.

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.

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.

CLOSE CELL FOAM PERFORMANCE IS GOVERNED BY:
• The number of bubbles or pockets • The size of the bubbles • What the bubbles are filled with

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.

WHERE TO INSULATE

Zone map

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

Lower Utilities However....
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....

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.

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.

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.

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.

Install Two-Stage Air Conditioning
Newer high-efficiency air conditioners run at 50-70% 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, two-stage units use less electricity and have longer run times. When a system is running, it is dehumidifying more moisture in the home.

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

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.

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.

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.

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

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

Any Questions

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