HVAC - Chapter 131: Humidification
Exam Question: At -18°C What is the maximum amount of moisture air can hold?
-18°C cannot hold any more than 0.0008 kg of moisture
Exam Question: At 5°C What is the maximum amount of moisture air can hold?
5°C air can hold a maximum of 0.005kg of moisture
What is an Air Washers main Purpose?
It's main purpose is the humidification of air, but in combination with humidification, it is also used to heat, cool, and dehumidify or clean the air
What do most waters contain in solution?
Most waters contain salts in solution.
What is the level in the tray controlled by?
The level in the ray is controlled by a float valve.
What are 3 options that can be used to control the temperature of the spray water in an air washer?
1.) Only part of the spray water is recirculated and hot or cold water is added as needed 2.) The spray water is recirculated through a heat exchanger and is either heated or cooled by hot or chilled water 3.) Heating or cooling coil is directly mounted in the sump of the washer
What are Two Sections of Humidifiers?
1.) Residential & Warm Air System Humidifiers 2.) Industrial & Commercial Humidifiers
Exam Question: At 21°C What is the maximum amount of moisture air can hold? Hint _____kg or moisture per kg of air
21°C air can hold a maximum of 0.015kg or moisture per kg of air
Exam Question What does a Humidistat control in an Atomizing Humidifier?
A Humidistat controls the water supply to the spray by means of a solenoid valve
Exam Question A certain amount of moisture is supplied by normal living processes such as? But This amount is usually insufficient to maintain the required...?
A certain amount of moisture is supplied by normal living processes, such as Cooking, Washing, and Breathing, but this amount is usually insufficient to maintain the required relative humidity
What controls the rotation of the pad?
A humidistat mounted in the living area on the return duct; controls rotation of the pad
What are placed in a vertical position in the tray? Which part of is immersed in the water?
A number of absorbent plates are placed in a vertical position in the tray, their lower part immersed in the water.
What type of valve usually supplies the water to the pad?
A solenoid valve usually supplies water for the pad
What does The Pan Type Humidifier Consist of?
A water pan equipped with a float valve assembly, overflow and drain connections, as well as a steam or electric heating coil in the pan.
What is one of the most versatile pieces of equipment used in Air Conditioning systems?
Air Washers
What are 3 types of Industrial & Commercial Humidifiers?
Air Washers Steam Grid Humidifier Pan Type Humififier
What are all of these Symptoms caused by?
All of these symptoms are caused by lack of humidity in the air
Where is a Steam Grid Humidifier Installed?
Always installed in the return air duct
Where should an Air Washer Be installed? At what pressure should it be maintained? What does This Pressure Prevent?
An air washer should be installed on the suction side of the fan where it can be maintained at a pressure slightly below that of the atmosphere. This prevents leakage of water through the joints
Exam Question: What is the relative humidity of 21°C air that contains 0.0075 kg of moisture? Hint: 21°C air can hold a maximum of 0.015kg
Assume 21°C air contains 0.0075 kg of moisture. This amount is only 50% of the maximum amount of moisture this air can absorb, thus the relative humidity of this air is 50%
Exam Question: What is a Disadvantage of Atomizing Humidifiers?
Atomizing humidifiers have the disadvantage that, Since the water is sprayed into the air and then evaporates, the salts in solution in the water appear as a fine white dust which settles in ducts and rooms. Regular cleaning must be required to remove this dust
Where is the Pan Type Humidifier commonly used?
Commonly used in the supply plenum of smaller air furnaces
In the Pan Type Humidifier what does it consist of which is partially filled with water?
Consists of a shallow pan (or tray) partially filled with water.
What does an Air Washer primarily consist of?
Consists primarily of a casing and the spray chamber, in which a bank of spray nozzles are installed
What do Cylindrical pads rotate through?
Cylindrical pads rotate through a tray partially filled with water
What does dry air cause on people walking on wool or nylon carpet? What is the result of this?
Dry air causes static electric charge to build up on people walking on wool or nylon carpet. The result may be a painful electric shock caused by the discharge of this static charge when any metallic object or even another person is touched
What does dry air increase on the skin? What does this result in?
Dry air increases evaporation on the skin, resulting in a cold and uncomfortable feeling, even if room temperature is significantly high
What Else will strike the surface of the Eliminators? What washes them down?
Dust particles will also strike the surface of the eliminators and continuous stream of water from the flooding nozzles washes them down
Exam Question Where are Eliminators Installed? What are they used for?
Eliminators are installed at the outlet of the washer to prevent droplets of water from being carried away by the air
Exam Question From a health standpoint, which range of humidity is desirable? ___% to ___%
From a health standpoint, humidity between 35% - 50% is desirable.
What happens to furniture floors, and plants when dry air is present?
Furniture and floors dry out and become squeaky and plants wither.
How is Good Control of Humidity of A Steam Grid Humidifier achieved?
Good control of humidity is achieved by using a steam modulating control valve, actuated by a humidistat located in the room or in the return air steam
In addition to the last slide, additional moisture should be supplied by means of what?
Humidifiers
What is the definition of humidity?
Humidity: Refers to the presence of moisture in the air
What will happen If the spray water is below the dewpoint temperature of the entering air?
If the spray water is below the dewpoint temperature of the entering air, both cooling and dehumidification will be achieved
Exam Question If the water is softened by "Ion Exchange" what will be increased, and why?
If the water is softened by ion Exchange, the residue will actually be increased because the magnesium and calcium salts will be replaced by sodium salts
If the water temperature is also above the dry bulb temperature of the entering air What will occur?
If the water temperature is also above the dry bulb temperature of the entering air, heating of the air will also occur.
In its simplest form, what does the steam grid humidifier consist of?
In its simplest form, a steam grid humidifier consists of a perforated pipe wrapped with suitable felt wicking. It also comes complete with a drain pan to catch the condensate droplets
Steam Grid Humidifiers used in air conditioning systems achieve humidification by:
Injecting steam in the supply air stream
Where can a Pan Humidifier installed?
It can be installed inside the casing of an air handling apparatus, inside the supply air duct, or attached to the underside of that suct
What is usually not recommended in a Steam Grid Humidifier? What 3 things would occur if you did this?
It is not recommended to use an on-off control with this type of humidifier, because fogging, overheating, and wide fluctuations of relative humidity would occur
It makes use of the pressure difference between what two things?
It makes use of the pressure difference between supply and return plenum, created by the furnace blower, to draw warm air through the wetted pad.
How is moisture added to the air stream?
Moisture is added to the air stream by vaporizing the water in the pan
Where is the Bypass Type Wetted element Humidifier mounted What is it also connected to by means of a short length duct?
Mounted on the supply plenum of the furnace But is also connected to the return plenum by a short length of duct
Random Highlighted Note: Hot air Absorbs More or Less Water?
Note: Hot air absorbs more water
Other Air Washers can contain more banks of what to increase efficiency?
Other washers have 2 or even 3 banks of spray nozzles for increased efficiency
Exam Question What are the three types of humidifiers used in residential purposes?
Pan Wetted Element Atomizing
What two groups can the Wetted Element Humidifier be divided into?
Power Type Bypass Type
What is the definition of relative humidity?
Relative Humidity: The capability to hold moisture. The amount of moisture contained in the air, compared to the maximum moisture the air is capable of holding at that temperature
What affects the humidity in the air considerably?
Since only air at atmospheric pressure is dealt with here, the effect of pressure may be ignored, but air temperatures affect the humidity considerably.
What can a model equipped with a fan allow?
Some Models come equipped with a fan which allows remote mounting
Exam Question: What else can be removed in the Air Washer? But what is it not effective in the removal of? What is not removed at all?
Some odours are also removed by the air washer, but is not effective in the removal of greasy particles and soot; tobacco smoke is not removed at all
How does a spinning disk atomize the water into a fine mist?
Spinning Disc type: A rapidly rotating disc atomizes the water into a fine mist.
When Steam is Available, What type of humidifier can be used?
Steam Grid Humidifier
Where os steam supplied to in the Steam Grid Humidifier?
Steam is supplied to the steam jacket of the distribution manifold at supply pressure and temperature; it flows from there into a separating chamber
2 Types of Pan Type Humidifiers are?
The Electrically Heated Pan Humidifier The Steam Heated Pan Humidifier
What is the Electrically Heated Pan Humidifier equipped with to protect the element?
The Electrically Heated Pan Humidifier is epuipped with a low water cut-off switch to protect the element
Exam Question What 2 things must be used with The Steam Heated Pan Humidifier offer a high capacity and accurate humidity control
The Steam Heated Pan Humidifier offers high capacity and accurate humidity control if used with a modulating control valve and a steam pressure not exceeding 103 kPa (15psi)
Where does the air flow through? What does it come in contact with?
The air flows through the chamber and comes in contact with the spray water.
Relative humidity Decreases when:
The air temperature is raised without the addition of moisture to the air
Exam Question: Can the air absorb more or less of the moisture at high temperatures?
The higher the temperature of air, the more moisture it can absorb
How does the humidification rate vary?
The humidification rate varies with the temperature, humidity, level, and velocity of the air flowing over the wetted pads
Exam Question: How is the level in the tank of an Air Washer Maintained?
The level in the tank is maintained by a float-controlled make-up valve
Exam Question: Can the air be able to hold more or less of the moisture at Lower temperatures?
The lower the temperature of the air, the less moisture it will hold
What two "shapes" can this pad be?
The pad can either be flat or cylindrical.
Exam Question What range of capacity can a pan humidifier offer?
The pan humidifier offers a broad range of capacity
Exam Question: Where is The Spray water collected? What happens to it after this?
The spray water collects in the bottom tank and is usually recirculated to the sprays by a pump.
What does a Wetted Element Humidifier make use of through which warm air is forced?
The unit makes use of a water saturated evaporation pad through which warm air is forced
The use of What is recommended, so that solids don't plug up the spray nozzle?
The use of a fine screen in the supply line is recommended, so that solids don't plug up the spray nozzle
What does warm air passing over the pate cause the water to do?
The warm air passing over the plates causes the water to evaporate and the vapour is carried off by the air.
Exam Question The water is drawn to the surface of these plates by What type of action?
The water is drawn to the surface of these plates by Hydroscopic Action.
What two ways can the water supplied to the flat pad?
The water is supplied to the flat pad either by gravity from a distribution pan above the pad or by a spray
Exam Question What do these units have to draw warm air from the furnace plenum, or from the room. Where does it force the air though? Where does the humidified air get returned to?
These units have a small fan to draw warm air from the furnace plenum or from the room, force it through the wetted pad and return the humidified air to the plenum or the room
What are Eliminators designed to change? What does this cause?
They are designed that they can change the direction of the airflow several times. Causing Droplets to impinge and run down the surface of the eliminators into the bottom of the tank
What happens if too much salt is left behind in the evaporation plates or pads?
They can build up to such an extent that clogging occurs and proper evaporation is prevented
Exam Question What type of Humidification rate does the Pan Type Humidifier supply?
This humidifier supplies a very low humidification rate
What is this unit used as? Is it portable or stationary?
This unit is used as a room unit, either portable or stationary
To achieve Satisfactory results, What should the steam pressure be? What 2 things does this range of pressure prevent?
To achieve Satisfactory results, the steam pressure should be in the range of 35 - 70 kPa (5.1psi to 10.2psi) to prevent splashing of condensate and objectionable increase in the temperature of the supply air
How can Humidifiers be kept in top condition? Hint: 2 Things should be cleaned 2 Things should be Checked
To keep humidifiers in top condition, the plate units should be cleaned by soaking them in a slightly acid solution and then washing them in soapy water. The Tray or pan should also be cleaned out to remove the salt buildup The Float and Solenoid Valve should be checked for leakage
With the Use Of an Air Washer, control can be obtained?
Use of an air washer, considerable amount of control can be obtained over both the air temperature, and humidity.
What is it usually equipped with instead of a fan?
Usually equipped with a rotating wetted pad, but not with a fan.
In an Atomizing Humidifier how is water broken up into small particles (3 Ways)
Water is broken up into small particles by using either a spinning disc or cone, or a spray nozzle
Exam Question: When the AirWasher Is used for Humidification the temperature of the spray water must be above what?
When the Airwasher is used for humidification, the temperature of the spray water must be above the dewpoint temperature of the entering air.
What happens to relative humidity When the air temperature is raised without the addition of moisture? What does this explain?
When the air temperature is raised without the addition of moisture, the relative humidity drops, which explains why indoor air can get so dry during cold weather even though air at the outside temperature is saturated
What happens to these salts when the water is evaporated in the humidifier? Where do the salts go?
When the water is evaporated in the humidifier, these salts stay behind in the evaporation plates and pads
How can Humidification be achieved with a Steam Grid Humidifier?
humidification can be achieved with a steam grid humidifier by injecting steam into the supply of air
