Gas Trade 2 Training
Unit 23 - Forced-Air Add-on Devices
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Unit 23
Forced-Air Add-on Devices
Most add-on devices are optional, but filters are not. A forced-air
furnace must never be operated without a filter installed. Without
air filtration, dust and lint will build up on the furnace’s internal
parts, resulting in loss of efficiency, equipment damage, and
possible fire.
Add-on devices such as filters, air cleaners, humidifiers, and
cooling coils improve the air quality in a building heated by a
forced-air furnace.
Filters and air cleaners of various kinds remove particulate matter
from the air. Humidifiers increase the relative humidity, increasing
comfort for building occupants. Cooling coils allow the forced-air
furnace to function as a central air conditioner.
At the end of this unit you will be able to:
Gas Trade 2 Training
© CSA Group
•
select, install, and maintain appropriate air filters and
air cleaners
•
select, install, and maintain appropriate humidifiers
•
inspect and clean an add-on cooling coil
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Unit 23
Table of Contents
Chapter 1 Air filters and cleaners
Types and applications ....................................... 3
Media filters ........................................................ 7
Electrostatic filters ............................................ 17
Electronic air cleaners ...................................... 19
Assignment 1.................................................... 33
Chapter 2 Humidifiers
Function and control ......................................... 39
Installation ........................................................ 45
Operation and service ...................................... 51
Assignment 2.................................................... 57
Chapter 3 Cooling coils
Checking and cleaning cooling coils ................. 61
Assignment 3.................................................... 67
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Chapter 1
Air filters and cleaners
Purpose
A forced-air furnace cannot be operated without air filtration. The gas
technician/fitter must be familiar with the various types of filters
available, be able to install them correctly, and instruct customers on their
maintenance to ensure safe, efficient operation of the gas furnace.
It is important for the gas technician/fitter to understand the advantages
and disadvantages of media and electrostatic filters and electronic air
cleaners, so they can help customers choose the air filtration system best
suited to their needs.
Learning
outcomes
1. Describe three types of air cleaning equipment (media filters,
electrostatic filters, and electronic air cleaners) that can be used with
forced-air furnaces.
2. Describe the function, installation, and maintenance of media filters.
3. Describe the function, installation, and maintenance of electrostatic
filters.
4. Describe the function, installation, and maintenance of electrostatic
filters.
Sections
Types and applications ......................................................... 3
Choosing the correct system .............................................................. 5
Media filters .......................................................................... 7
Function .............................................................................................. 7
Installation and location ...................................................................... 9
Instructions to the customer ............................................................. 10
Maintenance and service .................................................................. 15
Electrostatic filters .............................................................. 17
Function ............................................................................................ 17
Installation and location .................................................................... 18
Instructions to the customer ............................................................. 18
Maintenance and service .................................................................. 18
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Electronic air cleaners ........................................................ 19
Function ............................................................................................ 19
Installation and location .................................................................... 21
Instructions to the customer ............................................................. 25
Maintenance and service .................................................................. 28
Assignment 1 ...................................................................... 33
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SECTION 1
Types and applications
All forced-air furnaces require air filtration to operate safely and
efficiently. Some furnaces are intended to be used with specific types of
filters, but in many cases the appropriate filter or air cleaner must be
chosen and added on to the forced-air furnace.
Ensuring proper air cleaning requires effort by both the technician/fitter
and the customer. All air cleaning devices, whether filters or air cleaners,
require ongoing maintenance and cleaning. Some of this maintenance
must be done by the customer.
The gas technician/fitter must understand:
•
operation of the filter or air cleaner
•
benefits and disadvantages of the filter or air cleaner
•
installation procedures
•
requirements for customer cleaning and maintenance
•
service procedures.
The customer must understand:
•
importance of regular cleaning for efficiency, safety, and air quality
•
cleaning schedule required for their unit
•
cleaning procedures and basic maintenance.
The particles you breathe in a house come from a variety of sources
including:

dust on floors or other surfaces that is disturbed by activity in the
house

dust generated by smoking, burning candles, cooking, doing laundry,
etc.

hair and skin flakes from humans or pets

particles from the outside air that come into your home with
infiltrating air.
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Some particles are so small that they are inhaled and then exhaled without
being trapped in your lungs. Some larger particles are trapped in your nose
and throat and never reach your lungs. Still other particles are too large to
be inhaled. The particles most dangerous to you are those that enter your
lungs and lodge there.
You can see the particles of dust that accumulate on a television screen,
shelves, and furniture, but you cannot see the unsafe particles. Unsafe
particles can be easily inhaled into your lungs and provoke respiratory
illness. Although you would probably like to keep visible dust out of your
home, the main health risk comes from unsafe particles, which include
tobacco smoke, spores, bacteria, and viruses.
There are three basic possibilities for air filtration, all of which will be
discussed in detail in this chapter.
•
Media filters
Media filters, sometimes called mechanical filters, are the simplest
form of air filtration. They are made from such media as fiberglass ,
and positioned in the air stream. Air is forced through the filter and
particles removed. The filter media can be reusable or disposable.
Media filters of high, low, and medium efficiency are available.
•
Electrostatic air filters
Electrostatic air filters are media filters made from a material that
generates a static charge in response to air flow. The static charge
attracts and holds more particles than media filters to the medium.
•
Electronic air cleaners
Electronic air cleaners (EAC) also use an electrostatic charge to
remove and collect particulate contaminants from the circulated air
system. An EAC uses an external power source to generate the charge
that attracts particles, and charged plates, rather than a media filter, to
collect them.
Filter ratings
MERV stands for Minimum Efficiency Reporting Value. MERV is a
numerical value given to furnace filters in order to identify their filtering
abilities.
The MERV rating system is now an international industry standard set up
by the committee that oversees the furnace filter industry. This standard is
used for determining a furnace filter's ability to capture and hold dirt and
dust in specific size ranges.
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MERV ratings range from 1 – 16 and measurements are in microns. The
higher the MERV rating, the greater the filtering capability.
HEPA or Hi Efficiency Particle Air filters, which remove a very high
percentage of airborne contaminants, are often specified for various
commercial, industrial and institutional applications. The pressure drop
caused by their tight fabrication should be assessed for suitability with
fan units prior to use or to ensure duct static pressures are maintained.
Choosing
the correct
system
Several factors should be considered when choosing an air filtration
system:
•
degree of air cleanliness required
•
amount and type of dust in the air to be filtered
•
operating resistance to air flow (pressure drop)
•
space available for filtration equipment
•
initial costs of the system
•
ongoing costs of maintaining or replacing filters
•
operating costs, predicted life of the system, and efficiency of the
system.
Each type of air filtration approach has advantages and disadvantages that
are addressed in Sections 2 to 4.
The following table, derived from a study by the Canada Mortgage and
Housing Corporation (CMHC), outlines the operating costs of various
filter types.
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Table 1-1 Relative costs of air filter types
Filter
Maintenance and Amount of clean Cost of clean
capital costs, per air produced
air per year
year, over 15
(litres/second) ($/litres/second)
years ($)
25 mm pleated
48
17
3.36
25 mm premium
100
97
1.13
Charged media
43
44
1.25
100 mm pleated
93
60
1.71
HEPA bypass
240
175
2.03
ESP
67
298
0.26
Source: CMHC
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SECTION 2
Media filters
Media filters are the simplest form of air filtration. Three types of media
filters are most commonly used in residential installations: slab filters,
hammock filters, and pleated filters. Extended panel filters and moving
curtain filters, while more efficient, are usually used only in industrial or
commercial applications.
Function
Media filters physically remove particles from the air stream.
•
Hammock filters
Hammock filters are located on a frame or hammock that surrounds
the fan in the forced-air furnace (see Figure 1-1). If a forced-air
furnace is intended to be used with a hammock filter, the filter holder
will be factory installed.
Figure 1-1 Hammock filter
•
Slab filters
Slab filters consist of layers of filter material, usually fiberglass, held
in place by a cardboard frame (Figure 1-2). The fibers are treated with
oil or a similar adhesive. Filters for residential use are usually about
one inch thick. Most slab filters are designed for one-time use and
must be discarded when they are dirty.
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Figure 1-2 Slab filter
•
Pleated Media Filters
Pleated media filters represent the most popular type of filter choice
available today. They come in a variety of sizes and thicknesses. Paper
pleating increases the filter surface and improves performance.
A 5 inch depth pleated media filter can replace an electronic air filter
and reside in the same cabinet, or a custom air filter rack can be
installed to accommodate the size.
Figure 1-3 Pleated media filter
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Advantages and disadvantages of media filters
•
Advantages
–
–
•
Installation
and location
initial cost and upkeep are low
efficient for the removal of lint.
Disadvantages
–
–
low efficiency on normal atmospheric dust
air flow decreases as particles collect in filter
–
pleated media filters are more costly and restrict airflow.
Slab filters should be positioned according to the forced-air furnace
manufacturer’s instructions. In some cases the filter may be installed in
the plenum. When a slab-type filter is installed in a left or right return air
inlet on an upflow furnace, the factory-supplied filter may have to be
trimmed to fit. However, the effective filter area should be no less than
that recommended by the furnace manufacturer.
A filter rack must be installed to hold the filter in position. The filter rack
is usually located between the furnace casing and the return-air plenum.
Installing the filter rack
Appropriately sized filter racks are usually shipped with the furnace that
uses them. They are most commonly installed on furnaces with a side air
return.
1. The side of the furnace cabinet will likely have embossed angles
indicating the location of the racks (Figure 1-4a).
2. Cut the return opening, using the angles as guides.
3. Mount the filter rack over the opening (Figure 1-4b).
4. Proceed with the ductwork.
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(a)
(b)
Embossed
angles
Figure 1-4 Installing a filter rack
Impact on air flow
All media filters, whether mechanical or electrostatic, add resistance to air
flow. The thickness of the filter should conform to original thickness
specifications for the forced-air furnace. Adding extra filters to the filter
chamber in an attempt to improve indoor air quality can seriously impede
furnace operation. This should be explained to the customer.
As filters fill with particles, the air volume flowing through them
decrease. Restrictions in air flow cause problems in both heating and
cooling units. Abnormally high circulating air temperatures can occur in
heating cycles, causing the furnace to switch off on the high limit control
and seriously limit the furnace’s ability to heat the house. Freeze-ups of
the A-coil can also occur in cooling cycles.
Instructions
to the
customer
Regular cleaning of air cleaners and filters is crucial for optimum cleaner
efficiency.
Dirty filters:
•
are the most common cause of inadequate heating or cooling
performance
•
create temperature changes that are detrimental to the operation of the
furnace
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•
decrease operational air flow in systems with add-on air conditioning
may cause liquid refrigerant to return to the compressor during the
running cycle since there is insufficient air flow to vaporize the
refrigerant. This condition is called floodback and may damage the
compressor.
•
cost money, since excessive accumulation can block the air flow,
forcing the unit to work harder and use more energy.
Filter cleaning must be done on a regular, and frequent, basis—more
frequently than service calls are required. It is the responsibility of the gas
technician/fitter to point out the filter’s location to the user and to establish
a filter change or cleaning schedule. The gas technician/fitter must be sure
the customer understands the installation procedure for new filters, and
knows what size and type of filter is required.
Caution!
A forced-air furnace must never be operated without a filter installed.
Dust and lint will build up on the furnace’s internal parts, resulting in loss
of efficiency, equipment damage, and possible fire.
Replacing and cleaning filters
Filters should be inspected every month in the heating season, and cleaned
or replaced as required. They must be cleaned or replaced at least twice a
year, and any time they become clogged or as manufactures instructions
require them to be cleaned or replaced.
Replacement furnace filters are available from the dealer. The replacement
filter must be the same size and type as was originally supplied with the
furnace.
A dirty filter can cause high temperature rise across a furnace due to the
restrictive nature of the air flow. This may continue unknown to the
homeowner until such time as the outdoor temperature drops and they
suddenly realize that the furnace is not heating to the set temperature.
Downflow or Low Boy furnaces
Downflow furnaces contain two or four disposable slab air filters. They
are located in a filter cabinet on top of the furnace (Figure 1-5). Typical
filter replacement instructions follow.
1. Remove the two screws holding the filter box door in place and
remove the filter box door assembly.
2. Pull the filters out of the box, flexing them as necessary to get them
past the flue pipe.
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3. Insert the replacement filters. Make sure they are properly positioned
in retaining clips on the back panel.
4. Re-install the filter box door assembly and secure it with the two
screws.
Remove filters
from right side
Figure 1-5 Typical filter position on a downflow furnace
Upflow or High Boy furnaces
Upflow furnaces may contain a cleanable, reusable hammock filter within
the furnace blower compartment in either a bottom or side (left or right)
return air inlet. Figure 1-6 illustrates these two options.
1. Power to the unit must be disconnected before the blower door is
removed.
2. Remove the blower access door.
3. Loosen the filter retaining wire at the front of the unit.
4. When replacing the cleaned filter, make sure the filter retaining wire is
secured in place at both the front and back of the unit.
5. Replace the blower access door and restore the power.
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Filter
retainer
Filter
retainer
Filter
Filter
Blower access
door
Blower access
door
Figure 1-6 Possible filter positions on an upflow furnace
Filter frames
Filters may be located outside the furnace in a filter frame (Figure 1-7).
The filters in a filter frame may be either disposable or reusable slab
filters. They should slide out easily for replacement (if disposable) or
cleaning (if reusable).
Access
Figure 1-7 Access to filters in a side filter frame
Specific media filters
Consult the manufacturer’s instructions for the specific unit before
showing the customer how to replace or clean the filter. The instructions
here are provided as a general guideline.
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Hammock filters
Hammock filters usually contain disposable filter material that must be
replaced, as described below.
1. Before you remove the filter unit, place a floor covering material on
the floor.
2. Slide the entire filter out of the unit.
3. Loosen the screws that hold the media to the rack and remove it.
4. Wrap the old media in newspaper and discard it.
5. Unroll new media and cut it to the correct size.
6. Attach the media to the rack. One side of the media is usually coated
with oil, to enhance particle collection. This coated side should be
opposite the blower. (In an upflow unit, the coated side will face the
return air duct work.)
7. Slide the filter back into the blower compartment.
Reusable slab filters
Reusable slab filters are made from polyurethane and coated with an oilbased filter spray.
1. Remove the filter from the unit.
2. Remove the media from the filter frame.
3. Wash or vacuum the media. Use hot water and detergent for washing.
4. Squeeze water from the media and return it to the frame.
5. Coat the side of the media opposite the blower with a filter spray to
enhance particle collection. The filter spray must be applied before the
filter is repositioned in the furnace. Do not re-oil the filter in place. If
re-oiling is done while the filter is in position, oil will be sprayed on
the blower assembly and heat exchange surfaces.
6. Reposition the filter in the unit.
Disposable slab
Disposable slab filters are usually made from fiberglass and cardboard.
1. Remove the filter from the unit.
2.
Discard old filter with regular household garbage.
3. Place new filter in unit. The new filter must be the same size. If there
are arrows on the filter frame, they must be placed to match the system
air flow.
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Caution!
Disposable filters must be discarded, not reused. Reused filters will not
remove particles effectively.
Maintenance
and service
Other than cleaning reusable filters, and replacing disposable ones, little
maintenance can be done on media filter systems. When the furnace is
being inspected, the technician/fitter should include an inspection of the
filters. Reusable filters need to be replaced if they are damaged.
Disposable filters should not be vacuumed. Vacuuming will remove
mineral oils along with the dirt, and the filter will no longer work.
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SECTION 3
Electrostatic filters
Electrostatic filters may replace standard media filters if more filtration
is necessary.
Function
Electrostatic air filters use a combination of static electricity and filtering
media to remove particles from the air. The filter media is usually made of
layers of nylon or woven polyethylene fiber encased in a frame (see
Figure 1-8). In appearance it is similar to a disposable slab filter. As the
air stream travels through the filter, static electricity is generated. The
static charge affects the particles, which are then more likely to cling to
the filter medium. Most electrostatic air filters are washable and reusable.
Figure 1-8 Electrostatic filter
Advantages and disadvantages of electrostatic
filters
•
Advantages
– no electricity required
– more efficient than media filters without electrostatic charge.
•
Disadvantages
–
less efficient than electronic air cleaners.
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Installation
and location
Instructions
to the
customer
Maintenance
and service
Because electrostatic filters are a form of slab filter, they are installed in
the same position and way as slab filters: either inside the plenum or in a
filter frame. Consult the manufacturer’s specifications for installation
instructions.
The electrostatic air filter must be regularly cleaned to ensure proper
furnace function. The typical electrostatic filter is reusable. It can be
cleaned in the following ways:
•
vacuuming
If the filter is lightly soiled, vacuuming will be sufficient to remove
the particles. The upstream side of the filter should be vacuumed first,
and the downstream side second. Some electrostatic filters can be
vacuumed in place. Consult the manufacturer’s instructions for
specifics.
•
flushing with clean water
From time to time, the filter should be flushed thoroughly with clean
water. This can be done with a hose or shower nozzle. It is not
necessary to dry the filter before returning it to position, but excess
water should be shaken from it to prevent it from dripping into the
ductwork.
•
washing with detergent
If the filter is greasy, it should be washed with detergent. This can be
done in a bathtub, but care must be taken not to scratch the tub with
the filter frame. The filter should be rinsed with clear water before it is
returned.
The electrostatic air filter should be inspected by the technician/fitter
when the furnace is inspected. Damaged filters must be replaced.
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SECTION 4
Electronic air cleaners
An electronic air cleaner (EAC) may be free-standing, or may be designed
to be installed into central heating and cooling systems. The basic
operation is the same. In this Chapter, EACs designed to be installed into
the heating and cooling system are discussed.
Function
Electronic air cleaners have four sections: pre-filter, charging section,
collecting section, and power pack or voltage section.
•
Pre-filter
The pre-filter screens large particles before they enter the electrostatic
field. It may be composed of fine wire mesh, expanded aluminum,
or foam. The large particles removed by the pre-filter might cause
excessive arcing (and excess ozone production) if they were allowed to
enter the high-voltage section of the air cleaner cell.
Note: The pre-filter serves the same purpose as the slab or hammock
filter in the furnace blower compartment, so when an electronic air
cleaner is installed any existing slab or hammock filter must be
removed.
•
Charging section
The charging section (cell) consists of a band of small-diameter wire
filaments or ionizer wires. They are supplied with high dc voltage
(between 6 and 25 kV dc) from the power pack. The wires are
suspended equidistant between grounded plates. The high voltage
on the wires creates an electrostatic field, also called an ionizing
field. The positive ions create flow across the airstream. As airborne
particles pass through the field, they become positively or negatively
charged (Figure 1-9).
•
Collecting section
The collector cell contains a series of parallel plates. Alternate plates
are charged with a positive direct current voltage of 4 to 10 kV dc.
Plates that are not charged are at ground potential. The charged
particles passing into this section are attracted to the plates by the
electric field on the charges they carry. These capture and hold
contaminated particles of the opposite charge. Retention may be
augmented by oils or adhesives on the plates.
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•
Power pack or voltage section
The power pack consists of a step-up transformer and a rectifier circuit
(also called a voltage doubler). The step-up transformer increases
incoming 120 V ac current to 3000–3500 V at the collector cells. The
rectifier circuit converts this to 7500–8500 V dc at the charging cells.
System switch
The air cleaner is equipped with a manual system switch.
Air proving switch
The air proving switch is used to make sure that the electronic air cleaner
is functioning only when the furnace blower is in operation.
Air flow
Path of ions
Air flow
Wires at high
positive potential
-
Positively charged
particle
- Alternate plates
+ grounded
- Intermediate plates
+ charged to high
- positive potential
+
+
- Theoretical paths of
charged dust particles
Figure 1-9 Cross-section of ionizing electronic air cleaner
Advantages and disadvantages of electronic
air cleaners
•
Advantages
– system resistance remains unchanged as particles are collected
– fine particulate matter such as cigarette smoke and pollen is
removed
– collection of particles does not impair system operation
– highly efficient.
•
Disadvantages
– odours of vapours such as tobacco smoke are not removed. (To
reduce these odours an activated carbon filter may be added
downstream of the EAC to filter out odours.)
– high initial cost
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– ozone gas is produced with a noticeable odour created by an
electrical arc.
– customer-performed maintenance and cleaning are more complicated
than for media filters.
As a result of some of these disadvantages, EACs are not as popular today
as they once were. EACs produce ozone levels in the house air, but not
above the safe concentrations recommended by health guidelines.
Installation
and location
Electronic air cleaners are typically installed in the return air plenum.
They may be installed in the return air duct close to the blower
compartment, or between the plenum and the blower.
Air cleaners can be installed in the outdoor-air intake ducts of buildings
and residences or in the recirculation and bypass air ducts. Air cleaners are
always placed ahead of heating or cooling coils and other air-conditioning
equipment in the system. This protects the other equipment from dust and
increases its efficiency.
Sheet metal modifications
If the duct is a different size from the air cleaner cabinet, gradual
transitions are recommended. Gradual transitions reduce air turbulence
and increase efficiency. The expansion should be no more than
20 degrees, or about 4 inches per running ft (100 mm per 300 linear mm)
on each side of a transition fitting (Figure 1-10). If there are turns in the
duct adjacent to the unit, turning vanes should be installed to ensure even
air distribution across the face of the electronic cells. This will help to
keep the blower and evaporator coil clean and ensure the unit functions
efficiently.
20 degree expansion per side per fitting
(4 inches per running ft)
(100 mm per 300 linear mm)
Return
air duct
Transition
fitting
Electronic
air cleaner cabinet
Figure 1-10 Transition fitting for electronic air cleaner installation
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Installation of electronic air cleaners
Electronic air cleaners must be installed according to manufacturer’s
instructions. The example provided here is only intended as a general
guideline for the major steps.
Electronic air cleaners:
•
must filter the entire return air stream
•
must not exceed acceptable restrictions to air flow
•
must be installed with clearances that match manufacturer’s
specifications and allow for service access. If necessary, a duct
offset can be used to provide space for an electronic air cleaner
(see Figure 1-11).
•
should be installed upstream from the humidifier, if at all possible.
Moisture from the humidifier will cause mineral and salt buildup in the
EAC. If the EAC must be installed downstream from the humidifier,
the distance between the two units should be as great as possible. This
will enhance the performance and minimize problems with both units.
Less than
7 inches
(175 mm)
Offset
At least
7 inches
(175 mm)
1
Turning vanes help
distribute airflow evenly
Figure 1-11 Duct offset to allow space for an electronic air cleaner
Step 1: Preparation
As much dust as possible should be removed from the heating system
before the electronic air cleaner is installed.
1. Clean the blower compartment. Remove and discard the furnace filter.
2. Power vacuum the ductwork to remove accumulated dust in an
existing home, or construction dust in a new home. Clean the furnace
fan blades as required. Since the electronic air cleaner removes
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particles only from circulating air, it cannot remove dust that has
settled in the blower compartment or distribution ducts.
Step 2: Attach cabinet to furnace
1. Remove and set aside the access door, electronic cell(s), and
pre-filters.
Note: Electronic cells and ionizing wires are very delicate and must
be handled with caution. The power door must be replaced accurately
and securely.
2. Align the cabinet with the return air opening.
3. Create an opening in the furnace to match air cleaner cabinet opening.
4. Install a transition when furnace and air cleaner openings are different
sizes.
5. Be sure the unit is firmly supported and level. Place blocks under the
cabinet if necessary.
6. Attach the cabinet securely to the furnace. Either attach the cabinet
directly or use a starting collar fitted in the furnace opening. Either
drill holes and fasten with sheet metal screws or rivets, or use slip
joints.
Step 3: Install turning vanes if necessary
Turning vanes should be installed if the electronic air cleaner must be
located close to a turn in the ductwork. The vanes will ensure even air
flow over the face of the unit (Figure 1-12).
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Electronic
air cleaner
Turning
vanes
Figure 1-12 Turning vanes distribute air flow evenly
Step 4: Fasten cabinet to ductwork
Install a transition when the opening on the air cleaner and the opening on
the duct are different sizes.
Step 5: Wiring
Electronic air cleaners function only when the blower is operating and air
is in motion. When properly installed, the EAC is electrically or
mechanically interlocked with the furnace or cooling system blower
circuit, and can only operate when the furnace blower is energized. The
interlock is accomplished by installing a sail switch in the return air duct.
When the blower is energized, the air movement causes a fin on the sail
switch to move, closing a set of electrical contacts to the EAC and
energizing it. All electrical and building codes must be followed in
conjunction with manufactures instructions.
Ozone production
A properly functioning EAC will produce a small amount of ozone. This
ozone odour may be noticeable. The gas technician/fitter should explain
this odour to the building occupants. A strong ozone odour can indicate
continuous arcing and brush discharge in the electronic air cleaner and
indicates that service is needed.
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An activated carbon filter can reduce the odour of ozone. The activated
carbon filter must be installed downstream from the air cleaner. Since
some activated charcoal filters are combustible, it is important that
particles from the air filter not be able to fall into the EAC.
Note: High ozone odours can occur if there is too little air flow through
the filter.
Instructions
to the
customer
Electronic air cleaners require cleaning every one to six months. In a home
with several people and pets, where residents smoke tobacco and have
hobbies such as woodworking, frequent cleaning will be necessary. In a
smaller household with no smokers, pets, or individuals with dusty
hobbies, less frequent cleaning will be needed.
Since cleaning must be done frequently, and other service more rarely, the
customer must know how to clean the electronic air cleaner. Some
customers may also be happy to replace broken ionizing wires themselves.
All other servicing should be done by a trained technician/fitter.
The technician/fitter must:
•
show the customer the location of the power switch (and test switch, if
the EAC includes one)
•
ensure that the customer knows how to remove and clean filters and
cells, according to the manufacturer’s instructions for the unit.
A wash reminder schedule is included with most electronic air cleaners
and should be posted in a convenient place for customer reference. Some
air cleaners have an indicator light that comes on to indicate that the cells
are dirty and air cleaning efficiency is diminished. Ideally the cells should
be washed frequently enough that this light never comes on.
Caution!
Power to the electronic air cleaner must be turned off before cells are
cleaned. Turning the power off discharges the electronic cells. Sometimes
it takes a few minutes for the charge on the cells to dissipate. Pressing the
test button after the unit is turned off will dissipate the charge to ground.
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Cleaning the cells
This whole procedure can be done by the customer. The technician/fitter
should be sure that the customer understands the steps involved.
1. Slide cells out of cabinet. Be careful: cells may have sharp edges.
2. Wash the cells either by soaking them at a coin-operated do-it-yourself
car wash or in an automatic dishwasher (see details below). Care must
be taken not to damage the ionizing wires, no matter which method is
used. Detergent is usually used for cleaning. Follow the
manufacturer’s specific instructions for cleaning materials.
3. After washing, inspect the cells for dirt or residue. Repeat the washing
process if necessary.
4. Before reassembling the EAC, clean the pre-filter. The pre-filter
screen may be washed with detergent or vacuumed, whichever is more
convenient. Do not wash the pre-filter in the dishwasher or a car wash.
Since the pre-filter contains lint that can become caught in cells, do not
soak it at the same time as the cells.
5. Before reassembling the EAC, inspect the ionizing wires and replace
any that are broken. (See details below.)
6. Reassemble the EAC.
7. If the EAC has a drying unit, engage it.
8. Turn power on at main disconnect.
Note: Some electronic air cleaners will not operate until they are
completely dry. Others will operate, but wet cells and pre-filters may
cause arcing. If the unit is equipped with a Check LED, the light may
come on when cells and pre-filters are wet. Leave the electronic air
cleaner turned off for two or three hours until the cells and pre-filter are
completely dry to avoid these problems.
Dishwasher method
Before washing the cells in the dishwasher, check the dishwasher manual.
Some manufacturers of dishwashers do not recommend using them to
wash electronic cells.
•
Place cells on the bottom rack with the air flow arrows pointing up.
•
Be sure they are placed in such a way as to allow good water
circulation.
•
Use regular dishwashing detergent.
•
Run them through a complete wash cycle.
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•
Do not allow the dishwasher to run through the dry cycle. The dry
cycle will bake on any contaminants that remain on the cells and
impair air cleaner efficiency.
•
Allow the cells to cool completely in the dishwasher, or wear
protective gloves, to avoid burns when removing the cells.
•
Hot water may accumulate in the tubs supporting the collector plates.
Tip the cells to drain these tubes.
•
Wipe the ionizer wires and contact board on the end of the cell gently,
using a small damp cloth.
•
If dirt or residue remains in the dishwasher, run the dishwasher again,
empty, to clean it.
Soaking method
•
Cells should not be soaked in a bathtub, since their sharp edges can
scratch the tub finish.
•
Fill a container large enough to immerse one or both cells with very
hot water.
•
Dissolve 3/4 cup of regular automatic dishwashing detergent per cell.
If the detergent does not dissolve readily, or forms a scum on the
water, use softened water or try another brand.
•
After the detergent is completely dissolved, lower the cell(s) into the
container and soak each cell for 15–20 minutes.
•
Lift the cells up and down a few times, then remove them.
•
Rinse the cells with a fine spray and soak again in hot clean water for
5–15 minutes.
•
Stand the cells upright to drain.
Checking and replacing ionization wires
The fine tungsten wires in the charging section of the electronic cell are
brittle and can easily break or become damaged. The customer should be
shown how to inspect the cell from the upstream side, to be sure no wires
are broken or out of position. Broken wires can cause visible arcing or
sparking. They must be replaced (Figure 1-13). Replacement wires are
supplied cut to length with eyelets on both ends for installation.
Some customers may prefer to have the technician/fitter replace ionizing
wires rather than doing it themselves.
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Replace broken wires
1. Remove the broken wire, being careful not to damage the spring
connector. Be sure all parts of the wire are removed.
2. Hook the eyelet of the new ionization wire over the spring connector
on one end of the cell.
3. Hold the opposite eyelet with needlenose pliers and stretch the wire
the length of the cell.
4. Depress the opposite spring connector and hook the eyelet over it.
Note: Use caution when working on electronic air cleaners; always
ensure the power supply is off.
Spring
connectors
Press
down
Eyelet
Ionizer
wire
Eyelet
Ionizer
wire
Needlenose
pliers
Courtesy of Honeywell Limited
Figure 1-13 Replacing ionization wires
Maintenance
and service
Cleaning of cells and replacement of ionizing wires can be done by the
customer, but other maintenance and service must be done by a trained
technician/fitter.
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Basic maintenance
Before the beginning of the heating and cooling seasons, the solid state
components and ionizing wires of the electronic air cleaner should be
inspected. The exact procedure for checking the unit will vary depending
on the manufacturer, so the manufacturer’s instructions must be consulted.
A typical procedure follows.
Check components
Checking the components at beginning of the heating and cooling seasons
is basic preventive maintenance for the electronic air cleaner. Checking
the components requires a voltmeter or multimeter.
1. Be sure the power from the main disconnect to the EAC is in the “on”
position.
2. To check the operation of the sail switch (or electrical blower
interlock), energize the furnace blower. If the EAC does not operate,
the sail switch may be faulty.
3. Check to see that the voltage indicator light is on. If the light is not on,
but the unit operates, the light is faulty.
4. Push the Test Button on the front of the EAC access door. Pushing the
button shorts the hot side of the collector section to ground and should
produce one or more loud snapping sounds in the section. This
indicates that the EAC is working properly. The test button will
discharge the cells.
5. Remove the access door.
6. With the voltmeter or multi-meter set to ac, check the voltage to the
power pack. (It should read 120 V ac). If the power pack is not
working, the solid state power supply within the power supply box can
be replaced.
7. With the voltmeter or multi-meter set to dc, check the voltage to the
collecting section plates (3000–3500 V dc).
8. With the voltmeter or multi-meter set to dc, check the voltage to
charging ionization wires (it should read 7500–8500 V dc).
Caution!
Electronic air cleaners operate at high voltage to charge particles. Follow
manufacturer’s instructions carefully when servicing them to avoid a
hazard.
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Troubleshooting
Visible arcing or sparks and higher-than-expected ozone odour should be
investigated by the technician/fitter.
If there is visible arcing or sparking, check the cell for short circuits using
an ohmmeter. Make sure power to the EAC is off and cells are discharged.
Check the resistance between the frame of the cell and the ionizer, and the
frame of the cell and the collector contacts. In each case the resistance
should be infinite.
If a cell is sparking continuously in one place, the plates need to be
repositioned. Consult the manufacturer’s instructions for correct
positioning of plates.
If the customer complains of an ozone odour:
•
make sure the air cleaner shuts off when the furnace blower is not
active
•
make sure there is adequate air flow through the unit.
Germicidal UV Lamp
Ultraviolet (UV) lamps (Figure 1-14) effectively destroy micro-organisms
that pass by the bulb, including germs, viruses, bacteria, and fungi (such as
mold). UV light radiation is recommended by the Centers of Disease
Control to prevent illness and disease.
UV lamp strengths:

Ability to destroy micro-organisms, such as germs, viruses,
bacteria, and fungi (including mold).

Helps prevent illness and disease.
UV lamp weaknesses:

No effect on particulates, including most allergens.

No effect on chemical fumes, gases, or cigarette smoke.

No effect on odours, unless designed to produce ozone, which may
not be desired under all circumstances. Some UV lamps are
designed not to produce ozone.
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Figure 1-14: UV lamp
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Assignment 1
When you have completed the following questions, ask your instructor for the
Answer Key.
1.
Why are air cleaners installed ahead of heating or cooling coils and air conditioners?
2.
What are two ways in which a mechanical filter could restrict air flow?
3.
Name three types of air cleaners that can be used with a forced-air furnace.
4.
Which type of air cleaner is usually the least expensive?
5.
Which type of air cleaner is usually the most expensive?
6.
Name two advantages of an electronic air cleaner.
7.
Do electronic air cleaners remove smoke odours from the conditioned air?
8.
How can smoke odours be reduced?
9.
What must the gas technician/fitter do before installing any air cleaner?
10. If there are arrows on a filter frame, which way must they face?
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11. Why should re-usable filters be re-oiled before they are replaced in the furnace?
12. What must be done before opening the blower door on a forced-air furnace?
13. How frequently should furnace filters be inspected in the heating season?
14. How frequently should filters be replaced?
15. Why can disposable filters not be re-used?
16. Name three problems that can result from operating a forced-air furnace without a filter?
17. What is the most common cause of inadequate heating or cooling performance?
18. What damage can a dirty filter do in a system that includes add-on air conditioning?
19. How can clean filters save the customer money?
20. What are the four components of an electronic air cleaner?
21. What can happen if ionizer wires are broken?
22. What can happen if the electronic air filter is turned on when cells are wet?
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23. If cells are washed in a dishwasher, why should the drying cycle not be run?
24. How frequently should an electronic air cleaner in a residential installation be cleaned?
25. Name three factors that may be present in a home that would suggest cleaning must be more
frequent.
26. Describe the basic function of an electronic air cleaner.
27. If the power pack is not working, what should be done?
28. List three methods for cleaning the cells of an electronic air cleaner.
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Chapter 2
Humidifiers
Purpose
Since the comfort of building occupants depends on both air temperature
and relative humidity, the gas technician/fitter should understand
humidification.
There are many types of humidifiers. They must be installed carefully so
they do not damage the heating and cooling equipment.
Learning
outcomes
1. Describe the function of different types of humidifiers and their
control.
2. Describe installation procedures for humidifiers.
3. Describe operation requirements and service procedures for various
types of humidifiers.
Sections
Function and control ........................................................... 39
Control of the humidifier.................................................................... 40
Wetted element humidifiers .............................................................. 41
Atomizing humidifiers........................................................................ 43
Steam humidifiers ............................................................................. 44
Installation .......................................................................... 45
Sizing ................................................................................................ 45
Location ............................................................................................ 45
Other installation requirements ......................................................... 48
Operation and service ........................................................ 51
Common operation requirements ..................................................... 51
Service guidelines for specific types................................................. 52
Instructions to the customer ............................................................. 53
Troubleshooting ................................................................................ 54
Assignment 2 ...................................................................... 57
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SECTION 1
Function and control
The basic concept of a central humidifier is simple. A small water line that
is connected to the household plumbing carries water to a humidifying
unit located somewhere in the ductwork of the forced-air furnace. Inside
the humidifying unit, the water evaporates into the passing air and thereby
increases the air's humidity level. Where central humidifiers differ,
however, is in how the evaporation is accomplished, what happens to any
excess water, and what controls are available to regulate the
humidification:
Relative humidity is a measurement of the percentage amount of water
vapour contained in the air, compared to the amount that can be contained
(100%) when the air is saturated at the same temperature.
Warm air can hold more water than cold air, so relative humidity changes
with the temperature. In warm desert climates (such as Arizona), relative
humidity is always low. In cold climates, such as are found in much of
Canada, the relative humidity inside is low in the winter when the
temperature is low outside.
The comfort level of a room is a function of both temperature and relative
humidity. When a room is too dry
•
the room may feel colder than its actual temperature
•
there may be high levels of static electricity
•
building occupants may be more susceptible to colds and other
airborne viruses, since excessive dryness reduces the effectiveness of
the nasal membranes.
A humidifier adds moisture to the air, increasing the relative humidity and
the comfort level. In most cases a relative humidity of 40% is the most
comfortable for building occupants.
Humidifiers may be either stand-alone devices or an integrated part of the
building’s heating and cooling system. They can be installed either in the
furnace plenum or duct, or attached to the plenum or duct so as to
introduce water vapour into the air stream.
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Control
of the
humidifier
Most humidifiers are controlled by humidistats.
Humidistats
The basic control for humidifiers is a humidistat, which turns the
humidifier on or off according to what it senses as the level of air
humidity—just as a common household thermostat controls temperature.
However, if the humidifier relies on the furnace blower to force air
through it, the unit will only work when the furnace is running. Since a
forced-air furnace cycles on and off according to temperature, there can be
times when the humidifier should be on but the furnace is off. Humidifiers
that contain their own fans can independently (and thus better) regulate
the humidity or advise the customer to operate the furnace fan constantly
in dry periods by adjusting the thermostat fan auto/on switch to the on
position. Humidistats are also available (on modern systems) with fan
contacts to actuate the fan of a furnace when humidification is required.
The humidistat includes two settings: one for relative humidity, and one
for the outside air temperature (usually in degrees Fahrenheit). Building
occupants set the humidistat by selecting the desired relative humidity and
adjusting the temperature gauge to the approximate outside temperature.
Humidistats can be mechanically or electronically controlled.
•
Mechanically controlled
The mechanically controlled humidistat (Figure 2-1) contains a strip of
moisture-sensitive plastic film that elongates as humidity rises. When
humidity reaches the preset level, the strip triggers a switch that turns
the humidifier off. When humidity falls the strip shrinks and starts the
humidifier.
•
Electronically controlled
Electronically controlled humidistats (Figure 2-2) contain electrical
sensors that vary in resistance as the relative humidity changes. These
humidistats can detect very small changes in relative humidity. They
are used in settings where precise control is needed, such as
laboratories.
The position of the humidistat is important. If the humidistat is not in the
right place, the relative humidity will not be measured correctly and the
building may be less comfortable. The humidistat is normally mounted in
the area where air is being controlled. A location near the thermostat is
convenient for building occupants.
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Figure 2-1 Manual humidistat
Figure 2-2 Digital humidistat control
Wettedelement
humidifiers
All wetted-element humidifiers operate on the same principle. An open
textured medium, the evaporating surface, is wetted and the water it
contains evaporates into the air. The medium may be a fixed pad that is
wetted by a spray or fed by gravity, or it may be dipped into a water
reservoir on an electrically-powered paddle, drum or rotating belt. Wettedelement humidifiers are controlled by humidistats.
Drum humidifiers
Duct-mounted drum humidifiers contain a 24 V ac motor and a wheel or
drum covered with foam. When the humidistat calls for humidity, the
drum rotates through a water reservoir. This saturates the foam. Warm air
from the supply plenum passes through the humidifier, and picks up
moisture from the media. The moistened air enters the return air plenum
and is distributed throughout the home by the furnace blower. The
reservoir contains a float and water valve to automatically control water
level and prevent overflows. A drum humidifier is shown in Figure 2-3.
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Moist air
Water supply
to float valve
Dry air
Water level
Figure 2-3 Drum humidifier for in-duct installation
Evaporator-pad humidifier
Similar to the drum humidifier, the evaporator-pad humidifier is ductmounted and is connected between the warm-air supply plenum and the
return air supply (also referred to as by-pass type) . Air flows from the
warm-air supply plenum through a moisture-laden evaporator pad, picking
up moisture and returning moist air to the return air supply of the furnace.
In the model illustrated in Figure 2-4, the pad is “wetted” by water
controlled through a solenoid valve and distributed over the pad by a
distributor trough at the top of the humidifier. Water not evaporated
drains from the bottom of the humidifier.
Trough cover assembly
Water supply
tubing
Water distribution
trough
Evaporator-pad
Solenoid valve
assembly
Drain pan
Drain tubing
Figure 2-4 Evaporator-pad humidifier
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Spray humidifiers
Spray humidifiers use a sprayed stream of water, rather than a reservoir, to
wet the medium. When the humidistat calls for humidity, a solenoid is
energized and opens a water valve. The open valve allows water to flow
from a cold water pipe through the 24 V ac solenoid valve and water line
to a nozzle, where it is sprayed on the humidifier medium. From this point
the operation is the same as a drum humidifier.
Atomizing
humidifiers
Atomizing humidifiers introduce small droplets of water directly into
either the duct air stream or the conditioned space. There are several ways
in which the water can be atomized: centrifugal force and spray nozzle are
the most common type of atomizing. Ultrasonic vibrations can also be
used.
Centrifugal atomizing humidifiers
Centrifugal atomizing humidifiers contain a spinning disc or cone that
breaks the water into a mist, or a rotating disc which slings water into the
air from a reservoir. This type is shown in Figure 2-5.
Water
Figure 2-5 Centrifugal atomizing humidifier
Spray-nozzle atomizing humidifiers
Spray-nozzle atomizing humidifiers have a fine spray nozzle that creates
fine droplets and sends them into the duct airstream. The nozzle may use
water pressure alone, or a mixture of air and water.
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Atomizing humidifiers are often portable or console-type units, but they
can also be installed so that the water will be directed into a ducted central
system. If they are connected to the ducts, they should only be used when
the furnace is operating. If the fan is not running, the moisture they
introduce can accumulate and cause corrosion, mildew, and other moisture
problems.
Note: Atomizing humidifiers should not be used with hard water. The
minerals contained in hard water leave the evaporating water vapour
as dust that will be distributed through the building.
Steam
humidifiers
Since steam is water vapour at high temperature, introducing steam into
the airstream is an efficient way to add water vapour to the air.
There are several kinds of steam humidifiers, many used only in
industrial or commercial installations. Generally steam humidifiers
(Figure 2-6) are of two types: those that are self-contained (containing
a heating element) and those that inject steam from a boiler into the
space or into the duct system. Steam humidifiers connected to duct
systems must be placed where the air can absorb the vapour, to ensure
that condensation does not occur in the ducts. Steam humidifiers use
less water than other types of units.
Figure 2-6 Steam humidifier
Self-contained
Self-contained steam humidifiers convert tap water to steam by electrical
energy. They can be free-standing and unconnected to the duct system, or
can inject steam into the duct system.
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SECTION 2
Installation
Because there are so many types of humidifiers, detailed descriptions
of humidifier installation are not provided. Follow the manufacturer’s
instructions for the specific model and type of humidifier to be installed.
Size and correct location must be considered for any installation.
Sizing
Before a humidifier is installed the correct size must be determined.
Several factors help to determine the size required:
•
size of the area to be humidified (in cu ft)
•
the construction or “tightness” of the building
•
Code requirements for air changes per hour
•
lowest outdoor temperature in the area
•
level of relative humidity desired.
Manufacturers’ specifications should be consulted to ensure that the
unit chosen is appropriate for the space to be humidified.
Location
The manufacturer’s specifications will describe where specific humidifiers
should be positioned. Humidifiers can be installed in four different
locations:
•
•
In a bypass duct
Wetted-element, or steam humidifiers can be used in a bypass duct.
The bypass duct is a loop that forms a bypass from supply air plenum
and return air plenum of the main heating system (Figure 2-7).
Humidifiers installed in this location are passive: that is, they do not
contain a fan or other method of moving air. Air circulates through the
units because of differences in pressure between the warm and cool
side of the furnace.
The bypass humidifier may be mounted on either the supply plenum or
duct or the cold air return plenum or duct. The bypass duct must
connect the return and supply-side plenum or ducts, wherever the
humidifier is actually mounted.
In the supply or return-air plenum
Wetted-element or atomizing humidifiers can be installed in a plenum.
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•
Under the supply duct
Steam or wetted-element humidifiers can be mounted to an opening on
the underside of a supply duct. It is best to choose the supply duct that
serves the largest area in the building. This makes distribution of
humid air more efficient.
•
In the supply duct
Wetted-element or atomizing humidifiers can be used. Atomizing
humidifiers must be wired to operate only when the furnace fan is
operating.
Humidifiers must not exhaust onto air conditioning coils, air filters,
electronic air cleaners, blowers, or turns in a duct. They must not be
located in the furnace casing or above a heat exchanger. They should be
positioned so if water spills, it will not spill onto electrical components.
The humidifier location must allow access for service and maintenance.
If a humidifier is used with an electronic air cleaner, it must be located
downstream from the electronic air cleaner to avoid damage to the EAC.
Figure 2-7 Bypass wetted-element humidifier
•
Select a location for the bypass on the opposite plenum. The sidewalls
of humidifiers are interchangeable to allow bypass duct mounting on
either side of the humidifier.
•
Select a location that cannot damage the air conditioner A-coil during
installation.
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•
Select a location where the duct provided is adequate to connect the
humidifier to the bypass.
–
Do not locate the humidifier or bypass on a furnace body.
–
Allow adequate clearance in front of and above the humidifier so you
can easily remove the cover to perform routine maintenance.
–
Mount the humidifier at least 3 inches (78 mm) above the furnace
body to allow adequate space for the solenoid valve and drain line.
–
Mount the humidifier in a conditioned space to prevent freezing.
Selecting location for humidistat
•
Select a location for the humidistat on the return plenum or on the wall
in the living space.
–
Mounting on the return plenum is the easiest installation for the
control wiring circuit.
For return duct mounting, the humidistat should be mounted upstream
from the humidifier or bypass so that it can properly sense the relative
humidity of the living space. Locate the control at least 8 inches (203 mm)
upstream from the humidifier in the return air duct.
Fan humidifiers
Fan humidifiers use the fan inside the humidifier to pull duct air through
the humidifier (Figure 2-8). Access to only the supply or the return is
required.
Figure 2-8 Fan humidifier
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Other
installation
requirements
Minor water supply connections, electrical connections, sheet metal
modifications, and drains may be considered as part of the installation
process.
Water supply
Hard water (water that contains a high mineral content) can cause various
problems in humidifiers. Nozzles, tubes, and evaporative elements may
collect precipitated solids and become clogged. Mineral solids that enter
the air stream can leave a layer of white dust on furniture and floors
throughout the home.
There are various ways to avoid this problem.
•
The water supply to the humidifier can be softened. This process
usually adds sodium to the water. Since the sodium itself precipitates
out in humidifier reservoirs over an extended period, provision must
be made for the reservoir to be flushed out on an ongoing or periodic
basis.
•
Chemicals that prevent scaling (the precipitation of minerals) can be
added to the humidifier pan. Consult the manufacturer’s literature
before adding any chemicals to the humidifier.
Various methods are used for tapping into a water supply system to supply
water to a humidifier. For copper water tubing systems, a saddle valve
(Figure 2-9) often comes with various manufacturers of humidifiers
installation packages. Though they are considered “easy to install”, this
type of connection should not be recommended. A full-size tee fitting and
approved valve should be installed on the water line. The saddle valve
shown below is prone to failure and can cause enormous property damage.
In Ontario, the OBC states that they “shall not be installed”.
Figure 2-9 saddle valve
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Furnace-humidifier electrical connection
Atomizing humidifiers installed in a duct or plenum must operate only
when the furnace blower is operating. Atomizing humidifiers introduce
droplets of water into the ducts. If the air is not moving the drops will fall
on the duct surface, causing moisture accumulation. This moisture can
encourage the growth of mildew, compromising indoor air quality. It can
also cause corrosion.
To ensure the atomizing humidifier works only when the blower is
operating, an electrical interlock is required. The interlock is accomplished
by installing a sail switch in the return air duct. When the blower is
energized, the air movement causes a fin on the sail switch to move,
closing a set of electrical contacts to the atomizing humidifier and
energizing it.
Evaporative humidifiers (wetted-element) may operate independently of
the furnace, so no interlock is required.
Power bypass humidifiers include a transformer, which must be used. The
humidifier must not be connected to the transformer on the furnace, if
there is one, since this could overload the furnace transformer. The
humidifier transformer should not be wired in to the thermostat circuit. If
it is, the thermostat would receive a different current draw depending on
whether or not the humidistat was calling for moisture.
If a humidifier transformer is installed on a furnace with a direct drive
motor, the wiring and control system must prevent the humidifier
transformer from overvoltage created by the motor’s idle windings.
Follow all manufacturers wiring diagrams.
Sheet metal modifications
When a humidifier is installed in or under a duct, in a plenum, or in a
bypass duct, modifications must be made to the sheet metal. Follow the
manufacturer’s instructions for the specific humidifier concerning the size
of the openings required and proper sealing of openings.
Drain
Ideally, all the water flowing into the humidifying unit would evaporate,
but in reality most systems have to contend with leftover water. The usual
solution is to provide a drain tube, but this means that the humidifier must
have access to a drain pipe. Some designs retain and recycle the incoming
water until it all evaporates, but the trade-off for this approach is that the
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reduction in fresh water can be used to carry away any mineral deposits
and prevent potential mold buildup. Thus, while drain less designs
conserve water and do not need drains, they require more frequent
cleaning and maintenance.
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SECTION 3
Operation and service
The operation of the humidifier should be checked when the forced-air
furnace is inspected prior to the start of the heating season.
It is especially important to be sure that the humidifier is clean before
the heating season starts. When water remains in a humidifier for an
extended period (for example, over the summer) it may become a breeding
environment for fungi, bacteria, algae, and viruses. If the reservoir is not
cleaned before the furnace blower is turned on, these contaminants can be
distributed throughout the house. This will lower indoor air quality and
add to indoor air pollution.
Common
operation
requirements
Factors such as water level, mechanical operation, and humidistat function
should be checked. The guidelines for operation given here are general.
Check the manufacturer’s specifications for specific operation
requirements.
•
Water level correct
If the water level in the reservoir is too high, water can overflow into
ducts, ultimately causing corrosion and/or development of mildew.
The water level must be set to the manufacturer’s specifications.
•
Float valve assembly operating
The float valve assembly must be working and adjusted properly to
maintain the correct water level.
•
Humidistat working
To check the operation of the humidistat, it is necessary to have an
independent measure of the relative humidity in the building. A sling
psychrometer can provide this confirmation. The operation of the sling
psychrometer is explained in the troubleshooting section of this
section.
•
Clean overflow/drain line and reservoir pan.
The hose may need to be removed for cleaning. Check to be sure the
drain is not blocked.
The reservoir pan should be cleaned at the beginning and end of the
heating season, and more frequently if the pan seems slimy. The
technician/fitter must be sure that the customer understands how to
clean his or her humidifier according to manufacturer’s instructions.
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Service
guidelines for
specific types
Always check the manufacturer’s manual for guidelines specific to the
humidifier being serviced.
•
•
•
Wetted-element humidifiers
If the wetted element is mounted on a drum or paddle, the drum or
paddle must be turning for the humidifier to operate correctly.
The media in wetted-element humidifiers should be cleaned or
replaced at the beginning of every season. The humidifier pad must be
kept clean to permit proper absorption and evaporation of water. If the
media is a cleanable type, it can be washed with detergent. Mineral
(scale) deposits can be scraped loose lightly with a putty knife if
necessary.
The humidifier pad should be replaced if it will no longer conform to
the drum properly after cleaning.
Atomizing humidifiers
The nozzle must be spraying freely, or the drum turning.
Steam humidifiers
Steam generation must be occurring, and the nozzle must not be
blocked.
Wetted-element spray humidifiers
The nozzles on spray humidifiers must be inspected to ensure they have
not become blocked by dirt or mineral deposits.
1. Turn humidistat off.
2. Clean or replace media. Install the media diagonally into the cabinet
for the purposes of this tune-up, so the nozzle can be seen from the
front opening.
3. Turn on the water supply.
4. Open the damper to the humidifier.
5. Turn on the furnace blower.
6. Set the humidistat so it calls for humidity. The solenoid water valve
should open.
7. Check the nozzle spray. If the spray is uneven or irregular, replace the
nozzle.
8. Replace the filter medium in the normal position.
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Drum-type humidifiers
Drum-type humidifiers include a clutch assembly that must be inspected
and cleaned.
1. Clean mineral deposits from the clutch assembly. Detergent can be
used. Scale (mineral deposits) can be scraped with a putty knife.
2. Clean the drain pan.
3. Clean the orifice between the water source and the float valve.
4. Turn on the furnace blower and set the humidistat so it calls for
humidity. The motor should rotate.
5. Adjust water level screw.
Instructions
to the
customer
The customer must perform seasonal maintenance on the humidifier and
adjust it as necessary.
•
Fall
If the humidifier contains a media pad, it should be cleaned before the
heating season begins. If there is a reservoir, it should be cleaned with
vinegar and water.
If the humidifier is a bypass type, the bypass duct damper must be
opened.
The float level should be checked and adjusted as necessary and the
humidistat set to the desired relative humidity, approximately 40%.
•
Winter
The customer should check the windows of the building for
condensation, a sign of excess humidity, and adjust the humidifier as
necessary. The customer should check the level of water in the
humidifier periodically.
•
Summer
The humidifier reservoir should be drained. If there is a bypass duct
damper, it should be closed.
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Troubleshooting
When a customer reports a lack of humidity:
•
check the relative humidity in the conditioned space using a sling
psychrometer
•
troubleshoot the humidifier, especially the humidistat, water supply,
and electrical system.
Note that in extreme weather conditions few humidifiers will be able to
provide the desired humidity level.
Testing relative humidity
The sling psychrometer (Figure 2-10) measures air temperature using two
thermometers, a wet bulb and a dry bulb, mounted on a base. The
apparatus has a handle that allows it to rotate rapidly in the air. As the
psychrometer moves, air flows over the thermometers. Moisture is
evaporated from the wet bulb. When the temperature stabilizes on the two
thermometers, readings are taken. Readings are compared to tables
provided with the device to find the relative humidity based on the two
temperatures.
Dry bulb
thermometer
Sock
Handle
Wet bulb
thermometer
Wet bulb
temperature
scale
Dry bulb
temperature
scale
Courtesy of American Publishers, Inc.
Figure 2-10 Sling psychrometer
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Modern electronic devices use temperature of condensation, changes in
electrical resistance, and changes in electrical capacitance to measure
humidity changes. This allows a technician/fitter to measure relative
humidity without a sling action.
A digital psychrometer (Figure 2-11) is an example of modern electronic
device that is now available to gas technicians/fitters.
T1
DP T
DI
GI
T/
T1 DP
°C
/°
F
M
RE IN/M
SE AX
T
TA
L
PS
T2
W DP
B
YC
HR
OM
ET
ER
°F
°C
MA
MIN
HLD
X
HO
LD
DP
T2 /WB
Figure 2-11 Digital psychrometer
Troubleshooting the humidifier
•
Humidistat
When the relative humidity has been tested, set the humidistat for a
higher level and see if it activates. If the humidistat is functioning and
the relative humidity in the conditioned space is not what it is calling
for, the humidistat may be incorrectly calibrated. It may be possible to
recalibrate the humidistat, or it may need to be replaced.
•
Water supply
Make sure the supply line has not become plugged and that the float
valve is adjusted properly, so an optimum level of water is maintained
in the reservoir. If the float is damaged, it can be replaced.
If the humidifier overflows, and the level/float setting is correct, the
seat on the entire float assembly may need to be replaced
If the humidifier is based on a wetted element, make sure the medium
is not clogged, dirty, or saturated with mineral deposits. Clean or
replace it if necessary. Damaged elements must also be replaced to
prevent water in liquid form from entering the ducts.
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In an atomizing humidifier, make sure the drum is turning properly,
and the spray nozzle is not blocked.
•
Electrical connections
If the humidifier is not functioning at all, the problem may be
electrical. Check circuit breakers, the humidistat, and low-voltage
controls if there are any. If the humidifier has a motor, as some
atomizing and wetted element types do, check it to see if it is burned
out.
Mineral deposits may cause a humidifier to switch itself off. If a
component is locked or bound because of a mineral buildup, in some
humidifiers a thermal fault overload protector may open, shutting the
unit off. In this case the component should be cleaned or replaced.
Other potential problems
There are other potential problems that should be repaired, although they
will not prevent the humidifier from functioning.
•
Dust
If excessive dust is caused by a humidifier, the dust will be white,
since it is caused by mineral buildup. The media should be cleaned or
replaced.
•
Moisture in the ducts
Moisture may be found in the ducts if an atomizing humidifier is
installed, and the humidifier is operating when the furnace blower is
not. The atomizing humidifier must operate only when the furnace
blower is on and the furnace is operating. Check to be sure it is not
operating when the “fan only” mode is selected, since heat is required
to evaporate the water droplets created by the atomizing humidifier.
•
Water overflow
The float valve may need to be cleaned, replaced, or adjusted if water
has overflowed. The drainage/overflow line should be checked in case
it has become blocked.
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Assignment 2
When you have completed the following questions, ask your instructor for the
Answer Key.
1.
Why should atomizing humidifiers operate only when the furnace blower is operating?
2.
What three problems may be caused by relative humidity that is too low?
3.
What is the approximately ideal level of relative humidity for optimum comfort in a
residence?
4.
What is the major difference between atomizing humidifiers and other types of humidifiers?
5.
If excessive dust in a building is coming from the humidifier, how can it be identified?
6.
Name two common problems that can result from water overflow from a humidifier.
7.
What device controls the operation of a humidifier?
8.
If a humidifier is used in a system with an electronic air cleaner, where should the
humidifier be mounted?
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9.
How frequently should the water-holding reservoirs in humidifiers be cleaned?
10. Why is it important to clean the holding reservoir thoroughly?
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Chapter 3
Cooling coils
Purpose
The installation and major servicing of cooling coils in conjunction
with gas-fired forced-air furnaces is done by air conditioning
technicians, not gas technicians/fitters. However, the gas
technician/fitter will be required to inspect and clean the cooling
coil as part of regular furnace servicing.
Learning
outcomes
1. Describe how to check cooling coils for proper function and to
clean cooling coils.
Sections
Checking and cleaning cooling coils ................................... 61
Measuring temperature change ........................................................ 62
Measuring pressure drop across coil ................................................ 63
Importance of coil cleanliness ........................................................... 65
Cleaning the cooling coil ................................................................... 65
Assignment 3 ...................................................................... 67
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SECTION 1
Checking and cleaning
cooling coils
Adding a cooling coil to a forced air furnace adapts it for use as a central
air conditioner. Although the installation and servicing of the air
conditioning unit is done by air conditioning technicians, the cooling coil
must be cleaned as part of regular furnace maintenance. A dirty coil, like a
dirty furnace filter, restricts air flow. Figure 3-1 shows a typical cooling
coil.
Courtesy of Bryant Heating and Cooling Systems
Figure 3-1 A typical cooling coil
This type of air conditioning system consists of a cooling coil and a
condenser. The coil (sometimes called an “A” coil because of its shape)
may be mounted in the supply plenum, or in a cabinet between the supply
plenum and the duct. The condenser is usually located outside the
building.
•
Two lines circulate refrigerant between the “A” coil and the condenser
coil.
•
The compressor moves the refrigerant around the loop.
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•
As the furnace forces air through the “A” coil, the coil absorbs heat
from the air, causing the liquid refrigerant to change to the vapour
state.
•
The refrigerant vapour moves to the condenser coil, where heat is
removed to the outdoors, causing the vaporous refrigerant to return to
a liquid state.
•
The liquid refrigerant returns to the cooling coil.
Cooling coil units are available for up-flow, down-flow, and horizontal
furnaces. The coil is housed in a cabinet. Figure 3-2 shows possible
locations of the cooling coil cabinet. The liquid used as a coolant varies
depending on the specific unit.
Return
Supply
Cooling
coil
Downflow
furnace
Upflow
furnace
Supply
Figure 3-2 Possible locations of the cooling coil cabinet
Measuring
temperature
change
The same method is used to measure either the temperature drop across
a cooling coil or temperature rise across the heat exchanger.
1. Punch or drill a hole in the supply and return air plenums. Where
possible the holes should be about three feet from the furnace.
2. Place a thermometer into the air flow through each of the holes.
3. Operate the equipment for about five minutes, with the fan running to
establish the normal air temperature rise or drop. This term means the
difference between supply air temperature and return air temperature.
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4. To calculate temperature drop across the coil, subtract the temperature
at the supply side from the temperature on the return side.
To calculate temperature rise across the heat exchanger, subtract the
return side temperature from the supply side temperature.
Measuring
pressure
drop
across coil
Measuring the pressure drop across the cooling coil is one way of
checking the operation of the system. If the measured pressure drop is too
great, the cooling coil unit may need to be cleaned or the blower may need
to be adjusted. The manufacturer’s manual describes the acceptable
pressure drop for the unit.
Pressure drop across the coil can be measured with a magnehelic gauge or
a manometer.
The static pressure check must be done on a coil that is dry and free of
condensate. To measure the pressure drop using a manometer:
1. Find the quarter-inch holes in the inlet and outlet of the cooling coil
unit provided for measuring pressure drop and temperature
differences. Drill holes in the cooling coil cabinet, if none are
provided. Take care not to drill into the cooling coil. The holes should
be on the centreline of the coil.
2. Turn on the blower only.
3. Insert an awl or screwdriver into the measurement holes and open up
the insulation behind them.
4. Level the manometer.
5. Check the rubber hoses from the manometer for leaks.
6. Insert the hose into the holes in the cooling coil cabinet so that about
1/4 inch extends into the cabinet. Seal around the hole with putty. The
hose from the lower end of the incline manometer should go into the
downstream hole. The pressure differential between the pressure of the
air entering and leaving the coil is the pressure drop through the coil
(Figure 3-3).
7. Refer to the manufacturer’s manual for the correct pressure drop and
air volume.
8. Clean the unit and retest before adjusting blower speed. Then, if
necessary, adjust the blower speed to obtain the correct pressure drop
and air volume.
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MIN
MAX
HOLD
PSI
In - Wg
Mbar
ZERO
MIN/MAX
HOLD
SCALE
Downstream
air flow
Pressure
taps
Manometer
Upstream
air flow
Figure 3-3 Check pressure drop across coils using an incline manometer or
digital manometer.
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Importance
of coil
cleanliness
Internal and external surfaces of the cooling coil must be clean. Several
problems can result from a dirty coil.
•
During the cooling season, the coil will not deliver its full cooling
capacity.
•
Air flow to the building will be reduced.
•
During the heating season, both temperature rise across the furnace
and stack temperature will be increased.
The coil should be checked visually for cleanliness when the furnace is
cleaned. In cases where the coil is located in a cabinet, an access door
is provided. If the coil is mounted in the plenum, it may be necessary to
cut an inspection port. Care must be taken to ensure that the coil is not
damaged if a port must be cut.
Cleaning
the cooling
coil
The cooling coil must be cleaned when it is dirty. For the gas
technician/fitter, this involves cleaning the exterior of the coil itself, and
the fins through which air is forced over the coil. Cleaning of interior
surfaces of the coil (inside the lines) is usually done by an air conditioning
specialist.
Exact cleaning procedures vary depending on the unit that has been
installed. Consult the manufacturer’s instructions for specifics. The
following is a typical cleaning procedure.
1. Check the fins for accumulated dirt or dust. If the fins are clogged
or dirty, clean them with a vacuum cleaner, wire brush, or a fin comb.
Use the vacuum, brush, or comb carefully so as not to damage the coil.
2. Inspect the tubing and connections for signs of oil leaks. Spots of oil
indicate a leak that must be repaired by the air conditioning technician.
3. Outer surfaces of the lines can be brushed or cleaned with a vacuum
cleaner. If necessary, they can be washed with low-pressure water and
mild detergent. If grease and dirt have accumulated, it may be
necessary to remove the coils and wash off the accumulation with
steam, compressed air and water, or hot water.
Note: This should be done by an air conditioning technician.
4. Check and clean the condensate drain system. Clean the drip tray of
accumulated dust or dirt. Probe the drain hole with a screwdriver to be
sure it is not clogged. Pour a small amount of water in the drip tray
and watch to ensure it drains properly.
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COOLING
COILS
CHAPTER 3
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CHAPTER
3
COOLING COILS
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Assignment 3
When you have completed the following questions, ask your instructor for the
Answer Key.
1.
Why would a cooling coil be added to a forced air furnace?
2.
List four problems that might develop in a central furnace if the cooling coil is not kept
clean.
3.
If there are no viewing ports allowing the technician/fitter to view the coil, what must be
done?
4.
Why should static pressure across the coil be measured?
5.
Where should the test holes for measuring static pressure be drilled?
6.
What devices are used to measure pressure drop across the coil?
7.
What adjustments should be made if the pressure drop across the coil is too great?
8.
What does an oil leak from the coil indicate?
9.
How can the external surfaces of a coil be cleaned?
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COOLING
COILS
CHAPTER 3
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10. What additional kind of cleaning must be done if untreated water is used as the cooling
medium?
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