Data Manual

50
COOLING
Room air conditioner sizing is all about matching the room
size to the air conditioner size. Since air conditioners
remove both heat and humidity from the air, a unit that
is too large, will cool the room before it has a chance to
remove the humidity. The result will be a room that's not
very comfortable – cool, but feeling damp and clammy.
Most musty odors in rooms are due to excess humidity.
Using a smaller-capacity unit or using Dry Air 25 units
will provide better dehumidification. The largest factor in
causing mold and mildew in the room is excess moisture.
A smaller unit running longer or a Dry Air 25 model can
remove more moisture. Mold behind wall coverings that
do not allow water vapor to pass through—vinyl wallpaper
or oil-based paints, for example—is not a problem of
excessive moisture in the room, but rather is caused by
moisture trapped in the walls.
Since larger capacity units typically are louder, oversized
air conditioners also create guest complaints due to the
noise and short cycling.
HEATING
Using a resistance heater larger than required—using
a 4.8 kW heater when a 3.4 kW heater would suffice,
for example—may not cost any more in electrical
consumption since the larger heater will operate, for
less time. The “demand charge” portion of the utility
bill—which is based on the highest electrical load for
a period of time—may be a significant portion of the
utility bill. Some customers have reported the demand
charge actually being more than the usage charge. In a
100-room property it would be possible for the demand
of the 4.8 kW heater versus a 3.4 kW heater to be 140
kW more than the demand charge if the lower wattage
heaters were used. Working with the utility companies to
understand their method of billing and taking advantage
of any rebates they may offer can reduce the utility bill.
A heat load analysis should be performed to determine
the heating and cooling load required for the space in
question. How much heat is coming into the space that
the air conditioner must remove and how much heat is
lost during the winter months that must be replaced. The
heat load analysis takes many factors into play, including
cubic footage of space, location and construction type/
materials. Getting the right size means getting the
comfort and the energy efficiency right.
KEY TERMS
Capacity - The capacity of an air conditioner is measured
by the amount of cooling it can do when running
continuously. The total capacity is the sum of the latent
capacity (ability to remove moisture from the air)
and sensible capacity (ability to reduce the dry-bulb
temperature). Each of these capacities is rated in BTUs per
hour (Btu/h).
Air conditioner capacity is rated per AHRI 310/380
conditions at 95°F drybulb and 75°F wetbulb outside with
an inside temperature of 80°F drybulb and 67°F wetbulb.
LATENT SYSTEM CAPACITY
The total capacity of an air conditioner is made up of the
sensible capacity (the output of the unit used to remove
heat from the air in the area being conditioned) and the
latent capacity (the output of the unit used to dehumidify
the air in the area being conditioned). For humid climates
and applications, the sensible/latent capacity split of the
unit should be considered.
The latent system capacity is 1.00 minus the sensible
capacity. (If the sensible capacity is listed at 74% the latent
capacity is 26%. This means that 74% of the capacity of
the unit is used to remove heat from the air and 26% is
used to remove moisture from the air at standard test
conditions.)
Latent Cooling Load - The net amount of moisture added
to the inside air by plants, people, cooking, infiltration, and
any other moisture source. The amount of moisture in the
air can be calculated from a combination of dry-bulb and
wet-bulb temperature measurements.
Sensible Cooling Load - The heat gain of the room due to
conduction, solar radiation, infiltration, appliances, people,
and pets. Burning a light bulb, for example, adds only
sensible load to the house. This sensible load raises the
dry-bulb temperature.
Dry-bulb Temperature - The temperature measured by a
standard thermometer.
Wet-bulb Temperature - When a wet wick is placed
over a standard thermometer and air is blown across the
surface, the water evaporates and cools the thermometer
below the dry-bulb temperature. This cooler temperature
(called the wet-bulb temperature) depends on how much
moisture is in the air.
EER - The Energy Efficiency Ratio is the efficiency of the
air conditioner. It is capacity in BTUs per hour divided by
the electrical input in watts.
AZ65 SERIES SPECIFICATIONS
ARCHITECTS & ENGINEERS DATA MANUAL AZ45/AZ65 SERIES