Catalogue

14 UV-PRC004-EN
Application Considerations
Performance
Application of this product should be within the catalogs airflow and unit performance. The Trane
Official Product Selection System (TOPSS™) will aid in the selection process for a set of given
conditions. If this program has not been made available, ask a local Trane sales account manager
to supply the desired selections or provide a copy of the program.
Ventilation for Acceptable IAQ
Supplying proper ventilation to a classroom is challenging. The various rooms that make up a
school are forever changing in their proper ventilation needs. Building occupants and their
activities generate pollutants that heighten the ventilation requirements. And because of this
intermittent occupancy, the ventilation frequency of a classroom is constantly on the move.
Ventilation systems dilute and remove indoor contaminants, while mechanical heating and cooling
systems control the indoor temperature and humidity. Supplying an adequate amount of fresh air
to an occupied classroom is necessary for good indoor air quality. IAQ should be considered a top
priority in the school environment because children are still developing physically and are more
likely to suffer the consequences of indoor pollutants. For this reason, air quality in schools is of
particular concern. Proper conditioning of the indoor air is more than a quality issue; it
encompasses the safety and stewardship of our investment in the students, staff and facility. The
beauty of a classroom unit ventilator is its ability to provide heating, cooling, ventilation and
dehumidification as a single-zone system.
ASHRAE Control Cycles
There are a variety of control systems available in unit ventilators. The exact method of controlling
the amount of outside air and heating capacity can vary. However, all systems provide a sequence
of operation designed to provide rapid classroom warm-up and increasing amount of ventilation
air to offset classroom overheating. Reasons for classroom overheating can include:
• Sun or solar heat produced through large glass areas in a school.
• Lighting.
•Students
To help supply proper ventilation to these fluctuating heat gains, the Trane unit ventilator is
desig
ned to provide rapid classroom warm-up and increasing amounts of ventilation air to offset
classroom overheating.
ASHRAE Cycle I. All standard unit ventilator cycles automatically close the outside air damper
whenever maximum heating capacity is required. As room temperature approaches the comfort
setpoint, the outside air damper opens fully, and the unit handles 100 percent outside air. Unit
capacity is then controlled by modulating the heating element capacity.
ASHRAE Cycle I is typically used in areas where a large quantity of outdoor air is required to offset
the air being exhausted to relieve the room of unpleasant odors and particles.
ASHRAE Cycle II. ASHRAE Cycle II is the most widely used ventilation control. Similar to Cycle
I, the outside air damper is closed during warm-up. But with Cycle II, the unit handles recirculated
air through the return air system. As temperature approaches the comfort setting, the outside air
damper opens to admit a predetermined minimum amount of outside air. This minimum has been
established by local code requirements and good engineering practices per AHRI-840. Unit
capacity is controlled by varying the heating element output. If room temperature rises above the
comfort setting, the heating element is turned off and an increasing amount of outside air is
admitted until only outside air is being delivered.
ASHRAE Cycle II is a very economical control sequence often referred to as integrated
economizing. This design supports optimum ventilation and provides the greatest energy savings.
This is further proof of why AHRI-840 certification is important in minimizing energy consumption
through economizer performance.
UV-PRC004-EN.book Page 14 Monday, February 4, 2013 11:01 AM