Handbook of air conditioning and refrigeration / Shan K

6.44 CHAPTER SIX
Trace 600 Input—Job
from the TFM method. For many commercial buildings, when the air system is shut down during
an unoccupied period, the external heat gains entering the space cannot be reasonably allocated
over the cool-down period and the successive operating hours.
● TETD-TA1 and TETD-TA2. The TETD-TA1 method adopts the transfer function method to calculate
heat gain, and TETD-TA2 uses an approximate TETD to calculate heat gain which adopts a
decrement factor � and a time lag � to describe the amplitude and time-delay characteristics of the
heat wave inside an exterior wall or a concrete roof slab. Both TETD-TA1 and TETD-TA2 use the
time-averaging (TA) method to convert the heat gain to space cooling load. The TA technique
lacks scientific support.
● TETD-PO. This method also adopts an approximate TETD to calculate the heat gain. It uses Post
Office RMRG weighting factors to convert a heat gain of 100 percent radiative to space cooling
load, and Post Office RMRX weighting factors to convert a heat gain which is not 100 percent
radiative, such as heat gains from people, lights, and equipment.
There are six heating load calculation methods. Five of them—CEC-DOE2, CLTD-CLF,
TETD-TA1, TETD-TA2, and TETD-PO—have already been described in the cooling load calculation
methodology. The sixth heating load calculation method is called the UATD method. In the
UATD method, heat losses are calculated based on the U value � area � temperature difference,
which is the temperature difference of the outdoor and indoor design temperatures. Heat losses are
also considered as instantaneous heating load.
For peak load calculation at winter design conditions, internal heat gains are not taken into
account in the UATD method. However, for energy use calculation, internal heat gains need to be
taken into account according to the load schedules. Otherwise the heating energy use becomes too
conservative.
There are 11 job cards: Cards 01 to 05 are used to describe the name of the project, its location, the
client of the project, the program user, and comments. Card 08, climatic information, lists the name
of weather file, summer and winter clearness numbers, outdoor dry- and wet-bulb temperatures,
ground reflectance, as well as the building orientation. Card 09, load simulation periods, covers the
first and last month of cooling design, summer period, and daylight savings time. It also covers the
peak cooling load hour.
In card 10, load simulation parameters (optional), the selection of cooling and heating load
methodology has been described in preceding paragraphs. In addition, the input data cover airflow
input and output units, percentage of wall load included in the return air, and room circulation rate
when the transfer function method is used in the conversion of heat gain to space cooling load. Outdoor
air dry-bulb temperature and humidity ratio are also required to determine the state of the supply
air during psychrometric analysis.
The sensible and latent loads due to the ventilation outdoor air intake are a component of cooling
coil load. They do not affect the supply airflow and the size of the supply fan if the mixture of
outdoor and recirculating air is extracted by the supply fan.
Card 11, energy simulation parameters (optional), describes the first and last months of energy
simulation, holiday and calendar type, and the conditioned floor area. It also determines the input
data of calculation level whether it is at room, zone, or air system level.
Card 12, resource utilization factors (optional), covers the input data of energy utilization
factors which indicate the inefficiency of producing and transfering energy, of electricity, gas,
oil, steam, hot water, chilled water, and coal. Card 13, daylighting parameters (optional),
describes the atmospheric moisture, atmospheric turbidity, or a measure of aerosols that
affects daylighting, inside visible reflectivity, and geometry method, such as glass percentage
(GLAS-PCT).