Because the parallel FPTU fan was off for cooling operations, there were no differences in primary fan, primary chiller, or preheat coil
energy use for the four cases in Table 6.
In the AHU shown in Figure 2, which has no preheat coil
and operates at essentially 100% outdoor air at minimum flow, the freeze-stat would regularly trip when outside air temperatures approached freezing.
The annual energy use (kWh) of the FPTU fan, the FPTU heating coil, the primary fan (AHU), the chiller, the preheat coil
, and total plant are listed in Table 7.
The output from Energy-Plus included the annual energy usage of the primary cooling coil, primary supply fan, preheat coil
, terminal unit fans, and heating coil.
The baseline data center ventilation unit would have a preheat coil
to protect the AHU from freezing and still be able to operate year-round.
[T.sub.min] = minimum temperature leaving preheat coil
, [degrees]F ([degrees]C)
Although this approach requires the installation of a small preheat coil
, it allows the wheel to continue operating at full energy-recovery capacity even during the coldest times of the year.
In Region IV, the OA DBT is below freezing much of the time, so to avoid low-temperature incidences (freezing) at the cooling coil (if chilled water), a freeze-proof preheat coil
is required to elevate the OA DBT to about 40[degrees]F (4.4[degrees]C).
The warm deck is only connected to the return air and has a preheat coil
. The supply air handler airflows are controlled by the positions of the dual-duct terminal dampers.
The integration of DOASs with parallel terminal systems has been hailed as a significant paradigm shift and the general layout of a DOAS, consisting of a preheat coil
, an enthalpy wheel, a deep cooling coil, a sensible heat exchanger, and the prime movers, has been discussed by Mumma and his research team at Pennsylvania State University (Mumma and Shank 2001; Mumma 2001).
The preheat coil
is set to 10[degrees]F below the supply air setpoint temperature.
As shown in Figure 2, a preheat coil
can be used to preheat the return air, and by doing so, the sensible cooling capacity can be reduced or eliminated, as needed.