The outside air, OA from the zone is passed through the DX coil
of the DOAS system to get conditioned outside air, OA'.
oa] is lower than the standard rating condition at 35[degrees]C (95[degrees]F) for both the ASHP and DX coil
The indoor coil model is an extension of the DX coil
model that exists in EnergyPlus (Raustad 2013).
For a zero-superheat dry DX coil
, there is only sensible cooling, and the local heat transfer rate is thus given by
When the temperature drop of about 20[degrees]F(11 [degrees]C) across the dX coil
results in a discharge temperature below the comfort setpoint of 53[degrees]F(12[degrees]C), the economizer controller will reduce the economizer airflow to keep the discharge air temperature from getting too low.
A part of the return air mixes with the outside air from the DOAS and is cooled by the heat pump DX coil
, while the rest of the return air leaves the building by passing through the enthalpy wheel located in the rooftop DOAS unit.
Although the current VRF DX coil
model has a variable capacity, it utilizes a constant-speed fan component.
However, in practice, the evaporating and condensing temperature can only be changed within a certain range due to some mechanism limitations; for example, the maximum and minimum condensing pressure requirements, minimum refrigerant vapor velocity requirement for good oil return, no formation of frost on the DX coil
The low limit is set based on the lowest supply air temperature for comfort and no frost formation on the DX coil
, typically 45 [degrees] F (7.
The evap cooler is located upstream of the DX coil
and all working fluid air is directed across the DX condenser coil.
For example, the selection of the rated air flow rate has a significant impact on the DX coil
sensible cooling capacity.
0 Normal mode same with No Latent as Case 1 Degradation Fan off short time when compressor cycles off No moisture evaporation from wet coil, modeled by turning off latent degradation in DX coil
model 7 DX System with 350 47.