Psychrometric software
Psychrometric Air-Conditioning calculation (Android): a PsychroAC
calculate and plot air-conditioning cooling & dehumidification pyschrometric process; with precool air unit, heat pipe, run-around coil, heat recovery unit . . .
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Go to a PsychroAC module:
Precool Coil / Precool Air Unit (PAU) module
aPsychroAC: Precool Coil / Precool Air Unit (PAU) module
This standalone module is provided as a quick design and analysis tool for Precool Coil or Precool Air Unit (PAU).
In air-conditioning applications, PAU or precool coil is used to precool incoming hot and humid outdoor air which has high latent load. The treated or conditioned air (CA) is then fed to AHU. In this way, the outdoor air load is splitted from the room load.
The OA inputs accept Conditioned Air (CA) conditions such as treated outdoor air from Heat Recovery Wheel (HRW), Run-Around Coil (RAC), Heat Pipe (HP), etc. You can import HRW, RAC or HP module for the calculation of CA conditions.
Feature . . . Export CA Conditions The calculated SA (CA) Tdb, RH and airflow can be fed (exported) to the main AHU module as precooled (treated) outdoor air. The current activity's state is retained when you recall back this module for input changes, etc.
Design Approach explained . . . Two methods of sizing are modelled:
(1) 'SA to AHU' method, i.e. 'cold' supply air delivered to AHU.
You generally start by setting the desired Off Coil temperature to be delivered to the AHU. To handle all the OA latent load, the Off Coil setpoint is usually just below the Room air dewpoint. If the PAU requires to handle some or all of the room latent (moisture) load, then the Off Coil setpoint needs to be much lower than the Room air dewpoint.
(2) 'SA to Room' method, i.e. 'space neutral' supply air delivered directly into the air-conditioned space.
You specify the desired space neutral air temperature in addition to the desired Off Coil temperature. In this method, the conditioned OA is reheated to the space neutral air temperature and supplied directly into the room. Note that all the sensible cooling that is done during the coil process is wasted in this method.
All airflows calculated are actual airflow, i.e. with air density variations. The governing equations used are:
sensible heat = m x Cp x dT
latent heat = m x hfg x dW
Psychro Chart . . . Psychro chart showing the precool coil process is plotted for each calculation. The psychro chart can be saved as an image file.
Calculation Examples . . . The following design calculations are done with aPsychroAC program.
Worked Example 1 - SA to AHU (SI units)
Given:
Summer design conditions: 34 oC DB, 40% RH
Room design conditions: 24 oC DB, 50% RH
OA ventilation airflow = 5535 CMH
OA is to be precooled to 10 oC DB, 87% RH
Ignore fan heat gain, if any.
ADP = Apparatus dew point
BF = Bypass fator
DB = Dry bulb
WB = Wet bulb
Tdb = Dry bulb temp (oC)
RH = Relative humidity (%)
w = Moisture content (g/kg)
m = Mass flowrate (kg/s)
h = Enthalpy (kJ/kg)
OA/On = Outdoor Air / On coil
RA = Room Air
Off = off coil
SA (CA) = Supply Air / Conditioned Air
PAU inputs
PAU inputs
PAU results
PAU results
PAU psychro chart plot
