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 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 . . .

 

 

 

 

                  

To take a glance at all pocketEngineer software and OS requirements, click Overview.

 

Go to a PsychroAC module:

 Main (AHU) module

 Precool Coil / Precool Air Unit (PAU) Module > > >

 Heat Recovery Wheel (HRW) Module > > >

 Heat Pipe (HP) Module > > >

 Run-around Coil Module > > > 

  Air-Mixing Module > > >

 

 aPsychroAC: Psychrometric Air-Conditioning processes

Air-Conditioning psychrometric cooling & dehumidification process is a complex thing. Plotting psychrometric chart has never been an easy task for design engineers. Not anymore! with aPsychroAC, you can do various psychrometric calculations and plot psychro chart in a few clicks at anytime, anywhere...

 

Complex calculation software can be difficult to understand and use. aPsychroAC is intentionally designed not to be complex, but rather simple, practical, easy to understand and use. The main objective of engineering this software is to help HVAC designers in providing quick design solutions for the following air-conditioning design applications:

 

- Summer conditions (not for Winter conditions).

- Cooling & dehumidification processes (not for system with humidifier, etc).

- Heat recovery systems.

 

 

The OA inputs accept Conditioned Air (CA) conditions such as treated outdoor air from Precool Coil / Precool Air Unit (PAU), Heat Recovery Wheel (HRW), Run-Around Coil (RAC), Heat Pipe (HP), etc.

 

Precool Coil / PAU, HRW, RAC and HP calculations are included as separate modules with "Export CA" feature. The calculated SA (CA) conditions can be fed (exported) to the main AHU module as precooled (treated) outdoor air. You can recall back the PAU, HRW, RAC or HP module with its current activity's state retained. 

 

 



 

Highlights:

- Carrier ESHF (Effective Sensible Heat Factor) method or Supply Air Temperature method

- Recirculating or 100% OA (for SA Temperature method only) system

- Reheat option

- Fan heat gain option (draw-thru arrangement only)

- Plot & save psychrometric chart

- Built-in guides and explanations

- rhoAIR module

- Air mixing psychrometric module

- Precool Coil / Precool Air Unit (PAU) module

- Heat Recovery Wheel (HRW) module

- Heat Pipe (HP) module

- Run-Around Coil (RAC) module

- Save-result-to-file function with built-in text file viewer

- in SI-IP Units

 

 Design Approach explained . . . 
Two widely used design approaches to psychrometric air-conditioning calculations are modelled in aPsychroAC. They are
 
(1) Carrier ESHF (Effective Sensible Heat Factor) method
(2) SA (Supply Air) Temperature method.
 
In the Carrier ESHF method, you start with specifying the coil performance, i.e., coil BF (bypass factor) that is generally representative of the type of equipment you intend to select. The supply air temperature condition is then calculated.
 
In the SA Temperature method, you start with fixing the supply air temperature condition. The coil performance is then calculated. The norm range of design temperature difference between SA and RA temperatures is about 15 - 22 oF (8 - 12 oC) with a common design target of 18 - 20 oF (10 - 11 oC).
 
The two methods give comparable results but not exactly the same (in aPsychroAC) for the following reasons:
 
- in Carrier ESHF method, fixed constant is used in the governing equations as given in Carrier system design manual.
- in SA Temperature method, mass flow rate and specific volume of the state-point air is calculated.

  

 

SI formula used in aPsychroAC program

 Carrier ESHF Method

 SA Temperature Method

sensible heat =

1.20 x air flowrate x dT m x Cp x dT

latent heat =

3.0 x air flowrate x dW m x hfg x dW

dT = difference in temperature

dW = difference in moisture content

m = mass flowrate of air = air flowrate/specific volume of air

Cp = specific heat of air = 1.02 kJ/(kgoC) in aPsychroAC

hfg = enthalpy of vaporisation = 2500 kJ/kg in aPsychroAC

 

 Re-circulating or 100% OA System . . .  
Both re-circulating and 100% OA systems can be performed. For 100% OA system, it is more friendly to adopt the SA Temperature approach. Therefore, the option of 100% OA system is limited to the SA Temperature method. For 100% re-circulating system, input OA Airflow = 0.
 

 Psychrometric Chart . . .  

No more manual plotting of psychro chart. With aPsychroAC, psychro chart showing the air-conditioning process is automatically plotted for each calculation. The psychro chart tells you the results in a graphical manner as shown in the chart below. The psychro chart can be saved as an image file for your calculation report.

 

 

 

 

 Input Data. . .  

Only two information is required from your cooling load calculation, i.e., RSH (room sensible heat) and RLH (room latent heat).

 
OA ventilation airflow is usually determined by nos. of people x recommended outdoor air requirements.  

 

 

 

 Effect of Coil BF (Bypass Factor) . . .  

Coil BF represents that portion of the air which is considered to pass thru the coil completely unaltered.

 

Smaller BF has the following effects:

(a) higher coil ADP; increases apparatus COP

(b) lower supply air temperature; less supply airflow, smaller fan

(c) more rows of coil; higher fan static

 

In actual air-conditioning cooling coil application, the BF will be greater than zero. Carrier system design manual recommends the typical coil BF for various design applications as follows:

 

Coil BFType of ApplicationExample 

0.30 - 0.50

A small total load or a load that is somewhat larger with a low sensible heat factor (high latent load) 

Residence 
0.20 - 0.30

Typical comfort application with a relatively small total load or a low sensible heat factor with a somewhat larger load 

 Residence, Small Retail Shop, Factory
0.10 - 0.20

Typical comfort application 

 Dept. Store, Bank, Factory
0.05 - 0.10

Applications with high internal sensible loads or requiring a large amount of outdoor air for ventilation 

 Office Block, Dept. Store, Restaurant, Factory
0 - 0.10

All outdoor air applications 

Hospital Operating Room, Factory 

 

Relationship of Coil ADP, Supply Air & Chilled Water Temperature . . .

Coil ADP (Apparatus Dew Point) is the coil surface dew point temperature required to accomplish a cooling & dehumidifying process. Coil ADP is at the point where the GSHF line crosses the saturation line on the psychro chart. The relationship of coil ADP to SA & chilled water temperature is as follows:

 

Chilled Water Temp < Coil ADP < SA Temp

 

In DX system, lower coil ADP means lower saturated suction (refrigerant) temperature at the compressor inlet. In chilled water system, lower coil ADP means lower chilled water supply temperature. This results in less efficient range (higher kW/Ton) of operation.

 

In aPsychroAC, you will be prompted when no coil ADP is found, i.e., the ESHF line or GSHF line does not intersect the saturation line as displayed below:

 

 

 

In the above situation, REHEAT is necessary to complete the process. 

 

 

Did you know? . . . slope of ESHF line 

From the ESHF value, one can calculate the slope of the ESHF line by using the following approximation:

 

slope of ESHF line, Tan (angle) = (1/2451)*[(1-ESHF)/ESHF]  

 

 

 Calculation   Examples. . .  

 

For comparison example with E20, see more examples here . . . 

 

For Operating Room example with Heat Recovery device, see example here . . . 

 

 

The following design calculations are done with aPsychroAC program.  

 

Worked Example 1 - recirculated system (in IP units)

Given:

Summer design conditions: 95 oF DB, 75 oF WB

Indoor design conditions: 75 oF DB, 50% RH  

RSH = 200 MBtu/hr

RLH = 50 MBtu/hr

OA ventilation airflow = 2000 CFM

BF = 0.15

Assume the total pressure of the suppy air fan is 3".

 

Results: (using Carrier ESHF method)

 Coil ADP (oF)50.8 
 Coil sensible (MBtu/hr)265.7 
 Coil total load (MBtu/hr)363.3 
 Coil total load (Ton)30.3 
 OA sensible (MBtu/hr)42.9 
 OA total load (MBtu/hr)89.6 
 ERSH (MBtu/hr)229.2 
 ERLH (MBtu/hr)57.0 
 ESHF0.801 
 SA airflow (CFM)10392 
 SA temperature (oF)57.1 
 Supply Fan load (MBtu/hr)22.7 
  OARAMA/onoff 
 Tdb 95.075.0  78.855.0 
 RH 39.8 50.0 48.4 89.4
 w 0.0141 0.0092 0.0102 0.0082
 m 146.9 616.3 763.2 763.2
 h 38.31 28.11 30.07 22.13
Tdb = Dry bulb temp (oF)
RH = Relative humidity (%)
w = Moisture content (lb/lb)
m = Mass flowrate (lb/min)
h = Enthalpy (Btu/lb)
OA = Outdoor Air
RA = Room/Return Air
MA/on = Mixed Air / on coil
off = off coil

 

 

Worked Example 2 - recirculated + reheat (in SI units)

Given:

Outdoor design conditions: 34 oC DB, 40% RH

Indoor design conditions: 24 oC DB, 50% RH  

RSH = 60 kW

RLH = 40 kW

OA ventilation airflow = 4700 CMH

SA Temperature = 14 oC

Selected Coil BF shall be about 0.15

Assume the fan heat gain load is part of the Reheat load.

 

Results: (using SA Temperature method)

 Coil ADP (oC)6.3 
 Coil BF 0.15
 Coil sensible (kW)102.9
 Coil total load (kW)157.8
 Coil total load (Ton)44.9
 OA sensible (kW)15.0
 OA total load (kW)29.9
GSHF0.652
 SA airflow (CMH)17408.5
 SA temperature (oC)14 
 Supply Fan load (kW)0.0
 Reheat (kW)27.9
  OARAMA/onoff 
 Tdb 34.024.0 26.59.3
 RH 40.0 50.0 47.7 90.3
 w 13.3522 9.2985 10.3108 6.5785
 m 1.47 4.41 5.88 5.88
 h 68.44 47.81 52.96 25.97
Tdb = Dry bulb temp (oC)
RH = Relative humidity (%)
w = Moisture content (g/kg)
m = Mass flowrate (kg/s)
h = Enthalpy (kJ/kg)
OA = Outdoor Air
RA = Room/Return Air
MA/on = Mixed Air / on coil
off = off coil

 

Worked Example 3 - 100% Outdoor Air (in SI units)

Given:

100% outdoor air summer air-conditioning system

Outdoor design conditions: 34 oC DB, 40% RH

Indoor design conditions: 24 oC DB, 50% RH  

RSH = 400 kW

RLH = 100 kW

SA Temperature = 14 oC

Assume the total pressure of the suppy air fan is 750Pa.

 

Results: (using SA Temperature method)

 Coil ADP (oC)9.8 
 Coil BF 0.13
 Coil sensible (kW)844.1
 Coil total load (kW)1341.5
 Coil total load (Ton)381.5
 OA sensible (kW)400.0
 OA total load (kW)797.4
GSHF0.629
 OA airflow (LPS)34855 
 SA airflow (LPS)32325.1
 SA temperature (oC)14.0 
 Supply Fan load (kW)44.1
  OARAMA/onoff 
 Tdb 34.024.0 -12.9
 RH 40.0 50.0 - 89.5
 w 13.3522 9.2985 -8.2785
 m 39.22 - - 39,.22
 h 68.44 47.81 - 33.84
Tdb = Dry bulb temp (oC)
RH = Relative humidity (%)
w = Moisture content (g/kg)
m = Mass flowrate (kg/s)
h = Enthalpy (kJ/kg)
OA = Outdoor Air
RA = Room/Return Air
MA/on = Mixed Air / on coil
off = off coil

 

more calculation EXAMPLES >>>

 

 

For Operating Room example with Heat Recovery device, see example here . . . 

 

 



 

aPsychroAC (Android)

Price: 
at Android Market   

 

OS requirements: Android        

 

 

To Purchase & Download to your Android device:

 

 

 

@ Android Market

   

For product enquiry, email me.

 

 

 

in SI and IP Units 

 

Carrier ESHF Method - inputs

 

 

Carrier ESHF Method - results

 

 

Psychro chart plot

 

 

 

 Calculation Method - Approach options

 

 

 

 

 SA Temperature Method (with 100% OA option) 

 

 

Menu

 

 

Air Mixing module

 

 

Heat Pipe (HP) module

 

 

Precool Coil / Precool Air Unit (PAU) module

 

 

Heat Recovery Wheel (HRW) module

 

 

Run-Around Coil (RAC) module