Air Conditioning Hot and Chilled Water Systems Design

The computer program PYTHON is a WINDOWS based program that analyses water piping systems for air conditioning applications. It provides for the analysis of hot and chilled water closed loop systems and also open loop systems such as condenser water piping systems. The program can however also handle other fluids by entry of the fluid density, viscosity and specific heat. The program handles systems with primary and secondary circuits and is based on the methods and data in the AIRAH/IHRACE Application Manual Air Conditioning Water Piping (DA16). It includes all the fittings and associated pressure loss data in this manual readily accessible through drop down lists.


The Piping Schematic

The program provides for graphical input of the piping layout in schematic form with separate layers for supply, return and plant room piping. Primary and secondry sytems with separate pumps can be modelled. The pipework system components, including boilers, chillers, head tanks, coils, condensers, etc., are all entered by selection from a floating toolbox.

Pop-up dialogue boxes allow entry of the various parameters associated with each piping system component (pipe material, coil loads, number of fittings, elevations, etc.) and master defaults such as coil connections and fittings are provided to minimise data input. Nodes are automatically inserted and numbered as the piping system is developed.

The calculations are carried out in a series of spread sheets. In the first of these the pressure losses throughout the system and the pressure at each node is calculated using the Colebrook White formula.

Pop up Dialogue Boxes for Coil, Chiller and Pump for entry of Data

The Pressure Loss Spreadsheet

The Heat Loss Spreadsheet

In a second spreadsheet the heat loss or gain from all the pipes in the system are calculated, adjusting coil water flows to account for the heat loss/gain along the pipes to each coil. In chilled water systems a check is made for the possibility of condensation formation.

In a third spreadsheet, each coil circuit is analysed and a control valve selection made based on the required valve authority. Two and Three way control valve can be modelled. The out-of-balance pressure loss required to be taken up by balancing valves is also calculated along with the required flow and head for each pump.

The cost of the piping system in terms of material quantities and fabrication and erection man-hours is also determined for all pipes, fittings, insulation and pipe system components.

The Control Valve Selection Spreadsheet

The program also determines the total lengths of pipes by material type and size and the number of fittings by type and size in a Cost Estimating Spreaedsheet. The pressure and temperature at each node is also displayed in another Screen and a summary of all the results is included in a Summary Results Form. Specific columns from each spreadsheet can be selected for printing.

The Summary Results Screen

The program can also analyse open circuit systems such as condenser circuits with cooling towers, condensers etc.

Open Circuit System with Two Cooling Towers and a Condenser

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