This case study showcases Flownex's ability to balance central air conditioning systems by determining orifice sizes or damper openings to achieve a required mass flow of 0.02 kg/s in each room. Flownex's built-in orifice sizing feature calculates orifice ratios for pipe elements with fixed mass flows, ensuring balanced air distribution efficiently.
CHALLENGE
The challenge of this case study is balancing an air distribution system by determining the orifice sizes or damper openings to ensure required flow at certain points in the system. In particular, this example demonstrates the balancing of a central air conditioning distribution system. All the rooms that need to be supplied are similar and a mass flow of 0.02 kg/s is required in each.
BENEFITS
Flownex has a built in orifice sizing capability specifically designed to assist in modeling flow balancing problems. The user can specify that the orifice ratios are calculated for all Pipe elements for which a fixed mass flow was specified to obtain the specified mass flow.
SOLUTION
The capability of Flownex to easily simulate flow balancing problems was demonstrated in this example. The orifice ratios were determined that would give specific flow rates at each outlet of a central air conditioning distribution system. Flownex has a built in functionality that assists in solving orifice ratios for Pipe elements for which fixed mass flows are specified.
SYSTEM DESCRIPTION
The configuration considered in this example is shown in Figure 1. The inlet pressure and required mass flow at each outlet are known.
OBJECTIVE OF SIMULATION
The objective of the simulation is to determine the orifice ratio or damper opening in each outlet pipe to obtain balanced flow given appropriate input data for all the components as well as boundary conditions. This example illustrates the capability of Flownex to easily simulate such problems through the use of its build in orifice sizing functionality and the orifice model incorporated with the Pipe element.
FLOWNEX MODEL
The Flownex model of the system is shown in Figure 2. The distribution ducts are modelled in Flownex using the Pipe element. A fixed mass flow of 0.02 kg/s is specified on each outlet Pipe element as specified in the problem statement. The inlet boundary pressure is specified on the inlet node (Node 1). The geometry and loss factors for each pipe are specified on the relevant Pipe element.
DESCRIPTION OF SIMULATION
Flownex has a built in orifice sizing capability specifically designed to assist in modeling flow balancing problems. The user can specify that the orifice ratios are calculated for all Pipe elements for which a fixed mass flow was specified to obtain the specified mass flow. For this example, a reference pressure (atmospheric pressure) was specified to use as the outlet pressure for all outlet ducts.
RESULTS
Table 1 gives the required orifice ratios for each parallel pipe determined by Flownex. The pipe numbers coincide with the numbers given in Figure 2.
Table 1: Orifice ratios determined by Flownex.
| Pipe number | Orifice Diameter |
| 12 | 0.021082 |
| 13 | 0.021081 |
| 14 | 0.021079 |
| 15 | 0.021076 |
| 16 | 0.021076 |
| 17 | 0.021078 |
| 18 | 0.021078 |
| 19 | 0.021064 |
| 20 | 0.021064 |
| 26 | 0.021091 |
| 27 | 0.021091 |
| 28 | 0.021090 |
| 29 | 0.021087 |
| 30 | 0.021078 |
CONCLUSION
The capability of Flownex to easily simulate flow balancing problems was demonstrated in this example.
The orifice ratios were determined that would give specific flow rates at each outlet of a central air conditioning distribution system. Flownex has a built in functionality that assists in solving orifice ratios for Pipe elements for which fixed mass flows are specified.