jailcd2019-111： A Simulation Study on the Capacity Control of a Direct-Expansion Variable-air-volume Air Conditioning System

Abstract

A direct-expansion (DX) variable-air-volume (VAV) air conditioning (A/C) system which integrates a VAV  air-distribution sub-system and a DX refrigeration plant, is believed to be highly energy-efficient.Using a  complete dynamic mathematical model forDXVAVA/C systems which is well validated by experimental data, the  simulation  study  for the  capacity  control  for  a DX VAV A/C  system  equipped with variable-speed  compressor and EEV was carried out. The closed-loop responses of the DX VAV A/C system was obtained  after being subjected to: (1) a step-change in space internal thermal load; (2) a step-change in the set-point of space air temperature. The total simulated operation period is 5400 s, i.e., 90 min. Ten minutes after starting  time, i.e., t=600 s, the internal sensible load in Space A which is one of two air-conditioned spaces in the DX  VAV A/C system was step changed down to 1080 W, or a 50% reduction. At t=3000 s, the set-point of air  temperature in Space B was step-changed from 25 ℃ down to 24 ℃ .From the analysis of simulated results, it  can be concluded that the application of variable-speed compressor together with EEV could achieve the  continuous,  quick  and  precise  capacity  control  for  the  DX  VAV  A/C  system  and  therefore  space  air  temperatures can be satisfactorily controlled at their set-points during the whole operation period.