Essentials
SELELE MASHILO
Selele Mashilo has a mechanical engineering diploma from Tshwane University of Technology and
a refrigeration and air-conditioning diploma from Unisa. His experience includes over a decade in
government as deputy-director building services before rejoining the private sector in 1998 as HVAC&R
project engineer. He is the former chairperson of the Refrigeration and Air Conditioning Empowerment
Forum of SA (RAEFSA), the Air Conditioning and Refrigeration Industrial Council of SA (ACRICSA), and
Black Energy Services Companies (BESCO).
AIR-CONDITIONING
SYSTEM SELECTION (VRF)
By Selele Mashilo
As we continue looking at air conditioning equipment selection, we move on to
Variable Refrigerant Flow (VRF) systems and the basics of how these work.
W
hen a building is divided into number of zones, it has
always been difficult to supply cooling and heating
simultaneously from one machine or source. Rooftop units or
package units can supply either cooling or heating at one time.
Electric elements were at some stage used at the air terminals
to control room temperature. VRF systems are designed to
achieve various temperatures at various zones from the same
outdoor unit. They are called heat recovery variable refrigerant
flow (HR VRF) systems.
VRF CONCEPT
The system is arranged in such a way that one outdoor unit can
supply many indoor units. Fresh air into the zones is supplied
by small ducting reticulated in the building through either
standalone air terminals or ducting coupled to the indoor units.
Figure 1 shows a three-pipe system from the outdoor to
the BS box and two pipes from the BS box to the indoor unit.
Continued on page 61
Figure 1:
VRF system
arrangement.
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RACA Journal I June 2019
59