Overview; General Information; Working Principle & System Principle - McQuay MDS030A Design & Installation Manual

Design & installation Guide For McQuay MDS Multi System
C H A P T E R
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Overview

1.1 General information

The MDS(Multi Digital Scroll) air conditioning system is operated by a digital compressor and is
accommodated by multiple evaporators (indoor units). It is touted as the next-generation modular
system in the world of high-efficiency air conditioning. lt has undoubtedly changed the face of cooling
associated with high-storied buildings. It provides a broad range of different applications for settings
such as offices, hotels and schools. With its easy installation and simple controlling system, the MDS
will more than meet the demands of the air conditioning market.
1.2 Working principle & system principle
1.2.1Working principle
The beauty of this technology is its inherent simplicity. The standard digital scroll compressor has
a unique feature called axial compliance. This allows the fixed scroll to move in the axial direction, by
very small amounts, to ensure that the fixed and orbiting scrolls are always loaded together with the
optimal force.
This optimal force holding the 2 scrolls to-
gether at all operating condi tions ensure the
high efficiency of Copeland scrolls. The Digital
Scroll operation builds on this principle.
The Digital Scroll operates in two stages -
the "loaded state", when the solenoid valve is
normally closed and "unloaded state", when
the solenoid valve is open. During the loaded
state the compressor operates like a standard
scroll and delivers full capacity and mass flow.
However, during the unloaded state, there is no capacity and no mass flow through the compressor.
At this stage, let us introduce the concept of a cycle time. A cycle time consists of a "Loaded State"
time and "Unloaded State" time. The duration of these 2-time segments determine the capacity
modulation of the compressor. Example: In a 20 seconds cycle time, if the loaded state time is 10 seconds
and the unloaded state time is 10 seconds, the compressor modulation is (10 seconds x 100% + 10
seconds x 0%)/ 20 = 50% (Figure 3). If for the same cycle time, the loaded state time is 15 seconds
and the unloaded state time is 5 seconds, the compressor modulation is 75%. The capacity is a time
averaged summation of the loaded state and unloaded state. By varying the loaded state time and
unloaded state time, any capacity (10%-100%) can be delivered by the compressor.
PWM vale
fixed scroll
(movable in axial direction)
Orbiting scroll
(Rotatable in radial direction)