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Design & installation Guide For McQuay MDS Multi System
CHAPTER
1
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 undoubt-
edly 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
1.2.1 Working Principle
The beauty of this technology is its inher-
ent 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
together at all operating conditions en-
sure 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%. If for the same cycle time, the loaded state time is 15
fixed scroll
(movable in axial direction)
PWM vale
Orbiting scroll
(Rotatable in radial direction)
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