INSIGHT
THE ART OF AIR HANDLING
IS FINE CONTROL OF THE
REFRIGERANT
By Michael Young, sales engineer, Trox
When conducting an analysis on the energy consumption of a standard
air conditioning system to that of a VRF system, you will notice a
substantial difference in performance and price.
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The system then increases the pulse per second setting on the
expansion valve which then also increases the compressor speed
as the cooling requirements increase. Once the system reaches
0.5⁰C of the set point, the controller changes the superheat
setting to 4⁰C and constantly monitors the temperature
fluctuation around the set point and dead band limits.
By operating at 4⁰C super heat setting, the exact amount of
refrigerant is fed to the evaporator while idling the compressor at
the required speed to meet the current room load.
So, the goal is to implement a control system that varies the
operation of components in relation to the thermal load profile
of the space.
I know how you feel right now. You have read this article and
you may feel overwhelmed or wish someone could explain all
these different concepts. The good news is that we are here to
support and help you accomplish your goals.
So, we would like to invite you to attend a FREE 1-hour
refrigerant superheat training course where we will share
the working principles behind a refrigerant system and how
control philosophy and components can increase energy
savings. Seats are limited to 20 people so Call 073 17 123 11
now to reserve your spot. RACA
A
ll commercial DX air-conditioning systems contain four
basic elements: a compressor, condenser, expansion
valve and evaporator. So why is there such a large difference
in price and energy consumption when comparing a standard
system and VRF?
While it is true that all commercial DX air conditioning systems
contain the same basic fundamental components, the key
differentiator is how each component is controlled and the type
of components that are installed.
Standard non inverter DX air-conditioning systems are
cheap, but the compressor and fans operate with an on or off
type of control philosophy. A VRF is more expensive but the four
major components operate with a modulating type of control
philosophy and have modulating capabilities.
So, let’s see how control philosophy is one of the key
differentiators between these two types of systems. So, with a
commercial DX type of air conditioning system, refrigerant mass
flow is the factor that influences how the system will behave.
Let’s first begin with a standard air conditioning system with
no inverter capabilities and with a constant superheat setting
of say 5⁰C. When the loads are high, the system opens the
expansion valve and feeds refrigerant to the evaporator so the
superheat setting of 5⁰C is maintained.
When the temperature within the space decreases below
the lower bandwidth limit, the system switches off. The unit
switches on when the room temperature rises above the upper
bandwidth limit and so the cycle begins again.
The high energy consumption lies with the constant on/off
operations of the compressor which makes this type of system
cheap but not as energy-efficient as a VRF unit.
A VRF system is different as all components operate at a
modulated state. When the unit is switched on, the expansion
valve opens to 141 pulses per second. This then adjusts the
compressor speed in relation to the expansion valve setting
and the system aims to reach a superheat target setting
of 1 – 4⁰C.
The key differentiator is how each component is controlled and the
type of components that are installed.
RACA Journal I April 2020
31