36
Varies between
VM
and
VS
according to
load when free cooling is available and S2 is
neither actively heating nor cooling.
S2
ECONOMISER
FREE
COOLING
OPERATION
S2 designated units supplied by Nordair with
automatic control dampers on fresh air intake
and recirculation, each with individual 0-10V
actuators and pre-wired to internal power supply
and terminal rail for external wiring by electrical
contractor.
Damper Control Strategy:-
Heating Minimum fresh air which means:
Where there are entrance doors to
outside:-
•
100% recirculation providing the return air
duct is of sufficient capacity to accom-
modate the full AHU design air volume.
•
Maximum
recirculation
volume
achievable keeping total supply air vol-
ume within 70% of full design where return
air duct is of insufficient size for the full
AHU design air volume.
For basement and first floor areas with no
entrances to outside:-
•
85% recirculation providing the return air
duct is of sufficient capacity to ac-
commodate the 85% air volume.
•
Maximum recirculation volume achievable
keeping total supply air volume within 70%
of full design where return air duct is of in-
sufficient size 85% air volume.
Cooling T
O
<T
R
100% fresh air subject to
minimum 10
o
C supply by modulation.
Cooling T
O
>T
R
Minimum Fresh air.
S2 Condensing Units General
Condensing units procured by HVAC contractor.
For each condensing unit - Mitsubishi FTC
controller, leaving air temperature sensor and
liquid line pipe sensor procured and factory fitted
by Nordair and wired to terminal rail for external
connections.
Liquid line sensor fitted in spring clip brazed to
pipe to facilitate removal during pipe brazing on
site to prevent heat damage. It is essential that
the sensor is replaced with good contact to the
pipe otherwise the Mitsubishi system will fault.
Mitsubishi key pad controller with LCD screen
supplied with each S1 unit for access to
Mitsubishi controls if required by plugging into
AHU mounted socket provided in S1 and S2 air
handling units.
(Note: Keypad controller should not normally be
required for commissioning).
Condenser power supplies from factory fitted
mcb’s in AHU via terminal rail with external
wiring by electrical contractor with local isolator
at each condensing unit.
Hardwired control cabling from factory fitted
FTC’s in AHU via terminal rail with external
wiring by electrical contractor.
Mod-bus ‘daisy chain’ network cabling to be
connected to condensers when Mitsubishi
confirm availability – initially for monitoring
purposes only.
Condenser operation interlocked with supply fan
run control, fire alarm activation and no flow/fault
alarm from supply fan inverter.
S2 Cooling
Stages (condensers) 1 and 2 (and 3 where
applicable) activated by Trend from T2 room
sensor.
Trend dictates required supply air temperature
via 0-10v output simultaneously to each
Mitsubishi FTC controller.
Each Mitsubishi FTC controller controls relevant
condenser output to achieve supply air set point
as dictated by Trend 0-10v output.
Minimum cooling set point (supply air) 12
o
C.
Consecutive cooling stages activated by Trend
to provide overlap to encourage multiple stages
at part load in preference to single stage at or
near full load. This is to derive maximum benefit
from increased COP at part condenser load.
All stages cooling held off below 12
o
C ambient.
S2 Heating Control Heatpump Only (where
no gas or electric heating installed)
Stages (condensers) 1 and 2 (and 3 where
applicable) activated by Trend from T2 sensor.
7. Controls cont.