Heating
The unit’s heating mode of operation is determined by the
control temperature and the heating setpoint temperature. The
unit enters the heating mode of operation by comparing the
control temperature to the heating setpoint.
The control temperature can be either the return temperature
or the space temperature.
The return temperature is typically used for VAV units and the
space temperature is typically used for CAV units.
The unit goes into the heating mode of operation when the
control temperature (return or space temperature) is below the
heating setpoint by more than ½ the deadband.
For example, a standard air conditioning unit with supplemental
gas, electric, or hot water heat with a heating setpoint of 68.0ºF
and a deadband of 1.0ºF would enter heating mode if the
control temperature reached 67.4ºF. When this takes place,
the heating mode of operation will begin and the 1st Stage of
heating operation will start.
Heat Pump
(DPS 003–015 ton)
The heating mode of operations will be slightly different for heat
pump units. It is the manufacturer’s recommendation that all
Rebel heat pump units be purchased with supplemental gas,
electric, or hot water heat. When the control temperature drops
below the heating setpoint by half the deadband the unit will
energize the four way valve and initiate mechanical heating.
On heat pumps mechanical heating is the primary source of
heat and will always be the unit’s first attempt to meet the
application’s load. After start-up the variable compressor
will ramp up to meet the DAT Setpoint. If the mechanical
heating capacity at the ambient conditions is capable of
meeting the building load the variable speed compressor will
stabilize at some value below its maximum speed. If the heat
pump’s capacity is insufficient at the ambient conditions the
supplemental (gas, electric, hot water) heat will be enabled and
gradually ramp/stage on to make up the capacity shortage.
If the combined capacity of the heat pump’s mechanical and
supplemental heating is greater than the building load the
supplemental supply will ramp/stage down. The unit will always
seek to operate with mechanical heating as much as possible.
Periodically during heating operations the unit will need to
enter defrost to remove frost build up from the outdoor coil.
During defrost mechanical heating will be unavailable and the
supplemental heat will ramp/stage up to meet the DAT set-point.
Defrost
(DPS 003–015 ton)
Defrost is a temporary and infrequent period during normal
heating operations on Rebel heat pumps. The purpose of
defrost is to remove frost that has built up on the outdoor coil
during mechanical heating. In heating mode the outdoor coil
acts as an evaporator to “pull” heat out of the ambient air. As a
result the surface temperature of the outdoor coil is below the
ambient temperature and depending on conditions maybe below
freezing. During prolonged mechanical heating while the surface
temperature of the outdoor coil is below 32ºF frost will form.
The defrost operation is similar to mechanical cooling. In defrost
the four way valve will de-energize and the hot gas from the
compressor will be forced into the outdoor coil, rejecting heating
to the ambient, and melting any frost formed on the coil. To
speed up the melting process during a defrost cycle the OA
damper will close and the outdoor fan will de-energize. During
this period the supplemental (gas, electric, hot water) heat will
ramp/stage up to maintain the unit’s DAT Setpoint.
Rebel heat pump unit’s have demand based defrost control
and will operate in defrost only as long as necessary to remove
frost from the outdoor coil.
Charging
Rebel units have advanced charge management systems
that obsolete many common techniques for determining
over or under charged conditions. The charge management
system means that super heat and subcooling values will
float to achieve the peak real time energy efficiency possible
at current operating conditions (building load and ambient
temperature). Rebel units also use electronic expansion valves
that can not be adjusted manually. Refrigerant should never
be added or removed from the system based on the desire to
achieve an arbitrary subcooling value. It will always be Daikin's
recommendation that unit’s suspected of being over/under
charged have all of their refrigerant removed, leak tested with
nitrogen, and then re-charged based on the unit name plate.
Table 9: Refrigerant Charge
Unit Size
Cooling Model
Heat Pump Model
Standard Unit Standard Unit
w/ MHGRH
Standard Unit Standard Unit
w/ MHGRH
3C
10 .5
12 .9
12 .0
14 .4
3M
6 .6
11 .3
4C
11 .1
13 .5
12 .6
15 .0
4M
6 .5
11 .3
5
15 .3
18 .2
16 .8
19 .7
6
15 .3
18 .2
16 .8
19 .7
7 .5
11 .1
17 .8
26 .0
31 .2
10
20 .0
25 .8
40 .0
45 .8
12
20 .0
25 .8
40 .0
45 .8
15
24 .4
30 .2
46 .0
51 .8
3C & 4C with fin tube outdoor coils
3M & 4M with micro-channel outdoor coils
IM 1125-7 • REBEL ROOFTOPS
26
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Содержание Rebel DPS003A
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