Enertech AV Series - Section 8: Controls; Sequence of Operations; Pump Start

Enertech Global, LLC 43
AV : MD/ME - Rev. A Models
Installaon and Operaons Manual

Idle
The system is o and waing for a call.
Pump Start
The load pump runs at maximum speed and the EEV
(Electronic Expansion Valve) opens completely to equalize the
system and prepare for the compressor to start. The diverng
valve and reversing valve move into posion accordingly.
The reversing valve is energized only in cooling.
The diverng valve is energized only in hot water heang.
This state runs for one minute to allow temperatures and
pressures to equalize and provide relevant sensor informaon.

This step is primarily a vericaon of condions.
If the pressures have not equalized, the system will not
connue to the running phase. Also, the system will verify that
the load temperature does not exceed the required target
temperature (see the next secon “Variable Speed Control”).
Compressor Start
The EEV moves to the starng posion and the compressor
starts at 2700 RPM (minimum speed 1650 RPM).
Run
The compressor modulates speed according to the required
load. The EEV modulates as needed to maintain 8°F superheat.
The pump modulates to maintain ΔT across the heat
exchangers. See the next secon, “Variable Speed Control”,
for more informaon.
Compressor Stop
Aer all calls have been sased, the compressor ramps down
gradually to zero RPM.
Pump Stop
The pump maintains its current speed for one minute as it
slowly ramps down to turn o.
Note: Zone controls must allow post purge aer a call to allow
the internal load pump to stop.
ASC
The an-short cycle mer prevents the compressor from
running for three minutes aer the unit has been shut down.
All calls will be held unl the ASC mer has expired. The three
minute ASC is in addion to the pump start and stop duraons
to provide an industry standard ve minute an-shortcycle of
the compressor.

• The compressor ramps down to the minimum speed, in
correlaon to the operang envelope, for 30-60 seconds.
The pump will slow down as compressor capacity ramps
down.
• The reversing valve is energized or de-energized if
switching from heang to cooling or cooling to heang. If
the system is switching from heang to hot water or hot
water to heang, the reversing valve does not change.
• The zone valves in the Indoor Module switch from the
hydronic load to the domesc hot water tank or the zone
valves switch from DHW to hydronic heang/cooling.
• Aer the valves have transioned, the system resumes to
its normal running mode where the pump, compressor,
and EEV modulate accordingly. Note that when switching
from DHW to cooling or cooling to DHW, the valves will
not switch to hydronic load or DHW tank if the leaving
load temperature is not within 20°F of the target
temperature. This approach eliminates hot water going
to a fan coil in cooling mode or chilled water going to the
DHW tank.
When the higher priority call is sased, and there is sll a call
holding, the system will transion back to the original call in
the same manner. The compressor is able to connue running
and thus no ASC delay is experienced.
Variable Speed Control
The use of the variable speed compressor and pump includes
advanced control algorithms to match the load demand of
the space. The control described here takes place during the
“Run” poron in the system sequence of operaon described
in the previous secon.
Compressor
Control of the compressor is based on the target temperature
of the system. The system monitors the current load out
temperature and compares to the target temperature. Using
the control algorithm, the system seeks to maintain the exact
target temperature. Outlet temperature above or below
the target temperature causes the compressor to throle
faster or slower as needed. In radiant oor heang, with an
outdoor thermistor, the outdoor reset dictates the targeted
load temperature. In cooling and hot water, the stac menu
sengs control the target temperature.
This control allows the system to react to changing condions.
As zone valves open and close, the compressor speed is
adjusted to meet the current demand.
In some small load situaons, such as very small radiant
zones, the system may not be able to run slow enough to
avoid thermal runaway. To accommodate this situaon, the
compressor can shut down when the load outlet temperature
over/under shoots its target by 3°F. During this me, the
pump will connue to circulate and the So Idle mer is
started.
The compressor will be cycled on again when the So Idle
mer expires AND the outlet temperature has dropped below
the target temperature. All priories are sll obeyed during
this me. If the call becomes sased the system will shut
down normally.
Note: It is recommended to size zones in order to avoid this
cycling condion. It is preferred to avoid compressor cycling
and improve eciency.
Pump
When the pump is in “auto” mode, it controls to maintain
ΔT (Default 5°F) across the heat exchangers. To do so, load
entering and leaving temperatures are connually monitored.
A sensed ΔT above the 5°F setpoint will cause the pump to run
faster. Below the setpoint causes the pump to run slower –
down to the set minimum speed.
Note: If, aer setup, the EME/EMD detects the minimum
ow rate of less than 5.0 GPM, it will aempt to increase the
minimum ow percentage unl 5.0 GPM is achieved.
Secon 8: Controls