18
G e o t h e r m a l H e a t i n g a n d C o o l i n g
Trilogy
®
Variable
(VE) Series IOM - 60Hz HFC-410A
C r e a t e d : 4 O c t o b e r, 2 0 1 9
Multiple Unit Piping and Flushing
Often projects require more than one heat pump. Where
possible, it makes sense for multiple units to share a common
ground loop. Common ground loops for multiple units bring
new challenges including the need to avoid backward flow
through inactive units, increased pumping requirements,
and more complex flushing needs. Below are guidelines for
multiple unit piping and flushing on a common loop.
Units equipped with an internal flow controller (vFlow
™
)
include an internal variable speed circulator controlled by
the EXM microprocessor, internal 3-way flushing valves and
an internal bladder type expansion tank. The internal pump
includes an internal check valve. The pump curves for the
internal circulator are shown in Figures 13a and 13b. The
internal expansion tank will operate as a pressure battery
for the geothermal system. It will absorb fluid from the loop
when loop pressure rises and inject fluid into the loop when
loop pressure falls. In this way the expansion tank will help
to maintain a more constant loop pressure and avoid flat
loops due to seasonal pressure changes in the loop.
When using the internal variable speed pump as the loop
pump in multiple unit installations it is important to ensure
that the variable speed pump can provide adequate flow
through the heat pump against the loop head when all units
are operating.
It may be possible to flush a multiple unit system through
the unit’s flushing valves. Flushing pressure drop of the
valve may be calculated to determine if it is acceptable.
Engineering data for the 3-way flushing valves can be found
in Table 2.
for flushing, we will have to flush with a minimum of 4 circuits
x 4 gpm/circuit = 16 gpm total. A check of other piping sizes
used must be done to ensure that 16 gpm total flow will flush
all piping.
Pressure drop through the flushing valve can be calculated
using the following formula.
ΔP = (GPM/Cv)
2
where,
ΔP = pressure drop in psi through the valve while flushing
GPM = flushing flow in gallons per minute
Cv = valve Cv in flushing mode
We know from Table 2 that the Cv for the flushing valve in a
VE0930 is 10.3 in the flushing mode (90° flow). Therefore,
ΔP = (GPM/Cv)
2
= (16/10.3)
2
= 2.4 psi per valve (there are
two flushing valves). So long as the flushing pump is able to
provide 16 gpm at the flushing pressure drop of the loop plus
the 2.4 x 2 valves = 4.8 psi (11 ft of hd) of the flushing valves,
the internal flushing valves may be used. If the flushing
pump is not able to overcome the pressure drop of the
internal flushing valves, then larger external flushing valves
must be used.
Unit Configuration
Multiple vFlow
™
units with internal variable-speed flow
controller and check valve, piped in parallel sharing a
common loop MUST be properly configured. Use the iGate
™
Connect thermostat to configure the loop.
Note: An access
code is required to enter the Installation Settings menu
from the iGate Connect thermostat. The access code
is 4795.
It must be entered using the arrow keys on the
thermostat to select each number and the OK button to enter
each one.
Go to MAIN MENU>SETTINGS>INSTALLATION
SETTINGS>EQUIPMENT>UNIT CONFIG>LOOP
CONFIG to ensure the unit is configured for a variable
speed internal pump (VS Pump). Then, to configure
the unit for multiple units on a single loop go to MAIN
MENU>SETTINGS>INSTALLATION SETTINGS>
EQUIPMENT>LOOP PUMP CONFIG>LOOP OPTION and
select ‘Parallel’. This will set the unit to use special control
logic for parallel units on a common ground loop.
For example, if a system includes two VE0930 units and four
¾ loop circuits we can calculate the flushing pressure drop as
follows. From Table 1 we know that it will take 4 gpm to flush
each ¾” circuit. If there is no provision to isolate the circuits
Table 2: Internal 3-Way Flushing Valve Data
Model
Inlet Flushing
Valve
Outlet Flushing
Valve
VE*0930
3/4" FPT
3/4” MPT
VE*1860
3/4” FPT
1” MPT
Valve Size
Straight Flow
(Normal Operation) Cv
90° Flow
(Flushing) Cv
¾”
25
10.3
1”
58
14.5
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CAUTION!
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CAUTION!
Never exceed a pressure of 100 psig or a flow
rate of 30 gpm in a Trilogy unit. Pressure greater than 100
psig or flow rates greater than 30 gpm will damage the unit
sensors causing the unit to miscommunicate certain data
points and may cause the unit to nuisance fault.
Pump Settings
Loop Option Single
Heating Delta T 7.0º F
Cooling Delta T 10.0º F
Source Anti-Freeze No
Figure 16: Thermostat Screen - Pump Settings
