18
G e o t h e r m a l H e a t i n g a n d Co o l i n g
Tranquility
®
30 Digital (TE) Series IOM - 60Hz HFC-410A
R e v. : O c t o b e r 5 , 2 0 2 1
Multiple Unit Piping and Flushing
Figure 16a: Multiple Units with Internal Flow Controllers
Multiple Units with Internal Flow Controllers
The simplest multiple unit system is one with two (or more) units utilizing internal Flow Controllers with no external pumps
or flushing valves. In this case the units are piped in parallel and use the internal flushing valves to flush the system. The
variable speed pump includes an internal check valve to prevent back (short circuiting) flow through the units.
In this case, flush the loop through the internal flushing valves in the unit farthest from the loop first. Once the loop is flushed,
then change the internal flushing valves to flush the heat pump. Next, move the flushing cart to the next closest unit to the
loop.
Again, flush the loop through the internal flushing valves. This is important as there may be air/debris in the lines from this unit
to the common piping. Once flushing begins the air will be move into the loop and will need to be flushed out. After the loop
is flushed through the second unit, change the flushing valves to flush the second unit. This process should be repeated for
additional units working from the farthest from the loop to the closest to the loop.
This type of application can generally be employed for systems to 12 tons depending on loop design. However, it is important
perform appropriate calculations to confirm that the variable speed pump can provide adequate flow through all heat pumps
against the loop head when all units are operating.
Multiple Units with Internal Flow Controllers and External Flushing Valves
When the number of units or flushing requirements reaches a point where it is no longer feasible to flush through the internal
valves (generally systems of more than 12 tons depending on loop design), external flushing valves should be installed. In this
case, three-way flushing valves should be used or additional isolation valves must be installed to be able to isolate the loop
during flushing.
First, flush the ground loop. The installer should close the indoor loop shut-off valve (or the internal flushing valves in all units)
and open the ground loop shut-off valve to prevent flow through the indoor loop while flushing the ground loop.
Once the ground loop is flushed, close the ground loop shut-off valve and open the indoor loop valve(s) to flush the units and
indoor piping. Remember that there is an internal check valve in the variable speed pump and that backward flow the unit is
not possible.
Multiple Units with Internal Flow Controllers
Water Out
Water In
Heat Pump
B
Water Out
Water In
Heat Pump
A
To Ground
Loop
Size for Heat Pump
‘A’ Flow
Size for Heat Pump
‘B’ Flow
Size for ‘A’ + ‘B’ Flow
