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Domestic Hot Water Circulation - Bosch Greentherm T9800 SEC 160/199 Applications Manual

Indoor residential and commercial tankless water heaters
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Application Manual

4.3 Domestic hot water circulation

If the Bosch tankless water heater provides the heat source for
recirculated water , the heat exchanger warranty is decreased. Please
refer to www.boschheatingandcooling.com for detailed warranty
period information.
Flow can be verified in the diagnostic menu. Refer to the Diagnostic Menu
section of your Greentherm installation manual for details.
System conditions vary and each pump must be sized by a
professional to insure performance.
Refer to pump manufacturers fl ow vs pressure specifi cations to select a pump
that can provide adequate fl ow while overcoming the pressure loss through the
Greentherm and the recirculation loop. Refer to fi gure 2 to determine pressure loss.
Use only bronze or stainless steel pumps. Do not use pumps of iron
construction as they will oxidize and clog the inlet fi lter on the
appliance.
When properly installed in a direct recirculation application the Greentherm
will regulate water temperature in a recirculation loop. A thermostatic mixing
valve should be used if your setpoint is greater than 120°F.
When the loop temperature is within 1.8°F degrees of setpoint the pump will
turn off.
When the loop temperature is 1.8°F degrees less than the setpoint the
pump will turn on.
Greentherm pump will also turn off after approximately 1 minute in cases
where there is no flow thru the recirculation loop such as when a crossover
valve is installed at the farthest fixture. Unit will check for flow after
approximately 4 minutes by operating the pump for 10 seconds in order to
determine if the crossover valve has reopened.
Bosch Thermotechnology Corp. | 06.2017
Wiring Detail
Accessory:
Recirculation Pump Kit
(part# 7 736 504 585)
Wire pump line voltage
to terminal block of
accessory cable
EXAMPLE:
Greentherm temperature setting: 120°F
Pump turn ON temperature </= 118°F
To minimize energy costs:
1.
Insulate all pipes in the recirculation loop.
2.
Use the scheduling menu in the Greentherm to deactivate the
recirc function when not needed (i.e. sleeping, at work...etc.)
Recirculation Loop Pressure Drop at 2GPM (Feet of Head)
Material
10ft Pipe
½" Type L Copper
¾" Type L Copper
¾" Pex
⅝" Pex
½" Pex
Table 4 Source: 2009 International Plumbing Code
For other desired gpm fl ow rates, please consult IPC for appropriate pressure drop.
EXAMPLE:
Sizing a pump for a 2gpm direct DHW recirc system with a GreenthermT 9800 SE
199 and have 150 ft total loop length.
Head Loss
Loop Component
9.00 ft
T 9800 SE 199 (See Fig.2, page 10)
1.20 ft
80 ft of ¾" copper
5.90 ft
70 ft of ½" copper return
0.24 ft
8 x ¾" 90 elbows
0.10 ft
2 x ¾" Tees (branch)
0.72 ft
8 x ½" 90 elbows
+ 0.18 ft
1 x ½" Tee (branch)
17.34 ft
Minimum Pump Head at 2.0 gpm
Once the loop head loss has been calculated, use the pump manufacturer's
performance curves to select the proper potable water circulator at the required fl ow
rate.
Accessory cable connects
to Tankless control board
Tankless unit
outer cover
5 amp
External recirculation
fuse
pump (field supplied)
Greentherm T9800 SE(C) 160/199 | 11
90° Elbow
45° Elbow
0.85
0.09
0.05
0.15
0.03
0.01
0.25
0.02
N/A
0.53
0.04
N/A
1.3
0.12
N/A
Data subject to change
Tee Branch
0.18
0.05
0.03
0.06
0.18

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