Tank Loading - Bosch Greentherm T9800 SEC 160/199 Applications Manual

Application Manual

4.4 Tank loading

Tank loading pairs tankless water heaters with storage tanks to maximize peak fl ow
for high demand applications. A tank load system, because of the added storage, can
provide a high peak fl ow with fewer tankless units and lower installed cost.
Tank loading is recommend for high cycle applications such as commercial kitchens with
hand sprayers.
These guidelines should be followed to maximize system output:

Ensure flow through each water heater is between 3.5-5.0 gpm. See
recommended pump models in application section of this manual.

For best performance, plumb the system or configure the tank to draw cold
supply water into the water heater during hot water use.

Maintain a 20 degree temperature difference between tankless set-point
and desired tank temperature.

Do not use a cascading kit in a tank loading application.

When multiple tankless water heaters are used, the total equivalent length
of piping to each unit should be kept roughly equal. A reverse return piping
scheme is recommended to equalize flow through each water heater.

For tank temperature settings above 120°F, the Bosch commercial model
should be used.
Recirculation Loop Pressure Drop at 2GPM (Feet of Head)
Material 10ft Pipe
¾" Type L Copper 0.48
1" Type L Copper 0.14
1.25" Type L Copper 0.06
1.5" Type L Copper 0.03
2" Type L Copper 0.01
Table 5 Source: 2009 International Plumbing Code
Wiring Detail for Tankloading Application
Accessory:
External NTC Kit
(part# 7 736 504 583)
or
Aquastat Connector
(part# 7 736 504 584
Bosch Thermotechnology Corp. | 06.2017
90° Elbow 45° Elbow Tee Branch
0.1 0.03 0.15
0.04 0.02 0.07
0.02 0.01 0.04
<0.01
0.01 0.02
<0.01 <0.01 0.01
Accessory:
Recirculation Pump Kit
(part# 7 736 504 585)
Wire pump line voltage
to terminal block of
accessory cable
Route wiring thru
cable grommets
To NTC sensor or
aquastat in tank
Pressure drop vs. fl ow
# of units T9800 SE 160
1 20 feet of head @ 4gpm
2 20 feet of head @ 8gpm
3 20 feet of head @ 12gpm
4 20 feet of head @ 16gpm
5 20 feet of head @ 20gpm
6 20 feet of head @ 24gpm
7 20 feet of head @ 28gpm
8 20 feet of head @ 32gpm
9 20 feet of head @ 36gpm
10 20 feet of head @ 40gpm
Table 6
EXAMPLE:
Sizing a pump for a 4GPM tank loading DHW system with a T 9800 SE 199 and a 20
ft total loop length.
Head Loss Loop Component
22.00 ft T 9800 SE 199 (See Fig.2)
1.00 ft 20 ft of ¾ copper
0.80 ft 8 x ¾" 90 elbows
+ 0.30 ft 2 x ¾" Tees (branch)
24.1ft Minimum Pump Head at 4.0 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
5 amp
fuse
Greentherm T9800 SE(C) 160/199 | 13
T9800 SE 199
21 feet of head @ 4gpm
21 feet of head @ 8gpm
21 feet of head @ 12gpm
21 feet of head @ 16gpm
21 feet of head @ 20gpm
21 feet of head @ 24gpm
21 feet of head @ 28gpm
21 feet of head @ 32gpm
21 feet of head @ 36gpm
21 feet of head @ 40gpm
Tankless unit
outer cover
Tank loading
pump
Data subject to change