Domestic Hot Water Circulation; Tank Loading - Bosch GWH 715 ES Applications Manual

Bosch applications manual

5.2 Domestic hot water circulation

Must provide a recirculation flow above 1.7 GPM. This can be
verified in the control unit diagnostics section of the installation
manual; mode P4 – 3d.
Note: The Grundfos model 15-55 has been tested and shown to
work on recirculating systems up to 120 feet of total pipe length.
System conditions vary and each pump must be sized by a profes-
sional to insure performance.
Refer to pump manufacturers flow vs pressure specifications to
select a pump that can provide the flow rate greater than 1.7 gpm
while overcoming the pressure loss through:
• Tankless water heater (see Chapter 6.1)
• All building supply and return plumbing in the circulation loop
(reference local plumbing codes, standards, or practices)
System pressure drop
90 degree elbow
45 degree elbow
10 ft of straight pipe ½"
10 ft of straight pipe ¾"
Source: International Plumbing Code 2003 edition.
Examples:
1) Average house (less than 2500 square feet)
a) Total loop length approximately 120 ft
b) Pump recommendation: Grundfos UP 15-55 or equivalent.
2) Large house (2500 to 5000 square feet)
a) Total loop length approximately 240 ft
b) Pump recommendation: Grundfos UP 25-64 or equivalent.
NOTE: 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.
Recommendations for domestic hot water recirculation
An Aquastat, with a 5° F differential to control the pump, is
recommended.
The usage of a timer is recommended to limit the energy
consumption. The timer should also limit recirculation pump
operation to the time of day when occupants are home and likely
to use hot water.
Water heater set point must be minimum of 14° F above the
Aquastat setpoint.
Example: Tankless water heater setpoint = 122°F
Aquastat setpoint
Keep hot water piping insulated to limit heat loss.
Set temperature on the GWH 920 ESC must not exceed 140°F.
BOSCH THERMOTECHNOLOGY CORPORATION
Pressure drop ¾" copper (PSI)
0.088
0.053
1.3
0.35
= 108°F

5.3 Tank loading

# of Pressure drop vs. fl ow
heaters Models: C800ES,
C920ES, C920ESC
1 4gpm @ 40 feet of head
2 8gpm @ 40 feet of head
3 12gpm @ 40 feet of head
4 16gpm @ 40 feet of head
These guidelines should be followed to maximize system output:
•
Ensure fl ow through each water heater is between 3.5-5.0 gpm
•
Isolation valves or boiler drains should installed to facilitate
descaling in applications with hard water.
•
Whenever possible, plumb the system or confi gure the tank to
draw cold supply water into the water heater during hot water
use.
We recommend Grundfos UP26-99, Taco 009 or equivalent potable
water circulators.
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Table 2
Pressure drop vs. fl ow
Model: 715ES
4gpm @ 32 feet of head
8gpm @ 32 feet of head
12gpm @ 32 feet of head
16gpm @ 32 feet of head
Bosch applications manual | 06.2009