User Guide

Plumbing Design Assistance Manual l Chapter 5 – System design and layout l 55
Hot-water system
design
Uponor AquaPEX piping
is tested and listed to PEX
5106 NSF-pw (CL5). Per
ASTM F876, the CL5 chlorine
resistance rating is intended
for an end-use condition of
100 percent at 140°F/60°C,
which is the highest chlorine-
resistance rating available
through ASTM. Products
marked with a '5' in the rst
digit of the four-digit code
and also bearing the CL5
designation [e.g., PEX 5106
NSF-pw (CL5)] indicate the
product is approved for use
in continuous, domestic,
hot-water circulation systems
with up to 140°F/60°C water
temperatures.
Recirculated
hot-water systems
To maintain satisfactory
temperatures, hot-water
systems are often recirculated.
Several recirculating methods
are available:
• Manual control — Should
be used only when hot water
is needed 24 hours a day. If
that is not the case, manual
control is not cost-effective.
• Thermostatic aquastat —
Used to shut off the pump
during peak demands of hot
water when circulation is not
needed.
• Timed — Utilized during
specic hours of operation
when people are most likely
to use hot-water xtures.
• Combination aquastat/
timed — Combines
the capabilities of the
aquastat system with timed
control, reducing energy
consumption.
Uponor AquaPEX is rated for
use in continuous-circulation
domestic-water systems
with temperatures up to
140°F/60°C.
Sizing and maximum
velocity
Uponor requires that the
velocity of the dedicated
recirculation piping shall not
exceed 2 ft./sec. and that the
hot-water piping system (which
includes the recirculation
lines) meets the following
requirements stated in the
ASPE Plumbing Engineering
Design Handbook, Volume 2,
Plumbing Systems:
1. Calculate the heat loss
rates of the hot-water
supply piping.
2. Calculate the heat loss
rates of the hot-water
circulating piping.
3. Calculate the circulation
rates for all parts of the
circulating piping and
the total circulation rate
required.
4. Determine the allowable
uniform friction head loss
and the total head required
to overcome friction losses
in the piping when the water
is owing at the required
circulation rate.
5. Calculate the rates of ow
for various piping sizes
that will give the uniform
pressure drop established
in Step 4, and tabulate the
results.
6. Size the system based
upon the tabulation set
up in Step 5.
7. With the sizes established
in Step 6, repeat Steps 2
through 6 as a check on
the assumptions made.
While Uponor recommends
the more accurate process
above, the following
streamlined method is also
available:
1. Allow ½ gpm for each small
hot-water riser (¾" to 1"), 1
gpm for each medium-sized
hot-water riser (1¼" to 1½"),
and 2 gpm for each large-
sized hot-water riser
(2" and larger).
2. Add 1 gpm for each group
of 20 hot-water-supplied
xtures.
Balancing of
recirculated hot-water
systems
Circulated hot-water
systems require balancing to
maintain satisfactory system
temperatures. If systems
are not properly balanced,
circulated water has the
tendency to short circuit
through the shortest loop in
the system, thus creating
high velocities in that loop
and resulting in hot water
delays to remote loops.
Hot-water recirculated lines
should be insulated, and they
typically require little ow to
maintain satisfactory system
temperatures. Uponor limits
maximum velocity to 2 ft./sec.
in dedicated hot-water return
piping using Uponor AquaPEX
(see Table 5-8).
For system balancing, use
calibrated devices such
as balancing valves. Each
balancing valve requires a
check valve, either in-line or
incorporated into the balancing
valve assembly, to prevent
reverse ow.
Nominal
pipe size
Velocity
(ft./sec.)
Flow rate
(gpm)
Friction loss per
foot at 120ºF/48.9ºC
½" 2 1.1 0.0195
¾" 2 2.2 0.0126
1" 2 3.6 0.0092
1¼" 2 5.4 0.0072
1½" 2 7.5 0.0059
2" 2 12.9 0.0042
2½" 2 19.8 0.0033
3" 2 28.1 0.0026
Table 5-8: Uponor AquaPEX ow rates at 2 ft./sec.