PLUS LINE
A7 Recirculation and heat tracing
Maintaining domestic water temperature in the supply piping
Two options are available to maintain supply temperature available at or near the fixtures on storage water heating systems:
·Recirculation
Recirculation is used to reduce wait time for water use, to minimize hot water and energy waste caused during the waiting period, and to prevent degradation of the system supply water temperature. ASPE recommends recirculation when the distance from the water heater to the furthest fixture exceeds 100 feet or the time lag for hot water to reach a fixture(s) exceeds 30 seconds. Consult local codes and American Society of Plumbing Engineers (ASPE) Domestic Water Heating Design Manual, 1998, for further information.
·Self-regulating heat tracing
Time delay at fixtures
Table 2 is from the ASPE Domestic Water Heating Design Manual, 1998. It shows the time required for usable hot water to arrive at a fixture based on the fixture flow rate (available from industry and manufacturer’s data) and the length and diameter of the
You can use Table 2 as a guide to determining the location of circula- tion return lines relative to fixtures.
These branches must be balanced to prevent pipe ero- sion and unacceptable time delays at some fixtures.
Balancing options include circuit setters, memory stop valves or factory preset devices (with flow metering provision in the piping).
Components required
For residential applications, consult pump manufactur- er’s data for pump selection and additional components required.
On most commercial systems, install the devices shown in Figure 9, page 23, and any other devices or piping methods required by local codes. The check valves are required to prevent fixtures from taking hot water through the return lines. Shutoff valves are needed to allow cleaning and replacing balancing devices. Include strainers to remove sediment which could damage the pump and/or affect the flow balancing devices.
Size the pump and piping based on the temperature drop allowed between the water available at the water heater and the water delivered at the fixture. The return piping will almost always be smaller than the supply piping, but should never be smaller than ½” to prevent problems with the pump.
Make provision for removal of air in all return lines. Where the returns cannot be vented by topmost fixtures in the system, install automatic air venting at the top of the return piping.
Balancing
When multiple branches are connected to the supply piping, each branch must be connected to the recirculation system. At each of these connec- tions to the return piping, install shutoff valves, a flow metering device, check valve and a strainer as shown in Figure 9 on page 23. Check local codes for specific installation requirements.
Connecting to the water heater
Install a recirculation dip tube in the AUX tapping on top of the water heater. This requires mounting the T&P relief valve as shown for Option 2 in the piping diagrams, pages 10 and 12. See Figure 10, page 23, for the piping required to the water heater.
Table 2
Time lag to obtain hot water at fixture for branch lengths of 10 and 25 feet
(ASPE Domestic Water Heating Design Manual)
Time in seconds required to get hot water at fixture (from ASPE)
Fixture flow rate (GPM) - |
|
| 0.5 |
| 1.5 |
| 2.5 |
| 4.0 | |
Piping length (feet) - |
| 10 | 25 | 10 | 25 | 10 | 25 | 10 | 25 | |
Copper pipe | ½" | 25 | 63 | 8 | 21 | 5 | 13 | 3 | 8 | |
|
| ¾" | 48 | 119 | 16 | 40 | 10 | 24 | 6 | 15 |
Steel pipe | ½" | 63 | 157 | 21 | 52 | 13 | 31 | 8 | 20 | |
|
| ¾" | 91 | 228 | 30 | 76 | 18 | 46 | 11 | 28 |
CPVC pipe | ½" | 64 | 159 | 21 | 53 | 13 | 62 | 8 | 20 | |
|
| ¾" | 95 | 238 | 32 | 79 | 19 | 48 | 12 | 30 |
NOTE: Select branch size and length for less than 31 seconds delay.
22 | Part Number |
