Catalogue

10 WSHP-PRC020D-EN
Application Considerations
Note: Pressure ratings for risers are typically greater than the maximum pressure rating of the
coaxial water-to-refrigerant heat exchangers.This is true with exception ofType M copper
in a 3" diameter.The maximum pressure rating forType M, 3" diameter copper is 380 psig.
All other diameters forType M copper, and all 1" through 3"Type L copper are greater than
the 400 psig rating on the coaxial water-to-refrigerant heat exchanger.
Riser Sizing
The proper selection of riser diameter is critical when designing a cost effective job. If the riser
diameter is too small, the flow of water to the heat pump may be restricted, making the pumping
power requirement excessive. On the other hand, if the riser diameter is too large, the cost of the
equipment may become unnecessarily high.
To determine the riser size, calculate the flow at a particular riser. Riser columns will begin with
large diameters at the bottom of the column and decrease diameter as the water travels up toward
the top floor.The GPM at the first floor is determined by totaling the GPM of all the units on the
riser column.The GPM for the second floor is then determined by taking the total GPM and
subtracting the flow from the first floor.
The proper size of the riser is determined by calculating the velocity of the water in the riser.The
maximum water velocity that a riser should experience is about 6 or 7 feet/second. Table 2, p. 10
can be used as a quick reference chart for determining the maximum GPM allowed for a given riser
size. Riser flow diagram can be found in the
2009 ASHRAE Fundamentals Handbook and may be
used to calculate the precise water velocity for a given riser diameter and flow.
Note: Table 2, p. 10 is for general design calculation reference. It is not intended to take the place
of an engineered piping design.
Type M (standard)
Riser Size (in.) I.D. (in.) O.D. (in.) Copper Wall Thickness (in.)
1½ 1.527 1.625 0.049
2 2.009 2.125 0.058
2½ 2.495 2.625 0.065
3 2.981 3.125 0.072
Table 2. Maximum riser flow rate
Riser Size (in.) Max. GPM Water Velocity (ft./sec.) Head Loss (ft.100 ft.)
1 16 6.2 15.6
1¼ 24 6.1 11.8
1½ 34 6.1 9.38
2 58 6.0 6.6
2½ 90 6.0 5.1
3 130 6.1 4.2
Table 1. Riser characteristics (continued)