Catalogue

WSHP-PRC020D-EN 11
Application Considerations
Central Plant Control
Proper central plant control is critical to the operation of a water-source heat pump system. Loss
of waterflow or loop temperatures outside of the recommended range will severely impact the
operation of the equipment.The following should be followed as minimum operational
recommendation for the central plant:
• Heat rejector control (i.e. closed circuit cooling tower, or geothermal loop)
• Heat adder (i.e. boiler or geothermal loop)
• Circulating pumps
• Sensing elements
Riser Size Example
Assume a six story building is served by a high-rise water-source
heat pump. When referencing the catalog, determine each high-
rise heat pump uses 3 gallons per minute to meet the required
capacity of the 1-ton unit. What is the minimum riser diameter
that can be used on each floor?
With this arrangement, determine the volume of water used at
each floor is 3 GPM.The top floor riser therefore only needs to
be sized for 3 GPM. Referring to Table 2, p. 10, we know that a 1-
inch type M riser can handle up to 16 GPM, therefore the riser
size is determined to be 1-inch.
The first floor will see 18 GPM through the riser. Since 18 GPM
will result in more than 6 ft./second in a 1” riser, it would be
advisable to move to a 1¼” riser.
Piping Layout of the Riser
Two methods may be used when piping a riser column.These
include direct return or reverse return.
Advantages may be seen in both types of piping methods. For
a direct return installation, the riser system is straightforward
leaving little confusion about properly sized risers.This provides
a more cost effective advantage during the installation process.
The disadvantages of this system is the pressure drop.The total
pressure drop on the unit for the sixth floor is much greater than
the total pressure drop on the unit for the first floor.This means
that the riser column will require balancing from floor-to-floor
during installation.
Piping advantages for the reverse return system include the
ability to design the riser column so that the total system
pressure drop through each unit is equalized.The overall
pressure drop is also lower, allowing some energy savings
potential.This piping method however does not eliminate the
need for proper balancing at each unit.
The disadvantage of this system relates to cost and complexity.
The reverse return method typically costs more because of the
additional pipe required for each riser column.