A50-8331.eps, Framing Rough-In Detail

The direct return system shows the most common piping ar- rangement. This is the most cost effective method of piping to install since the water is supplied and returned to a riser column at the same place, at the bottom or top of the building. Howev- er, this type of system requires more effort to individually bal- ance water flow to the units. The risers are normally capped at the ends opposite the main supply and return piping and may require a field-installed flush and vent loop.

The first reverse return system shows a system, which is commonly used to minimize individual unit water flow balanc- ing and is often referred to as “self balancing.” This riser ar- rangement has a natural affinity to balance the flow to each unit in the riser column. However, individual unit balancing may still be required. This piping system is used on 2-pipe systems only and has an individual return for each riser column.

The second reverse return system shows a system with a common reverse return riser installed separately from the individual unit riser columns. This riser arrangement allows for more flexibility in individual unit riser sizing but has the same general characteristics as the “reverse return” system described above. It may also be a better fit for the particular structural and architectural requirements of the building. This piping system may also be used on 4-pipe systems.

Regardless of the system selected, optimum performance can only be achieved through adjustment to the recommended water flow at each individual unit (see Table 1 for individual unit water flow requirements).

RISER MATERIAL, SIZING, AND INSULATION — Some of the factors affecting riser application and sizing are noise, tube erosion and economics. Water source heat pumps maybe supplied with factory-installed risers; the riser material, diameter, length and insulation thickness must be determined for each unit based on its positioning within the building. Figure 8 displays riser tube diameter sizes as a function of flow (gpm), friction loss and water velocity. For maximum riser velocity on pressure drop per 100 ft, refer to ASHRAE (Amer- ican Society of Heating, Refrigeration, and Air Conditioning

Engineers) Fundamentals Handbook for Riser Sizing. Gener- ally, riser copper type, size, length and insulation thickness are determined by the location of the water source heat pump unit in the building. Chilled water and hot water risers are available in Type-M, Type-L copper, varying diameters from 3/4 to 21/2 in., and with either no insulation, 1/2 or 3/4 in. thick closed cell foam insulation. Condensate risers are available in Type-M copper, varying diameters from 3/4 to 11/4 in., and with no insulation, 1/2 or 3/4 in. thick closed cell foam insulation. All factory-supplied risers and riser extensions are insulated for the full length of the riser, eliminating the need for field insulation. Insulation is not required on loop water piping except where the piping runs through unheated areas, outside the building or when the loop water temperature is below the minimum expected dew point of the pipe ambient conditions. Insulation is required if loop water temperature drops below the dew point (insulation is required for the ground loop applications in most climates).

Riser sizing is generally based on the water flow require- ments of each unit and the units on higher and lower floors that tie into the same riser column depending on the piping system chosen. Water piping is often designed at approximately 5 ft/s. Keeping this in mind, risers can be reduced in size as the water flow decreases from floor to floor. For low-rise buildings, riser sizes can be of a single diameter.

The reduced material handling on site will often offset the extra costs associated with the larger risers.

RISER EXPANSION — Generally, in medium to high-rise buildings, allowances must be made for pipe expansion. In ap- plications supplemented with factory (or field) supplied be- tween the floor riser extensions, assemble and install exten- sions before installing cabinet.

NOTE: Riser assemblies are designed to accommodate a maximum of 11/8 in. expansion and contraction up to a total movement of 21/4 inches. If the total calculated rise expansion exceeds 21/4 in., expansion devices must be used (field provided).

TO ABOVE FLOOR