Quick Select High Rise Fan Coil Riser Selection How-To June 2010 UNT-PRC015-EN
Introduction The purpose of this manual is to aid in the selection and pricing of water pipe risers for high rise fan coils. Because of the volatility in copper cost, the proper selection of riser diameter is critical to designing a cost effective job. If the riser diameter is too small, the water velocity through the riser pipe may cause excessive water pressure drop due to friction loss and/or erosion of the pipe.
Table of Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 General Information on Riser Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Know the Riser Design—Design Return versus Reverse Return . . . . . . . . . . . . . 6 Riser Selection and Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Riser Connections . . . . . . . . . . . .
General Information on Riser Systems The riser is a vertical pipe system, usually copper, that carries the chilled water and hot water supply and return and coil condensate to and from a fan coil air handler. Other materials can be used, but copper pipe is desirable due to its light weight, ease of installation, widespread availability, durability and reasonable cost. Riser systems are installed in multi-story buildings where high rise fan coil units are installed floor-by-floor on top of each other.
General Information on Riser Systems Hot water, cold water, and condensate risers are factory insulated to avoid condensation and/or heat loss. Factory insulation is recommended to minimize installation costs and assure quality control on the insulation application. Two-pipe and four-pipe riser systems are available. Two-pipe risers provide pipes for hot or chilled water supply and return only, but not both hot and chilled water simultaneously.
Know the Riser Design—Design Return versus Reverse Return There are two typical methods used for piping a riser column: Direct return is the most common/popular method. Advantages of this system are: • It is cost-effective and simple. • Straightforward installation. • Very little confusion about properly sizing the risers. Disadvantages of this system are: • The pressure drop is not equal at each unit on the column. A means of balancing water flows at each floor must be provided.
Know the Riser Design—Design Return versus Reverse Return • Higher cost and complexity—An additional riser pipe is required for each riser column (one additional pipe for a 2-pipe system and two additional pipes for a 4-pipe system). • There is additional complexity with the riser design and installation: – The supply-side risers will begin with the larger diameter riser at the bottom of the column and the smaller diameter riser at the top.
Riser Selection and Sizing • Determine gpm through the riser pipes. Total the flow rates (gpms) of all units on the riser column. Individual units’ flow rates are determined by their specific selection. Direct-return riser columns begin with the largest diameter riser pipe carrying the most gpm at the bottom of the column. As water is diverted out of a riser into a fan coil, water volume is subtracted and riser pipe diameters will decrease (within specified velocity limits).
Riser Selection and Sizing Actual project velocity limits may be different than these based on the type of service or annual operating hours or other guidelines as defined in job specifications.
Riser Connections Each branch run-out in the coil section must be centered in the expansion slot on the side or back panel before joining risers. Risers are coupled/connected together with a swaged connection. (A swage connection might be referred to as a ”bell” connection also.) The swage or bell is the expanded portion of the riser pipe where an adjoining pipe of nominal diameter is inserted. A riser can be swaged on the top or bottom.
Riser Connections An alternate to swage and braze connections is a compression-coupling system like the Viega ProPress® system (see www.viega-na.com). This system eliminates the need for swage connections and brazing. It provides for quick, secure, leak-free connections on riser systems. Check with local suppliers, contractors and plumbing codes for suitability on a job site.
Expansion Compensation Do not rigidly fasten the risers within each unit. They must be free to move within the pipe chase with normal vertical expansion and contraction movements. The built-in risers must be anchored at some point to the building structure by the installing contractor. The unit design will accommodate up to 1-1/8 inch expansion and contraction (2-1/4 inch total movement) of the riser assemblies.
Determining Riser Length The required riser length is determined by knowing the floor-to-floor height of the building and adding the length of the riser that fits into the swaged connection. When a unit is ordered, the riser length and the desired vertical location of the riser on the unit must be specified. The positioning of the riser is important. This determines the location along the building structure or in-between floors where the riser brazing joints will be made.
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