Layout of the hot water distribution system that establishes venting of trapped air through the plumbing fixtures above-whether up-feed, down-feed or up- and down-feed system configurations-can be the most important factor in avoiding balancing and adjustment problems during initial system commissioning. This arrangement has been shown to be much less problematic than systems where the return pipe is above the highest plumbing fixtures as a vertical extension of the hot water distribution riser. The air is then vented out of the plumbing fixtures above with each use of the fixtures. Distribution layouts that establish the connection of the return pipe to the hot water distribution riser at the floor below the highest plumbing fixtures allow air to bypass the return system connection to the riser.
This reduces andĮventually prevents adequate return circulation flow rates from occurring. Location of the return pump on a nonresidential floor, preferably with other mechanical equipment, to conceal objectionable noise.Ī major cause of poor performance in hot water return systems is “air binding,” caused when air released from the heated water rises and collects at the top of a zone.Control of flow rates and direction with gauge-reading flow control devices and check valves at each connection of a return pipe to a hot water distribution riser.Correct sizing of return pump and return piping to avoid velocity erosion in piping.Provisions for effective air removal at the top of each zone. ’04 PME article, “Design Considerations for Pressure Reducing Valve Stations In Domestic Water Systems,” has been shown to be effective in many working installations and has become the standard practice in many marketplaces for the mentioned design conditions.ĭesigners and engineers may enhance the effectiveness of this means of justifying the pressure differential between multiple distribution zones into a central riser, with thoughtful distribution system layouts that include: The problem here is to “centralize” returns from zones with different pressures back to the water heating equipment at the roof. Longevity of the water heating equipment is increased by the reduction of the operating pressure at the equipment, from near 150 psi for a basement location to approximately 25 psi for a roof location.īuildings that require multiple water pressure zones to limit useable water pressure at plumbing fixtures to the code-required maximums, and that also require circulated return systems from domestic hot water distribution risers, present a unique design challenge.Gas pipe is cheaper and smaller in diameter than flue pipe, returning square footage to the architectural floor plans and providing a construction cost savings.Therefore, a rooftop location for the equipment offers many long-term economic and design benefits.
When natural gas is the preferred source of energy for domestic water heating in high-rise buildings, the static pressure of the proposed hot water distribution system will exceed the maximum relief valve pressure setting of 150 psi for the listed T&Ps required at the water heating equipment. Locating water heating equipment on the roof of a high-rise helps increase its longevity, but it can be a challenge for the designer.
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