High-rise buildings present MEP engineers with a number of design considerations and challenges that are neither commonly addressed nor given formal guidelines for resolution. The design of efficient and reliable plumbing systems in high-rise structures requires careful awareness of water pressure issues, water access logistics, heater efficiency, drainage problems, vent stack problems, and a myriad of other maintenance concerns. By taking the size of these buildings into account, understanding the constraints imposed by gravity, and being aware of established plumbing design principles, any MEP engineer can tackle the numerous challenges that these formidable buildings present.
Low Water Pressure
Low water pressure issues can derive from a number of sources. At times, low pressure may be attributable to an insufficient municipal water supply; in such instances, it is necessary to implement a pressure-boosting system to compensate. Nonetheless, internal plumbing problems may be the cause of water pressure issues in situations where the supply pressure is verified to be adequate. Keep in mind that unnecessarily implementing a booster pump in situations where insufficient pressure is due to internal piping issues incurs unnecessary energy costs; in addition, it may result in excessive water pressure that may damage valves, pipes, and any number of other elements in a plumbing system. Fixing the system is preferable to bandaging it with a booster pump.
Clogged pipes are often the culprit in causing low water pressure in old installations.
There may or may not be external and obvious damage to the installation, only performance assessments can assuredly diagnose a blocked pipe issue. If the damage is not extensive, the piping may be refurbished and reused, otherwise, it may need to be replaced. In addition to clogged pipes, insufficiently-sized piping and valve malfunctions may also cause flow and pressure restriction.
Water Access Logistics
High-rises are large, tall structures with internal plumbing systems that, to be in compliance with established building codes, must overcome the downward force of gravity and provide water throughout a building, top to bottom. Plumbing in tall buildings requires high pressure-rated pipes to deal with the greater water pressure that these systems require to properly function. MEP engineers must consider the minimum required pressure for piping on the top floor of a pressure zone and ensure that aforesaid fixtures can adequately maintain pressure throughout peak flow periods.
Optimal design for a high-rise plumbing system uses a different booster pump for each pressure zone. Each pressure zone, depending on floor-to-floor distance, may span around 10 floors. The top floor of the pressure zone must meet some minimum pressure requirement while the bottom floor of the zone is its most pressurized point, it is either at or below 80 PSI (the maximum allowed by New York building codes). A distributed booster pump set up is more efficient than a design that utilizes a single pump package at the base of a building, which is mediated by pressure-reducing valves (to mitigate pressure on the lower floors); such designs needlessly waste energy.
Water Heater Efficiency
The efficiency of a water heater system does not necessarily correspond with optimal cost-savings; regional energy price differences are more influential on water heating costs than individual design nuances. In some areas, such as New York, natural gas rates are far cheaper than electricity, rendering a natural gas solution far more attractive than an efficient electrical heating system. However, electrical heating systems in New York can potentially achieve near cost-parity with natural gas systems if they are sufficiently optimized. This can be accomplished with electrical heat pumps that can have a coefficient of performance (COP) of 2.5 or more, which is a significant improvement over conventional heating systems which have a COP of 1. Efficiency improvements can be coupled with renewables to further drive cost reduction to such an extent that, even in a high-rate region like New York, electrical heating solutions can be substantially cheaper than natural gas.
Drainage and Venting Issues
Drainage and venting issues in high-rise structures are essentially scaled-up variants of general plumbing problems that beset most modern buildings. The air provided by venting systems enables fluid to move down drainpipes and avoid generating negative pressure zones as a result of waste material movement. Negative pressure can emerge in drainage systems as a result of defective venting systems, usually the result of blocked or damaged vent stacks. The impact of air fluctuations on drainage systems can be managed with relief vents, yoke vents, and vent connections at stack bases.
General Maintenance Issues
A notable maintenance issue for plumbing systems is the maintenance staff itself. Knowledgable and capable staff should be hired to maintain these delicate and expensive systems; the cost of recklessness is both high and easily-avoidable. In lieu of staff with domain-expertise, employers should invest in training their inexperienced staff in order for them to understand and properly deal with plumbing troubleshooting issues; doing so will save a great deal of money down the line.
Another common maintenance dilemma is improper booster pump start-up after prolonged power failure. If there is a power outage and tenants are able to continue to draw water from the piping system, there is a risk that the domestic booster pumps will start up with an empty water riser, resulting in blown-up pipes; the booster pumps should be shut down in such instances. This lends further credence to the point that knowledgable, well-trained maintenance staff is essential for the upkeep of plumbing systems, especially for demanding high-rise structures.
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High-rises are imposing structures that are comprised of many interlocking mechanical systems, and their occupants expect these systems to function properly on a daily basis. These structures pose a multitude of maintenance and design challenges such as water pressure troubleshooting, water distribution logistics, heater efficiency, drain-waste-vent-system maintenance, and other maintenance and design issues. MEP engineers, if they are sufficiently well-informed of the challenges these structures present, can readily meet these challenges with solutions.
