Consulting-Specifying Engineer - August 2007 - (Page 38)

Exterior wall Machine Governor Controller Machine room (positive pressure) Hoistway and machine room pressurization unit VFD SF Motorized OA damper OA Ropes Holes through floor for ropes Air through holes from ropes Roof Supply air register Fourth floor Hoistway pressurization sensors with an averager wired to VFD Guide rails Supply duct for hoistway pressurization (avoid interference with counter weight and car movement) Hoistway Third floor Fire floor Water from fire protection system Second floor Hoistway pressurization sensors with an averager wired to VFD Car Water-resistant NEMA 4 enclosures First floor 100% capacity and must be interchangeable in operation bimonthly to maintain reliability through use. In colder climates, machine room systems should be specified with low outdoor ambient temperature down to 0°F because the machine room may still require cooling during outdoor winter days. Condensation from AC systems in machine rooms is handled by an insulated condensation waste drips into an indoor open, vented sanitary waste system. No floor drains are allowed in machine rooms and curbing from the remainder of the floor is not uncommon. In warmer climates, a dry well into the ground may be used for condensate waste discharge. A dual-condensate waste pump is recommended because machine rooms are unoccupied 90% of the time. While some buildings are provided with chilled and hot water systems for HVAC applications, serving the elevator machine room with one of or both of these systems is not recommended because any water leakage could be disastrous to the elevator system. Additionally, the building could be in the heating mode while the elevator machine room may require cooling. Renovation projects In renovation design such as an elevator system modernization or a replacement project, most older machine rooms and controllers were ventilated with outside air using a motorized damper with an air intake louve, interlocked with a wall- or roof-mounted exhaust fan. When replacing the elevator system, it is best to remove this system and install a new split AC unit because the existing ventilation system may not meet the new cooling load requirements. The microprocessor components of the controller are more sensitive to heat and humidity than older relay controllers. The renovated machine room should not have any type of air transfer openings between it and the hoistway. Any existing floor openings should be closed off, covered with steel plates that are flush with the floor and caulked airtight. The only unavoidable air transfer is at the holes in the floor where car ropes travel between elevator car and elevator machine. The piston action, due to elevator car movement inside the hoistway, will cause (Continued on page 40) Ground floor Hoistway pressurization sensors with an averager wired to VFD Counter weight Basement Pit Buffer Sump pump Figure 2: Elevator hoistway with pressurization detail rooms between 60°F and 80°F with 35% to 60% relative humidity. The heating system for the machine room also is a built-in unit. AC systems for machine rooms The most common and practical AC systems for machine rooms are the ductless split type with automatic heating/cooling heating switchover (see Figure 1). This system’s lifetime is approximately 10 years and costs $8,000 to $13,000 (installed). Capacities of the ductless split AC range from 6,000 BTU/hr. to 48,000 BTU/hr. In a survey of machine room AC systems, one manufacturer had a 60,000-BTU/hr. cooling capacity for one- or two-unit rooms. For semi-standby AC systems, it is acceptable to provide two identical split type AC systems, each handling 50% of the load. For hospitals, the standby system is designed for 38 Consulting-Specifying Engineer • AUGUST, 2007

Table of Contents Feed for the Digital Edition of Consulting-Specifying Engineer - August 2007

Contents M/E Roundtable Giants 100 Pullout Poster Giants Stand Tall: CSE Giants 100 Report Electrical Design for Tall Buildings HVAC and Fire Safety for Elevator Systems How to Beat the Codes GAS Technology Supplement Recovering Waste Heat from Boilers New Applications for Tankless Water Heating Systmes Techniques Improve for Powder Coating MDF New Tools Available for Heat Treating Steel Direct Drive Engines

Consulting-Specifying Engineer - August 2007

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