Vertical Transportation
9.4 HVAC INVOLVEMENT WITH THE VERTICAL TRANSPORTATION SYSTEM
The HVAC designer has limited involvement with the vertical transportation sys- tem. The involvement will be to provide adequate cooling to the elevator machine room and to vent the elevator shaft so that it will conform to the codes that are in effect regarding the elevator system. The need for the elevator machine room at the top of each shaft for each cab may well result, as discussed in chapter 5, in the use of the floor on which the elevator machine room is located as a mechanical equipment room for air conditioning and plumbing equipment, including fans, coils, heat exchangers, refrigera- tion machines, and boilers. In this case, the providing of cooling and any required vent- ing of the shaft to atmosphere is simplified when compared to the case where the area around the elevator machine room were to be used for general office occupancy.
Figure 9-5. Typical size of commercial ser- vice elevator. Capacity: 6000 lb (2800 kg).
9.4.1 Elevator Machine Room Cooling
The elevator machine room in a building has cooling loads that consist not only of the electric motor that drives the hoisting mechanism for the elevators, but also of exten- sive heat-generating electronic controls for the elevators. The electronic components that are part of the system will require that the elevator machine room be cooled in hot weather to a maximum temperature of 80°F (27°C) and be heated in cold weather so the space temperature will not drop below 60°F (16°C). One means of maintaining the tem- perature between these allowable levels is to provide a package DX condenser water unit in the elevator machine room, but, due to possible significant operational availabil- ity restrictions on the use of a water-cooled unit, the HVAC designer is cautioned to review that alternative with the building developer. The use of a package DX condenser water unit may well be necessary for a low-rise or mid-rise elevator bank for which the elevator machine room is in the middle of the building, unless the elevator machine room location results in the use of the remainder of the floor as a mechanical equipment room. For the elevator machine room for the elevator bank that serves the top of the building, it is possible to use air-cooled DX equipment, which will not require the oper- ation of the condenser water system on a 24/7 basis.
The ultimate size of the water-cooled or air-cooled DX unit will be determined by the information provided by the elevator manufacturer who is selected as the provider of the elevators for the project. For the initial design stages, the necessary general infor- mation to allow the project to be designed and bid can be provided by the elevator con- sultant. The amount of cooling as the electronic devices and motor drives for the hoist have evolved can be significant. With current elevator designs, the DX unit may require 10 to 15 tons (35 to 52 kW) or more of capacity in a single elevator machine room.
9.4.2 Elevator Hoistway and Machine Room Venting
All elevators that are installed in the United States must conform to ASME A17.1, Safety Code for Elevators and Escalators, as it is modified by the local applicable build- ing code. These modifications can vary by jurisdiction, with many areas modifying the code by stated amendments of the A17.1 code.
One of the requirements of many codes is the inclusion of a vent opening at the top
of each elevator shaft that is 3.5 percent of the plan area of the hoistway or 3 ft2 (0.27
m2) per elevator, whichever is greater. The rationale for the opening is not entirely
clear, but it was probably originally intended to allow the venting of smoke during a building fire. Regardless of the reason for its inclusion, the HVAC project design, where the vent is required, subject to the exclusions detailed below, must provide a duct that connects the vent to atmosphere. This is simple at the top of the building, but for a low-rise or mid-rise elevator in which the elevator machine room for the elevator bank is not in a mechanical equipment room, the extension of the connecting duct to atmo- sphere may be troublesome.
When designing super tall buildings, where elevator speeds are greater than 1,400 fpm (7 mps), vents at the bottom of the shafts may be required by code to facilitate the rapid escape of air when the high-speed car is traveling in the down direction.
Under many codes, including the model International Building Code (IBC), for a commercial office building that is fully sprinklered, the need for the vent and its exten- sion to atmosphere may be waived for passenger elevators. The vent is still required for a dedicated service car, but this is normally easily handled, since the service car will be serving all floors in the building and the extension of the vent opening is a simple task where the elevator terminates at the top floor of the building.
In addition, under the International Building Code, the vent may be closed under normal building operating conditions by including an automatic damper in the atmo- spheric vent. This automatic damper must open upon the detection of smoke by any of the elevator lobby smoke detectors that are provided in the project. The elevator smoke detectors are disccussed in chapter 10, “Life Safety Systems.”