The number and position of emergency exits within both cell and control room spaces will be determined by national safety legislation and local building codes that will vary from country to country, but will be planned to give the shortest route to the building exterior. All doors and emergency exit routes have to be designated with the legislatively required battery-illuminated signs. All emergency doors must open outwards from the source of danger and their use must not be inhibited by stored or discarded objects blocking the escape route.
In the UK it is not uncommon to have only one door into the test cell as shown inFigure 4.4but, as stated elsewhere, such facilities restrict entry to the cell when engines are running. In the USA one wall of engine test cells is normally formed by an external wall of the shell building, into which an emergency exit door is fitted with a “burst bar” opening device. Under some US building codes and in gas-fueled cells elsewhere, the cell has to be fitted with an explosion panel opening into an unoccupied external zone; the external rear cell door may also serve this purpose. Control rooms invariably have to be fitted with two entry/exit doors, as a minimum, including one designated and signed as the emergency exit.
Many test cells and control rooms are visually and audibly confusing spaces, particularly to visitors; good design and clear signage is required to minimize this confusion and thus improve the inherent safety of the facility.
The confusing use of multiple signs has become so common, particularly during facility construction, as to become a safety hazard in its own right, and is now warned against in British Standard 5944.
All workers in the facility must be trained and practiced in the required actions in the case of specified emergencies and all visitors should be briefed in the use of emergency exits in the case of any emergency identified by their host.
Transducer Boxes and Booms
The signals from each of the transducers with which the UUT is fitted (Chapter 12) flow through individual cables to a nearby marshaling box. In modern systems most signal conditioning and analog-to-digital conversion (ADC) is carried out by electronics within these transducer2boxes, which then send the data to the control computer system via one or more digital cables under the control of a communication bus such as the IEEE 1394 interface (Firewire). These boxes may be either mounted on an adjustable boom
2. The only transducers (energy converting and measuring devices) actually installed within the box are those measuring pressure, fed by Teflon lines from the UUT. Other measurements come into the dedicated conditioning cards inside the box by way of cables connected directly to transducers mounted on the UUT.
cantilevered and hinged from the cell wall, or on a pillar mounted from the bedplate but, since they may be housing very expensive electronics, due care needs taken in the support and location so that damage is not caused by gross vibration and overheating. Boom-mounted boxes that may be close to and immediately above the engine need to be force-ventilated and temperature monitored. Well-designed booms are made of hollow aluminum extrusions, of the type used in sailing-boat masts, and have a fan at the wall end blowing air through the whole structure.
Boom-mounted transducer boxes can be of considerable size and weight;
because of the convenience of their location the contents and attachments tend to increase during the process of cell development.
Because of this high, cantilevered load, the ability of the wall to take the stresses imposed must be carefully checked; frequently it is found necessary to build into the wall, or attach to it, a special support pillar.
Fuel booms are often used to take fuel flow and return lines between the engine on test and wall-mounted conditioning units. These are of light construction and must not be used to attach other instrumentation or cables.
Test Cell Flooring and Subfloor Construction
The floor, or seismic block when fitted (see Chapter 7), must be provided with arrangements for bolting down the engine and dynamometer. A low-cost solution is to precisely level, and cast in position, two or more cast-iron T-slotted rails. The machined surfaces of these rails form the datum for all subsequent alignments and they must be set and leveled with great care and fixed without distortion. The use of fabricated steel-box beams has proven to be a false economy.
Sometimes complete cast-iron floor slabs containing multiple T-slots are incorporated in the concrete cell floor, but this configuration tends to trap liquids and debris unless effective drainage is provided. All cast-iron floor slabs can become very slippery so good housekeeping practices and equipment are essential.
The air-sprung bedplate discussed in detail in Chapter 9 is the modern standard design. However, the building construction plan must make arrange- ments for the maneuvering into place of these large and heavy objects before suitable access is closed by building work.
Concrete floors should have a surface finish that does not become unduly slippery when fluids have been spilt; special “nonslip”, marine, deck paints are recommended over the more cosmetically pleasing smooth finishes. High- gloss, self-leveling floor surfaces have found wide favor in new factories but when fuels, lubricants, or cooling fluids are spilt on them they become dangerously slippery. Whatever the finish used, it must be able to resist chemical attack from the fluids, including fuels, used in the cell.
Chapter | 4 Powertrain Test Facility Design and Construction 63
Even without the presence of a seismic block, which provides the oppor- tunity, it is good practice to provide floor channels on each side of the bed, as they are particularly useful for running fluid services and drain pipes in a safe, uncluttered manner. However, regulations in most countries call for spaces below floor level to be scavenged by the ventilating system to avoid any possibility of the build-up of explosive vapor, thus slightly complicating the cell design (see Chapter 6).
All floor channels should be covered with well-fitting plates capable of supporting the loads that are planned to run over them. To enable easy removal for maintenance each plate should not weigh more than about 20 kg, and be provided with lifting holes. The plates can be cut as necessary to accommodate service connections.
Fuel service pipes, once commonly run underground and in floor trenches, should nowadays follow modern environmental and safety best practice, and remain in view above ground in cells and be easily accessible.
Facility and Cell Doors
Modern test facilities have to house many large electrical cabinets, all of which may be up to 2.2 m high when installed but over 2.4 m high during trans- portation through the building due to the additional height of pallets, skates, etc.
The “simple” task of maneuvering heavy cabinets to their final installation position is frequently turned into an expensive problem due to intermediate doors of inadequate height or intermediate flooring of inadequate strength;
foresight is required.
Cell doors that meet the requirements of noise attenuation and fire containment are inevitably heavy and require more than normal effort to move them; this is a safety consideration to be kept in mind when designing the cell.
Forced or induced ventilation fans can cause pressure differences across doors, making it dangerous (door flies open when unlatched) or impossible to open a large door. The recommended cell depression for ventilation control is 50 Pa (see Chapter 6).
Test cell doors where operators are permitted to enter when tests are running must be either on slides or be outward opening. The double-walled and double- doored cell shown in Figure 4.6is interlocked to prevent entry because the inner door opens inwards; the unusual double sections are required to contain the very high noise levels of F1 and other race engines.
There are designs of both sliding and hinged doors that are suspended and drop to seal in the closed position. Sliding doors have the disadvantage of creating “dead” wall space when open. Doors opening into normally occupied work spaces should be provided with small observation windows and may be subject to regulations regarding the provision of Exit signs.
Interlocking the cell doors with the control system to prevent human access during chosen operating conditions is a common safety strategy and is certainly
advised in educational and production facilities. The usual operation of such an interlock is to force the engine into a “no load/idle” state when a door begins to open.
Cell Windows
The degree to which a well-constructed test cell can form a hazard containment box may depend critically on the number and type of windows fitted into the cell walls and doors.
The different glass types suitable for cell windows are sold either as
“bulletproof” (BS EN 1063:2000) or “bandit proof” (BS 5544). There are also quite separate fire-resistant types of glass such as Pilkington PyrodurÒ. The decision as to whether it is more likely for a large lump of engine (bandit) or
FIGURE 4.6 Double pairs of cell doors built into a high-noise, acoustic-panel-contructed engine test cell.(Photo courtesy of Enviosound Ltd.)
Chapter | 4 Powertrain Test Facility Design and Construction 65
a high-speed fragment of turbocharger (bullet) to hit the window has the potential to prolong many an H&S meeting and will not be resolved in this volume. However, good practice would suggest that the glass (and its frame) on the cell side should have the highest fire resistance and the control room side glass should be the most impact resistant.
To achieve good sound attenuation, two sheets of glass with an air gap of some 80 mm is necessary. Many motor-sport or aero-engine cells have three panes of glass with at least one set at an angle to the vertical to minimize internal reflections.
Cell Walls and Roof
Test cell walls are required to meet certain special demands in addition to those normally associated with an industrial building. They, or the frame within which they are built, must support the load imposed by any crane installed in the cell, plus the weight of any equipment mounted on, or suspended below, the roof. They must be of sufficient strength and suitable construction to support wall-mounted instrumentation cabinets, fuel systems, and any equipment carried on booms cantilevered out from the walls. They should provide the necessary degree of sound attenuation and must comply with requirements regarding fire retention (usually a minimum of one hour containment).
High-density building blocks provide good sound insulation that may be enhanced by filling the voids with dried casting sand after being laid and before the roof is fitted; however, this leads to problems when creating wall pene- trations after the original construction because of sand and dust leakage from the void above the penetration. Walls of whatever construction usually require some form of internal acoustic treatment, such as 50-mm-thick sound- absorbent panels, to reduce the level of reverberation in the cell. Such panels can be effective on walls and ceilings, even if some areas are left uncovered for the mounting of equipment. The alternative, easier to clean, option of having cast concrete walls that are ceramic tiled are seen in facilities remote from office spaces and where test operators are not allowed in the cell during engine running.
The key feature oftest cell roofs, much disliked by structural engineers, is the number, position, shape, and size of penetrations required by the ventilation ducts and various services. It is vital that the major penetrations are identified early in the facility planning as they may affect the choice of best construction method. In the author’s experience penetrations, additional to those planned and provided during the early build stage, are invariably required by one or more subcontractors even when their requirements have been discussed in detail at the planning stage.
The roof of a test cell often has to support the services housed above, which may include large and heavy electrical cabinets. Modern construction tech- niques, such as the use of “rib-decking” (Figure 4.7), which consists of
a corrugated metal ceiling that provides the base of a reinforced concrete roof that is poured in situ, are commonly used.
An alternative is hollow-core concrete planking (Figure 4.8), but the internal voids in this material mean that a substantial topping of concrete screed is required to obtain good sound insulation. The comments above concerning large penetrations are particularly true if concrete planking is used because major post-installation modification is extremely difficult.
Suspended ceilings made from fire-retardant materials that are hung from hangers fixed into the roof can be fitted in cells if the “industrial” look of concrete or corrugated metal is unacceptable, but this has to be shaped around every roof-penetrating service duct and pipe, and is usually only financially justified in high-profile research or motor-sport sites.
Lighting
The typical test cell ceiling may be cluttered with fire-sprinkler systems, exhaust outlets, ventilation ducting, and a lifting beam. The position of lights is
Concrete floor decking
Reinforced concrete floor poured onto
metal decking
Metal rib-decking ceiling surface
FIGURE 4.7 Section through metal and concrete “rib-decking” construction of a cell roof.
FIGURE 4.8 Section through a concrete plank, which gives a quick and high-strength cell roof construction but can be difficult to modify post- installation.
Chapter | 4 Powertrain Test Facility Design and Construction 67
often a late consideration, but is of vital importance. Lighting units must be securely mounted so as not to move in the ventilation “wind” and give a high and even level of lighting without causing glare into the control room window.
Unless special and unusual conditions or regulations apply, cell lighting does not need to be explosion proof; however, units may be working in an atmo- sphere of soot- and oil-laden fumes and need to be sufficiently robust and be easily cleaned. Lighting units fitted with complex and flimsy diffuser units are not suitable.
The detailed design of a lighting system is a matter for the specialist.
The “lumen” method of lighting design gives the average level of illumina- tion on a working plane for a particular number of “luminaries” (light sources) of specified power arranged in a symmetrical pattern. Factors such as the propor- tions of the room and the albedo of walls and ceiling are taken into account.
The unit of illumination in the International System of Units is known as the lux, in turn defined as a radiant power of one lumen per square meter. The unit of luminous intensity of a (point) source is the candela, defined as a source that emits one lumen per unit solid angle or “steradian”. The efficiency of light sources in terms of candela per watt varies widely, depending on the type of source and the spectrum of light that it emits.
The IES Code lays down recommended levels of illumination in lux for different visual tasks. A level of 500 lux in a horizontal plane 500 mm above the cell floor should be satisfactory for most cell work, but areas of deep shadow must be avoided. In special cells where in-situ inspections take place, the lighting levels may be variable between 500 and 1000 lux.
Emergency lighting with a battery life of at least one hour and an illumi- nation level in the range 30–80 lux should be provided in both test cell and control room.
It is sometimes very useful to be able to turn off the cell lights from the control desk, whether to watch for sparks or red-hot surfaces or simply to hide the interior of the cell from unauthorized eyes.
Cell Support Service Spaces
The design criteria of the individual services are covered in other chapters, but at the planning stage suitable spaces have to be reserved for the following systems listed in order of space required:
l Ventilation plant (including fans, inlet, and outlet louvres) and ducting (including sound attenuation section) (see Chapter 6)
l Engine exhaust system (see Chapters 9 and 16)
l Electrical power distribution cabinets, including large drive cabinets in the case of AC dynamometers (see Chapter 5)
l Fluid services, including cooling water, chilled water, fuel, and compressed air (see Chapter 7).
In addition to these standard services, space in some facilities needs to include:
l Combustion air treatment unit (see Chapter 6)
l Exhaust gas emissions equipment (see Chapter 16).
It is very common to mount these services above the cell on the roof slab and it is often desirable, although rarely possible, for the services of individual cells to be contained within the footprint of the cell below.
Control Room Design
The role and profile of the staff using the control room is of fundamental importance to the design of that work space and to the operation of the test department. There is no “correct” solution; the profile has to be optimized for the particular roles and needs of each site.
While there is no ideal control room layout that would suit all sites, there are some general features that should be avoided.
The multiple screens used in modern control rooms present the control system designer with a major problem in seeing “the wood for the trees” and organizing a coherent display. In most cases the suppliers of control and data acquisition systems have passed the problem to the user by allowing them freedom to produce their own customized display screens. The problem, while transferred, has not been solved and the answers will differ between cells having different tasks. Some form of optimization and discipline of data display is required within the user organization if serious misunderstandings or operational errors are to be avoided; such lack of discipline is not only inefficient but unsafe.
It is advisable to use articulated support booms for screens that are needed only during particular phases of tests. The displays and controls for secondary equipment such as cell services are usually housed in a 1900 racked cabinet positioned at the side of the control desk, while instruments used only inter- mittently, such as fuel or smoke meters, can be installed towards the top and operated if necessary from a standing position.
An analog dial display of speed, torque and, in the case of engine testing, oil pressure is considered by most experts to be vital for manual control panels in order for the operator to judge rate of change during initial start-up and running.
As an example of a poor layout and subsequent development,Figure 4.9 shows one of two control desk areas, in close proximity. These were incre- mentally modified from the mid 1980s to the early 2000s and show a number of design and consequential housekeeping problems that create problems for the operators:
l Operators’ work area is confined and cramped with controls and displays in positions dictated by available floor or desk space rather than ergonomic considerations.
l The window has been rendered useless and unnecessary by display units.
Chapter | 4 Powertrain Test Facility Design and Construction 69