Electrical buildings, sometimes referred to as “e-houses” or “electrical houses”, are prefabricated walk-in enclosures that contain sensitive electrical and mechanical equipment that requires protection. In this article, you will learn about the engineering and design of electrical houses, construction and integration, applications, as well as repair and maintenance considerations.
Engineering & Design
The design of an electrical building begins by understanding the desired function of the housed equipment. For instance, it may be to create remote power, control a lineup of pumps, or provide step-down functions from the main voltage line. Once the equipment is defined and specified, it must be integrated into a lineup.
Each e-house design varies and depends on regulatory standards and customer specifications. Equipment spacing and provision, interconnect wiring, structural design, and cooling considerations are major design considerations.
Equipment Spacing and Provisions
Electrical equipment installation must meet NEC (National Electrical Code) requirements for spacing. Space requirements exist to prevent inadvertent energization, thus protecting equipment and users. Sec. 110.26(a)(1) defines working space depth requirements in front of exposed live parts. Sec. 110.26(a)(3) requires a minimum headroom clearance of 6-ft or the equipment height, whichever is greater.
Provisions are necessary for cut-outs to accommodate wiring. The style of wiring and the cut-out size depends on whether the cable entry is from the top or bottom. Typical wire styles include:
- Non-Metallic (NM) Sheathed Cable.
- Underground Feeder (UF) Cable.
- THHN/THWN Wire.
Access floors provide the entry of cables into an electrical system. The ideal access floor will be determined with respect to the cable entry point.
If the cable enters from the bottom, cables are either routed underneath the structural skid or when space or project requirements dictate, via a computer floor. A computer floor, also referred to as a raised floor, provides additional space for cable runs. Computer floors feature a frame with removable panels that creates a passageway for electrical cables. Low profile and traditional are the two general types of computer floors. Low profile floors take less ceiling height (less than 6”) and are light-weight and easy to construct. However, the low amount of underfloor height makes it a poor fit for some applications.
Traditional computer floors are higher than 6”, with standard heights typically being greater than 12”. These floors are rugged, heavy-duty, and give wires/cables access to ample space. However, they are not as flexible or as easy to use as low profile floors. Managing the system’s cables with this type requires removing access floor panels. Overall, both types provide an effective means of hidden electrical services and easy routing but at a greater cost to the project.
Top entry wiring provides a passageway of electrical systems through the ceiling of the e-house via the use of raceways and cable trays. Raceway cable runs may include conduit, tubing, wireway, and other NEC code compliant wire enclosures. Per code, cable tray falls under the description of a structural support, rather than a raceway. Cable tray’s structure and support must comply with required strength calculations.
Nevertheless, the ideal entry point will heavily depend on the design of the panel and the amount of workspace available.
Programmable Logic Controllers (PLC) are industrial computers responsible for system control and running industrial processes. In e-houses, they are required for conducting electrical system processes, as they give orders and pass information to equipment. Wires are interconnected within the e-house equipment and PLC through control wiring. Control wiring acts as the “nervous system” of the control system and receives signals via a PLC. The proper cable size and length for the e-house system must be determined prior to construction. Calculating the appropriate cable size is based on acceptable loss, voltage, and amps.
E-house design depends on customer and project specifications. Designs include mobile, semi-mobile, fixed, and onboard. All types generally consist of the same structural design, including a frame, skid/wheel mounted base, walls, ceiling, and door(s).
In order to design the frame of the e-house, the following parameters must be considered.
- Weight of the e-house.
- Wind load.
- Seismic factors (earthquake condition).
- Weight and position of the equipment inside the e-house.
- Quantity of supports on which the e-house will be installed.
Structural calculations for stress and deformation (to which the e-house frame will be subject in the place of installation, during shipment and hoisting) are completed once the parameters are obtained.
For non-critical applications, a frame involves only the base material. For “blast e-houses” that require blast-resistant protection, the framing involves the walls are well.
Skid/Wheel Mounted Base
Due to its mobile design, a skid or a wheel mounted base will be utilized for easy transportation. Carbon steel is the dominant material for base design, although stainless steel or aluminum may be used. Carbon steel typically provides an optimal blend of strength and cost-effectiveness. In rare cases, the corrosion-resistant properties of stainless are employed. Even rarer cases call for the lightweight properties of aluminum. The floor may be fixed or removable with ribbed or smooth plates.
The wall sheets of an e-house usually consist of interlocking galvanized sheet metal whose thickness depends on seismic and transport loads. The length of each individual panel depends on the insulation required. Typically, the depth of the wall thickness is 3″ or 4″ where greater insulative properties are required. Materials such as rock wool and rigid foam board are specified to provide the proper insulative properties. After the insulation is installed in the wall, liners are attached to finish out the wall.
Ceiling & Roof
The frame provides trusses to which ceiling panels attach. Roof insulation inserts between the ceiling panels and the roof panels. Depending on customer specs, the roof could contain a lightning protection system (LPS) along with a gutter for water runoff. A top catwalk and lifeline anchorage system may also be supplied to ensure quick and safe access to the roof.
Doors typically require a fire rating, pressure sealed construction, and implementation of the same thermal insulation used in the walls and ceiling. Double doors for equipment and personnel or single door design. Materials should be carefully specified for hinges and gaskets (e.g rubber gasket on doors to prevent water, dust, sand ingress and stainless steel hinges). Drip caps may also be installed on the doors and external wall cut-outs to prevent moisture seepage.
Lights, equipment, air loss, and insulation deliver heat loss that must be overcome by an HVAC system. In extremely cold climates the heat will be the dominant factor. E-Houses surrounded by scorching weather require air conditioning systems to provide a suitable environment for the system to run. Fire detection and alarm system may also be requested. This optional system allows the interconnection between the control system of the customer’s plant and the HVAC unit. Thus, in case of fire, the HVAC equipment will be immediately shut down. Calculation of the appropriate HVAC size, with respect to expected loads for both heating and cooling duty, may be done here.
Construction and Integration
Skid base fabrication and assembly begins the construction phase. The skid may be open frame, but usually has a floor plate with cut-outs for the equipment. Base construction involves procuring, receiving, cutting, coping, and welding beams per the engineering design. Fabrication personnel or testing professionals provide verification of weld quality per project requirements.
Walls & Equipment
Walls are typically constructed with sheet metal carbon steel (10 – 22 gauge) and formed by a sheet metal bending machine to specific dimensions then affixed to the skid. For blast-resistant e-houses, the walls may be formed by steel plates. Walls may feature cutouts to allow for window installation or HVAC and equipment intrusion. Insulation is also installed depending on customer requirements and HVAC considerations. Sheet metal liners attach to the interior of e-house walls to provide a finished look.
Equipment enters and is set in place via floor jacks, forklifts, or overhead cranes. The dragging force between the skid and floor plate must not exceed live+dead load specifications. In exterior environments, this process typically waits until the roof and ceiling are installed.
Roof & Ceiling
After wall assembly, doors and transoms are connected to the structure. Doors are installed along with transoms. Transoms are a removable panel above the door, that allows for tall equipment to be moved into the building as needed. Roof panels are placed after the walls are finished. Roof insulation and a drop ceiling panels complete the interior.
Coatings ensure protection against elements. A standard two-coat painting system is applied to the exterior of the building. In battery rooms, an acid and corrosive resistant coating protects the walls and floors from accidental battery acid discharge. Anti-slippage floor paint prevents accidental falls.
FAT (Factory Acceptance Testing) ensures that the system operates as desired. FATs may require fully equipment energization in which case supplemental generators provide the requisite power. Other testing procedures such as the following must also be met prior to shipment:
- Visual and dimensional inspection
- Electrical continuity
- Insulation resistance
- Withstand voltage test
- Routine tests on equipment
- Functional tests on complete assembly (electrical panel boards, air conditioning, etc.)
Transport to the end destination typically involves forklift, overhead cranes, or gantry cranes to place the e-house onto a truck. Additional equipment such as platforms, ladders, railings, and handrails ship separately and are assembled at site.
Generally, most major electrical equipment is already pre-installed, wired and tested at the worksite before shipment. E-Houses only require input power and field connections, so all other interconnections are installed and tested at the worksite prior to shipment. External connections will be adapted to overhead or underground conduit systems.
Wiring for the power source, motor leads and field devices is typically installed once the e-house arrives to its final destination. Cable runs can be minimized by placing the e-house near the process being controlled.
Complete and running e-houses can be applied to a multitude of different systems, including the following:
- Transformer unit
- Panel unit
- IT/Operation room
- Automation room
- Restroom (requires Air Change calculations)
- Battery room (requires Air Change calculations)
- HVAC room
- Locker room
E-houses are a good fit for any application where sensitive equipment must be protected and modular construction is economically viable.
Repair and Maintenance Considerations
Regular maintenance of e-houses is crucial, as any minor failure can cause serious complications and immediate availability of a technical expert is often difficult to acquire. To prevent such complications, the following maintenance procedures are heavily recommended.
- Regular checkups on structural integrity. This may involve checks on fastener tightness, water intrusion, and floor deflection.
- Inspecting wire and all associated electrical components (overheated? short circuit?).
- Examine all materials for any degradation.
Failure to perform regular maintenance may result in operability loss, fluid leakage, material degradation, grime buildup, etc. This leads to costly repair considerations. Proper e-house maintenance ensures smooth running operations for decades.