In the previous topic, the Electrical Design Requirements for Health Care Facilities – Part One , We talk about Health care facility definition, types, preliminary design consideration and electrical load types.
Today, we will talk about the power sources, Voltage considerations and electrical distribution system for health care facilities as follows.
Power sources in health care facilities:
Generally, the power sources that can be used in the electrical networks of health care facilities are as follows: (see fig.1)
- The normal power source.
- The alternate power source.
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| Fig (1) |
1- The normal power source
The normal power source which may be one of the following:
- The electric utility power.
- On-site power generator(s) and in this case the alternate power source required can be another power generator unit or the electric utility.
2- The Alternate Power Source
Alternate power source Definition:
- One or more generator sets, or battery systems where permitted, intended to provide power during the interruption of the normal electrical services or the public utility electrical service intended to provide power during interruption of service normally provided by the generating facilities on the premises.
- Alternate power source by an on-site power source such as:
- Generator set(s) driven by some form of prime mover(s) and located on the premises.
- Another generating unit(s) where the normal source consists of a generating unit(s) located on the premises.
- An external utility service when the normal source consists of a generating unit(s) located on the premises.
- Uninterruptible power supply (UPS) (which can be applied as the principal alternate for large computing centers or other critical, sensitive loads).
- battery/inverter system ( which can be applied as the principal alternate for nursing homes, residential custodial care facilities, and other health care facilities provided they meet the conditions outlined in NFPA 99-1996).
Typically, the alternate sources of power are supplied to the loads through a series of automatic and/or manual transfer switches. The transfer switches can be non-delayed automatic, delayed automatic or manual transfer depending on the requirements of the specific branch of the EES (Essential Electrical System) that they are feeding.
It is permissible to feed multiple branches or systems of the EES from a single automatic transfer switch provided that the maximum demand on the EES does not exceed 150 kVA. This configuration called as (Radial – Generator) is typically seen in smaller health care facilities that must meet ESS Type 1 requirements.
Health care Facilities voltage classification:
Health care Facilities are primarily people- and public-oriented and because of their different sizes and types, they can need electrical supply with different voltage classes , for examples simple medical office /clinic will need an electrical supply with low voltage class (under 1000 V) from public Low Voltage grid while a large hospital will need an electrical supply with medium voltage class (UP to 20KV) Via public or in-house MV substations, for more information about different voltage classes , please review the following links:
For more information about Electrical System Configurations press on the link
Special voltage considerations for health care facilities:
- The proper selection, regulation, and quality of utilization voltages is extremely important because of the extensive use of sensitive medical equipment that is available in many different voltage ratings.
- The voltage levels selected will depend on the utility voltage available, the size of the health care facility, the loads served, expansion requirements, the building layout, voltage regulation requirements, and cost.
- Typically, a large health care facility will be supplied power at a medium voltage level from the utility and it will be stepped-down to either 480Y/277 V or 208Y/120 V for utilization.
- Either 480 V or 208 V can be used to supply mechanical equipment (chillers, fans, pumps, etc.), medical equipment (radiology, medical air pumps, etc.), and other support equipment such as laboratory equipment and kitchen equipment.
- If 480 V is present, however, it is preferred. From initial cost considerations, ongoing operating cost reasons, and isolation from sensitive 120 loads, the 480 V level is the better choice for these equipment.
- The use of 277 V lighting in lieu of 120 V in large health care facilities is common. The application of 277 V lighting in hospitals, however, differs from other commercial facilities because of the requirement for the four divisions of the electrical system (normal, critical branch, life safety branch, and the equipment system). Depending on other equipment requirements, applying 277 V lighting may increase the number of 480Y/277V panels on each floor and/or in each electrical room.
- There is no general rule on when to apply 277 V lighting. Each individual application should be analyzed to determine its feasibility. Typical benefits of 277 V lighting include reduced system losses, reduced number of branch circuits for lighting, reduced sizes of power conductors, reduced heat gains on the air conditioning system due to power losses, and segregation of the harmonics of the electronic ballasts in luminaires from the medical equipment operating at 208Y/120 V.
- Once the nominal utilization voltages have been selected, the voltage of all medical equipment to be installed in the facility should be carefully checked to assure proper application.
- If the equipment is new, it should be ordered to one of the planned utilization voltages. If this is not possible, then buck/boost autotransformer, or standard two-winding transformers should be considered to supply rated voltage to the equipment.
- A common misapplication includes the use of nominally rated 230 V motors installed on a 208 V system.
Electrical Distribution systems in health care facilities:
We will study the Electrical Distribution systems for the following health care facilities:
- Hospitals.
- Nursing homes and residential custodial care facilities.
- Other health care facilities (excluding hospitals, nursing homes, and residential custodial care facilities where the facility administers inhalation anesthetics or requires electromechanical life support devices).
1- Electrical Distribution Systems for Hospitals
Electrical Distribution Systems for Hospitals is basically divided into two sub-systems as follows:
- The normal electrical system (non-essential).
- The essential electrical system.
Note: Both systems are supplied by the normal power source; however, the essential electrical system can be transferred to the alternate power supply whenever the normal power source experiences a power failure.
in the next Topic, I will continue explaining the Electrical Distribution Systems for Hospitals. so, please keep following.
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