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What engineering considerations are there when upgrading hospital backup generators?

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With UK hospitals experiencing year on year growth in patients — up 21% from 2009 to 2019 — and 2020 as a year like no other, healthcare operators are thinking hard about their back up power. Here Bradley Morrissey, bid manager at Finning UK & Ireland, explains the engineering considerations when upgrading hospital backup generators.

Healthcare power is mission critical — a continuous power source is necessary to power everything from mechanical ventilators in intensive care, to medical imaging equipment and even the lighting and lifts needed for safe movement around the building.

Diesel generators are a popular choice for hospitals due to the reliability they offer. However, there are several engineering considerations at play dictating what equipment is suitable for a specific healthcare facility.

Size matters

Healthcare sites can consume over two million kWh of electricity a year, but this varies significantly from facility to facility. The first, and often most important, consideration is generator size — the backup generator must be able to provide enough power to keep all required equipment running.

A genset package should be designed in line with the Health Technical Memoranda (HTM) regulations, which includes being correctly sized to meet performance requirements. There are also software tools available that allow the user to determine which generator best fits the performance requirements for the facility’s load, ensuring that they select the correct genset size.

There are, however, multiple ways of achieving the same power output. In many facilities, a custom package is the best option, as healthcare operators can choose technology that achieves cost savings, is adapted to the available space, and offers excellent performance. For example, if a facility is running multiple gensets, it could be more effective to run fewer at a different rating.

A major factor in what size generator a facility can incorporate, is the dimensions of the engine room, as many hospitals have limited space. There are ways of reducing the amount of space a generator package takes, such as removing the radiators and putting them in a remote location. However, the most straightforward solution for hospitals with small engine rooms is to opt for a power dense engine.

Power density is a measure of the size of a genset compared with its output and is the result of significant work by engine manufacturers. Standard hospital generators have increased from 2.5MVA to 3.0MVA, a considerable improvement. Power dense solutions have an added benefit in that they require less ancillary equipment – they are cheaper to transport, install and maintain.


Gensets are designed with two main cooling options – the most popular is a custom genset mounted radiator sized to suit the application and environment; the second is a remote radiator located separately, for example on the roof.

However, the room must have enough ventilation to cool the engine down, to prevent overheating – maximum engine room temperature is around 50°C for a typical generator. Many hospitals have small plant rooms where airflow is a problem, making this an important consideration

Operators can work with specialist engineers who will design a package that works well alongside existing equipment and in its surrounding environment. This may include altering the ventilation by adding extra fans or additional cooling mechanisms.

If this isn’t feasible, the alternative is to redesign the engine package so that it requires less airflow. Hospital operators should check that their engine provider has considered this, and that ventilation is included in its quote, otherwise it may result in extra costs later on.


Engine noise can be a source of disturbance if not well managed. An acoustics specialist is best placed to perform a noise study and provide the details for acceptable noise levels to the engineering team. The engineers will then size the attenuators to make sure enough noise is absorbed. If required, lining the engine room with absorbing material as outlined by the design calculations will reduce the noise bouncing off the flat surfaces of the room.

Hospital operators can enquire with their genset supplier, to see if it is able to do factory testing on the genset package, to check its performance before installing it.

Ancillary equipment

Hospitals must also consider the ancillary equipment needed to support their engine. For example, the HTM regulations lay out that the hospital must have at least 200 hours of continuous fuel supply on site, which will dictate the size of fuel storage.

Hospitals with limited space may require a custom design to be able to safely store this amount of fuel on site. It is also important to ensure that an appropriately sized fuel polishing system is included, to remove water, sediment and microbial contamination from the fuel and ensure that the generators are ready when they are needed.

The genset provider should also secure a competitive, commercially viable and technically compliant generator package, including acoustics, enclosures and other plant room installations. The engineering team will also review the switchgear solution to check that it integrates with the wider site design and any legacy switchgear or equipment.


Finally, the hospital must consider emissions to ensure that they are compliant with the necessary regulations. Hospitals with a combined output of between 1 MWth and 50 MWth must comply with the Medium Combustion Plant Directive (MCPD). If the addition of a new genset takes a facility up into this bracket, adaptations like selective catalytic reduction (SCR) technology may be required for compliance, although standby generators are exempt under certain circumstances.


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