11/04/2010 by David Slade.

The simple reason diesel engines respond much faster to load transients than gas engines is because fuel introduction on a diesel engine is done directly into the combustion chamber, at the next engine cycle from a load change, if the control system is fast enough, the different fuel rate can be introduced.  On the gas engine, fuel is introduced upstream, on older engines at the carburator mixer, on newer engine its at the valve, on medium speed gas engines at the inlet port of the cylinder head.  All points of fuel introduction produce delay before the cylinder sees the desired fuel change.

Gas engines do have a number of issues operating “island mode” when compared to diesels.  Properly designed, applied and integrated systems can operate effectively as prime applications, including maintaining very low emissions with installed after-treatment and heat recovery systems.

Transient capability is VERY different between gas and diesel.  Newer design gas engines not only have issues with load acceptance, but in many ratings, have a worse time with load rejection.  Also, gas engines have significant degradation in transient capabilites between “normal” service intervals.  Issues such as valve lash, spark plug condition, and ignition component health, like extenders and transformers, all affect engines ability to respond to load changes and maintain stable operation.  Also, newer engines have very different response characteristics depending on load level, low load pickup on some engines is extremely poor, mid range load pickup can be best if sufficient turbo response is available.  Top end transient response can be erratic as control system limitations, emission control and available turbo response all can fight each other.  So a 25% load transient may be acceptable at 25-50% and 50-75%, but unacceptable at 0-25% and 75-100%.  It is also quite possible the engine will not tolerate a 25% load rejection.

Also be aware that the applied protection settings for voltage and frequency deviation may not allow for desired transient operation, and using volts/Hz for improved recovery may affect operation of system loads like VFD’s and UPS systems.

New gas engines also have a much harder time with running extended periods at “low load”, actual load levels that would be defined as low load can vary, but gas engines suffer increased problems with spark plug life, especially multi-torch type spark plugs due to accelerated deposit levels.  Increased cylinder deposits also affect engine combustion, detonation levels, and emissions outputs, so assuring the engines are properly matched to the system load profiles is essential in maintaining stable plant operations.

As pointed out above, older engine designs with simpler and more robust controls systems were easier to apply in island applications, newer engines needing to meet reduced fuel consumption, reduced emissions and higher power densities have to give up something, and transient response suffers in these engines.

Island mode covers a fairly broad topic, engines can be successfully operated in prime, peaking and non-critical applications. From past experience, I am firmly opposed to using a gas engine as a critical standby unit for life safety.  Current design gas engines have a huge number of shutdowns programmed into their ECM’s, a large number of these designed to protect the engine, adding complexity and reducing reliablity.  Gas engines have ignition systems, spark plugs on cylinders open to the atmoshpere corrode, ignition wiring deteriorates, tranformers get internal faults, and ignition sources, such as magnetos or ignition modules can appear to operate correctly at no or low loads during testing and fail when called to operate at higher loads.  Fuel systems components, such as gas regulators and carburators, can stick and bind, diaphragm materials deteriorate, springs fatigue.  Even newer fuel systems components, such as the Raptor valve have relatively high failure rates.  While no engine is 100% reliable.  Gas engineers are known to have a very large number of fails to start or failure to operate as expected with gas engines in standby service as compared to a much larger population of diesel engines.

Compounding the problems with using a gas engine as a critical standby unit are two issues, in my opinion.  First, planning restraints regarding air quality control in conservation areas and noise in built up area shave greatly reduced the number of available hours a unit can be run for maintenance.  Second, most customers don’t want to run their unit under load, while some do install permanent load banks or do regular site load testing, their number is small compared to the total population.  And since most standby systems are low cost installations, good monitoring and trending systems for engine mechanical or electrical parameters are likely not installed.  So these engines don’t run enough hours at a high enough load in a year to assure their engine systems are functioning correctly.  So if you’re going to apply a gas engine in critical standby service, you have to be aware it has a higher incidence of failure, needs more maintenance, and can have reduced performance in between service intervals than a comparable rated diesel engine

Posted in Island mode, Generator | No Comments »

09/04/2010 by David Slade.

As defined under The Distribution Code of Licensed Distribution Network Operators (UK):

A Generator including a Customer With Own Generation whose Generation Sets are directly connected to the DNO’s Distribution System or to an Other Authorised Distributor connected to the DNO’s Distribution System.
The definition of Embedded Generator also includes the OTSO in relation to any Embedded Transmission System

Posted in Distribution System, Generator, DNO | No Comments »

13/06/2009 by David Slade.

Overview

Section 20 of the London Buildings Acts (and subsequent amendments) is concerned with the danger arising from fire within certain classes of building which by reason of height, cubic extent and/or use necessitate special consideration. The principles incorporated the provision of fire-fighting facilities that would enable the fire brigade to tackle the fire with utmost speed, but also provide warning of fire, contain an outbreak of fire and to prevent its spread.

This is quick guide to section 20 building requirements. But remember, always seek professional guidance.

Especially in relation to escape routes, building services, sprinkler or other automatic fire extinguishing,  or suppressant system, including hose reels; smoke extraction / venting system,  and vertical transport (including fireman’s lifts).

The London Building Act (Amendment) Act: 1939 Section 20
(Buildings of excess height and / or additional cubic extent)
(As amended 1985 & 2005)

Do the proposed works attract an application under this Legislation?

NEW BUILDINGS:
Application will be required if the building is:

• More than 30 metres in height;
• More than 25 metres in height with an area of any floor more than 930m 2.
• A building of the warehouse class, or is a building or part of a building used for the purpose of trade or manufacture exceeding 7100m3 (250,000ft3) in cubical extent  unless it is divided  by division walls (with 4hr FR) such that no part of the building exceeds 7100m3 (see note 1).

EXISTING BUILDINGS (NON-SECTION 20):

If the proposed works bring the building into one or more of the above listed categories the building will then become subject to the above legislation requiring an application.

EXISTING SECTION 20 BUILDINGS:
An Application is necessary if the works affect any of the following:

• Sprinkler or other automatic fire extinguishing or suppressant system, including hose reels;
• Smoke extraction / venting system;
• A change to the access to the site for the Fire & Rescue Service;
• Work that affects or impacts on any special fire risk areas (see Note: 2).

INITIAL NOTICES:
Where Approved Inspectors propose works within a building subject to LBA Section 20 it is mandatory that this local Legislation is recognised in the Initial Notice; failure to do so will result in rejection of the Initial Notice. Please note that this is irrespective of whether the proposed works impact on the criteria listed above or not. If the Council decides that a Section 20 Application is necessary then the Council will ask for this but will not delay validating the Initial Notice, providing that this local Legislation is expressly referred to in the Initial Notice, and confirmation is given that if necessary an application will be submitted in due course.

NOTES:
1)A building of the warehouse class means a warehouse, manufacturing, brewery, distillery with a cubic extent exceeding 4,247m3 (150,000ft 3) which is neither a public nor a domestic building. Please note for the purposes of this legislation the definition of a domestic building includes office use.
Height is taken from street level at the centre of the face of the building to the ceiling level of the top storey. Where more than half the roof is covered by a plant room such room becomes the top storey.

Cubic extent in relation to the measurement of a building means the space contained within the external surfaces and roof and the upper surface of the floor of its lowest storey but including any space within any enclosure on the roof of the building used exclusively for accommodating a water tank of lift gear or any like apparatus.

2.  Special Fire risk Areas:

• Heat producing appliance above 220 kilowatts (heat);
• Internal combustion engine producing above 44 kilowatts (power);
• Oil-filled transformer or switchgear over 250 litres of oil and voltage above 1000 volts;

Flammable or combustible solids, liquids or gas manufactured, treated, handled or stored in quantities likely to constitute a fire hazard including any of the following:
i.    Fuel oil, diesel or petroleum;
ii.    Nitrate film or celluloid;
iii.   Cellulose or flammable liquid spraying

Posted in smoke extraction, venting system, fireman's lift, sprinkler, switchgear, diesel or petroleum, Generator, Transformers - Liquid filled, section 20 building, Fuel oil, Buildings | No Comments »

13/06/2009 by David Slade.

Introduction

In order to design a suitable Data Centre for an organisation it is vital to consider a multitude of interconnected factors. In the fast moving world of IT, where the physical sizes of types of technology assets can change regularly, it is a challenging task to design a Data Centre that will cater for the needs of an organisation for the next ten years or more. This document will discuss some of the factors to be considered when developing the design of a Data Centre, and will provide advice on how to maximise the opportunities for future proofing the facility.

Location
Historically, most companies have based their Data Centre facilities within the same buildings as their staff. If this is the proposed strategy for your new facility, then you need to consider whether the Data Centre should be located on a basement floor or on an office floor. Typically, basement rents are approximately one quarter of office floor rents, and your stakeholders will probably prefer that you do not take up valuable office floor space with technology equipment that does not necessarily justify a prime location on the floor. Another factor to consider is support. If your
support staff require access to the facility on a regular basis then you need to determine whether it is acceptable for them to be continually going from the office floor to the basement.

Size
This is probably the most challenging factor of Data Centre design. In addition to rental costs, it is expensive to provide power and cooling facilities to large areas so you will be under pressure to make sure that the Data Centre is not excessively large for the requirements of the organisation. However, it can be equally expensive and time-consuming to extend a Data Centre that is initially designed too small. A reasonable method for calculating the size of the room is to plan for day one and then to add an additional 30% space for expansion. You also need to factor in whether mechanical and electrical plant will be located within the Data Centre and if so, to ensure that these devices are coordinated with the overall design of the room

Power
The design of the power solution will depend on the business need for the Data Centre to ‘stay up’. Where the failure of a Data Centre has direct financial implications for a company, then a business case needs to be established to understand the costs of a failure versus the expense of installing a highly resilient power solution. Similarly, if a temporary Data Centre failure does not directly affect the revenue generation of the organisation, then it could be seen as a waste of money to specify a highly resilient solution.
There are a number of resiliency factors to consider:

• Cabinet Power. Ideally, power strips within a cabinet should be fed from two separate Power Distribution Units (PDUs). This is relatively easy to implement at design stage but can be expensive to change later. Breaker sizes also need to be considered carefully, and will be defined by the equipment that you are planning to install on day one as well as the likely requirements for ‘future’ equipment.

• An Uninterrupted Power Supply (UPS) will allow devices to stay up while mains power is restored, or at least will allow equipment to be shut down safely. You might specify a central UPS that supports all Data Centre active equipment, or alternatively you might install separate UPS devices for each individual system. The important factor to consider is how long the IT team needs to safely power down systems in the instance of a mains power failure. The UPS design will be based on this important time period.

• A Generator can keep equipment running in the case of an extended failure of mains power. Generators can take up a significant amount of space as there is a requirement for the storage of fuel to run the generator. However, they are vital to organisations who cannot afford a power outage to affect their IT  operation.

Air Conditioning
As with power, the required level of resiliency will be determined by the costs to the business of Data Centre failure. An important consideration is that air conditioning units require chilled water to cool the environment, and where possible you want to ensure that water does not get inside your Data Centre. Consultants are now recommending the construction of a service corridor outside the Data Centre. This corridor contains the air conditioning units, which can blow cold air in to the room, but can also be serviced outside the room. The wall between the service corridor and the Data Centre is water sealed; therefore if an air conditioning unit should fail the water will not be able to penetrate the Data Centre.

Where it is necessary to install air conditioning units within the Data Centre, thought should be given to leak detection and also to the ongoing servicing of the units. Thought also needs to be given to UPS support for the air conditioning equipment: there is little value in IT equipment remaining up and running if it will overheat and fail due to a lack of available cooling.

Raised Floor
The height of the raised floor will be determined by a number of factors:

• Distance between the slab and the soffit. This distance might limit the amount of available space for the raised floor void.

• Height of the raised floor across the rest of the office space. Normally, the office floor will have a raised height of 200mm whereas the Data Centre raised floor height will be anywhere from 300mm to 750mm. In order the bridge the gap between these heights, steps and\or a ramp will need to be installed and space restrictions within the room might prove prohibitive.

• Depth of structured cabling. The air conditioning units generally tend to push cold air in to the floor void. For this system to work effectively there needs to be sufficient space for the air to circulate. Therefore, a large volume of structured cabling will require a higher raised floor to allow the cold air to circulate above it.

When installing a raised floor, thought also needs to be given to the size of floor tile that is specified. The majority of floor tiles are 600mm square, whereas the cabinets are 800mm square. When designing the cabinet layout, care should be taken to ensure that no tiles are ‘trapped’ and that the tile cut-outs are in sensible positions.

Suspended Ceiling
Consultants are now recommending that suspended ceilings are not installed in Data Centres. The recommended solution is for suspended light fittings to be hung from the soffit, and also for power to be presented at high level within containment also hung from the soffit. There are a number of advantages to this solution:

• Cost savings are achieved by removing the suspended ceiling from the construction budget.

• There is a greater fire risk when power and data cabling are located in close proximity. By locating data cabling in the floor void and power at high level, the risk of fire is significantly reduced.

• It is easier to control maintenance works within the Data Centre. The electricians will not need to get in to floor void, and the data cabling engineers will not be working anywhere near power.

• It is easy to ensure that cabinets are fed by power from two separate PDUs.

When power is installed within the floor void, power strips are often cabled to the same PDU and this is not known until failure occurs. When power is visible at high level, it is easy to identify poorly configured cabinets.

Whilst power at high level is an ideal solution, thought needs to be given to the configuration of cabinets. Only recently manufactured cabinets will have holes in the top for power cables to pass through, therefore older cabinets might need to be modified if no holes exist.

Fire Suppression

Most office floors are protected from fire by sprinkler systems (this is a requirement of ‘Section 20’ buildings). Data Centres also require protection, and this will normally take the form of a ‘pre-action’ sprinkler system or a gas based fire suppression system.

The following items are worth considering in your design:

• If power is presented at high level, there is a minimal risk of fire within a Data Centre. In this case, a sprinkler system might be the most cost effective system as it is highly unlikely to be ever be set off.

• Most gas based fire suppression systems work on the principle of reducing the percentage of oxygen within an enclosed space in order to extinguish a fire. These solutions require that the room is fully sealed to ensure that the gas does not seep out of the room when it is released. When carrying out new installations which require running cables in to the room, engineers need to ensure that the room is sealed after any work. If this does not happen then the gas might fail to extinguish the fire.

• The gas required to protect the space needs to ideally be stored relatively close to the Data Centre. Where you are protecting a large area, the gas bottles can take up a large amount of space within your building.

• The main positive of the gas based system is that if one piece of equipment catches fire, then the fire will be extinguished with hopefully no damage being done to your other equipment. Sprinkler systems can not necessarily claim this advantage.

• Fire protection can also be enhanced by the installation of a fire detection ‘sniffer’ aspirating system (VESDA) which samples the air and gives early warning of any hot spots within the room.
• Alternatively there are also water misting systems and N2 Oxy reduction systems, that have sometimes been installed.

Security
The criticality of most Data Centre facilities means that security is a vital element of the design process.

Items that need to be considered include:

• Is it acceptable for the Data Centre to be visible from outside the building? If no, then windows might need to be blacked out or an interior wall built between the glass façade of the building and the Data Centre.

• How many doors does a person need to get through before they can get access to the Data Centre? There is a balance to be found between locating a facility near to a goods lift to facilitate easy delivery of new hardware, and exposing the facility to risk of intrusion from external parties.

• It is good practice to ensure that security cameras monitor all entrances to the Data Centre.

• A permit to work system should be established for all Data Centres. Access to maintenance staff should only be allowed when the proper supervision is in place.

Operating Model
When designing the Data Centre, it is important to think through the operating model of the facility. If cabinets or servers need to be brought in to the Data Centre on a regular basis, you need to ensure that the facility is easily accessible from the goods lift, and also that the Data Centre doors are sufficiently high and wide to allow
cabinets to be taken in and out.

Mechanical consultants are also now recommending a hot aisle\cold aisle principle for cooling Data Centres. This requires that rows of cabinets face each other. This design will work effectively in a ‘lights out’ Data Centre but if you run a facility where cabinets are constantly being worked on, then it would be difficult for support staff to work on two cabinets that face each other. Therefore, the mechanical and electrical services designs need to reflect the operating model of the facility.

Off-Site Hosting Facilities
Companies are now able to benefit from remote Data Centre hosting facilities offered by third party vendors. These sites are designed to be highly resilient and to cater specifically for only the IT requirements of an organisation. One major advantage is that the IT strategy of an organisation can become relatively independent of the Facilities strategy.

For example if an organisation decided to relocate to a new HQ building, the majority of equipment can remain in the remote Data Centre, thus significantly reducing the cost and risk of the project.

The majority of remote Data Centres are also able to offer scaleable facilities. For example, on day one you might rent 12 data cabinets, with the option of increasing this whenever you need extra space. You can also build in to the contract an option to reduce space should the equipment you install become smaller in the future.
Again, this can significantly reduce financial risk for the IT Director.

Whilst these off-site facilities might initially seem expensive, when compared with the true cost of building and managing your own Data Centre, they can seem competitive.

The main negative of a remote Data Centre is that control is ceded to the third party that runs the facility. Whilst the majority of providers run highly professional facilities, they are unlikely to understand the urgency of fault diagnosis and resolution that your own internal staff would take for granted.

Summary
The sections above highlight a number of key areas that need to be considered when designing a Data Centre. As a facility of this kind is normally designed for a minimum ten-year period, it is unlikely that you can design the perfect environment. The best you can hope to do is to consider all of the design parameters outlined above and fit them to the technology requirements of your organisation.

Posted in Air Conditioning, Raised Floors, leak detection, Oxy reduction system, section 20 building, Facilities strategy, Suspended Ceilings, Fire Suppression, Uninterrupted Power Supply (UPS), Power Distribution Units (PDUs), Generator, resiliency, Section 20 buildings, Data Centre Design | 1 Comment »