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Technical questions - high NOx boilers, sound levels and data centre coolingJune 2008

BSRIA's technical librarian Stephen Loyd shares the answers to the more frequent technical enquiries from BSRIA members. This month members want to know about high NOx boilers, ventilation for toilets and the right sound levels for fire alarms.

The banning of high nox boilers

My client has advised me that boiler plant with a NOx level greater than 70 mg/kWh will not be acceptable in future. Is there a law stipulating this?

NOx is a term that refers to the two gases NO and NO2. They contribute to smog and acid rain so emissions should be minimised. Manufacturers will select the NOx class of their boilers from a table of five classes, given in European Standard EN 483: 2000.

Class 5 is the best performing class with 70 mg/kWh, and it would seem that, in this case, the client is specifying that only low NOx will be considered in future projects. Boilers are currently available on the European market that emit as little as 30 mg/kWh NOx.

Data centre cooling loads

What are the cooling loads for a data-centre?

The conventional approach to data centre cooling has been to use down-flow computer room air conditioners on raised floor plenums to distribute cold air through perforated tiles.

This solution has been effective for heat densities of 2-3 kW per rack. However, because of an increase in heat densities caused by server technologies, this type of cooling solution is over-burdened.

An average design density is now 8-10 kW per rack. This is expected to grow to 20 kW per rack by about 2010. In some cases, blade server technology is driving heat densities in excess of 30 kW per cabinet. In order to deal with higher heat densities, a common data-centre cooling design will require cooling systems to be sited closer to the heat source.

The effects of British Summer Time

What is the likely effect on carbon emissions of maintaining British Summer Time in winter and introducing double British Summer Time in summer?

This was the topic of a recent Parliamentary question. The answer from the Secretary of State for Environment, Food and Rural Affairs was that the Building Research Establishment (BRE) has estimated that adopting British Summer Time all year round would lead to an approximate one percent increase in CO2 emissions.

Switching to continental time (BST in the winter and BST plus one hour in the summer) would increase carbon dioxide emissions by about two percent.

Continental time was found to generate savings from domestic lighting and cooling in non-domestic buildings, but these effects are likely to be offset by increases in non-domestic heating and lighting, and by a small increase in domestic heating.

Toilet ventilation extract

Can I connect a WC extract into another extract system?

Approved Document F of the Building Regulations provides the basic legal requirements.

For many years an approach recommended in British Standard 5720 Code of Practice for Mechanical Ventilation and Air Conditioning in Buildings was permitted by the Regulations. This clearly stated that certain areas of a building (including lavatories) require separate and independent mechanical ventilation systems.

The British Standard was withdrawn in June 2004. The 2006 version of Approved Document F makes no specific requirement for lavatories to be provided with separate and independent mechanical ventilation.

Sound levels for fire alarms

Is there a maximum sound level for fire alarms?

Excessive sound pressure levels can cause disorientation or even damage to hearing. The provision of a larger number of quieter sounders is preferable to a few very loud sounders.

A recommendation in British Standard 5839 Part 1 states that the sound pressure level of alarm signals should not be greater than 120 dB(A) at any normally accessible point. Advice is given on taking sound measurements.

Sound systems for the disabled

What provision should I make for the hard of hearing in an auditorium?

Part M of the Building Regulations requires the inclusive provision of access and facilities for the disabled in all buildings. Audio induction-loop systems are increasingly being specified as part of audio visual and electrical installations in theatres and auditoriums.

An induction-loop system transmits an audio signal directly into a hearing aid via a magnetic field, greatly reducing background noise, competing sounds, reverberation and other acoustic distortions that reduce clarity of sound.

The magnetic field is created by driving a loop or series of loops with a specialised audio amplifier.

Gas and electricity meters

Is there a requirement to physically segregate gas and electricity meters?

Clause 15.2.3 of the Institution of Gas Engineers publication GM6 states that any purpose-designed meter enclosure must not be used for purposes other than for regulating and metering the incoming gas supply.

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