CASE STUDY NUMBER ONE FOR ENERGY EFFICIENCY

The energy required to heat, cool, ventilate and light Cellnet’s new Service Provision Division HQ

at No1 Leeds City Office Park is only 25% of that needed by a typical prestige office building –

and this despite it being fully air conditioned. A Trend building management system has made a

vital contribution to this high level of energy efficiency. As well as controlling all the HVAC

services – which include chilled ceilings – it has enabled remote monitoring of their performance,

and this has led to problems being quickly identified and put right. Most of the system was

supplied, engineered and commissioned by AES Control Systems of Northampton – to Oscar

Faber’s detailed design and specification.

No 1 Leeds Office Park was developed

by British Gas Properties and provides

6500m2 of office space. The subject of

an EU grant (under the Thermie

scheme), it is one of eight ‘Energy

Comfort 2000’ projects, whose

purpose has been to develop

concepts for commercial and public

building which significantly reduce

energy consumption.

The building combines a range of

features designed to limit energy

usage, such as a high thermal mass,

high levels of insulation, high utilisation

of natural light and solar shading.

Originally, it was intended that the

offices would be cooled partly by

natural ventilation and partly by a low

velocity mechanical system, with

occasional use of forced night

ventilation in the summer. However,

when the premises were let to mobile

phone operator Cellnet, it became

immediately apparent that this would

not meet their needs – largely because

the building was to be used 24 hours a

day. Some form of air conditioning was

unavoidable.

Oscar Faber – who Cellnet had

appointed as the building services,

structural and IT consultants for the fit-

out – developed a novel solution.

Based on an initial concept devised by

Sonofoss Design Services Ltd, it

involved the installation of large chilled

ceiling panels throughout most of the

three-storey building. It was also

necessary to upgrade the existing H&V

plant. This included installing an extra

boiler and adding cooling and

humidification to the main air handling

unit, which delivers air, at floor level, to

the whole building. Yet, though the

services have been substantially

uprated, energy consumption is in fact

slightly less than the level originally

predicted for the building.

Because they have a large surface

area and the ‘coolth’ they provide is

over 50% radiant, the ceiling panels

can be supplied with water at relatively

high temperature (14-18ºC). This is

primarily supplied (via a heat

exchanger, secondary circuit and zone

valves), by a cooling tower circuit.

Should this be unable to maintain the

temperature setpoint then chilled

water is directly injected into the

secondary, the source being a pair of

200kW chillers (with heat recovery)

whose main function is to serve

computer room air conditioning plant.

In practice the cooling tower circuit

First published: IQ News June 1999

Cellnet 2pp 2/11/06 09:53 Page 1

Trend Control Systems LimitedP.O. Box 34, Horsham, West Sussex, RH12 2YF, UK. Tel: +44 (0)1403 211888 Fax: +44 (0)1403 241608 www.trend-controls.com

copes unaided virtually all of the time.

Indeed, the chilled water valve has

gone months without opening at all.

All of the cooling/chilled water plant is

automatically controlled and monitored

by the Trend BMS, as is the air

handling plant, boilers and heating/hot

water circuits. Many of the strategies it

implements are designed to save

energy by avoiding unnecessary plant

operation. For instance, on the cooling

tower circuit it closely regulates pump

and tower fan speeds (via inverter

drives) in strict accordance with

demand. In operating the main AHU, it

constantly monitors air quality

throughout the space and controls the

recirculation damper and fan speeds

accordingly, one effect of which is to

prevent energy wastage when building

occupancy levels fall. Among its many

other tasks, the BMS also controls the

AHU’s heat recovery system to achieve

maximum savings.

The BMS comprises nine Trend IQ

intelligent controllers of various sizes.

Two were installed when the original

plant went in and AES has had to

modify and expand the control

strategies these implement. Owing to

the IQ’s ease of configuration this did

not present problems. The system’s

main operator interface is a graphics-

based Trend 945 supervisor, which is

used by the building’s facilities

manager and maintenance team.

Northampton-based Sonofoss also

has a 945, through which they can

remotely monitor the building (via

modem) – a facility that has proved

extremely valuable. For example it

allowed Sonofoss to spot that the

AHU’s heat recovery dampers were

working incorrectly – just the sort of

fault which could have gone unnoticed

for months and cost thousands of

pounds in wasted energy. It has also

revealed ways in which the control

strategies can be enhanced.

The system has also been monitoring

the site’s gas and electricity

consumption and the figures have

been used in a report on the building

produced by consultants ECD. Data

collected during a four month

monitoring period showed a total

energy usage equating to carbon

dioxide emissions of just 37kg/m2/yr.

Though excellent energy efficiency has

already been achieved there is still

scope for further savings through

measures such as fine tuning of certain

control settings and modifying some

aspects of how plant is operated.

AES Control Systems can be

contacted on 01604 790606.

Current issue: Oct 2006

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