Do low energy buildings really deliver results? Last month, Thomas Lane found two new-build offices that failed to live up to all their green credentials. Here, he reveals if two refurbished offices performed any better

Low-energy refurbishment should be the greenest game in town. Reusing office buildings cuts down on the energy embodied in the materials and if carefully done can massively reduce energy consumption, plus provide a much better working environment for staff. If done sensitively, it can also improve the quality of life for the general public by transforming concrete blots on the landscape into decent-looking schemes. Crucially, in these cash-strapped times, it also saves lots of money.

But how much energy does it really save? Does refurbishing old crocks rather than building afresh really make staff more comfortable and imbue them with a new sense of pride in their place of work?

Answering the question is difficult because not many people have monitored energy use and staff satisfaction levels before and after refurbishing their building. It’s costly and time-consuming and if the building owner doesn’t think the results are flattering they are unlikely to publish them widely.

In the second of two features looking at post-occupancy building performance we bring some answers to this difficult question. We have teamed up with the Carbon Trust and consultancy and research body BSRIA to bring you the true story of how office refurbishment affects building performance. With funding from the Department of Climate Change, the Carbon Trust offered advice and support as part of its low-carbon building accelerator programme, which is designed to reduce carbon emissions in existing buildings. The two buildings featured have been monitored for a year after completion by consultants Hoare Lea and Arup. BSRIA’s Rod Bunn, who was behind the PROBE series of post-occupancy evaluations in the nineties, has waded through boxes of raw data and number-crunched it into shape. Here is what Bunn found.

ELIZABETH II COURT

Projects

Prior to refurbishment, this was a tired, sixties office situated in the heart of Winchester. Not only did it blight the city but it leaked water, guzzled energy and sapped the morale of the staff forced to endure its long, dingy corridors. They had nothing good to say about it, giving it one of the lowest scores in 20 years of Building Use Studies (BUS) surveys. Carbon dioxide emissions were 72kgCO2/m2 each year. The objective was to transform this monster by slashing emissions in half to just 35kgCO2/m2 each year.

Carbon emissions have now dropped to 43kgCO2/m2 a year, which misses the target, but is a big improvement. Staff are happier too, rating the building average to good.

The building

The building is occupied by Hampshire council and consists of three blocks arranged around a courtyard that was originally used for car parking. The project was done in two phases to ease staff decanting costs. The 3,000m2 east block was finished first and is the subject of this evaluation. All three blocks were stripped back to the concrete frame and new cladding and services installed at a cost of £40m, which is much less than the £75m needed for a new building. The refurbished building achieved a BREEAM “excellent” rating. The dingy cellular accommodation has been swept away and replaced with open-plan offices.

Building design and low-energy features

The project is a collaboration between architect Bennetts Associates and environmental engineer Ernest Griffiths, and is a good example of low-energy design uncomplicated by biomass, ground source heat pumps or solar panels. The duo had previously worked together on several naturally ventilated buildings and wanted the same solution for this scheme. But the noisy city centre location meant opening windows would disturb staff, so an innovative solution was adopted. Fresh air is drawn through the windows on the quiet courtyard side and is extracted via regularly spaced chimneys on the street side of the building at high level to mitigate noise. The building management system automatically controls air flow rates via motorised window actuators and sashes inside the chimneys. The building also has mechanical ventilation for when it is too cold to open the windows. Air is supplied by small low pressure-loss air-handling units on each floor which minimise ductwork runs, cutting energy use. Heat is recovered from the IT suite and used for space heating; additional heat is supplied by gas boilers.

Natural light has been maximised and suspended fluorescent luminaires are used in the office areas. The lights have movement sensors and programmable light level sensors.

Energy use results

The building is not far off its design targets. Regulated energy use, which covers heating, ventilation, hot water, cooling, lighting and pumps is 99kWh/m2 each year. Total annual energy use is 131kWh/m2 , 6% more than the design target of 123kWh/m2. This target was based on a modified Energy Consumption Guide 19, or ECON19, benchmark - a set of nineties best practice standards for different types of office building. Gas use is lower than the design estimate: 54kWh/m2 per year compared with 57kWh/m2. But 17% more electricity is used than the design estimate of 66kWh/m2 per year.

Carbon dioxide emissions

CO2 emissions for the first year of occupation were 43kgCO2/m2 each year, 20% higher than the design target of 35kgCO2/m2. Although the building is emitting more CO2 than the design prediction, this figure is much better than the new-build offices we featured last month (1 July, page 38).

Projects

The long dingy corridors and cellular accommodation was replaced with light and airy open plan offices. The concrete soffit was left exposed to help regulate internal temperatures which is a key part of the natural ventilation strategy

What went wrong?

There is nothing fundamentally wrong with this building; it is more of a case of fine-tuning it to bring energy use down to the modelled prediction. For example, the sashes in the ventilation chimneys were opening prematurely which meant cold air was dumped onto people sitting near them. Adjusting the CO2 sensors to operate at a higher setpoint resolved the problem.

Another issue was people pulling blinds down to counter glare from the early morning sun but not raising them once the sun is higher in the sky, so the lights stay on.

Hampshire council says the presence of just a few people working at weekends brings on the mechanical ventilation, water heaters and chillers, which manages to take energy use up to 50% of a typical day. The systems have been altered to avoid this.

What the users think

The scores for occupant satisfaction have leapt up and it is in the top 40% of buildings surveyed. This represents an improvement of 59%. People are happy with air and temperature quality all year round. The natural ventilation strategy works well with summer internal temperatures in the range of 22-26ºC. People are positive about the design and feel the building gives a positive image to visitors.

What this tells us

This project demonstrates that refurbishment can cut CO2 emissions almost in half and provide vastly better facilities for staff. This building is performing close to the design prediction but isn’t quite there yet. Fortunately, Hampshire council is an experienced, hands-on client, so fine-tuning should see further energy reductions.

Despite the experienced team this project suffers from some of the same problems that commonly afflict new build when it comes to reducing energy use. The building is extensively metered but there were problems with the accuracy of some of systems, which has made gathering data problematic.

Getting staff to understand how the building works is also crucial, and although the council appointed office champions, it was difficult to get them to engage with technical issues. Building service guides weren’t issued to staff and some of the instructions next to room controllers were incorrect.

THE CLIENT’S REACTION

Steve Hall, Hampshire council's director of engineering services says the monitoring shows the building is performing largely as expected. "While we have not managed to achieve what we set out to, we have done very well to get to this point," he says. Hall describes it as the "beginning of a journey" because he wants to get the building to perform as predicted. "It's easy to get the big, quick wins, its fine-tuning to get the last 5-10% of energy savings that is tricky," he says.

The fine-tuning includes setting the lights to go off automatically after 15 minutes rather than 20 to save energy. Hall has also cut back energy use on Saturdays (see "What went wrong?", below). The mechanical ventilation is now switched off and the heating period has been reduced, as Hall says the building will retain heat. The effects of this change won't be known until next winter.

Hall will also run a low-key campaign to make staff aware of the impact they have on energy use and how to control the building, which will hopefully cut energy use.

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NORTH WALES POLICE

Projects

Overheating was one of the biggest problems afflicting North Wales Police HQ. This has been tackled by adding brise soleil and reducing the glazed areas

North Wales Police headquarters in Colwyn Bay, Conwy, was typical of seventies concrete-framed buildings in that it was leaky, badly insulated, uncomfortable and sucked up energy. Large areas of glazing meant summer overheating was a particular problem, with temperatures hitting 34ºC during the hot months. Unsurprisingly this was reflected in the BUS occupant survey, with complaints about high temperatures and poor air quality topping the list of grumbles. CO2 emissions were 74kgCO2/m2 each year.

This was a light-touch refurbishment compared with Elizabeth II Court, reflected in the budget of £2.4m. The design team wanted to reduce emissions by a minimum of 30% but unfortunately the building is some way off this, with measured reduction of 18%. At least the building is more comfortable - staff now rate it average to good.

The building

The 4,267m2 building functions as an administrative centre for North Wales police. It features horizontal bands of windows allowing plenty of light into the naturally ventilated cellular offices. Corridors and core areas were mechanically ventilated.

The main problem was high levels of solar gain, especially on the south and west facades. Heating was via inefficient perimeter warm-air convectors. With no local control on the heating system, rooms were either too hot or too cold in the winter.

Refurbishment objectives focused on tackling the overheating problem, upgrading the heating system and modernising the working environment. With help from the Carbon Trust the team was encouraged to cut CO2 emissions below the client target of 20%.

Building design and low-energy features

The thermal performance was improved by upgrading the building envelope to meet 2006 Part L. This included an air pressure test result of 7m3/h/m2 at 50Pa. The overheating issue was tackled by fitting brises-soleil to the east, west and south facades. New windows were fitted and the glazed area reduced by incorporating solid panels in previously glazed areas. The brises-soleil and reduced glazing area allowed the natural ventilation strategy to be kept. The windows feature a motorised toplight operated by the building management system and a manually openable bottom light. A light shelf was fitted between the two opening lights to reflect daylight onto the ceiling - reducing the need for artificial lighting. The lighting was replaced by daylight-dimmable occupancy sensor controlled florescent fittings.

Apart from the relatively recent boilers, the heating system was replaced. Heat is now supplied by radiators fitted with thermostatic valves. The building management system was replaced and now has state-of-the-art features, such as the ability to tailor the on/off times to temperatures outside the building, adjustment of water system temperatures to suit external conditions and multiple zoning throughout the building. No low or zero-carbon technologies were fitted.

Energy use results

The building hosts a large, energy-intensive server facility serving the entire force. Electrical demand for these servers was separated from the energy needed for heating, lighting, pumps and fans, cooling, office equipment and catering. The energy use for the server room prior to refurbishment was 113kW/m2 a year. Measured energy use for the room after refurbishment was 82kW/m2.

Disappointingly, measured energy use, excluding the server room, is over three times higher than the design prediction. The building is using 168kW/m2 each year, while the prediction was for 51kW/m2. However this is 24% better than before refurbishment when energy use was 207kW/m2. Gas use is particularly high, at 87kW/m2 per year, four and a half times the prediction of 19kW/m2.

Carbon dioxide emissions

On advice from the Carbon Trust, the client set a minimum target of reducing the building's CO2 emissions by 20%. However, the design team went for a target of 30%.

The refurbished server room emits 44.6kgCO2/m2 each year while heating, lighting, pumps and fans, cooling, officeequipment and catering in the rest of the building emits 61kgCO2/m2.

This is 18% better than the 74kgCO2/m2 emitted by the building before refurbishment, but falls short of the client's and designer's aspirations; the building emits 65% more CO2 than the design prediction of 22kg/CO2/m2.

What went wrong?

The figures for energy use come with a big caveat. There were problems with the meters, including inaccurate readings and malfunctions. These problems mean only five months worth of data was available, so energy use for the year has been extrapolated.

However, this doesn't disguise the fact that actual energy consumed is above the targets. The refurbishment has suffered more than its fair share of problems. Work started in November 2007 and was meant to have been completed by August 2008. The contractor David Maclean went bust and was replaced by City Build. The building also suffered a fire in a roof-top plant room during the construction period. All this contributed to the project busting the £2.4m budget. Although the police are in the building, it still hasn't been formally handed over. Commissioning the services has been so protracted that these either didn't conform to the specification or commissioning couldn't proceed.

According to Hoare Lea, which carried out the monitoring, excessive energy use is down to problems with the heating control system, particularly with the valves controlling heat flow to individual zones. In naturally ventilated buildings, winter overheating is easily controlled by simply opening the window. More people than anticipated are leaving equipment on at the weekend. The gap between the brises-soleil and the light shelf, intended to direct light onto the ceiling, caused glare for some occupants when the sun was at certain angles. Users taped cardboard on the upper portion of the window to get round the problem, but Hoare Lea says this means the lights come on to compensate. The gap between the light shelf and the top window pane has been reduced in a bid to fix the problem.

What the users think

Before refurbishment, the building use study results placed it in the bottom 10% of buildings. Users were deeply unhappy with summer temperatures - a temperature of 41ºC was recorded in one instance. They were also unhappy with summer and winter air quality. They said the building was uncomfortable and unhealthy; its only redeeming features were good lighting and acoustics.

The good news is users are much happier with their refurbished building. It scores average to good, with winter air quality, comfort, design and image to visitors coming out above average. Lighting was at the low end of the "satisfactory" benchmark, possibly because of the problems with glare.

projects

Close up of the brise soleil and reduced glazed areas

What this tells us

On a positive note, building users are much happier with their working environment than before, plus the building is emitting 18% less carbon dioxide. But it could have been better. The upheaval caused by the contractor going bust hasn't helped as a stable team working collaboratively is vital to achieving the low-carbon goal. A clear commissioning plan coupled with time to implement it is essential to ensuring that the building is functioning optimally, but this wasn't possible because of these problems. That said, if the faults with the heating system can be fixed and the system re-commissioned then gas use should fall.

Predicted energy use is based on an ideal scenario where people religiously turn things off and know exactly when to open and close windows. A staff awareness campaign is essential if energy use is to drop towards the levels predicted.

Even so, the Carbon Trust says the building is unlikely ever to achieve the predicted gas consumption values because the modelling doesn't reflect reality - people will have the windows open when the heating is on. Also, as the specification and design changes, thermal models need to be updated, to reflect the effect these alterations will have on the building's
likely energy performance. "If you freeze the thermal simulation model two years before construction starts, don't be surprised if energy bills are three times higher than predicted," warns Bunn.

THE CLIENT'S REACTION

North Wales Police says it has achieved its objectives, describing the building as "a million times better than before". "The building still has teething problems but to all intents and purposes we have got what we wanted out of the refurbishment," says Liz Bryan, the force's projects co-ordinator. She describes the internal environment as significantly better, with users being able to control the heating,. The night cooling strategy, where windows are only opened when the building is occupied, is working well despite security concerns.

She is unhappy that energy consumed by the force-wide data centre is included in the figures within the full report (available online) saying this skews the results. These figures have been separated out in this feature for clarity. Bryan also describes the design predictions as "seriously flawed" and is happy that the building is performing close to the force's target of a 20% reduction in emissions. She adds that it is hard to be precise about gas use as the figures include other buildings on the site. Hoare Lea says that, because gas meters weren't working properly, gas use was apportioned across the whole site.

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