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SPACE Craigmillar, Edinburgh

SPACE Craigmillar, Edinburgh

Monitoring work undertaken to help inform future refurbishment projects

Overview

The Scottish Energy Centre at Edinburgh Napier University joined CastleRock Edinvar to undertake a feasibility study, investigating the improvements that can be achieved through retrofitting an envelope improvement system.

TSB funding allowed for a side-by-side comparative study to be conducted, using in-situ U-value measurements and infra-red images to compare a thermal enhanced office space with a similar office with no thermal enhancement.

The building in question was constructed as Craigmillar Primary School in the 1930's. Now 'B' listed, and following the school's closure in 1999, the building was fully refurbished by owners CastleRock Edinvar in 2005, to provide 1,651 sq. m of office accommodation and 337 sq. m of community arts and theatre spaces.

In 2012, the Scottish Energy Centre were asked to identify potential thermal improvements that could be made to the building.

Approach

The Scottish Energy Centre undertook an investigation, conducting measurements to identify the thermal performance of the existing building fabric, compared to that which received an envelope upgrade. The measurements were carried out in two adjacent rooms, the 'control' room and the upgraded room.

Both rooms are on the South facing facade of the building, and most of the thermal improvements were made to the South facing, external, listed face of these rooms. Both rooms are 6.2m by 7.9m, with one main entrance and four 1.2m x 1.9m windows. The control room is taken to be representative of the existing fabric of the rest of the structure.

 

Control Room - Existing Fabric

Windows

The windows in the control room are single glazed, timber sash and case and are representative of the windows all along the front facade.

Walls

The existing make-up of the South wall construction, above the windows was:

  • 500mm pre-cast concrete lintel
  • 75mm unventilated air gap
  • 50mm mineral wool insulation
  • 12.5mm plasterboard on 50mm metal framing.

 

Below the window, the South wall construction consisted of:

  • 25mm roughcast external render
  • 230mm solid brickwork
  • 50mm mineral wool insulation
  • 170mm unventilated air gap
  • 12.5mm plasterboard internal lining.

 

The North wall construction, prior to any upgrades included:

  • 25mm roughcast external render
  • 90mm solid brickwork
  • 110mm cavity
  • 110mm brick
  • 50mm unventilated air gap
  • 50mm stud framing with 12.5mm plasterboard.

 

The mineral wool insulation was added to internal faces of the external walls during refurbishment in 2006.

 

Upgraded Room - Thermal Upgrades

Windows

The windows in the upgraded room were improved by the installation of a toughened, low emissivity secondary glazing unit, in an openable uPVC frame. The secondary units are installed internally, with an approx. 100mm air gap between the units and the existing windows.

A radiant heat barrier, window blind was also installed, between the glazing units.

Walls

The South wall area, above the suspended ceiling tiles, was improved by the addition of 75mm hemp insulation, in the air gap between the concrete lintel and the existing mineral wool. In addition, 100mm hemp insulation was added to the ceiling, both between the joists, and above them. The wall area below the window gained 170mm of bead insulation, which was blown into the gap between the mineral wool and the plasterboard.

The North wall areas, had blown bead insulation pumped into the 110mm cavity, plus hemp insulation was laid between and above the joists at ceiling level as with the South wall.

 

Testing Methodology

U-value measurement equipment was installed in eight locations, across the two rooms on 24th September 2012. Measurements were taken for two weeks, then the results were analysed. The methodology used, followed a well-established format, using Hukseflux heat flux transducers as per the details in the full case study.

A thermographic survey was also conducted, to visually display areas of heat loss through the building fabric. Thermographic surveys can help identify gaps in insulation or cold bridging. There are specific environmental conditions that are required to conduct a thermographic survey, including internal/external temperature differences and weather conditions. Download the case study document on the right for full details.

Temperature probes were installed within the space between the existing and secondary glazing units, two on either side of the heat barrier blind.

Performance

U-value Measurements

In-situ U-value measurements were taken on the windows, North wall (top) and South wall (above and below window).

The addition of the secondary glazing was seen to improve the U-value of the window from 5.2W/m²K (control room) to 0.6W/m²K (upgraded room). These figures were comparable with measurements in other refurbishment monitoring projects carried out by Scottish Energy Centre. This suggests that the addition of the radiant heat barrier blind has had no significant effect.

Temperature probes were installed within the window space, to measure the temperature differential on either side of the heat barrier blind. Results showed a noticeable increase in temperature difference on either side of the blinds, as temperatures peaked around 4 - 5pm. It was felt however, that the trapped heat may not be able to circulate back into the room, due to the thermal properties of the secondary glazing.

 

Heat flow mats were installed on the wall areas above the suspended ceilings, to measure the 'control' and upgraded U-values of the fabric. The measurements indicated that the addition of the hemp insulation, improved the U-value from 0.43W/m²K to 0.24W/m²K. The area below the window was also tested and also demonstrated an improved thermal performance, with U-values reducing from 0.36W/m²K to 0.12W/m²K.

The North wall U-value also reduced, from 1.11W/m²K to 0.53W/m²K. While a significant reduction, this is not as low a value as had been expected. Reasoning for this is detailed in the 'lessons' section.

 

Thermographic Surveying

The thermographic survey results in images like that in the picture below. The four upper windows on the right are the control room, and the subsequent (darker) four windows are the upgraded room. Their darker colour demonstrates a reduction in the heat loss through the windows.

 Thermal SPACE

Thermogram © Scottish Energy Centre

Thermographic surveys on the control and upgraded walls, also showed a reduction in heat loss from the areas above the suspended ceiling tiles, and below the windows.

Lessons

Ideally, data would have been collected for six weeks, but time constraints associated with the funding programme, required results to be provided sooner. As a result of the shortened monitoring period, a review of the error analysis of the results suggested that the South facade results could be subject to uncertainty of between ±50 and ±65%. Normally U-value testing is subject to uncertainty of ±10%.

 

Retrofitting insulation in isolated areas of wall presented issues with maintaining continuity of the thermal envelope. In addition, thermal performance on the North wall was not as improved as had been expected. This may be for several reasons, including uncertainties due to the short monitoring period, settling of the blown insulation or external air infiltrating the air gap. Thermographic images confirmed heat loss through air leakage paths directly below the suspended ceiling, which may result from a problem with continuity and lapping of insulation.

Further investigative work, including air tightness testing will be conducted to explore and resolve these issues. A longer period of U-value testing will also be carried out, to reduce the errors to within the ±10% uncertainty level.

 

The upgrades to the windows have been found to be particularly successful.

Links

Scottish Energy Centre, Edinburgh Napier University

Castle Rock Edinvar Housing Association

SPACE Offices

 

Resource Efficient Scotland supported the preparation and presentation of this case study for the Retrofit Scotland website.

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