Envision sees growing interest in Post Occupancy Evaluation

Envision has recently been instructed on a number of Post Occupancy Evaluations and Building Energy Audits. This article describes our capabilities by giving reference to a recently completed review we undertook for Costco.

Drawing on our sustainability and engineering capabilities, Envision has seen a strong rise in interest in post occupancy evaluation, particularly amongst our owner-operator clients who are interested in the on-going performance of the building from a cost and wellbeing perspective.  Envision is able to combine a number of our technical and analytical skills to consider a buildings performance in use.  An example of our track record can be seen with a recently completed post occupancy evaluation for Costco Wholesale. Envision was instructed by Costco to review the performance of their Wembley warehouse, 1 year after first opening.  This review was undertaken as part of Costco’s commitment to sustainability and a requirement to achieve BREEAM for the site.

Building Overview

The Wembley warehouse includes a number of sustainable design features to reach BREEAM Excellent:

• Electric Vehicle Charging – The warehouse includes 57 electric charging points, with space for further points to be installed at a later date, should these be required.
• Optimised Roof lights and LED lighting –  The lighting strategy was developed through building simulation to ensure that the building achieves at least a 2% daylight factor across 80% of the main sales floor and staff offices. This is complimented by a full LED lighting scheme with automated photo dimming.
• Decentralised Energy Adaptability –  The development has incorporated a capped connection which allows Costco to become connected to any district heating schemes that may become available in the future.
• PV Installation – A 42 kWp PV array was installed on the roof of the Costco Warehouse. This renewable energy technology was designed to generate 40,283 kWh electricity per annum, reduced the CO² emissions of the building by 6.48%. A review of the PV generation over the first year indicates that the array has outperformed the design requirements.

Key Building Achievements 

• EPC A Rated.
• 46.25% under Building Regulations.
• Score of 41 under the Considerate Constructors Scheme
• BREEAM Excellent (fully fitted) BREEAM 2011

Comparison of actual vs Design

Energy use was predicted at design stage through a dynamic simulation model. The analysis estimated the electrical consumption over the first 12 months of occupation would be 1,059,072 kWh annum. The actual consumption was 2,980,019 – an increase of 2.8 times. Energy assessments often underestimate consumption levels leading to real consumption levels of 2.5-10 times the predicted. The use of TM54 analysis can be used at the design stage to more accurately predict operation energy use and reduce the energy performance gap.

Costco implemented a number of water efficiency measures within the warehouse to attain BREAM Excellent. Through the design stage, the building was expected to lead to a 40% saving in potable water demand by comparison to a notional baseline. This indicated that the building should use 1.27 m3 /FTE staff member / year. Water consumption was recorded as 300 m3 per annum, equivalent to 1.7 m3 per FTE staff member. Targets applied at the design stage were therefore considered to be accurate.

Lessons Learned

• The BREEAM process provided a helpful platform for Costco to design and audit the sustainability features of the building. Regular BREEAM reviews were undertaken at key project team meetings to ensure that the whole team was engaged through the process.
• A standard Costco Warehouse is expected to achieve BREEAM Very Good. The achievement of BREEAM Excellent meant that Costco had to invest in additional aspects of the building beyond the standard specification. The cost uplift of this was estimated to be approximately £500,000. A 3 % uplift on construction costs.
• The sustainability features of the building are welcomed by staff and building occupants. The natural light within the building is particularly effective, especially the addition of windows within the office areas.
•  Following the Post Occupancy Evaluation it was found that energy modelling used for building regulation compliance does not accurately reflect the operational energy use of a Costco Warehouse. The use of TM54 energy analysis could be used to better predict the energy demand of a warehouse in operation.
•  The BRE water calculation provided a reasonably accurate assessment of water use within the warehouse. Comparisons with other buildings in Costco’s portfolio indicates that Wembley uses less water than other recently constructed warehouses.
•  Rainwater harvesting was considered through a life cycle cost analysis. This process determined that there was no whole life cost advantage for the installation of rainwater harvesting, and greater savings could be achieved through the utilisation of highly efficient equipment.
•  There is a handover process at the end of construction for the facilities and warehouse staff. Soft landings could be further improved with repeat training sessions programmed after the store opening, so that aspects of building controls could be discussed in greater detail.
•  The electric vehicle charging points have had limited uptake within the building, with very few people using these during their visits to the warehouse in the first year. The ongoing use of these will be monitored, with greater use in the future with the increasing uptake of EV.
•  A large number of staff cycle to the warehouse, however the showers are not regularly used. Lockers are well used. Future travel planning initiatives may look to consider these factors.

How can Envision Help?

Envision can undertake an independent assessment of a building in operation. We apply various techniques depending on the nature of the evaluation and the client’s requirements. This can include undertaking a review of the original design targets, carrying out on-site measurements, reviews of metering data and utility bills,  building system inspections, staff and building user interviews and questionnaires; and, liaison with the client or building owner.

Envision can provide a key findings report and lessons learned to brief the client team. Such knowledge can be embedded in the design of future projects and passed back to building occupants.

Please contact us if you would like to discuss.