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How to make sure your in-use sustainability sums add up

Header Image

Words:
Jess Hrivnak

The RIBA 2030 Climate Challenge is asking architects to check their buildings' energy performance against sustainability targets. This first of a mini series sets out why operational energy calculations matter and how to go about them on a live project

Many practices have now committed to the RIBA 2030 Climate Challenge and aiming for clear sustainability targets. Part of the process is submitting the project performance data to RIBA via the Data Submission Form.

But what analysis is required in order to submit completed projects?

Objective of the energy targets and why measured sustainability outcomes matter

The objective of the operational energy targets in the Challenge is to ambitiously increase the efficiency of buildings to reduce their impact on the planet and be more economical to run. Building fabric therefore needs to be high performing, systems have to be effective and user consumption must avoid being profligate.

To deliver this objective, the architectural sector needs to understand if, where and how any shortcomings between predicted energy performance and actual energy use occur and tweak the designs of the next generation of projects in light of lessons learned.

The importance of collaboration with clients

The focus of the Challenge on the delivered performance efficiency in completed projects is a radical call to the architectural community to get ‘stuck in’ with the analysis of measured data. It is a task that some may feel less comfortable undertaking.

RIBA recognises that a building’s performance data may not be in the project team’s direct ownership, however architects have an influential role in liaising with clients to obtain usage data.

To this end RIBA has produced supporting PDF documents: ‘How to Talk to Clients About the 2030 Climate Challenge’ and ‘A Client Guide to the RIBA 2030 Climate Challenge’  

Which aspects of project performance do you need to check against the RIBA Targets?

  • Energy data from the building is required. This is ideally 12-months of data (as summer and winter seasons must be represented).
  • The data must include energy delivered by the grid whatever the tariff, including 100 per cent green electricity tariffs, and energy used from on-site renewables.
  • The building’s gross internal floor area (GIA) is also required.

How to do the calculations

Energy performance in buildings is commonly measured in kWh/m2/yr, ie kilowatt hours of energy per square metre of building per year. It is sometimes referred to as an Energy Use Intensity (EUI) figure.

A kilowatt hour (kWh) is a composite unit of energy equal to one kilowatt (kW) sustained for (multiplied by) one hour. It is commonly used by utility companies to bill customers for their energy consumption. KWh energy consumption figures are therefore easy to obtain.  

By way of explanation:

(A) = Annual consumption of imported (grid) energy

KWh energy consumption figures (A) can be taken directly from gas and electricity utility bills or BMS reports or as the difference between manual meter readings taken one year apart (or monthly over a year).

An Excel spreadsheet to enter the monthly consumption is an easy way to track this. Air/ground source heat pumps are included here as these technologies use grid electricity efficiently, but do not generate it themselves.

(B) = Annual consumption of on-site renewable energy

If on-site renewables (such as PV panels) are present, the renewable energy in kWh (B) that is used directly on site, ie not sold back to the grid, must be calculated.

This is the total generated renewable energy minus the energy exported back to the grid. For PVs, the inverter will show the total on-site generated electricity and a smart export meter will show the amount sent back to the grid.

If no smart export meter is present, it can be assumed that 50 per cent of the generated energy is used on site and 50 per cent is sold back to the grid (as assumed by the Feed-In Tariff Scheme).

The sum of (A) and (B) will provide the annual operational energy consumption of the property.

Lastly, the building’s gross internal floor area (GIA) needs to be obtained in square metres. This can be taken from building plans. All floor levels must be included (C).

RIBA 2030 Climate Challenge target metrics for domestic /residental.
RIBA 2030 Climate Challenge target metrics for domestic /residental.

Case study: Zetland Road Passivhaus, Manchester 

Developer and environmental consultancy Ecospheric's exemplary retrofit of two Victorian semi-detached dwellings achieved a 95 per cent reduction in space heating demand. They were the first homes in Europe to attain EnerPHIt Plus certification.

Post-occupancy data for number 6 Zetland Road is shared here (see the table above) courtesy of Ecospheric and shows how to assess alignment with the RIBA 2030 Climate Challenge Targets .

On this project, the occupier wrote down the meter readings every month and shared these with the design team (see below). The property did not have a smart export meter installed, therefore assumptions on PV energy sold back to the grid have been made using FITs rate of 50 per cent.

  • Zetland Road house electricity meter.
    Zetland Road house electricity meter. Credit: Ecospheric. Image annotations, Jess Hrivnak.
  • Zetland Road house PV generation meter.
    Zetland Road house PV generation meter. Credit: Ecospheric. Image annotations, Jess Hrivnak.
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  • 6 Zetland Road, Manchester: basement and ground floors.
    6 Zetland Road, Manchester: basement and ground floors. Credit: Ecospheric
  • 6 Zetland Road, Manchester: first and second floors.
    6 Zetland Road, Manchester: first and second floors. Credit: Ecospheric
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6 Zetland Road: the PV generation is only just above 50 per cent of predicted due to initial problems with the system. It is expected that the generation will increase now these have been resolved. The RIBA 2030 Climate Challenge targets are based on Gross Internal Floor Area (GIA). Treated Floor Area (TFA) is the Passivhaus measure and is very similar, but slightly different, from GIA. Typically, TFA equates to 90 per cent of GIA. The figures provided have been adjusted.
6 Zetland Road: the PV generation is only just above 50 per cent of predicted due to initial problems with the system. It is expected that the generation will increase now these have been resolved. The RIBA 2030 Climate Challenge targets are based on Gross Internal Floor Area (GIA). Treated Floor Area (TFA) is the Passivhaus measure and is very similar, but slightly different, from GIA. Typically, TFA equates to 90 per cent of GIA. The figures provided have been adjusted. Credit: Data courtesy of Ecospheric. Image, Jess Hrivnak

Ecospheric have taken this learning onboard and aim to install smart import/export meters in all their buildings going forwards.

This case study demonstrates that, as occupants adjust to their new homes and systems are tweaked, energy performance improves.

It also demonstrates how traditionally perceived ‘difficult to treat’ Victorian properties can be retrofitted to align with ambitious energy targets.

Jess Hrivnak is RIBA’s sustainable development adviser and sustainability consultant

For more on this, see RIBA 2030 Climate Challenge

Main image: Zetland Road Passivhaus, Ecospheric. Rick McCullagh.


 

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