Monitoring Retrofit Performance: Proving Improvements Work

Housing providers are investing millions in energy efficiency retrofits—external wall insulation, heat pumps, new windows. But how do you know these improvements are delivering expected benefits? Too often, "performance" is assumed based on design calculations rather than measured in reality.

The Performance Gap

What Is the Performance Gap?

The "performance gap" describes the difference between predicted energy performance (from design models and EPC calculations) and actual in-use performance. Studies consistently find that:

• Real energy consumption often exceeds predictions by 20-50%
• Some retrofits underperform expectations significantly
• Variation between similar properties is higher than expected

Why the Gap Exists

Several factors contribute:

• Installation quality: Gap-free insulation in theory, gaps in practice
• Occupant behaviour: Different from standard assumptions
• System commissioning: Heat pumps not optimised for the property
• Design assumptions: Models that don't reflect reality

Why Monitoring Matters

Accountability

Funders and regulators increasingly expect evidence:

• SHDF requires monitoring of a proportion of retrofits
• Funders want to see return on investment
• Boards need assurance that money is well spent

Learning and Improvement

Monitoring enables continuous improvement:

• Identify which approaches work best
• Spot installation issues early
• Refine specifications for future projects

Tenant Outcomes

Retrofits should improve tenant wellbeing:

• Are homes warmer?
• Have humidity problems reduced?
• Are energy bills actually lower?

What to Monitor

Temperature

The most basic metric but essential:

• Internal temperature: Are homes reaching comfortable levels?
• Temperature stability: Less fluctuation indicates better insulation
• Heat-up time: How long to warm from cold?
• Cool-down rate: How quickly heat is lost when heating is off?

Humidity

Critical for retrofit monitoring:

• Has relative humidity improved?
• Any condensation risk from reduced ventilation?
• Dew point margin on surfaces

Poorly planned retrofits can actually increase humidity problems by making properties more airtight without adequate ventilation.

Energy Consumption

Direct measurement of energy use:

• Smart meter data (gas and electricity)
• Heat pump performance (COP measurement)
• Comparison with pre-retrofit baseline

Air Quality (Optional)

For comprehensive assessment:

• CO2 levels (ventilation adequacy)
• VOC levels (material off-gassing)
• Particulate matter

Monitoring Approach

Pre-Retrofit Baseline

Monitoring before works is essential:

• Install sensors at least one heating season before retrofit
• Capture "before" performance data
• Understand existing conditions and occupant behaviour

Without baseline data, you can't measure improvement.

During Works

If sensors remain in place:

• Record any disruption period
• Note commissioning activities
• Identify when "steady state" is reached

Post-Retrofit

Continue monitoring after completion:

• At least one full heating season
• Compare to baseline on like-for-like basis
• Account for weather differences between periods

Analysing Results

Weather Normalisation

Winter 2023 and winter 2024 weren't identical. To compare fairly:

• Use degree-days to normalise for weather
• Compare similar periods (not just calendar dates)
• Account for external temperature differences

Occupancy Factors

Changes in occupancy affect results:

• Same household before and after?
• Changes in number of occupants?
• Different heating behaviour?

Comfort vs. Efficiency Trade-off

Be aware of "comfort taking":

Tenants in improved properties often choose to be warmer rather than use less energy. This is a valid outcome (improved wellbeing) but means energy savings may be lower than predicted.

Heat Pump Specific Monitoring

Why Heat Pumps Need Extra Attention

Heat pumps are more sensitive to installation and operation:

• Performance depends heavily on flow temperatures
• Undersized systems struggle in cold weather
• Tenant operation affects efficiency dramatically

Key Metrics

• Coefficient of Performance (COP): Heat output vs. electrical input
• Flow and return temperatures: Are they appropriate?
• Run time patterns: Is the system cycling excessively?
• Supplementary heating use: Are backup heaters firing frequently?

Reporting Requirements

SHDF Requirements

Social Housing Decarbonisation Fund requires:

• Monitoring of a proportion of retrofitted properties
• Performance data collection for specified periods
• Reporting through specified channels

Internal Reporting

Keep your stakeholders informed:

• Regular updates to investment decision-makers
• Performance dashboards for operational teams
• Tenant feedback mechanisms

Common Issues Found Through Monitoring

Installation Defects

Issues monitoring can reveal:

• Thermal bridges from incomplete insulation
• Air leakage at junctions
• Condensation from inadequate ventilation strategy

Commissioning Problems

Heat pump issues commonly found:

• Flow temperatures set too high
• Controls not optimised
• Weather compensation not configured correctly

Occupant Issues

Behaviour-related findings:

• Heating system not understood
• Windows opened excessively
• Ventilation systems switched off