Author: Federico Re Ferrè
Key Points
- The estimated energy consumption for energy-efficient or new buildings have become increasingly optimistic, yet they often fail to meet expectations.
- Theenergy performance gap is the difference between the estimated energy consumption and the actually measured.
- The energy performance gap is problematic not only from an environmental but also from an economic perspective.
- These performance gaps between the ideal and the reality can be observed all over the world and stem from the responsibilities of all the actors involved.
- Reducing the energy performance gap requires an integrated approach that involves all stakeholders in the building process.
As part of theenergy efficiency We set out in search of savings more and more substantial in order to reduce the return times of the investments; by doing so, the estimated consumption of energy-efficient buildings or new have become increasingly optimistic not but often managing to meet expectations.
Table of Contents
- What is meant by the energy performance gap?
- Economic and Environmental Impacts of the Energy Performance Gap
- The Designer’s Responsibilities During the Simulation Phase
- Manufacturer’s Responsibilities During Construction and Commissioning
- Responsibilities of the Occupants
- Frequently Asked Questions About the Energy Performance Gap
- Strategies for Reducing the Energy Performance Gap
What is meant by the “energy performance gap”?
We are therefore witnessing what is referred to in English technical literature as “energy performance gap” (which can be translated as “energy performance gap” and often abbreviated as EPG) or the difference between the estimated energy consumption and that one in fact measured for a a single building or for a group of buildings.
Economic and Environmental Impacts of the Energy Performance Gap
Theenergy performance gap turns out to be problematic not only from an environmental but also from an economic since energy-efficiency measures energy fail fail to pay for themselves within the expected timeframe, thus failing to justify the client’s initial expenses.
These performance gaps between idealized and actual can be observed worldwide and stem from the responsibility of all the actors involved, from the client to theend user including the designer. Below is a list of some of the gap most significant ones found in recent literature.
| Study | Type and number of buildings | Energy Performance Gap |
| Frankel & Turner 2008: How Accurate Is Energy Modeling? | 90 LEED-certified buildings | Energy Use Intensity (EUI) is approximately 8% higher than estimated |
| Carbon Trust 2011: Closing the Gap | 28 buildings in the “Low Carbon Buildings Program” | The average gap is 16% higher than the projected performance |
| Green Building Council of Australia (GBCA) 2013: Achieving the Green Dream: Predicted vs. Actual | 70 Green Star-rated buildings with NABERS energy certification | There appears to be a 25% gap, although 75% of the buildings ultimately do achieve the projected performance |
| Innovate UK Building Performance Evaluation Program (2016) | 48 projects involving 56 non-residential buildings | The carbon footprint was found to be approximately 3.8 times higher than estimated |
| van Dronkelaar et al., “Review of the Performance Gap in Non-Residential Buildings” (2016) | 62 non-residential buildings | The difference between the estimated energy consumption and the actual measured energy consumption is 34% |
| CarbonBuzz (ongoing, started in 2012) | 60 buildings, mostly schools, offices, and university campuses | On average, the buildings consume between 1.5 and 2.5 times the estimated energy |
| Sidewalk Labs Toronto Multi-Unit Residential Building Study (2019) | 19 multifamily buildings in Toronto | The buildings consume about 13% more energy than projected |
The causes of theenergy performance gap are many and from various sources. Let’s take a look at them below.
The Designer’s Responsibilities During the Simulation Phase
The designer certainly plays a crucial role since they are responsible for size the systems to custom for theuse and the occupants. I common mistakes that can creep into the design phase are as follows.
Inappropriate Hypotheses and Assumptions
Very often information such as actual hours of use is difficult to estimate, as it can change frequently—especially for buildings with unpredictable uses.
Difficulty in predicting the future scenario
In some cases, buildings that are completely renovated may undergo changes in their designated use , which may result in baseline consumption figures no longer reliable as a baseline.
Difficulty finding all the information
A great deal of information, such as the actual stratigraphy of the walls, theefficiency of the regulation and other factors can be difficult to find unless invasive tests and sometimes time-consuming.
Overestimation of the Efficiency of Technologies
Some technologies exhibit nominal efficiencies well above those operational; this is the case with condensing boilers and heat pumps , which have drastic reductions in efficiency depending on weather conditions andfield operation (extremely cold climates that reduce the COP of heat pumps, high-temperature terminals, and longer cold seasons that prevent the constant condensation of boiler flue gases).
Inappropriate energy modeling
The use of outdated that is not up to date or difficulty replicating the exact geometry of the building.
Adoption of inefficient or oversized systems
Machines oversized may sometimes have lower efficiency because they are forced to operate at part-load conditions that are too low.
Manufacturer’s Responsibilities During Construction and Commissioning
After the design we move on to the construction and commissioning , during which additional uncertainties may arise, which contribute to the possibility of an energy performance gap.
Low-quality building materials
The use of materials with lower performance than those specified by the designer such as insulation with the lowest thermal conductivity for insulating opaque surfaces or windows and doors with higher U-values.
Low-quality building systems equipment
Similar to what we saw with the construction work, there may also be low-quality choices on the systems side, such as equipment with lower efficiency, remote control systems that are less precise.
Unskilled labor
The presence of skilled workers is often necessary for the proper execution of the work; workers with little or no experience may make mistakes:
- Making a mistake when proper installation of insulation , resulting in unevenness and thermal bridges;
- to make a mistake the location of room sensors preventsoptimal system control;
- not properly calibrating thermostatic valves in the field.
Changes Made During Construction
It is possible to make changes to the design on-site, but this sometimes leads to changes to the systems in a way that prevents them from functioning as intended.
Inadequate or Absent Commissioning
The commissioning is a vital part of the process because it determines whether the system can operate properly while meeting the efficiency requirements, air quality , and comfort. Cutting this process short for reasons of time and cost can result in the systems not operating as intended under design conditions.
Responsibilities of the Occupants
In the final phase—when the occupants begin using the building—additional problems may arise.
Unethical Behavior by Users
Users often don’t pay attention to rules of safe driving ofbuilding and leaving doors and windows open (thereby causing rooms to cool down during cold weather and heat up during hot weather) or forgetting to turn off the lights and HVAC systems when the spaces are unoccupied.
Lack of user training
TheNew systems may have different operating procedures that require initial training for users in order to make the most of all the benefits and avoid waste.
A advanced system by management that takes advantage of thethermal inertia of thebuilding for ensure comfort Minimizing consumption is pointless if users prefer the traditional lighting ceremony at set times, for example; lights with twilight sensors that adjust the brightness to match natural light They are useless if the user wants to continue with theOn/Off Use without modulation.
This and many other cases are clear examples of how educating users can help save energy.
Under-consumption effect (pre-rebound)
It has been noted that sometimes the buildings under poor conditions of energy efficiency consume less than in In reality, they should because of the occupant behavior who are used to a reduced comfort or that They want to save money keeping setpoint by temperature more lower than they should be (or even by keeping the systems turned off during certain periods).
If a building, prior to theenergy retrofit is already using less than it should without realizing it, this will result in smaller savings because a portion of the energy was never used in the first place.
Frequently Asked Questions About the Energy Performance Gap
Does the energy performance gap apply only to new buildings?
No, this phenomenon occurs in both new buildings and renovated ones. In the Extensive Renovations the risk may be greater due to the difficulty of knowing exactly what the existing structural characteristics.
How can the energy performance gap be prevented during the design phase?
Key strategies include theuse of software for certified , conservative assumptions regarding user behavior, safety margins regarding plant performance, client involvement in defining realistic usage profiles.
Strategies for Reducing the Energy Performance Gap
Reduce theEnergy Performance Gap requires an integrated approach that involves all stakeholders in the construction process.
The most effective strategies include:
- a calibrated modeling (for example, using dynamic simulation software),
- rigorous commissioning with systematic of system performance prior to delivery,
- Continuous monitoring with installation of BMS systems and IoT sensors for real-time monitoring of consumption,
- user training on best management practices
- Performance-Based Contracts: contractual guarantees based on actual measurements (Energy Performance Contracting).
Only throughconstant attention at every stage of the life cycle of the building is it possible to bridge the gap between design and reality, ensuring that investments in energy efficiency yield environmental benefits and economicbenefits expected.
For more information on how to reduce theEnergy Performance Gap please contact our team Enertech Solution.
