April 16th 2023

IES Digital Twins support performance verification of Affordable A-Rated Homes

IES Digital Twins support performance verification of Affordable A-Rated Homes

Working in partnership with Ó Cualann Cohousing Alliance and Trinity College Dublin, IES used their Digital Twin technology to assess 46 A-rated designed homes within an affordable housing development. The project aimed to identify whether the energy performance of A-Rated dwellings aligns to their high efficiency design intent, while also assessing impacts on Indoor Environmental Quality (IEQ) and operational energy costs for the homeowners. 

Wireless IoT (Internet of Things) sensors were installed to measure temperature, relative humidity, CO2, lux levels and motion, and each home was monitored over a 12 month period. To ensure comparable analysis of results, the sensors were placed in the same locations in each home. Electricity and gas data was also gathered from utility bills and low-cost electricity monitors, placed retroactively in the homes. 

Physics based models of each building were created using the IES Virtual Environment (VE) and data from the IoT sensors was integrated into the IES data analytics platform, iSCAN. Each sensor sends data every 5 minutes to the iSCAN platform, resulting in a total 66,240 data points being collected each day for the Ó Cualann Cohousing Alliance. 

The models were then calibrated to the International Performance Measurement and Verification Protocol (IPMVP) standard, and this was used to create a representative Digital Twin of each dwelling in use. These Digital Twins are highly accurate virtual replicas of the real-life building, providing further insights with respect to space heating, domestic hot water (DHW), lighting and appliances/small power. The calibration process ensures a high level of accuracy, meaning there could be a high level of confidence in the results. These models were then used to make comparisons with respect to how the buildings were performing against their design intent and identified operational and behavioural changes that could be made to improve performance. 

The predicted Energy Use Intensity (EUI) calculated by the energy certificates across all dwellings was on average 48kWh/m2/yr and, from discussions with homeowners, this is the energy consumption they were expecting to see reflected in their bills. However, these energy certificates are used to compare a building as an asset and rarely reflect a building's true operational performance. For example, they ensure that the construction of the building is to a high standard, including the building's envelope and systems, but they do not take into account small power or plug loads, nor do they take into account operational use and behaviour of the occupants. As such, a home with a young family of 5 will have a very different final energy bill compared to a home occupied by an elderly couple. 

Using the Digital Twins, it was calculated that the average EUI for the dwellings, in reality, was ~111kWh/m2/yr and, in some cases, much higher. This is almost double the EUI indicated by the energy certificates. Space heating requirements for two of the dwellings was more than double the design intent (in one case this was a result of gas boilers being left on for many unnecessary hours during the day, while in another the domestic hot water required was significantly high, likely due to the behaviour of the occupants). Lighting also varied between dwellings, with the results suggesting unnecessary use of lighting in some homes.

This highlights the need for education around the purpose of energy performance certificates. These should be used to ensure construction is of high quality, but should not be used as an operational target for the building owner to try and conform to, nor should the building owner expect their energy bill to match the energy performance certificate. More education on how occupants should use their homes to reduce energy consumption is also required. 

When a Housing Association commissions an Affordable Housing Development, they have the buying power to expect excellence and their strategy is to provide a home that is “affordable”.  While there is no strict definition of Affordable Housing, a rule of thumb applied for this scheme was that the total costs of the household, including mortgage and utility bills, should not be more than 1/3 of total household income.

The Housing Association also have a duty of care to the resident to ensure that they receive this level of excellence. If the homeowner is not aware of how they should use their A-Rated home to ensure it complies to the design intent, their energy bills can be significantly higher than anticipated. As a result, the Housing Association will have failed in its goal to enable affordable houses and the homeowner could go into debt. This is critical in current times with rising energy costs. Some Local Authorities are now making the operational performance of the dwelling a Key Performance Indicator of the Affordable Home to ensure the final outcome is a success to all parties involved. This can only be achieved with measurement and verification (M&V) protocols, which can be enabled by platforms such as iSCAN

Another important aspect of the project was to assess the indoor environmental quality (IEQ) of the homes, and the potential impact upon occupants. While, on paper, A-rated buildings are subject to highly specific standards to ensure that user comfort is not compromised, the increase in energy efficiency and air tightness often results in IEQ issues, as a result of increased temperatures, high CO2 and humidity levels. 

Unfortunately, A-rated buildings are seldom monitored to gain a better understanding of the IEQ at an operational level. However, using the Digital Twins, IES were able to gather and analyse information on:

(i)    Average and max temperature, relative humidity and CO2 in each room;
(ii)    the % of time that the temperature is greater than 25oC; 
(iii)    the % of time that relative humidity is greater than 60% and greater than 80%; 
(iv)    the % of time that CO2 is between 1,000ppm and 1,500ppm and greater than 1,500ppm. 

The results in the study uncovered high levels of relative humidity, as well as high levels of CO2 and long periods where the CO2 was outside recommended thresholds. This highlighted the importance of monitoring IEQ and raised some serious questions with respect to the CO2 levels in A-Rated dwellings. 

Due to the fact that poor IEQ can effect residents' health, wellbeing and activeness, all housing associations have a responsibility to ensure IEQ remains within the recommended thresholds otherwise the residents will experience these negative impacts and other related issues impacting on their wellbeing. This also has potential knock on impacts to the health system and increases costs at a government level as well as putting a strain on the health system.

Finally, the study considered the affordability of the homes. This was an important aspect of the project for Ó Cualann Cohousing Alliance, as a not for profit company whose vision is to see fully integrated, cooperative homes at affordable prices in sustainable communities.

Examining a number of dwellings, if the energy certificate was used as a metric for estimating the energy bill, the certificate estimated the energy bill at 7% of the overall mortgage of the property.

However, the results from this study indicated that the real energy bill of the properties was on average almost twice of that estimated by the energy certificate and a significant 12% of the mortgage cost. Now, amidst the current energy cost crisis, these costs may be significantly higher, raising serious questions around affordability for residents of housing associations.

The study highlights the importance of Digital Twins and how not to use compliance tools, such as energy performance certificates, as metrics for estimating operational energy use.

The results emphasised that, if left unchecked, A-Rated dwellings can perform far worse than their design intent. However, the IES Digital Twin made it possible for homeowners to upload their utility bills, check these against the design intent of the dwelling and, where significant gaps occur, receive recommendations for improvements.

Overall, IES’ digital twin technology was proven to have a crucial role to play, not only in ensuring more accurate performance predictions at the design phase, but also as an ongoing digital asset to monitor and optimise the performance of the homes once in use. In addition to the outputs from the Digital Twins themselves, IES were able to support Ó Cualann Cohousing Alliance in producing an operational guide for homeowners/tenants with advice to help them use their energy-efficient home as designed, thereby helping them to reduce their energy consumption, save money and also make their homes healthier and more comfortable places to live.

"IES technology has provided Ó Cualann with an accurate post occupancy solution to demonstrate the use of energy and ventilation across our houses. This gives us a clear indication of how our houses are performing, where there are issues and how we can make improvements. We want to ensure that our houses are futureproofed in terms of energy and ventilation requirements and ensure the negative effects of poor IEQ do not affect our current or future occupants. This partnership with an innovative company like IES also shows how Ó Cualann are leading the way in becoming one of the most sustainable housing providers in Ireland and we look forward to working with IES to bring the rest of our portfolio on board and to find out what further enhancements can be made."

Hugh Brennan, Chief Executive, Ó Cualann Cohousing Alliance