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Research: Zero-Carbon Dwellings Demand Design Approach Shift

Research: Zero-Carbon Dwellings Demand Design Approach Shift

 From ASHRAE Journal Newsletter: March 22, 2022

 As building decarbonization policies and regulations are becoming more pervasive, net zero carbon performance has not yet been achieved on the housing development level, according to a researcher at Oxford Brookes University’s Low Carbon Building Group.

The U.K.-based researcher, Luka Oreskovic, and others recently published a study in ASHRAE’s Science and Technology for the Built Environment that systematically examines the in-use energy and carbon performance of a large case study housing development in England, designed to be net true zero carbon.

The study confirms the argument that integrating zero-carbon dwellings demands a shift toward an outcome-focused design approach.

Oreskovic spoke with ASHRAE Journal about the research and what it means for the future of building decarbonization:

Why is this research significant?

In-use performance evaluations are rarely conducted, and typically capture a small number of low-carbon dwellings. This study captured a development of 157 monitored dwellings and will be used to achieve one of the most ambitious carbon performance targets: net true zero carbon, including all energy uses and only on-site measures.  

How does this research fit into the U.K.’s decarbonization efforts?

Building decarbonization plays an important role in the UK's net-zero economy target for 2050. Industry experts deem that U.K. building regulations need to be rapidly tightened towards the net-zero dwellings standard by 2025.

Considering the performance gap has been frequently detected in dwellings, studies like these are vital for understanding how far we are from delivering net-zero dwellings, which perform as intended. 

Were any of the findings surprising? If so, why?

Based on the evidence of our study and similar evaluations of net-zero dwellings, net zero carbon performance has not yet been achieved on the development level. This finding is concerning, considering the anticipated mainstreaming for zero-carbon dwellings.

In the current policy context, narrowing this performance gap would require the design teams to look beyond the regulatory requirements, consider the trends in energy networks and use system efficiencies proved by empirical studies.

Building regulations play a key role in driving change in the culture of housing delivery, including designing for compliance towards designing for ongoing performance, using multiple performance metrics and monitoring and reporting of actual performance.

It was also surprising to see how the community heating systems can seem very efficient on paper but can be even more carbon intensive compared to conventional gas boilers. 

In five of eight housing developments mentioned in the paper, operational issues of the community heating system resulted in carbon intensity of heat by up to ten times more than the design projections. The study saw underperformance in some development cases of 20–200 dwellings, which leads to insufficient heat load requirements.

Biomass systems frequently caused severe technical issues during operation, which lead to their replacement with gas boilers and other carbon-intensive alternatives. Rapid decarbonization of the U.K.’s electricity grid quickly diminished the projected carbon reductions of gas-fueled combined heat and power (CHP) systems.

What are some suggestions for improving the underperforming community heating system?

In order to deliver zero carbon in larger housing developments, it is vital that the delivery of district and community heating systems in the U.K. mature.  

Instead of just complying with the building regulations, design teams should be interested in ensuring projected performance keeps being achieved through time. Promised low-carbon intensity of heat needs to be proven in the past empirical studies before these systems are proposed again in new developments. 

Rapid technological advancements and changes in the energy networks can make system efficiencies and carbon factors used in building regulations obsolete. While expected during the initial stages of a development, reduced efficiency of the community system can be compensated by designing to surpass the target performance in the following years. 

What do you want ASHRAE Journal readers to know about this research?

 The findings of this study suggested:

  • Low energy use in the level of Passivhaus dwellings (76 kWh/m2/year in this case study) could be achieved in less airtight and insulated homes—if the electricity use is significantly reduced. 
  • The impact of occupant factors in low-energy dwellings might be even higher than previously thought. 
  • Low self-consumption rates of photovoltaic (PV) electricity (23% in this case study) in net-zero dwellings call for the provision of home batteries. 
  • The aspired true zero-carbon performance was not achieved. As found in similar studies, this was attributed to the underperforming community heating system.
  • The anticipated mainstreaming of zero-carbon dwellings demand a shift toward an outcome-focused design approach.

What are the next steps for this research?

We plan to evaluate the actual environmental behaviors (energy, transportation, waste and food) against the case study development's aspiration to enable more sustainable lifestyles.