6th December 2017

The December 2017 issue of the CIBSE journal features a CPD module sponsored by Monodraught.  It continues our series of CPDs which provides a more in-depth look at trends in building performance and thermal comfort.  The article was written by Professor Tim Dwyer (based on work by Richard Jack, Dennis Loveday, David Allinson and Kevin Lomas*).  

New Monodraught sponsored CPD in CIBSE journal.

The article looks at a project designed to assess the practical reliability of co-heating tests.  The “performance gap” between designers’ expectation of the thermal characteristics of a building and the reality of the building operation highlights the need to assess properly post-construction building performance.

Whole house performance measurements have shown that the “performance gap” exists.  In the vast majority of cases, both the energy consumption and the total heat loss through the building fabric are higher than predicted.  This includes existing, newly built and retrofitted buildings as well as high performance projects.  The problem is likely to be caused by a combination of factors, including underperformance of individual building elements and a lack of airtightness.  A reliable test of the whole house is needed to provide an accurate reflection of real performance.

The co-heating test

The co-heating test is a pseudo-steady state test, where the amount of energy required to maintain a constant, raised indoor temperature is measured, as well as the total heat-transfer rate.  The thermal performance of a building fabric can be described by two main heat flow mechanisms: heat transfer through the fabric of the building and heat lost as the result of air infiltration.

The project

The Building Research Establishment (BRE), at Garston, Hertfordshire, provided access for the project.  The team tested a pair of identical adjacent well-insulated and well-constructed detached test houses.  These houses effectively have thermal performance similar to, but slightly worse than, that required by 2013 Building Regulations.

Seven test teams from different organizations successively undertook co-heating tests on the same house, whilst BRE undertook coincident tests in the other house.

During the test, the internal air temperature inside the building was maintained (using electrical heating equipment) at a constant raised level for approximately two weeks.  Fans were used to mix the house air and all internal doors were left open.  Maintaining a constant internal air temperature throughout the building is vital in a co-heating test to ensure accurate measurements of the whole building’s performance.

Six different methods of estimating solar gain were used in the project, most of which required some measurement of the total solar irradiance.  In this project most test teams carried out only one whole building air infiltration-rate measurement.

The method used to account for solar gains remains and area of uncertainty and produced the most variation between test teams.

The results indicate that the co-heating test is reasonably robust to different measurement methods, weather conditions and data-analysis methods.  The project was performed using a single detached house, and further testing in a wider sample of houses designs and situations is recommended as the next step towards the development of a standardised co-heating test.

Ventilation Building performance

Monodraught have recently expanded its own ventilation range in the education and commercial sector.  As an established ventilation specialist, we now offer both natural, hybrid and mechanical ventilation systems.  Many of Monodraught’s ventilation products such as hybrid thermal mixing and MVHR units include heating which is generally provided by fully controllable low temperature hot water heat exchangers. 

Our solutions provide good thermal comfort and IAQ and have been designed with building regulations and energy consumption in mind.  The low carbon systems provide high levels of acoustic attenuation, ideal for a classroom or college application.  Our controls allow users and facility managers to adjust ventilation, monitor performance and ensure that systems are operating correctly. 

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