Gerard Thacker, Associate Director at Greengauge, shares his thoughts on the beneficial inter-relationship between building services and building physics
As a building services engineer who has undertaken Passivhaus training, I see more and more how the two disciplines can work well together when problem-solving for both new-build and retrofit projects.
One of the reasons Greengauge was originally set up was to offer “an integrated approach where building physics, building services and building design come together for better outcomes” and we have really experienced the benefits of having these interdisciplinary skills in-house in three recent – and diverse – projects.
Schools estate retrofit
We have been advising a local authority on retrofitting their schools estate. The original brief was to develop a heat decarbonisation plan to switch the schools over to heat pumps from their current gas and oil boilers.
Internal monitoring of temperature, humidity and CO2 demonstrated that many of the schools were cold and uncomfortable, often not reaching their Winter design temperatures until the end of the day, and high levels of CO2, suggesting that occupants were not opening the windows due to the cold draughts which this created.
Having modelled the projects in PHPP we knew that the costs of running heat pumps in these uninsulated, draughty buildings would be massive – as would the heat pumps.
Our building physics knowledge therefore helped to inform a more wholistic approach involving:
- Early installation of MVHR systems to address air quality issues, control moisture and reduce heat loads.
- Early installation of heat pumps, sized for the eventual target heat losses but initially running in tandem with existing boilers until fabric improvements can be undertaken. This bivalent approach has been set up using the heat pumps’ own integral controls to prioritise the heat pump for base warmth, with the gas boilers kicking in only on very cold days.
- A rolling refurbishment of the schools’ building fabric, with roof insulation generally being undertaken in the first school summer holiday phase, alongside the MVHR and heat pump work which typically involves running ductwork and pipework in attics and the other measures following on. This allows the work to be phased in a more manageable way to suit the availability of suitable local contractors.
Knowledge of both mechanical services and building physics has allowed us to come at the problem from two directions and find a sensible middle ground.
AECB retrofit of a listed building
In another recent retrofit project we were initially brought in to provide services design for some new teaching spaces in a previously unheated building, but our knowledge of building physics also allowed us to help the project architect to significantly improve the building’s fabric efficiency and hence reduce the size of the new heating system required. Through workshops at the early project stages, we were able to steer the fabric strategy towards the use of a layer of insulated plaster, which is good for both airtightness and bringing a continuous layer of insulation through into tricky window reveals etc., supplemented by closely bonded wood fibre insulation. Both of these materials have good water vapour transport properties to allow the surface of the existing structure to dry out and hence reducing the risk of interstitial condensation. Our eventual input included providing WUFI moisture analysis services – to work out the maximum thickness of new Internal Wall Insulation (IWI) without creating moisture problems – and carrying out thermal bridge modelling to check that some of the more difficult interfaces between the new insulation and existing structure were not going to create problematic cold bridges. This work, alongside our PHPP modelling, enabled the listed building to achieve AECB Retrofit status.
Newbuild Passivhaus development
Another example of the symbiosis between building services and building physics was demonstrated in a recent newbuild project in Devizes which required our mechanical services knowledge to fit suitably sized MVHR ductwork into buildings with challenging planning constraints on storey heights, but the architect also benefited from our PHPP knowledge, which helped to inform the optimal locations for MVHR units, hot water cylinders etc. and where to run the insulation and airtightness line relative to the service voids to avoid bridging these with ductwork. This helped to ensure that Passivhaus levels of performance could be achieved.
