Retrofit Plus Insights by Prof Lubo Jankovic, Birmingham City University

Introduction

Retrofit Plus project transforms existing poorly performing buildings into Passivhaus standard buildings. The retrofit is carried out by Beattie Passive using their TCosy system. BCU are providing research for this project to assist the design team with the retrofit strategy.

At the start of the project the objective was to go for full zero carbon retrofit. Half way through the project a national scheme called Green Deal was discontinued and the funding for renewable energy in Retrofit Plus disappeared as result. Our revised objective was to put the buildings to be retrofitted onto a trajectory to zero carbon so that full zero carbon performance can be achieved at a later date.

The buildings to be retrofitted were provided to the project by Birmingham City Council (Figure 1).

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Figure 1 Two semi-detached houses to be retrofitted

Establishing pre-retrofit base case

 A 3D laser scan was carried out by the University, in order to create a model that can be used for off-site measurements by the project lead industrial partner Beattie Passive, in order to manufacture the retrofit system in their factory. Eight different laser scans were taken, one high resolution and one low resolution from each of the corners of the buildings, and the scans were ‘stitched-up’ to create a unified model (Figure 2).

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Figure 2 Unified point cloud from multiple 3D laser scans for off-site analysis and measurements

Subsequently, BCU staff delivered training to Beattie Passive to enable their staff to use the 3D scan for off site measurements. This minimised the travel for Beattie Passive from their base in Norfolk to the retrofit site in Birmingham.

A team of surveyors was brought in to establish details about construction types, such as materials, layers, thicknesses, condition of the constructions etc. The buildings were identified as Wimpey No-Fines type, characterised with concrete construction – concrete without the sand fraction. This building type was constructed with concrete cast in situ and was not fitted with any thermal insulation. Over 300,000 buildings of this type have been constructed in the UK, and most of them require urgent retrofit.

A number of thermal images of the building were taken, and these corroborate the absence of thermal insulation in walls (figure 3). Brighter colours in this Figure indicate areas of high heat loss to the outside that coincide with the internal positions of central heating radiators.

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Figure 3 Thermal image of the building with bright colours indicating high heat losses from central heating radiators

As result of the high heat losses identified through the survey, building occupants spend more energy to keep warm. Even with higher energy bills it is harder to be comfortable in a house where most of the heat disappears through un-insulated walls.

A University PhD student carried out a detailed internal survey in order to create CAD drawings of the building.  These helped to create a series of computer models that will be used for design analysis (Figure 4).

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Figure 4 computer model development from IES Virtual Environment (top left) via DesignBuilder (top right) to EnergyPlus (bottom right) and JEPus+EA (bottom left)

This computer modeling path was chosen to enable initial student input in IES VE to be transferred to a modeling tool capable of calibration and design optimization (JEPlus+EA).

Finally, the computer model of the building was calibrated with gas and electricity data obtained from the house occupants for the past two years. The results of the calibration determined the parameters of the model that resulted in the minimum error between computer simulated energy consumption and actual energy consumption recorded in the energy bills. The errors of the calibrated model were 0.17% in respect of electricity consumption and 0.33% in respect of gas consumption, meaning that the model was 99.83% accurate in respect of electricity consumption and 99.67% accurate in respect of gas consumption.

The model calibration was the final stage of establishing the pre-retrofit base case, and it resulted in an accurate computer model for design analysis.

Design analysis

The pre-retrofit base case in the previous step created an accurate computer model that can be ‘pushed and poked’ to see what happens with different design interventions. Unlike the most of design projects in which up to half a dozen model variations are investigated, we adopted a multi-objective approach in which several thousand design options were to be investigated.

The technical parameters for optimisation were:

  • three different thicknesses of TCosy wall insulation: 150mm, 200mm and 225mm, combined in pairs with the identical TCosy roof insulation thicknesses;
  • infiltration air changes per hour;
  • fuel type (gas or biomass);
  • lighting power density; and
  • two different PV arrays (East side of the roof only, and East and West side combined).

The user behaviour parameters for optimisation were:

  • room set temperature and
  • clothing level.

The objectives of the optimisation analysis were to minimise CO2 emissions and maximise thermal comfort. A total of 4860 simulation cases were investigated in order to select a subset of best cases to be considered for final design.

The results of design analysis are shown in Figure 5, where a trajectory from a minimum intervention to zero carbon retrofit is plotted using the results of individual design simulations.

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Figure 5 Trajectory to zero carbon

The trajectory in Figure 5 starts with a minimum intervention in point 1: 150mm wall and roof insulation TCosy system is added, whilst using the existing gas boiler, keeping the infiltration rate high, and without adding any PV. The resultant room set temperature is low (16 oC); the level of occupant clothing is high (1.4 clo), indicating the use of clothing levels higher than woolly pullovers; and carbon emissions are high: 2,565 kgCO2 per year. As we progress from point 1 via point 2 to point 3, which is based on TCosy 225mm insulation, the room set temperature increases to 21oC, the clothing level reduces to 0.8 clo (a shirt instead of a pullover) and carbon emissions are reduced to -336 kgCO2 per year with the application of renewable energy. The overall reduction of energy consumption is estimated to be significant, well over 80%.

These results indicate that deep retrofit does not only result in energy consumption reduction and carbon emission reduction, but it also creates opportunities for improvements of occupants’ wellbeing.

Prof Lubo Jankovic, Birmingham City University

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