Where:
U = In-situ u-value
Ti = Internal surface temperature Te = External surface temperature Q = Heat flux
rint= Interior wall surface resistance rext= External wall surface resistance rhf= Heat flux sensor surface resistance
Both techniques provide a valid measure of in-situ u-value, but the analysis will be limited to those calculated using air temperature data due to the lack of surface temperature data in some of the experiments undertaken.
4.7 MVHR System Function
Whilst the effect of the MVHR system operation on the fabric performance and whole house HLC value was assessed through use of the coheating test procedure, the evaluation work extended to the assessment of the function and installation of the MVHR systems installed in the E.On and Tarmac Houses.
4.7.1 Methodology
An assessment of the flow rates at each of the supply and extract ducts within the two dwellings houses was undertaken. A Testo 417 vane anemometer was used to obtain readings of the air flow at each outlet (specification included in Appendix 4). This device has an integral air flow and temperature vane, and has the capability to provide timed and multi-point mean calculations. It is accurate to +/- 0.1 m/s and +/- 0.5°C (Testo Inc, 2011).
Equation 4-4 - U-value Calculation - Surface Temperature Method) (Baker, 2011, p. 37)
On each occasion, the houses were heated to 21°C and the anemometer was held over each supply and extract vent within the dwelling living spaces in turn.
Mean values of flow rate (m/s) and temperature (°C) measured over a 30 second time period were recorded. The flow rate values were later converted to l/s and air changes per hour (ACH) units.
A FLIR T400 thermal imaging camera was used to investigate areas of potential heat loss from both the MVHR system control unit and heat exchanger, and the ducting work in the loft space. A power meter was installed in order to measure the electrical consumption of the system. Thermocouples were placed in the supply and extract ductwork to a depth of 70mm at a distance of 500mm from the main control box, as shown in Figure 4-6.
Figure 4-6 - MVHR System Measurement Locations Source: (Efficiency Meets Sustainability, 2011) (Altered by Author)
4.7.2 Analysis
The measured outputs enabled calculation of the Temperature Efficiency through the methodology outlined in Equation 4-5 (Lowe et al., 1997, p. 35):
t =T2- T1/ T3- T1
Where:
t= Temperature Efficiency of the MVHR System T1= Temperature of Intake Air (°C)
T2= Temperature of Supply Air (°C) T3= Temperature of Extract Air (°C)
This parameter provides an indication of the performance of an MVHR system, and the experimental calculated values can be compared to manufacturer design-stage data and utilised in SAP 2009 assessments in order to evaluate post-installation function.
4.8 Conclusions
The primary purpose of this section has been to provide an overview of the core methods as utilised throughout the experimental and analytical work undertaken during the course of this research programme. The main areas of investigation are the performance of the building fabric and installed ventilation systems, at both the design and post-construction stages. SAP 2009 methodology is employed as the primary means of evaluating predicted levels of dwelling performance. Throughout the evaluation of the two selected case-study properties, coheating testing and heat flow monitoring provide essential tools for assessing the as-built thermal performance of the building fabric.
Measurement of system temperatures, power inputs and air throughput rates can enable assessment of MVHR system performance.
Whilst the general concepts pertinent to each evaluation method have now been described, the specific details relating to the actual experiments performed will be outlined subsequently in the context of the remaining
Equation 4-5 - Temperature Efficiency of MVHR System (Lowe et al., 1997, p. 35)
5 THE RETRO-FIT CONTEXT
As identified in Section 1.1, whilst much progress is being made towards the improvement of the fabric of new build dwellings in order to enhance thermal performance, the existing building stock presents a potentially more complex problem. The UK has over 8.5 million houses that are in excess of 60 years old (Energy Saving Trust (EST), 2007b, p. 4), resulting in slow progress towards lower domestic carbon emissions through replacement with more efficient properties alone. This poses a dilemma for policy makers, developers and local authorities at the strategic level and home owners at a more localised level – is the best solution to abandon older houses (relocation of occupants and major demolition/rebuild projects) or to refurbish and retro-fit existing properties?
(Power, A, 2008).
Housing demolition rates are relatively low in the UK, and several studies have been undertaken to assess the impact of increased demolition rates within different scenarios to achieve Government energy targets. It has been observed that higher demolition levels may not present a significant contribution in reducing energy demands and carbon emissions, when compared to the impact of wide-scale renovation schemes (Johnston et al., 2005; Lowe, 2007; Natarajan et al., 2007).
With this in mind, the role that the improvement of the existing housing stock could have in providing more efficient properties cannot be ignored, although the mechanisms by which this is implemented at Government level could impact upon uptake and effectiveness of improvement measures (Dowson et al., 2012; Killip, 2011). It is largely dependent upon the ability of the wider community to understand the concept of sustainable retro-fit, which may include improvements to the fabric or systems integrated into a dwelling that result in a reduced energy demand, or inclusion of localised power generation from renewable sources (Swan, W. et al., 2013).
Research into effective retrofitting practises and techniques is essential in order to inform and aid those undertaking such work at an individual dwelling or whole development scale. As such, Project CALEBRE (Consumer-Appealing Low Energy Technologies for Building Retrofitting) (www.calebre.org.uk/) has been undertaken as a partnership between several leading universities, with £2 million of funding provided by E.On and the Research Councils UK (RCUK) Energy Programme. Central to this project was the construction of the E.On 2016 Research House, completed in 2008 as a three bedroom new-build property but built to 1930’s equivalent building standards (Banfill et al., 2011b).
Over a four year period, the house has been upgraded to exceed 2010 Building Regulations standards through a staged programme of retrofit measures (Loveday et al., 2011).
This property is representative of the large number of hard to treat dwellings in the UK, and so has been investigated in order to evaluate the performance of a retro-fit dwelling. The remainder of this chapter will present an overview of the design and construction of the building, and report on the findings relating to the design stage and post construction fabric and systems evaluations undertaken.