Lessons from AIMC4 for cost-effective fabric-first low-energy housing

Transcription

1 Information Paper Lessons from AIMC4 for cost-effective fabric-first low-energy housing Part 6: Ventilation and Indoor Air Quality Christopher Gaze Image courtesy of Stewart Milne Group AIMC4 homes at Portlethan, Aberdeen

2 2 Lessons from AIMC4 for cost-effective fabric-first low-energy housing Acknowledgement The as-built testing and post occupancy evaluation of the homes was conducted by Colin Sinclair of BRE Scotland.

3 Part 6: Ventilation and Indoor Air Quality 3 Introduction This Information Paper is Part 6 of a series of 7 Information Papers about the AIMC4 applied research project which was created to research, develop and pioneer the volume production of low-carbon homes for the future that would achieve Level 4 (energy) of the Code for Sustainable Homes without the use of renewable energy. This paper focuses on the ventilation and indoor air quality from specification through to occupant experience; it also contains a discussion on dynamic insulation. The paper follows on from Part 3, which focuses on the technical design step and links to Part 5 which looks at as-built and post occupancy performance. What is AIMC4? AIMC4 is a unique partnership of companies, created to research, develop and pioneer the volume production of the low carbon homes for the future. It stands for the Application of Innovative Materials, Products and Processes to meet the Code for Sustainable Homes Level 4 Energy Performance. The AIMC4 Consortium was set up in 2009 to develop and apply innovative materials, products and processes to meet the Governments Code for Sustainable Homes, Level 4 energy performance, through innovative fabric and building services solutions only, thus embedding reduced carbon emissions within the performance of the dwelling. The Consortium members comprise developers, Stewart Milne Group, Crest Nicholson PLC and Barratt Developments PLC, who were responsible for the design and build of the energy efficient homes, the Building Research Establishment (BRE) advising on innovative solutions and evaluating the technical issues and H+H UK Ltd a supplier of Aircrete concrete products. BRE Scotland analysed and evaluated both the performance of the homes and occupant responses and behaviours. The ground breaking project was worth 6.4m, of which 3.2m was invested by the UK s innovation agency, the Technology Strategy Board with the other 3.2m coming from the members. The key to the success of the project has been to engage with both known and new suppliers at all levels to develop design solutions and processes to deliver Code 4 (energy) homes through energy efficient fabric and building services solutions, without the use of renewable technologies. Achieving this goal will not only assist in meeting the Government target of zero carbon homes by 2016, but will reduce costs, create new UK supply chains, generate new build systems and processes and ensure homes are designed that meet consumer needs without confusing or costly technologies. What is the Code for Sustainable Homes? The Code for Sustainable homes is part of the Government s programme to improve the sustainability of new dwellings, in particular with a view to national targets for reducing carbon dioxide emissions, but taking a more holistic approach by considering a wide range of environmental and social impacts of new homes. It is used in England, Wales and Northern Ireland. The Code has six performance levels Levels 1 to 6, and assesses both new dwellings and the development site against nine categories. The category of relevance to this project is the mandatory requirement for energy efficiency at Code Level 4 The Co-operative Group s Manchester headquarters (see Code for Sustainable Homes, Technical Guide, November 2010, Department for Communities and Local Government), that requires an improvement in dwelling emission rates of 25% over those set out in the English Building Regulations 2010 Approved Document Part L1A (in earlier versions of the Code this used to be a 44% improvement over the 2006 Regulations which is roughly equivalent). At the start of the project it was anticipated that this dwelling emission rate would be incorporated into English Building Regulations in 2013.

4 4 Lessons from AIMC4 for cost-effective fabric-first low-energy housing Describing the homes A full description of the specification of the AIMC4 homes can be found in AIMC4 Information Paper 3. The descriptors used in this paper, match those in Information Paper 5 and have been anonymised to preserve privacy, so that comments and usage patterns cannot be traced back to specific homes or their occupants. Table 1: House Descriptions of the Monitored Homes Home Ventilation strategy and presence/absence of WWHR MEV1 MEV with manual boost control and WWHR MEV2 MEV with manual boost control and WWHR MEV3 MEV with manual boost control and WWHR MEV4 MEV with manual boost control and WWHR MEV5 MEV with manual boost control and WWHR MEV6C MEV with automated controls and WWHR. MEV7C MEV with automated controls and WWHR DI1 Dynamic Insulation1 Property with MEV and WWHR DI2 Dynamic Insulation1 Property with MEV and WWHR IEF1 IEF and WWHR IEF2 IEF and WWHR IEF3 IEF and WWHR MVHR1 MVHR (no WWHR) MVHR2 MVHR (no WWHR) MVHR3 MVHR (no WWHR) MVHR4 MVHR (no WWHR) Image courtesy of Crest Nicholson AIMC4 homes at Epsom 1 Further information can be found in AIMC4 Information Paper 3

5 Part 6: Ventilation and Indoor Air Quality 5 Background to the ventilation systems From the beginning the AIMC4 Consortium set out to look at different ventilation strategies. Information Paper 4 showed how the intention to minimise both installation risk and the need for user interaction were important when selecting products. On that basis intermittent extract fans (IEF) would normally be the first choice, in that their installation is well understood and that occupants are more familiar with them. Mechanical Extract Ventilation (MEV) is more complex to install, but relatively easy for occupants to use, whereas Mechanical Ventilation with Heat Recovery (MVHR) is the most costly and complex to install, and can be misunderstood and mismanaged by home occupants, although it does have advantages over the other systems (see below). Intermittent Extract Fans (IEF) Systems IEF systems are well known in the UK and are the standard method used to ventilate new build homes. The method is sometimes referred to as natural ventilation. It involves the installation of fans into wet rooms - i.e. kitchens, bathrooms and toilets, to extract pollutants and stale/humid air. Fresh air comes into the house through the trickle vents fitted in the windows. The fans in the bathrooms and toilets are often operated by the light switch and go off after a time delay. This is normally the most cost effective of the systems to install, but uses more energy than MEV to operate. It is commonly assumed that IEF is used in homes with an airtightness greater than 3m 3 /m 2 hr@50pa. MEV or MVHR is then usually adopted if homes are more airtight. In AIMC4 it was decided to trial three houses with IEF with quite ambitious airtightness values of m 3 /m 2 hr@50pa to see how they performed, as this gives some benefits in the SAP calculations and users are more familiar with their operation, than the operation of MEV or MVHR. Mechanical Extract Ventilation (MEV) Systems MEV systems are in many ways similar to IEF except that instead of having a fan in each wet room there is a single central fan. MEV systems run continuously, but there is a boost provision to remove odours or improve air quality. The system is commonly used in countries such as Holland, and is becoming more common in the UK, especially in bigger properties with more than one bath/shower room where it can be more cost effective to install than IEF. As ductwork is involved, more consideration has to be given at the design and construction phases with regard to routing and installation. AIMC4 specified standard MEV in seven homes. These were spread over four sites. They were installed with either a manual boost switch that users could turn on and off or in two cases an automatic system that sensed when the shower or cooker was operating to give the boost facility. This is done by sensors that detect hot water or electric current, whichever is appropriate. Mechanical Ventilation with Heat Recovery (MVHR) Systems MVHR systems are generally more complex and therefore more expensive than IEF and MEV systems due to the number of components, controls and the fact that they both supply and extract. MVHR systems normally consist of a unit that incorporates a fan and a heat exchanger. It is the heat exchanger that transfers the heat out of the warm, humid air that has been extracted from the wet rooms to the incoming external fresh air supply; both air streams are kept separate via an independent ductwork arrangement. The MVHR system, depending on the type of ductwork, may also include plenum chambers to allow the numerous supply and extraction ducts required to service each room to be connected to the fan unit itself. MVHR systems rely heavily on good design and commissioning to ensure that they can function and operate in line with the design intent. Where MVHR is specified improved levels of airtightness are required than in those homes using standard MEV (excluding the dynamic insulation homes) or IEF to make sure that the heat recovery is effective. MVHR is not common in the UK and there have been problems with installations 2. Additionally filters have to be cleaned or changed as these become clogged over time to the detriment of heat recovery and fan performance, as well as indoor air quality. Home occupants tend to not be attuned to the necessity for this, relatively simple, maintenance requirement. For all of these reasons, MVHR has tended to be the ventilation strategy of last resort in the UK, used for example, in inner city homes where noise and air quality are issues. It should be noted, however, that MVHR is used widely in Northern Europe, and not just for PassivHaus homes, in which it is mandatory. For example, MVHR has been required in Sweden since the 1960s, where its advantages for comfort, energy efficiency and filtered air are widely appreciated in their climate. MVHR was used in five AIMC4 homes. All the units had a summer by-pass. The project monitored four of the units. It was not possible to monitor the fifth, as there was a delay in selling it. Two types of unit were used. They were chosen primarily, but not only, for their efficiency rating in SAP calculations. The specification of MVHR allows for heat to be recovered from the warm exhaust air. This meant that it was not necessary to specify waste water heat recovery (WWHR) to meet the energy requirements of the AIMC4 specification. However the cost of installing MVHR is greater than the combined cost of installing MEV and WWHR (see Information Paper 7 for more details on costings). 2 NF 52 Assessment of MVHR systems and air quality in zero carbon homes, Andy Dengel, NHBC Foundation, August 2013

6 6 Lessons from AIMC4 for cost-effective fabric-first low-energy housing Dynamic Insulation Systems The decision to trial dynamic insulation was to understand whether it was a viable solution to achieve a high level of fabric-first specification while minimising wall thickness. Dynamic insulation allows for external walls to be thinner than normal walls, for the same U-value. Air is brought in from the outside through vents in the external walls, which have the appearance of normal air-bricks (see Figure 1). Larger undercuts are required for internal doors to allow for the easy movement of air around the home. Two homes with dynamic insulation were built on two different sites. Figure 1: Dynamic Insulation external vent inlet Dynamic insulation uses MEV to drag the incoming air up through the external walls (the homes have no trickle vents), where it is pre-warmed by the heat transferring through the walls from the inside environment to the outside (see Figure 2). The principle is a sort of fabric based ventilation with heat recovery system and as such, these homes also need to have improved levels of airtightness (3 m 3 /m 2 hr@50pa or less). This is not the case for standard MEV homes or homes using IEF. More details are in Information Paper 3. Figure 2: Dynamic Insulation schematic Duct layout design The design of duct layouts for the MVHR and MEV homes was managed in two different ways. For some of the units this was subcontracted to a consultancy firm, and for the rest was to be carried out by the manufacturer. This second approach caused significant problems for two of the developers who were using two different manufacturers. In both cases the manufacturers were unresponsive in supplying layout drawings and lacked understanding of the implications of their ductwork designs for the structure of the homes and for other services. It was surprising that this was the case, not least for a high profile project such as AIMC4, which had involved both suppliers fully from the design stage. As a result, the duct routes and outlet positions ended up being designed by the respective developers and then approved by the manufacturer.

7 Part 6: Ventilation and Indoor Air Quality 7 Installation There were some issues with installation within the MEV1-4 homes, which resulted in flexible ducting being used instead of rigid due to access problems that had not been envisaged at the design stage (see Figure 3). This will have had an impact on fan efficiency, which will be explored later. Figure 4 shows the plenum chambers for one of the MVHR systems. In this case the ductwork looks like flexible ducting, but is in fact smooth bore semi-rigid ductwork. Semi-rigid ducting often requires plenum chambers to allow for connection to the MVHR fan unit. The main difficulty for the delivery of the homes with the monitored MVHR units was the late delivery of some of the ductwork. The installation, however, went well. The key aspects which facilitated the installation were that: service runs and ductwork were mapped onto the structure using colour coding. toolbox talks were used. semi-rigid duct work was specified which is easier to install than rigid ducts, whilst not affecting the efficiency of the MVHR fans within SAP. the colour coding of the MVHR ducting itself (blue for fresh air and red for exhaust) which simplified assembly. good site supervision. The four monitored MVHR units were installed within the dwelling space so that customers could see when filters needed cleaning/ changing and have easy access to them. Figure 3: Installation of MEV ductwork Figure 4: Installation of MVHR systems using semi-rigid colour coded ducting Post Occupancy Evaluation Most of the homes were viewed as being comfortable by their occupants (see Information Paper 5 for more details), but some of the MVHR homes reported occasional discomfort due to overheating in the hottest times of the year. However, this is probably more a feature of their form (two and a half storey) and their southerly aspect, than the method of ventilation. In two of these properties the occupants had thought that the MVHR system would provide enough cool air to control the temperature of their homes and when the homes had become hot, in the summer, they had been left in doubt as to whether they were running the systems properly. The occupants of home DI2 said on their first interview, just after moving in, that they were not aware of the dynamic insulation system. They had more concerns over winter ventilation than summer and felt the quantity of ventilation was heavily dependent on the direction and speed of external wind, but they could not feel a draught directly from any of the vents. This ventilation issue, led to one of the upstairs bedrooms feeling particularly cold (see Information Paper 5 for further information on actual temperatures in this room) and the lounge also feeling cool. The temperature data in Information Paper 5 indicates that the rooms felt cold due primarily to air movement rather than actual room temperature. The bedroom was rectified by removing the northern external wall vent and upsizing the radiator. At the same time the occupants had found some of the rooms to be stuffy and as a result some trickle vents were installed into the windows. After the conclusion of project monitoring it was found necessary to remove the northern external wall vent from the lounge as well, to help control the ventilation further. This has left the house with dynamic ventilation only in the southern gable wall. Home DI1 had experienced draughts from the dynamic insulation system, in this case running under doors and from a specific vent in one of the bedrooms. They did manually throttle back the ventilation in the winter, but were not happy that it could not be closed off completely, as would be the case with traditional window trickle vents. However it has not been necessary to modify the home. Both sets of occupants of these homes said that they would have valued more education on the system, but that they were feeling fairly comfortable twelve months after handover.

8 8 Lessons from AIMC4 for cost-effective fabric-first low-energy housing Relative Humidity and Carbon Dioxide Levels Relative humidity levels of between 30 and 70% are generally viewed as being comfortable. Relative humidity was measured in at least four rooms in each house, typically including the kitchen, the living/dining room and two bedrooms. All the homes had humidity levels in this comfortable range for at least 97% of the time, except two homes DI2 and IEF3. Neither of these were extreme examples; Home DI2 was bit drier in two rooms, which might have been due to the dynamic insulation airflows. Home IEF3 was more humid in the kitchen and one of the bedrooms (possibly due to lifestyle). The carbon dioxide levels in the homes are shown in Figure 5. Concentrations of carbon dioxide up to 1000ppm are typical for occupied indoor spaces with good ventilation. Over 1000ppm and occupants may start to feel drowsy or complain about the air quality. In UK schools the carbon dioxide levels when measured at the seated head height position and averaged over the whole day should not exceed 1500ppm. Against this benchmark, the AIMC4 homes have performed well. The occupants when interviewed were all satisfied with the air quality in their homes, with the exception of MVHR4 who in the summer quarter stated they were neutral, as the home could be a bit stuffy at that time of year. This shows that all the strategies served their primary purpose of providing good ventilation. Fan power consumption It is interesting note the fan power consumption for the different dwellings (see Figure 6). The MVHR systems are all performing well in comparison to the SAP prediction which is an indication of good installation and commissioning. The MEV systems that have the automated controls (homes MEV6C and MEV7C) are performing better than SAP predicted. However the MEV systems in homes MEV1, MEV2, MEV4 and MEV5, which all have manual boost controls, are all using more energy. Other factors may be at play, other than the fact that an automated system is better at optimising the boost time on the fans than a manual system. For example: some of the MEV systems with manual controls not being installed or commissioned optimally (for example due to the use of flexible instead of rigid ductwork in homes MEV1-4) or the nature and use of the manual controls on these systems. With regard to the last point, the manual controls are switched on and have to be manually switched off again. Only one of the MEV households with a manual boost (home MEV3) used less power than SAP predicted and it was this household that showed the most interest in the operation of the boost facility. These results suggest that they were only putting the system to boost when required. The occupants of MEV1, MEV2 and MEV4 all describe their systems as running automatically, with MEV1 and MEV2 both saying that they have never used the boost in the kitchen; this may mean that the boost has been left permanently on. Figure 5: Carbon Dioxide concentrations Percentage of measured time (%) <500ppm ppm ppm 10 0 MEV1 MEV2 MEV3 MEV4 MEV5 MEV6C MEV7C DI1 DI2 MVHR1 MVHR2 MVHR3 MVHR4 IEF1 IEF2 3 Of the seventeen homes built by the AIMC4 consortium, one could not be monitored and in another the carbon dioxide sensor failed to collect data.

9 Part 6: Ventilation and Indoor Air Quality 9 There are no measured or reported differences between the experience of those household with automated boost and manual boost systems in terms of air quality or user friendliness. This suggests that consideration should be given to automating mechanical ventilation in all properties; after-all manual control is still available through opening the windows. However, the sample size for AIMC4 is small and more research is needed. Figure 6: Energy Consumption of fans as a percentage of SAP 450% 400% Percentage of fan power as shown in SAP 350% 300% 250% 200% 150% 100% 50% Lessons Learnt 0% MEV1 MEV2 MEV3 MEV4 MEV5 MEV6C MEV7C MVHR1 MVHR2 MVHR3 MVHR4 DI1 DI2 No problems were reported with the air quality or on-going maintenance of the ventilation systems in the AIMC4 homes; there are, however, some lessons to be taken from their specification, installation, commissioning and the way in which occupants are informed about their operation: IEF IEF ventilation can be used in low energy housing, but: it does require a better insulated fabric than would otherwise be the case, for an equivalent home, of the same energy performance, that used MEV or MVHR, and, as with the application of all forms of ventilation in more insulated and airtight building fabrics, care needs to be taken to ensure that indoor air quality is not compromised. Manufacturers support for MEV and MVHR If manufacturers are to provide a design service they must make great efforts to understand the needs of developers, the effect of their routing on other services, the structural elements of the homes and make greater efforts to improve their design capacity and responsiveness. Additionally, they should provide the designed fan speed when they provide these layouts, so that fans can be optimally specified for the actual design of the home and commissioned correctly. Developers when tendering for work need to establish whether manufacturers have adequate skills and capacity to provide a design service. MEV and MVHR installation Care needs to be taken in the installation and commissioning of ventilation systems; especially for those elements that might affect fan efficiency, such as duct routes, ductwork type, commissioning with clean filters installed and adjusting the fan speed to the minimum required for effective operation. It is common practice to install units in the roof space, but consideration should be given with regard to access for maintenance and in the case of MVHR; filter changing or cleaning. Additionally there is a risk of duct damage. MEV MEV systems should have some means, such as a light, to inform occupants if they are malfunctioning. MVHR Occupants need to be carefully briefed so that they understand how the systems operate. In the case of MVHR, it is important that the automatic functioning of the summer bypass is clearly understood and that it is made clear that the system is not going to cool the air. MVHR systems need clearly marked warning lights in areas where they are likely to be observed to alert occupants when to change/ clean filters or whether the unit has malfunctioned. Semi-rigid ductwork is much easier to install than rigid ductwork Colour coding ductwork is a useful aid to assembly. Boost control Occupants were just as satisfied with air quality in homes with automated boost control as those in homes where they could control the boost manually. Most people with a manual boost do not appear to have operated it optimally for energy use. Those with automated control were not frustrated by the absence of manual boost control. Consideration should be given to researching further whether SAP should mandate the automation of boost control to help the as-built performance more closely reflect design performance. Dynamic insulation As might be expected when trialling a novel product, there were teething problems with the dynamic insulation system. Since the use of dynamic insulation in the AIMC4 homes the product has been redesigned by the supplier to improve ventilation control. These changes are designed to address the problems of wind driven effects on the ventilation balance. The operation of dynamic insulation homes is different from conventional homes and the occupants need to be fully briefed.

10 Acknowledgements The writing of this Information Paper was funded by the Technology Strategy Board. Stewart Milne Group, Crest Nicholson plc, Barratt Developments plc and H+H UK Ltd funded the publishing of this series of papers. BRE has written this Information Paper on behalf of the AIMC4 consortium. BRE is committed to providing impartial and authoritative information on all aspects of the built environment. We make every effort to ensure the accuracy and quality of information and guidance when it is published. However, we can take no responsibility for the subsequent use of this information, nor for any errors or omissions it may contain. AIMC4 publications are available from June as joint authors: Stewart Milne Group Crest Nicholson plc Barratt Developments plc H+H UK Ltd BRE together the joint authors. The joint authors assert their right under s78 Copyright Designs & Patents Act 1988 to be recognised as the authors of this copyright work.