Tuesday, 16 February 2010

Colin Hone of Aereco asks some questions about the manic rush into the use of heat recovery products...

As the industry heads to 2010 and the new regulations for building new homes loom ever nearer, the subject of providing efficient ventilation for the new air tight houses is top of the agenda for house builders.

In BREG 2010 Part L, which come into force October 2010, the Government proposes a 25 per cent improvement in energy efficiency standards for buildings, with new Part F ventilation standards to take account of higher air tightness standards. The provision of natural ventilation and local intermittent fans in these better sealed homes will become more challenging, meaning there will be an increased trend towards continuous mechanical ventilation systems.

With leaky old houses there was no problem about ventilation because the air was able to circulate effectively. However the downside of that was that energy leaked out too and now we have to build houses that keep the energy inside where it is needed, using less of it thereby making it more efficient and cheaper to run while cutting emissions at the same time.

I have 27 years’ experience of the building industry with half of those spent in the ventilation industry. So, what is the best method - for domestic ventilation - in the future?

‘Heat recovery’ seems to be the phrase that is being bandied around the industry as the cure-all solution for ventilation in new dwellings, but is it all it is cracked up to be?

Despite what some in the industry may believe it is not the only solution and possibly not even the best. So, why this stampede towards HR ventilation systems?

I think it is because contractors don’t have all the facts at hand: all the publicity at the moment is about heat recovery systems so the industry is having a knee jerk reaction towards it without considering the alternative. Contractors and clients are saying: ’Heat recovery! Marvellous – it will save the planet!’ after all is a great name, but they need to take an informed view and consider all options. I am not saying heat recovery systems don’t have their place but they are not the one and only solution to ventilating airtight houses.

Because of the emphasis currently being put on HR systems, people are surprised when they hear about the Demand Control Ventilation (DCV) passive stack system and think it is new technology. Far from it – it is tried and tested and has a long record of turning in positive results. DCV is not a term that is heard extensively in the UK it is used in more than 4.5 million homes on mainland Europe and in Asia with no hint of problems, ever.

Quite often, one of the big downsides to HR systems is that the filters must be changed at least once or twice a year (quiet often systems are left to run during the latter stage of house completion and dust particles are drawn into the filters, this often means the HR unit has dirty filters even before the house is occupied). Another is that tenants and homeowners worried about the fans being switched on all the time may be tempted to isolate them to save money and to cut down on noise levels. It is a fact of life that tenants in social housing tend to be less well off than those in the private sector and thus more likely to worry about energy costs.

And, even in private homes will homeowners invest the time and money in fitting new filters annually? If there is no ventilation in wet rooms and no clean air circulating around these new air tight dwellings, this is a potential health hazard and in dwellings where people smoke, it could be potentially fatal.

A recent NHBC report gives weight to these concerns about whether the filters will be cleaned regularly and also points out that: ‘The requirement for cleaning fan units and ductwork needs to be thoroughly investigated. Evidence from the USA suggests that a market has been created which is based on fear, with cleaning costs being high. The rate of build-up of dust and dirt within fan units and ducts in UK dwellings needs evaluating and guidance produced on good practice maintenance.’

A draft study from the BRE in May has also found widespread failure to maintain filters. ‘There is no market for replacement filters, with several manufacturers reporting no filter sales at all. Even basic maintenance is not undertaken,’ says the report.

With these worries about HR systems in practice, it makes sense to install a DCV system in both social and private housing. With the Passive DCV and Mechanical DCV systems, there are no filter changes, no electricity is used to operate the Passive DCV system and it is virtually maintenance free. In fact, it can be planned into the life of the actual building with considerable savings. It ticks all the boxes both ecologically and cost wise.

The DCV ventilation units incorporate humidity sensors on the grilles which automatically react to occupancy. When the house is empty, the system operates on minimum, producing a trickle of air. When the house is occupied the humidity sensitive grilles sense that and automatically increase ventilation, a totally modulated system.

With the Mechanical DCV system air renewal is ensured by a single acoustic fan (which can be placed in a cupboard or a ceiling void). Connected to the fan, the extract units located in the wet rooms determine the air renewal for the whole dwelling. Humidity sensitive air inlets control the distribution of the fresh air according to the needs of each main room.

Individual Humidity sensitive, or presence detection, extract units distribute the available airflow generated by the fan and regulate extraction rates according to the needs of each wet room. So, rooms with a high requirement for fresh air engender greater pressure and airflow than the empty rooms. Rather than recovering part of the heat from extracted air based on a high constant airflow, the single flow modulated ventilation decreases the airflow when the need is low, and increases it when needed.

The DCV passive stack system is humidity sensitive and offers nearly the same performance as an installed 80 per cent heat recovery system – and at half the price.¹ The technology satisfies all the requirements of the Code for Sustainable Homes (CSH) and is also ideal for refurbishment projects as it can be easily retrofitted. This is a viable alternative to heat recovery ventilation systems in dwellings and commercial buildings which has been used on the European continent and around the world successfully for many years.

Even the most expensive DCV installation is at least 25-30 per cent less than the cost of installing a HR system. HR has to be ducted into all habitable rooms as well as wet rooms. With the DCV system ducting is placed in wet rooms only. The special humidity sensitive grilles on the air inlets, which in modern houses are usually found on the windows, automatically allow air in when it is needed.

¹Price comparison is based on a standard Aereco DCV system versus a standard heat recovery system: products plus installation.