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Simplicity proves key to retrofit heat recovery

The UK’s ageing housing stock is a major concern for the government if it is to meet its goals to reduce carbon output over the next decade or so. There is no shortage of options available to assist with this, especially with the ongoing advances in renewable energy technology.

One of the main factors to consider, however, is that there is no single solution that is suitable for all properties. Given the considerable diversity of types of living accommodation throughout the country, this is hardly surprising. But a little thought and investigation can go a long way to making a considerable difference.

A recent project in north-west London offers support for this argument, allowing a heat recovery system to be replaced in 78 flats with minimum disruption to tenants. This has resulted in a system being installed that will reduce electricity bills while improving the quality of air, which in itself provides a number of benefits to occupants.

The building concerned is Hazlewood Tower, designed and built in the mid-1960s. It is typical of many other types of tower blocks built around this time in all major conurbations around the UK, with concrete providing the main fabric of the building.

Problems such as cold bridging can be an issue in buildings such as these, resulting in condensation, mould growth and damage to walls and ceilings in extreme cases, which can additionally result in negative health issues for occupants.

Hazlewood Tower is managed by Kensington and Chelsea Tenant Management Organisation (TMO) and owned by the Royal Borough of Kensington Chelsea. Maintenance is contracted out to S&F Services of Beckenham, Kent, with mechanical and electrical consultancy services provided by Calford Seadon.

The system being replaced was fitted in 1986 and was deemed ready for replacement last year, after providing 24 years’ service. The original Johnson & Starley units have now been replaced with the company’s latest model, the LEHT 155 heat exchanger.

Minimum of fuss

One of the main successes of the project was that it involved very little disruption for the majority of the tenants, with old units swapped for new with the minimum of remedial repairs required.

The project was scheduled to run over eight weeks and was one of nine that Kensington & Chelsea TMO put out to tender as a group. S&F Services director Brian Smith tells H&V News that he was delighted to be awarded this project, one of nine under a single contract.

The other projects all involved some form of energy-saving in line with Kensington and Chelsea TMO’s drive to provide more energy-efficient installations for its tenants and reduce the carbon footprint of the borough.

Wherever possible at Hazlewood Tower, the existing ducting that had been installed in the flats with the original solution was utilised for the new system. Although new ducting was installed in some instances, the majority of cases simply involved the fitting of new units.

The ducting serves to remove warm, moist air through 4-inch circular valves. These are fitted in the kitchens and bedrooms and allow the air to be delivered to the heat exchange unit. The units are installed within kitchen wall cupboards in most cases and therefore hidden from view.

Two exterior vents serve to extract the damp air, once it has passed through the exchanger, and draw in fresh air, which is then passed through the unit and distributed around the living space. Vents are also fitted into the ducting in non-wet rooms, but these act as a diffuser, rather than an extractor.

Moisture is drained away through 10 mm pipes that run behind the wall and into the wastewater pipe under the sink, so again nothing is visible to anyone using the kitchen. The act of extracting warm, damp air also serves to reduce condensation and remove odours.

The lowering of moisture content and removal of air borne contaminants is additionally beneficial to those suffering from various forms of respiratory diseases. Filters are fitted to all inlet vents and act as a barrier to restrict other pollutants being drawn into living spaces.

While all vents require cleaning, with interior versions also needing to have filters exchanged on an annual basis, this is a simple process. The manufacturer advises that this practice be included within annual maintenance contracts.

Tenants in control

The heat exchange units within Hazlewood Tower are also supplied with JS6 controllers, allowing occupants to choose between normal and boost settings. The latter is designed for use during the cooking of meals or when baths or showers are taken.

The extraction setting is used for cold periods, with a manual bypass option for the warmer, summer months. The system also includes a fire damper to provide automatic shut down in an emergency.

Further advantages are claimed through silent running of the heat exchangers. While the lack of background noise can serve to reduce instances of irritation from end-users, it also means that they are largely forgotten - especially as most are installed out of sight - with the result that tenants are much less likely to attempt to turn the system off in the belief that this is saving them money.

The subject of running cost provides further focus on the efficiency of the system. The manufacturer estimates that this is in the region of two or three pence a day.

Because instances of condensation and mould are also reduced, there are further potential savings to be made by avoiding electrically assisted removal of moisture and repairs to the fabric of the building caused by airborne damp.

S&F Services was responsible for establishing the health and safety procedures and tenant liaison. It set up an 0800 number for tenants to call to obtain free advice on the project and carried out a tenant satisfaction survey on completion, which showed high levels of acceptance from the occupants.

S&F also carried out a conditional survey, which was not part of the contract but is standard practice to pinpoint emerging issues for the client. The company has worked with Calford Seadon on a number of other projects, said Mr Smith.

The project went according to plan, he says, and he was “absolutely delighted” to receive 100 per cent excess. Mr Smith adds that he found the heat exchange system very quiet to run, efficient and cheap to run. “We’ve actually specified this just to treat condensation on some projects,” he points out.