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With domestic emissions continuing to make a sizeable impact on CO 2 emissions, architects are well aware that Part L is about to become a lot more rigorous. Project architects have been coping and, so far, the existing ways of working have been simple enough: make sure condensing boilers are specified and get the relevant boxes ticked on all the various checklists.

We may argue that the task is made harder by value engineering, a process that often erodes the specification before the project reaches site.

But, in reality, this barely scratches the surface. The fact is that the technologies that have kept residents warm in winter and cool in summer are no longer efficient enough. The effective integration of truly sustainable heating and ventilation now depends on a forward-thinking design team and, more and more vitally, the client's approach to development, finance and housing management.

MORE THAN A PASS Part L envisages a holistic approach to the design of new developments to minimise their energy consumption. This will, in time, reduce the role of traditional heating and ventilation in favour of better use of building and glazing orientation and insulation, better control of air tightness and the use of passive stack ventilation. In future, the design team and housing association development and management teams will have to work in a more integrated way from the outset, at RIBA Stage A and B.

Achieving regulatory compliance will be one of the main aims but ways will also need to be found for registered social landlords (RSLs) to benefit from future energy cost savings at the outset when they need capital to build.

Meanwhile, intermediate strategies are needed to meet regulatory targets.

Housing associations are constrained by the scheme development standards to produce developments that at least gain an Ecohomes 'pass'.

But many architects aim to design for an 'excellent' rating.

Certain factors are key to this:

the client must be committed, and have strong integrated management; the technology must be robust; and the strategies adopted must be appropriate to the scale of the development. Two examples highlight some of these issues.

TEST OF ROBUSTNESS A 'green' or 'sustainable' technology's test of robustness is simple to measure: it must make more sense to use it properly than to try to get round it.

The combination boiler with thermostatic radiator valves is an example. Turn on the tap, and hot water comes out. Set the central-heating time clock for when you are there and the room will be warm. This should be the benchmark for heating.

The current design and operation of trickle ventilation shows the opposite. Where it does not clog up of its own accord, its function is not explained to residents; as insulation standards rise, the attendant condensation problems will only get worse.

Pollard Thomas Edwards architects (PTEa) has been involved with a programme to regenerate an estate of tower blocks overlooking Sefton Park in Liverpool. In addition to the improvement and reuse of existing stock, we proposed measures to improve the energy efficiency of the flats, combining economic advantages for the tenants with reduced emissions.

Phase 1 included 'whole house' heat recovery equipment to eliminate condensation problems while increasing energy efficiency. The units are mounted in the kitchens and recover up to 70 per cent of the heat from the kitchen and bathroom extracts, while removing humid air. They also supply fresh, dry warmed air to the kitchen, hall and bathroom - the quality of the supplied air is such that the use of heat recovery units is recommended for asthma sufferers.

Most importantly, this addresses a common management problem in affordable housing - that of tenants turning off or disconnecting kitchen and bathroom extract fans because they are extracting heat that the tenant has paid for along with humidity. The result is condensation, often severe, and an unpleasant environment in which, for example, mould thrives.

The heat recovery units at Sefton Park are performing as planned but the perception among some tenants is rather different - they see an illuminated switch and assume that it is costing them money, and turn it off. As a result of this, the tenants asked for the heat recovery units to be omitted from the second phase of the development. Clients need to work with their design teams to convey convincingly to residents that the units are saving them money.

When these lines of communication have been established, the way will be clear to introduce more sustainable technologies, such as CHP (combined heat and power) and micro CHP systems. The heat recovery units meet the robustness test - all that is lacking is residents' understanding that they do.

It is often difficult for the development and housingmanagement departments of housing associations to maintain regular contact, given their very different day-to-day concerns, but this contact will increasingly become essential if the sustainability targets of Part L and its planned revisions are to be met.

GOOD MANAGEMENT While larger associations have the resources to sponsor large innovative projects with the attendant risks and fee costs, small RSLs can be very effective through good management. I remember a small London association which would only allow one model of extract fan to be specified, since all others tried had been noisy enough to encourage tenants to disconnect them.

PTEa's project at Bermondsey Spa for Hyde Housing Association was won in competition, partly through a strong commitment to reducing carbon emissions in use. In addition to good practice in optimising orientation for energy conservation, insulation, ventilation control, heat recovery and using low-energy appliances, we proposed a CHP plant for heating and electricity generation and a borehole for water supply. The development of 73 flats, with just over 1,300m 2 of community and commercial uses at ground floor, is said to be on the threshold of being viable to support CHP, although detailed consideration of life-cycle costs might lower this threshold.

The housing association will sign up with an energy provider, which will run the CHP plant and sell surplus energy to back to the grid.

This contractual arrangement has prevented many private developers and some RSLs from adopting CHP schemes, as it increases their exposure to risk while it is mainly residents that feel the economic benefits.

Changes to Part L and the compulsory introduction of renewable energy sources are likely to change the way we meter and charge for our fuel.

To offset this additional management burden, the energy provider can sell broadband and cable services through their monitoring cabling, and share profits with the RSL or developer.

The CHP plant at Bermondsey Spa should reduce CO 2 output by about 50 tonnes, and energy costs to users by 10 per cent. Management arrangements that are attractive to developers and customers as well as to RSLs will have to be developed for CHP and micro CHP to be widely used - but if this can be done then the potential benefits are impressive, and the CHP power plant can easily be replaced with efficient heat generators as technologies improve.

For the client, the use of CHP in addition to the many other innovative features of the project, was a big step in both development and management terms, so that the inclusion of a borehole water supply was seen as over ambitious. If the CHP plant proves its worth as expected, and in time perhaps even generates additional revenue as outlined above, Hyde will be significantly closer to realising the integrated development and housing management approach that will in future be indispensable for successful RSLs.

Patrick Devlin is an architect with Pollard Thomas Edwards architects.

With thanks to Mike Humphries of Peter Deer Associates

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